The InAs/Ga1-xInxSb type-II superlattice (T2SL) is the most investigated III-V T2SL material for mid- and long-wavelength infrared (MWIR and LWIR) photodetectors. T2SLs are predicted to have a number of advantages over the currently used bulk HgCdTe, including a decreased dependence of the bandgap on compositional non-uniformity, the ability to leverage III-V manufacturing capabilities, the lower cost of substrates, and lower dark currents due to lower Auger recombination rates through band engineering and smaller tunneling currents resulting from higher electron effective mass. However, the reported minority carrier lifetimes at 77 K are 50 80 ns for MWIR InAs/Ga1-xInxSb T2SLs and 10 40 ns for LWIR InAs/Ga1-xInxSb T2SLs as compared to 1 s for Hg0.78Cd0.22Te (~ 10 m bandgap). The short minority carrier lifetime has been attributed to Shockley-Read-Hall (SRH) recombination and is detrimental to the devices dark current and quantum efficiency. The PI demonstrated the first MWIR laser using strained InAs/InAs1-xSbx T2SLs on InAs substrates and strain-balanced InAs/InAs1-xSbx T2SL structures on GaSb substrates for both MWIR and LWIR photodetector applications in the mid-90s. Recently, his group demonstrated a carrier lifetime of >412 ns at 77 K under low-excitation for an InAs/InAs0.72Sb0.28 T2SL as determined by time-resolved photoluminescence (TRPL) measurements in 2011. Since then, many new world records for the carry lifetime in MWIR and LWIR have been reported by other groups, further confirming that InAs/InAs1-xSbx T2SLs are indeed very promising. This improvement in minority carrier lifetime have enabled LWIR T2SL photodetectors to operate at higher temperatures and better performance. However, despite these breakthroughs, the fundamental reasons why the carry lifetime in Ga-free T2SLs is so much longer than that in the conventional InAs/GaxIn1-xSb T2SLs is still not very clear and needs further in-depth investigation. The PI proposes an innovative way to carry out a fundamental study of middle gap states in Gafree T2SLs using pressure-dependent photoluminescence measurements. It is known that under hydrostatic pressure, the bandgap of extended states in semiconductors increases linearly with the pressure, while defect states are localized and have little change with pressure. Taking advantage of this effect, we plan to carry out pressure-dependent photoluminescence measurements on Ga-free T2SLs to find out whether there is a critical point beyond which the PL intensity decreases due to the appearance of those defect energy levels in the middle of the bandgap. Our preliminary results indicate that this effect is indeed happening. This program will carry out a more in-depth study to further confirm our preliminary findings.
|Effective start/end date||8/1/14 → 4/30/15|
- DOD-ARMY-ARL: Army Research Office (ARO): $32,362.00