Demonstration of nonpolar GaN-based vertical-cavity surface-emitting lasers

Nonpolar and semipolar orientations of gallium nitride offer several advantages for vertical-cavity surface-emitting lasers (VCSELs), including enhanced radiative efficiencies and higher optical gain compared to c-plane oriented VCSELs. Additionally, anisotropic gain within the quantum well plane should result in a consistent and well-defined polarization direction of the emission in nonpolar and semipolar VCSELs. We report the first known electrically-injected nonpolar m-plane GaN VCSELs, operating under pulsed injection at room temperature. As predicted, m-plane GaN VCSELs exhibit polarization locking, with the polarization direction consistently oriented along the a-direction of the wurtzite crystal structure. We also report a novel fabrication method, utilizing photoelectrochemical etching of a sacrificial InGaN region for substrate removal and cavity length definition. This method allows for the use of dielectric DBR mirrors with freestanding GaN substrates, while maintaining precise control of cavity length by placement of the sacrificial layer during epitaxial growth. Initial device results include a wavelength of 411.9 nm with a FWHM of 0.25 nm and a maximum observed power output of 19.5 uW. Devices exhibit polarization ratios higher than .7 above threshold (with no additional measures taken to account for spontaneous emission or to reduce collection of scattered light).