Transport Property
The velocity at which holes move through a semiconductor lattice when subjected to an electric field depends on the effective mass associated with the light hole valence band. Because the energy surface of the light hole band has a high curvature, light hole mobility is considerably greater than that of heavy holes. This parameter influences the high frequency response of p-type transistors and optoelectronic components.
Band Structure
Degeneracy at the valence band edge splits the hole population. While light hole mobility is high the overall hole transport is often dominated by heavy holes.
Device Speed
Fast switching in bipolar junction transistors and high speed photodetectors relies on the rapid movement of charge carriers. Improvements in light hole mobility lead to lower base resistance and higher cutoff frequencies in specialized silicon germanium devices. Designing for high mobility requires minimizing ionized impurity scattering which slows the carriers down.
Metrological Standard
Precise values are extracted from cyclotron resonance or magnetoresistance measurements at cryogenic temperatures to isolate different hole species. Standardized wafers for high speed analog circuits are qualified based on the measured mobility within the epitaxial layers. The accuracy of these measurements depends on the uniformity of the applied magnetic field and the purity of the semiconductor sample.
