Pulsed laser deposition of thin films and superlattices based on ZnO

Abstract

The pulsed laser deposition (PLD) technique has been applied for the epitaxial growth of ZnO for more than two decades. The emergence of high-temperature stability of the excitonic lasing was first demonstrated in a microcrystalline ZnO film grown by PLD leading to recent remarkable growth in this field. A number of attempts have been made to improve the crystallinity for realizing p-type materials in the quest for ZnO-based short wavelength light emitting devices (LEDs). In this paper, we describe practical advantages of PLD and currently accomplished intrinsic properties of ZnO films according to the abundant literature. We find that correlation between Hall mobility and lateral grain size captures the effect of grain boundaries for the films grown on sapphire substrates. On the other hand, advantages of the use of lattice-matched ScAlMgO4 substrate are evidenced by the lower residual electron density, higher mobility and sharper exciton peaks in the photoluminescence and absorption spectra. We also focus on the wide-band-gap ternary alloy, MgxZn1−xO, especially in terms of the composition dependence of its lattice parameters and band-gap in two different crystallographic phases, to discuss the stability of this metastable compound. The studies on the PLD growth of multilayer and superlattices are briefly reviewed. We finally present the current capability of electron and hole doping by incorporating Ga and N into films grown on (0001) ScAlMgO4 substrates. We conclude that the PLD technique and related technologies have now mature to meet the requirements for fabricating UV-LEDs.