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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 14 — Jul. 2, 2012
  • pp: 14921–14927
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Room-temperature electroluminescence from germanium in an Al0.3Ga0.7As/Ge heterojunction light-emitting diode by Γ-valley transport

Seongjae Cho, Byung-Gook Park, Changjae Yang, Stanley Cheung, Euijoon Yoon, Theodore I. Kamins, S. J. Ben Yoo, and James S. Harris, Jr.  »View Author Affiliations


Optics Express, Vol. 20, Issue 14, pp. 14921-14927 (2012)
http://dx.doi.org/10.1364/OE.20.014921


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Abstract

Group-IV materials for monolithic integration with silicon optoelectronic systems are being extensively studied. As a part of efforts, light emission from germanium has been pursued with the objective of evolving germanium into an efficient light source for optical communication systems. In this study, we demonstrate room-temperature electroluminescence from germanium in an Al0.3Ga0.7As/Ge heterojunction light-emitting diode without any complicated manipulation for alternating material properties of germanium. Electroluminescence peaks were observed near 1550 nm and the energy around this wavelength corresponds to that emitted from direct recombination at the Γ-valley of germanium.

© 2012 OSA

1. Introduction

Recently, optical devices based on group-IV materials have been widely studied for possible applications in the integrated silicon (Si) photonics systems [1

1. Y.-H. Kuo, Y. K. Lee, Y. Ge, S. Ren, J. E. Roth, T. I. Kamins, D. A. B. Miller, and J. S. Harris, “Strong quantum-confined Stark effect in germanium quantum-well structures on silicon,” Nature 437(7063), 1334–1336 (2005). [CrossRef] [PubMed]

7

7. K.-Y. Park, W.-S. Oh, J.-C. Choi, and W.-Y. Choi, “Design of 250-Mb/s Low-Power Fiber Optic Transmitter and Receiver ICs for POF Applications,” J. Semicond. Technol. Sci. 11(3), 221–228 (2011). [CrossRef]

]. Germanium (Ge) is considered as one of the most promising candidate materials compatible with Si complementary metal-oxide-semiconductor (CMOS) circuits since Ge can be grown on Si using relaxed SixGe1-x buffer layers to reduce the effect of the 3.96% lattice mismatch between Ge and Si[6

6. S. N. Chattopadhyay, C. B. Overton, S. Vetter, M. Azadeh, B. H. Olson, and N. E. Naga, “Optically Controlled Silicon MESFET Fabrication and Characterizations for Optical Modulator/Demodulator,” J. Semicond. Technol. Sci. 10(3), 213–224 (2010). [CrossRef]

-8

8. T. H. Loh, H. S. Nguyen, R. Murthy, M. B. Yu, W. Y. Loh, G. Q. Lo, N. Balasubramanian, D. L. Kwong, J. Wang, and S. J. Lee, “Selective epitaxial germanium on silicon-on-insulator high speed photodetectors using low-temperature ultrathin Si0.8Ge0.2 buffer,” Appl. Phys. Lett. 91(7), 073503 (2007). [CrossRef]

]. Given the fact that light emission is the most efficient for direct-bandgap materials, in which electrons can transfer from the conduction band to the valence band with momentum conservation, various approaches for operating indirect-bandgap Ge as a direct-bandgap material by straining, alloying, or band-filling have been investigated [9

9. Z. Huang, N. Kong, X. Guo, M. Liu, N. Duan, A. L. Beck, S. K. Banerjee, and J. C. Campbell, “21-GHz-Bandwidth Germanium-on-Silicon Photodiode Using Thin SiGe Buffer Layers,” IEEE J. Sel. Top. Quantum Electron. 12(6), 1450–1454 (2006). [CrossRef]

16

16. G. Shambat, S.-L. Cheng, J. Lu, Y. Nishi, and J. Vučković, “Direct band Ge photoluminescence near 1.6 μm coupled to Ge-on-Si microdisk resonators,” Appl. Phys. Lett. 97(24), 241102 (2010). [CrossRef]

]. Since Ge has a local conduction band minimum at the Γ-valley (k = 0), light emission is expected if a sufficient number of electrons can be injected into this valley. Transport along valleys aligned in the k-space can be an efficient method of electron injection across a heterojunction [17

