Correlation among growth conditions, crystal structures and optical properties of InN

Abstract

This paper addresses band-gap issues of InN. InN films of various qualities were prepared by radio-frequency plasma-assisted molecular-beam epitaxy (RF-MBE). Correlation among photoluminescence (PL) peak energy, carrier concentration, electron mobility, PL intensity, PL line width, and X-ray rocking curve (XRC) line width indicated that the InN sample with the smallest PL peak energy of ∼0.67 eV (at room temperature) had the highest electron mobility, the strongest PL intensity even with the smallest electron concentration, the sharpest PL and (0002) XRC peaks. Dependence of PL peak energy on carrier concentration can be explained mostly by the Burstein-Moss shift. Temperature dependence of PL peak energy was normal with smaller values at higher temperatures. These experimental results suggest that the PL should originate from fundamental inter-band transitions and not likely from mid-gap levels associated with crystal defects. These results also suggest that the true band-gap energy of InN should be less than 0.67 eV and probably around 0.65 eV at room temperature. This assessment was further supported by In-composition dependence of PL peak energy for In-rich In1–xGaxN films (also grown by RF-MBE), where room temperature PL peak energy exhibited a monotonic and smooth decrease with the increase in In-composition, approaching to ∼ 0.67 eV of InN. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)