V. Sundara Raja

Effect of post-deposition annealing on the growth of Cu2ZnSnSe4 thin films for a solar cell absorber layer

The effect of substrate temperature and post-deposition annealing on the growth and properties of Cu2ZnSnSe4 thin films, a potential candidate for a solar cell absorber layer, is investigated. The substrate temperature (Ts) is chosen to be in the range 523–673 K and the annealing temperature (Tpa) is kept at 723 K. Powder x-ray diffraction (XRD) patterns of as-deposited films revealed that the films deposited at Ts = 523 K and 573 K contain Cu2−xSe as a secondary phase. Single phase, polycrystalline Cu2ZnSnSe4 films are obtained at Ts = 623 K and films deposited at Ts = 673 K have ZnSe as a secondary phase along with Cu2ZnSnSe4. Direct band gap of as-deposited CZTSe films is found to lie between 1.40 eV and 1.65 eV depending on Ts. XRD patterns of post-deposition annealed films revealed that the films deposited at Ts = 523–623 K are single phase CZTSe and films deposited at Ts = 673 K still contain ZnSe secondary phase. CZTSe films are found to exhibit kesterite structure with the lattice parameters a = 0.568 nm and c = 1.136 nm. Optical absorption studies of post-deposition annealed films show that there is a slight increase in the band gap on annealing, due to decrease in the Cu content. Electrical resistivity of the films is found to lie in the range 0.02–2.6 Ω cm depending on Ts.

Optical, structural and electrical properties of tin doped indium oxide thin films prepared by spray-pyrolysis technique

Tin doped indium oxide (In2O3:Sn) or indium tin oxide (ITO) thin films have been successfully deposited by the low cost spray-pyrolysis method. Low sheet resistance and high mobility films were obtained when the films were deposited at the substrate temperature of 793 K. The direct optical bandgaps for the films deposited at 793 (a) and 753 K (b) were found to be 3.46 and 3.40 eV, respectively. Similarly, the indirect bandgaps for a- and b-type films were found to be 3.0 and 2.75 eV, respectively. The Burstein-Moss shift was observed in the films. The refractive index (n) and extinction coefficient (k) were found to be in the range of 2.1 to 1.1 and 0.6 to 0.01, respectively. The various scattering mechanisms such as lattice, ionized impurity, neutral impurity, grain boundary and alloy scattering due to variation of theoretical mobilities with temperature are discussed, in order to compare experimental results. In the lattice scattering mechanism, the quantum size effect phenomena were employed to estimate the energy dilation (EI). The a-type films exhibited SnO2 as secondary phase whereas b-type films showed single phase In2O3:Sn with high sheet resistance. The lattice constants were found to be 10.16 and 10.09 A for a- and b-type films, respectively.

Growth and characterization of co-evaporated Cu2ZnSnSe4 thin films for photovoltaic applications

Cu2ZnSnSe4 thin films are deposited using the four-source co-evaporation technique onto glass substrates held at 523, 573, 623 and 673 K and in situ annealed at 723 K for 1 h in a selenium atmosphere. XRD studies revealed that the films deposited at 523 and 573 K and annealed at 723 K contain ZnSe as a secondary phase. However, films deposited at 673 K and annealed at 723 K have Cu2−xSe as a secondary phase along with Cu2ZnSnSe4. Single phase, polycrystalline Cu2ZnSnSe4 films are obtained at a substrate temperature (Ts) of 623 K on in situ annealing at 723 K. The structure is found to be kesterite and the lattice parameters are a = 0.569 nm, c = 1.141 nm. The direct optical band gap of the films is found to lie between 1.42 and 1.57 eV for films deposited at different substrate temperatures. Electrical resistivity of the films is in the range 0.1–0.8 Ω cm depending on Ts.

Preparation and characterization of all spray-deposited p-CuIn(S0.5Se0.5)2/n-CdZnS:In thin film solar cells

Abstract All spray-deposited p-CuIn(S 0.5 Se 0.5 ) 2 /n-CdZnS: In heterojunction solar cells in the backwall configuration were fabricated. The cell exhibited an open-circuit voltage of 325 mV and a short-circuit current density of 10.3 mA/cm 2 under an illumination of 100 mW/cm 2 . The conversion efficiency of the cell was found to be 1.1%.

