Exciton confinement in homo- and heteroepitaxial ZnO/Zn1 − xMgxO quantum wells with x < 0.1

Abstract

ZnO/Zn 1 À x Mg x O single quantum well (SQW) structures with well widths d W between 1.1 nm and 10.4 nm were grown by plasma-assisted molecular beam epitaxy both heteroepitaxially on c-plane sapphire and homoepitaxially on (000 1)-oriented bulk ZnO. A significantly reduced Mg incorporation in the top barrier related to the generation of stacking faults is observed for heteroepitaxial samples. Exciton localization is observed for both types of samples, while an enhancement of the exciton binding energy compared to bulk ZnO is only found for homoepitaxial SQWs for 2 nm d W 4 nm. Consistently, for homoepitaxial samples, the carrier dynamics are mainly governed by radiative recombination and carrier cooling processes at temperatures below 170 K, whereas thermally activated non-radiative recombination dominates in heteroepitaxial samples. The effects of polarization-induced electric fields are concealed for Mg concentrations x < 0.1 due to the reduction of the exciton binding energy, the screening by residual carriers as well as the asymmetric barrier structure in heteroepitaxial wells.

Self-assembly of ordered wurtzite/rock salt heterostructures—A new view on phase separation in MgxZn1−xO

“…The wurtzite-(wz-)ZnO/Mg x Zn 1-x O material system holds several advantages for application in optoelectronic devices such as the high bulk exciton binding energy of 59 meV [1,2] which increases beyond 100 meV in quantum structures [3][4][5]. Furthermore, the direct band gap extends from 3.3 eV to 4.5 eV when the Mg fraction x is increased up to 0.44 [6][7][8].…”

Photoluminescence of Layered Semiconductor Materials for Emission-Color Conversion of Blue Micro Light-Emitting Diode (µLED)

“…Additionally, for GaS 0.65 Se 0.35 , the occurrence of microscopic composition fluctuations that are Ga-S and Ga-Se condensations, resulting in the distribution of density of states near the band edge. This usually occurs for other disordered compound alloys, such as AlInGaN and ZnMgO [18,19]. On the other hand, background noise was detected in the PL spectrum of GaSe because the excitation efficiency using blue light is lower than that of GaS 0.65 Se 0.35 owing to the large energy difference.…”

Effects of phosphorus doping by plasma immersion ion implantation on the structural and optical characteristics of Zn0.85Mg0.15O thin films

“…25 A peak at 3.452 eV was observed for the sample annealed at 900 C, which can be attributed to the delocalized exciton; this peak was also observed in as-annealed samples. 20,26,27 In the case of the implanted sample annealed at 1000 C, this peak was replaced by the localized exciton peak around 3.422 eV. 20,26,27 The difference between the localized and delocalized excitons can be described in terms of the wave function.…”

“…20,26,27 In the case of the implanted sample annealed at 1000 C, this peak was replaced by the localized exciton peak around 3.422 eV. 20,26,27 The difference between the localized and delocalized excitons can be described in terms of the wave function. The wave function of a delocalized exciton is always a propagating wave, while that of a localized exciton decays with distance.…”