Optical gain of zinc-blende InGaN quantum wells across the green–orange gap from atomistically determined alloy broadening

No semiconductor laser diode yet covers the green–orange gap (540–620 nm) between the wavelength limits of wurtzite InGaN and AlGaInP. Zinc-blende (cubic, ZB) InGaN quantum wells grown along (001) carry no spontaneous or piezoelectric polarization, so the quantum-confined Stark effect that limits polar c-plane wells at high indium content is absent in principle. We treat these wells with an eight-band k ⋅ p model with self-consistent Poisson coupling and Berggren–Sernelius bandgap renormalization. We first map the coherent design space and find that 3.1 nm wells remain coherent up to an indium composition of x ≈ 0.36, which covers the green-to-red range. We then compute the inhomogeneous broadening from atomistic alloy-disordered supercells. The broadening is hole-dominated and Gaussian, with a standard deviation σinh ≈ σh of order 40 meV (38.1, 42.9, and 44.2 meV at x = 0.22, 0.28, and 0.32). This linewidth is not fitted to any spectrum and sets an intrinsic lower bound on the broad linewidths measured so far. Included in the model, the disorder places the computed emission peak of a reported ZB InGaN well within its measured red photoluminescence band. It also flattens the density dependence of this peak by suppressing the bandgap-renormalization redshift. The predominantly TE-polarized gain tunes continuously from the green (≈524 nm) to the red (≈650 nm) and is, in principle, sufficient for laser operation. These results establish ZB InGaN as a candidate gain medium for green-to-red laser diodes.