Demonstration of n-GaN:Si NWs having ultrahigh density and aspect ratio via a 3-step growth method using MOCVD

Abstract

A novel 3-step growth method is developed for growing n-GaN:Si nanowires (NWs) on a Si (111) substrate using the MOCVD process and this method is being reported for the first time. The aim of this study was to produce GaN NWs of high density and aspect ratio so that advanced GaN NW-based devices of larger effective surface area and high efficiency could be realized further. The results presented in this study succeeded to demonstrate n-GaN:Si NWs of ultrahigh density and aspect ratio. In the case of the 3-step growth recipe, the introduction of an intermediate growth step at a comparatively low temperature of 850 °C gave rise to longer n-GaN:Si NWs of density in the order of 10⁸ cm⁻² which is rare for a cost-effective technique like MOCVD. The increase in the NW density is attributed to a thin boundary layer produced during non-pulsed growth at the intermediate temperature. This paper also established the effects of the flow rate of a group-III precursor on the geometry and material properties of n-GaN:Si NWs. For the 3-step growth method, the optimal growth conditions were achieved with the 0.4 sccm TMGa flow at the final step. Comparative studies were done in detail between the 2-step and the 3-step growth methods and how the NW density and height were controlled. A five-fold increment in the photocurrent was noticed for n-GaN:Si NWs grown with the 3-step growth method when compared with the 2-step growth method. Judging from these results, it can be thought that the 3-step method is highly useful in the fabrication of optoelectronic devices using group III-nitride NWs such as photoconductive devices and LEDs.