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Room Temperature Indium Phosphide Nanowire Lasers

September 2014

Near-infrared lasers are in great demand for a variety of applications including spectroscopy, optical communication and medical diagnosis and down scaling the footprint of infrared lasers to the nanoscale has significant outcomes for three-dimensional device integration.

Indium phosphide (InP), being a direct bandgap semiconductor with very low surface recombination velocity, is highly relevant as a platform for infrared lasers. To achieve room temperature lasing from single InP nanowire, high quantum efficiency, low surface recombination velocity and good morphology are essential. Hence, the development of high quality InP nanowires with well controlled and variable dimensions has been the subject of intense research efforts.

Qian Gao, a PhD student working at the Department of Electronic Materials Engineering in the Research School of Physics and Engineering at The Australian National University has reported successful growth of high quality InP nanowires of various diameters using selective area metal-organic vapour-phase epitaxy (previously reported in our September 2013 newsletter).

Figure 1

Figure 1. Room temperature lasing characteristics: spectral narrowing and clamping of spontaneous emission.

Recently, with these high quality InP nanowires, low threshold room-temperature lasing has been achieved. The InP nanowires were first transferred to an indium tin oxide (ITO) coated glass substrate and then optically pumped at room temperature. Figure 1 (above) shows the lasing spectra from a single InP nanowire which also demonstrates clamping of the spontaneous emission above threshold. The clamping of spontaneous emission results from the clamping of the carrier density at threshold, and is an important indicator for the onset of lasing. Excellent material quality and suitable morphology are important for supporting the optical mode and reduce the lasing threshold.

To grow these high quality InP nanowires with proper dimensions, patterned substrates were needed before growth, and various tools and facilities of the ANFF ACT Node have been used for preparing these patterned substrates. To pattern the InP substrates, 30 nm of SiO2 was firstly deposited on (111)A InP substrates using the Plasmalab 100 Dual Frequency plasma enhanced chemical vapour deposition (PECVD) tool. The RAITH 150 electron-beam lithography (EBL) system was then used to pattern these substrates, followed by chemical etching through the pattern to form the arrays of holes. Figure 2 (below) schematically shows the processing sequence used for patterning of the InP substrates. Figure 2

Figure 2. Schematic of the processing sequence used for selective-area epitaxy growth of InP nanowires. (a) InP substrate with SiO2.
(b) The hexagonal array pattern opened up on SiO2 mask. (c) The nanowire array grown on SiO2 patterned substrate.

The structural uniformity and high crystal quality of the InP NWs enables low threshold, room temperature lasing from single NWs under optical pumping, opening up new possibilities for both fundamental quantum optics, as well as optoelectronic/photovoltaic device applications. To utilise these InP nanowires as practical devices, comprehensive fabrication processes have to be further developed and optimised with the assistance from the highly skilled ANFF staff.

Story courtesy of Qian Gao, Department of Electronic Materials Engineering, RSPE, ANU.