On the doping of isotopically controlled germanium by nuclear transmutation with a high concentration of shallow donor impurities

Abstract

Experimental results are presented of the neutron transmutation doping (NTD) of isotopically controlled crystals, irradiated with a high dose of neutron flux (up to ). A series of heavily doped samples of n-Ge:As with small compensation ratio was obtained. Two novel effects connected with high neutron dose have been observed: (i) the dependence of the free electron concentration on , linear at small n, saturates at ; (ii) if the NTD procedure is applied to samples previously highly doped by As, the final value of n even decreases (a `negative doping'). These effects are explained by the enhancement of the formation of complexes of an As impurity with radiation damage at high , which leads to a decrease of n.