Development of ZnMgCdO-based alloys and heterostructures for optical applications

Abstract

This paper reviews of some of the recent progress made in the development of high quality MgZnO and ZnCdO layers grown epitaxially by RF-plasma molecular beam epitaxy (MBE). We summarize optical and electrical properties of high quality Cd x Zn 1-x O alloys with Cd mole fraction from 0.02 to 0.78 and discuss phase separation phenomenon which may be present in ternary alloys. A single-crystal wurtzite structure of CdZnO alloys for this entire range of compositions was confirmed by X-ray diffraction. Compositional analysis was performed using SIMS and RBS. Strong optical emission in the 380 nm to 574 nm spectral range was achieved at RT from Cd x Zn 1-x O with various compositions, demonstrating a great potential for use in LEDs. Compositional fluctuations in a Cd 0.16 Zn 0.84 O films were not detected by spatially resolved CL measurements, although intensity fluctuation with features of ~0.5 μm diameter were seen on the intensity maps. Dependence of the fundamental optical band gap on the composition of Cd x Zn 1-x O alloys, band gap bowing, and the possible effect of composition micro-fluctuations in ternary Cd x Zn 1-x O alloys on the optical bandgap is also discussed. Time resolved photoluminescence shows multi-exponential decay with 21 psec. and 49±3 psec. lifetimes, suggesting that composition micro-fluctuations may be present in Cd 0.16 Zn 0.84 O film. High conductivity and optical transparency of the CdZnO films with high Cd-mole fraction is attractive for making high performance electrodes. We also report on crystallographic and optical properties of CdZnO/ZnO multiple quantum wells (MQW).