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Gallium concentration lowers threshold in InP QDs

The concentration of gallium in the confining layers immediately above the indium phosphide self assembled quantum dots strongly influences their properties
A Cardiff University based project has produced InP self assembled quantum dots that can deliver a  threshold current density of 130 A cm-2 for a 2 mm broad area oxide stripe laser with uncoated facets.

Not a bad achievement. And the researchers have also managed to reduce threshold temperature sensitivity in the material.

Lower power consumption is required for today’s compact and portable biophotonic applications such as OCT and lab-on-a-chip.

These structures, with their low threshold, reduced temperature sensitivity and broad gain spectrum have the potential to fulfill these requirements.

The scientists at Cardiff adjusted the composition of a key epitaxial layer to improve material quality, reduce the threshold and its temperature sensitivity whilst also allowing some tuning of the laser wavelength.

The properties of InP self assembled quantum dots are strongly influenced by the compositions of the confining layers immediately above and below them.

The group varied the fraction of gallium in the upper confining layer from 0.43 to 0.58 in a series of epitaxial structures. Laser threshold measurements and spectroscopy showed a range of laser wavelengths of 696 – 725 nm available. The improvements in threshold were most pronounced at a gallium fraction of 0.54.

The graph below shows the results of the scientists.

The scientists are now concentrating on optimising and tailoring these versatile materials for a variety of device applications.

Further details of this work have been published in the article, "The effect of strained confinement layers in InP self-assembled quantum dot material," by Stella N Elliott et al 2012 in the journal, Semiconductor Science & Technology. DOI :10.1088/0268-1242/27/9/094008

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