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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 3 — Jan. 31, 2011
  • pp: 2729–2738
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Laterally-current-injected light-emitting diodes based on nanocrystalline-Si/SiO2 superlattice

L. Ding, M. B. Yu, Xiaoguang Tu, G. Q. Lo, S. Tripathy, and T. P. Chen  »View Author Affiliations


Optics Express, Vol. 19, Issue 3, pp. 2729-2738 (2011)
http://dx.doi.org/10.1364/OE.19.002729


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Abstract

Laterally electrically-pumped Si light-emitting diodes (LEDs) based on truncated nanocrystalline-Si (nc-Si)/SiO2 quantum wells are fabricated with complementary-metal-semiconductor-oxide (CMOS) process. Visible electroluminescence (EL) can be observed under a reverse bias larger than ~6 V. The light emission would probably originate from the spontaneous hot-carrier relaxations within the conduction and the valance bands when the device is sufficiently reverse-biased. The EL spectral profile is found to be modulated by varying structure parameters of the interdigitated finger electrodes. Up to ~20 times EL intensity enhancement is achieved as compared to vertical-current-injection LED prepared using the same material system. Based on the lateral-current-injection scheme, a Si/SiO2 MQW LED with Fabry-Perot (FP) microcavity and an on-chip waveguided LED that emits at 1.55-µm are proposed.

© 2011 OSA

1. Introduction

The successful fabrication of complementary-metal-semiconductor-oxide (CMOS)-compatible high-efficiency light-emitting diodes (LEDs) will surmount the last obstacle for Si photonics. Intensive research effort [1

1. L. T. Canham, “Silicon quantum wire array fabrication by electrochemical and chemical dissolution of wafers,” Appl. Phys. Lett. 57(10), 1046–1048 (1990). [CrossRef]

12

12. M. Zacharias, J. Bläsing, P. Veit, L. Tsybeskov, K. Hirschman, and P. M. Fauchet, “Thermal crystallization of amorphous Si/SiO2 superlattice,” Appl. Phys. Lett. 74(18), 2614–2616 (1999). [CrossRef]

] has been devoted to the realization of low-voltage electrically-pumped Si-based LEDs since the first observation of efficient luminescence from porous Si due to the quantum confinement effect of nano-scaled dimension of the material [1

1. L. T. Canham, “Silicon quantum wire array fabrication by electrochemical and chemical dissolution of wafers,” Appl. Phys. Lett. 57(10), 1046–1048 (1990). [CrossRef]

9

9. M. Wang, A. Anopchenko, A. Marconi, E. Moser, S. Prezioso, L. Pavesi, G. Pucker, P. Bellutti, and L. Vanzetti, “Light emitting devices based on nanocrystalline-silicon multilayer structure,” Physica E 41(6), 912–915 (2009). [CrossRef]

]. Among all the Si nano-structures, multiple quantum wells (MQWs) consisting of alternating ultra-thin layers of nanocrystalline-Si (nc-Si) and dielectric films has received intensive research attention in aspects of both photoluminescence (PL) and electroluminescence (EL) [5

5. W. K. Tan, M. B. Yu, Q. Chen, J. D. Ye, G. Q. Lo, and D. L. Kwong, “Re light emission from controlled multilayer stack comprising of thin amorphous silicon and silicon nitride layers,” Appl. Phys. Lett. 90(22), 221103 (2007). [CrossRef]

9

9. M. Wang, A. Anopchenko, A. Marconi, E. Moser, S. Prezioso, L. Pavesi, G. Pucker, P. Bellutti, and L. Vanzetti, “Light emitting devices based on nanocrystalline-silicon multilayer structure,” Physica E 41(6), 912–915 (2009). [CrossRef]

], since the initial proposal of Si/SiO2 superlattice as the Si-based quantum well light source [10

10. R. Tsu, “Silicon based quantum wells,” Nature 364(6432), 19 (1993). [CrossRef]

]. However, it is a disadvantage that efficient carrier injection is difficult to be achieved in the conventional vertical-current-injection nc-Si/SiO2 MQW LEDs, because the current transport is limited by the highly-insulating SiO2 layers. However, MQW lasers based on III-V compounds consist of alternating small and large bandgap materials which are both semi-conductive. Therefore, the current-injection is a unique issue for the Si/dielectric MQW devices in which the large bandgap material is highly-insulating. A further disadvantage of conventional structures employing vertical-current-injection scheme is the large difference of carrier densities in the individual quantum well. In a conventional MQW device, electrons and holes are injected into the wells in the direction vertical to the well surfaces. The mobility of electrons is much higher than that of holes, and thus electrons move faster than holes under a voltage bias. Therefore, the carrier density is higher in quantum wells near the p-electrode than in those near n-electrode under a voltage bias. Accordingly, the well numbers cannot be increased arbitrarily due to large difference of carrier intensities in each individual quantum well. This problem has been well illustrated and studied by Tessler [11

11. N. Tessler, and G. Eisenstein, “Transient carrier response in multiple quantum well lasers,” in Proceeding of 13th IEEE Semicon. Laser Conf. pp. 44–45 (1992).

