OSA's Digital Library

Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 16, Iss. 5 — Mar. 3, 2008
  • pp: 3242–3248
« Show journal navigation

Terahertz quantum cascade lasers with copper metal-metal waveguides operating up to 178 K

Mikhail A. Belkin, Jonathan A. Fan, Sahand Hormoz, Federico Capasso, Suraj P. Khanna, Mohamed Lachab, A. Giles Davies, and Edmund H. Linfield  »View Author Affiliations


Optics Express, Vol. 16, Issue 5, pp. 3242-3248 (2008)
http://dx.doi.org/10.1364/OE.16.003242


View Full Text Article

Acrobat PDF (155 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

We report terahertz quantum cascade lasers operating in pulsed mode at an emission frequency of 3 THz and up to a maximum temperature of 178 K. The improvement in the maximum operating temperature is achieved by using a three-quantum-well active region design with resonant-phonon depopulation and by utilizing copper, instead of gold, for the cladding material in the metal-metal waveguides.

© 2008 Optical Society of America

1. Introduction

Terahertz (THz) quantum cascade lasers (QCLs) are an emergent compact source for narrowband THz radiation in the wavelength range ~60–300 µm (~1–5 THz) [1-7

1. R. Köhler, A. Tredicucci, F. Beltram, H. E. Beere, E. H. Linfield, A. G. Davies, D. A. Ritchie, R. C. Iotti, and F. Rossi, “Terahertz semiconductor-heterostructure laser,” Nature 417, 156 (2002). [CrossRef] [PubMed]

]. Currently, these devices operate only at cryogenic temperatures, which limit their usefulness in applications such as spectroscopy, heterodyne detection, and screening. To achieve good performance in these devices, the optical mode must be strongly confined within the active region. This is a challenge because the active region thickness is effectively limited to ~10 µm, owing to the time taken to grow the material by techniques such as molecular beam epitaxy (MBE), and this thickness is an order of magnitude smaller than the free space emission wavelength. As a result, advances in waveguide design have been critical in advancing THz QCL performance. In particular, the implementation of the semi-insulating surface-plasmon waveguide was crucial for the demonstration of the first THz QCL [1

1. R. Köhler, A. Tredicucci, F. Beltram, H. E. Beere, E. H. Linfield, A. G. Davies, D. A. Ritchie, R. C. Iotti, and F. Rossi, “Terahertz semiconductor-heterostructure laser,” Nature 417, 156 (2002). [CrossRef] [PubMed]

]. Improvements in the temperature performance of THz QCLs were further achieved with the development of the metal-metal (MM) waveguide design [3

3. B. S. Williams, S. Kumar, H. Callebaut, Q. Hu, and J. L. Reno, “Terahertz quantum-cascade laser at λ≈100 µm using metal waveguide for mode confinement,” Appl. Phys. Lett. 83, 2124–2126 (2003). [CrossRef]

,4

4. B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Operation of terahertz quantum-cascade lasers at 164 K in pulsed mode and at 117 K in continuous-wave mode,” Opt. Express 13, 3331 (2005). [CrossRef] [PubMed]

,8

8. K. Unterrainer, R. Colombelli, C. Gmachl, F. Capasso, H. Y. Hwang, D. L. Sivco, and A. Y. Cho, “Quantum cascade lasers with double metal-semiconductor waveguide resonators,” Appl. Phys. Lett. 80, 3060 (2002). [CrossRef]

], which consists of metal films on both sides of the active region and which provides a mode confinement factor of nearly 100% [9

9. S. Kohen, B. S. Williams, and Q. Hu, “Electromagnetic modeling of terahertz quantum cascade laser waveguides and resonators,” J. Appl. Phys. 97, 053106 (2005). [CrossRef]

]. Currently, a highest operating temperature of 169 K has been achieved in THz QCLs with MM waveguides and an active region based on a resonant-phonon depopulation scheme [4

4. B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Operation of terahertz quantum-cascade lasers at 164 K in pulsed mode and at 117 K in continuous-wave mode,” Opt. Express 13, 3331 (2005). [CrossRef] [PubMed]

,10

10. S. Kumar, B. S. Williams, Q. Qin, A. W. M. Lee, Q. Hu, J. L. Reno, Z. R. Wasilewski, and H. C. Liu, “Terahertz quantum-cascade lasers with resonant-phonon depopulation: high temperature and low-frequency operation,” in Proceedings of the Ninth International Conference on Intersubband Transitions in Quantum Wells, D. Indjin, Z. Ikonic, P. Harrison, and R.W. Kelsall, eds. (University of Leeds, Leeds, U.K., 2007), p. T16.

