Inhomogeneities in MOVPE InN

Abstract This paper reports the in‐depth and in‐plane inhomogeneities in InN films. Samples of InN are grown on sapphire substrates without or with a buffer using the atmospheric‐pressure MOVPE. For the in‐depth inhomogeneity analysis, the conventional PL measurement using an excitation source with a different wavelength is made from both the front surface and the film/substrate interface sides of samples. The measurement reveals that samples grown for a long time without buffer contain a deteriorated layer, which shows a higher PL peak energy, near the film/substrate interface. Such a layer is never found on the surface side. The deterioration is markedly enhanced when the sample is annealed in an NH₃ flow. Since the coexistence of TMI and NH₃ (growth environment) suppresses the deterioration and the InN samples used in this experiment have an In‐polarity, such a deterioration is hydrogen‐related degradation on the N‐face of InN film. In‐plane inhomogeneity of InN grown with a different buffer is studied by analyzing PL and absorption data. A wider PL spectrum and a larger discrepancy between PL peak energy and absorption edge, those are observed for films grown without buffer, are well explained by taking account of a large in‐plane inhomogeneity in the samples. The existence of the large in‐plane inhomogeneity is confirmed by the near‐field PL mapping obtained by the SNOM. The SNOM analysis also shows that, although the use of the buffer improves the apparent in‐plane uniformity, such a film has a fine inhomogeneity due to small grains of the buffer. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)