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Optics Express

Optics Express

  • Editor: J. H. Eberly
  • Vol. 2, Iss. 4 — Feb. 16, 1998
  • pp: 137–142
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High-temperature HgTe/CdTe multiple-quantum-well lasers

I. Vurgaftman and J. R. Meyer  »View Author Affiliations


Optics Express, Vol. 2, Issue 4, pp. 137-142 (1998)
http://dx.doi.org/10.1364/OE.2.000137


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Abstract

While most previous studies of Hg-based mid-IR lasers have focused on either bulk Hg1-x Cd x Te alloys or thick (> 100 Å) Hg1-x Cd x Te quantum wells with relatively large x, we show that much thinner (20–30 Å) HgTe binary wells may be engineered to suppress both Auger recombination and intervalence free carrier absorption. On the basis of detailed numerical simulations, we predict 4.3 μm cw emission at temperatures up to 220 K for optical pumping and 105 K for diode operation. In pulsed mode, we expect maximum lasing temperatures more than 100 K higher than any prior Hg-based mid-IR result.

© Optical Society of America

While Hg1-xCdxTe mid-IR lasers were first demonstrated over 30 years ago1

1. I. Melngailis and A. J. Strauss, Appl. Phys. Lett. 8, 179 (1966).

and a large number of experimental investigations have been carried out over the past decade,2–7

2. J. M. Arias, M. Zandian, R. Zucca, and J. Singh, Semicond. Sci. Technol. 8, S255 (1993). [CrossRef]

in recent years the level of performance has failed to keep pace with the rapid advance of interband III-V mid-IR lasers.8

8. H. K. Choi, S. J. Eglash, and G. W. Turner, Appl. Phys. Lett. 64, 2474 (1994). [CrossRef]

, 9

9. C. L. Felix, J. R. Meyer, I. Vurgaftman, C.-H. Lin, S. J. Murry, D. Zhang, and S.-S. Pei, IEEE Photonics Technol. Lett. 9, 734 (1997). [CrossRef]

Although the emission of 1.3 W per facet peak power has been reported for pulsed optical pumping at 88 K,6

6. H. Q. Le, A. Sanchez, J. M. Arias, M. Zandian, R. R. Zucca, and Y.-Z. Liu, Inst. Phys. Conf. Ser. 144, 24 (1995).

to our knowledge the highest operating temperature (T max) observed to date for a wavelength ≤ 3.0 ¼m has been 154 K. There have been several attempts to enhance the performance through the use of a Hg1-xCdxTe/Hg1-yCdyTe multiple-quantum-well (MQW) active region3

3. J. Bleuse, N. Magnea, J.-L. Pautrat, and H. Mariette, Semicond. Sci. Technol. 8, S286 (1993). [CrossRef]

,6

6. H. Q. Le, A. Sanchez, J. M. Arias, M. Zandian, R. R. Zucca, and Y.-Z. Liu, Inst. Phys. Conf. Ser. 144, 24 (1995).

,7

7. J. Bonnet-Gamard, J. Bleuse, N. Magnea, and J. L. Pautrat, J. Cryst. Growth 159, 613 (1996). [CrossRef]

rather than a Hg1-xCdxTe alloy double heterostructure. However, only incremental improvements in T max have been observed, and it has been suggested on theoretical grounds that at longer wavelengths (e.g., 4.5 μm) the optimum active region would be an alloy.10

10. J. Singh and R. Zucca, J. Appl. Phys. 72, 2043 (1992). [CrossRef]

Fig. 1. In-plane bandstructure at 77 K for a MQW consisting of 150 Å Hg0.65Cd0.35Te wells and 100 Å Hg0.15Cd0.85Te barriers grown along the (100) direction.
Fig. 2. In-plane bandstructure at 150 K for a MQW consisting of 24 Å-thick HgTe wells and 60 Å Hg0.1Cd0.9Te barriers grown along the (211) direction. The dashed line shows the heavy-hole dispersion for a bulk HgCdTe alloy with the same bandgap.

