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Study On Bulk GaN Growth By Hydride Vapor Phase Epitaxy

Posted on:2011-08-19Degree:DoctorType:Dissertation
Country:ChinaCandidate:R WangFull Text:PDF
GTID:1118330362452711Subject:Microelectronics and Solid State Electronics
Abstract/Summary:PDF Full Text Request
There are many outstanding characters for GaN material such as wide band gap, stable chemical property, high temperature resistance and corrosion resistance. GaN devices have radiation-resistance, high-frequency and high-power performances, so it is widely used in lightshow, photomemory, illumination, optical detection, aerospace and civil mobile communication fields. GaN bulk crystal can not be grown by the method of melt growth for its melting point is over 2500℃. Hydride vapor phase epitaxy (HVPE) suits to grow thick GaN films because it has faster growth ratio, which can reach about scores of microns per hour, and the required equipment is simple. Freestanding GaN substrate or GaN bulk crystal can be obtained by peeling away thick GaN film from the substrate.Preparation of thick GaN film is the main target of the dissertation.Based on the theories of epitaxial lateral overgrowth (ELOG) and buffer technology, adopting optimized growth parameters such as substrate temperature, the pressure of Ar gas and the power of radio frequency sputtering, three-dimensional-island and uniform-sized ZnO buffer layers with single <0002> orientation were grown on Al2O3(0001) substrates and Si(111) substrates by radio frequency magnetron sputtering (RFMS). The three-dimensional-island structure can reduce the lattice mismatch, decrease the threading dislocation density (TDD) of GaN film and is benefit for the film to peel away from the substrate. The surface voids of ZnO buffer layers can play a key role that is similar to the mask of ELOG.The high-quality thick GaN films grown on Al2O3(0001) and Si(111) substrate with high-property RF-ZnO buffers layers were fabricated through optimizing the HVPE system process parameters such as growth temperature, V/III ratio and the kind of carrier gas. The TDD of thick GaN films was estimated and the performance of optics and electricity were measured. At room temperature, it was found that H2 and N2 adopted as carrier gas in sequence was effective and yellow luminescence disappeared in PL spectrum, which indicated that the density of crystal defects reduced. The full width at half maximum (FWHM) of double crystal X-ray diffraction (DCXRD) (0002) peak of GaN films on RF-ZnO/Al2O3(0001) substrate got 265 arcsec and (1012) peak got 414 acrsec. Hall test of GaN/RF-ZnO/Al2O3(0001) indicated the GaN films had high quality, lower impurity content and less scatter of the carrier. Hall mobility got 436cm2/V·s and sheet resistance got 3.17×106?/□. Composite structure of LT-GaN/RF-ZnO was adopted on Si(111) substrates to grow thick GaN films. The RF-ZnO buffers avoid the poly-crystallization of GaN films which is from the formation amorphous state SiNx films or the autolysis of Ga drop in Si(111) substrate. Low temperature GaN (LT-GaN) interlayer reduced the lattice mismatch, and prevented the RF-ZnO layer from pyrolysing and reaction at high temperature.Preliminary studies of other kinds of thick GaN films had been done as the following : One was preparation through adopting LT-GaN interlayer between GaN layer and nitrided Al2O3(0001) substrate, another was preparation by using TiN as a mask layer on Al2O3(0001) substrate. The problem that N polar face of GaN films on nitrided Al2O3(0001) substrates and oxidation of nano-grade Ti films on Al2O3(0001) substrates led to bad crystal quality.Initial research about laser lift-off (LLO) and chemical corrosion of thick GaN films had been also done.
Keywords/Search Tags:HVPE, ZnO buffer, radio frequency magnetron sputtering, threading dislocations density, yellow luminescence, sheet resistance
PDF Full Text Request
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