]. The inefficient current-injection as well as the limited number of quantum wells prevents the vertical Si MQW light source from achieving a high gain of power. Although there have been many investigations on the LEDs based on vertical-current-injection nc-Si/dielectric superlattice, very few researchers investigated on the nc-Si MQW LED by injecting carriers parallel to the surface of multilayer films. In the lateral-current-injection MQWs, the carriers can be more efficiently injected into all well layers without being affected by two-dimensional potential barriers. In addition, there is no lowering in the injection efficiency even if the thickness of large-bandgap well is increased or the number of multi-quantum well layers is increased.

This paper demonstrates a MQW-based Si LED based on laterally injecting current directly into the nanocrystalline Si (nc-Si) films without carrier tunneling across SiO2. With the lateral current injection structure, the effective current injection efficiency is largely increased as the applied voltage is fully applied across the active region instead of dielectrics which cannot be avoided in vertical-current-injection nc-Si/SiO2 MQW LEDs. This leads to a significant enhancement of EL intensity. Since there is no top electrode on the active region, further enhancement can be achieved by light-extraction enhancement techniques directly applied on the active region. Moreover, by advantageously avoiding the top electrode, this lateral configuration allows for the easy fabrication of a new type of CMOS-compatible, low-loss, waveguide-based light source.

2. Device fabrication

Ten periods of alternating α-Si and SiO2 layers were deposited as the active region on top of a layer of 500-nm-thick thermal SiO2 on Si substrate. Ultra-thin α-Si films were deposited by plasma-enhanced chemical vapor deposition (PECVD) using SiH4 as the source gas diluted by He. The thickness of α-Si is ranging from 2 to 10 nm, while the SiO2 thickness was kept at 3 nm. Afterwards, the films were annealed in N2 ambient for 1 hour at high temperatures to induce crystallization of ultra-thin α-Si films. To choose the annealing temperature, the thermal annealing was carried out for a duration of 1 hour at the temperatures from 600 to 1100 °C. Micro-Raman spectroscopy and Transmission electron microscopy (TEM) and have been employed to study the structure properties of the materials. The micro-Raman measurements were performed at 325 nm. For the samples that were used to perform Raman measurements, we initially deposited a layer of 2-µm SiO2 beneath the Si/SiO2 multilayer to isolate the Raman signal from Si substrate. Figure 1
Fig. 1 Raman spectra of as-deposited sample (i.e., without annealing) and the samples annealed for 1 hour at the temperature of 700, 900, 1000, and 1100 °C.
shows the evolution of the Raman spectra for as-deposited samples and the samples with high temperature annealing for duration of 1 hour at the temperature of up to 1100 °C. It can be seen in Fig. 1 that the Raman speak around 520 cm−1 which is identified to crystalline Si is increased with the annealing temperature. One can conclude from the figure that the crystalline content of Si is increased with the annealing temperature when it is higher than 700 °C, which is in agreement with study on nanocrystallization of α-Si/SiO2 superlattices by high temperature thermal annealing [12

12. M. Zacharias, J. Bläsing, P. Veit, L. Tsybeskov, K. Hirschman, and P. M. Fauchet, “Thermal crystallization of amorphous Si/SiO2 superlattice,” Appl. Phys. Lett. 74(18), 2614–2616 (1999). [CrossRef]

]. In this study, we choose 1100-°C as the annealing temperature to induce nanocrystallization, because 1100-°C annealing can induce the most crystalline state concluded from the Raman spectrum evolution with annealing temperature. As shown in Fig. 2
Fig. 2 High resolution transmission electron microscopic (HR-TEM) images of α-Si/SiO2 multilayers (a) 10-nm-Si/ 3-nm-SiO2 and (b) 3-nm-Si/3-nm-SiO2.
, TEM images also confirm the presence of the crystalline state in Si thin layer even for 3-nm Si layers. However, the fully crystalline state of thin Si layers is difficult in thinner (<5 nm) Si layers due to the extremely higher thermal budget required (i.e., >1200 °C) as indicated in Ref [12

12. M. Zacharias, J. Bläsing, P. Veit, L. Tsybeskov, K. Hirschman, and P. M. Fauchet, “Thermal crystallization of amorphous Si/SiO2 superlattice,” Appl. Phys. Lett. 74(18), 2614–2616 (1999). [CrossRef]

]. Therefore, we would claim that the ultra-thin Si layer is in a mix phase of nanocrystalline and amorphous state after annealing at 1100 °C especially for thinner (<5 nm) Si layers, and this is supported by the TEM images shown in Fig. 2. For a clear and simple description, it should be point out that in this paper the thin Si film is denoted as α-Si before annealing and nc-Si after annealing although it is not rigorously correct in terms of the film structural state.