]. Copper-to-copper thermocompression wafer bonding [4

4. B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Operation of terahertz quantum-cascade lasers at 164 K in pulsed mode and at 117 K in continuous-wave mode,” Opt. Express 13, 3331 (2005). [CrossRef] [PubMed]

,11

11. K. N. Chen, A. Fan, C. S. Tan, R. Reif, and C. Y. Yen, “Microstructure evolution and abnormal grain growth during copper wafer bonding,” Appl. Phys. Lett. 81, 3774 (2002). [CrossRef]

] was used to fabricate these waveguides [4

4. B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Operation of terahertz quantum-cascade lasers at 164 K in pulsed mode and at 117 K in continuous-wave mode,” Opt. Express 13, 3331 (2005). [CrossRef] [PubMed]

,10

10. S. Kumar, B. S. Williams, Q. Qin, A. W. M. Lee, Q. Hu, J. L. Reno, Z. R. Wasilewski, and H. C. Liu, “Terahertz quantum-cascade lasers with resonant-phonon depopulation: high temperature and low-frequency operation,” in Proceedings of the Ninth International Conference on Intersubband Transitions in Quantum Wells, D. Indjin, Z. Ikonic, P. Harrison, and R.W. Kelsall, eds. (University of Leeds, Leeds, U.K., 2007), p. T16.

] in order to improve their thermal properties, compared to waveguides processed with indium-gold bonding [3

3. B. S. Williams, S. Kumar, H. Callebaut, Q. Hu, and J. L. Reno, “Terahertz quantum-cascade laser at λ≈100 µm using metal waveguide for mode confinement,” Appl. Phys. Lett. 83, 2124–2126 (2003). [CrossRef]

,8

8. K. Unterrainer, R. Colombelli, C. Gmachl, F. Capasso, H. Y. Hwang, D. L. Sivco, and A. Y. Cho, “Quantum cascade lasers with double metal-semiconductor waveguide resonators,” Appl. Phys. Lett. 80, 3060 (2002). [CrossRef]

]. However, the top metal cladding in these devices was made of gold to allow dry-etching of ridges, using the top contact as a self-aligned mask [3

3. B. S. Williams, S. Kumar, H. Callebaut, Q. Hu, and J. L. Reno, “Terahertz quantum-cascade laser at λ≈100 µm using metal waveguide for mode confinement,” Appl. Phys. Lett. 83, 2124–2126 (2003). [CrossRef]

,4

4. B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Operation of terahertz quantum-cascade lasers at 164 K in pulsed mode and at 117 K in continuous-wave mode,” Opt. Express 13, 3331 (2005). [CrossRef] [PubMed]

].

Further improvements in the maximum operating temperatures of THz QCLs can be achieved by improving both the active region and waveguide designs. In THz QCLs with MM waveguides, 30-70% of the waveguide losses may originate from the losses associated with the metal claddings, the precise value depending on the emission wavelength, the active region design, and doping (see Ref. [3

3. B. S. Williams, S. Kumar, H. Callebaut, Q. Hu, and J. L. Reno, “Terahertz quantum-cascade laser at λ≈100 µm using metal waveguide for mode confinement,” Appl. Phys. Lett. 83, 2124–2126 (2003). [CrossRef]

] and Fig. 1). The optical losses of the metal cladding can vary depending on the type of metal used [12

12. M. Bahriz, V. Moreau, J. Palomo, R. Colombelli, D. A. Austin, J. W. Cockburn, L. R. Wilson, A. B. Krysa, and J. R. Roberts, “Room-temperature operation of λ≈7.5 µm surface-plasmon quantum cascade lasers,” Appl. Phys. Lett. 88, 181103 (2006). [CrossRef]

