Shu Jin

Electrical conductivity enhancement in nanocrystalline (RE2O3)0.08(ZrO2)0.92 (RE=Sc, Y) thin films

Dense, crack-free, uniform, and homogeneous (RE2O3)0.08(ZrO2)0.92 (RE=Sc, Y) nanocrystalline thin films were fabricated by a simple sol-gel method and characterized by impedance studies. At temperatures beyond 600 °C, the electrical conductivity of (Sc2O3)0.08(ZrO2)0.92 and (Y2O3)0.08(ZrO2)0.92 nanocrystals in pure cubic phase was ten times higher than that of the corresponding bulk materials. The decrease of grain boundary resistance related to interfacial effect is predominately responsible for the electrical conductivity enhancement.

Relationship of background carrier concentration and defects in GaN grown by metalorganic vapor phase epitaxy

Experimental results show that the background carrier concentrations in GaN films grown by metalorganic vapor phase epitaxy are related to defects. A thermal equilibrium method was used to calculate the background carrier concentration related to intrinsic defects in an ideal GaN crystal. The results show that the N vacancy concentration does not exceed 2×1017 cm−3 in GaN grown at temperatures ranging from 800 to 1500 K. It can be concluded that the N vacancy is one of the major sources of carriers when the carrier concentration n 2×1017 cm−3; this conclusion may lead to ways for further improving the quality of GaN films.

Microstructures and optical properties of nanocrystalline rare earth stabilized zirconia thin films deposited by a simple sol–gel method

Abstract Dense, crack-free and homogeneous nanocrystalline (ZrO2)0.92(RE2O3)0.08 (RE=Sc, Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu) thin films (about 200 nm in thickness) have been fabricated on quartz substrate by a simple sol–gel spin coating technique. The films can crystallize in a pure cubic fluorite structure at a low annealing temperature of 600 °C. The optical band gaps of the films annealed within 600–900 °C were determined by an ultraviolet and visible spectrophotometer, and are in the range of 4.88–5.44 eV. It is also shown that the optical band gaps of the films not only depend on the ionic size of the rare earth doped, but also mostly decrease with increase in annealing temperature due to the size-dependent effect.

TWO LOCAL VIBRATIONAL MODES RELATED TO HYDROGEN IN GAN

We have observed two absorption bands located at around 1730 and 2960 cm−1 in the infrared (IR) absorption spectra from undoped GaN samples which are grown using low pressure metalorganic vapor phase epitaxy and irradiated by gamma ray and then exposed to a radio frequency hydrogen plasma. Proton implantation followed by gamma-ray irradiation of the GaN samples can also activate the IR band at around 1730 cm−1. Based on the experimental results, we tentatively ascribe the 1730 cm−1 band to the local vibrational modes of Ga–H complexes in the vicinity of N vacancies and the 2960 cm−1 band to those of either N–H complexes in the vicinity of Ga vacancies or C–H complexes.

Minority electron mobility in a p-n GaN photodetector

Photoconductive transients and responsivity in a GaN p-n UV photodetector under different applied voltages are investigated at room temperature. The electron mobility of minority carriers in the p-GaN epilayer has been measured by a diffusion time-of-flight technique, and was found to be about 0.12 cm2 V-1 s-1 with the bias between 1 V and 12 V. The difference of the electron mobilities between the minority carriers in p-GaN and the majority carriers in n-GaN is explained by different scattering mechanisms. The neutral impurity and phonon scattering mechanisms dominate the minority electron mobility in p-GaN. The photoconductive responsivity increases nearly linearly at low voltage and saturates at about 10 V, corresponding to a saturation field of approximately 3.7 × 104 V cm-1 . The implication of these results for applications of GaN UV detectors is also discussed.

Growth and doping characteristics of InGaN films grown by low pressure MOCVD

Abstract High quality InxGa1−xN films with x values up to 0.3 were grown by low pressure MOCVD. It was found that x values in InxGa1−xN films near exponentially decrease with growth temperature. The doping characteristics of InGaN films with Si and Zn were studied. At optimum growth conditions, the PL intensity of Zn doped InGaN film is about 30 times stronger than that of undoped InGaN film. The PL intensity of Si-doped InGaN film is strong as 13 times as that of undoped InGaN film.

Effects of thermal convection on growth rate of GaN by MOVPE

It was demonstrated that GaN growth rate by MOVPE depended on the reactor pressure, inclined angle of slanted susceptor, and the temperature gradient over substrate in the vertical direction, which were contributed to the thermal convection in gas-phase. The growth process was controlled by mass transported limited, that can be classified into the input rate limited and the diffusion limited, or their combination depending on the configuration of reactor and the experimental conditions.

Effects of isochronal thermal annealing and hydrogenation on photoluminescence from n-type GaN films grown by metalorganic vapor phase epitaxy

Abstract We have investigated the behavior of three emission bands located at around 375, 580 and 750 nm in photoluminescence (PL) spectra from n -type GaN films grown by the metalorganic vapor phase epitaxy method in the isochronal annealing process and in a similar process after the films have been hydrogenated using a hydrogen plasma. The PL intensities of the two bands located at around 375 nm and 750 nm vs isochronal annealing temperature show similar rules, but the isochronal annealing behavior of PL intensity for the band located at around 580 nm differs obviously from that of the two bands mentioned above. Hydrogenation has an obvious effect on the isochronal annealing behavior of PL intensity, e.g. decreases the number of peaks in the curves of PL intensity vs isochronal annealing temperature.