E. R. Gertner

Long and middle wavelength infrared photodiodes fabricated with Hg1−x CdxTe grown by molecular‐beam epitaxy

Long and middle wavelength infrared (LWIR, MWIR) p+‐n photodiodes have been fabricated with Hg1−xCdxTe (0.20<x<0.30) grown by molecular‐beam epitaxy (MBE). The epilayers were grown on (211)B lattice‐matched ZnCdTe substrates. The surface morphology was smooth and free of in‐plane twins. The Cd concentration (x) was uniform across the wafer, with standard deviations (Δx) as low as 0.0017. Structural properties were measured by double‐crystal x‐ray rocking curve and dislocation etching; FWHM values as low as 34 arcsec and etch pit density values as low as 1×105 cm−2 were measured. p+ ‐n homojunctions were formed by arsenic diffusion; unpassivated mesa photodiodes were fabricated by standard photolithographic techniques. MWIR and LWIR photodiodes fabricated with MBE material exhibited good diode performance, comparable to that obtained on photodiodes fabricated with the more matured technique of liquid‐phase epitaxy. 77‐K R0A products of the diodes measured were 6.35×107, 22.3, and 1.76 Ω cm2 with cutoff wav...

Backside‐illuminated InAsSb/GaSb broadband detectors

This letter reports the achievement of a high‐performance, broad‐spectral‐band infrared detector with the InAs1−xSbx alloy system using a backside‐illuminated heterostructure approach. The basic structure of the detector is obtained with InAs1−xSbx grown by a liquid phase epitaxy technique on a GaSb substrate under lattice‐matched or nearly lattice‐matched conditions. The measured photoresponse covers the spectral range 1.7–4.2 μm with an external quantum efficiency of 65% without antireflective coating. The typical zero‐bias resistance area product is in excess of 109 Ω cm2. The typical leakage current desity is less than 10−9 A/cm2 for 100 mV reverse bias. All parameters were measured at 77 K.

The Pb-Sn-Te phase diagram and its application to the liquid phase epitaxial growth of Pb1−xSnxTe

Abstract The ternary phase diagram of Pb 1− x Sn x Te has been calculated using a modified simple solution thermodynamic model. Interaction parameters between the binary solids and between elements in the liquid have been determined by fitting a polynomial in temperature to experimental liquidus and solidus data. The resulting calculation is in excellent agreement with extensive measurements of the solidus. The principal features of interest are that for x ≲ 0.18, the Sn composition in the solid is approximately the same as that in the liquid and independent of growth temperature. As the Sn content of the liquid increases to 0.30, the solid composition, x , saturates to a value dependent primarily on the growth temperature with the largest values of x corresponding to the highest growth temperature.

Backside‐illuminated InAs1−xSbx‐InAs narrow‐band photodetectors

High‐performance backside‐illuminated photodiodes have been fabricated for the first time from InAs1−xSbx‐InAs heterostructures prepared by liquid‐phase‐epitaxy technique. The peak wavelength can be tuned compositionally from 3.1 to over 7.0 μm at 77 K. The half‐width of the spectral responses as narrow as 1760 A (at 4.0 μm) have been achieved. Internal quantum efficiencies of 90% and zero‐bias‐resistance–area products of 2×107 Ω cm2 have been obtained at 77 K.

Infrared diodes fabricated with HgCdTe grown by molecular beam epitaxy on GaAs substrates

Infrared photodiodes fabricated with HgCdTe epilayers grown on GaAs substrates by molecular beam epitaxy (MBE) are reported here for the first time. Growth was carried out on the (211)B orientation of GaAs, and the as‐grown epilayer (x=0.24) was p type. The n‐p junction was formed by Be ion implantation, the resistance‐area product (R0 A) at zero bias was 1.4×103 Ω cm2 , the wavelength cutoff was 8.0 μm, and the quantum efficiency was 22%; all were measured at 77 K. We show that in the diffusion regime diodes fabricated with MBE HgCdTe/GaAs have comparable R0 A product values to those made with HgCdTe grown by bulk techniques. This result discloses new possibilities for advanced monolithic HgCdTe devices based on GaAs integrated circuit technology.