Growth and characterization of CuIn1−xAlxSe2 thin films deposited by co-evaporation

CuIn1−xAlxSe2 thin films (x = 0–1.0) were prepared by the four-source co-evaporation technique onto soda lime glass substrates held at 673 K. The films are found to be nearly stoichiometric as determined from Rutherford back scattering (RBS) analysis. Surface analysis of the films was carried out by x-ray photoelectron spectroscopy. X-ray diffraction and scanning electron microscopy are used to examine the structure of the films. The films are found to be single phase and chalcopyrite in structure. The lattice parameters are found to vary nonlinearly with x. Optical absorption studies reveal a three-fold optical band structure and the band gaps are found to increase nonlinearly with the increase in Al content. Crystal field and spin–orbit parameters are determined from the band gaps using a quasi-cubic model. The deformation potential and the percentage of d-orbital contribution to p–d hybridization are determined using the deduced crystal field and spin-orbit parameters. All the films are p-type conducting and the resistivity is found to increase with the increase in Al content. Room temperature Hall mobility and the carrier concentration of the films are determined.

Optical and structural properties of co-evaporated CuIn0.5Al0.5Se2 thin films

CuIn0.5Al0.5Se2 thin films are successfully prepared using a four-source co-evaporation technique on soda-lime glass substrates held at a substrate temperature of 673 K. Powder x-ray diffraction studies reveal that the films are polycrystalline in nature with chalcopyrite structure. The optical band gaps, calculated from spectral transmittance data, are found to be 1.56 ± 0.02 eV, 1.60 ± 0.02 eV and 1.85 ± 0.02 eV. Considering the three fold optical structure of chalcopyrite compounds, these are attributed to fundamental absorption and additional transitions arising out of crystal field and spin–orbit interactions. The crystal field (ΔCF) and spin–orbit (ΔSO) splitting parameters deduced from these optical band gaps are found to be −0.06 eV and 0.26 eV, respectively. The deformation potential estimated by using a quasi-cubic model is found to be −2.0 eV. The percentage of hybridization of the orbitals was determined using a linear hybridization model. The films are p-type conducting with a room temperature resistivity of 80 Ω cm.

Structural and optical properties of spray-deposited CuIn(S1−xSex)2 thin films

Abstract Cun(S1−xSex)2 films have been prepared by spray pyrolysis on heated glass substrates. Films with x = 0.0, 0.3, 0.5, 0.7, 0.9 and 1.0 have been deposited. The substrate temperatures employed for the deposition of CuInS2, CuInSe2 and CuIn(S1−xSex)2 were 550, 623 and 603 K respectively. The films exhibit p-type conductivity. They are found to be single phase and polycrystalline in nature, with the chalcopyrite structure. The lattice parameters (a and c) and the optical band gap of the films vary linearly with composition over the entire range investigated.

Measurement of third-order elastic constants of GaSb

Abstract The six independent third-order elastic constants (TOEC) of single crystal GaSb at 300 K have been determined experimentally using pulse interference technique.

Effect of substrate temperature on the properties of spray-deposited CuInS2 thin films

Abstract The effect of substrate temperature on the structural, electrical and optical properties of spray-deposited CuInS 2 thin films has been investigated. The substrate temperature has been varied from 500 to 600 K in steps of 25 K. Single-phase, near-stoichiometric CuInS 2 thin films with chalcopyrite structure have been obtained at a substrate temperature of 550 K. The optical band gap and electrical resistivity of these films are found to be 1.34 eV and 150 Ω cm respectively.

AES and XPS analyses of CuIn(S1-xSex)2thin films grown by spray pyrolysis technique

Abstract Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) analyses of CuIn(S 1−x Se x ) 2 thin films (x = 0.0, 0.5, 0.7 and 1.0) deposited by spray pyrolysis technique have been carried out. AES spectra of as-deposited films showed carbon, chlorine and oxygen as surface contaminants. Sputter etched spectra showed no trace of carbon and chlorine, but about 1.2% oxygen was found to be present. XPS analysis of CuIn(S 1−x Se x ) 2 thin films prepared under optimized conditions revealed the absence of binary secondary phases. However, Cu 2 S or CuS was found to be secondary phase in CuIn(S 0.5 Se 0.5 ) 2 thin films.