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In this paper we report on p‐type arsenic doping of CdTe and HgTe/CdTe superlattices by photoassisted and conventional molecular‐beam epitaxy (MBE). We also report on some of the problems involved in doping and growing the HgTe/CdTe superlattice system by theoretically examining two key aspects of its growth: (i) growth of CdTe at low temperatures under Cd‐stabilized conditions, and (ii) effect of laser excitation on the growing CdTe surface. p‐Type arsenic‐doped CdTe and HgTe/CdTe superlattice epilayers were grown on (100) CdTe and CdZnTe substrates at low temperatures under cation‐stabilized conditions obtained either with excess Cd, or excess Hg fluxes. As‐grown arsenic‐doped CdTe layers had room temperature carrier concentrations in the 1014–1016 cm−3 range, and hole mobilities of about 35–65 cm2/V s. Low‐temperature photoluminescence spectra of arsenic‐doped CdTe epilayers grown by photoassisted MBE showed an emission peak at 1.51 eV, which is associated to the AsTe acceptor (arsenic occupying a Te site) with a 92 meV ionization energy. CdTe epilayers grown at low temperatures with photoassisted MBE have superior structural, optical, and electrical properties than those grown by conventional MBE. Arsenic doping of the HgTe/CdTe superlattice structure has resulted in in situ growth of p‐type modulation‐doped superlattices with enhanced mobilities. Undoped superlattices grown under the same conditions are n‐type. These results represent a significant step towards the in situ fabrication of photodiodes and other advanced devices based on HgTe/CdTe doped superlattice structures.

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.

ESCA studies have been carried out on a number of Pb1−xSnxTe surfaces with the goal of correlating surface chemistry with surface leakage currents observed in Pb1−xSnxTe infrared detectors. A diode array structure has been developed which permits I–V and ESCA measurements to be carried out on the same surface. It is possible to reprocess this array to change the surface chemistry without altering the bulk semiconductor characteristics. ESCA results have established the existence of thick (hundreds of angstrom) elemental Te0 layers on several chemically processed device surfaces. These surfaces are shown to produce exceptionally low surface leakage currents at 77 K which suggests that Te0 may be a surface passivant for Pb1−xSnxTe. A dimensional analysis model has been developed which seems capable of estimating surface and bulk contributions to leakage currents.

To identify the dominant physical mechanisms determining current–voltage and spectral noise current characteristics, a comprehensive experimental study of Hg1−x Cdx Te (x=0.22) photodiodes has been performed. Over the voltage range −400 mV≤V≤100 mV and temperature region 5 K

We report measurements on the minority carrier lifetime in n‐type and p‐type LPE Hg1−xCdxTe/CdTe with x∼0.2. For n‐HgCdTe, we have measured lifetimes of 4–7 μs at 77 K for passivated samples. These values are comparable to the results reported for bulk material. For p‐HgCdTe epilayers with thickness ≤20 μm, the measured lifetime is 15–20 ns at 77 K and is suspected to be limited by surface recombination. With excitation through the CdTe substrate, we have attempted to measure the bulk lifetime; preliminary results are reported.