Based on the film system fabricated above, two types of LED structures, i.e., line emission (i.e., Type-I) and enhanced surface emission structure with interdigitated finger electrode (i.e., Type-II), were fabricated based on truncated nc-Si/SiO2 MQW with lateral-current-injection scheme. Three-dimensional (3D) schematics of the two types of structures are shown in Fig. 3(a)
Fig. 3 (a) 3D schematic and EL photo of Type-I device with line emission. (b) 3D schematic and EL photo of Type-II device with interdigitated finger electrode. (c) Simplified process flow showing the key steps of fabricating a lateral-current-injection nc-Si/SiO2 MQW LED with interdigitated finger electrodes. (i) Deposition of nc-Si/SiO2 MQWs. (ii) Active region patterning and etching. (iii) Deposition of poly-Si and implantation to form p + and n + electrode. (iv) Poly-Si patterning and etching to form a grating-like structure on the active region.
and 3(b), respectively. For a clear demonstration, EL photos at room temperature under electrical pumping for both of the two types LED devices are included in the respective figures.

After the nc-Si/SiO2 multilayers was deposited and annealed, a layer of 100-nm SiO2 was deposited on top of the multilayer to passivate the active region. The active region was defined by deep UV lithography and reactive ion etching through the multilayer to expose the thermal oxide. For Type-I devices, the active region was patterned into a narrow line of width ranging from 0.5 to 3 µm. As regard to Type-II devices, the active region was patterned into interdigitated finger structures to have a large surface area for emission. Afterwards, a layer of 160-nm poly-Si was deposited by low pressure chemical vapor deposition (LPCVD) followed by high-dose implantation of boron and phosphorous for p + and n + electrode formation, respectively. The emission window was formed by etching the poly-Si on top of the active region. Finally, the fabricated devices were annealed in N2 ambient for 1 hour at 1000 °C for dopant activation.

Taking the Type-II device as an example, the fabrication process flow was summarized in Fig. 3(c). In this study, the finger width and spacing are denoted by a and w, as shown in Fig. 3(c). After opening the emission window by etching poly-Si on top of the nc-Si/SiO2 multilayer, a grating-like structure consisting of periodic array of poly-Si and air were formed, as shown in Fig. 1(c).

3. Results and analysis

Visible EL emission can be observed by naked eye in daylight under a reverse bias larger than ~6 V, as shown in Fig. 3(a) for Type-I device and 3(b) for Type-II device. The EL spectra were taken by a PDS-1 photomultiplier tube (PMT) detector together with a monochromator. Figure 4(a)
Fig. 4 (a) EL spectrum under a reverse bias of 10 V for Type-I device with line emission width of 1 µm. (b) I-V characteristics and the integrated EL intensity as a function of applied voltage. The nc-Si film thickness is 10 nm.
shows the EL spectrum for Type-I device with line emission width of 1 µm under a bias of −10 V. It can be seen that it is a broad EL spectrum covering the entire visible spectrum. A linear relationship is observed between the reverse current and integrated EL intensity, as shown in Fig. 4(b). The current-voltage (I-V) curve shows linear characteristics when the device is under forward bias and reverse-bias if the voltage is larger than ~6 V. More detailed study shows that the linear relationship between EL intensity and current is valid over the entire detected EL spectrum.

As shown in Fig. 3(a), the structure can be regarded as ten p-i-n junctions in a parallel connection, in which i regions are the nc-Si films. As well known, the electric field in i-region of a revised p-i-n junction is much higher than that of a forward-biased p-i-n junction. When the junction field is large enough, hot carriers can be generated in the i-region. There have been intensive research activities over the past two decades on the hot-carrier induced EL under reverse bias [13

13. M. Freitag, V. Perebeinos, J. Chen, A. Stein, J. C. Tsang, J. A. Misewich, R. Martel, and P. Avouris, “Hot carrier electroluminescence from a single carbon nanotube,” Nano Lett. 4(6), 1063–1066 (2004). [CrossRef]

18

18. H. Aharoni and M. du Plessis, “Low-operating-voltage integrated silicon light-emitting devices,” IEEE J. Quantum Electron. 40(5), 557–563 (2004). [CrossRef]

]. Similar EL spectra have been observed in silicon p-n junction under reverse bias. The origin of the emission in Si p-n junctions has been attributed to different mechanisms such as the Bremsstrahlung effect [15

15. A. L. Lacaita, F. Zappa, S. Bigliardi, and M. Manfredi, “On the Bremsstrahlung origin of hot-carrier-induced photons in Silicon device,” IEEE Tran. Electron Device 40(3), 577–582 (1993). [CrossRef]

, 16

16. J. Bude, N. Sano, and A. Yoshii, “Hot-carrier luminescence in Si,” Phys. Rev. B Condens. Matter 45(11), 5848–5856 (1992). [CrossRef] [PubMed]

], the intra-conduction recombination [16

16. J. Bude, N. Sano, and A. Yoshii, “Hot-carrier luminescence in Si,” Phys. Rev. B Condens. Matter 45(11), 5848–5856 (1992). [CrossRef] [PubMed]

], and the hot carrier recombination [16

16. J. Bude, N. Sano, and A. Yoshii, “Hot-carrier luminescence in Si,” Phys. Rev. B Condens. Matter 45(11), 5848–5856 (1992). [CrossRef] [PubMed]

]. As regarding to our results, the linear relationship between the EL intensity and the reverse current rules out the contribution from direct electron-hole radiative recombination. The EL measurements were also carried out at various temperatures from room temperature to 300 °C, and no obvious change was found. This result suggests that the phonon-assisted recombination should not play an important role. Bremsstrahlung luminescence is also negligible because the dopant concentration in our device is much lower than 5×1020 cm−3, above which the Bremsstrahlung process can take place [16

