Photoreflectance studies on InGaP/GaAs heterojunction structure

• Main Authors: Chen, Chih-Sheng, 陳志昇
• Other Authors: Prof. Gwo-Jen Jan
• Format: Others
• Language: en_US
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/14504812589925497614

碩士 === 國立臺灣大學 === 光電工程學研究所 === 89 === InGaP/GaAs material is introduced in an alternative material to traditional AlGaAs/GaAs applications. Due to the Al-free in InGaP/GaAs materials and the lattice-match InGaP/GaAs hetero- interface by gas source molecular beam epitaxy (GSMBE) system growth, the lifetime and the operating limitations in electro-optical applications can be improved effectively. The InGaP/GaAs samples in this thesis were grown on different temperature by the GSMBE system. Abnormal S-shape curve on the temperature dependant photoluminescence (PL) experiment results showed the different temperature dependant behaviors with the GaAs, InP, and GaP bulks. This caused the traditional band-to-band energy measuring method by the low temperature PL spectroscopy faced a great challenge on such direct band gap samples. The photoreflectance (PR) spectroscopy was employed for measuring the critical energies in the band diagram of InGaP/GaAs. The spectrum of modulation spectroscopy is sensitively to the critical points in the joint density of states and is independent of the occupation probability factors. According to the basic theory of PR, we got a higher precision measuring result for the characterization of the anomalous S-shape PL data. The value of band gap and crystal splitting energies and the temperature dependent data are measured and fitted by the Varshni and Bose-Einstein expressions. All the parameters in both expressions for all three samples were determined. The photoluminescence excitation (PLE) spectroscopy was introduced for the re-confirmation with the PR results. Two higher growth temperature samples showed the Franz-Keldysh oscillations (FKOs) nearly the GaAs band gap at 300K PR spectra. These two samples’ major luminescence mechanisms were changed in a special temper- ature range. Another anomalous energy in all samples showed an unusually luminescence mechanism and this dominated the most of the electron-hole recombination path at low temperature. This pheno- menon made the major low temperature luminescence was not controlled by the band gap transition.