Tsun-Neng Yang

The effect of a-GaAs/a-Si double buffer layers on GaAs-on-Si as determined by transmission electron microscopy

A high-quality GaAs epilayer was successfully grown on a Si substrate using a-GaAs/a-Si double buffers, which were crystallized by thermal cyclic annealing. Double crystal x-ray diffraction measurements showed that the full width at half maximum of the rocking curve for the GaAs epilayer was only 102 arcs. The effect of a-GaAs/a-Si double buffers was examined in detail by transmission electron microscopy. Transmission electron microscopy characterizations revealed obvious bending behaviour of dislocations in the a-GaAs/a-Si buffered epilayer. Most threading dislocations and planar defects were confined within the crystallized double buffers. The dislocation density was reduced to 2.6 × 106 cm−2 at a thickness of 1.0 µm in the first epitaxial layer and was further improved to under 1.3 × 106 cm−2 in the second epitaxial layer. Transmission electron microscopy observation and analysis revealed a defect reduction mechanism.

Intrinsic p-type ZnO films fabricated by atmospheric pressure metal organic chemical vapor deposition

The structural, electrical, and optical properties of ZnO films fabricated by atmospheric pressure metal organic chemical vapor deposition (AP-MOCVD) under various gas flow ratios of [H2O]/[DEZn] (VI/II ratio) ranging from 0.55 to 2.74 were systematically examined. Hall effect measurements exhibited an evident effect of the VI/II ratio on the conduction type of the intrinsic films. An n-type film was fabricated at the VI/II ratio=0.55; however, p-type ZnO films with the hole concentration of the order of 1017 cm−3 could be achieved at VI/II ratios higher than 1.0. In particular, the highest mobility of 91.6 cm2/V s and the lowest resistivity of 0.369 Ω cm have been achieved for the specimen fabricated at the VI/II ratio=1.10. Moreover, room-temperature photoluminescence (PL) measurements demonstrated an interstitial Zn (Zni) donor defect related emission at 2.9 eV for the n-type film, while a Zn vacancy (VZn) acceptor defect related one at 3.09 eV for the p-type films. The existence of material intrinsic ...

Characterizations of Ga-doped ZnO films on Si (111) prepared by atmospheric pressure metal-organic chemical vapor deposition

Gallium-doped ZnO films were grown on p-Si(111) substrates by atmospheric pressure metal-organic chemical vapor deposition (AP-MOCVD) using diethylzinc and water as reactant gases and triethyl gallium (TEG) as a n-type dopant gas. The structural, electrical, and optical properties of ZnO:Ga films obtained by varying the flow rate of TEG from 0.56to3.35μmol∕min were examined. X-ray diffraction patterns and scanning electron microscopy images indicated that Ga doping plays a role in forming microstructures in ZnO films. A flat surface with a predominant orientation (101) was obtained for the ZnO:Ga film fabricated at a flow rate of TEG=2.79μmol∕min. This film also revealed a lowest resistivity of 4.54×10−4Ωcm, as measured using the van der Pauw method. Moreover, low temperature photoluminescence (PL) emission recorded at 12K demonstrated the Burstein Moss shift of PL line from 3.365to3.403eV and a line broadening from 100to165meV as the TEG flow rate varied from 0.56to2.79μmol∕min. This blueshift behavior o...

Optical studies of InN epilayers on Si substrates with different buffer layers

We have investigated the photoluminescence (PL) and time-resolved PL from the InN epilayers grown on Si substrates with different buffer layers. The narrowest value of the full width at half maximum of the PL peak is 52 meV with the AlN/AlGaN/GaN triple buffer layer, which is better than previous reports on similar InN epilayers on Si substrates. Based on the emission-energy dependence of the PL decays, the localization energy of carriers is also the least for the InN with a triple buffer layer. According to the x-ray diffraction measurements, we suggest that the reduced lattice mismatch between the InN epilayer and the top buffer layer is responsible for improvement of sample quality using the buffer-layer technique.

Luminescence mechanisms of silicon-rich nitride films fabricated by atmospheric pressure chemical vapor deposition in N2 and H2 atmospheres

This work examines possible luminescence mechanisms of silicon-rich nitride (SRN) films that were fabricated by atmospheric pressure chemical vapor deposition (APCVD). Under an ambient gas of either H2 or N2, two SRN films were deposited using the same precursors of Si and N. While photoluminescence (PL) measurements of both as-deposited specimens revealed an intense luminescence band (1.8–3.8 eV), which was observable by the naked eye, a detailed examination of the high energy band of the PL spectra over 2.8 eV yielded different results for those samples that were fabricated in different ambiences. To determine the reason for these differences, Fourier-transform infrared spectroscopy and x-ray photoelectron spectroscopy were conducted, suggesting unique chemical bonds and elemental ratio of nitrogen to silicon in SRN films. Further analysis involving plan-view high-resolution transmission electron microscopic observations of SRN films demonstrated the embedding of Si quantum dots (Si QDs), but with some ...

