Periodic gratings with complex shapes are designed by machine learning as emitters for a thermophotovoltaic system with a GaSb photovoltaic absorber operating at 1000K in order to maximize thermophotovoltaic efficiency. We also demonstrate complex-shaped GaN grating VCSEL mirrors designed by machine learning for high reflectivity and a wide stopband with center wavelength of 500nm. The results obtained indicate a 50% increase in stopbandwidth for the complex-shaped grating over that of a rectangular grating.
Magnesium oxide (MgO) is a promising dielectric for use with GaN due its similar crystal structure and lattice constant, large bandgap, and high dielectric constant. We report on the structural properties of MgO films deposited on GaN templates on sapphire substrates via the atomic layer deposition (ALD) technique. Analysis of the crystal quality and structure as a function of surface treatment and growth temperature are presented. I-V and C-V measurements of MgO/GaN metal-oxide-semiconductor capacitance structures are also presented.
The self-consistent 6-band k∙p calculations of AlGaInN barriers surrounding the InGaN quantum well (QW) emitting at ~495 nm show ~ 30% increase in material gain and ~ 40% reduction in threshold current density, compared to the conventional InGaN / GaN QW structure. Following the guidance of our computational study, the InGaN / AlGaInN multiple QW structures with different AlGaInN alloy compositions lattice-matched to GaN are grown via MOVPE. The use of InGaN / AlInN QW structure resulted in improved luminescence, and the results of InGaN / AlGaInN with larger compositional range will also be presented.
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