Eur. Phys. J. B 52, 311-314 (2006)
https://doi.org/10.1140/epjb/e2006-00302-y

Effects of a cap layer on built-in electric fields of Al_xGa_1-xN/GaN heterostructures non-destructively probed by Franz-Keldysh oscillations

¹ R & D Department, High Frequency and Optical Device Works, Mitsubishi Electric Corporation, 4-1 Mizuhara, Itami, Hyogo, 664-8641, Japan
² Department of Applied Physics, Graduate School of Engineering, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka, 558-8585, Japan

Corresponding author: ^a Takeuchi.Hideo@db.MitsubishiElectric.co.jp

Received: 26 April 2006
Published online: 1 August 2006

Abstract

We have investigated electric field strengths in the Al_xGa_1-xN layer, F_AlGaN's, of Al_xGa_1-xN/GaN heterostructures with and without a GaN cap layer using photoreflectance (PR) spectroscopy. Franz-Keldysh oscillations (FKOs) from the Al_xGa_1-xN layer are clearly observed in the PR spectra. It is found from analysis of the FKOs that stacking of the cap layer causes a remarkable enhancement of F_AlGaN. This fact demonstrates that the FKO profile is a non-destructive probe for a change of built-in electric field strength induced by a cap layer. Numerical calculations of F_AlGaN based on a Schrödinger-Poisson equation clarify that the magnitude of the enhancement of F_AlGaN is dominated by the cap-layer thickness.