Magnetically induced impurity banding in n-InSb

Abstract

A detailed study of the effect of a strong magnetic field on donor levels in n-InSb has been made by means of Hall-effect and resistivity measurements down to 1.5°K, using field strengths up to 28,000 G. The results of these measurements indicate that donor levels which are split off from the conduction band under the influence of the magnetic field form a narrow impurity band with finite mobility. The position of the impurity band (i.e. donor ionization energy) and the mobility of electrons in the impurity band have been determined as a function of magnetic field strength. The impurity band mobility can be understood in terms of quantum-mechanical resonance jump- ing of electrons between donors by taking into account the dependence of the donor wave function on magnetic field strength, although there are some quantitative difficulties when the magnetic field is parallel to the current. Experimental confirmation of our impurity banding model is provided by non-ohmic effects which indicate the occurrence of impact ionization of donors in electric fields of the order of 1 V cm .