Effects of a cap layer on built-in electric fields of AlxGa1-xN/GaN heterostructures non-destructively probed by Franz-Keldysh oscillations
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
Published online: 1 August 2006
We have investigated electric field strengths in the AlxGa1-xN layer, FAlGaN's, of AlxGa1-xN/GaN heterostructures with and without a GaN cap layer using photoreflectance (PR) spectroscopy. Franz-Keldysh oscillations (FKOs) from the AlxGa1-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 FAlGaN. 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 FAlGaN based on a Schrödinger-Poisson equation clarify that the magnitude of the enhancement of FAlGaN is dominated by the cap-layer thickness.
PACS: 78.40.Fy – Semiconductors / 78.67.Pt – Multilayers; superlattices / 77.65.-j – Piezoelectricity and electromechanical effects
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2006