Abstract
Two-dimensional InGaN/GaN multiple-quantum-wells (MQW) LED structure was nanotextured into quasi-one-dimensional nanowires (NWs) with different average diameters with a combination approach of Ni nanoislands as mask + dry etching. Such nanotexturing bring out several appealing effects including deeper localization of carriers and significant improvement in quantum efficiency (e.g., from 4.76% of the planar MQW structure to 12.5% of the 160 nm MQW NWs) of light emission in the whole interested temperature range from 4 K to 300 K. With the aid of localized-state ensemble (LSE) luminescence model, the photoluminescence spectra of the samples are quantitatively interpreted in the entire temperature range. In terms of distinctive temperature dependence of photoluminescence from these samples, a concept of “negative” thermal activation energy is tentatively proposed for the MQW NWs samples. These findings could lead to a deeper insight into the physical nature of localization and luminescence mechanism of excitons in InGaN/GaN nanowires.
Highlights
Two-dimensional InGaN/GaN multiple-quantum-wells (MQW) light-emitting diodes (LEDs) structure was nanotextured into quasi-one-dimensional nanowires (NWs) with different average diameters with a combination approach of Ni nanoislands as mask + dry etching
Such nanotexturing bring out several appealing effects including deeper localization of carriers and significant improvement in quantum efficiency of light emission in the whole interested temperature range from 4 K to 300 K
With the aid of localized-state ensemble (LSE) luminescence model, the photoluminescence spectra of the samples are quantitatively interpreted in the entire temperature range
Summary
The starting sample used in this study was a typical MQW LED structure consisting of layers in the order from top to bottom: a 0.2 μm p-type GaN:Mg top layer, 5 periods of In0.2Ga0.8N/GaN MQWs with barrier’s (well’s) thickness of 30 nm (3 nm), and a 3.0 μm n-type GaN:Si buffer bottom layer, which was grown on c-plane sapphire with metalorganic chemical vapor deposition. Other preparation details of the NWs can be referred to a publication[24]. Micro-Raman scattering spectra were measured on an integrated WITec Alpha scanning confocal micro-Raman system with the back-scattering geometric configuration[14]. In the Raman scattering measurements, the 514.5 nm line of an argon ion gas laser was used as the excitation source. Variable-temperature PL spectral measurements were carried out on a home-made PL system using a Kimmon 325 nm He-Cd laser as the excitation light source. The maximum output power of the He-Cd laser was 38 mW. In the PL measurements, the samples were mounted on the cold figure of a Janis closed cycle cryostat proving a varying temperature range of 3.6–300 K. A detailed description of the PL setup can be referred to a previous publication[25]
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