]. In Fig. 1, we compare the calculated waveguide losses for 10µm-thick and infinitely wide MM THz QCL waveguides with claddings made of gold and copper. For the data shown in Fig. 1(a), we considered a “lossless” active region with a refractive index of 3.5; for the data shown in Fig. 1(b), we considered an active region doped to 5×1015 cm-3, which is a typical average doping level for QCLs emitting between 2 – 5 THz, see, e.g., Ref. [4

4. B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Operation of terahertz quantum-cascade lasers at 164 K in pulsed mode and at 117 K in continuous-wave mode,” Opt. Express 13, 3331 (2005). [CrossRef] [PubMed]

]. In both cases, a one-dimensional waveguide solver was used for the calculations and the optical constants for the metals were taken from Ref. [13

13. M. A. Ordal, R. J. Bell, R. W. Alexander, Jr., L. L. Long, and M. R. Querry, “Optical properties of fourteen metals in the infrared and far infrared: Al, Co, Cu, Au, Fe, Pb, Mo, Ni, Pd, Pt, Ag, Ti, V and W,” Appl. Opt. 24, 4493 (1985). [CrossRef] [PubMed]

], with the refractive index of the QCL active region being calculated using the Drude-Lorentz approximation with parameters taken from Ref. [9

9. S. Kohen, B. S. Williams, and Q. Hu, “Electromagnetic modeling of terahertz quantum cascade laser waveguides and resonators,” J. Appl. Phys. 97, 053106 (2005). [CrossRef]

]. The thin contact layers of highly-doped GaAs and the thin metal layers of titanium or tantalum present in real devices were ignored as they were calculated to give negligible contributions to the waveguide losses.

Fig. 1. (a). Calculated waveguide losses for different wavelengths in a metal-metal waveguide assuming a “lossless” active region. (b) Calculated waveguide losses in a metal-metal waveguide assuming a realistic active region design with an average doping of 5×1015 cm-3. We note that long-wavelength, λ>200 µm, QCLs typically use lower doped active regions.
Fig. 2. Calculated temperature dependence of waveguide losses for 100 µm wavelength in a metal-metal waveguide assuming a “lossless” active region. Optical constants of metals were estimated using Eq. (1). The data for temperatures below 80 K is very sensitive to the purity of metals and is not shown.

The optical constants of metals, reported in Ref. [13

13. M. A. Ordal, R. J. Bell, R. W. Alexander, Jr., L. L. Long, and M. R. Querry, “Optical properties of fourteen metals in the infrared and far infrared: Al, Co, Cu, Au, Fe, Pb, Mo, Ni, Pd, Pt, Ag, Ti, V and W,” Appl. Opt. 24, 4493 (1985). [CrossRef] [PubMed]

], were measured at room temperature. Because the properties of metals change with temperature, it may be possible that MM waveguides with gold claddings have comparable or lower waveguide losses than MM waveguide with copper claddings at THz QCL operating temperatures. To estimate the temperature dependence of the optical constants of copper and gold, we used an approximate expression [14

14. M. Born and E. Wolf, Principles of Optics (Cambridge University Press, 1999).

]:

Re(n)Im(n)2πσω
(1)

where Re(n) and Im(n) are the real and imaginary part of the refractive index of a metal, σ is the electrical conductivity of the metal, and ω is the frequency of light. The electrical conductivities of copper and gold, measured at different temperatures, are well-known [15

15. “Electrical Resistivity of Pure Metals,” in CRC Handbook of Chemistry and Physics, 88th Edition (Internet Version 2008), D. R. Lide, ed. (CRC Press/Taylor and Francis, Boca Raton, Fla., 2008).

]. In Fig. 2, we plot the temperature dependence of the optical losses at 3 THz for 10µm-thick and infinitely wide MM waveguides with claddings made of gold and copper, calculated using the optical constants of metals obtained with Eq. (1). The data indicate that MM waveguides with copper claddings have smaller optical losses than MM waveguides with gold claddings even at cryogenic temperatures.

