Inhomogeneities in MOVPE InN
|Akio Yamamoto 1, Hiroshi Miwa 1, Wen Jun Wang 2, Akihiro Hashimoto 1|
1. University of Fukui (U. Fukui), 3-9-1 Bunkyo, Fukui 910-8507, Japan
This paper reports in-depth and in-plane inhomogeneities in MOVPE InN studied using a different kind of PL measurement. Samples of InN are grown on sapphire substrates without or with a GaN buffer, using an atmospheric-pressure MOVPE system. The lowest carrier concentration and the highest mobility obtained for grown films are 4.5×1018cm-3 and 1100 cm2/Vs, respectively. For the in-depth inhomogeneity analysis, the macroscopic PL measurement is made from both the front surface and the film/substrate interface sides of an InN film using an excitation source with a different wavelength (325, 442 and 633 nm). PL peak energy near the front surface is almost independent of the excitation wavelength, implying that the property near the front surface is not changed with depth. PL peak energy from the interface side is higher than that near the front surface and is markedly increased with decreasing the excitation wavelength. Especially, a sample grown without buffer and then annealed in an NH3 flow shows a higher peak energy by about 100 meV than those measured from the front side. Such a higher PL peak energy is due to the Burstein-Moss shift and shows the existence of a higher carrier concentration region near the interface. In-plane inhomogeneity of samples is studied using the Scanning Near-Field Optical Microscopy (SNOM) system (Type NFS-220FK, JASCO Corp., Japan). Employing the illumination-collection mode with a fiber probe of a 100-500 nmφ aperture size, a near-field PL spectrum and its intensity mapping are successfully obtained for InN films at room temperature. By monitoring a probe movement at each point of measurement, surface topography is also obtained. Inhomogeneities detected by the near-field PL mapping are dependent on the growth conditions of samples. Especially, the use of the buffer is found to improve effectively the in-plane uniformity of the near-field PL intensity. This seems to be due to the uniform nucleation of InN on the buffer.
Presentation: invited oral at E-MRS Fall Meeting 2005, Symposium A, by Akio Yamamoto
See On-line Journal of E-MRS Fall Meeting 2005
Submitted: 2005-05-20 08:36 Revised: 2009-06-07 00:44