To simulate the performance of Hg-based mid-IR lasers, we first calculate the TE-mode optical gain, recombination rate, and electronic heat capacity as a function of carrier density and temperature.21

21. J. R. Meyer, C. A. Hoffman, F. J. Bartoli, and L. R. Ram-Mohan, Appl. Phys. Lett. 67, 757 (1995). [CrossRef]

These dependences are input in tabular form to the rate equations for the carrier density and temperature, which are coupled to the photon-propagation and lattice-temperature equations.22

22. I. Vurgaftman and J. R. Meyer, IEEE J. Sel. Topics Quantum. Electron. 3, 75 (1997). [CrossRef]

Calculations have been performed in the limits of pulsed pumping with low duty cycle, for which lattice heating is negligible, and cw operation. Although it will be shown elsewhere that similar performance enhancements may be expected for Hg-based vertical-cavity surface emitting lasers (VCSELs) (recently demonstrated experimentally by Pautrat et al.23

23. J. L. Pautrat, E. Hadji, J. Bleuse, and N. Magnea, J. Electron. Mater. 26, 667 (1997). [CrossRef]

) here we assume an edge-emitting geometry. The optical waveguide employs the CdTe substrate as a lower optical cladding layer, in conjunction with a top cladding of Hg0.1Cd0.9Te. For pulsed operation, the sample may be mounted epi-side up with a top cladding as thin as 1.5 μm. On the other hand, for cw operation the best results are obtained for epi-side-down mounting. In that somewhat thicker top cladding of 2.5 μm is required to optically isolate the active region from the metallized top thermal contact.

Fig. 3. Calculated cw (solid) and pulsed (dashed curves) output power per facet for an optically pumped bulk Hg0.7Cd0.3Te alloy emitting at 4.3 μm as a function of pump intensity at several representative temperatures. The cavity length of 1 mm and the stripe width of 200 μm are the same in Fig. 3–6.
Fig. 4. Calculated cw (solid curves) and pulsed (dashed curves) output power per facet for an optically pumped quantum-well structure of Fig. 2 emitting at 4.3 μm as a function of pump intensity at several representative temperatures.

To test the consistency of our modeling with experimental data from the literature and also to provide a comparison for the MQW results presented below, we first treat the case of a double heterostructure laser with a bulk Hg0.7Cd0.3Te alloy active region that is 0.5 μm thick. Optical pumping at 1.06 μm is assumed for a stripe width of 200 μm, cavity length of 1 mm, and emission wavelength of 4.3 μm. Bulk values are employed for the Auger recombination coefficient7

7. J. Bonnet-Gamard, J. Bleuse, N. Magnea, and J. L. Pautrat, J. Cryst. Growth 159, 613 (1996). [CrossRef]

,13

13. V. C. Lopes, A. J. Syllaios, and M. C. Chen, Semicond. Sci. Technol. 8, 824 (1993). [CrossRef]

3 ≈ 5 × 1026 cm6/s, independent of T) and free-carrier absorption cross section (8 × 10-16 cm-2 at T = 90 K).12

12. J. A. Mroczkowski and D. A. Nelson, J. Appl. Phys. 54, 2041 (1983). [CrossRef]

Results of the simulations for both pulsed and cw optical pumping are shown in Fig. 3. The maximum pulsed operating temperature of 105 K is quite consistent with the best experimental result of 90 K for this wavelength range.5

5. A. Ravid, G. Cinader, and A. Zussman, J. Appl. Phys. 74, 15 (1993). [CrossRef]

The simulation for a wider-gap alloy emitting at λ = 3.1 μm predicts T max = 185 K, which is again only slightly higher than the best reported experimental results4

4. A. Ravid, A. Sher, G. Cinader, and A. Zussman, J. Appl. Phys. 73, 7102 (1993). [CrossRef]

,6

6. H. Q. Le, A. Sanchez, J. M. Arias, M. Zandian, R. R. Zucca, and Y.-Z. Liu, Inst. Phys. Conf. Ser. 144, 24 (1995).

,7

7. J. Bonnet-Gamard, J. Bleuse, N. Magnea, and J. L. Pautrat, J. Cryst. Growth 159, 613 (1996). [CrossRef]

for active regions consisting of both alloys and thick quantum wells (which we expect to have comparable Auger coefficients and free carrier absorption cross sections).

