Eur. Phys. J. Appl. Phys.
Volume 37, Number 2, February 2007
|Page(s)||119 - 122|
|Section||Semiconductors and Related Materials|
|Published online||17 January 2007|
High sensitivity of Franz-Keldysh oscillations in photoreflectance spectra for probing morphology in AlxGa 1−xN/GaN heterostructures
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: Takeuchi.Hideo@db.MitsubishiElectric.co.jp
Revised: 16 October 2006
Accepted: 24 October 2006
Published online: 17 January 2007
We demonstrate that Franz-Keldysh oscillations (FKOs) observed by photoreflectance (PR) spectroscopy are highly sensitive to the surface morphology of AlxGa1−xN layers in AlxGa1−x N heterostructures. Three Al0.2Ga0.8N/GaN heterostructures with different surface-morphology profiles, which are confirmed with atomic force microscopy, have been investigated. The X-ray-diffraction patterns are hardly affected by the Al0.2Ga0.8N/GaN-layer morphology. In contrast, it is revealed that cracks and pits dominating the morphology remarkably reduce the amplitude of the FKOs from the Al0.2Ga0.8N/GaN layer, which is attributed to the following two mechanisms related to the cracks and pits. One is lifetime broadening due to carrier scattering, and the other is the suppression of the modulation magnitude for the built-in electric field, which is caused by the trapping and recombination of photogenerated carriers at the surface.
PACS: 78.40.Fy – Semiconductors / 78.67.Pt – Multilayers; superlattices / 77.65.-j – Piezoelectricity and electromechanical effects
© EDP Sciences, 2007
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