THE EFFECTS OF THE MAGNITUDE OF THE MODULATION FIELD ON ELECTROREFLECTANCE SPECTROSCOPY OF UNDOPED-N(+) TYPE DOPED GAAS

The electroreflectance (ER) spectra of an undoped-n(+) type doped GaAs has been measured at various amplitudes of modulating fields (delta F ). Many Franz-Keldysh oscillations were observed above the band gap en ergy, thus enabling the electric field (F) in the undoped layer to be determined. The F is obtained by applying fast Fourier transformation to the ER spectra. When delta F is small, the power spectrum can be cl early resolved into two peaks, which corresponds to heavy- and light-h ole transitions. When delta F is less than similar to 1/8 of the built -in field (F(bi)similar to 77 420 V/cm), the F deduced from the ER is almost independent of delta F. However, when larger than this, F is in creased with delta F. Also, when delta F is increased to larger than s imilar to 1/8 of F-bi, a shoulder appears on the right side of the hea vy-hole peak of the power spectrum. The separation between the main pe ak and the shoulder of the heavy-hole peak becomes wider as delta F be comes larger. (C) 1998 American Institute of Physics.