Anisotropy of effective masses in CuInSe2

Anisotropy of the valence band is experimentally demonstrated in CuInSe2, a key component of the absorber layer in one of the leading thin-film solar cell technology. By changing the orientation of applied magnetic fields with respect to the crystal lattice, we measure considerable differences in the diamagnetic shifts and effective g-factors for the A and B free excitons. The resulting free exciton reduced masses are combined with a perturbation model for non-degenerate independent excitons and theoretical dielectric constants to provide the anisotropic effective hole masses, revealing anisotropies of 5.5 (4.2) for the A (B) valence bands

The Comparative Investigations of Structural and Optical Properties of GaSb nanocrystals / Si layers

Optical and structural properties of GaSb nanocrystals fabricated by co-implantation of Ga and Sb ions in single crystalline Si (100), followed by thermal treatment are investigated. In the first group of samples named Si / GaSb the implantation of Ga ions was followed by Sb implantation, whereas in the second group of samples named Si / SbGa with increased by factor 1.4 ion fluence the order of implantation was inverted. The presence of nanocrystals in both kinds of samples was proved by TEM and RS experiments. Low-temperature PL measurements show a PL broad band in the region at 0.75-1.1 eV for Si / SbGa samples annealed at 900 °C. No PL was observed in the Si/SbGa samples after annealing at 1100 °C. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3516

Effects of annealing regims on the structural and optical properties of inas and gasb nanocryctals created by ion-beam synthesis in Si matrix

We have studied the ion-beam synthesis of InAs and GaSb nanocrystals in Si by high-fluence implantation of (As+In) and (Ga+Sb) ions followed a thermal annealing. In order to characterize the implanted samples Rutherford backscattering spectrometry in combination with the channelling (RBS/C), transmission electron microscopy (TEM), Raman spectrometry (RS) and low-temperature photoluminescence (PL) techniques were employed. It was demonstrated that by introducing getter, varying the ion implantation temperature, ion fluences and post-implantation annealing duration and temperature it is possible to form InAs and GaSb nanocrystals in the range of sizes of (2 – 80) nm and create different types of secondary defects distribution. RS results confirm the crystalline state of the clusters in the silicon matrix after high-fluence implantation of heavy (As+In) and (Ga+Sb) ions. Significant redistribution of implanted species has been revealed after “hot” implantation and post-implantation annealing. We have suggested that it is caused by non-equilibrium diffusion. A broad band in the spectral region of 0.7 – 1.1 eV is detected in the photoluminescence spectra of the samples. The nature of this PL band is discussed.We have studied the ion-beam synthesis of InAs and GaSb nanocrystals in Si by high-fluence implantation of (As+In) and (Ga+Sb) ions followed a thermal annealing. In order to characterize the implanted samples Rutherford backscattering spectrometry in combination with the channelling (RBS/C), transmission electron microscopy (TEM), Raman spectrometry (RS) and low-temperature photoluminescence (PL) techniques were employed. It was demonstrated that by introducing getter, varying the ion implantation temperature, ion fluences and post-implantation annealing duration and temperature it is possible to form InAs and GaSb nanocrystals in the range of sizes of (2 – 80) nm and create different types of secondary defects distribution. RS results confirm the crystalline state of the clusters in the silicon matrix after high-fluence implantation of heavy (As+In) and (Ga+Sb) ions. Significant redistribution of implanted species has been revealed after “hot” implantation and post-implantation annealing. We have suggested that it is caused by non-equilibrium diffusion. A broad band in the spectral region of 0.7 – 1.1 eV is detected in the photoluminescence spectra of the samples. The nature of this PL band is discussed. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2083

Strong Room-Temperature Photoluminescence of Si-rich and N-rich Silicon-Nitride Films

