ABSTRACT
Recently, ZnO-based semiconductors have been attracting increasing attention as promising candidates for optoelectronic applications in ultraviolet (UV) regions [1,2]. Because ZnO has a very large exciton binding energy (60 meV), it allows ef‹cient excitonic emission at high temperature [3]. As is well known, an exciton-related lasing process can easily achieve higher gain and lower threshold, ZnO desirable to develop optoelectronic devices based on excitonic effect. In addition, in order to obtain high-performance light-emitting diode (LED) devices, one of the key techniques is to construct a heterojunction to realize double con‹nement actions for electrons and photons in optoelectronic devices. Because the ionic radius of Mg2+ (0.57 Å) is close to that of Zn2+ (0.6 Å), MgxZn1−xO alloy is considered to be a suitable potential barrier material by doping Mg as a substitute for Zn2+ ion in ZnO [4,5]. However, ZnO and MgO belong to wurtzite structure and rocksalt structure, respectively. The difference between ZnO and MgO with regard to their thermally stable structure results in phase separation of MgxZn1−xO at high Mg composition. It is suggested that the Mg content of x = 0.33 is the solubility limit of MgxZn1−xO thin ‹lms for the wurtzite structure [7]. Hence, the main researches are concentrated on the growth and
CONTENTS
9.1 Introduction ........................................................................................................................223 9.2 Experimental ...................................................................................................................... 226
9.2.1 Materials Growth ................................................................................................... 226 9.2.2 Characterization Techniques ...............................................................................227
