TEMPERATURE-DEPENDENCE OF FERMI-LEVEL OBTAINED BY ELECTROREFLECTANCE SPECTROSCOPY OF UNDOPED N(-TYPE DOPED GAAS())

The electroreflectance (ER) spectra of an undoped n(+)-type doped GaAs have been measured over a range of temperature from 25 to 400 K. Many Franz-Keldysh oscillations were observed above the band-gap energy, w hich enabled the electric field strength and, hence, also the Fermi le vel to be determined. The photovoltaic effect is shown to be negligibl e, even at the low temperature. The experiment shows that the Fermi le vel decreases with increasing temperature and has almost the same temp erature dependence as the energy gap. It is pinned at about 0.63 of en ergy gap below the conduction band. (C) 1997 American Institute of Phy sics.