Photoreflectance of AlGaN/GaN Heterostructure Measured by Using Mercury Lamp as Pump Beam
Photoreflectance (PR) spectra of a GaN thin film and an AlGaN/GaN heterostructure were measured by using a HeCd laser or a mercury lamp as a pump beam. The wavelengths (λ) of the HeCd laser and the mercury lamp are 325 nm and 253.7 nm, respectively. The energy of the HeCd laser is lower than band-gap energy of AlxGa1-xN (x > 0.2), so electron-hole pairs cannot be generated in the AlGaN layer. Hence, the PR of the AlGaN was measured by using Argon ion laser (λ =300 nm) or quadrupled Nd:YAG (λ =266 nm) rather than HeCd laser in the previous works. In this work, the mercury lamp was used as the pump beam. Although the mercury lamp is a diffused source, it is not a hindrance to the PR measurements. The signal to noise ratio is improved by using defocused pump and probe beams in the PR measurement.
Yuan Ming Huang
Y. L. Peng et al., "Photoreflectance of AlGaN/GaN Heterostructure Measured by Using Mercury Lamp as Pump Beam", Materials Science Forum, Vols. 663-665, pp. 365-368, 2011