Doubly-valent rare-earth ions in halide crystals

The spray pyrolysis technique is employed to prepare thin films of SnS on glass substrates and SnS2 on glass as well as fluorine doped tin oxide (FTO) coated glass substrates. The pyrolysis temperatures of SnS and SnS2 are 350 °C and 275 °C, respectively. The films are found to be n-type semiconductors. The SnS thin film is amorphous, whereas the SnS2 shows polycrystalline structure and the calculated average grain size is 115 A for SnS2 on glass and 324 A on the FTO substrate. From an analysis of the high absorption region data a direct-allowed transition at 2.44 eV has been observed for SnS2 . In the optical investigations of SnS layers an non-direct-allowed transition at 1 eV is revealed. The corresponding absorption coefficients near the fundamental absorption edge are ~2 × 104 cm-1 and 4.6 × 103 cm-1 for SnS2 and SnS thin films. The room temperature dark conductivity of SnS is of the order of 10-3 -1 cm-1 and 10-4 -10-3 -1 cm-1 for SnS2 films. The corresponding photoconductivity values of SnS, SnS2 on glass and SnS2 on FTO are ten, four and two times higher than the dark conductivity.

https://iopscience.iop.org/article/10.1088/0022-3727/33/9/304/pdf

Spray pyrolytic deposition and characterization of SnS and SnS2 thin films

The electrical conductivity and the Hall effect are investigated in the temperature region from 77 to 1000 K on undoped ZnO single crystals grown by vapour phase transport. The growth conditions were systematically altered to get crystals with definite non-stoichiometry. The electrical properties are related to these growth conditions. The analysis of the Hall data yields the phase boundary ZnO/Zn and a formation enthalpy of 1.5 eV for the dominant native donor. This donor is suggested to be the oxygen vacancy. The Hall mobility is analysed with regard of new aspects giving a smaller anisotropy than in earlier analyses.

Electrical properties and non‐stoichiometry in ZnO single crystals

In the field of photovoltaics, semiconductors of the III-V group such as GaAs and InP have been considered as the most efficient absorber materials due to their direct energy band gap and high mobility. In these compounds, arsenic and phosphorus are highly toxic and expensive. In this work we present systematic preparation of low cost SnS thin films and characterize these films to test their suitability for photovoltaic applications. We have observed that the films (with thickness ≅0.5μm) grown at the substrate temperature of 275°C exhibit a low resistive single SnS phase and have a direct optical band gap of 1.35eV with an absorption coefficient of ∼105cm−1. SnS films could be alternative semiconductor materials as absorbers for the fabrication of photovoltaic devices.

Microstructure dependent physical properties of evaporated tin sulfide films

We demonstrate the fabrication of an all-dielectric omnidirectional mirror for visible frequencies. The dielectric reflector consists of a stack of 19 alternating layers of tin (IV) sulfide and silica. Using a combination of thermal evaporation (for tin sulfide) and thick electron-beam evaporation (for silica), we have achieved a refractive-index contrast of 2.6/1.46 , one of the highest refractive-index contrasts demonstrated in one-dimensional photonic bandgap systems designed for the visible frequency range. The tin sulfide-silica material system developed allowed the formation of a broadband visible reflector with an omnidirectional range greater than 10%. Possible applications of the system include efficient reflectors, high-frequency waveguides for communications and power delivery, and high- Q cavities.

Dielectric omnidirectional visible reflector.

The optical gap Eo and photocurrent peak Ep were investigated in amorphous SnS2 films evaporated onto glass substrates kept at a temperature from 294 to 609 K. For substrate temperatures up to 343 K, the film grew into an amorphous state with Eo=1.05+or-0.1 eV and Ep=2.1+or-0.05 eV. With increasing temperature, Eo increased markedly to 1.93 eV, while Ep decreased to 1.50 eV. By considering the results of radial distribution function obtained from the analysis of X-ray diffraction, the increase of Eo was explained in terms of a transition from an amorphous to a polycrystalline state. The substrate temperature dependence of the density of states was discussed including the result of two-step activation processes of electrical conductivity.

https://iopscience.iop.org/article/10.1088/0022-3727/22/1/019/pdf

Effects of substrate temperature on absorption edge and photocurrent in evaporated amorphous SnS2 films

Crystal Growth and Photoconductive Effects of Stannic Chalcogenides

In heavily manganese doped CaF 2 , three kinds of Mn 2+ centers and exchange coupled pairs other than the usual Mn 2+ centers in cubic crystal fields were found at room temperature. The spin Hamiltonian parameters are (I) g =2.00, | D |=740(G), E =36(G), A =80(G), a s =12(G) and a p =2∼3(G); (II) g =2.00, | D |=938(G), E =20(G), A =67(G), a s =11.2(G) and a p =1∼2(G); (III) g =2.00, | D |=1250(G), E =0(G), A =64(G) and a [111] =15.1(G), respectively.

ESR Study of Manganese Complexes in Heavily Doped CaF 2 Crystals

ESR study of europium ions in hydrolyzed CaF2:Eu crystals

In RbCl: Eu 2+ crystals, there are found three groups of EPR spectra with an intensity ratio of 2: 1: 1, which are attributed to off-center displacements of Eu 2+ ions along [111] axis from normal lattice sites. The spectra of the off-center Eu 2+ ions can be described by combining the spin Hamiltonian in an orthorhombic field and the perturbation terms depending on the magnetic field as follows; \(\mathscr{H}{=}g\beta\textbf{\itshape HS}+\sum_{l{=}1}^{3}\sum_{m{=}0}^{l}\text{B\)_2l^2m O _2l^2m\(}+\textbf{\itshape AIS}+u\beta[S_{x}^{3}H_{x}+S_{y}^{3}H_{y}+S_{z}^{3}H_{z}-\frac{1}{5}(\textbf{\itshape SH})[3S(S+1)-1]]+U[S_{x}^{3}I_{x}+S_{y}^{3}I_{y}+S_{z}^{3}I_{z}-\frac{1}{5}(\textbf{\itshape SI})[3S(S+1)-1]]\), where g =1.995, b 2 0 =294.6, b 2 2 =-139.8, A 151 =-31.3, u =-0.2∼0.9, U =0∼-0.05 (10 -4 cm -1 ) at room temperature. The displacement is estimated from the angles between the principal axes and [110] directions to be 0.082 a ( a : anion to cation distance), and the induced dipole moment to be 2.57 ...

Minoru Sumita

Papers

Effects of substrate temperature on absorption edge and photocurrent in evaporated amorphous SnS2 films

Crystal Growth and Photoconductive Effects of Stannic Chalcogenides

ESR Study of Manganese Complexes in Heavily Doped CaF 2 Crystals

ESR study of europium ions in hydrolyzed CaF2:Eu crystals

ERR of Off-Center Eu 2+ Ions with Resolved Structures in RbCl