Momentum relaxation of electrons in InN

Abstract

2 V -1 s -1 at 77 K to 445 cm 2 V -1 s -1 at 300 K while the carrier concentration is independent on temperature. We consider the ef- fect of optical phonon scattering, ionised impurity scattering and dislocation scattering to model the ob- served temperature dependence of the mobility. 1 Introduction During the last few years, research in wurtzite InN has attracted much attention world-wide because of its wide range of potential applications in optoelectronic devices. In fact, together with GaN, InN forms an alloy, InxGa1-xN, with a band gap that can span from the near infrared to the ultraviolet. The band gap of InN has been recently updated from 1.9 eV, a value that was initially re- ported for materials grown by sputtering, to 0.7-0.8 eV (1) at room temperature. This much lower band gap energy agrees well with the recent theoretical calculations (2) and was observed in materials grown using MBE and MOVPE (1, 3-5). The recent dispute over the band gap of InN has focused the attention on its optical properties, while data on the electrical properties are still scarce. Very little is known about the fundamental interactions such as e-e, e-phonon, e-h, h-phonon etc. Further work needs to be done to establish an understanding of these interactions in In x Ga 1-x N. InN electron mobility shows a very week temperature dependence that was tentatively interpreted as due to a reduced electron-optical phonon interaction (6). This conclusion is rather surprising since InN, together with the other III-N compounds, is a highly polar material. In fact the lack of inversion symmetry of the wurtzite structure together with the strong ionic nature of the In-N chemical bond leads to a strong spontaneous and piezoelectric polari- zation. The electron and polar optical mode interaction is then expected to play an important role limiting the mobility at high temperatures. Moreover, a strong interaction should result in the saturation of the drift velocity at high electric fields at a much lower value than the theoretical predictions, as we have recently reported (7). This has relevant implications in high power and high speed devices. In this paper we aim to investigate the most important scattering mechanisms that limit the mobility in InN grown by MBE on sapphire at high temperatures. 2 Experimental results and discussion In this work we have investigated a 0.1 µm thick InN layer grown by molecular beam epitaxy on sapphire substrate. Conventional Hall bars were fabricated by li-