Design, Growth and Fabrication of Nitride-based Semipolar (2021) Laser Diodes.

摘要

Nonpolar and semipolar planes on wurtzite nitride have attracted much attention due to their eliminated and reduced polarization-related electric field in the quantum wells (QWs). Violet and blue nonpolar m-plane laser diodes (LDs) have been demonstrated under continuous wave operation. However, the operation in green spectral region has been limited due to low In incorporation and the formation of basal plane stacking faults on m-plane. With decent In incorporation on semipolar planes, high performance green light-emitting diodes (LEDs) and LDs have been demonstrated on (202¯1) plane. On the other hand, low efficiency droop and high optical polarization ratio were also observed on semipolar (202¯1¯) LEDs.;The polarity has strong impacts on the growth characteristics and device performance on semipolar planes. With a 15 degree inclination angle of m-plane toward the N-polar surface, (202¯1¯) plane possesses a N-polar-like surface chemistry. The morphology of epitaxial growth on (202¯1¯) surface is sensitive to growth conditions such as the growth temperature and the growth rate. Striation morphologies along the a-axis were observed on InGaN QWs grown on (202¯1¯) substrates, indicating a high adatom diffusion anisotropy.;However, the piezoelectric polarizations of InGaN QWs on the (202¯1¯) plane are parallel to those on the Ga-polar plane with a quarter magnitude. Polarization-related electric fields in the (202¯1¯) QWs cancel the built-in electric fields in the p-n junction, resulting in a nearly-flat QW potential profile under zero bias. By band diagram simulations, the potential profile of (202¯1¯) QWs is insensitive to the applied bias and current injection. Along with high compositional homogeneity in the QWs, the semipolar (202¯1¯) LEDs and LDs showed minimal wavelength blueshift over three orders of injection current levels.;Index-guided ridge lasers with cleaved facets were fabricated. Polishing and dry-etching were applied on the backside surface after lapping to improve the contact characteristics. To suppress the morphologies, InGaN/GaN superlattices were used as guiding layers instead of conventional bulk InGaN layers. Semipolar (202¯1¯) laser diodes with lasing wavelength up to 505 nm were demonstrated with 4 nm blueshift between the spontaneous emission and lasing.