Preparation Of Epitaxial Thin Film Lead Salt Infrared Detectors

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Abstract
Photovoltaic diode infrared detectors are fabricated by depositing metallic lead on p-type lead-salt epitaxial films. The films are grown from the vapor phase by a modified hot wall technique, under pressures on the order of 5 x 10-6 Torr. The carrier concentration of these films is typically in the low 1017 cm-3, and the mobility is a few thousands cm /V sec at 77 K. The lead salts for the growth process are prepared by heating the elemental materials in sealed quartz ampoules. The substrates used for these films are usually BaF2 with a {111} cleavage plane. The formation of Schottky barrier junctions on lead salt films has been reported to be dependent on the chemistry of the interface, such as the presence of oxygen. Furthermore it was found recently that the presence of chlorine vastly improved the I-V characteristics of diode junctions. A simple process for introducing chlorine to the semiconductor surface prior to lead deposition was developed. This process has proved to yield good quality diodes with consistency.

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