Growth of InN on Si (111) by atmospheric-pressure metal-organic chemical vapor deposition using InN/AlN double-buffer layers

Indium nitride (InN) epilayers have been successfully grown on Si (111) substrates with low-temperature (450°C) grown InN and high-temperature (1050°C) grown AlN (InN∕AlN) double-buffer layers by atmospheric-pressure metal-organic chemical vapor deposition (AP-MOCVD). X-ray diffraction characterizations indicated that highly (0001)-oriented hexagonal InN was grown on Si (111) substrate. Photoluminescence (PL) analyses performed at room temperature showed a strong emission at 0.72eV with a full width at half maximum of 121meV. Excitation intensity dependent measurements demonstrated the PL mechanism to be the band-to-band transition. Time-resolved PL could be fitted by a single exponential exhibiting an ordered film and a recombination lifetime of around 0.85ns. In particular, transmission electron microscopy characterizations indicated that the use of AlN first buffer is very important to achieve a structurally uniform (0001)-oriented InN epilayer on Si (111) by AP-MOCVD.

Fabrication of Whitely Luminescent Silicon-Rich Nitride Films by Atmospheric Pressure Chemical Vapor Deposition

Silicon-rich nitride (SRN) films that can exhibit an intense white-light emission were fabricated by atmospheric pressure chemical vapor deposition. SRN films were deposited on Si substrates using gaseous SiH2Cl2 (DCS) and NH3 as the source materials for Si and N, respectively. The deposition temperature was kept at 850 °C, and H2 was used as the carrier gas with its flow rate modulated to maintain chamber pressure at 1 atm during the deposition. The optical properties of films obtained at various deposition times from 15 to 60 min were examined by photoluminescence (PL) measurement. An intense luminescence band (1.5–3.5 eV) was observed by the naked eye for all as-deposited samples. Besides, time-resolved PL exhibited a short radiative lifetime of about 1 ns for SRN films. Moreover, high resolution plan-view transmission electron microscopy demonstrated the existence of Si dots in SRN films with the dot sizes ranging from 2 to 6 nm and a dot density of about 4×1012/cm2. On the basis of the results obtained, we considered that the related luminescence mechanism for SRN films is connected to crystalline Si dots produced therein.

Luminescence Mechanism of SiOx Films Grown by Atmospheric-Pressure Halide Chemical Vapor Deposition

Strong red-light luminescence was exhibited by nonstoichiometric silicon oxide (SiOx) films grown by atmospheric-pressure halide chemical vapor deposition. The temperature-dependent photoluminescence (PL) measurements and theoretical calculation of emission energy demonstrated that the PL of our samples originated from the energy level of the interface between Si quantum dots (Si-QDs) and a SiO2 matrix. Moreover, the continuous-wave PL spectra showed that the PL intensity can be enhanced by thermal annealing in CO2 environment. The radiative lifetime determined from the time-resolved PL measurement was increased by increasing CO2 thermal annealing temperature. The high-resolution transmission electron microscopy showed single-crystalline Si-QDs embedded in the SiOx films. According to the results obtained, the emission peak of the PL spectra of the SiOx films was probably due to the energy level of the interface region transition, and the nonradiative centers (or dangling bond, defect center) can be passivated using CO2 thermal annealing.

Optical Characterization of CuInSe2 Thin Films Grown by Metal Organic Chemical Vapor Deposition

We studied the photoluminescence (PL) in CuInSe2 thin films grown by metal organic chemical vapor deposition (MOCVD) using a Cu precursor and two gases. By X-ray diffraction (XRD) and PL analysis, we found that the best quality of CuInSe2 thin films can be obtained when the deposition time of the trimethylindium (TMI) gas is 30 min. The improvement of the quality of CuInSe2 thin films after rapid thermal annealing (RTA) is evident from the full width at half maximum (FWHM) of PL. The FWHM of the PL peak is minimum when the RTA temperature is 500 ?C. It is found the binding energy of the impurity level in CuInSe2 thin films increases after RTA, revealing that the thermal stability of CuInSe2 thin films is improved after RTA.