Temperature Dependence of the Photoreflectance Lineshape for GaN Films Grown by Molecular Beam Epitaxy

✍ Scribed by Behn, U. ;Thamm, A. ;Brandt, O. ;Grahn, H.T.

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 101 KB
• Volume: 180
• Category: Article
• ISSN: 0031-8965
• DOI: 10.1002/1521-396x(200007)180:1<381::aid-pssa381>3.0.co;2-r

✦ Synopsis

The photoreflectance (PR) lineshape of GaN films grown by molecular beam epitaxy was investigated in the temperature range of 10 to 400 K. At low temperatures, the lineshape is dominated by excitonic transitions and can be reasonably well fitted using the first derivative of a Gaussianbroadened oscillator. At higher temperatures, the lineshape is more Franz-Keldysh like, but still influenced by excitonic effects. Typical Franz-Keldysh oscillations appear on the high-energy side of the PR spectra, from which the surface electric field can be estimated. At room temperature, we find a remarkable sensitivity of the PR lineshape to the ambient medium. A small change in surface electric field and a large decrease of the PR amplitude are observed, when the ambient medium is changed from air to vacuum. We address this effect to an UV-light induced desorption of oxygen from the sample surface.