Stimulated emission from GaN nanocolumns

Stimulated emission with very low threshold excitation power density was observed for GaN nanocolumns grown on (0001) sapphire substrate by RF-plasma assisted molecular beam epitaxy. The photopump measurements were carried out under 355 nm Nd: YAG laser excitation with the surface emission configuration. The threshold excitation power density was 198 kW/cm(2) at room temperature. The peak wave-length shifted from 370.2 to 370.9 nm when increasing the excitation power from 130 to 440 kW/cm(2). The peak intensity increased nonlinearly with excitation power. For the lower excitation condition using a 325 nm He-Cd laser, the spontaneous emission peak was observed at 363.2 nm and the intensity was 20similar to30 times stronger than for a 3.7 mum-thick MOCVD-grown GaN film with a dislocation density of 3similar to5 x 109 cm(-2). With this configuration the peak intensity was increased propotionally with excitation power. These results indicate that GaN nanocolumns have high potential to realize high performance optical devices. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.