Optical properties of excitons in ZnO-based quantum well heterostructures

Abstract

Recently the developments in the field of II-VI-oxides have been spectacular. Various epitaxial methods has been used to grow epitaxial ZnO layers. Not only epilayers but also sufficiently good-quality multiple quantum wells (MQWs) have also been grown by laser molecular-beam epitaxy (laser-MBE). We discuss mainly the experimental aspect of the optical properties of excitons in ZnO-based MQW heterostructures. Systematic temperature-dependent studies of optical absorption and photoluminescence in these MQWs were used to evaluate the well-width dependence and the composition dependence of the major excitonic properties. Based on these data, the localization of excitons, the influence of exciton-phonon interaction, and quantum-confined Stark effects are discussed.The optical spectra of dense excitonic systems are shown to be determined mainly by the interaction process between excitons and biexcitons. The high-density excitonic effects play a role for the observation of roomtemperature stimulated emission in the ZnO MQWs. The binding energies of exciton and biexciton are enhanced from the bulk values, as a result of quantum-confinement effects.

Exploration of Electronic Functionalities in Metal Oxides by Combinatorial Lattice Engineering

“…This can be enhanced to 110 meV in multi quantum well structures, which again surpasses to the energy of optical phonon mode in ZnO (72 meV). 103 Therefore, low threshold and highly efficient lasers can be expected. These expectations have been already demonstrated in optical pumping experiments for ZnO epitaxial films and superlattices.…”

“…Indeed, the basic optical properties in Mg x Zn 1¹x O/ZnO superlattices were elucidated in detail for these two libraries. 103,113,114 The most important challenge was to produce p-type ZnO. ZnO is well known as naturally n-type semiconductor due to Zn interstitial and many other defects.…”

Люминесцентные свойства тонких пленок Cd-=SUB=-x-=/SUB=-Zn-=SUB=-1-x-=/SUB=-O

“…Большой интерес представляет прямозон-ный полупроводник оксид цинка благодаря широкой запрещенной зоне, E g = 3.37 эВ, и рекордной среди полупроводников энергии связи экситонов 60 мэВ, что обеспечивает эффективную экситонную эмиссию при бо-лее высоких температурах по сравнению с оптическими полупроводниками A III B V [5].…”

Observation of Room Temperature Photoluminescence from Asymmetric CuGaO<SUB>2</SUB>/ZnO/ZnMgO Multiple Quantum Well <I>Structures</I>

“…Together with high thermal conductivity, high luminous efficiency and mechanical and chemical robustness, ZnO and its alloys have great prospects in optoelectronics applications in the wavelength range from ultraviolet to the red. 1 Moreover, excitons in ZnO-based quantum well (QW) heterostructures exhibit high stability * Author to whom correspondence should be addressed. compared to bulk semiconductors and III-V QWs due to the enhancement in the binding energy 2 3 and the reduction in the exciton-phonon coupling 4 caused by quantum confinement.…”