17. P. Cheng, B. G. Park, S. Kim, and J. S. Harris, “The X-valley transport in GaAs/AlAs triple barrier structures,” J. Appl. Phys. 65(12), 5199–5201 (1989). [CrossRef]

,18

18. D. Arnold, K. Hess, and G. J. Iafrate, “Electron transport in heterostructure hot-electron diodes,” Appl. Phys. Lett. 53(5), 373–375 (1988). [CrossRef]

]. Aluminium gallium arsenide (AlGaAs) is a III-V compound material that can be grown on Ge with little lattice mismatch. AlxGa1-xAs, a ternary alloy, has a direct-bandgap for Al compositions up to approximately 40%, while it turns into an indirect-bandgap semiconductor for higher Al mole fractions [19

19. A. K. Saxena, “The conduction band structure and deep levels in Ga1-xAlxAs alloys from a high-pressure experiment,” J. Phys. C Solid State Phys. 13(23), 4323–4334 (1980). [CrossRef]

,20

20. B. G. Streetman and S. Banerjee, Solid State Electronics Devices (Prentice Hall, 2000).

]. Thus, it is a potential source of electrons for light emission in Ge.

In this work, a heterojunction near-infrared (IR) light-emitting diode (LED) operating at room temperature was fabricated and investigated. We applied the Γ-Γ transport mechanism in Al0.3Ga0.7As/Ge heterojunctions to inject carriers into the Γ-valley of Ge, by which a strong electroluminescence (EL) from Ge region was obtained at 300 K without introducing any complicated processing for intent to manipulate the material characteristics of Ge.

2. Device design and fabrication

The electron affinities of Ge (χGe) and AlxGa1-xAs (χAlxGa1-xAs) at the Γ-valleys are 4.0 – (0.8 – 0.66) = 3.86 eV and 4.07 – 1.1x eV, respectively. Here, 4.0 eV, 0.8 eV, and 0.66 eV are electron affinity at L-valley, Γ-valley energy bandgap, and L-valley energy bandgap of Ge, respectively. To achieve Γ-Γ transport across an AlxGa1-xAs/Ge heterojunction without a potential energy barrier to electron injection from AlxGa1-xAs into Ge, χGe|ΓχAlxGa1-xAs (|Γ denotes the value at Γ-valley) should be nonnegative. For this condition, the following two inequalities should hold simultaneously:

χGe|ΓχAlxGa1xAs=3.86(4.071.1x)0,forremovingenergybarrier
(1)
x0.4,forobtainingAlxGa1xAswithdirectbandgap
(2)

The simultaneous equation gives a solution of 0.2 ≤ x ≤ 0.4 and an Al fraction in this range should enable highly efficient Γ-Γ transport. In the experiment, x was selected to be 0.3 to get Al0.3Ga0.7As and the corresponding conduction-band offset at k = 0 was 0.12 eV. An intrinsic Al0.3Ga0.7As layer was inserted between the p+ Ge substrate and the n+ Al0.3Ga0.7As layer to reduce the leakage current due to band-to-band tunneling, for device reliability [21

21. S. M. Sze and K. K. Ng, Physics of Semiconductor Devices (Wiley-Interscience, 2007).

].

Figure 1(a)
Fig. 1 Energy-band diagrams of the Al0.3Ga0.7As/Ge heterojunction. (a) Energy-band diagram obtained by numerical device simulation at a forward bias of 1 V. (b) Schematic view of the energy-band diagram conditions in terms of (E) and k near the heterojunction for Γ-Γ transport.
illustrates the energy-band diagram obtained by a two-dimensional (2D) numerical device simulation, at an operating voltage of 1 V [22

22. ATLAS User’s Manual (Silvaco International, Santa Clara, 2011).

]. It is confirmed that the conduction-band energy of the intrinsic Al0.3Ga0.7As layer is above the conduction-band minimum at the Γ-valley of p+ Ge. Figure 1(a) also emphasizes that the wider bandgap of Al0.3Ga0.7As provides transparency to the IR light emitted by radiative recombination in Ge, which is another advantage of an AlxGa1-xAs/Ge heterojunction besides its good lattice match. Figure 1(b) demonstrates two criteria for Γ-Γ transport mechanism in this work: a non-negative Γ-valley offset by which the electrons injected from Al0.3Ga0.7As cathode into Ge substrate experiences no energy barrier and the momentum alignment of local minimum points in the conduction bands of Al0.3Ga0.7As and Ge at k = 0.