For the same stripe width and cavity length as in Fig. 3, the simulation of the optically-pumped MQW device emitting at the same wavelength yields the L-I characteristics illustrated in Fig. 4, where results are shown for both cw (solid) and pulsed (dashed) operation at several temperatures. Note that the maximum operating temperatures of 225 K for cw and 260 K for pulsed exceed those calculated for the alloy active region by more than 100 K. We also predict that this device should be capable of producing more than 1 W of cw output power at thermoelectric (TE)-cooler temperatures, and has a threshold pump intensity as low as 2.5 kW/cm2 at 200 K. Analogous QW devices emitting at λ ≈ 3 μm should operate up to temperatures well above 300 K in pulsed mode. Simulations with different input parameters confirm that both the longer Auger lifetimes and the suppressed intervalence absorption losses are critical to these performance improvements.

Although optical pumping may be acceptable for a restricted range of applications, a more practical device technology is the diode laser, in which electrons and holes are electrically injected into the active quantum wells. In the diode simulations, we have assumed that the top and bottom optical claddings are doped n and p-type, respectively, to an average concentration of 3 × 1017 cm-3. For cw operation, we again assume epi-side-down mounting. In this case the internal spacer layers have been eliminated in order to avoid injection nonuniformities, especially of the holes. The quantum wells are taken to have the same well and barrier thicknesses as in the optically pumped structure discussed above. Since the optimal number of quantum wells is again found to be on the order of N = 10, we increase the optical confinement by placing doped, 0.2-μm-thick Hg0.55Cd0.45Te high-index spacer layers between each cladding layer and the active quantum wells. The resulting optical loss in the cladding and high-index regions is calculated to be comparable to that in the active region.

Pulsed L-I characteristics for the QW diode are shown in Fig. 5. The maximum operating temperature is calculated to be 190 K, at which the laser turns on at a threshold current density of 9 kA/cm2. Although the diode should be capable of producing pulsed, multi-mode output powers exceeding 1 W, quite high injection currents are required to reach that range. Results for cw operation of the same device are shown in Fig. 6. Here the threshold current density is 600 A/cm2 at the T max of 105 K. Nearly 100 mW of cw power should be achievable when operation is at 77 K.

We finally emphasize that the Auger and free-carrier absorption suppression factors employed here should be viewed as rough lower bounds on what may be attainable. One stategy which would yield an even more favorable valence band structure is to compressively strain the HgTe quantum wells by growing on a Cd1-xZnxTe substrate or buffer layer with 0.10 ≤ x ≤ 0.15, and then employing tensile-strained Cd1-yZnyTe barrier layers (with y > x) to compensate the compressive strain in the wells. This would push the L1 band down even further with respect to H1, and provide an even greater range of energies over which the in-plane mass of the H1 holes is quite light.

Fig. 5. Calculated pulsed output power per facet for an electrically pumped quantum-well structure (Fig. 2) emitting at 4.3 μm as a function of injected current density at several temperatures.
Fig. 6. Calculated cw output power per facet for an electrically pumped quantum-well structure (Fig. 2) emitting at 4.3 μm as a function of injected current density at several temperatures.

To summarize, we have theoretically demonstrated the feasibility of fabricating Hg-based mid-IR lasers that operate to temperatures more than 100 K beyond any experimental results reported to date. We showed that whereas the properties of most previously studied structures consisting of thick Hg1-xCdxTe QWs with relatively large x are in many ways quite similar to those of bulk alloys, the optimum MQW structure contains thin binary HgTe wells coupled with barrier layers that maximize the band offsets. This should result in the significant suppression of both Auger-1 and Auger-7 nonradiative recombination as well as internal absorption losses due to intervalence transitions. Our simulations show that operation at TE-cooler temperatures should be attainable for cw optically-pumped lasers and pulsed diode lasers at wavelengths as long as 4.5 μm. Performance levels exceeding those indicated in Figs. 4–6 should be attainable at shorter mid-IR wavelengths, e.g.,, in the 3–3.5 μm range.

References

1.

I. Melngailis and A. J. Strauss, Appl. Phys. Lett. 8, 179 (1966).

2.

J. M. Arias, M. Zandian, R. Zucca, and J. Singh, Semicond. Sci. Technol. 8, S255 (1993). [CrossRef]

3.

