We have investigated quantitatively on the origins of residual electrons in InN layers to make clear some roles of oxygen incorporation for band-gap widening. It has been found out that a linear relation was observed between oxygen and residual electron concentrations for InN layers grown by RF-MOMBE using TMIn source, although the residual electron concentration is super-linearly dependent on oxygen concentration for InN layers grown by RF-MBE using metal In source. The experimental results strongly indicate that oxygen atoms and/or nitrogen vacancies induced by oxygen incorporation are major origins of the residual carrier concentrations.1 Introduction Recent progress of InN studies by many groups has been showing that band-gap energy (E g ) is about 0.65 eV [1][2][3]. Band-gap widening is caused by residual electrons through the BursteinMoss effect and major candidates of the origins of residual electrons are considered to be nitrogen vacancies or impurities such as oxygen (O) and carbon (C). However, it has not been understood yet well. We have already reported that the usage of trimethylindium (TMIn) has a suppression effect to oxygen contaminations by formation of highly volatile products such as CO and/or CO 2 , produced by thermal decomposition process of TMIn during a radio frequency nitrogen plasma assisted metal organic molecular beam epitaxy (RF-MOMBE) under oxygen contaminated back grounds and that clearly red shift of absorption edge (E g ) was obtained. Moreover, we have also reported that simultaneous irradiation of Ga beam during growth is additionally very effective to suppress oxygen contamination and further red shifts of E g have been achieved as a result of the additional suppression effect [4], and we have proposed a possible model for such suppression of O contamination by formation of highly volatile products such as Ga 2 O and CO 2 during conventional RF-MOMBE growth by using TMIn [5]. In this paper, we have quantitatively investigated on the origins of residual electrons in RF-MOMBE grown InN layers to make clear some roles of oxygen incorporation for the band-gap widening.

No abstract

Mosaicity control is necessary for improvement of crystal quality of III‐V nitride semiconductor materials, especially for InN. However, the mosaicity control for both of the tilt and the twist angle fluctuations has not been achieved still now in the direct growth of InN on the sapphire substrate by nitridation. Moreover, the role of nitridation process has not been so much clear from the view point of the mosaicity control. In this paper, we propose a new nitridation technique, two‐step nitridation, combined with the high‐ and the low‐ temperature nitridation to reduce the mosaicity and also to make clear the roles of the nitridation process in the InN growth. As the result of the new nitridation technique, the considerably improvement of the tilt and the twist angle fluctuations has been successfully achieved in the direct growth of InN without any buffer layer. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

In the InN growth on sapphire substrates, it is difficult to control both of tilt and twist angle fluctuations at same time. It is necessary to understand initial growth stage such as the role of nitridation process to improve the mosaicity. Low‐temperature nitridation technique brings the drastically improvement of the tilt angle fluctuation, although the twist angle fluctuation becomes worse. Such experimental results strongly indicate that there is some trade‐off relation between the tilt and the twist angle fluctuations as a function of the nitridation condition such as the nitridation time. In this paper, we discuss about such trade‐off relation in the direct growth of InN on the nitridation sapphire substrates and also propose a simple model of initial nitridation process to explain it. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)