We investigate the anisotropic optical gain in non-$c$-plane InGaN quantum wells with 20% indium content including band-gap renormalization and the screening of the quantum confined Stark effect. Waveguide modes and their polarizations are determined as TE and TM modes or extraordinary and ordinary modes, depending on the birefringence and the orientation of the laser diode’s ridge waveguide relative to the $c$ axis. The band structures and optical matrix elements along the polarization directions are calculated using a $6\times 6$ $k\cdot p$ Hamiltonian and a self-consistent Schrödinger-Poisson solver. From these calculations the reduced density of states and the optical gain for the different polarizations are determined in the free-carrier picture with an ad hoc inclusion of the band-gap renormalization and compared to a $c$-plane quantum well. It is found that for high indium concentrations the gain can be significantly increased by going from the $c$ plane to a semipolar or a nonpolar crystal orientation. However, due to birefringence and composition of the topmost valence-band wave function, the ridge has to be oriented along the $\left[\overline{1}\overline{1}23\right]$ direction for semipolar and along the [0001] direction for nonpolar laser diodes.

• Received 22 April 2009

DOI:https://doi.org/10.1103/PhysRevB.80.115320