Hideki Nishimura

Photoluminescence spectra of p-GaSe doped with Cd

Impurity levels in Cd‐doped GaSe have been studied by using photoluminescence (PL) measurements. The PL spectra at 77 K are dominated by three new emission bands at 1.95, 1.75, and 1.62 eV. The PL intensity and the peak energy of the 1.95 and 1.62 eV emission bands are measured as a function of the temperature. It is shown that the 1.95 eV emission band is due to the transition between the conduction band and the acceptor level at 0.18 eV above the valence band. The 1.62 eV emission band is caused by the transition from the donor level at 0.37 eV below the conduction band to the acceptor level at 0.13 eV above the valence band. The PL intensity increases with increasing Cd concentration.

Temperature dependence of photoluminescence of layer semiconductor p-GaTe

The photoluminescence (PL) spectra of undoped p-GaTe at 97 K are dominated by two emission bands at 1.76 and 1.59 eV. For the 1.76 eV emission band, the behavior of the peak energy and full-width at half-maximum as a function of temperature shows the characteristics of the recombination mechanism for the free exciton. We find, from the temperature dependence of the PL intensity of the 1.59 eV emission band, that the band is caused by the transition from the donor level to the acceptor level located at 0.15 eV above the valence band.

Structural Phase Transitions of Ga2Se3 and GaSe under High Pressure

High pressure X-ray powder diffraction studies have been made on α-Ga 2 Se 3 up to 27 GPa and e-GaSe up to 64 GPa by using synchrotron radiation. A structural phase transition is observed for α-Ga 2 Se 3 at 14 GPa, as is observed in β-Ga 2 Se 3 , The diffraction patterns of the high pressure phases of α- and β-Ga 2 Se 3 are almost the same, showing that the structures of the high pressure phases of both α- and β-Ga 2 Se 3 are the same. On the other hand, the structural phase transition for e-GaSe is observed near 25 GPa. The diffraction pattern of the high pressure phase of GaSe is similar to that of Ga 2 Se 3 . This shows that the high pressure phase of GaSe is similar to that of Ga 2 Se 3 , although the atomic concentrations in the alloys are different between Ga 2 Se 3 and GaSe. Most of the diffraction profile of the high pressure phase is explained by a NaCI type structural model, suggesting that the high pressure phase has a structure similar to NaCI.

Optical and Electrical Properties of p-GaAe Doped with Sb

Measurements of photoluminescence (PL) and Hall effect have been made on Sb-doped p-GaSe. The PL spectra at 77 K are dominated by two new emission bands at 1.75 and 1.66 eV. The 1. 66 emission band is enhanced by adding Sb. The temperature dependences of the peak energy and the PL intensity of 1.66 eV emission band reveal that the acceptor level is located at 0. 09 eV above the valence band. The deep acceptor level located at 0. 57 eV above the valence band is detected by using Hall effect measurements. We found that the deep acceptor level is probably associated with defects or defect complexes formed by Sb atoms in the interlayer

Photoconductivity and Photoacoustie Spectra of Trigonal, Rhombohedral, Orthorhombic, and α-, β-, and γ-Monoclinic Selenium

Photoconductivity and photoacoustic spectra of all known crystalline allotropes of selenium have been measured. Both the photocurrent peaks and the absorption edges have a tendency to shift monotonously to lower energy region with the increase in density, even though the constituents of the crystals are different, suggesting that the band gap decreases with the increase in intermolecular interaction.

Optical Properties of Ga2Se3 under High Pressure

The optical absorption spectrum of β-Ga2Se3 has been measured at pressures up to 7 GPa using a diamond anvil cell. The exciton absorption is observed in the optical absorption spectrum at ambient pressure. With increasing pressure, the exciton line shifts to the higher energy region. From the shift of the exciton line with pressure, the pressure dependence of the band gap energy (dEg/dP) is estimated to be (45 ± 4) meV/GPa at ambient pressure. This pressure coefficient agrees well with that obtained previously by photoluminescence measurements. The pressure coefficient of the band gap and the intensity of the exciton line decrease gradually with pressure, and become almost zero at 7 GPa, what suggests that a pressure induced direct- to indirect-gap semiconductor transition occurs.