  InGaN-based visible LEDs find commercial applications for solid-state
lighting and displays, but lattice mismatch limits the thickness of InGaN
quantum wells that can be grown on GaN with high crystalline quality. Since
narrower wells operate at a higher carrier density for a given current density,
they increase the fraction of carriers lost to Auger recombination and lower
the efficiency. The incorporation of boron, a smaller group-III element, into
InGaN alloys is a promising method to eliminate the lattice mismatch and
realize high-power, high-efficiency visible LEDs with thick active regions. In
this work we apply predictive calculations based on hybrid density functional
theory to investigate the thermodynamic, structural, and electronic properties
of BInGaN alloys. Our results show that BInGaN alloys with a B:In ratio of 2:3
are better lattice matched to GaN compared to InGaN and, for indium fractions
less than 0.2, nearly lattice matched. Deviations from Vegard's law appear as
bowing of the in-plane lattice constant with respect to composition. Our
thermodynamics calculations demonstrate that the solubility of boron is higher
in InGaN than in pure GaN. Varying the Ga mole fraction while keeping the B:In
ratio constant enables the adjustment of the (direct) gap in the 1.75-3.39 eV
range, which covers the entire visible spectrum. Holes are strongly localized
in non-bonded N 2p states caused by local bond planarization near boron atoms.
Our results indicate that BInGaN alloys are promising for fabricating nitride
heterostructures with thick active regions for high-power, high-efficiency
LEDs.
