Abstract
An optically pumped multi-color laser has been achieved using an InGaN/GaN based micro-disk with an undercut structure on a silicon substrate. The micro-disk laser has been fabricated by means of a combination of a cost-effective microsphere lithography technique and subsequent dry/wet etching processes. The microdisk laser is approximately 1 μm in diameter. The structure was designed in such a way that the vertical components of the whispering gallery (WG) modes formed can be effectively suppressed. Consequently, three clean lasing peaks at 442 nm, 493 nm and 522 nm have been achieved at room temperature by simply using a continuous-wave diode laser as an optical pumping source. Time–resolved micro photoluminescence (PL) measurements have been performed in order to further confirm the lasing by investigating the excitonic recombination dynamics of these lasing peaks. A three dimensional finite-difference-time-domain (FDTD) simulation has been used for the structure design.
Highlights
Integrated multi-color lasers in the visible spectral region or white lasers are expected to find a wide range of applications, such as full colour high definition displays[1,2,3,4,5,6], generation vehicle headlighting, biosensors[7, 8], visible light communications or even lighting[9], etc
III-nitrides exhibit major advantages compared with II–VI semiconductors in the visible spectral region
Injection current will have to go through different active regions where a threshold for lasing in each region needs to be met, leading to a challenge for achieving multiple colour lasing as a result of high injection current required
Summary
The microdisks were fabricated from an InGaN/GaN MQW epi-wafer, which was grown by MOCVD on an (111) silicon substrate. The epi-wafer was fabricated into single microdisk structures by a combination of a silica microsphere lithography approach and subsequent dry/etching processes. The silica micro-particles with a diameter of approximately 1 μm diluted in DI water with 1:50 concentration were deposited directly on the surface of the epi-wafer using a spin coating method at a high rotation speed (7000 rpm), serving as micro masks for subsequent dry-etching. Time-resolved micro-photoluminescence measurements have been carried out in a micro-PL system, where a 375 nm pulsed diode laser is used as an optical pumping source and the system is equipped with a monochromator (Horiba iHR550) and an air-cooled CCD. The slope of the time decay is used to calculate the Q-factor of each resonance
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