A unipolar, barrier-integrated HgCdTe nBn photodetector with all n-type doping and a type-I band lineup is experimentally demonstrated. Planar mid-wave infrared (MWIR) nBn devices exhibit current-voltage (I-V) characteristics that are consistent with band inversion in reverse bias, indicating a barrier-influenced behavior. Dark current saturation is observed beyond a reverse bias of approximately −0.8 V. Bias-dependent photoresponse is observed in the mid-wave infrared with a cut-off wavelength around 5.7 μm. Numerical modeling based on experimental results predicts an internal peak quantum efficiency of approximately 66%.

Mid-wave infrared HgCdTe nBn photodetector

Comparison and competition between MCT and QW structure material for use in IR detectors

An n-type mercury cadmium telluride (HgCdTe) unipolar nBn infrared detector structure is proposed as a means of achieving performance limited by intrinsic thermal carrier generation without requirements for p-type doping. Numerical modeling was utilized to calculate the current–voltage and optical response characteristics and detectivity values for HgCdTe nBn and p–n junction devices with a cut-off wavelength of 12 μm for temperatures between 50 K and 300 K. Calculations demonstrate similar dark current density, responsivity, and detectivity values within 10% for the long-wavelength infrared (LWIR) nBn detector compared with the p–n junction structure for temperatures from 50 K to 95 K. These results show that the HgCdTe nBn device may be a promising alternative for achieving high performance using a simplified device structure while circumventing issues related to p-type doping in current p–n junction technology such as achieving low, controllable doping concentrations, and serving as a basis for next-generation device structures.

Design and Modeling of HgCdTe nBn Detectors

Photoluminescence spectroscopy of excitons for evaluation of high-quality CdTe crystals

Ion bombardment often leads to compositional changes in the surface layers of multicomponent targets. Such changes due to noble gas ion sputtering are discussed for InP and GaAs. The analyses show that the compositional change in InP (i.e., indium enrichment) is mainly due to preferential sputtering. In the case of GaAs. the changes are due to radiation-induced diffusion and segregation effects. Brief mention is made of compositional changes in a few other systems. The discussion on sputter-induced topography development deals mainly with InP because ion bombardment leads to dramatic topographical effects in this material. Ripple development on GaAs is also briefly discussed. Radiation damage has been well researched, and its mechanism and effects usually differ substantially when going from one semiconductor group to another. Bombardment-induced damage is briefly discussed for InP, GaAs, SiC, some II-VI semiconductors, and HgCdTe.

Sputtering of compound semiconductor surfaces. II: Compositional changes and radiation-induced topography and damage

The characteristics of ion implanted HgCdTe epitaxial layers have been explored. A bimodal distribution in damage near the implanted surface has been correlated with a bimodal distribution in implant‐induced donor concentration. The implant induced junction depth has been found to be controllable and stable under a range of annealing conditions. Differential capacitance measurements have shown that the carrier concentration in the junction region is 10–100 times lower than the as‐grown acceptor concentration in the base material. These and other observations have been qualitatively explained by a model based on the hypothesis that Hg interstitials (or possibly Te vacancies) formed during the implant are donors whose distribution is largely controlled by damage near the layer surface.

Behavior of implantation‐induced defects in HgCdTe

A high‐resolution and nondestructive optical characterization technique called laser beam‐induced current (LBIC) has been developed and utilized to obtain maps of electrically active defects in liquid phase epitaxy HgCdTe. The LBIC technique is also suitable for studying the p–n junction detector elements in an array nondestructively, without requiring any electrical contacts to individual detector elements.

Spatial mapping of electrically active defects in HgCdTe using laser beam‐induced current

This work reports on two significantly different methods to form junctions in Hg1−xCdxTe by ion implantation: a ‘‘displaced Hg diffusion source’’ for n‐on‐p junctions and an ‘‘implanted species diffusion source’’ for p‐on‐n devices. For each one, the role of background impurities, stoichiometric defects, and implanted species of junction formation have been determined. In spite of superficial damage created by the implant, these methods produced implanted junctions of either type with low damage in the near‐junction region, resulting in excellent electrical characteristics.

Ion implanted junction formation in Hg1−xCdxTe

SIMS has been used on both unimplanted and B‐ion implanted LPE grown HgCdTe to study the distribution of the Li impurity background. In unimplanted layers Li decorates some types of crystal defects and also reflects the p/n distribution in the layer. In implanted layers Li decorates the implantation‐induced damage and also reveals the junction region. Ion‐implanted junctions have been evaluated by Hall, differential Hall, EBIC, C–V, and TEM techniques and the results correlated with the features exhibited by the Li distribution. The Li distribution analysis reinforces our previous understanding that implanted junctions are several microns deep, n+/p−, graded in the p region and formed by implant‐induced native donors.

Some aspects of Li behavior in ion implanted HgCdTe

The imaging cathodoluminescence capability of a scanning electron microscope (SEM) was complemented by etch pit (EP) measurements and secondary ion mass spectroscopy (SIMS) to characterize structures of HgCdTe LPE grown both on CdTe and CdTe/sapphire (PACE‐1) (Ref. 1: W. E. Tennant, IEDM Technical Digest 1983, 704) substrates. In addition to providing the source for luminescence, the high‐power‐density SEM beam was exploited to perform in situ annealing which improved the CL efficiency and aided in the analysis. Selected CL/SEM data are shown for substrates, epilayers and interfaces. CdTe Bridgman grown substrates exhibited defect structures (twins, dislocations, precipitates, subgrain structure) and substantial differences in CL efficiency and response to electron beam (EB) annealing. Cd annealing of Bridgman substrates increases CL efficiency, removes sensitivity to EB annealing, and causes impurity redistribution as measured by SIMS. PACE‐1 substrates show higher defect density, an absence of subgrains...

Cathodoluminescence of HgCdTe and CdTe on CdTe and sapphire

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