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Issue Eur. Phys. J. Appl. Phys.
Volume 37, Number 2, February 2007
Page(s) 119 - 122
Section Semiconductors and Related Materials
DOI 10.1051/epjap:2007009
Published online 17 January 2007

Eur. Phys. J. Appl. Phys. 37, 119-122 (2007)
DOI: 10.1051/epjap:2007009

High sensitivity of Franz-Keldysh oscillations in photoreflectance spectra for probing morphology in Al$_{\sf x}$Ga$_{1-{\sf x}}$N/GaN heterostructures

H. Takeuchi1, Y. Yamamoto1, Y. Kamo1, T. Kunii1, T. Oku1, S. Wakaiki2 and M. Nakayama2

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

Takeuchi.Hideo@db.MitsubishiElectric.co.jp

(Received: 6 September 2006 / Received in final form: 16 October 2006 / Accepted: 24 October 2006 / Published online: 17 January 2007)

Abstract
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-xN 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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