Micro-pixel light emitting diodes: Impact of the chip process on microscopic electro- and photoluminescence

Abstract

We investigated the influence of a μ-pixelated chip process on the photoluminescence (PL) and electroluminescence (EL) of a monolithic InGaN/GaN based blue light emitting diode with a continuous n-GaN layer. Particularly, we observed the impact of the metallic p-contact on the PL emission wavelength. A PL wavelength shift in the order of 10 nm between contacted and isolated areas was assigned to screening of internal piezoelectric fields due to charge carrier accumulation. μPL and μEL mappings revealed correlated emission wavelength and intensity inhomogeneities, caused by the epitaxial growth process. The edges of single pixels were investigated in detail via resonant confocal bias-dependent μPL. No influence on the intensity was observed beyond 300 nm away from the edge, which indicated a good working edge passivation. Due to the low lateral p-GaN conductivity, the μPL intensity was enhanced at isolated areas.

Surface Recombinations in III-Nitride Micro-LEDs Probed by Photon-Correlation Cathodoluminescence

“…First, the optical properties have been probed by micro-photoluminescence (µ-PL), 3,7 and electroluminescence (EL) spectroscopies. 1,2,8 In addition, cathodoluminescence (CL) spectroscopy has been used to study precisely the edge effects with an excellent spatial resolution.…”

A Direct Epitaxial Approach To Achieving Ultrasmall and Ultrabright InGaN Micro Light-Emitting Diodes (μLEDs)

“…III-nitride μLEDs are exclusively fabricated by means of combining a standard photolithography technique and subsequent dry-etching processes on a standard III-nitride LED wafer. − Generally speaking, surface damage will be unavoidably introduced by dry-etching processes, which enhances nonradiative recombination leading to reduction in optical performance. − This issue is minor and can be safely ignored for broad area LEDs with a dimension of >100 μm. However, this issue becomes increasingly severe with decreasing μLED dimension, eventually becoming a major factor and thus leading to severe degradation in optical performance. ,, Although sidewall passivation using dielectric materials can to some degree reduce plasma induced damage to μLEDs during dry-etching processes, the improvement is marginal even if an advanced atomic layer deposition (ALD) technique instead of a standard plasma-enhanced chemical vapor deposition (PECVD) technique is used for surface passivation .…”

Processing and Characterization of Monolithic Passive-Matrix GaN-Based MicroLED Arrays With Pixel Sizes From 5 to 50 µm

“…wavelength of 450 to 460 nm and exhibit a blue shift with increasing current density, which is generally attributed to a screening of spontaneous and piezoelectric fields in the quantum wells at higher carrier densities [29], [30]. This trend appears for all pixel sizes, but is less prominent in case of the small 5 µm pixels, which might be due to a more homogeneous current spreading or higher non-radiative recombination and therefore smaller carrier concentration [26].…”