ABSTRACT

Abstract. The electrical properties of a (l-lOl)GaN grown on an Si substrate were studied as a function of Si doping density. It was found that un-intentionally doped samples exhibited p-type conduction, while the doping of Si changed the type of conduction from p-type to n-type. The cathodeluminescence spectra at 4 K exhibited a strong edge emission peak at 357 nm followed by a defect-related emission at 370 nm. The intensity of the latter was enhanced by the Si doping and we found slight blue shift of the emission energy. 12

1. Introduction Ill-nitrides have been utilized in ultraviolet light emitting diodes and blue/violet laser diodes [1,2]. Most of the materials so far have been grown on (0001) plane of sapphire or SiC substrate. The heterostructure grown on such a crystal is subject to strong piezoelectric and/or pyroelectric field [3], which is to restrict the performance of optical/electronic devices. In order to reduce the field effect, several attempts have been reported on the growth of GaN on different crystal plane [4,5]. The present authors demonstrated the metalorganic vapour phase epitaxy (MOVPE) of (l-lOl)GaN on a 7 degree off-axis (OOl)Si substrate [6]. By tilting the angle of the c axis on the substrate surface, they could reduce the thermal expansion coefficient mismatch between the GaN grown layer and the Si substrate. As the result, they achieved a flat (1-101) surface without cracks in the grown layer. In this particular method, the top (1-101) surface is terminated with N atoms, which is contrast to the fact that the (0001) face is terminated with Ga atoms. This will modify the surface morphology as well as the growth modes. Actually, the growth rate was found to be lower than that found on the (0001) face. Thus the behaviour of the impurity incorporation might be modified as well. In the previous paper, we reported that un-intentionally doped GaN/AIN heterostructure shows p-type conduction [7]. In this paper, we will demonstrate that the doping of Si changes the type of conduction from p-type to n-type. In addition, the variation of the optical properties will be discussed in terms of the Si doping level.