For the device fabrication, p+ Ge (001) substrates with 6° off-cut toward the [111] direction were prepared (Fig. 2(a)
Fig. 2 Process architecture for device fabrication. (a) Ge substrate preparation. (b) Epitaxial growths. (c) Active definition. (d) n-type and (e) p-type contacts. (f) Final critical dimensions.
). The doping concentration of the Ge substrate was Ga 2 × 1018 cm−3. Intrinsic Al0.3Ga0.7As, n+ Al0.3Ga0.7As, and n+ GaAs cladding layers were epitaxially grown in sequence by metal-organic chemical vapor deposition (MOCVD), without exposure to air between growths (Fig. 2(b)). The device active region was defined and isolated to form a circular mesa structure by photolithography and chlorine-based dry etching (Fig. 2(c)). Au (40 nm)/Ge (12 nm)/Ni (12 nm)/and Au (200 nm) were sequentially deposited by e-beam evaporation and lifted off to form an ohmic contact with the top cathode layer (Fig. 2(d)). n+ GaAs cladding layer plays roles of lowering the ohmic contact resistance and blocking the penetration of metal species into the Al0.3Ga0.7As cathode26. Subsequently, an ohmic contact with the substrate anode was established by deposition and lift-off of Ti (40 nm)/Pt (40 nm)/Au (200 nm) (bottom to top) multi-layer metals (Fig. 2(e)). The deposition rate of each layer was precisely adjusted to be in the range of 1–2 Å/s by real-time monitoring to obtain high-quality metal layers. Rapid thermal annealing (RTA) in a forming gas ambient of N2 with 4% H2 was carried out to reduce the contact resistance with the n-type material by improving adhesion and completely diffusing Ge into Au. The forming gas ambient during RTA also passivated the dry-etched side surfaces of the epitaxial layers. The process time (ramp-up for 15 s and steady-state for 10 s) and temperature (380°C, slightly higher than the eutectic point of Au-Ge) were chosen to avoid roughening of the electrode surfaces and metal penetration in the semiconductor materials [23

23. K. J. Choi, S. Y. Han, J.-L. Lee, J. K. Moon, M. Park, and H. Kim, “Au/Ge/Ni/Au and Pd/Ge/Ti/Au Ohmic Contacts to AlxGa1-xAs/InGaAs (x = 0.75) Pseudomorphic High Electron Mobility Transistor,” J. Korean Phys. Soc. 43, 253–258 (2003).

25

25. T. S. Kuan, P. E. Batson, T. N. Jackson, H. Rupprecht, and E. L. Wilkie, “Electron microscope studies of an alloyed Au/Ni/Au-Ge ohmic contact to GaAs,” J. Appl. Phys. 54(12), 6952–6957 (1983). [CrossRef]

]. Figure 2(f) shows the critical dimensions of the fabricated LED. The diameter of the circular mesa was 500 μm, with a 200-μm window for surface emission, a 100-μm-wide ring contact, and an adequate 50-μm alignment margin. The width of the p-type metal contact was 200 μm.

3. Material characterization

A θ-2θ high-resolution X-ray diffraction (HRXRD) measurement was performed to determine the Al content in the AlxGa1-xAs layer. The red line shown in Fig. 3(a)
Fig. 3 Material analyses. (a) HRXRD measurement and simulation results for analyzing the Al content. (b) ECV measurement results of doping profile versus depth (cathode). TEM images of (c) Heterostructure epitaxial layers on Ge substrate and (d) the Al0.3Ga0.7As/Ge interface.
represents the θ-2θ HRXRD spectrum of the GaAs/AlxGa1-xAs/Ge structure. The Al content in AlxGa1-xAs grown on the Ge substrate was also characterized by a fitting program, as shown with the black line in the same figure. The peaks corresponding to the Ge substrate in both the experimental data and the simulation were matched to allow an exact comparison of the two spectra. The best fitting result indicated that the Al content was 30.5% in the AlxGa1-xAs layer. The thicknesses of the cladding, n+ Al0.3Ga0.7As, and the intrinsic Al0.3Ga0.7As layers were 100 nm, 150 nm, and 150 nm, respectively. The carrier concentrations of the in situ-doped regions were characterized by an electrochemical capacitance-voltage (ECV) measurement, the results of which are shown in Fig. 3(b).

