Type-II superlattices (T2SLs) have several fundamental advantages over bulk infrared-sensitive materials due to larger band edge effective masses and the ability to have their band structures engineered to suppress Auger recombination, leading to lowering tunneling currents, longer carrier lifetimes and higher ideal sensitivity. Realizing in practice the potential performance gains relies heavily on reducing the number or efficacy of defects that form Shockley-Read-Hall (SRH) recombination centers, which otherwise limit carrier lifetimes. InAs/GaInSb T2SLs typically have relatively short minority carrier lifetimes in comparison with bulk HgCdTe, which has limited the detectivities of photodetectors based on these T2SLs at both cryogenic and ambient operating temperatures. Studies have shown that InAs/InAsSb T2SLs lattice matched to GaSb substrates are comparable in ideal photodiode performance to InAs/GaInSb ones. Reducing the electrical activity of defects by passivating them with hydrogen is equivalent to lowering their density, and has proven successful in other semiconductor systems. We report here results from Ga-free and Ga-containing T2SLs exposed to inductively-coupled plasmas (ICPs). Our technical approach consisted of characterizing the basic material properties of LWIR InAs/InAsSb T2SL wafers and device performance of LWIR InAs/GaSb T2SL photodiodes that were bulk-passivated with atomic hydrogen, and comparing with unpassivated samples. On average, the in-plane Hall electron mobility increased from 1800 cm2/Vs to 6800 cm2/Vs after hydrogenation. ICP hydrogenation also improved the minority carrier lifetime for each of the explored ICP conditions. Lifetime values increased from an average of 80 ns before hydrogenation to almost 200 ns, a relative increase of over 200%, suggest that some recombination-mediating defects have been at least partially passivated. The Hall mobility improvements were found to be rather stable over the considered short periods of room temperature storage.
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Spatial noise and the loss of photogenerated current due material non-uniformities limit the performance of long wavelength infrared (LWIR) HgCdTe detector arrays. Reducing the electrical activity of defects is equivalent to lowering their density, thereby allowing detection and discrimination over longer ranges. Infrared focal plane arrays (IRFPAs) in other spectral bands will also benefit from detectivity and uniformity improvements. Larger signal-to-noise ratios permit either improved accuracy of detection/discrimination when an IRFPA is employed under current operating conditions, or provide similar performance with the IRFPA operating under less stringent conditions such as higher system temperature, increased system jitter or damaged read out integrated circuit (ROIC) wells. The bulk passivation of semiconductors with hydrogen continues to be investigated for its potential to become a tool for the fabrication of high performance devices. Inductively coupled plasmas have been shown to improve the quality and uniformity of semiconductor materials and devices. The retention of the benefits following various aging conditions is discussed here.
