T. C. Harman

LONG‐WAVELENGTH INFRARED Pb1−xSnxTe DIODE LASERS

Diode lasers with emission wavelengths as long as 28 μ have been fabricated using Pb1−xSnxTe with x up to 0.27. Properties of laser diodes at 77°K and 12°K have been measured for a number of compositions in the range 0.15 ≤ x ≤ 0.27. The vapor growth and annealing‐diffusion steps were performed in a special quartz ampoule which remained sealed throughout the process. Threshold current densities were dependent on diode surface conditions and could be reduced by at least 50% by etching.

TYPE CONVERSION AND n‐p JUNCTION FORMATION IN Hg1−xCdxTe PRODUCED BY PROTON BOMBARDMENT

We have fabricated n‐p junction photovoltaic detectors in Hg1−xCdxTe with x=0.50, 0.31, and 0.25 using proton bombardment to create the n‐type layer. Peak detection sensitivities were in the wavelength range 1.6–6 μm. Although high‐sensitivity photodiodes were obtained with each composition, the best results were obtained with the x=0.31 material, which has a peak response at 3.8 μm. At 77°K, 15‐mil×15‐mil diodes made with this material had zero‐bias impedances of several megaohms. The peak detectivity at 3.8μ was 9×1011 cmHz1/2/W in reduced background and the quantum efficiency at the peak was 29%.

Infrared Spectroscopy of CO Using a Tunable PbSSe Diode Laser

The P(9) fundamental infrared absorption line of carbon monoxide at 2107.4 cm−1 has been studied with high resolution using a cw current tunable PbS0.82Se0.18 diode laser. Both the Doppler linewidth of 150 MHz and the absorption coefficient at line center of 2.1 cm−1/Torr at room temperature have been measured directly for the first time with an estimated resolution of 1% of the linewidth.

TEMPERATURE AND COMPOSITIONAL DEPENDENCE OF LASER EMISSION IN Pb1−xSnxSe

Laser emission has been obtained in Pb1−xSnxSe diodes with x up to 0.28, and the temperature dependence of the emission has been studied in the range from 1.5 to 100°K. The results strongly support a band model in which the conduction and valence band edge states cross as the Sn content is increased from 0 to 0.28. For x ≤ 0.10, the temperature coefficient of the energy gap is positive whereas for x ≥ 0.19, the temperature coefficient is negative as predicted by the band model. Also, the results provide evidence that the energy gap is direct on both sides of the crossover point which at 4.2°K occurs for x ≈ 0.15.

n‐p JUNCTION PHOTOVOLTAIC DETECTORS IN PbTe PRODUCED BY PROTON BOMBARDMENT

n‐p junction photovoltaic detectors in PbTe have been fabricated using proton bombardment to create the n‐type layer. At 77°K, zero‐bias resistance area products of 300 Ω cm2 were observed for diodes with dimensions as large as 15 mil square. Peak detectivities at 5 μm in reduced background as high as 3.3×1011 cm Hz1/2/W were observed. Diode quantum efficiencies were typically greater than 30% at 5 μm.

DIODE LASERS OF Pb1−ySnySe AND Pb1−xSnxTe

Infrared laser emission at a number of wavelengths between 9.4 μ and 13.7 μ has been obtained from diodes of Pb1−ySnySe and Pb1−xSnxTe at 12°K and 77°K. Diodes were fabricated from vapor‐grown Pb1−ySnySe and both vapor‐grown and Bridgman‐grown Pb1−xSnxTe. Emission data indicate that, as in Pb1−xSnxTe, the energy gap in Pb1−ySnySe decreases with increasing Sn concentration, becoming zero at 12°K for some value of y within the range 0.11 ≤ y ≤ 0.14.

LASER EMISSION FROM METAL‐SEMICONDUCTOR BARRIERS ON PbTe AND Pb0.8Sn0.2Te

Laser emission is obtained from forward biased evaporated metal barriers on degenerate p‐PbTe and p‐Pb0.8Sn0.2Te at T=4.2°K. Metals with small work functions such as In, Pb, and Zn produce a degenerate inverted n‐type surface region on p‐type samples without chemical doping. Low‐threshold laser emission has been obtained from these barriers on p‐PbTe at λ = 6.4μ and from Pb barriers on p‐Pb0.8Sn0.2Te at λ = 15μ.

Observation of nuclear hyperfine splitting in the infrared vibration—rotation absorption spectrum of the no molecule

Abstract Nuclear hyperfine splitting of several absorption lines in the Q branch of the fundamental 2 Π 1 2 vibration—rotation band of 14 N 16 O has been observed using a turnable PbSSe semiconductor laser operating near 5.4μm

PHOTOCONDUCTIVITY IN SINGLE‐CRYSTAL Pb1−xSnx Te

Photoconductivity at wavelengths up to 15 μ at 77°K and up to 20 μ at 4.2°K has been observed in Bridgman‐grown and subsequently annealed crystals of Pb1−xSnx Te which had carrier concentrations ranging from 2 to 8 × 1015 cm−3 with a mobility of about 3 × 104 cm2/V‐sec at 77°K. Detectivity values generally were between 108 and 109 cm/W‐sec1/2 at 77°K and greater than 1010 cm/W‐sec1/2 at 4.2°K. Photoconductive lifetimes of about 10−8 at 77°K and higher temperatures and 10−6 sec at 4.2°K were measured by means of light pulses from a GaAs diode laser.

PbS MIS devices for charge‐coupled infrared imaging applications

Results of an experimental investigation of PbS MIS devices suggest the feasibility of developing a monolithic two‐dimensional infrared charge‐coupled imaging device (CCID). This CCID would be operable at 77 K and have moderate imaging sensitivity out to about 3.5 μm. Measurements on MIS capacitors fabricated with a pyrolytic SiO2 insulator have shown that the PbS surface potential is variable with bias from accumulation through inversion, the interface state density is ∼1×1012 cm−2 eV−1, and the storage time at 77 K is about 2 sec. Calculations indicate that efficient charge transfer should be achievable with fat‐zero operation, and that imaging sensitivity will probably be controlled by the degree of uniformity that can be attained.