J. Bleuse, N. Magnea, J.-L. Pautrat, and H. Mariette, Semicond. Sci. Technol. 8, S286 (1993). [CrossRef]

4.

A. Ravid, A. Sher, G. Cinader, and A. Zussman, J. Appl. Phys. 73, 7102 (1993). [CrossRef]

5.

A. Ravid, G. Cinader, and A. Zussman, J. Appl. Phys. 74, 15 (1993). [CrossRef]

6.

H. Q. Le, A. Sanchez, J. M. Arias, M. Zandian, R. R. Zucca, and Y.-Z. Liu, Inst. Phys. Conf. Ser. 144, 24 (1995).

7.

J. Bonnet-Gamard, J. Bleuse, N. Magnea, and J. L. Pautrat, J. Cryst. Growth 159, 613 (1996). [CrossRef]

8.

H. K. Choi, S. J. Eglash, and G. W. Turner, Appl. Phys. Lett. 64, 2474 (1994). [CrossRef]

9.

C. L. Felix, J. R. Meyer, I. Vurgaftman, C.-H. Lin, S. J. Murry, D. Zhang, and S.-S. Pei, IEEE Photonics Technol. Lett. 9, 734 (1997). [CrossRef]

10.

J. Singh and R. Zucca, J. Appl. Phys. 72, 2043 (1992). [CrossRef]

11.

M. E. Flatte, C. H. Grein, H. Ehrenreich, R. H. Miles, and H. Cruz, J. Appl. Phys. 78, 4552 (1995). [CrossRef]

12.

J. A. Mroczkowski and D. A. Nelson, J. Appl. Phys. 54, 2041 (1983). [CrossRef]

13.

V. C. Lopes, A. J. Syllaios, and M. C. Chen, Semicond. Sci. Technol. 8, 824 (1993). [CrossRef]

14.

J. I. Malin, C. L. Felix, J. R. Meyer, C. A. Hoffman, J. F. Pinto, C.-H. Lin, P. C. Chang, S. J. Murry, and S.-S. Pei, Electron. Lett. 32, 1593 (1996). [CrossRef]

15.

Z. Yang, Z. Yu, Y. Lansari, S. Hwang, J. W. Cook Jr., and J. F. Schetzina, Phys. Rev. B 49, 8096 (1994). [CrossRef]

16.

J. B. Choi, K. H. Yoo, J. W. Han, T. W. Kang, J. R. Meyer, C. A. Hoffman, G. Karczewski, J. K. Furdyna, and J. P. Faurie, Phys. Rev. B 49, 11060 (1994). [CrossRef]

17.

M. von Truchsess, V. Latussek, F. Goschenhofer, C. R. Becker, G. Landwehr, E. Batke, R. Sizmann, and P. Helgesen, Phys. Rev. B 51, 17618 (1995). [CrossRef]

18.

H. P. Hjalmarson and S. R. Kurtz, Appl. Phys. Lett. 69, 949 (1996). [CrossRef]

19.

C. H. Grein, P. M. Young, and H. Ehrenreich, J. Appl. Phys. 76, 1940 (1994). [CrossRef]

20.

B. M. Vul, V. M. Sal’man, and V. A. Chapnin, Fiz. Tekh. Poluprovodn.4, 67 (1970) [Sov. Phys. Semicond.4, 52 (1970)].

21.

J. R. Meyer, C. A. Hoffman, F. J. Bartoli, and L. R. Ram-Mohan, Appl. Phys. Lett. 67, 757 (1995). [CrossRef]

22.

I. Vurgaftman and J. R. Meyer, IEEE J. Sel. Topics Quantum. Electron. 3, 75 (1997). [CrossRef]

23.