The device layers were doped with Si by adding SiH4 to the gas mixture during epitaxial growth. The targeted doping concentrations were 4 × 1018 cm−3 and 5 × 1018 cm−3 for the cladding and Al0.3Ga0.7As layers, respectively, including effects of dopant diffusion during growth and subsequent thermal processing. These values were accurately achieved, as confirmed in the figure. Figures 3(c) and 3(d) show the transmission electron microscope (TEM) images showing the heterostructure of the epitaxial layers grown on the Ge substrate with low resolution and the interface of the Al0.3Ga0.7As/Ge heterojunction with higher resolution. Defects such as voids and atomic clusters between layers were not observed. Theoretically, Ge/Al0.3Ga0.7As and Al0.3Ga0.7As/GaAs have only 0.171% and 0.047% lattice mismatches, respectively; this result is consistent with the high-quality interface indicated by TEM. The HRXRD analysis and TEM inspection results supports that the material growth conditions in this experiment allowed Γ-Γ transport across the Al0.3Ga0.7As/Ge heterojunction.

4. Optical measurement results

Figure 4(a)
Fig. 4 Measurement results. (a) Optical measurement setup. (b) EL intensities with wavelength and (c) IR CCD camera image from the fabricated Al0.3Ga0.7As/Ge heterojunction LED.
illustrates the optical measurement setup. The light emitted from the top facet of the device was coupled into a Corning multi-mode fiber with a 62.5-μm diameter core and measured with a Yokogawa AQ6370B optical spectrum analyzer (OSA) capable of 0.02 nm wavelength resolution and wide dynamic range (70 dB), enabling sensitivity down to −80 dBm. The fiber was mounted on x-y-z stage to obtain the optical coupling distance from the LED top facet and measure with an HP 81536A power sensor. After the optical measurement, the components in the dotted box (optical lens and OSA) were replaced by visualization equipment (IR camera) to capture the images of IR emission. Figure 4(b) shows the measured EL intensities versus wavelength. The LED was excited by current supplied by an ILX Lightwave LDX-3220 constant-current source. The curves in the figure indicate the measured EL at different current levels. Current injection was varied from 50 mA to 500 mA (the supply maximum), corresponding to current densities from 25.5 A/cm2 to 255 A/cm2. The wavelength where the EL peaks are expected is near 1.24/EG,Ge = 1.24/0.8 = 1.55 μm, where EG,Ge is the energy bandgap of the Ge Γ-valley. A spectral redshift of the EL peak wavelength is observed as the current injection is increased from 25.5 A/cm2 to 255 A/cm2.

The peak intensity is roughly proportional to the current density, while the full-width-half-maximum (FWHM) remains more or less the same (~160 nm). This trend implies that the output power is roughly proportional to the current density, which may enable us to rule out the possibility of luminescence caused by the spill-over of L-valley electrons into the Γ-valley due to the band filling of the L-valley [26

26. G. Mak and H. M. van Driel; “Femtosecond transmission spectroscopy at the direct band edge of germanium,” Phys. Rev. B Condens. Matter 49(23), 16817–16820 (1994). [CrossRef] [PubMed]

28

28. J. Wagner and L. Viňa, “Radiative recombination in heavily doped p-type germanium,” Phys. Rev. B 30(12), 7030–7036 (1984). [CrossRef]

]. The spill-over effect would result in a very nonlinear optical power vs. current density relationship, since the optical emission would be negligible until the L-valley is filled, while it would increase rapidly once the L-valley is filled. The redshift in the peak wavelength is mainly due to heating, which reduces the effective energy bandgap at the Γ-valley [29

29. Y. Varshni, “Temperature dependence of the energy gap in semiconductors,” Physica 34(1), 149–154 (1967). [CrossRef]

31

31. J. Kettle, R. M. Perks, and P. Dunstan, “Localised joule heating in AlGaInP light emitting diodes,” Electron. Lett. 42(19), 1122–1123 (2006). [CrossRef]