Si-rich and N-rich silicon nitride films were deposited at low temperature 300 °C by using plasmaenhanced chemical vapor deposition (PECVD). The optical and structural properties of these films have been investigated by ellipsometry, Rutherford backscattering (RBS), transmission electron microscopy (TEM), Raman spectroscopy (RS) and photoluminescence (PL). The formation of silicon clusters in both Sirich and N-rich silicon nitride films after annealing at 900 °C and 1000 °C for hour in N2 ambient has been shown by TEM. Dependency of PL spectra on stoichiometry and post-annealing temperature was analyzed. The contribution of Si and N-related defects in emitting properties of Si-rich and N-rich SiNx has been discussed. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3516

Optical spectroscopy studies of Cu2ZnSnSe4 thin films

Cu2ZnSnSe4 thin films were synthesised by selenisation of magnetron sputtered metal precursors. The band gap determined from the absorption spectra increases from 1.01 eV at 300 K to 1.05 eV at 4.2 K. In lower quality films photoluminescence spectra show a broad, low intensity asymmetric band associated with a recombination of free electrons and holes localised on acceptors in the presence of spatial potential fluctuations. In high quality material the luminescence band becomes intense and narrow resolving two phonon replicas. Its shifts at changing excitation power suggest donor–acceptor pair recombination mechanisms. The proposed model involving two pairs of donors and acceptors is supported by the evolution of the band intensity and spectral position with temperature. Energy levels of the donors and acceptors are estimated using Arrhenius quenching analysis

Influence of the growth method on the photoluminescence spectra and electronic properties of CuInS2 single crystals

A comparative analysis of free and bound excitons in the photoluminescence (PL) spectra of CuInS2 single crystals grown by the traveling heater (THM) and the chemical vapor transport (CVT) methods is presented. The values of the binding energy of the A free exciton (18.5 and 19.7 meV), determined by measurements of the spectral positions of the ground and excited states, allowed the Bohr radii (3.8 and 3.7 nm), bandgaps (1.5536 and 1.5548 eV) and dielectric constants (10.2 and 9.9) to be calculated for CuInS2 crystals grown by THM and CVT, respectively

Excited states of the A free exciton in CuInS2

High quality CuInS2 single crystals, grown by the traveling heater method in an indium solvent, were studied using reflectance and photoluminescence at 4.2 K. The first, EAn=2=1.5494 eV, and second, EAn=3=1.5532 eV, excited states of the A free exciton have been observed in the photoluminescence spectra. Accurate values of the A exciton binding energy EFE A =18.5 meV and Bohr radius aB A=3.8 nm, bandgap Eg=1.5540 eV at 4.2 K and static dielectric constant =10.2 have been derived assuming a hydrogenic model

Diamagnetic shifts of free excitons in cuins2 in magnetic fields

Single crystals of CuInS2 were studied with reflectance (RF) and photoluminescence (PL) at 4.2 K in magnetic fields up to 10 T. The diamagnetic energy shifts observed for the free excitonic lines in both the RF and PL spectra were used to calculate the reduced masses (0.141m0, 0.142m0, and 0.114m0), binding energies (18.46, 18.59, and 14.90 meV), Bohr radii (3.82, 3.79, and 4.73 nm), and hole effective masses (1.20m0, 1.28m0, and 0.40m0) for the ALPB, AUPB, and BC excitons, respectively, using a low-field perturbation approach

Characterisation of Cu(In,Ga)Se-2-based thin film solar cells on polyimide

Thin films of Cu(In,Ga)Se2 (CIGS) were deposited at temperatures below 450 °C on polyimide (PI) substrates coated with Mo in a roll-to-roll set up by a combination of co-evaporation and ion-beam techniques. Flexible solar cells ITO/i-ZnO/CdS/CIGS/Mo/PI with and without Na incorporation were then fabricated. The films and solar cells were examined by: X-ray fluorescence spectroscopy (XRF) and Auger electron spectroscopy (AES), to determine the elemental composition, as well as by X-ray diffraction for structure- and scanning electron microscopy (SEM) for morphology-analysis. Photoluminescence (PL) and PL-excitation (PLE) at temperatures from 4.2 to 78 K were also used to estimate the band-gap energy of CIGS, examine the electronic properties and defect nature. The aim of this study was to correlate the incorporation of Na with optical and structural parameters of the CIGS layers as well as with the solar cell performance