Free and bound excitonic effects in Al0.5Ga0.5N/Al0.35Ga0.65N MQWs with different Si-doping levels in the well layers.

Chenguang He,Lisheng Zhang,Zhixin Qin,Weikun Ge,Xinqiang Wang,Mengjun Hou,Shan Zhang,Bo Shen,Fujun Xu

doi:10.1038/srep13046

Chenguang He, Lisheng Zhang + Show 7 more

Open Access

https://doi.org/10.1038/srep13046

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Abstract

Free exciton (FX) and bound exciton (BX) in Al0.5Ga0.5N/Al0.35Ga0.65N multiple quantum wells (MQWs) with different Si-doping levels in the well layers are investigated by photoluminescence (PL) spectra. Low temperature (10 K) PL spectra identify a large binding energy of 87.4 meV for the BX in undoped sample, and 63.6 meV for the BX in Si-doped (2 × 1018 cm−3) sample. They are attributed to O-bound and Si-bound excitons, respectively. The large binding energies of BX are assumed to originate from the strong quantum confinement in the quantum wells, which also leads to a stronger FX PL peak intensity in comparison with BX at 10 K. Si-doping is found to suppress the FX quenching by reducing threading dislocation density (TDD) in the well layers, leading to a significant improvement of IQE from 33.7% to 45%.

Highlights

Free exciton (FX) and bound exciton (BX) in Al0.5Ga0.5N/Al0.35Ga0.65N multiple quantum wells (MQWs) with different Si-doping levels in the well layers are investigated by photoluminescence (PL) spectra
AlGaN-based deep ultraviolet light-emitting diodes (DUV-LEDs) have attracted considerable attentions owing to their wide application potentials in biomedical and analytical instrumentation, sterilization and decontamination, UV curing, and high density optical recording[1,2]
Impressive research efforts have achieved luminescence from 210 nm to 365 nm over the range of full Al compositions[1,2,3,4]. Despite these tremendous opportunities and progress, DUV-LEDs still suffer from relatively low external quantum efficiencies (EQEs) as well as output light power, in comparison with commercial blue LEDs

Summary

Methods

Three MQWs samples (sample-A, -B, and -C) were grown on. (0001) sapphire substrates by low pressure metal organic chemical vapor deposition (LP-MOCVD). Deposition was initiated from a 1-μ m-thick AlN layer, followed by a multi-period AlN/AlGaN superlattice (SL) layer and a 1-μ m-thick Si-doped AlGaN layer. A 4th harmonic of Q-switched YAG:Nd laser (λ = 266 nm, pulse width = 7 ns) was used for PL excitation, and an Ocean Optics USB2000+ VIS-NIR fiber optic spectrometer was employed to record the PL spectra. Excitation power tuning was realized by THORLABS NUK01 neutral density filters. The surface morphology for sample-A, -B, and -C after molten KOH etching was characterized by Bruker Dimension ICON-PT atomic force microscopy (AFM)

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