Microwave Hall mobilities of holes in germanium

Abstract

Hall mobilities of three p-type germanium crystals were measured at microwave frequencies of 9.5 G Hz from room temperature to near liquid helium temperatures by means of a newly designed bimodal rectangular cavity. The microwave Hall mobilities were compared with the corres ponding d.c. Hall mobilities. As the temperature was decreased, the microwave Hall mobility began to deviate from the d.c. Hall mobility at about 200°K for each of the less pure samples 439GP and GPl, but not until 150°K for the purest sample 439HGP. The difference between the microwave and d.c. Hall mobilities at low temperatures was greater in the order 439GP > GPl > 439HGP, whereas the purity of the samples followed the opposite order 439HGP > GPl > 439GP. The difference between the microwave and d.c. Hall mobilities can be explained in terms of a high frequency inertial effect in which the relaxation time depends upon scattering of the holes by impurities as well as by phonons. This inertial effect accounts for the experimental results: one, at low temperatures, the microwave Hall mobility was always lower than the corresponding d.c. Hall mobility; and two, an increase in impurity scattering always increased the difference between the microwave and d.c. mobilities of the holes.