The data in Figs. 1 and 2 demonstrate that, by using copper instead of gold, the waveguide losses in MM THz QCL waveguides can be significantly reduced. We also calculated the optical losses for MM THz waveguides with a silver cladding, using data from Ref. [13

13. M. A. Ordal, R. J. Bell, R. W. Alexander, Jr., L. L. Long, and M. R. Querry, “Optical properties of fourteen metals in the infrared and far infrared: Al, Co, Cu, Au, Fe, Pb, Mo, Ni, Pd, Pt, Ag, Ti, V and W,” Appl. Opt. 24, 4493 (1985). [CrossRef] [PubMed]

], and obtained that the waveguide losses are larger than those in copper MM waveguides. Silver also has smaller electrical conductivity than copper at temperatures up to ~180 K. We note, however, that the optical properties of metals in the THz frequency range have not been extensively studied, and vary with temperature, layer deposition quality, metal purity, and other empirical parameters.

2. Device structure, fabrication, and experimental results

To demonstrate the effect of the waveguide cladding material on the temperature performance of MM THz QCLs, we compared the performance of two sets of devices processed from the same active region material, but with two different MM waveguide cladding metals: gold and copper. The active region in our lasers was based on the three-well resonant-phonon design reported in Ref. [16

16. H. Luo, S. R. Laframboise, Z. R. Wasilewski, G. C. Aers, H. C. Liu, and J. C. Cao, “Terahertz quantum-cascade lasers based on a three-well active module,” Appl. Phys. Lett. 90, 041112 (2007). [CrossRef]

]. This design may have several advantages compared to the four-well resonant-phonon active region design reported in [4

4. B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Operation of terahertz quantum-cascade lasers at 164 K in pulsed mode and at 117 K in continuous-wave mode,” Opt. Express 13, 3331 (2005). [CrossRef] [PubMed]

]; the conduction band diagrams for both designs are shown in Fig. 3. In comparison to the four-well design, the three-well design has a simplified injector that may reduce the laser mode absorption losses in the injector states [16

16. H. Luo, S. R. Laframboise, Z. R. Wasilewski, G. C. Aers, H. C. Liu, and J. C. Cao, “Terahertz quantum-cascade lasers based on a three-well active module,” Appl. Phys. Lett. 90, 041112 (2007). [CrossRef]

], improve the gain linewidth, and allow for higher current throughput [17

17. J. Faist, “Wallplug efficiency of quantum cascade lasers: Critical parameters and fundamental limits,” Appl. Phys. Lett. 90, 253512 (2007). [CrossRef]

], whilst still providing comparable injection efficiency into the upper laser level under the operating bias voltage. We note that both designs have similar (to within 1 Å) injection and extraction barrier thicknesses, emission frequencies, and dipole matrix elements for the laser transition.

Devices were tested in pulsed mode with 30 ns pulses at a 1 kHz repetition rate. Peak powers were measured with a calibrated helium-cooled bolometer using two 2” diameter parabolic mirrors: one with a 5 cm focal length to collect light from the device and the other with a 15 cm focal length to refocus it onto the detector. Figure 4(a) displays the current density-voltage (I-V) characteristic of a representative device with gold cladding layers, as well as a typical emission spectrum. A step associated with the injector state aligning with the upper laser state can be clearly seen in the I-V characteristics at a current density of approximately 700 A/cm2; a second step in the I-V characteristics, at a current density of approximately 1350 A/cm2, is due to the misalignment of the injector and the upper laser states. Devices processed into MM waveguides with a gold cladding typically operated up to 160-164 K. The light output as a function of current density (L-I) for the best performing device with gold MM waveguides, which operated up to 168 K, is shown in Fig. 4(b). We note that the gold MM waveguide devices reported in the original publication [16

16. H. Luo, S. R. Laframboise, Z. R. Wasilewski, G. C. Aers, H. C. Liu, and J. C. Cao, “Terahertz quantum-cascade lasers based on a three-well active module,” Appl. Phys. Lett. 90, 041112 (2007). [CrossRef]

] operated only up to 142 K. The improved performance of our devices may stem from a better growth and/or processing quality, as well as lower doping density. Devices processed into MM waveguides with copper cladding typically operated up to 170-174 K. The L-I characteristics for the best-performing device with copper cladding, which operated up to 178 K, are shown in Fig. 5(a), with the dependence of threshold current density on temperature being shown in Fig. 5(b). At high temperatures, the threshold current density displays an asymptotic dependence of ~exp(T/T 0) with T0≈100 K. We observed a similar asymptotic dependence with similar T0 for devices processed into MM waveguides with gold cladding.

