Giang T. Dang

Successful Growth of Conductive Highly Crystalline Sn-Doped -Ga2O3 Thin Films by Fine-Channel Mist Chemical Vapor Deposition

Highly crystalline α-phase gallium oxide (Ga2O3) thin films were grown by fine-channel mist chemical vapor deposition on c-sapphire substrates at 400 °C at a deposition rate of more than 20 nm/min. The thin films were doped with Sn(IV) atoms, which were obtained from Sn(II) chloride by the reaction SnCl2+ H2O2+ 2HCl→SnCl4+ 2H2O. Conductive α-phase Ga2O3 thin films were successfully grown from source solutions containing less than 10 at. % Sn(IV). The source solution containing 4 at. % Sn(IV) resulted in obtaining a thin film with an n-type conductivity as high as 0.28 S cm-1, a mobility of 0.23 cm2 V-1 s-1, a carrier concentration of 7×1018 cm-3, and a full width at half maximum (FWHM) of the (0006) reflection X-ray rocking curve as low as 64 arcsec.

Pulsed laser excitation power dependence of photoluminescence peak energies in bulk ZnO

Photoluminescence (PL) spectra of hydrothermal bulk ZnO were measured in the temperature range from 5 to 298 K. The sample was excited by means of the 266-nm line of an Nd3+: YAG Q-switched pulsed laser with numerous average excitation powers in the range from 0.33 to 7.50 mW. At constant temperatures, the most intense PL peak red-shifts with average excitation power, whereas positions of other near-band-edge peaks remain unchanged. It was experimentally proven that the red-shift is not due to local heating at the excited spot. Rather, it is due to relaxation of photoexcited carriers to lower energy transitions as the most intense transition is saturated by high excitation photon density. Furthermore, the temperature dependence of energy of the most intense PL peak was fitted with the Varshni equation. The Varshni coefficients α and β decrease with increasing pulsed laser excitation power.

Photoluminescence of an Al0.5Ga0.5As/GaAs multiple quantum well in the temperature range from 5 to 400 K

Photoluminescence (PL) of an unintentionally doped Al0.5Ga0.5As/GaAs multiple quantum well (MQW) has been measured at temperatures from 5 to 400 K. It was found that the ratio of the intensity of the n=1 electron-light hole transition (1e-1lh) to that of the n=1 electron-heavy hole transition (1e-1hh) can be described by an exponential function of reciprocal temperature. The excitation-power dependence of the 1e-1hh transition PL intensity measured at temperatures from 5 to 296 K in steps of 15–20 K showed that the relative contribution of free-carrier recombination gradually increases from 5 to 120 K and then remains constant. This tendency was confirmed by the temperature dependence of the energy difference between the 1e-1hh transition and the bulk GaAs band gap.

Photoluminescence, morphology, and structure of hydrothermal ZnO implanted at room temperature with 60 keV Sn+ ions

Hydrothermal ZnO wafers implanted at room temperature with 60 keV Sn+ ions are examined by means of photoluminescence (PL), atomic force spectroscopy (AFM), and X-ray diffractometry techniques. The PL intensity significantly decreases in the wafers implanted to doses of 4.1 × 1013 ions/cm2 and higher. The AFM measurements indicate that surface roughness variation is not the cause of the significant decrease in PL intensity. Furthermore, the PL deep level (DL) band peak blueshifts after illuminating the implanted samples with the He-Cd laser 325 nm line; meanwhile, the DL band intensity first increases and then decreases with illumination time. These abnormal behaviors of the DL band are discussed.

Characteristics of ZnO Wafers Implanted with 60 keV Sn+ Ions at Room Temperature and at 110 K

ZnO wafers implanted with 60 keV Sn+ ions at room temperature (RT) and at 110 K are investigated by means of X‐ray diffraction (XRD) and photoluminescence (PL) techniques. The effect of implantation temperature is evident in the XRD and PL data. A yellow‐orange (YO) band near 600 nm appears in the PL spectra of the ZnO wafers implanted to the doses of 4×1014 and 8×1014 ions/cm2 at RT. The intensity of this band increases and the peak position blue‐shifts after illumination of the samples with the 325 nm line of a He‐Cd laser. The PL data suggests that the CB (conduction band)→VO+ and Zni+→VZn− transitions contribute to the photoemission of the YO band.

Incorporation of yttrium to yttrium iron garnet thin films fabricated by mist CVD

Yttrium iron garnet (YIG) thin films were deposited on c-plane sapphire substrates under atmospheric pressure by a mist CVD technique, and their chemical composition and optical properties were examined. The thin films deposited at 450 °C showed an [Y]/[Fe] ratio of 0.57, indicating the deposition of yttrium iron oxide, while the molar ratio of [Y]/[Fe] in the precursor solution was set at 1.5. A thermodynamic model was developed to explain the reaction paths of the YIG thin film fabrication process using thermogravimetric differential thermal analysis (TG-DTA) results. The model indicates that the decomposition rate of yttrium acetylacetonate [Y(acac)3 nH2O] was much lower than that of iron acetylacetonate [Fe(acac)3], providing a plausible explanation for the large difference between the composition ratio of the thin films and that of the precursor solutions.