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Lead-Tin Telluride Sputtered Thin Films for Infrared Sensors
Final technical rept. 15 Oct 1971-15 Oct 1974
GENERAL DYNAMICS CORP POMONA CA POMONA DIV
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A study was carried out aimed at preparing thin ternary compound films suitable for infrared sensor application. An investigation was pursued to control or optimize the structural, compositional, electrical and electro- optical film properties by means of well defined deposition parameters and conditions. Techniques were first developed for sputtering single crystal thin films of lead tin telluride PbSnTe on barium fluoride and calcium fluoride substrates. Both supported discharge and ion beam sputtering were used. The sputtering gas was argon. Most data was obtained by supported discharge sputtering. Thirteen sputtering targets of PbSnTe were used with ratios of tin to total metal lead plus tin of x 0.15 to x 0.32. Some targets were prepared metal or tellurium rich but most were stoichiometric, i.e. having the same number of tellurium atoms as metal atoms. The upper substrate temperature for single crystal growth was about 350 C and the lower temperature ranged from about 225 to 300 C for growth rates from 0.5 to 2.5 micrometers hr. Outside this temperature-growth rate regime the films were not single crystal. The x-value of the deposited film, which defines the energy gap, was found to be controllable by the x-value of the target, the substrate temperature, and the deposition rate. Aside from film x-values, the stoichiometry of the film materials was found to be also controllable by adjustment of the substrate temperature and deposition rate. Complete stoichiometry, which is associated with the lowest achievable carrier concentrations, was found to occur at critical temperature- rate products - which differ with different target x-values.
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