Heteroepitaxial ZnO transparent current spreading layers with low sheet resistances were deposited on GaN-based light emitting diodes using aqueous solution phase epitaxy at temperatures below 90°C. The performance of the LEDs was analyzed and compared to identical devices using electron-beam evaporated indium tin oxide transparent current spreading layers. White LEDs with ZnO layers provided high luminous efficacy–157 lm/W at 0.5A/cm2, and 84.8 lm/W at 35A/cm2, 24% and 50% higher, respectively, than devices with ITO layers. The improvement appears to be due to the enhanced current spreading and low optical absorption provided by the ZnO.

Device highlights  Demonstrated the first continuous wave LAE-ZnO () blue laser diode at UCSB  Demonstrated the first hydrothermally grown ZnO top clad () blue InGaN/GaN laser diode  Demonstrated the first ITO top clad limited area epitaxy () blue InGaN/GaN laser diode  Enhanced high current density device performance of GaN LEDs at by replacing ITO current spreading layer with ZnO:Ga Material growth and characterization  Performed MOCVD epitaxial growth of InGaN and AlGaN based blue and green laser diodes on LAE patterned semipolar GaN substrates  Developed and performed aqueous solution growth of ZnO transparent conducting oxide (TCO) for laser diode cladding and LED current spreading layers  Executed structural, optical and electrical characterization of MOCVD grown III-nitride material using X-ray diffraction (XRD), reciprocal space maps (RSMs), photoluminescence (PL), Cathodoluminescence (CL), fluorescence microscopy (FM), electroluminescence (EL), and secondary ion mass spectroscopy (SIMS)  Conducted full laser diode electrical and optical device characterization Laser diode processing and fabrication  Processed semipolar GaN substrates for limited area epitaxy (LAE)  Processed semipolar GaN-based edge emitting lasers with etched and polished facets  Improved dicing process for polished facet laser fabrication to increase device yield Device optical modeling and design  Employed Fimmwave software to simulate the effect of cladding and waveguide design on the optical modes of TCO top clad () GaN lasers in the blue and green spectral regions viii  Evaluated the performance of ZnO compared to ITO as the TCO top cladding layer for the design permutations of () GaN lasers in the blue and green spectral regions

Incorporating transparent conducting oxide (TCO) top cladding layers into III-nitride laser diodes (LDs) improves device design by reducing the growth time and temperature of the p-type layers. We investigate using ZnO instead of ITO as the top cladding TCO of a semipolar (202¯1) III-nitride LD. Numerical modeling indicates that replacing ITO with ZnO reduces the internal loss in a TCO clad LD due to the lower optical absorption in ZnO. Lasing was achieved at 453 nm with a threshold current density of 8.6 kA/cm and a threshold voltage of 10.3 V in a semipolar (202¯1) III-nitride LD with ZnO top cladding.