Crystals are at the heart of diodes. Not the kind you might find in quartz, formed naturally, but manufactured to form alloys, such as indium gallium nitride or InGaN. This alloy forms the light emitting region of LEDs, for illumination in the visible range, and of laser diodes (LDs) in the blue-UV range.
Research into making better crystals, with high crystalline quality, light emission efficiency and luminosity, is also at the heart of studies being done at Arizona State University by Research Scientist Alec Fischer and Doctoral Candidate Yong Wei in Professor Fernando Ponceis group in the Department of Physics.
The study revealed the fundamental aspect of a new approach to growing InGaN crystals for diodes, which promises to move photovoltaic solar cell technology toward record-breaking efficiencies.
The InGaN crystals are grown as layers in a sandwich-like arrangement on sapphire substrates. Typically, researchers have found that the atomic separation of the layers varies; a condition that can lead to high levels of strain, breakdowns in growth, and fluctuations in the alloy's chemical composition.
iBeing able to ease the strain and increase the uniformity in the composition of InGaN is very desirable, but difficult to achieve. Growth of these layers is similar to trying to smoothly fit together two honeycombs with different cell sizes, where size difference disrupts a periodic arrangement of the cells,i Ponce said.
The researchers developed an approach where pulses of molecules were introduced to achieve the desired alloy composition. The method, developed by Doolittle, is called metal-modulated epitaxy.
The study is published in the journal Applied Physics Letters.
--ANI (Posted on 26-10-2013)