J.T. Longo

Infrared focal planes in intrinsic semiconductors

In this paper, we review the state-of-the-art of intrinsic semiconductor detector arrays and project future areas of development. Infrared focal planes in intrinsic semiconductors offer advantages over extrinsic semiconductor structures in both operating temperature and quantum efficiency. Although the device function of spectral filtering and detection of the incident photon flux is now well understood in intrinsic semiconductors, the function of signal processing has only recently been investigated. As a result, research is directed toward implementation of both hybrid devices, in which the signal processing is accomplished in a silicon multiplexer which is physically and electrically interfaced with an intrinsic semiconductor detector array, and monolithic charge transfer devices in which detection and signal processing are accomplished in the same semiconductor. In the monolithic approach, charge transfer devices have been demonstrated in InSb, and it is likely that similar devices will be realized in InSb related alloys and HgCdTe in the near future. Demonstration of a non-MIS charge transfer design would open up the monolithic approach to the IV-VI alloys. Hybrid focal planes incorporating ≳ 1000 element photodiode arrays have been realized in the III-V and the IV-VI alloys; the detector-multiplexer interface circuit will remain one of the key technical issues in the achievement of a high-performance hybrid focal plane.

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.

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.

Investigation of leakage characteristics of PbSnTes̵bndPbTe inverted heterostructure diodes

Abstract The results of a study of the overall electrical characteristics of PbSnTe diodes are presented and interpreted on the basis of a simple p-n junction model. These diodes are made from a PbSnTe epilayer grown by a liquid-phase epitaxy technique on a PbTe wafer substrate. The diodes have a 50% spectral cutoff at 11.5 μm when operated at 85K, which shifts to 14.5 μm at T = 15K. Major contributions to the bulk current are diffusion current at T > 80K, and generation-recombination current for 80 >T ≳ 30K. Surface related leakage is predominant at T 1 × 10−3 cm2) at T ≲ 60K.

Liquid phase epitaxial growth of InAsxSbyPl-x-y layers on InAs

High quality InAsxSbyPl-x-y quaternary layers, which are lattice matched to InAs, have been grown successfully on InAs substrates by liquid phase epitaxy. Both Graded and constant composition InAsxSbyPl-x-y layers have been grown. In addition, the graded InAsxSbyPl-x-y layer has been used as a buffer layer for the growth of InAsl-xSbx on an InAs substrate.

Recent Developments In Intrinsic Semiconductor Detectors

A significant effort in any research and development program involving large infrared detector arrays is parameter measurement and evaluation. In fact, the major portion of the program cost is in some way involved with measurements. For this reason and because of the acquisition of several programs requiring large numbers of deliverable arrays, a computer based automated data acquisition system has been implemented for the infrared device effort at the Science Center. A Data General Eclipse S/200 computer with two 10 mega byte disks is utilized. Data acquisition from remote locations is effected by daisy chaining as many as fifteen Hewlett Packard multiprogrammer units at 100 foot intervals. Graphical display of the results as well as operator interaction with the program is conducted using Tektronix 4010 series terminals. The new Data General advanced operating system (AOS) allows independently called time sharing operations from each terminal. A Versatec printer/plotter is used for hard copy of the screen image as well as for a line printer. Test programs for current vs. voltage (IV), capacitance vs. voltage, spectral responsitivity, optical area measurement using an automatic blackbody scan and multiplexer video data acquisition programs have been written and implemented. In addition to acquiring the data, the IV test program has a number of optional features. Included is the ability to control stepping of a cryogenically cooled automatic probe station, allowing completely unattended IV evaluation of a 1024 element array. Another important feature of the IV program is the option of addressing individual row and column elements of mated multiplexer/ diode arrays and measuring IV characteristics through the video output. Examples of the use of this system for evaluation of 32x32 PbSnTe and InAsSb arrays will be given.