Tantalum doping and high resistivity in aluminium antimonide

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Abstract
Aluminium antimonide crystals grown by the Czochralski method from melts doped with tantalum are found to have a lower residual acceptor concentration and increased free hole mobility than crystals from undoped melts. An investigation of the effect of tantalum on the segregation of particular impurities shows that tantalum will `getter' certain impurities, for example carbon and copper. The mechanism is obscure. The segregation of tantalum is found to be abnormal. A value of 0.80 has been obtained for the effective segregation coefficient of tellurium. Doping the melt with tantalum and tellurium has given n- and p-type crystals with resistivities from 104 to 1010 Ω cm at room temperature. The variation of resistivity with temperature reveals the presence of levels with activation energies from 0.40 to 0.80 ev. A value of 14.4 ± 1 has been obtained for the static dielectric constant of aluminium antimonide from capacity measurements on the high resistivity crystals. Photoconductive decay times of 0.5 to 1 msec have been observed in these high resistivity crystals.

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