16. J. Bude, N. Sano, and A. Yoshii, “Hot-carrier luminescence in Si,” Phys. Rev. B Condens. Matter 45(11), 5848–5856 (1992). [CrossRef] [PubMed]

]. Therefore, we are inclined to conclude that visible EL emission is originated from the spontaneous direct hot-carrier relaxations within the conduction (hot electrons) and the valance bands (hot holes). This paper presents a very initial study on hot-carrier EL from Si quantum wells with lateral-current-injection, thus more comprehensive work is required to quantitatively understand the exact mechanism of the hot-carrier-induced light emission from laterally current injected nc-Si/SiO2 MQWs. Regarding the system working based on hot carriers, the device reliability and life time is really a concern. In this study, we have done a continuous operation of 48 hours on both the Type-I and Type-II devices, and the devices did not show any noticeable degradation of the EL intensity with the working time.

The electrical and light emission properties of Type-II device have been also studied. I-V characteristics of Type-II devices shows a linear relationship similar to the electrical behavior of Type-I devices as shown in Fig. 4(b). However, the EL properties of Type–II devices are found to be significantly modified by the interdigitated finger structures. For example, Fig. 3(a) shows the EL spectrum of Type-II devices with the w of 1 µm and a of 2 µm. The EL spectrum of Type-I device is also included in Fig. 3(a) for comparison. It can be seen that overall EL intensity of Type-II device is significantly increased as compared to the Type-I device. The ~10-times intensity enhancement would be due to the much larger emission area formed by the interdigitated finger structures than that of the single line emission of Type I device. Another reason that would probably contributes to the EL intensity increase is that the textured top surface of Type-II device enhances the escape probability for internally generated photons, ideally by a factor of 2n 2, where n is the effective refractive index of the active region [19

19. M. A. Green, J. Zhao, A. Wang, P. J. Reece, and M. Gal, “Efficient silicon light-emitting diodes,” Nature 412(6849), 805–808 (2001). [CrossRef] [PubMed]

, 20

20. T. Trupke, J. Zhao, A. Wang, R. Corkish, and M. A. Green, “Very efficient light emission from bulk crystalline silicon,” Appl. Phys. Lett. 82(18), 2996–2998 (2003). [CrossRef]

]. It is necessary to point out that the finger width w cannot be larger than 3 µm, meanwhile the finger spacing a would better be larger than finger width w. Otherwise, a high voltage larger than 15 V is needed to generate hot carriers, which does not meets the CMOS requirement. As can be seen in the micrograph of Type-II device EL emission (left part of Fig. 3(b)), it is noticeable that the EL intensity is stronger in the area near p + region than in the area near n + region. It is another piece of evidence that the EL emission is originated from the hot-carrier relaxation under reverse-bias, because of the much lower impact ionization rate of holes in Si [21

21. S. Sze, Physics of Semiconductor Devices, (Wiley, New York, 1981), pp 45–47.

].

Other than the EL intensity enhancement, the EL spectral profile of Type-II device has been found to be modulated as compared to the Type-I device. As can be seen from Fig. 5(a)
Fig. 5 (a) EL spectra under a reverse voltage of 10 V for the Type-II device with w = 1 µm and a = 2 µm. (b) EL spectra under a reverse voltage of 10 V for the Type-II device with w = 1 µm and a = 10 µm. (c) Calculated transmission spectra of Type-II device with w = 1 µm and a = 2 µm. (d) Calculated transmission spectra of Type-II device with w = 1 µm and a = 10 µm. The nc-Si film thickness is 10 nm for the device in this figure.
, unlike the broadband emission over the entire visible spectrum without obvious peaks, the EL spectrum of Type-II device with w = 1 um and a = 2 µm presents a main peak at ~550 nm and a small peak at ~800 nm with much lower intensity. The EL spectra are also found to be modulated by varying the interdigitated finger parameters (i.e., width w and spacing a). Figure 5(b) shows the EL spectra of type-II device with w = 1 um and a = 10 um. As shown in the figure, it presents a main EL peak at ~650 nm and a shoulder peak at ~500 nm. The overall intensity is even higher than that of the Type-II device with w = 1 um and a = 2 um shown in Fig. 5(a). This is probably due to the much higher current density in the nc-Si films for the device with larger a, although the number of emission lines becomes smaller.

In order to understand the EL spectral peak shift due to the change of finger parameters, a nonlinear equation method based on plane-wave expansion is used to calculate the transmission spectra of the grating-like structure formed by fabricating the interdigitated finger electrodes. In the simulation, Rigorous Coupled Wave Analysis (RCWA) method was used to solve the Maxwell equations. The RCWA method uses the concept of a unit cell to handle both 2D and 3D periodic structures and is specifically tailored for multilayer structures. As shown in Fig. 5(c), a transverse-electric (TE) mode transmission peak at ~550 nm of can be found, which is in consistent with the EL emission peak shown in Fig. 5(a). The transmission peak at ~800 nm also can be found for the TE mode, which would contribute to the small EL emission peak at ~800 nm. The TE mode transmission spectra are more consistent with the EL emission spectra than the transverse-magnetic (TM) mode, indicating that the EL emission from laterally-current-injected nc-Si/SiO2 MQWs is dominated by TE mode. This phenomenon also can be observed from Fig. 5(b) and 5(d), i.e., the TE mode transmission shows a main peak at ~650 nm and a shoulder peak at ~500 nm which are both presented in the EL spectrum. We found that the EL spectrum almost does not change except for some peak intensity adjustment when the finger spacing a is larger than 10 µm, indicating the modulation effect of the grating-like electrode becomes negligible when the finger spacing is much larger than the emission wavelength by one order.

