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The history, status, and recent progress in the middle and long wavelength Hg 1-x HgCdTe photodetectors in Poland The Institute of Physics Polish Academy of SciencesThe HgCdTe research began in 1960 at the Institutes of Physics of Warsaw University and Polish Academy of Scien− ces (IFPAN), Warsaw. Bridgman technique with sealed thick wall quartz ampoules was used to grow material sui− table for research and experimental devices. The explosions caused by the high mercury pressure were quite frequent that time, resulting in a few series accidents. The grown ma− terial was used for optical and galvanomagnetic studies. The studies were aimed at determination of energy band struc− ture of the material. The Hg 1−x Cd x Te studies were for a long time the main topics of numerous meetings on solid state physics and electronics in Poland. The studies were impor− tant contribution to the understanding of fundamental pro− perties of the material.Simple photoconductive, photoelectromagnetic, and photovoltaic devices based on the bulk MCT crystals were demonstrated already in 1963 [5]. Interesting, the first pho− tovoltaic devices were based on n−on−p junctions that were formed at perimeter of MCT ingots during cool down pe− riod. Later, IFPAN scientists concentrated their efforts on diluted magnetic semiconductors such as Hg 1−x Mn x Te, less useful for infrared photodetectors. The Military University of TechnologyIn 1968, device−oriented research started at the Military Uni− versity of Technology (MUT), Warsaw (see Ref. 6 and related papers therein). Initially, modification of the isothermal vapour phase epitaxy (ISOVPE) discovered by Cohen−Solal et al. [7] in France, was applied. The original process relies on near− −equilibrium isothermal evaporation of HgTe upon a thick CdTe substrate [ Fig. 1(a)]. Interdiffusion of the grown layer with the substrate material yields variable gap structures.In the Polish modification [8] [ Fig. 1(b)], the hybryde substrates with thin CdTe layers were used rather than the bulk CdTe. The layers had been deposited by vacuum evapo− ration on low−cost and readily available substrates such as mica, silicon, sapphire and other. Limited amount of HgTe was then deposited by ISOVPE and the process was carried out up to complete homogenization. As the result, extremely uniform epitaxial layers were grown.

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