Infrared detector arrays by new technologies

Techniques for fabricating single-crystal and thin-film detector arrays for infrared remote sensing have been developed in the last few years in most advanced solid-state laboratories. Arrays of photovoltaic devices have been prepared by liquid-phase epitaxy and vapor transport, and by the formation of metal-semiconductor structures and by proton bombardment. A great improvement in infrared thin-film devices was also achieved in the last few years by the vacuum deposition of epitaxial and polycrystalline films. A new technique to obtain high-quality middle-infrared detector arrays has been developed by the use of RF sputtering. Ternary chalcogenide layers with interesting properties for fabricating multi-element detector arrays have been obtained by an RF multicathode sputtering. Pb
x
Sn
1-x
Te films, with a composition-dependent energy gap, have been deposited employing an RF multicathode sputtering system capable of simultaneous and sequential sputtering at different rates from three different targets. Single-crystal and polycrystalline films have been investigated in the course of developing bidimensional detector arrays. Heteroepitaxial films of Pb
x
Sn
1-x
Te at substrate temperatures lower than that needed in conventional evaporation techniques have been obtained using NaCl and BaF
2
substrates. Moreover, epitaxial films with electrical properties close to the best single-crystal values have been obtained on germanium substrates. Using the cosputtering technique, it has been possible to obtain n-type and p-type layers just by controlling the quantity of excess metal or tellurium, respectively. Polycrystalline photoconductive detectors deposited by RF sputtering have shown responsivity and detectivity values higher than previously reported. Exceptionally high responsivity values have been obtained-better than 10
⁶
V/W in PbTe films and 480 V/W in Pb
0.85
Sn
0.15
Te films. Peak detectivities D
λ
^*
(4.5 µ, 800, 1) > 8 × 10
¹⁰
cm ċ Hz
^1/2
/W in PbTe detectors and D
λ
^*
(8.5 µ, 800, 1) > 10
⁹
cm ċ Hz
^1/2
/W in Pb
x
Sn
1-x
Te detectors have been measured with a 2π-steradian field of view at an operating temperature of 77 K. These results are particularly important for the films deposited on germanium and silicon substrates, because of the easy incorporation of electronic readout elements into a completely integrated thermal vision system. Performance data are presented for blackbody and spectral detectivity, impedance, noise, and time constants. Distributions of measured data for linear staggered detector arrays are reported.