No abstract

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.

High wall-plug efficiency (WPE) micro-light-emitting diodes with metalorganic chemical vapor deposition-grown tunnel junction (TJ) contacts are demonstrated. By employing chemical treatments before sidewall activation, the 20 × 20 μm 2 TJ devices resulted in a voltage penalty of 0.2 V at 20 A cm −2 , compared to devices with indium-tin oxide (ITO) contacts. Moreover, the enhancement in light output power was more than 40% higher than ITO devices. Hence, the TJ devices yielded the peak external quantum efficiency (EQE) and WPE of 56% and 55%, respectively, indicating the improvements of 64% and 77% in peak EQE and WPE compared to ITO devices.

In this work, we propose using the low defect density wing region arising from epitaxial lateral overgrowth (ELO) for the development of Group III-nitride flip-chip vertical-cavity surface emitting lasers (VCSELs). The ELO wing is intended to be incorporated within the VCSEL cavity, supporting the n-side distributed Bragg reflector (DBR) mirror, and must therefore be very smooth. We measure the surface morphology of the interface surface of the ELO material after separation from the growth substrate, finding that the interface roughness changes with the composition and thickness of the ELO mask. Sub-nanometer surface roughness suitable for the placement of the DBR mirror is achieved using mask layers terminating in Si3N4, or via 300 nm thick sputtered SiO2.