| Zinc oxide (ZnO) is a direct wide band gap semiconductor with a large exciton binding energy of 60meV. Owing to its superior optoelectronic properties, ZnO is a promising candidate host for the application in violet-blue light emitting diodes, ultraviolet photodetectors and shortwavelength exciton-based lasers. Recently, the development in ZnO-based materials and devices has made significant progresses. Upon all these aspects, the researches on ZnO materials and devices have become a very active field in the modern semiconductor development.In this thesis, focusing on the basis and forefront study of ZnO material research, nitrogen-doped ZnO films, ZnMgO alloys and growth and optoelectronic properties on ZnMgO/ZnO heterostrustures have been studied in detail. Moreover, transport properties and photoluminescence properties of two-dimensional electron gas (2DEG) formed at the interface due to polarization effects have been investigated. The main results include the following:1,The influence of annealing temperature on optical and electrical properties of nitrogen-doped ZnO films has been investigated. High-temperature annealing is found to cause a transition of the conductive type of ZnO films verified from the Hall Effect measurement. Unintentionally doped carbon atoms are found to exist at different forms in the N-doped ZnO films grown by MOCVD growth method. High-temperature annealing also lead the aggregation of carbon clusters with its size significantly increased and notable improvement of ZnO film surface morpholohy and crystal structure attained.2,The optical properties of N-doped ZnO films has been investigated by temperature-dependent photoluminescence. For the first time, the green band with fine structures due to multi-phonon emission was observed in the N-doped ZnO films. The temperature-dependent photoluminescence spectra do reveal the correlations between the greenband and donor bound exciton (D°X) with its two-electron satellite (TES). Greenband was identified to the transitions between ground state and excited state of shallow donor to the deep acceptor Vzn·Finally, the fine structures with multi-phonon peaks observed in the green band was ascribed to the strong coupling of the electrons and the phonons in high quality N-doped ZnO films.3,The influence of MOCVD growth parameters on ZnMgO alloys and properties have been investigated systematically. ZnO substrate, large Mg/Zn gas ratio and higher growth pressure are found to be favorable to grow high Mg composition ZnMgO alloy. High flow rate of Mg MO source or high growth temperature may cause the formation of ZnMgO alloy with mix-phase or single cubic phase. However, it's interesting to find that rapid thermal annealing may cause the cubic phase transformed to mixed phase with obvious hexagonal phase observed in ZnMgO alloy, which is in favor of high-quality ZnMgO alloys by MOCVD technique.4,The influence of ZnMgO alloy structural parameters on the optoelectronic properties of ZnMgO/ZnO heterostrustures has been investigated. The dependence of the transport properties of two-dimentional electron gas (2DEG) formed due to polarization effects on the ZnMgO caplayer thickness has been revealed. The thickness and composition distribution of ZnMgO alloy layer shows obvious influence on photoluminescence, due to limited penetration depth of the excited laser in the ZnO based film. For the first time, three additional 2DEG-related emissions with small activation energy have been observed in low-temperature photoluminescence spectra. These emissions are reasonablely assigned to the transitions from 2DEG electrons to the photoexcited holes existed in different areas near the heterointerface respectively. |
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