Feb 7, 2013
Understanding today the light sources of tomorrow
Using both time-integrated and time-resolved photoluminescence spectroscopy (PL & TRPL), scientists based at Université de Montréal (Canada) have joined the debate of trying to explain the mechanism of emission in InGaN/GaN nanowires heterostructures and, arguably, have brought the discussion to a satisfactory conclusion.
Conventional white LEDs suffer the same flaw. Their internal efficiency significantly falls with the injection current. Try to pump up the output power too much and you get an overall efficiency that’s not much better than fluorescent tubes. This is the so called "efficiency droop".
Improving on broadly emission tunable InGaN/GaN nanowire heterostructures, researchers at McGill University (Canada) came up, in 2011, with a phosphor-free device made of multiple InGaN insertions stacked in GaN nanowires, which does not suffer such limitations.
Although PL and TRPL studies had already been carried out on similar heterostructures, the team succeeded in extending the time window enough to be able to observe the strong power law shape of the photoluminescence decay.
Using a simple charge separation model involving a bright and a dark state, the scientists faithfully reproduced the data. The behaviour of both the recombination and separation rate (two parameters involved in the model) with the energy of emission is coherent with carrier radiative recombination occurring on In-rich nanocluster sites.
A full description of the study and the samples can be found in the journal Nanotechnology.
About the author
Vincent Cardin is currently an MSc candidate in the Physics Department at the Université de Montréal under the direction of Prof. Richard Leonelli. Full credit should be given to Prof. Mi’s group (McGill University) concerning the growth and characterization of the nanowires. The study was supported by both the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Fonds de Recherche du Québec – Nature et Technologie (FRQ-NT).