4. Discussion

Indeed, low-voltage operation of Si-based vertical LED devices with nc-Si embedded in SiO2 has been reported [23

23. S. Fujita and N. Sugiyama, “Visible light-emitting devices with Schottky contacts on an ultrathin amorphous silicon layer containing silicon nanocrystals,” Appl. Phys. Lett. 74(2), 308–310 (1999). [CrossRef]

25

25. S. Prezioso, A. Anopchenko, Z. Gaburro, L. Pavesi, G. Pucker, L. Vanzetti, and P. Bellutti, “Electrical conduction and electroluminescence in nanocrystalline silicon-based light emitting devices,” J. Appl. Phys. 104(6), 063103 (2008). [CrossRef]

]. However, low-voltage operation and high efficiency is not enough for real LED application. In the previously reported vertical devices, the active region which is made of dielectric films embedded with nc-Si cannot be too thick due to the current injection will be very difficult in thick SiO2. Such devices with low-voltage operation (<5 V) were fabricated employing a MOS-like structure having the nc-Si embedded gate oxide embedded with the thickness less than tens of nanometers, and total emitting optical power cannot be increased too much due to the limitation of active region thickness. This problem can be solved by employing the proposed lateral-current-injection structure because the number of active region layers can be increased without decreasing the current injection.

This work provides a platform with more flexibility to re-design and integration. First, many light extraction techniques, such as Fabry-Perot (FP) cavity, photonic crystal structures, surface plasmons and so on, can be directly applied onto the bottom and top of the active region, since there is no electrode connected with the bottom and top surface of the active region. Of course, micro-cavity or photonic crystal structure can be fabricated in the vertical LED devices if people want to do them [26

26. A. Muscara, M. E. Castagna, S. Leonardi, S. Coffa, L. Caristia, and S. Lorenti, “Design and electro-optical characterization of Si-based resonant cavity light emitting devices at 850 nm,” J. Lumin. 121(2), 293–297 (2006). [CrossRef]

,27

27. C. D. Presti, A. Irrera, G. Franzò, I. Crupi, F. Priolo, F. Iacona, G. Di Stefano, A. Piana, D. Sanfilippo, and P. G. Fallica, “Photonic-crystal silicon nanoclusters light-emitting device,” Appl. Phys. Lett. 88(3), 033501 (2006). [CrossRef]

]. However, the top and bottom electrodes which were usually made of heavily doped poly-Si would make additional optical loss due to the scattering and free carrier absorption by reflecting the light in the cavity or photonic crystal structures. One cannot afford such additional loss of optical power especially for Si-based LED devices due to its already confirmed low emission efficiency. The lateral-current-injection structure is more suitable for micro-cavity and photonics crystal design due to the absence of absorptive top and bottom electrodes. For example, FP cavity formed by bottom and top Bragg reflectors can be easily employed with this lateral-current-injection nc-Si MQW LED, as shown in Fig. 8(a)
Fig. 8 (a) A proposed structure of lateral-current-injection LED based on truncated nc-Si/SiO2 MQWs with F-P cavity formed by bottom and top Bragg reflectors consisting of alternating SiO2 and Si3N4 films. (b) The cross-sectional schematic of a proposed on-chip waveguided LED with 1.55-µm emission based on the lateral-current -injection scheme reported in this study.
. FP cavity has been reported and easily fabricated based on nc-Si systems for PL studies [28

28. F. Giorgis, “Optical microcavities based on amorphous silicon-nitride Fabry-Perot structures,” Appl. Phys. Lett. 77(4), 522–524 (2000). [CrossRef]

]. An electrical-driven pumped slot-waveguide LED with FP microcavity has been proposed [29

29. C. A. Barrios and M. Lipson, “Electrically driven silicon resonant light emitting device based on slot-waveguide,” Opt. Express 13(25), 10092–10101 (2005). [CrossRef] [PubMed]

], and it needs to fill Er-doped SiO2 into the vertical slot with the width of tens of nanometers. It is difficult to realize with conventional CMOS tools, except using an atomic layer deposition (ALD) system which allows for high aspect-ratio nanostructure deposition and subsequent accurately controlled chemical mechanical polishing (CMP) process. As can be seen in Fig. 8(a), with the lateral current injection scheme, the LED structure with FP cavity can be easily fabricated with PECVD deposition, ultra-violet (UV) lithography, and plasma dry etching. Optical interconnects used for on-chip and chip-to-chip communication requires an efficient infrared waveguided light source. The infrared Si-based light source that emits at ~1.5 µm have been researched and investigated by doping Er doping into Si nanostructures [30

