Preparation Of ZnO Films For Surface Acoustic Wave And Fundamental Study Of The SAWF

ZnO is a direct wide-band gap semiconductor optical-electronic material with manyapplications, such as in ultraviolet laser, low-loss high-frequency surface acoustic wave (SAW)devices, buffer layers for III-nitride growth, and transparent electrode et al, which make itmore attractive to many research groups for a long time. Especially in 1996, the upsurge inZnO research is coming due to the realization of the light pumped exciton emitting anddiscovery of self-formed cavity. Subsequently, some groups make more progress in formationof the p type ZnO and p-n devices, the work in multi-element alloy materials were alsoexpanded. In this paper, high quality ZnO thin films on different substrates have beenobtained by MOCVD system designed for SAW application. At the same time, the propertiesand devices of SAW for ZnO films have been investigated in details, and good results havebeen achieved. First, the characteristics of the structure, optics, piezoelectric are studied systematicallyby the author, especially for the SAW filter of ZnO. It concluded that the smoother surfaceand high resistivity were the first requisite of high performance SAW filter. The differentsubstrate materials for SAW were discussed in this chapter, in which the diamond substrate ispreferred for high frequency SAW device. The frequency and temperature characteristic werestudied for multi-layer ZnO structure also. According to the principle of MOCVD and in order to solve the problem in ZnO growthprocess, new-type plasma enhanced MOCVD system has been designed and fabricated. Theprecursors ( DEZn and O2 ) have been introduced into the reactor by two gas lines,respectively. And the precursors arrive to the surface of sapphire substrate by two separatedspecial injectors. The substrate holder can be rotated at high speed and is uniformly heated bya special resistive heater. In order to balance the thermal flow, N2 is introduced into thereactor uniformly from the upside. All above designs can reduce the pre-reaction of DEZn andO2 during the ZnO growth and uniform ZnO films may be grown by this MOCVD system.Furthermore, the plasma generator has been added to the MOCVD system in order to improvedoping efficiency during ZnO growth process and obtain high resistivity or p-type ZnO films. High quality ZnO films have been grown on different sapphire substrates in optimized 4吉林大学博士论文growth condition by MOCVD. The XRD spectra show that the relationship between the ZnOfilm grown on C-plane and R-plane sapphire and the substrates is (0002)ZnO‖(0006) Al2O3 ? ? ?and (11 2 0) ZnO‖(02 2 4) Al2O3, respectively. The FWHM of ZnO (11 2 0) peak is about0.250. The datum indicates that the optimized temperature of ZnO film grown on R-planesapphire is higher than that on C-plane sapphire. The SEM and AFM photos of ZnO filmsshow that the growth mode is different for the two substrates, and the surface roughness isdecreased for the sample grown on R-Al2O3. Photoluminescence spectra of the ZnO filmsshow dominating exciton emission peak, and the deep-level emission which is obvious onZnO/C-Al2O3 film had hardly been observed. This implied that there are fewer interior defectsin ZnO/R-Al2O3. Finally, high resistivity and p type ZnO films are obtained in our group. High-quality ZnO films are grown on epi-GaN predeposited on c-Al2O3 substrates usinglow pressure metal-organic chemical vapour deposition (MOCVD). Detailed study of theX-ray diffraction spots and patterns by different diffractometers showed high structuralperfection of the zinc oxide layer, which indicated that the growth of ZnO film was stronglyc-oriented. The full-width at half-maximum (FWHM) of the ω-rocking curve was 0.29°.Surface morphology of the films studied by AFM showed that the growth of the ZnO filmfollowed the regular hexagonal column structure with about 500 nm grain d...