]. This redshift is equal to 0.14 nm/mA and is equivalent to an energy bandgap shrinkage of −7.11 × 10−5 eV/mA. A charge-coupled device (CCD) camera image was obtained to observe the emission of IR light from the fabricated LED as shown in Fig. 4(c). The image of the device was taken at a current injection of 255 A/cm2. A Hamamatsu IR C2741 camera controller and N2606 tube with sensitivity up to 1800 nm wavelength was connected to an Optem Zoom 70 tube microscope to image the EL intensity of the LED device.

5. Conclusion

A bulk-type Ge LED with an Al0.3Ga0.7As cathode epitaxially grown by MOCVD was fabricated and characterized. Although the band structure and properties of Ge was not modified, EL was successfully obtained through Γ-valley transport and injection into Ge, as confirmed by the optical spectrum measurement and IR image capturing. A redshift in the EL peak wavelengths due to joule heating near the heterojunction was observed. We demonstrated that a stronger light source for group-IV integrated optical systems can be provided by an AlxGa1-xAs/Ge heterojunction LED with accurately controlled Al fraction.

Acknowledgments

This work was supported by the Smart IT Convergence System Research Center funded by the Korean Ministry of Education, Science and Technology as Global Frontier Project (SIRC-2011-0031845), and in part by the World Class University (WCU) Hybrid Materials Program (R31-2008-000-10075-0). Dr. S. Cho is supported by the National Research Foundation of Korea Grant funded by the Korean Government (NRF-2011-357-D00155). This research was performed in part at the Stanford Nanofabrication Facility (a member of the National Nanotechnology Infrastructure Network) which is supported by the National Science Foundation under Grant ECS-9731293, its laboratory members, and the industrial members of the Stanford Center for Integrated Systems. The authors would also like to thank the technical support of the staff members of Korea Advanced Nano Fabrication Center.

References and links

1.

Y.-H. Kuo, Y. K. Lee, Y. Ge, S. Ren, J. E. Roth, T. I. Kamins, D. A. B. Miller, and J. S. Harris, “Strong quantum-confined Stark effect in germanium quantum-well structures on silicon,” Nature 437(7063), 1334–1336 (2005). [CrossRef] [PubMed]

2.

A. Mekis, “Silicon photonics: Lighting up the chip,” Nat. Photonics 2(7), 389–390 (2008). [CrossRef]

3.

H. J. Osten and P. Gaworzewski, “Charge transport in strained Si1-yCy and Si1-x-yGexCy alloys on Si (001),” J. Appl. Phys. 82(10), 4977–4981 (1997). [CrossRef]

4.

R. Ragan, K. S. Min, and H. A. Atwater, “Direct energy gap group IV semiconductor alloys and quantum dot arrays in SnxGe1-x/Ge and SnxSi1-x/Si alloy systems,” Mater. Sci. Eng. B 87(3), 204–213 (2001). [CrossRef]

5.

S. Cho, R. Chen, S. Koo, G. Shambat, H. Lin, N. Park, J. Vučković, T. I. Kamins, B.-G. Park, and J. S. Harris, “Fabrication and Analysis of Epitaxially Grown Ge1-xSnx Microdisk Resonator with 20-nm Free-Spectral Range,” IEEE Photon. Technol. Lett. 23(20), 1535–1537 (2011). [CrossRef]

6.

S. N. Chattopadhyay, C. B. Overton, S. Vetter, M. Azadeh, B. H. Olson, and N. E. Naga, “Optically Controlled Silicon MESFET Fabrication and Characterizations for Optical Modulator/Demodulator,” J. Semicond. Technol. Sci. 10(3), 213–224 (2010). [CrossRef]

7.

K.-Y. Park, W.-S. Oh, J.-C. Choi, and W.-Y. Choi, “Design of 250-Mb/s Low-Power Fiber Optic Transmitter and Receiver ICs for POF Applications,” J. Semicond. Technol. Sci. 11(3), 221–228 (2011). [CrossRef]

8.