Fig. 3. Conduction band diagrams of (a) three- and (b) four-quantum-well resonant-phonon active region designs, reported in Refs. [16] and [4] respectively. A single quantum-cascade stage is marked by a box. Both structures utilized the GaAs/Al0.15Ga0.85As material system. The layer sequences, starting from the injection barrier, are 48/96/20/74/42/161 Å for (a) and 49/79/25/66/41/156/33/90 Å for (b). Laser transitions are shown with arrows. Also shown are the transition dipole moments and emission energies for the laser transitions, calculated for single isolated modules of the structures. The four-quantum-well resonant-phonon active region design is shown for reference only; it is not used in our experiments.
Fig. 4. (a). Current density-voltage characteristic and an emission spectrum (inset) of a representative device processed with a gold metal-metal waveguide. Devices processed with a copper metal-metal waveguides displayed similar current density-voltage characteristics and emission spectra. (b) Light intensity-current density (LI) characteristics of the best-performing device with a gold metal-metal waveguide, 1.3mm-long and 150µm-wide. Inset: the LI characteristics of the device close to the maximum operating temperature of 168 K. The data are not corrected for an estimated 10% power collection efficiency.
Fig. 5. (a). The LI characteristics of a 1.4mm-long and 125µm-wide device with a copper metal-metal waveguide. Inset: the LI characteristics of the device close to the maximum operating temperature of 178 K. The data are not corrected for an estimated 10% power collection efficiency. Dips in the LI characteristics at current density ~1150 A/cm2 are due to some of the laser emission lines coincide with atmospheric absorption lines. (b) Threshold current density as a function of temperature for the device in (a). Inset: the LI characteristics of another device with a copper metal-metal waveguide, 1.6mm-long and 100µm-wide, close to its maximum operating temperature of 177 K.

3. Discussion

We attribute the observed improvement in temperature performance in copper MM waveguide devices to the superior optical properties of copper over those of gold. The differences in thermal properties between gold and copper are not expected to play an important role in determining the device performance since both copper and gold MM waveguide devices were processed following the same indium-bonding procedure and tested in pulsed mode with very short current pulses. We note that good thermal packaging is necessary for good continuous-wave (CW) performance, such as that reported in Ref. [4

4. B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Operation of terahertz quantum-cascade lasers at 164 K in pulsed mode and at 117 K in continuous-wave mode,” Opt. Express 13, 3331 (2005). [CrossRef] [PubMed]

] where copper-to-copper thermocompression wafer bonding was utilized. Our results indicate that, for the best CW performance, one may want to modify the processing procedure reported in Ref. [4

4. B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Operation of terahertz quantum-cascade lasers at 164 K in pulsed mode and at 117 K in continuous-wave mode,” Opt. Express 13, 3331 (2005). [CrossRef] [PubMed]

] to include a layer of copper in the top waveguide cladding for low-loss plasmon wave guiding.

The exact degree of improvement in temperature performance of a QCL owing to the reduction of waveguide losses depends on the characteristic temperature T0 of the active region. To a first approximation, we can assume that the waveguide losses do not change with temperature and, at high temperatures, the maximum laser gain scales with temperature as ~exp(-T/T 0), where T0 is the characteristic temperature deduced from the dependence of the threshold current density on temperature. Under these assumptions and neglecting small mirror losses in the MM waveguides [9

9. S. Kohen, B. S. Williams, and Q. Hu, “Electromagnetic modeling of terahertz quantum cascade laser waveguides and resonators,” J. Appl. Phys. 97, 053106 (2005). [CrossRef]

], the maximum operating temperatures for the devices with copper and gold waveguide claddings should scale as:

Tmax(Cu)Tmax(Au)=T0×In(α(Au)α(Cu))
(1)

where Tmax(Au), Tmax(Cu), α(Au), and α(Cu) are the maximum operating temperatures and waveguide losses for the MM waveguides with claddings made of gold and copper, respectively. Thus, for a given reduction in the waveguide losses, one may expect a larger improvement in the maximum operating temperatures for devices with larger T0.