30. F. Iacona, D. Pacifici, A. Irrera, M. Miritello, G. Franzò, F. Priolo, D. Sanfilippo, G. Di Stefano, and P. G. Fallica, “Electroluminescence at 1.54 µm in Er-doped Si nanoclusters-based devices,” Appl. Phys. Lett. 81(17), 3242–3244 (2002). [CrossRef]

,31

31. S. Yerci, R. Li, and L. Dal Negro, “Electroluminescence from Er-doped Si-rich silicon nitride light emitting diodes,” Appl. Phys. Lett. 97(8), 081109 (2010). [CrossRef]

]. Because this lateral-current-injection scheme excludes the top electrodes on the active region of MQW structure, one can expect the successful fabrication of an electrical-pumping waveguided light sources. Based on the lateral-current-injection nc-Si/SiO2 MQW LEDs presented in this work, we propose a waveguided light sources that can be fabricated in a standard CMOS line and monolithically integrated with electronic Si chips. The cross-sectional schematic of the proposed structure is shown in Fig. 8(b). The cladding material is SiO2 and waveguide core can be made of silicon nitride. The doped Er in the active region is used as medium for 1.55-µm light emission. The index contrast between oxide and nitride provides extra optical confinement besides the index difference between Si3N4 and the superlattice consisting of nc-Si/Si3N4.

5. Summary

In conclusion, a lateral-current-injection LED based on nc-Si/SiO2 quantum wells has been demonstrated. Strong visible EL can be observed when device is reversed biased. The device exhibits a linear relationship between the EL intensity and the reverse current. The EL can be enhanced and modulated using interdigitated finger structures. The emission modulation is well explained using the plane-wave expansion method. As compared to the vertical-current-injection LED fabricated with the same Si/SiO2 multilayers, the lateral-current-injection LED shows a ~20 times stronger EL intensity. Based on the LED structure with lateral-current-injection scheme, FP cavity can be easily applied and fabricated. Moreover, an nc-Si MQW waveguided LED has been proposed. It may open a way to the efficient on-chip light sources for optical interconnects.

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N. Tessler, and G. Eisenstein, “Transient carrier response in multiple quantum well lasers,” in Proceeding of 13th IEEE Semicon. Laser Conf. pp. 44–45 (1992).

12.

M. Zacharias, J. Bläsing, P. Veit, L. Tsybeskov, K. Hirschman, and P. M. Fauchet, “Thermal crystallization of amorphous Si/SiO2 superlattice,” Appl. Phys. Lett. 74(18), 2614–2616 (1999). [CrossRef]

13.

M. Freitag, V. Perebeinos, J. Chen, A. Stein, J. C. Tsang, J. A. Misewich, R. Martel, and P. Avouris, “Hot carrier electroluminescence from a single carbon nanotube,” Nano Lett. 4(6), 1063–1066 (2004). [CrossRef]

14.

C. W. Liu, S. T. Chang, W. T. Liu, M.-J. Chen, and C.-F. Lin, “Hot carrier recombination model of visible electroluminescence from metal-oxide-silicon tunneling diodes,” Appl. Phys. Lett. 77(26), 4347–4349 (2000). [CrossRef]

15.

A. L. Lacaita, F. Zappa, S. Bigliardi, and M. Manfredi, “On the Bremsstrahlung origin of hot-carrier-induced photons in Silicon device,” IEEE Tran. Electron Device 40(3), 577–582 (1993). [CrossRef]

16.

J. Bude, N. Sano, and A. Yoshii, “Hot-carrier luminescence in Si,” Phys. Rev. B Condens. Matter 45(11), 5848–5856 (1992). [CrossRef] [PubMed]

17.

B. K. Ridley, “Hot electrons in low-dimensional structures,” Rep. Prog. Phys. 54(2), 169–256 (1991). [CrossRef]

18.

H. Aharoni and M. du Plessis, “Low-operating-voltage integrated silicon light-emitting devices,” IEEE J. Quantum Electron. 40(5), 557–563 (2004). [CrossRef]

19.

M. A. Green, J. Zhao, A. Wang, P. J. Reece, and M. Gal, “Efficient silicon light-emitting diodes,” Nature 412(6849), 805–808 (2001). [CrossRef] [PubMed]

20.

T. Trupke, J. Zhao, A. Wang, R. Corkish, and M. A. Green, “Very efficient light emission from bulk crystalline silicon,” Appl. Phys. Lett. 82(18), 2996–2998 (2003). [CrossRef]

21.

S. Sze, Physics of Semiconductor Devices, (Wiley, New York, 1981), pp 45–47.

22.

S. Boninelli, F. Iacona, G. Franzo, C. Bongiorno, C. Spinella, and F. Priolo, “Thermal evolution and photoluminescence properties of nanometric Si layers,” Nanotechnology 16(12), 3012–3016 (2005). [CrossRef]

23.

S. Fujita and N. Sugiyama, “Visible light-emitting devices with Schottky contacts on an ultrathin amorphous silicon layer containing silicon nanocrystals,” Appl. Phys. Lett. 74(2), 308–310 (1999). [CrossRef]

24.

