Search

Long‐wavelength infrared molecular‐beam epitaxial (MBE) HgCdTe films with dislocation densities as low as 2.3 × 105 cm−2 on (211) GaAs and Si substrates have been obtained by postgrowth thermal annealing and thermal cycle annealing processes (300–490 °C). Experiments show that metalorganic chemical vapor deposition (MOCVD) HgCdTe epilayers require a higher thermal annealing temperature than MBE material and the difference in dislocation reduction between MBE and MOCVD HgCdTe materials is caused by dislocation movement under high‐temperature and thermal stress conditions. The CdTe buffer layer has been observed to play a significant role for the dislocation reduction in the HgCdTe epilayer grown on GaAs or Si alternative substrates. To study the role of dislocations on MBE HgCdTe/GaAs, systematic measurements of the minority carrier lifetime of MBE HgCdTe grown on both CdZnTe and GaAs substrates were carried out. A strong correlation between minority carrier lifetime and dislocation density is observed.

The feasibility of an all molecular‐beam epitaxially (MBE) grown, bias‐switchable, dual‐band HgCdTe detector is demonstrated. Detection in the midwavelength infrared (MWIR) band only or the long‐wavelength band (LWIR) only is accomplished by the proper selection of detector bias in the ≥±100 mV range. The devices were all grown in situ by the MBE on CdZnTe or GaAs substrates and consisted of three intentionally doped layers in an n–p–n sequence. At 77 K the floating base two terminal devices responded to the ∼4.9–8 μm spectral band with the application of ≥−100 mV to the bottom contact and to the ∼2.1–4.9 μm band with the application of ≥0 mV. Quantum efficiency depended on bias with a maximum of 59% for LWIR and 66% for MWIR wavelengths at −150 mV and ≥0 mV, respectively. The operation of the dual‐band detector is discussed. Significant design differences between the heterojunction phototransistor and the dual‐band detector are noted.

This study deals with the effects of perturbing the surfaces of unpassivated HgMnCdTe and HgCdTe short‐wavelength infrared photodiodes to further our understanding of these effects on dark currents. Perturbations include illuminating ultraviolet (UV)radiation in high vacuum and in various gaseous species. The change in dark current at 0.8 V reverse bias and its evolution with time was monitored in situ. By correlating the amount of excess dark current generated by UV radiation to the vacuum conditions, we conclude that it is a surface‐related problem. A drastic improvement in device performance was found by illuminating its surface with UV radiation in high vacuum. This simple treatment prevents the generation of excess and persistent dark current and stabilizes the leakage current at low reverse bias. This can be understood in terms of photodesorption of surfacecontaminants which induce deep level surface states, giving rise to the persistent dark current generation. By studying the effects of various gaseous species, we identified water molecules as the key surfacecontaminants. We also discovered an anomalous degradation in HgCdTe diodes when they were exposed to hydrogen and UV radiation simultaneously. This anomalous degradation can be interpreted as UV‐catalyzed chemical reduction of HgCdTe by hydrogen or the diffusion of hydrogen atoms into the bulk to change the junction characteristics.