Optical Properties of InGaN-Based Light Emitting Diodes Fabricated Through Dry and Wet Mesa Etching Process

Abstract

InGaN-based light emitting diodes (LEDs) were fabricated through a photoelectrochemical (PEC) wet mesa etching process to replace the conventional dry mesa etching process. The undercut structures were formed from a bandgap-selective lateral wet etching process that occurred at the InGaN/GaN multiple-quantum-well layers. By measuring the selective-area microphotoluminescence spectra focused on the mesa edge region, the blueshift wavelength of the photoluminescence spectrum in the wet mesa etched light emitting diode (WME-LED) was 9.1 nm (55 meV) that was compared to the conventional dry etching LED. The relative internal quantum efficiencies of WME-LED were calculated as 13.7% (at the first region), 21.8% (at the second region), and 24.5% (at the third region) from the mesa center to the edge. The flatband voltage of the WME-LED was −13 V to balance the piezoelectric field, calculated as −1.17 MV/cm, in the InGaN active layer. However, we did not observe any flatband voltage in the conventional LED up to −19 V (piezoelectric field larger than −1.9 MV/cm). By forming the bending undercut structure on p-type GaN:Mg layer, the lattice mismatch induces a compressed strain and a piezoelectric field in the InGaN active layer that can be partially released in the WME-LED by using a PEC wet mesa etching process.