P. Photopoulos and A. G. Nassiopoulou, “Room- and low-temperature voltage tunable electroluminescence from a single layer of silicon quantum dots in between two thin SiO2 layers,” Appl. Phys. Lett. 77(12), 1816–1818 (2000). [CrossRef]

25.

S. Prezioso, A. Anopchenko, Z. Gaburro, L. Pavesi, G. Pucker, L. Vanzetti, and P. Bellutti, “Electrical conduction and electroluminescence in nanocrystalline silicon-based light emitting devices,” J. Appl. Phys. 104(6), 063103 (2008). [CrossRef]

26.

A. Muscara, M. E. Castagna, S. Leonardi, S. Coffa, L. Caristia, and S. Lorenti, “Design and electro-optical characterization of Si-based resonant cavity light emitting devices at 850 nm,” J. Lumin. 121(2), 293–297 (2006). [CrossRef]

27.

C. D. Presti, A. Irrera, G. Franzò, I. Crupi, F. Priolo, F. Iacona, G. Di Stefano, A. Piana, D. Sanfilippo, and P. G. Fallica, “Photonic-crystal silicon nanoclusters light-emitting device,” Appl. Phys. Lett. 88(3), 033501 (2006). [CrossRef]

28.

F. Giorgis, “Optical microcavities based on amorphous silicon-nitride Fabry-Perot structures,” Appl. Phys. Lett. 77(4), 522–524 (2000). [CrossRef]

29.

C. A. Barrios and M. Lipson, “Electrically driven silicon resonant light emitting device based on slot-waveguide,” Opt. Express 13(25), 10092–10101 (2005). [CrossRef] [PubMed]

30.

F. Iacona, D. Pacifici, A. Irrera, M. Miritello, G. Franzò, F. Priolo, D. Sanfilippo, G. Di Stefano, and P. G. Fallica, “Electroluminescence at 1.54 µm in Er-doped Si nanoclusters-based devices,” Appl. Phys. Lett. 81(17), 3242–3244 (2002). [CrossRef]

31.

S. Yerci, R. Li, and L. Dal Negro, “Electroluminescence from Er-doped Si-rich silicon nitride light emitting diodes,” Appl. Phys. Lett. 97(8), 081109 (2010). [CrossRef]

OCIS Codes
(040.4200) Detectors : Multiple quantum well
(230.3670) Optical devices : Light-emitting diodes
(260.3800) Physical optics : Luminescence

ToC Category:
Optical Devices

History
Original Manuscript: August 6, 2010
Revised Manuscript: November 29, 2010
Manuscript Accepted: December 20, 2010
Published: January 28, 2011

Virtual Issues
Vol. 6, Iss. 2 Virtual Journal for Biomedical Optics

Citation
L. Ding, M. B. Yu, Xiaoguang Tu, G. Q. Lo, S. Tripathy, and T. P. Chen, "Laterally-current-injected light-emitting diodes based on nanocrystalline-Si/SiO2 superlattice," Opt. Express 19, 2729-2738 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-3-2729


