Observation and quantification of the direction reversal of the surface band bending in GaAs_1‐xN_x using terahertz electromagnetic wave and photoreflectance measurements

Abstract

We have investigated the polarity of terahertz (THz) electromagnetic waves from a GaAs1‐xNx epitaxial layer with x = 0.43% to clarify the effects of nitrogen incorporation on the direction of the surface band bending. The THz‐wave polarity of the GaAs1‐xNx sample is reversed compared with that of an i ‐GaAs/n ‐GaAs sample that has an upward surface band bending; namely, the GaAs1‐xNx sample has a downward band bending. The polarity reversal is attributed to the phenomenon that the conduction band bottom is lowered by the band anticrossing due to the nitrogen incorporation, which changes the direction of the surface band bending. We also measured the photoreflectance (PR) spectrum of the GaAs1‐xNx sample to quantify the surface electric field produced by the surface band bending. The PR spectrum exhibits the Franz‐Keldysh oscillations (FKOs) from the GaAs1‐xNx layer. From the FKOs, the surface electric field is estimated to be 24 kV/cm. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)