T. H. Loh, H. S. Nguyen, R. Murthy, M. B. Yu, W. Y. Loh, G. Q. Lo, N. Balasubramanian, D. L. Kwong, J. Wang, and S. J. Lee, “Selective epitaxial germanium on silicon-on-insulator high speed photodetectors using low-temperature ultrathin Si0.8Ge0.2 buffer,” Appl. Phys. Lett. 91(7), 073503 (2007). [CrossRef]

9.

Z. Huang, N. Kong, X. Guo, M. Liu, N. Duan, A. L. Beck, S. K. Banerjee, and J. C. Campbell, “21-GHz-Bandwidth Germanium-on-Silicon Photodiode Using Thin SiGe Buffer Layers,” IEEE J. Sel. Top. Quantum Electron. 12(6), 1450–1454 (2006). [CrossRef]

10.

Z. Huang, J. Oh, and J. C. Campbell, “Back-side-illuminated high-speed Ge photodetector fabricated on Si substrate using this SiGe buffer layer,” Appl. Phys. Lett. 85(15), 3286–3288 (2004). [CrossRef]

11.

Y. Huo, H. Lin, R. Chen, M. Makarova, Y. Rong, M. Li, T. I. Kamins, J. Vučković, and J. S. Harris, “Strong enhancement of direct transition photoluminescence with highly tensile-strained Ge grown by molecular beam epitaxy,” Appl. Phys. Lett. 98(1), 011111 (2011). [CrossRef]

12.

M. E. Taylor, G. He, H. A. Atwater, and A. Polman, “Solid phase epitaxy of diamond cubic SnxGe1-x alloys,” J. Appl. Phys. 80(8), 4384–4388 (1996). [CrossRef]

13.

V. R. D’Costa, Y.-Y. Fang, J. Tolle, J. Kouvetakis, and J. Menéndez, “Ternary SiGeSn alloys: New opportunities for strain and bandgap engineering using group IV semiconductors,” Thin Solid Films 518(9), 2531–2537 (2010). [CrossRef]

14.

H. Lin, R. Chen, Y. Huo, T. I. Kamins, and J. S. Harris, “Raman study of strained Ge1-xSnx alloys,” Appl. Phys. Lett. 98(26), 261917 (2011). [CrossRef]

15.

S.-L. Cheng, J. Lu, G. Shambat, H.-Y. Yu, K. Saraswat, J. Vučković, and Y. Nishi, “Room temperature 1.6 microm electroluminescence from Ge light emitting diode on Si substrate,” Opt. Express 17(12), 10019–10024 (2009). [CrossRef] [PubMed]

16.

G. Shambat, S.-L. Cheng, J. Lu, Y. Nishi, and J. Vučković, “Direct band Ge photoluminescence near 1.6 μm coupled to Ge-on-Si microdisk resonators,” Appl. Phys. Lett. 97(24), 241102 (2010). [CrossRef]

17.

P. Cheng, B. G. Park, S. Kim, and J. S. Harris, “The X-valley transport in GaAs/AlAs triple barrier structures,” J. Appl. Phys. 65(12), 5199–5201 (1989). [CrossRef]

18.

D. Arnold, K. Hess, and G. J. Iafrate, “Electron transport in heterostructure hot-electron diodes,” Appl. Phys. Lett. 53(5), 373–375 (1988). [CrossRef]

19.

A. K. Saxena, “The conduction band structure and deep levels in Ga1-xAlxAs alloys from a high-pressure experiment,” J. Phys. C Solid State Phys. 13(23), 4323–4334 (1980). [CrossRef]

20.

B. G. Streetman and S. Banerjee, Solid State Electronics Devices (Prentice Hall, 2000).

21.

S. M. Sze and K. K. Ng, Physics of Semiconductor Devices (Wiley-Interscience, 2007).

22.

ATLAS User’s Manual (Silvaco International, Santa Clara, 2011).

23.

K. J. Choi, S. Y. Han, J.-L. Lee, J. K. Moon, M. Park, and H. Kim, “Au/Ge/Ni/Au and Pd/Ge/Ti/Au Ohmic Contacts to AlxGa1-xAs/InGaAs (x = 0.75) Pseudomorphic High Electron Mobility Transistor,” J. Korean Phys. Soc. 43, 253–258 (2003).

24.

