Optical properties of cubic GaN and (In, Ga)N

We review our investigations of the optical properties of beta-GaN and beta-(In, Ga)N layers grown on GaAs(0 0 1) by plasma-assisted molecular beam epitaxy. For In contents up to 17%, the band gap of beta-(In, Ga)N layers, estimated by combining photoluminescence with spectroscopic ellipsometry as well as transmittance spectroscopy, shows good agreement with theoretical predictions from the literature. Using the theoretically predicted band gaps, we calculate 2.75 eV isoenergy contours for both beta-(In,Ga)N/GaN and alpha-(In, Ga)N/GaN quantum wells. Comparing these contours to calculations of the critical thickness, it becomes evident that blue-emitting alpha-(In, Ga)N/GaN quantum wells are above or at the border to plastic relaxation except for very thin quantum wells of high In content. In contrast, blue-emitting alpha-(In, Ga)N/GaN quantum wells lie below this border for a wide range of thickness and In content. (C) 1998 Elsevier Science B.V. All rights reserved.