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Optics Express

  • Editor: Michael Duncan
  • Vol. 13, Iss. 9 — May. 2, 2005
  • pp: 3331–3339
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Operation of terahertz quantum-cascade lasers at 164 K in pulsed mode and at 117 K in continuous-wave mode

Benjamin S. Williams, Sushil Kumar, Qing Hu, and John L. Reno  »View Author Affiliations


Optics Express, Vol. 13, Issue 9, pp. 3331-3339 (2005)
http://dx.doi.org/10.1364/OPEX.13.003331


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Abstract

We report the demonstration of a terahertz quantum-cascade laser that operates up to 164 K in pulsed mode and 117 K in continuous-wave mode at approximately 3.0 THz. The active region was based on a resonant-phonon depopulation scheme and a metal-metal waveguide was used for modal confinement. Copper to copper thermocompression wafer bonding was used to fabricate the waveguide, which displayed improved thermal properties compared to a previous indium-gold bonding method.

© 2005 Optical Society of America

1. Introduction

The terahertz frequency range (1–10 THz, 30–300 µm) has historically been technologically underdeveloped compared to the neighboring microwave and infrared spectral ranges, despite the fact that it has long been a subject of scientific interest. This is largely due to the lack of convenient techniques for radiation generation and detection. Recently, interest in the terahertz frequency range has exploded, driven in large part by the development of new sources. One such source is the terahertz quantum-cascade laser (QCL), in which photon generation takes place via electronic intersubband transitions in semiconductor heterostructures [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]

, 2

2. M. Rochat, L. Ajili, H. Willenberg, J. Faist, H. Beere, G. Davies, E. Linfield, and D. Ritchie, “Low-threshold terahertz quantum-cascade lasers,” Appl. Phys. Lett. 81, 1381 (2002). [CrossRef]

, 3

3. 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]

]. Such lasers have already been demonstrated in applications such as imaging [4

4. J. Darmo, V. Tamosiunas, G. Fasching, J. Kröll, K. Unterrainer, M. Beck, M. Giovannini, J. Faist, C. Kremser, and P. Debbage, “Imaging with a Terahertz quantum cascade laser,” Opt. Express 12, 1879 (2004). URL http://www.opticsexpress.org/abstract.cfm?URI=OPEX-12-9-1879. [CrossRef] [PubMed]

], spectroscopy [5

5. D. C. Larrabee, G. A. Khodaparast, F. K. Tittel, J. Kuno, G. Scalari, L. Ajili, J. Faist, H. Beere, G. Davies, E. Linfield, D. Ritchie, Y. Nakajima, M. Nakai, S. Sasa, M. Inoue, S. Chung, and M. B. Santos, “Application of terahertz quantum-cascade lasers to semiconductor cyclotron resonance,” Opt. Lett. 29, 122 (2004). [CrossRef] [PubMed]

], and as a local oscillator in a heterodyne receiver [6

6. J. R. Gao, J. N. Hovenier, Z. Q. Yang, J. J. A. Baselmans, A. Baryshev, M. Hajenius, T. M. Klapwijk, A. J. L. Adam, T. O. Klaassen, B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “A terahertz heterodyne receiver based on a quantum cascade laser and a superconducting bolometer,” submitted to Appl. Phys. Lett. (2005).

].

The first terahertz QCL — based on a chirped superlattice design with a novel surface-plasmon waveguide — operated only up to 50 K in pulsed mode, and did not lase at all in continuous-wave (cw) mode [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]

]. Since that initial breakthrough, major developments have taken place in both the multiple-quantum-well gain medium and the waveguide. Most notably, the resonant-phonon scheme takes advantage of sub-picosecond electron-longitudinal-optical (LO) phonon scattering to selectively depopulate the lower radiative state [7

7. M. A. Stroscio, M. Kisin, G. Belenky, and S. Luryi, “Phonon enhanced inverse population in asymmetric double quantum wells,” Appl. Phys. Lett. 75, 3258 (1999). [CrossRef]

, 3

3. 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]

]. Also, the use of a metal-metal ridge waveguide, similar in form to a microstrip transmission line, has been successfully used to provide a high-confinement, low-loss cavity for terahertz lasers [8

8. 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 (2003). [CrossRef]

]. Together, these advances have allowed cw lasing above the liquid nitrogen temperature up to 93 K [9

9. S. Kumar, B. S. Williams, S. Kohen, Q. Hu, and J. L. Reno, “Continuous-wave operation of terahertz quantum-cascade lasers above liquid-nitrogen temperature,” Appl. Phys. Lett. 84, 2494 (2004). [CrossRef]

], and pulsed lasing up to 137 K [10

10. B. S. Williams, S. Kumar, H. Callebaut, Q. Hu, and J. L. Reno, “Terahertz quantum-cascade laser operating up to 137 K,” Appl. Phys. Lett. 83, 5142 (2003). [CrossRef]

].

