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We have fabricated μLEDs of mesa sizes 10 × 10 and 15 × 15 μm2 on native (2021¯) semipolar substrates and on epitaxial lateral overgrown (ELO) wings of the (2021¯) substrate. The ELO μLEDs exhibited very low leakage current (less than 10−10 A) under forward bias (V < 2 V) and at reverse bias voltages, which was a reduction in several orders of magnitude when compared with planar μLEDs under the same fabrication and sidewall passivation scheme. Electrical characterization revealed that the mesa sidewall is less damaged in plasma dry etching in the ELO μLEDs due to a lower material defect density than the planar μLEDs. Moreover, the ELO μLEDs showed improved optical performance over the planar μLEDs.

We demonstrate removal of homoepitaxially grown semi-polar gallium nitride (GaN) layers from the native substrates. The weak link at the interface of the epitaxial lateral overgrowth and cleavable m-plane of the respective native semi-polar plane is used to separate homoepitaxial GaN from its native substrate. Homoepitaxial GaN layers of the semi-polar planes, ( 1011), ( 2021), ( 3031), ( 1011), ( 2021), and ( 3031) are successfully removed. This approach allows the reuse of expensive semi-polar GaN substrates, eliminating one barrier to market introduction of superior optoelectronic devices grown with semi-polar orientations.

Highly reliable operation of 405 nm laser diodes for high-density optical storage was demonstrated. Introduction of epitaxially grown AlON layer between the front facet and normal coating layer was shown to be effective to suppress catastrophic optical damage at the laser facet. Stable operation in excess of 1000 h was confirmed at an output power of 500 mW in a pulsed-mode at a case temperature of 80 °C.

A heterogeneously integrated InGaN laser diode (LD) on Si is proposed as a path toward visible wavelength photonic integrated circuits (PICs) on Si. Herein, InGaN films are vertically stacked on a TiO2 waveguide (WG) fabricated on a Si wafer by bonding. In the light propagation direction, it is composed of a hybrid InGaN/TiO2 section, a TiO2 WG, an adiabatic taper, and mirrors that can form a cavity. As the refractive index of GaN is well matched with that of TiO2, the optical transverse mode extends to both the GaN and TiO2 in a hybrid mode. Modes between a hybrid InGaN/TiO2 and a pure TiO2 WG can transfer with an adiabatic taper structure. The coupling loss is calculated to be less than 0.5 dB with fairly short taper length of 78 μm and tip width of 200 nm. GaN substrate removal and bonding are critical fabrication steps of this LD and PIC. The substrate removal is successfully done by photoelectrochemical etching. Although direct bonding of GaN wafers with thermal oxide on Si is successful, GaN epitaxial wafers are more difficult. An implication and remedy of this is discussed in terms of surface roughness of GaN epitaxial film.