HgCdTe on sapphire — A new approach to infrared detector arrays

Some of the limitations imposed by bulk CdTe substrates on epitaxial HgCdTe, such as wafer size, fragility, and uniformity, have led to the development of an alternate substrate to CdTe for epitaxial HgCdTe growths. Described here are the synthesis and some of the properties of an alternate hybrid CdTe/sapphire substrate, and the material and device properties of liquid phase epitaxial (LPE) grown HgCdTe on CdTe/sapphire substrates. Devices made in LPE grown HgCdTe layers on CdTe/sapphire have shown excellent electrical and optical properties and superior uniformity in diode-to-diode D* in midwave infrared (MWIR) focal planes at low temperature when compared to devices fabricated in HgCdTe grown on CdTe substrates. Diodes have typical resistance area product values of ⩾ 10 Ω cm2 at 195 K (cutoff wavelength λc = 4.2 μm), ⩾ 3 x 104 Ω cm2 at 120 K (λc = 4.45 μm) and ⩾ 1 x 106 Ω cm2 at 77 K (λc = 4.6 μm). Typical quantum efficiencies are 60–80% without anti-reflection coating. Analysis of the detectivity of a 1024 element MWIR hybrid focal plane array shows that the number of defective elements, even under low-to-moderate photon backgrounds (high 1012 photons cm-2 s-1), is less than 5%.

Material characteristics of Hg1−xCdx > Te grown by organometallic vapor phase epitaxy

Abstract We compare the material properties of Hg 1- x Cd x Te grown by conventioanal organometallic vapor phase epitaxy (OMVPE) with those obtained interdiffused multilayer OMVPE. Both are compared with material properties of state-of-the-art LPE Hg 1- x Cd x Te grown from Te-rich solutions. The Hg 1- x Cd x Te layers were grown on bulk CdTe, sapphire (Al 2 O 3 ) and GaAs substrates. Layers were characterized by optical microscopy, IR transmission, Hall effect, double crystal X-ray diffraction, electron microprobe and secondary ion mass spectroscopy (SIMS). Better crystallinity and smoother morphologies are obtained by conventional OMVPE; interdiffused multilayer OMVPE currently results in better compositional uniformity and reproducibility. The observed differences can be interpreted on the basis of growth kinetics. Both techniques yield Hg 1- x Cd x Te epitaxial layers with LPE-like qualities.

Liquid phase epitaxial growth of InAs1-xSbx on GaSb

Reported here, for the first time, is the lattice matched growth of InAs1-xSbx on GaSb. The thermodynamic incompatibility of the system, i.e., the strong tendency for the In-As-Sb liquid to dissolve the GaSb substrate, was solved via a novel liquid phase epitaxial growth technique. Liquid compositions for lattice matching conditions have been determined in the 400-600°C range. Epitaxial growth has been examined for (100), (111)B and (111)A orientations. Dislocation etch pit densities for lattice matched, and near lattice matched conditions are shown to be less than 104-cm−2 and 105-cm−4, respectively. The composition of the epitaxial layers are determined by the Gandolfi X-ray diffraction technique and compositional homogeneity has been confirmed by SEM X-ray analysis. Some material related device properties which demonstrate the reproducibility of the growth technique are presented.

High‐speed Pb1−xSnx Te photodiodes

Low‐capacitance (< 10 pF) Pb1−xSnxTe photodiodes operating near 77 °K (areas 1.7 × 10−4 cm2) have been obtained via liquid‐phase epitaxial growth of low‐carrier‐concentration material (low 1014 cm−3 to high 1015 cm−3). Response to a mode‐locked 1.06‐μm Nd:YAG laser with the devices terminated in 50 Ω indicated a frequency response to 400 MHz. With a 14‐Ω load and by exciting a photocurrent with radiation from a CO2 laser, the shot noise rolloff point was found to be 1200 MHz. Optimum parameters have not yet been achieved, as evidenced by the increase in frequency response with increase in reverse bias; these results represent only a lower limit to this materials capability.

High performance photovoltaic infrared devices in Hg1−xCdxTe on sapphire

A combination of organometallic and isothermal vapor phase epitaxy was used sequentially to grow CdTe and Hg1−xCdxTe on GaAs substrates. Photodiodes in the Hg1−xCdxTe show properties comparable to the best Hg1−xCdxTe grown by liquid phase epitaxy. Resistance‐area products were ≥107 Ω cm2 and >104 Ω cm2 at 77 K for Hg1−xCdxTe with cut‐off wavelength of 3.73 and 5.54 μm at 77 K, respectively. The backside‐illuminated spectral response was broadband with peak external quantum efficiencies typically >50% (without antireflection coating).