Processing of Semipolar and Nonpolar InGaN Based Laser Diodes

Laser diodes (LDs) based on InGaN quantum well (QW) structures emitting in the blue to green spectral region are of great interest for applications ranging from spectroscopy to laser projectors for mobile devices. Whereas LDs in the blue spectral region are available commercially, the so-called “green gap” is just at the point of being bridged. The necessity of creating InGaN QWs with high indium content in order to achieve longer wavelengths leads to an aggravation of epitaxial challenges. Optimal growth conditions for the active region become increasingly different from the surrounding GaN layers with increasing In content. Furthermore, the lattice mismatch between GaN and InGaN induces strong polarization fields along the commonly used polar directions, thus resulting in a reduced recombination rate, due to the quantum confined Stark effect (QCSE). The QCSE draws the wave functions of electrons and holes apart, thereby decrasing the wave function overlap. This inherent issue can be avoided or alleviated by the growth of the active region on nonpolar or semipolar planes [1].