In the case of our devices, Eq. (1) suggests that the substitution of gold with copper for the waveguide cladding resulted in an approximately 10% reduction in the waveguide losses. Similar results can be obtained by comparing the threshold current densities for the devices reported in Figs. 4(b) and 5(a). A 10% reduction in the waveguide losses is smaller than that expected from the data in Fig. 1 (~30%); the discrepancy is likely to stem from uncertainties in the real values of the optical constants of the metals and the QCL active region, as well as from losses introduced by imperfect processing.

4. Conclusion

We have demonstrated that substitution of gold for copper in MM THz QCL waveguides results in a reduction of the waveguide losses, which helps to increase the maximum operating temperatures of these devices. The processing procedures for the MM waveguides with copper and gold claddings are similar, and the devices with copper MM waveguides are robust and easy to wire-bond. Our MM THz QCLs with copper cladding, and an active region based on the three-quantum-well resonant-phonon depopulation design [16

16. H. Luo, S. R. Laframboise, Z. R. Wasilewski, G. C. Aers, H. C. Liu, and J. C. Cao, “Terahertz quantum-cascade lasers based on a three-well active module,” Appl. Phys. Lett. 90, 041112 (2007). [CrossRef]

], operated in pulsed mode up to the highest recorded temperature for THz QCLs to date, 178 K.

Acknowledgments

The structures were processed in the Center for Nanoscale Science (CNS) in Harvard University. Harvard-CNS is a member of the National Nanotechnology Infrastructure Network. Harvard University acknowledges support from the AFOSR under Contract No. FA9550-05-1-0435 (Gernot Pomrenke). J. F. acknowledges support from the NSF Graduate Fellowship. The University of Leeds acknowledges support from EPSRC (U.K.) and Her Majesty’s Government Communications Centre.

References and links

1.

R. Köhler, A. Tredicucci, F. Beltram, H. E. Beere, E. H. Linfield, A. G. Davies, D. A. Ritchie, R. C. Iotti, and F. Rossi, “Terahertz semiconductor-heterostructure laser,” Nature 417, 156 (2002). [CrossRef] [PubMed]

2.

B. S. Williams, H. Callebaut, S. Kumar, Q. Hu, and J. L. Reno, “3.4-THz quantum cascade laser based on longitudinal-optical-phonon scattering for depopulation,” Appl. Phys. Lett. 82, 1015 (2003). [CrossRef]

3.

B. S. Williams, S. Kumar, H. Callebaut, Q. Hu, and J. L. Reno, “Terahertz quantum-cascade laser at λ≈100 µm using metal waveguide for mode confinement,” Appl. Phys. Lett. 83, 2124–2126 (2003). [CrossRef]

4.

B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Operation of terahertz quantum-cascade lasers at 164 K in pulsed mode and at 117 K in continuous-wave mode,” Opt. Express 13, 3331 (2005). [CrossRef] [PubMed]

5.

A. Tredicucci, L. Mahler, T. Losco, J. Xu, C. Mauro, R. Köhler, H. E. Beere, D. A. Ritchie, and E. H. Linfield, “Advances in THz quantum cascade lasers: fulfilling the application potential,” Proc. SPIE 5738, 146 (2005). [CrossRef]

6.

C. Walther, M. Fischer, G. Scalari, R. Terazzi, N. Hoyler, and J. Faist, “Quantum cascade lasers operating from 1.2 to 1.6 THz,” Appl. Phys. Lett. 91, 131122 (2007). [CrossRef]

7.

B. S. Williams, “Terahertz Quantum Cascade Lasers,” Nature Photon. 1, 517–525 (2007). [CrossRef]

8.

