Intrinsic Oscillatory Photoconductivity and the Band Structure of GaAs

Oscillations as a function of incident light energy are reported for the photoconductive response of high-purity epitaxial GaAs at 4.2°K. The original report of Nahory is supplemented in several ways: As many as 15 oscillations are observed at low electric fields, corresponding to electron states 550 meV into the conduction band. These are approximately periodic with a period of 41.3±0.3 meV, which yields a constant effective-mass ratio of $\frac{m_e}{m_{\mathrm{hh}}}=0.\mathrm{}124\pm 0.010$, where $m_e$ and $m_{\mathrm{hh}}$ are the effective masses of the electron and heavy holes, respectively. As the field is raised above 0.5 V/cm, sample resistance gradually decreases owing to the growth of impact ionization of shallow donors. At the same time, the amplitude of the oscillations predominant at low field decreases while a longer-period oscillation remains relatively uneffected by the field increase. At 2 to 4 V/cm this oscillation dominates the photoresponse, displaying a period of approximately 82meV. It is argued that these oscillations are due to light holes. This interpretation yields a mass ratio $\frac{m_{\mathrm{lh}}}{m_e}=1.\mathrm{}22\pm 0.02$ near the zone center and an increasing light-hole mass as $k$ increases.