Martin Marietta Corporation

General Electric Company

Karl A Harris

Robert W Yanka

Thomas H Myers, Ii

Richard J Williams

Gregory K Dudoff

Thomas H Meyers, Iii

Lee M Mohnkern

An improved x-ray detector in the form of a p-i-n CdTe homojunction device is disclosed. The intrinsic ('i') layer is of high resistivity CdTe, while the n- and p-doped CdTe layers are epitaxially grown in a photo-assisted process in a molecular beam epitaxial apparatus. The n-dopant is conveniently indium, with an indium metal contact. The 'i' layer is optionally epitaxially grown in a photo-assisted process. The p-dopant is preferably arsenic. A PAMBE formed mercury telluride contact layer enhances the ohmic contact to the p-layer, and a gold contact is provided to the contact layer. The use of the PAMBE technique facilitates high quality crystal growth and activation of the dopants. The resulting CdTe p-i-n homojunction device has a wide band gap (1.45 eV) essential to room temperature operation.

CDTE x-ray detector for use at room temperature

A typical source of cadmium and tellurium is as a by-product of copper mining. Although attempts are made to remove impurities such as copper prior to commercially supplying them for forming material like cadmium telluride, cadmium zinc telluride and cadmium telluride selenide for use as a substrate to support electronic circuitry, processing during formation of the circuitry causes the impurities from the substrate to segregate into the circuitry, resulting in unacceptable electrical performance of the circuitry. A method for purifying the substrate prior to circuitry formation includes forming a sacrificial layer of mercury telluride or mercury cadmium telluride on the substrate, annealing the combination at elevated temperature with an overpressure of mercury and removing the sacrificial layer along with a contiguous portion of the substrate, if desired. The sacrificial layer may be formed by vapor phase type processes or even by liquid phase epitaxy.

Method of purifying substrate from unwanted heavy metals

The invention relates to molecular beam epitaxial (MBE) processing and more particularly to a two zone electrical furnace for use with high vapor pressure II-VI materials. The furnace is designed for use with effusion type crucibles requiring a lower temperature in the fill zone to control the flux and a higher temperature in the orifice zone to avoid clogging the customary collimating orifice. Each zone is heated by a distributively heated radiator, the fill zone radiator being of a tantalum foil construction of low thermal conductance, while the orifice zone radiator is a solid molybdenum cylinder of relatively high thermal conductance. The zones are joined by linking the two radiators by a thermally conductive path, while the shields and the distributed heaters of the respective zones are separated to reduce thermal coupling. The arrangement provides substantial independence between the temperature settings of the two zones and the molybdenum construction is free of erosion from tellurium based reagents.

Two-zone electrical furnace for molecular beam epitaxial apparatus

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Liverpool, NY, United States of America

Karl A Harris