There is strong interest in pushing operating temperatures to within the range achievable with thermoelectric coolers, and even higher. Achieving intersubband population inversion at terahertz frequencies is difficult because the photon energy ħω is relatively small (~10–20 meV), and is not much larger than the low temperature subband broadening (~4 meV). As a result, obtaining selective injection and depopulation of carriers in the closely spaced upper and lower radiative subbands is difficult, a problem which becomes worse for higher electronic temperatures and as level broadening increases. Furthermore, unlike mid-infrared QCLs, in terahertz QCLs ħω is less than the LO phonon energy (E LO=36 meV in GaAs), and the gain displays a strong dependence on the electronic temperature due to the thermal activation of nonradiative optical phonon scattering from the upper to the lower radiative state. While this scattering process is energetically forbidden for cold electrons, at high electronic temperatures Te it is expected to dominate the upper state lifetime, which takes the form τu1τhot1 exp[(ħω-E LO)/kBTe ], where τhot is the scattering time of an electron in the upper radiative subband with sufficient in-plane kinetic energy to emit an LO-phonon. Finally, thermal backfilling of the lower radiative state by carriers from the injector states reduces population inversion at high temperatures. These effects all depend sensitively on the device electronic temperature during operation, which, as expected, is significantly higher than the lattice temperature during operation due to the finite energy relaxation rate [11

11. V. B. Gorfinkel, S. Luryi, and B. Gelmont, “Theory of gain spectra for quantum cascade lasers and temperature dependence of their characteristics at low and moderate carrier concentrations,” IEEE J. Quantum Electron. 32, 1995 (1996). [CrossRef]

, 12

12. M. S. Vitiello, G. Scamarcio, V. Spagnolo, B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Measurement of subband electronic temperatures and population inversion in THz quantum-cascade lasers,” Appl. Phys. Lett. 86, 111115 (2005). [CrossRef]

]. However, analysis of the performance of existing resonant-phonon lasers suggests that to this point, while these effects degrade laser performance and lead to increased threshold current densities J th, they have not set fundamental limits on laser performance. Rather, device operation ceases at high temperatures when J th reaches the maximum achievable current density J max in a given design [9

9. S. Kumar, B. S. Williams, S. Kohen, Q. Hu, and J. L. Reno, “Continuous-wave operation of terahertz quantum-cascade lasers above liquid-nitrogen temperature,” Appl. Phys. Lett. 84, 2494 (2004). [CrossRef]

]; beyond this peak bias point, the injection subbands become misaligned with the upper radiative level and the device enters a negative differential resistance (NDR) regime. While increasing the doping level can increase J max [13

13. H. C. Liu, M. Wächter, D. Ban, Z. R. Wasilewski, M. Buchanan, G. C. Aers, J. C. Cao, S. L. Feng, B. S. Williams, and Q. Hu, “Effect of doping concentration on the performance of terahertz quantum-cascade lasers,” submitted to Appl. Phys. Lett. (2005).

], this comes at the cost of also increasing free carrier absorption inside the active region, which is very strong at long wavelengths. Hence, the design challenge is to increase J max without also increasing J th, which would otherwise prevent any net improvement in temperature performance.

2. Design and fabrication

Fig. 1. (a) Calculated conduction band schematic, with the four-well module outlined in a dotted box. Beginning with the left injection barrier, the layer thicknesses in Å are 49/79/25/66/41/156/33/90, and the 156 Å well is doped at 1.9×1016 cm-3, which yields a sheet density of 3.0×1010 cm-2 per module. (b) Scanning electron micrograph of the cleaved facet of a 23-µm-wide ridge waveguide. (c) Modal intensity for fundamental mode calculated with finite-element solver.

