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We have performed contactless electroreflectance studies of the interband excitonic transitions of GaN thin films in the temperature range between 15 and 475 K. The parameters that describe the temperature dependence of the interband transition energies and the broadening function, ⌫(T), of the excitonic features are evaluated. The exciton-longitudinal optical phonon coupling constant, which is determined from an analysis of ⌫(T), is considerably larger than that for a number of the cubic III-V semiconductors.

The composition and temperature dependence (20K

We have investigated an InGaAs/GaAs/GaAlAs vertical-cavity surface-emitting laser using surface photovoltage spectroscopy (SPS) in the temperature range of 15 K<T<400 K. For comparison purposes, we have also (a) measured temperature-dependent photoreflectance (PR) and normal-incidence reflectivity (NIR); and (b) calculated the number of photoexcited carriers (PEC), which is related to the SPS signal. The SPS spectra exhibit both the fundamental conduction to heavy-hole (1C–1H) excitonic transition and cavity mode plus a rich interference pattern related to the properties of the mirror stack. The PR data show only the 1C–1H excitonic transition (plus Franz–Keldysh oscillations) while the cavity mode is detected by NIR. The temperature variation of 1C–1H/cavity mode is the same for SPS and PR/SPS and NIR. The SPS interference pattern from the DBRs is in good agreement with the PEC calculation. This experiment demonstrates the considerable potential of SPS for the characterization of these devices.