T. G. Finstad, “The annealing behavior of Ge-Au-Ni, Ge-Au-Pt and Ge-Au-Pd trilayered films,” Thin Solid Films 47(3), 279–290 (1977). [CrossRef]

25.

T. S. Kuan, P. E. Batson, T. N. Jackson, H. Rupprecht, and E. L. Wilkie, “Electron microscope studies of an alloyed Au/Ni/Au-Ge ohmic contact to GaAs,” J. Appl. Phys. 54(12), 6952–6957 (1983). [CrossRef]

26.

G. Mak and H. M. van Driel; “Femtosecond transmission spectroscopy at the direct band edge of germanium,” Phys. Rev. B Condens. Matter 49(23), 16817–16820 (1994). [CrossRef] [PubMed]

27.

G. Grzybowski, R. Roucka, J. Mathews, L. Jiang, R. T. Beeler, J. Kouvetakis, and J. Ménendez, “Direct versus indirect optical recombination in Ge films grown on Si substrates,” Phys. Rev. B 84(20), 205307 (2011). [CrossRef]

28.

J. Wagner and L. Viňa, “Radiative recombination in heavily doped p-type germanium,” Phys. Rev. B 30(12), 7030–7036 (1984). [CrossRef]

29.

Y. Varshni, “Temperature dependence of the energy gap in semiconductors,” Physica 34(1), 149–154 (1967). [CrossRef]

30.

T. Mukai, M. Yamada, and S. Nakamura, “Current and temperature dependences of electroluminescence of InGaN-Based UV/blue/green light-emitting diodes,” Jpn. J. Appl. Phys. 37(Part 2, No. 11B), L1358–L1361 (1998). [CrossRef]

31.

J. Kettle, R. M. Perks, and P. Dunstan, “Localised joule heating in AlGaInP light emitting diodes,” Electron. Lett. 42(19), 1122–1123 (2006). [CrossRef]

OCIS Codes
(160.3130) Materials : Integrated optics materials
(230.3670) Optical devices : Light-emitting diodes
(230.3990) Optical devices : Micro-optical devices
(230.4000) Optical devices : Microstructure fabrication
(310.3840) Thin films : Materials and process characterization

ToC Category:
Optical Devices

History
Original Manuscript: April 18, 2012
Revised Manuscript: June 6, 2012
Manuscript Accepted: June 7, 2012
Published: June 19, 2012

Citation
Seongjae Cho, Byung-Gook Park, Changjae Yang, Stanley Cheung, Euijoon Yoon, Theodore I. Kamins, S. J. Ben Yoo, and James S. Harris, "Room-temperature electroluminescence from germanium in an Al0.3Ga0.7As/Ge heterojunction light-emitting diode by Γ-valley transport," Opt. Express 20, 14921-14927 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-14-14921


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References

  1. Y.-H. Kuo, Y. K. Lee, Y. Ge, S. Ren, J. E. Roth, T. I. Kamins, D. A. B. Miller, and J. S. Harris, “Strong quantum-confined Stark effect in germanium quantum-well structures on silicon,” Nature437(7063), 1334–1336 (2005). [CrossRef] [PubMed]
  2. A. Mekis, “Silicon photonics: Lighting up the chip,” Nat. Photonics2(7), 389–390 (2008). [CrossRef]
  3. H. J. Osten and P. Gaworzewski, “Charge transport in strained Si1-yCy and Si1-x-yGexCy alloys on Si (001),” J. Appl. Phys.82(10), 4977–4981 (1997). [CrossRef]
  4. R. Ragan, K. S. Min, and H. A. Atwater, “Direct energy gap group IV semiconductor alloys and quantum dot arrays in SnxGe1-x/Ge and SnxSi1-x/Si alloy systems,” Mater. Sci. Eng. B87(3), 204–213 (2001). [CrossRef]
  5. S. Cho, R. Chen, S. Koo, G. Shambat, H. Lin, N. Park, J. Vučković, T. I. Kamins, B.-G. Park, and J. S. Harris, “Fabrication and Analysis of Epitaxially Grown Ge1-xSnx Microdisk Resonator with 20-nm Free-Spectral Range,” IEEE Photon. Technol. Lett.23(20), 1535–1537 (2011). [CrossRef]
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