[Show abstract][Hide abstract] ABSTRACT: A well-controlled yet simple process to synthesize indium tin oxide (ITO) nanospheres of various sizes has been proposed and described. The process was also extended to grow multi-layers of ITO nanospheres stacked one on top of another. To obtain nanospheres, e-beam evaporated ITO films wee selectively wet-etched using a dilute HCl acid solution. Size of the ITO nanospheres was controlled by varying the thickness of the ITO film. This simple process is accomplished in only a few seconds during which ITO nanosphere formation takes place via coalescence. To understand the mechanism of nanospheres formation, variation of etching time, etchant concentration and ITO film thickness were employed. A model based on etching-reaction and coalescence is suggested to reproduce the evolution of the size of nanospheres with etching time and etchant concentration. A possible application of ITO nanospheres to enhance light output from a blue GaN based light-emitting diode is also demonstrated. (C) 2012 Elsevier B.V. All rights reserved.
[Show abstract][Hide abstract] ABSTRACT: A significant stress-relaxation was observed in GaN epilayers by integrating a heavily Si-doped GaN (n+-GaN) sacrificial layer in the undoped GaN (u-GaN) templates grown on sapphire substrates by metal-organic chemical vapor deposition (MOCVD). Selective GaN growth and electrochemical etching were exploited to achieve embedded air-gaps. Stress-relaxation and its local variations were probed by Raman mapping of high-frequency transverse-optical E2 (high) phonon mode of GaN. Enhanced In incorporation and improved light emission were observed in InGaN/GaN multi-quantum well (MQW) visible light emitting diode (LED) structures fabricated on stress-relaxed GaN-epilayers with embedded air-gaps. Relevant sources for stress reduction and improved optical emission have been discussed.