Tomoyoshi Aono

Absorption and Reflection of Vapor Grown Single Crystal Platelets of β-Ga2O3

Absorption and reflection spectra of β-Ga2O3 are measured with polarized light in the wavelength region near its absorption edge. The crystals of β-Ga2O3 are grown by using a Ga/HCl/O2/Ar vapor reaction system. The platelike crystals of β-Ga2O3 have (100), (010), and (001) surfaces, and the major surface is (100). The energies of the absorption edge are observed to be 4.90 eV for E//b, 4.54 eV for E//c, and 4.56 eV for E⊥b&c at room temperature. The energies for E//b and for E//c at 77 K are larger than those at room temperature by 40 meV and 220 meV, respectively. Reflection minima are observed at 5.06 eV and 5.30 eV for E//b, and at 4.63 eV and 5.30 eV for E//c at room temperature.

Near‐blue photoluminescence of Zn‐doped GaS single crystals

The photoluminescence and optical absorption properties of Zn‐doped GaS crystals prepared by the iodine vapor transport method are reported. Undoped GaS crystals are also used for comparison. Zn substituted for a Ga site acts as an acceptor having a deep energy level and forms a complex with the iodine coactivator, which can be the luminescence center. When increasing the charged amount of Zn, the near‐blue emission band of 2.47 eV at 97 K becomes dominant, while the 2.17‐eV emission band due to the Ga vacancies, which is dominant in the undoped crystals, gradually vanishes because of the reduction of the Ga vacancies. It is thus described that Zn is a promising dopant in GaS for near‐blue‐light‐emitting devices.

A comparative study of visible photoluminescence from anodized and from chemically stained silicon wafers

Photoluminescence characteristics of anodized porous layers and chemically stained films are compared. A luminescence and an absorption band observed commonly in both materials suggest existence of similar luminous materials, though anodized samples show additional absorption bands. Consideration of both the properties of porous silicons and anodization conditions suggests that the luminous material contains silicon suboxide. The luminous material, prepared even under pure anodization conditions, is not an anodized product, but a chemical product on the surface of anodized layers, formed simultaneously with anodization.

Thermal Crystallization of Amorphous Se Film

The crystallization of amorphous Se film was studied by measuring the rate at which Se molecules were thermally evaporated and sublimated from the film. It was found that the activation energy of the crystallization was equal to the average of the activation energies required for the evaporation and sublimation of Se molecules. Using this result, a model for the crystallization mechanism of amorphous Se is proposed.

Magneto-Seebeck Effect of Pb-Doped Bi–Sb

The Seebeck and the magneto-Seebeck coefficients, α and α(B), of Pb-doped Bi–Sb alloys have been measured at low temperatures, and are compared with those of undoped Bi–Sb alloys. α and α(B) of the undoped Bi–Sb crystal are negative, and the longitudinal Nernst coefficients Δα=α(B)-α have values of -50~-300 µV/kT in a magnetic field at low temperatures. α of Pb-doped Bi–Sb crystal (less than 0.5 mol% Pb) is positive below a critical temperature (120~150 K) and changes to negative above this temperature. However, Δα of Pb-doped Bi–Sb crystal is positive, +10~+50 µV/kT, in the whole temperature range.

The Nernst Effect of Bi-Sb Alloys

Temperature dependence of the transverse and longitudinal Nernst effect has been measured on Bi-Sb alloys containing 3-12 at% Sb in weak magnetic field. Nernst coefficient was found to differ for the heat flow along the binary and bisectrix axis. The influence of Sb admixture on the transverse coefficient appears for the binary axis at first and then for the bisectrix axis. When the temperature is made lower the transverse Nernst coefficient increases its magnitude monotonically without changing its sign. The longitudinal coefficient was found to have a sign opposite to the longitudinal coefficient. The results of these observations are shown to be explained by taking into account the fact that these alloys are intrinsic but the mobility ratio changes with Sb concentration.