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References

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  4. L. Ding, T. P. Chen, M. Yang, J. I. Wong, Z. Cen, Y. Liu, F. Zhu, and A. A. Tseng, “Relationship between current transport and electroluminescence in Si+-implanted SiO2 thin films,” IEEE Trans. Electron. Dev. 56(11), 2785–2791 (2009). [CrossRef]
  5. W. K. Tan, M. B. Yu, Q. Chen, J. D. Ye, G. Q. Lo, and D. L. Kwong, “Re light emission from controlled multilayer stack comprising of thin amorphous silicon and silicon nitride layers,” Appl. Phys. Lett. 90(22), 221103 (2007). [CrossRef]
  6. W. K. Tan, M. B. Yu, Q. Chen, W. Y. Loh, J. D. Ye, Z. H. Zhang, G. Q. Lo, and D.-L. Kwong, “Thin amorphous Si/Si3N4-based light emitting device prepared with low thermal budget,” IEEE Electron Device Lett. 29(3), 228–231 (2008). [CrossRef]
  7. A. Anopchenko, A. Marconi, E. Moser, S. Prezioso, M. Wang, L. Pavesi, G. Pucker, and P. Bellutti, “Low-voltage onset of electroluminescence in nanocrystalline-Si/SiO2 multilayers,” J. Appl. Phys. 106(3), 033104 (2009). [CrossRef]
  8. T. Creazzo, B. Redding, E. Marchena, J. Murakowski, and D. W. Prather, “Pulsed pumping of silicon nanocrystal light emitting devices,” Opt. Express 18(11), 10924–10930 (2010). [CrossRef] [PubMed]
  9. M. Wang, A. Anopchenko, A. Marconi, E. Moser, S. Prezioso, L. Pavesi, G. Pucker, P. Bellutti, and L. Vanzetti, “Light emitting devices based on nanocrystalline-silicon multilayer structure,” Physica E 41(6), 912–915 (2009). [CrossRef]
  10. R. Tsu, “Silicon based quantum wells,” Nature 364(6432), 19 (1993). [CrossRef]
  11. N. Tessler, and G. Eisenstein, “Transient carrier response in multiple quantum well lasers,” in Proceeding of 13th IEEE Semicon. Laser Conf. pp. 44–45 (1992).
  12. M. Zacharias, J. Bläsing, P. Veit, L. Tsybeskov, K. Hirschman, and P. M. Fauchet, “Thermal crystallization of amorphous Si/SiO2 superlattice,” Appl. Phys. Lett. 74(18), 2614–2616 (1999). [CrossRef]
  13. M. Freitag, V. Perebeinos, J. Chen, A. Stein, J. C. Tsang, J. A. Misewich, R. Martel, and P. Avouris, “Hot carrier electroluminescence from a single carbon nanotube,” Nano Lett. 4(6), 1063–1066 (2004). [CrossRef]
  14. C. W. Liu, S. T. Chang, W. T. Liu, M.-J. Chen, and C.-F. Lin, “Hot carrier recombination model of visible electroluminescence from metal-oxide-silicon tunneling diodes,” Appl. Phys. Lett. 77(26), 4347–4349 (2000). [CrossRef]
  15. A. L. Lacaita, F. Zappa, S. Bigliardi, and M. Manfredi, “On the Bremsstrahlung origin of hot-carrier-induced photons in Silicon device,” IEEE Tran. Electron Device 40(3), 577–582 (1993). [CrossRef]
  16. J. Bude, N. Sano, and A. Yoshii, “Hot-carrier luminescence in Si,” Phys. Rev. B Condens. Matter 45(11), 5848–5856 (1992). [CrossRef] [PubMed]
  17. B. K. Ridley, “Hot electrons in low-dimensional structures,” Rep. Prog. Phys. 54(2), 169–256 (1991). [CrossRef]
  18. H. Aharoni and M. du Plessis, “Low-operating-voltage integrated silicon light-emitting devices,” IEEE J. Quantum Electron. 40(5), 557–563 (2004). [CrossRef]
  19. M. A. Green, J. Zhao, A. Wang, P. J. Reece, and M. Gal, “Efficient silicon light-emitting diodes,” Nature 412(6849), 805–808 (2001). [CrossRef] [PubMed]
  20. T. Trupke, J. Zhao, A. Wang, R. Corkish, and M. A. Green, “Very efficient light emission from bulk crystalline silicon,” Appl. Phys. Lett. 82(18), 2996–2998 (2003). [CrossRef]
  21. S. Sze, Physics of Semiconductor Devices, (Wiley, New York, 1981), pp 45–47.
  22. S. Boninelli, F. Iacona, G. Franzo, C. Bongiorno, C. Spinella, and F. Priolo, “Thermal evolution and photoluminescence properties of nanometric Si layers,” Nanotechnology 16(12), 3012–3016 (2005). [CrossRef]
  23. S. Fujita and N. Sugiyama, “Visible light-emitting devices with Schottky contacts on an ultrathin amorphous silicon layer containing silicon nanocrystals,” Appl. Phys. Lett. 74(2), 308–310 (1999). [CrossRef]
  24. P. Photopoulos and A. G. Nassiopoulou, “Room- and low-temperature voltage tunable electroluminescence from a single layer of silicon quantum dots in between two thin SiO2 layers,” Appl. Phys. Lett. 77(12), 1816–1818 (2000). [CrossRef]
  25. S. Prezioso, A. Anopchenko, Z. Gaburro, L. Pavesi, G. Pucker, L. Vanzetti, and P. Bellutti, “Electrical conduction and electroluminescence in nanocrystalline silicon-based light emitting devices,” J. Appl. Phys. 104(6), 063103 (2008). [CrossRef]
  26. A. Muscara, M. E. Castagna, S. Leonardi, S. Coffa, L. Caristia, and S. Lorenti, “Design and electro-optical characterization of Si-based resonant cavity light emitting devices at 850 nm,” J. Lumin. 121(2), 293–297 (2006). [CrossRef]
  27. C. D. Presti, A. Irrera, G. Franzò, I. Crupi, F. Priolo, F. Iacona, G. Di Stefano, A. Piana, D. Sanfilippo, and P. G. Fallica, “Photonic-crystal silicon nanoclusters light-emitting device,” Appl. Phys. Lett. 88(3), 033501 (2006). [CrossRef]
  28. F. Giorgis, “Optical microcavities based on amorphous silicon-nitride Fabry-Perot structures,” Appl. Phys. Lett. 77(4), 522–524 (2000). [CrossRef]
  29. C. A. Barrios and M. Lipson, “Electrically driven silicon resonant light emitting device based on slot-waveguide,” Opt. Express 13(25), 10092–10101 (2005). [CrossRef] [PubMed]
  30. F. Iacona, D. Pacifici, A. Irrera, M. Miritello, G. Franzò, F. Priolo, D. Sanfilippo, G. Di Stefano, and P. G. Fallica, “Electroluminescence at 1.54 µm in Er-doped Si nanoclusters-based devices,” Appl. Phys. Lett. 81(17), 3242–3244 (2002). [CrossRef]
  31. S. Yerci, R. Li, and L. Dal Negro, “Electroluminescence from Er-doped Si-rich silicon nitride light emitting diodes,” Appl. Phys. Lett. 97(8), 081109 (2010). [CrossRef]

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