[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.
[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: GaN-based light-emitting diodes with peripheral microhole arrays (PMA-LEDs) have been grown, and fabricated, on SiO<sub>2</sub> hexagonal pattern masks using selective metal-organic chemical vapor deposition. The PMA-LED structure promises to enhance the light extraction efficiency via simple fabrication processes, as compared to conventional LED structures. The geometrical shape of the peripheral microhole structure serves to enhance the light extraction efficiency due to the effect of the PMA in facilitating multiple chances for photons to escape. Thus, the light output intensity of PMA-LED was 30% higher than that of conventional LEDs.