Determination of acceptor ionisation energies in CdxHg1-xTe

Variable temperature Hall measurements have been performed on p-type CdxHg1-xTe(CMT) with 0.18<x<0.32 grown by both Bridgman and modified Bridgman (accelerated crucible rotation technique, ACRT) techniques. Samples of material deliberately doped with acceptor impurities as well as undoped samples were studied in the as-grown state and after low-temperature (<400 degrees C) annealing. Carrier freeze out was observed in most samples and values for the ionisation energy Ea determined. For undoped material Ea was found to increase with increasing x and with decreasing acceptor concentration Na. The doped samples measured after isothermal annealing in a mercury rich atmosphere, to remove metal vacancies, were found to have lower Ea values that their undoped counterparts of similar x and Na. The Ea values obtained are compared with other values found in the literature. In the bulk-grown material it is not possible to distinguish between impurities simply from their Ea values but the technique can be used to differentiate material dominated by defects from that controlled by impurities. It is also concluded that Na, x and the degree of compensation need to be specified when quoting values for Ea in undoped and doped material.

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