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Abstract. The oxidation of GaN epilayers in dry oxygen has been investigated. The GaN epilayers, about 1 micro m thick, were grown on (0001) sapphire substrates by rapid thermal process/low pressure metalorganic chemical vapor deposition. Bulk theta - 2 theta X-ray diffraction (XRD) data showed that the slight oxidation of GaN began to occur at 800 Celsius tot 6 h. The oxide was identified as the monoclinic beta-Ga[sub 2]O[sub 3]. The GaN epilayers were completely oxidized at 1050 Celsius for 4 h or at 1100 Celsius for I h. For all samples, the strongest oxide's peak is (11-3), and (30-6) followed. There is a rapid oxidation process in the initial stage of oxidation, and a relatively slow process followed when the temperature was over 1000 Celsius. The oxidation of two stages was limited by the rate of an interracial reaction mechanism and by the diffusion mechanism, respectively. When the temperature reaches 1100 Celsius, the oxidation rate is very fast, which is considered as the results of the GaN decomposition at high temperature under atmosphere. The oxide layers were also observed by a scanning electron microscope, which shows a rough oxide surface and an expansion of the volume of 40%. The photoluminescence (PL) seriously influenced by the oxidation is also discussed. [ABSTRACT FROM AUTHOR]

Abstract. Epitaxial growth of high-quality hexagonal GaN films on sapphire substrates using light-radiation heating metal-organic chemical vapor deposition (LRH-MOCVD) is first reported. The deposition temperature is 950 Celsius, about 100 Celsius lower than that in normal rf-heating MOCVD growth. The FWHM of GaN (0002) peak of the X-ray diffraction rocking curve is 8.7 arc min. Photoluminescence spectrum of GaN film 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 GaN film is 1.7 x 10[sup 18]cm[sup -3] and the Hall mobility of it 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 parasite reaction between trimethylgallium and ammonia. [ABSTRACT FROM AUTHOR]

The SiCN film, which has the same crystal structure as 3C-SiC verified by X-ray diffraction and Raman scattering, has been formed on Si (111) substrate by constant-source diffusion using a chemical vapor deposition system. Via X-ray photoelectron spectroscopy, the film has been identified as the mixture of elemental Si and SiC 1 − x N x alloy, with the SiC 1 − x N x content decreases from 87.4% to 17.9% and the mole fraction x increases from 0.17 to 0.21, as the depth extends from the near surface to the interface. The measured composition distribution can be well explained by the constant-source diffusion model, confirms that the formation mechanism of the SiCN film is the diffusion of C and N into the Si substrate. This provides a new method for fabricating crystalline SiCN thin films. [ABSTRACT FROM AUTHOR]

Abstract: Zn1− x Ni x O (, 0.02 and 0.05) powders were prepared by a sol–gel method. We have studied the structure and magnetic properties of the samples by using X-ray diffraction (XRD), Raman scattering, superconducting quantum interference device (SQUID) and extended X-ray absorption fine structure (EXAFS). The SQUID results showed that all the samples exhibit ferromagnetism above room temperature. From the XRD spectra of the samples, it was obvious that there had no second phase while the Ni-doped concentration was lower than 5at%. Raman spectra showed an additional band, which is related to the vibration of Ni dopant. The EXAFS was used for the Ni K-edge to probe the local structures of the Ni dopant in ZnO, which show that Ni dopant was substituted for Zn atoms position up to 5at% Ni concentration. [Copyright &y& Elsevier]

Abstract: Indium nitride films, grown at 375 °C by low-pressure metal–organic chemical vapor deposition, have been annealed at temperatures ranging from 400 °C to 475 °C under an ambient ammonia atmosphere. According to our X-ray diffraction spectra of the annealed InN films, the integrated intensity of the InN (0002) diffraction peak reaches its minimum value at the temperature of 425 °C, but the full-width at half maximum of the InN (0002) peak shows an opposite change with the annealing temperature. These results indicate that the InN film annealed at 425 °C has the worst structural quality. Scanning electron microscope and X-ray photoelectron spectroscope measurements demonstrate that as the annealing temperature is increased to 425 °C, the density of indium grains on the surface increases greatly due to the volatilization of nitrogen atoms. Above 425 °C, the density of the indium grains begins to decrease, resulting from the desorption of indium. The indium grains formed during this annealing process are then supposed to be responsible for the degraded structural quality in the annealed InN. [Copyright &y& Elsevier]

