| GaN vertical-cavity surface-emitting lasers (VCSELs) are of increasing interest as sources of high-quality coherent light in the visible spectrum, particularly in blue wavelengths. These devices so far suffer from many problems, including low output power, low yield, and high costs. Nonpolar GaN offers many advantages for VCSELs. Anisotropic electric fields in the plane of the emitting quantum wells results in higher gain and crystallographically-oriented polarization of emitted light. This should result in the unique property of polarization locking, whereby the polarization direction of each device is identical, and determined by the crystal structure of the material in the device. Prior demonstrations of GaN VCSELs have relied on epitaxially-grown n-DBR mirrors, or mechanical polishing to remove the substrate to allow for deposition of dielectric DBR mirrors. Epitaxially-grown DBRs give epitaxial control of cavity length, but are very difficult and costly to grow. Mechanical polishing and deposition of dielectric DBRs simplifies fabrication, but gives no control of cavity length. This thesis reports on a novel fabrication method using photoelectrochemical (PEC) etching that gives epitaxial control of cavity length, while still allowing for the use of dielectric DBR mirrors. Using this novel fabrication method, the first nonpolar GaN-based VCSELs are demonstrated. These devices exhibit polarization locking, where each device is highly polarized parallel to the crystallographic a-direction of the wurtzite crystal structure. Electrically-injected lasing under pulsed operation at room temperature is reported, with an output power of approximately 20 uW at a wavelength of 411.9 nm. |