K. Unterrainer, R. Colombelli, C. Gmachl, F. Capasso, H. Y. Hwang, D. L. Sivco, and A. Y. Cho, “Quantum cascade lasers with double metal-semiconductor waveguide resonators,” Appl. Phys. Lett. 80, 3060 (2002). [CrossRef]

9.

S. Kohen, B. S. Williams, and Q. Hu, “Electromagnetic modeling of terahertz quantum cascade laser waveguides and resonators,” J. Appl. Phys. 97, 053106 (2005). [CrossRef]

10.

S. Kumar, B. S. Williams, Q. Qin, A. W. M. Lee, Q. Hu, J. L. Reno, Z. R. Wasilewski, and H. C. Liu, “Terahertz quantum-cascade lasers with resonant-phonon depopulation: high temperature and low-frequency operation,” in Proceedings of the Ninth International Conference on Intersubband Transitions in Quantum Wells, D. Indjin, Z. Ikonic, P. Harrison, and R.W. Kelsall, eds. (University of Leeds, Leeds, U.K., 2007), p. T16.

11.

K. N. Chen, A. Fan, C. S. Tan, R. Reif, and C. Y. Yen, “Microstructure evolution and abnormal grain growth during copper wafer bonding,” Appl. Phys. Lett. 81, 3774 (2002). [CrossRef]

12.

M. Bahriz, V. Moreau, J. Palomo, R. Colombelli, D. A. Austin, J. W. Cockburn, L. R. Wilson, A. B. Krysa, and J. R. Roberts, “Room-temperature operation of λ≈7.5 µm surface-plasmon quantum cascade lasers,” Appl. Phys. Lett. 88, 181103 (2006). [CrossRef]

13.

M. A. Ordal, R. J. Bell, R. W. Alexander, Jr., L. L. Long, and M. R. Querry, “Optical properties of fourteen metals in the infrared and far infrared: Al, Co, Cu, Au, Fe, Pb, Mo, Ni, Pd, Pt, Ag, Ti, V and W,” Appl. Opt. 24, 4493 (1985). [CrossRef] [PubMed]

14.

M. Born and E. Wolf, Principles of Optics (Cambridge University Press, 1999).

15.

“Electrical Resistivity of Pure Metals,” in CRC Handbook of Chemistry and Physics, 88th Edition (Internet Version 2008), D. R. Lide, ed. (CRC Press/Taylor and Francis, Boca Raton, Fla., 2008).

16.

H. Luo, S. R. Laframboise, Z. R. Wasilewski, G. C. Aers, H. C. Liu, and J. C. Cao, “Terahertz quantum-cascade lasers based on a three-well active module,” Appl. Phys. Lett. 90, 041112 (2007). [CrossRef]

17.

J. Faist, “Wallplug efficiency of quantum cascade lasers: Critical parameters and fundamental limits,” Appl. Phys. Lett. 90, 253512 (2007). [CrossRef]

OCIS Codes
(140.3070) Lasers and laser optics : Infrared and far-infrared lasers
(140.5960) Lasers and laser optics : Semiconductor lasers
(230.5590) Optical devices : Quantum-well, -wire and -dot devices

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: November 26, 2007
Revised Manuscript: January 11, 2008
Manuscript Accepted: January 12, 2008
Published: February 25, 2008

Citation
Mikhail A. Belkin, Jonathan A. Fan, Sahand Hormoz, Federico Capasso, Suraj P. Khanna, Mohamed Lachab, A. G. Davies, and Edmund H. Linfield, "Terahertz quantum cascade lasers with copper metal-metal waveguides operating up to 178 K," Opt. Express 16, 3242-3248 (2008)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-5-3242