Abstract: Indium nitride (InN) films have been deposited on sapphire substrates at 350–500 °C using low-pressure metalorganic chemical vapor deposition (LP-MOCVD). Increasing the growth temperature changes the structure of InN from cubic to hexagonal. At 500 °C, no InN can be grown on sapphire due to its decomposition. The X-ray diffraction (XRD) spectra of InN films show that the diffractions from In(101) reach a maximum at 425 °C and begin to decrease at the growth temperature higher than 425 °C. According to the scanning electron microscope (SEM) images of InN films, the In aggregation on the surface is observed at the growth temperature of 425 °C, which corresponds to the most intensive diffraction of In(101) in XRD spectra. In addition, the density of InN nucleation sites is reduced by increasing the growth temperature. As well as the increase of In desorption with the growth temperature, the decrease of InN nucleation sites are responsible for the most significant In aggregation at 425 °C. [Copyright &y& Elsevier]

Photoluminescence (PL), X-ray diffraction (XRD) and Raman spectra have been measured to characterize the effects of phosphorus on the optical and structural properties of GaN1−xPx alloys with x&les;15%, grown by means of light-radiation heating, low-pressure metal-organic chemical vapor deposition. The PL spectra of GaN1−xPx show the largest red shift of 100 meV from the band-edge emission of GaN. XRD rocking curves show that the (0 0 0 2) peak of GaN1−xPx shifts to smaller angles with increasing P content. The Raman spectra of GaN1−xPx, recorded in backscattering geometry, exhibit four new vibrational modes at 256, 314, 377 and 428 cm−1 compared with an undoped GaN sample. The modes at 377 and 428 cm−1 are attributed to gap modes related to the Ga–P bond vibrations, whereas the other two modes at 256 and 314 cm−1 are assigned to phosphorus clusters and disorder-activated scattering, respectively. The frequency of the A1 (LO) mode is found to decrease with increasing x at a much high rate of approximately 268 cm−1/x for x<0.03. This red shift is attributed to the effects of alloying and strain. Furthermore, we have not observed characterizations related to GaP resulted from the phase separation from PL, XRD and Raman spectra of all investigated GaN1−xPx samples. [Copyright &y& Elsevier]

Abstract: The LiNbO 3 thin films are successfully grown by pulsed-laser deposition on theAl 0.28 Ga 0.72 N/GaN substrate. The films are characterized by the X-ray diffraction and the X-ray photoelectron spectroscopy. The ferroelectric properties are measured by the piezoresponse force microscopy. An Al/SiO 2 /LiNbO 3 /Al 0.28 Ga 0.72 N/GaN structure is then fabricated and measured by high frequency capacitance–voltage at 1MHz. The mechanism of interaction between interfaces is revealed. [Copyright &y& Elsevier]

Abstract: The high-temperature characteristics of strain in Al0.22Ga0.78N layers, with and without a Si3N4 passivation layer, were investigated at temperatures from room temperature to 813 K by means of high-resolution X-ray diffraction. The results show that a small temperature-dependent strain relaxation occurs in the unpassivated Al0.22Ga0.78N layers when the temperature exceeds 523 K. After passivating, an additional tensile strain and an initial increase of the in-plane tensile strain with increasing temperature were observed in Al0.22Ga0.78N layers, and at higher temperatures the in-plane tensile strain only decreases slightly in the 100-nm-thick Al0.22Ga0.78N layer, but a pronounced temperature-dependent strain relaxation occurs in the 50-nm-thick one due to the fact that the thickness of the Al0.22Ga0.78N layer is close to the critical thickness, and hence the increase of tensile strain induced by passivation will result in partial strain relaxation via the formation of cracks or the glide motion and multiplication of dislocations. [Copyright &y& Elsevier]