The structure, labeled FL178C-M7, was grown via MBE (growth EA1121) with n=5×1018 cm-3 contact layers grown above (50-nm thick) and below (100-nm thick) the 10-µm-thick active region, and with a 200-nm Al0.55Ga0.45As etch-stop layer underlying the entire growth. The metal-metal waveguide structures were fabricated using a method similar to that described in Ref. [8

8. 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 (2003). [CrossRef]

], except that a Cu-Cu thermocompression bonding technique [15

15. 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 instead of the In-Au reactive bonding method. In this method, both the device wafer and an n+ receptor wafer were prepared by e-beam evaporation of Ta/Cu (30/500 nm) layers. The Ta layer serves as an adhesion layer and prevents Cu diffusion into the epitaxial layers [16

16. C.-Y. Chen, L. Chang, E. Y. Chang, S.-H. Chen, and D.-F. Chang, “Thermal stability of Cu/Ta/GaAs multilayers,” Appl. Phys. Lett. 77, 3367 (2000). [CrossRef]

]. The wafers were cleaved into 1 cm2 dies, and bonding was performed in an EV Group 501 wafer bonder under vacuum at 400°C for 60 min at a pressure of approximately 5 MPa. Following cooling, the devices were annealed for 30 min at 400°C in an N2 atmosphere. Device processing then continued according to the standard recipe. The device substrate was removed by lapping and selective etching, after which standard photolithography could be performed on the 10-µm-thick epitaxial layers. It was observed that dies that underwent the post-bond anneal displayed noticeably fewer stress cracks and defects in the epitaxial layer, which is consistent with previously observed strain relaxation in the copper layer [15

15. 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]

]. Compared to the In-Au reactive bonding method, which can be performed by hand on a hot plate, the Cu-Cu method is more demanding in terms of the higher pressures and temperatures required, and is more sensitive to particulate surface contamination.

Ti/Au (20/400 nm) contacts were deposited and used as self-aligned etch masks to define ridge waveguides via dry etching. Etching was performed in a Plasmaquest electron cyclotron reactive ion etcher using BCl3:N2 (15:5 sccm) at 5 mTorr, with a microwave power of 600 W, and an RF power of 15 W. The substrate was thinned to 170 µm to improve heat sinking, and devices were cleaved to form cavities of various lengths, with the facets left uncoated. A scanning electron micrograph of a typical 23-µm-wide ridge structure is shown in Fig. 1(b). The dry etch process results in shallow shoulders at the foot of the mesa which turn out to be helpful in allowing the cleave to propagate properly across the facet. Although the tearing process of the copper that occurs during cleaving obscures the bonding layer somewhat, it is observed to have very few voids, and displays good strength and adhesion, so that wire bonds can be made directly to the top of the ridge.

3. Results

The best continuous-wave performance was obtained from a narrower 23-µm-wide, 1.22-mm-long ridge structure, which lased up to 117 K. This device only lased up to 158 K in pulsed mode, which is likely due to slightly higher waveguide losses in the narrower ridge. The width to wavelength ratio of the device was w/λ 0≈0.22, which is the narrowest of any laser. In addition to L-I curves, voltage versus current (V-I), and differential resistance versus current (dV/dI-I) characteristics are shown in Fig. 3. Cw spectra were collected using a Nicolet 850 Fourier transform spectrometer with a room temperature deuterated triglycine sulfate (DTGS) pyroelectric detector. Typical spectra taken at several temperatures are shown in the Fig. 3 inset. The observed emission is often single mode, but multiple longitudinal modes were also seen at particular biases and temperatures. Because of the Stark shift of the gain peak, in general the device lases at higher frequency modes at higher temperatures, since the higher lasing thresholds lead to larger electric fields across the structure at the onset of lasing. At a heat sink temperature of 11 K, J th=440 A/cm2, with a maximum single facet optical power of 2.6 mW (uncorrected for collection efficiency). The output power was collected by a Winston cone placed near the laser facet, and measured with a thermopile detector (ScienTech, Model AC2500) placed directly in front of the cryostat window.

Lasing ceases when the device reaches a current density of J max≈835 A/cm2, which corresponds to the bias when the injector states become misaligned with the upper radiative state and the devices enters an NDR region. In addition to the improved value of T 0, part of the reason for the improvement of this laser compared to that from Ref. [9

9. S. Kumar, B. S. Williams, S. Kohen, Q. Hu, and J. L. Reno, “Continuous-wave operation of terahertz quantum-cascade lasers above liquid-nitrogen temperature,” Appl. Phys. Lett. 84, 2494 (2004). [CrossRef]

] is that J max is larger by more than 100 A/cm2, while J th has remained almost unchanged. The fact that J max changes very little with temperature, even as the upper state lifetime τ5 drops with the increase in thermally activated LO-phonon scattering, suggests that transport is limited by incoherent sequential tunneling through the injection barrier. Thus there may still be more room to optimize performance by thinning the injection barrier even further.

