Preparation Of ZnO Films Grown On Diamond Via MOCVD And Fundamental Study Of The SAW Devices

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 and piezoelectric are studied systematically bythe author, especially for the SAW filter of ZnO. It concluded that the smoother surface andhigh resistivity were the first requisite of high performance SAW filter. The different substratematerials for SAW were discussed in this chapter, in which the diamond substrate is preferredfor high frequency SAW device. The frequency and temperature characteristic were studiedfor 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. 3吉 林 大 学 硕 士 学 位 论 文 First, high-quality ZnO thin films have been grown on single-crystal Diamond substrateswith (111) orientation, by low-pressure metal–organic chemical vapour deposition. X-raydiffraction spectra and photoluminescence (PL) spectra clearly showed that the quality ofZnO films was improved by two-step growth method. Strong ultraviolet emissions and weakdeep-level emissions with different intensity were both observed in room-temperature PLspectrum. The change of surface morphology were also studied by atomic force microscopy(AFM). Raman scattering was performed at room temperature. The E2, A1(TO) and E1(TO)mode peaks were seen at 437.46, 383 and 414.87cm-1, which indicated a high crystallineintegrality of our samples. Piezoelectric ZnO layers with high resistivity for surface acoustic wave applicationshave been prepared on polycrystalline Diamond/Si substrates with (111) orientation byMetal-Organic Chemical Vapour Deposition. The characteristics of the films are optimizedthrough different growth methods. The comparative study of X-ray diffraction spectra andscanning electron microscopy shows that the final-prepared ZnO films had better c-axisconsistency. Zn and O elements in the final prepared ZnO films are investigated through x-rayphotoelectron spectroscopy, according to the statistical results, the Zn/O ratio is near 1.Raman scattering is also performed in back scattering configuration, E2 mode is observed infinal films, which is coincident with the group symmetry for the ZnO crystal structure.. Theresistivity of the films is also enhanced via the mo...