Regensburg 2010 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 65: GaN-based Devices

HL 65.1: Talk

Friday, March 26, 2010, 10:15–10:30, H15

Calculation of optical eigenmodes and gain in semipolar and nonpolar InGaN/GaN laser diodes — •Wolfgang Scheibenzuber and Ulrich Schwarz — Fraunhofer IAF, Freiburg, Deutschland

Growth on semipolar and nonpolar crystal planes poses a possibility to reduce polarization fields and thereby enhance stimulated emission in (Al,In)GaN laser diodes. In this case the anisotropic optical properties of wurtzite (Al,In)GaN influence the optical eigenmodes of the laser waveguide and the optical gain .

This contribution reports the calculation of the optical eigenmodes in semipolar and nonpolar laser diodes taking into account the birefringence of GaN. Furthermore it shows calculations of the optical gain in such devices based on self-consistent 6x6 k*p valence band calculations.

Depending on the orientation of the laser diode's ridge waveguide relative to the c-axis, the eigenmodes of the laser diode are TE-/TM-modes or extraordinary/ordinary modes polarized along the crystal directions. The polarization of the eigenmodes then enters the calculation of the optical gain. Resulting spectra for c-plane, semipolar and nonpolar structures are compared at different charge carrier densities. It is found that for high indium concentrations the gain can be significantly increased by going from the c-plane to a semipolar or nonpolar crystal orientation. However, due to birefringence and composition of the topmost valence band wavefunction, the ridge has to be oriented along the projection of the c-axis on the growth plane.