Sen-Mao Liao

Characterizations of ZnTe bulks grown by temperature gradient solution growth

In this work, zinc telluride (ZnTe) bulk crystals have been grown for the first time by the temperature gradient solution growth (TGSG) technique. Hall effect and capacitance–voltage (C–V) measurements were used to determine the room temperature electrical properties, and low temperature photoluminescence (PL) measurements were used to analyze the optical properties. As grown undoped ZnTe shows p-type conductivity with the carrier concentration (1–2) × 1015 cm−3, mobility about 50 cm2/V s, resistivity about 80–90 Ω cm. Otherwise, heavily doped p-ZnTe can be achieved by phosphorus doping. The carrier concentration demonstrates a logarithmic increase with the doping amount. The Hall carrier concentration up to 8×1017 cm−3 (4.7×1018 cm−3 from C–V measurement), resistivity low to around 0.15 Ω cm was achieved with a doping amount of 4000 ppm ZnP2. Besides, the room temperature PL spectra exhibits a pure green luminescence of energy 2.259 eV (λ=549.5 nm). The peak intensifies with increasing ZnP2 doping amount and begins to saturate when the added amount is over 8000 ppm. The 9 K PL spectra also demonstrates that the excitonic zone is much more intense than for deep level band, indicating a good sample quality. It is plausible that using the TGSG technique can afford high-quality phosphorus-doped p-type ZnTe substrates for device applications.

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...

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.

Photoluminescence characterization of GaN thin film grown by atmospheric pressure organometallic vapor phase epitaxy

Abstract Thin films of gallium nitride (GaN) were successfully prepared by our atmospheric pressure (AP) organometallic vapor phase epitaxy (OMVPE) system using GaN buffer layer over basal plane (0001) sapphire substrates. In the present study, strong band-edge photoluminescence (PL) in GaN films is observed. The variations of the growth temperature and ammonia/trimethylgallium (NH 3 /TMG) mass flow ratio with the full width at half maximum (FWHM) of band-edge luminescence ( I BE , respectively, indicate that we could obtain ranges of the growth temperature and the NH 3 /TMG ratio to have high quality GaN single crystal. The band-edge to deep-level luminescence ( I DL ) ratio ( I BE / I DL ) also reveals that we could obtain optimized appropriate growth temperature and the supply of active nitrogen of excellent optical properties.

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.