Properties of nanocrystalline GaN films deposited by reactive sputtering

Abstract

Nanocrystalline GaN films have been deposited near room temperature by reactive r.f. sputtering. The effects of varying the self-bias voltage of the sputtering target and the ratio of the argon and nitrogen flow rates were investigated by optical and FTIR spectroscopy. The deposition rate was found to be a quadratic function of the target bias and directly proportional to the argon concentration. At a fixed gas ratio of 33% nitrogen in argon, the optical band gap values are largest (3.2 eV) at the lowest target bias (-400 V). This is the region with the least band tailing, the lowest refractive index and negligible stress. At a fixed target bias of -800 V, as a function of gas flow rate, there is a region at approximately 50% nitrogen where the band gaps are at their maximum values and the E1(TO) absorption peak widths are at a minimum. © 2003 Elsevier Science B.V. All rights reserved.