A. Zemel

Anomalous Hall effect in p‐type Hg1−xCdxTe liquid‐phase‐epitaxial layers

This paper reports on the Hall characterization of narrow‐gap p‐type Hg1−xCdxTe epilayers grown by liquid‐phase epitaxy. The characterization couples variable magnetic field (0.5–10 kG) and temperature (from 15 to 300 K) data with an analysis procedure which includes n‐type conducting regions in the p‐type material. It is shown that the analysis of the magnetic field dependence of the Hall coefficient is a useful tool to study the anomalous electrical properties in p‐type Hg1−xCdxTe . The analysis, which is rather simple, yields consistent and meaningful results, and in some cases permits determination of the concentration of holes (in the p‐type material) and electrons (in the n‐type regions) and their mobilities. Although there is strong evidence that the n‐type conducting regions are located at the surface of the Hg1−xCdxTe samples, the possibility that in some cases the n‐type regions could be located within the material bulk or near the Hg1−xCdxTe substrate interface cannot be excluded.

Mercury zinc telluride, a new narrow‐gap semiconductor

For the first time the growth of single crystal solid solutions of Hg1−xZnxTe is demonstrated. Layers with compositions of x=0.16 and 0.23 having transmission cut‐on wavelengths of 9.1 and 4.1 μm at 80 K, respectively, were grown by liquid phase epitaxy on CdTe substrates. The optical and electrical characteristics of the epilayers are similar to those obtained for Hg1−xCdxTe alloys.

Properties of Hg1−xZnxTe grown by liquid‐phase epitaxy

Epilayers of Hg1−xZnxTe 0.16≤x≤0.26, were grown by liquid‐phase epitaxy on CdTe and nearly lattice matched Cd0.76Zn0.2Te substrates. The crystalline, electrical, and optical properties of the epilayers are described. Significant improvement of the epilayer surface morphology and crystallinity was achieved by lattice matching with the substrate. The temperature and composition dependence of the energy band gap in the spectral range relevant to IR photodetection was determined.

Mechanism of carrier transport across the junction of narrow band-gap planar n+p HgCdTe photodiodes grown by liquid-phase epitaxy

The dark current of n+p Hg1−xCdxTe (x∼0.22) photodiodes fabricated on layers grown by liquid-phase epitaxy was studied systematically as a function of applied voltage (reverse and forward), temperature, and junction dimensions. The carrier transport mechanisms in different ranges of bias voltage and temperature have been identified and interpreted using the conventional models for carrier transport mechanisms in p-n junction devices. It is found that the forward current is dominated by a combination of bulk- and surface-related tunneling currents. In large-area diodes bulk tunneling current dominates the diode current and in small-area diodes surface tunneling dominates the diode forward current. Most probably, the tunneling mechanism across the n+p junction is via energy levels located within the diode depletion region. Modification of the existing theoretical model for forward-bias tunneling in p-n junction devices is needed in order to account for the experimental findings. Above 90K, the reverse curre...

Carrier transport properties of p‐type Hg1−xCdxTe liquid phase epitaxial layers in the mixed conduction range

Galvanomagnetic measurements were made on p‐type Hg1−xCdxTe liquid phase epitaxial layers as a function of magnetic field and temperature. The dependence of the Hall coefficient on magnetic field was analyzed assuming mixed conduction of electrons and holes. The fitting of the theory to the experimental data permits determination of the concentration of holes and electrons and their mobilities over a range of temperatures. This leads to values of the intrinsic carrier concentration, which are in good agreement with those generated from theoretical calculations.

Forward tunneling current in HgCdTe photodiodes

Current voltage characteristics of narrow‐gap Hg1−xCdxTe photodiodes, fabricated on liquid phase epitaxy and metalorganic chemical vapor deposition grown layers, have been investigated. It is shown that the tunneling‐recombination process is the dominant mechanism that determines the dark current at forward and at low reverse bias. This mechanism also determines the junction zero‐bias resistance.

Degradation mechanisms of gamma irradiated LWIR HgCdTe photovoltaic detectors

Planar n/sup +/p Hg/sub 1-x/ Cd/sub x/Te (x=0.23) photodiodes passivated with ZnS were irradiated by a Co/sup 60/ gamma source. A strong increase in the reverse dark current was observed for doses above 0.3 Mrad(air). A similar effect is found by exposing the photodiodes to UV illumination from a high-pressure mercury lamp. By filtering the UV light it is shown that the degradation in the performance of the photodiodes is caused by the light or radiation absorbed in the ZnS layer above the implanted n-type region. C-V measurements of irradiated MIS devices showed a significant increase in the fast surface state density. Galvanomagnetic and lifetime measurements made on irradiated p-type HgCdTe layer showed no significant changes in the bulk transport parameters. Based on these findings, a model for the degradation mechanism is proposed. >

Metalorganic vapor phase epitaxy InSbp+nn+ photodiodes with low dark current

Photodiodes of InSb were fabricated on epilayers grown by metalorganic vapor phase epitaxy (MOVPE). Dark reverse current density as low as 1×10−7A∕cm2 at −0.1V bias, and zero-bias-resistance area products as high as 1×106Ωcm2 were measured. These values are comparable to the best values reported for InSb diodes grown by molecular-beam epitaxy. The very good uniformity of the diode dark current implies that MOVPE is a promising growth technique for the fabrication of state-of-the-art focal plane InSb detector arrays.

Mercury zinc telluride epilayers grown by LPE

Hg0.84Zn0.16Te epilayers were grown by liquid-phase epitaxy from Te-rich solutions. High quality epilayers were obtained on nearly lattice matched Cd0.76Zn0.24Te substrates.

Third-generation infrared detector program at SCD

Antimonide Based Compound Semiconductors (ABCS) and a new family of advanced analogue and digital silicon read-out integrated circuits form the basis of the SCD 3rd generation detector program, which builds on the firm platform of SCDs existing InSb-FPA technology. In order to cover the MWIR atmospheric window, we recently proposed the epitaxial alloys: InAs1-y Sby on GaSb with 0.07 < y < 0.11 and In1-zAlz Sb on InSb with 0 < z < 0.03. In this paper we focus on the results of some of our recent work on epitaxial In1-zAlz Sb grown on InSb by Molecular Beam Epitxay (MBE). In epitaxial InSb (z = 0), we demonstrate the performance of Focal Plane Arrays (FPAs) with a format of 320x256 pixels, at focal plane temperatures between 77K and 100K. An operability has been achieved which is in excess of 99.5%, with a Residual Non-Uniformity (RNU) at 95K of less than 0.03% (standard deviation/dynamic range). Moreover, after a two point Non-Uniformity Correction (NUC) has been applied at 95K, the RNU remains below ~0.1% at all focal plane temperatures down to 85K and up to 100K without the need to apply any further correction. This is a major improvement in both the temperature of operation and the temperature stability compared with implanted diodes made from bulk material. We also demonstrate rapid progress in the development of low current epitaxial InAlSb photodiodes with high uniformity and low dark current that offer a range of cut-off wavelengths shorter than in InSb. Preliminary results are presented on FPAs with a cut-off wavelength in the range λC~5μ.