Z.Z. Chen

Deposition and crystallization of amorphous GaN buffer layers on Si(111) substrates

The deposition and crystallization of amorphous GaN buffer layers on Si(1 1 1) is firstly investigated by using an atomic force microscope (AFM), X-ray diffraction (XRD) and a high-resolution transmission electron microscope (HRTEM). The amorphous GaN layers were deposited by MOCVD at 300°C. The islanding process by annealing at higher temperatures has been revealed by AFM. It is found that the amorphous layers begin to be crystallized by solid-phase epitaxy at 500°C in MOCVD, and the full-developed islands formed at about 600°C. XRD data show that the GaN peak appeared only after an annealing at higher temperatures. Cross-sectional HRTEM micrographs of the buffer region of the samples with amorphous GaN buffer layers reveal that many domains exist in the GaN buffer layers and these domains misorientate each other with a small angle. The boundaries between domains locate near the bunched steps, and, the films on a terrace between steps have the same crystal orientation. The amorphous buffer layer deposited at 300°C and the buffer layer directly deposited at 550°C are used in the growth of GaN epilayers, respectively. The XRD results and photoluminescence at room temperature of such GaN epilayers show that using the amorphous GaN buffer layer lead to monocrystalline and a narrower full-width at half-maximum (FWHM) of near band emission (16 nm) than using the buffer layer directly deposited at 550°C (FWHM of 21 nm). These results indicate that the quality of GaN epilayer on Si(1 1 1) can be improved by using the amorphous GaN buffer layer.

Growth of wurtzite GaN films on /spl alpha/-Al/sub 2/O/sub 3/ substrates using light radiation heating metal-organic chemical vapor deposition

Epitaxial growth of high quality hexagonal GaN films on sapphire substrates using light radiation heating metal-organic chemical vapor deposition (LRH-MOCVD) is reported. The deposition temperature is 950/spl deg/C, about 100/spl deg/C lower than that in normal rf-heating MOCVD growth. The FWHM of the GaN (0002) peak of X-ray diffraction rocking curve is 9.8 arc min. The photoluminescence spectrum of GaN shows that there is a very strong band-edge emission and no yellow-band luminescence. Hall measurement indicates that the n-type background carrier concentration of the GaN film is 1.7/spl times/10/sup 18/ cm/sup -3/ and the Hall mobility is 121.5 cm/sup 2//V.s. It is suggested that the radiation of light in GaN growth enhances the dissociation of ammonia and decreases the disadvantages of the parasitic reaction between trimethylgallium and ammonia.

High-Quality Photoconductive Ultraviolet GaN/6H-SiC Detector and Its Properties

The properties of photoconductive ultraviolet detector based on GaN epilayer grown on 6H-SiC substrate by metalorganic chemical vapor deposition were investigated in this paper. We obtained the detectable energy span of the device up to ultraviolet by photocurrent measurement. The spectral responsivity remained nearly constant for wavelengths from 250 to 365 nm and dropped by three orders of magnitude within 10 nm of the band edge (by 380 nm). The detector was measured to have a responsivity of 133 A/W at a wavelength of 360 nm under a 5-V bias, and the voltage-dependent responsivity was performed. Furthermore, an easy method was developed to determine the response time, and the relationship between response time and bias was obtained.

Microstructure and physical properties of GaN films on sapphire substrates

Transmission electron microscopy (TEM), x-ray diffraction (XRD), photoluminescence (PL) and Raman scattering measurements were applied to study the correlation between the microstructure and physical properties of the GaN films grown by light radiation heating metalorganic chemical vapor deposition (LRH-MOCVD), using GaN buffer layer on sapphire substrates. When the density of the threading dislocation (TD) increases about one order of magnitude, the yellow luminescence (YL) intensity is strengthened from negligible to two orders of magnitude higher than the band edge emission intensity. The full width of half maximum (FWHM) of the GaN (0002) peak of the XRD rocking curve was widened from 11 min to 15 min, and in Raman spectra, the width of E{sub 2} mode is broadened from 5 cm{sup {minus}1} to 7 cm{sup {minus}1}. A zippers structure at the interface of GaN/sapphire was observed by high-resolution electron microscope (HREM). Furthermore the origins of TD and relationship between physical properties and microstructures combining the growth conditions are discussed.

Fabrication and characterization of metal-ferroelectric-GaN structures

GaN-based metal-ferroelectric-semiconductor (MFS) structure has been fabricated by using ferroelectric Pb(Zr{sub 0.53}Ti{sub 0.47})O{sub 3} (PZT) instead of conventional oxides as gate insulators. The GaN and PZT films in the MFS structures have been characterized by various methods such as photoluminescence (PL), wide-angle X-ray diffraction (XRD) and high-resolution X-ray diffraction (HRXRD). The Electric properties of GaN MFS structure with different oxide thickness have been characterized by high-frequency C-V measurement. When the PZT films are as thick as 1 {micro}m, the GaN active layers can approach inversion under the bias of 15V, which cannot be observed in the traditional GaN MOS structures. When the PZT films are about 100 nm, the MFS structures can approach inversion just under 5V. All the marked improvements of C-V behaviors in GaN MFS structures are mainly attributed to the high dielectric constant and large polarization of the ferroelectric gate oxide.