Fig. 2. Optical power versus current measured from a 48-µm-wide, 0.99-mm-long ridge using 200-ns pulses repeated at 10 kHz. The lower inset shows an expanded version of the high temperature L-I curves. The upper inset displays the threshold current density versus temperature.

At 11 K, the maximum single-facet wall-plug efficiency is ~10-3 and the single-facet slope efficiency is measured to be approximately 30 mW/A after correction for the 90% cryostat window transmission. The theoretical slope efficiency in a cascade laser is given by

dLdI=12ħωeNmodαmαw+αmηi,
(1)

Fig. 3. Continuous-wave characteristics for a 23-µm-wide, 1.22-mm-long ridge at various heat sink temperatures, where the optical power is measured from a single facet. The lower panel displays the V-I and dV/dI-I characteristics at several temperatures. The upper inset shows typical spectra at several temperatures, and the lower inset displays the relative size of the threshold discontinuity in the differential resistance versus temperature.

In order to evaluate how closely the Cu-Cu bonding technique approaches ideal performance, a nonlinear finite-element solver was used to model two-dimensional heat flow out of the laser ridge. The thermal conductivity of the multiple-quantum-well active region was modeled as κactive≈0.5 W/cm·K to correspond with measurements of κ on a similar device [19

19. M. Chand and H. Maris. Personal communication.

], the bonding interface was modeled as a 1-µm-thick layer of Cu (κCu=4.3 W/cm·K at 150 K), and the n+ GaAs substrate was modeled with a temperature dependent thermal conductivity according to Ref. [20

20. J. S. Blakemore, “Semiconducting and other major properties of gallium arsenide,” J. Appl. Phys. 53, R123 (1982). [CrossRef]

] (κGaAs~2-1 W/cm·K for 100–150 K). To simulate cw operation at T max,cw, the bottom of the substrate was set to 117 K, and a heat source of 1.1×10 7 W/cm3 distributed uniformly across the active region. The results are shown in Fig. 4. Because of the high value of κCu, thermal resistance of the device is dominated by the temperature drop inside the active region, and spreading resistance in the substrate. The simulated maximum active region temperature is 149 K, 9 K lower than the measured T max,pulsed=158 K. While the discrepancy may partially arise from uncertainty in the value of κ active, this result suggests that there may be room for improvement in the interface bonding quality. An effective thermal resistance at the peak cw temperature (T sink=117 K) can be defined for the 23-µm-wide structure, by considering the active region as a lumped element and assuming that lasing ceases when the active region temperature T active=158 K. This gives a thermal resistance of RT =(T max,pulsed-T max,cw)/P≈14 K/W, where P is the total electrical power dissipated in the device. For comparison, several devices from the same wafer were fabricated with In-Au reactive wafer bonding, and the highest cw temperature that was reached was 76 K.

Fig. 4. (a) Two-dimensional heat flow model calculated with a nonlinear finite-element solver. The 800-µm-wide, 170-µm-thick n + GaAs substrate extends beyond the margins of the figure. The lower boundary is set to 117 K, and the active region is uniformly driven by a power source of 1.1×107 W/cm3, which corresponds lasing conditions at T sink=117 K cw operation.

4. Conclusion

Acknowledgments

The authors thank A. Fan for his expertise and assistance with the copper bonding. This work is supported by AFOSR, NASA, and NSF. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.

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.

M. Rochat, L. Ajili, H. Willenberg, J. Faist, H. Beere, G. Davies, E. Linfield, and D. Ritchie, “Low-threshold terahertz quantum-cascade lasers,” Appl. Phys. Lett. 81, 1381 (2002). [CrossRef]

3.

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]

4.

J. Darmo, V. Tamosiunas, G. Fasching, J. Kröll, K. Unterrainer, M. Beck, M. Giovannini, J. Faist, C. Kremser, and P. Debbage, “Imaging with a Terahertz quantum cascade laser,” Opt. Express 12, 1879 (2004). URL http://www.opticsexpress.org/abstract.cfm?URI=OPEX-12-9-1879. [CrossRef] [PubMed]

5.