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. R. Köhler, A. Tredicucci, F. Beltram, H. E. Beere, E. H. Linfield, A. G. Davies, D. A. Ritchie, R. C. Iotti, and F. Rossi, "Terahertz semiconductor-heterostructure laser," Nature 417, 156 (2002). [CrossRef] [PubMed]
  2. B. S. Williams, H. Callebaut, S. Kumar, Q. Hu, and J. L. Reno, "3.4-THz quantum cascade laser based on longitudinal-optical-phonon scattering for depopulation," Appl. Phys. Lett. 82, 1015 (2003). [CrossRef]
  3. B. S. Williams, S. Kumar, H. Callebaut, Q. Hu, and J. L. Reno, "Terahertz quantum-cascade laser at ? ? 100 ?m using metal waveguide for mode confinement," Appl. Phys. Lett. 83, 2124-2126 (2003). [CrossRef]
  4. B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, "Operation of terahertz quantum-cascade lasers at 164 K in pulsed mode and at 117 K in continuous-wave mode," Opt. Express 13, 3331 (2005). [CrossRef] [PubMed]
  5. A. Tredicucci, L. Mahler, T. Losco, J. Xu, C. Mauro, R. Köhler, H. E. Beere, D. A. Ritchie, and E. H.  Linfield, "Advances in THz quantum cascade lasers: fulfilling the application potential," Proc. SPIE 5738, 146 (2005). [CrossRef]
  6. C. Walther, M. Fischer, G. Scalari, R. Terazzi, N. Hoyler, and J. Faist, "Quantum cascade lasers operating from 1.2 to 1.6 THz," Appl. Phys. Lett. 91, 131122 (2007). [CrossRef]
  7. B. S. Williams, "Terahertz Quantum Cascade Lasers," Nature Photon. 1, 517-525 (2007). [CrossRef]
  8. K. Unterrainer, R. Colombelli, C. Gmachl, F. Capasso, H. Y. Hwang, D. L. Sivco, and A. Y. Cho, "Quantum cascade lasers with double metal-semiconductor waveguide resonators," Appl. Phys. Lett. 80, 3060 (2002). [CrossRef]
  9. S. Kohen, B. S. Williams, and Q. Hu, "Electromagnetic modeling of terahertz quantum cascade laser waveguides and resonators," J. Appl. Phys. 97, 053106 (2005). [CrossRef]
  10. S. Kumar, B. S. Williams, Q. Qin, A. W. M. Lee, Q. Hu, J. L. Reno, Z. R. Wasilewski, H. C. Liu, "Terahertz quantum-cascade lasers with resonant-phonon depopulation: high temperature and low-frequency operation," in Proceedings of the Ninth International Conference on Intersubband Transitions in Quantum Wells, D. Indjin, Z. Ikonic, P. Harrison, and R.W. Kelsall, eds. (University of Leeds, Leeds, U.K., 2007), T16.
  11. K. N. Chen, A. Fan, C. S. Tan, R. Reif, and C. Y. Yen, "Microstructure evolution and abnormal grain growth during copper wafer bonding," Appl. Phys. Lett. 81, 3774 (2002). [CrossRef]
  12. M. Bahriz, V. Moreau, J. Palomo, R. Colombelli, D. A. Austin, J. W. Cockburn, L. R. Wilson, A. B. Krysa, J. R. Roberts, "Room-temperature operation of ??7.5 µm surface-plasmon quantum cascade lasers," Appl. Phys. Lett. 88, 181103 (2006). [CrossRef]
  13. M. A. Ordal, R. J. Bell, R. W. Alexander Jr., L. L. Long, and M. R. Querry, "Optical properties of fourteen metals in the infrared and far infrared: Al, Co, Cu, Au, Fe, Pb, Mo, Ni, Pd, Pt, Ag, Ti, V and W," Appl. Opt. 24, 4493 (1985). [CrossRef] [PubMed]
  14. M. Born and E. Wolf, Principles of Optics (Cambridge University Press, 1999).
  15. "Electrical Resistivity of Pure Metals," in CRC Handbook of Chemistry and Physics, 88th Edition (Internet Version 2008), D. R. Lide, ed. (CRC Press/Taylor and Francis, Boca Raton, Fla., 2008.
  16. H. Luo, S. R. Laframboise, Z. R. Wasilewski, G. C. Aers, H. C. Liu, J. C. Cao, "Terahertz quantum-cascade lasers based on a three-well active module," Appl. Phys. Lett. 90, 041112 (2007). [CrossRef]
  17. J. Faist, "Wallplug efficiency of quantum cascade lasers: Critical parameters and fundamental limits," Appl. Phys. Lett. 90, 253512 (2007). [CrossRef]

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.


« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited