No abstract

This paper reports the photoluminescence (PL) spectra and the optical absorption edge at room temperature for MOVPE grown InN films as a function of growth temperature and background carrier concentration. A strong PL band with a peak energy in the range 0.7-0.9 eV is observed at room temperature. A sample grown at around 600 °C shows the highest PL intensity and the lowest peak energy. With decreasing the growth temperature from 600 °C, the PL intensity is markedly decreased and the peak energy is shifted toward the higher energy side. The absorption edge shows a similar change with the PL peak energy when the growth temperature is decreased. The difference between absorption edge and the PL peak energy is 50-100 meVand it increases with increasing the carrier concentration. The changes in PL peak energy and absorption edge with carrier concentration are not so steep compared to the absorption edge change predicted by Davydov et al. This may be explained by the increase in electron effective mass with increasing the carrier concentration reported by Wu et al. [Phys. Rev. B 66, 201403 (2002)].

No abstract

A microscopic ultraviolet photoelectron spectrometer (micro-UPS) is developed using a Schwarzschild objective coated with the two-color multilayer which reflects efficiently both He-I (21.2 eV) and He-II (40.8 eV) resonance lines. The spot size by the use of a pinhole of 300 µm diameter is 5 µm, which was measured using the visible light from a Xe lamp. In the present micro-UPS, a pinhole of 2 mm diameter is used to gain sufficient photon intensity, so that the spot size is 25 µm. The valence band spectra of a NiWO4 microcrystal, which cannot be grown in sufficient size, were measured by the present micro-UPS. The origin of atomic orbitals constituting the valence band of NiWO4 was elucidated.