Infrared photodetectors, used in applications for sensing and imaging, such as military target recognition, astronomy, chemical/gas detection, and night vision enhancement, are predominantly comprised of an expensive II-VI material, HgCdTe. III-V type-II superlattices (SLs) have been studied as viable alternatives for HgCdTe due to the SL advantages over HgCdTe: greater control of the alloy composition, resulting in more uniform materials and cutoff wavelengths across the wafer; stronger bonds and structural stability; less expensive, closely lattice-matched substrates, i.e., GaSb; mature III-V growth and processing technologies; lower band-to-band tunneling due to the larger electron effective masses; and reduced Auger recombination enabling operation at higher temperatures and longer wavelengths. The performance of InAs/Ga1-xInxSb SLs is approaching that of HgCdTe, but the minority carrier lifetime is limited by Shockley-Read-Hall (SRH) recombination and is several orders of magnitude lower than that of HgCdTe, reducing the photodetector quantum efficiency and increasing the dark current. This dissertation work focuses on InAs/InAs1-xSbx SLs, which represent another promising alternative for infrared laser and detector applications due to possible lower SRH recombination and the absence of gallium, which simplifies the SL interfaces and growth processes.
InAs/InAs1-xSbx SLs strain-balanced to GaSb substrates were designed for the mid- and long-wavelength infrared (MWIR and LWIR) spectral ranges and were grown using MOCVD and MBE by various groups. Detailed characterization using high-resolution x-ray diffraction, atomic force microscopy, photoluminescence (PL), and photoconductance revealed the excellent structural and optical properties of the MBE materials.
Two key material parameters were studied in detail: the valence band offset (VBO) and minority carrier lifetime. The VBO between InAs and InAs1-xSbx strained on GaSb with x = 0.28 – 0.41 was best described by Qv = ΔEv/ΔEg = 1.75 ± 0.03. Time-resolved PL experiments on a LWIR SL revealed a minority carrier lifetime of 412 ns at 77 K, one order of magnitude greater than that of InAs/Ga1-xInxSb LWIR SLs due to less SRH recombination. MWIR SLs also had 100’s of ns lifetimes that were dominated by radiative recombination due to shorter periods and larger wave function overlaps. These results allow InAs/InAs1-xSbx SLs to be designed for LWIR photodetectors with minority carrier lifetimes approaching those of HgCdTe, lower dark currents, and higher operating temperatures.