D. C. Larrabee, G. A. Khodaparast, F. K. Tittel, J. Kuno, G. Scalari, L. Ajili, J. Faist, H. Beere, G. Davies, E. Linfield, D. Ritchie, Y. Nakajima, M. Nakai, S. Sasa, M. Inoue, S. Chung, and M. B. Santos, “Application of terahertz quantum-cascade lasers to semiconductor cyclotron resonance,” Opt. Lett. 29, 122 (2004). [CrossRef] [PubMed]

6.

J. R. Gao, J. N. Hovenier, Z. Q. Yang, J. J. A. Baselmans, A. Baryshev, M. Hajenius, T. M. Klapwijk, A. J. L. Adam, T. O. Klaassen, B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “A terahertz heterodyne receiver based on a quantum cascade laser and a superconducting bolometer,” submitted to Appl. Phys. Lett. (2005).

7.

M. A. Stroscio, M. Kisin, G. Belenky, and S. Luryi, “Phonon enhanced inverse population in asymmetric double quantum wells,” Appl. Phys. Lett. 75, 3258 (1999). [CrossRef]

8.

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 (2003). [CrossRef]

9.

S. Kumar, B. S. Williams, S. Kohen, Q. Hu, and J. L. Reno, “Continuous-wave operation of terahertz quantum-cascade lasers above liquid-nitrogen temperature,” Appl. Phys. Lett. 84, 2494 (2004). [CrossRef]

10.

B. S. Williams, S. Kumar, H. Callebaut, Q. Hu, and J. L. Reno, “Terahertz quantum-cascade laser operating up to 137 K,” Appl. Phys. Lett. 83, 5142 (2003). [CrossRef]

11.

V. B. Gorfinkel, S. Luryi, and B. Gelmont, “Theory of gain spectra for quantum cascade lasers and temperature dependence of their characteristics at low and moderate carrier concentrations,” IEEE J. Quantum Electron. 32, 1995 (1996). [CrossRef]

12.

M. S. Vitiello, G. Scamarcio, V. Spagnolo, B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Measurement of subband electronic temperatures and population inversion in THz quantum-cascade lasers,” Appl. Phys. Lett. 86, 111115 (2005). [CrossRef]

13.

H. C. Liu, M. Wächter, D. Ban, Z. R. Wasilewski, M. Buchanan, G. C. Aers, J. C. Cao, S. L. Feng, B. S. Williams, and Q. Hu, “Effect of doping concentration on the performance of terahertz quantum-cascade lasers,” submitted to Appl. Phys. Lett. (2005).

14.

L. Ajili, G. Scalari, J. Faist, H. Beere, E. Linfield, D. Ritchie, and G. Davies, “High power quantum cascade lasers operating at λ≅=87 and 130 µm,” Appl. Phys. Lett. 85, 3986 (2004). [CrossRef]

15.

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]

16.

C.-Y. Chen, L. Chang, E. Y. Chang, S.-H. Chen, and D.-F. Chang, “Thermal stability of Cu/Ta/GaAs multilayers,” Appl. Phys. Lett. 77, 3367 (2000). [CrossRef]

17.

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]

18.

C. Sirtori, F. Capasso, J. Faist, A. L. Hutchinson, D. L. Sivco, and A. Y. Cho, “Resonant tunneling in quantum cascade lasers,” IEEE J. Quantum Electron. 34, 1722 (1998). [CrossRef]

19.

M. Chand and H. Maris. Personal communication.

20.

J. S. Blakemore, “Semiconducting and other major properties of gallium arsenide,” J. Appl. Phys. 53, R123 (1982). [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:
Research Papers

History
Original Manuscript: March 30, 2005
Revised Manuscript: April 14, 2005
Published: May 2, 2005

Citation
Benjamin Williams, Sushil Kumar, Qing Hu, and John Reno, "Operation of terahertz quantum-cascade lasers at 164 K in pulsed mode and at 117 K in continuous-wave mode," Opt. Express 13, 3331-3339 (2005)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-13-9-3331