J. L. Pautrat, E. Hadji, J. Bleuse, and N. Magnea, J. Electron. Mater. 26, 667 (1997). [CrossRef]

OCIS Codes
(140.2020) Lasers and laser optics : Diode lasers
(140.5960) Lasers and laser optics : Semiconductor lasers
(160.6000) Materials : Semiconductor materials

ToC Category:
Focus Issue: Quantum well laser design

History
Original Manuscript: October 8, 1997
Published: February 16, 1998

Citation
Igor Vurgaftman and Jerry Meyer, "High-temperature HgTe/CdTe multiple-quantum-well lasers," Opt. Express 2, 137-142 (1998)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-2-4-137


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References

  1. I. Melngailis and A. J. Strauss, Appl. Phys. Lett. 8, 179 (1966).
  2. J. M. Arias, M. Zandian, R. Zucca, and J. Singh, Semicond. Sci. Technol. 8, S255 (1993). [CrossRef]
  3. J. Bleuse, N. Magnea, J.-L. Pautrat, and H. Mariette, Semicond. Sci. Technol. 8, S286 (1993). [CrossRef]
  4. A. Ravid, A. Sher, G. Cinader, and A. Zussman, J. Appl. Phys. 73, 7102 (1993). [CrossRef]
  5. A. Ravid, G. Cinader, and A. Zussman, J. Appl. Phys. 74, 15 (1993). [CrossRef]
  6. H.Q. Le, A. Sanchez, J.M. Arias, M. Zandian, R. R. Zucca, and Y.-Z.Liu, Inst. Phys. Conf. Ser. 144, 24 (1995).
  7. J. Bonnet-Gamard, J. Bleuse, N. Magnea, and J. L. Pautrat, J. Cryst. Growth 159, 613 (1996). [CrossRef]
  8. H. K. Choi, S. J. Eglash, and G. W. Turner, Appl. Phys. Lett. 64, 2474 (1994). [CrossRef]
  9. C. L. Felix, J. R. Meyer, I. Vurgaftman, C.-H. Lin, S. J. Murry, D. Zhang, and S.-S. Pei, IEEE Photonics Technol. Lett. 9, 734 (1997). [CrossRef]
  10. J. Singh and R. Zucca, J. Appl. Phys. 72, 2043 (1992). [CrossRef]
  11. M. E. Flatte, C. H. Grein, H. Ehrenreich, R. H. Miles, and H. Cruz, J. Appl. Phys. 78, 4552 (1995). [CrossRef]
  12. J. A. Mroczkowski and D. A. Nelson, J. Appl. Phys. 54, 2041 (1983). [CrossRef]
  13. V. C. Lopes, A. J. Syllaios, and M. C. Chen, Semicond. Sci. Technol. 8, 824 (1993). [CrossRef]
  14. J.I. Malin, C.L. Felix, J. R. Meyer, C. A.Hoffman, J.F.Pinto, C.-H.Lin, P. C.Chang, S. J. Murry, and S.-S. Pei, Electron. Lett. 32, 1593 (1996). [CrossRef]
  15. Z. Yang, Z. Yu, Y. Lansari, S. Hwang, J. W. Cook, Jr., and J. F. Schetzina, Phys. Rev. B 49, 8096 (1994). [CrossRef]
  16. J. B. Choi, K. H. Yoo, J. W. Han, T. W. Kang, J. R. Meyer, C. A. Hoffman, G. Karczewski, J. K. Furdyna, and J. P. Faurie, Phys. Rev. B 49, 11060 (1994). [CrossRef]
  17. M. von Truchsess, V. Latussek, F. Goschenhofer, C. R. Becker, G. Landwehr, E. Batke, R. Sizmann, and P. Helgesen, Phys. Rev. B 51, 17618 (1995). [CrossRef]
  18. H. P. Hjalmarson and S. R. Kurtz, Appl. Phys. Lett. 69, 949 (1996). [CrossRef]
  19. C. H. Grein, P. M. Young, and H. Ehrenreich, J. Appl. Phys. 76, 1940 (1994). [CrossRef]
  20. B. M. Vul, V. M. Sal'man, and V. A. Chapnin, Fiz. Tekh. Poluprovodn. 4, 67 (1970) [Sov. Phys. Semicond. 4, 52 (1970)].
  21. J. R. Meyer, C. A. Hoffman, F. J. Bartoli, and L. R. Ram-Mohan, Appl. Phys. Lett. 67, 757 (1995). [CrossRef]
  22. I. Vurgaftman and J. R. Meyer, IEEE J. Sel. Topics Quantum. Electron. 3, 75 (1997). [CrossRef]
  23. J. L. Pautrat, E. Hadji, J. Bleuse, and N. Magnea, J. Electron. Mater. 26, 667 (1997). [CrossRef]

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