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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. M. Rochat, L. Ajili, H. Willenberg, J. Faist, H. Beere, G. Davies, E. Linfield, and D. Ritchie, �??Low-threshold terahertz quantum-cascade lasers,�?? Appl. Phys. Lett. 81, 1381 (2002). [CrossRef]
  3. 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]
  4. J. Darmo, V. Tamosiunas, G. Fasching, J. Kröll, K. Unterrainer, M. Beck, M. Giovannini, J. Faist, C. Kremser, and P. Debbage, �??Imaging with a Terahertz quantum cascade laser,�?? Opt. Express 12, 1879 (2004). URL <a href="http://www.opticsexpress.org/abstract.cfm?URI=OPEX-12-9-1879.">http://www.opticsexpress.org/abstract.cfm?URI=OPEX-12-9-1879.</a> [CrossRef] [PubMed]
  5. D. C. Larrabee, G. A. Khodaparast, F. K. Tittel, J. Kuno, G. Scalari, L. Ajili, J. Faist, H. Beere, G. Davies, E. Linfield, D. Ritchie, Y. Nakajima, M. Nakai, S. Sasa, M. Inoue, S. Chung, and M. B. Santos, �??Application of terahertz quantum-cascade lasers to semiconductor cyclotron resonance,�?? Opt. Lett. 29, 122 (2004). [CrossRef] [PubMed]
  6. J. R. Gao, J. N. Hovenier, Z. Q. Yang, J. J. A. Baselmans, A. Baryshev, M. Hajenius, T. M. Klapwijk, A. J. L. Adam, T. O. Klaassen, B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, �??A terahertz heterodyne receiver based on a quantum cascade laser and a superconducting bolometer,�?? submitted to Appl. Phys. Lett. (2005).
  7. M. A. Stroscio, M. Kisin, G. Belenky, and S. Luryi, �??Phonon enhanced inverse population in asymmetric double quantum wells,�?? Appl. Phys. Lett. 75, 3258 (1999). [CrossRef]
  8. 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 (2003). [CrossRef]
  9. S. Kumar, B. S. Williams, S. Kohen, Q. Hu, and J. L. Reno, �??Continuous-wave operation of terahertz quantum-cascade lasers above liquid-nitrogen temperature,�?? Appl. Phys. Lett. 84, 2494 (2004). [CrossRef]
  10. B. S. Williams, S. Kumar, H. Callebaut, Q. Hu, and J. L. Reno, �??Terahertz quantum-cascade laser operating up to 137 K,�?? Appl. Phys. Lett. 83, 5142 (2003). [CrossRef]
  11. V. B. Gorfinkel, S. Luryi, and B. Gelmont, �??Theory of gain spectra for quantum cascade lasers and temperature dependence of their characteristics at low and moderate carrier concentrations,�?? IEEE J. Quantum Electron. 32, 1995 (1996). [CrossRef]
  12. M. S. Vitiello, G. Scamarcio, V. Spagnolo, B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, �??Measurement of subband electronic temperatures and population inversion in THz quantum-cascade lasers,�?? Appl. Phys. Lett. 86, 111115 (2005). [CrossRef]
  13. H. C. Liu, M.Wächter, D. Ban, Z. R.Wasilewski, M. Buchanan, G. C. Aers, J. C. Cao, S. L. Feng, B. S.Williams, and Q. Hu, �??Effect of doping concentration on the performance of terahertz quantum-cascade lasers,�?? submitted to Appl. Phys. Lett. (2005).
  14. L. Ajili, G. Scalari, J. Faist, H. Beere, E. Linfield, D. Ritchie, and G. Davies, �??High power quantum cascade lasers operating at λ �?� 87 and 130 μm,�?? Appl. Phys. Lett. 85, 3986 (2004). [CrossRef]
  15. 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]
  16. C.-Y. Chen, L. Chang, E. Y. Chang, S.-H. Chen, and D.-F. Chang, �??Thermal stability of Cu/Ta/GaAs multilayers,�?? Appl. Phys. Lett. 77, 3367 (2000). [CrossRef]
  17. 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]
  18. C. Sirtori, F. Capasso, J. Faist, A. L. Hutchinson, D. L. Sivco, and A. Y. Cho, �??Resonant tunneling in quantum cascade lasers,�?? IEEE J. Quantum Electron. 34, 1722 (1998). [CrossRef]
  19. M. Chand and H. Maris. Personal communication.
  20. J. S. Blakemore, �??Semiconducting and other major properties of gallium arsenide,�?? J. Appl. Phys. 53, R123 (1982). [CrossRef]

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