Yuriy Kudriavtsev

Formation of pn Homojunction in Cu(InGa)Se2 Thin Film Solar Cells by Zn Doping

In this study, a pn homojunction was intentionally fabricated in the Cu(InGa)Se2 (CIGS) layer by Zn doping. For Zn doping of the CIGS layer, Zn was evaporated after CIGS formation, and a potential improvement in cell performance was confirmed by this technique. Furthermore, Zn diffusion into the CIGS film was investigated by secondary ion mass spectroscopy (SIMS). A conductivity-type conversion from p-type to n-type was studied by the measurement of the cross-sectional electron beam-induced current (junction EBIC: JEBIC) and the spectral response of solar cells. A conversion efficiency of 11.5% has been achieved using the Zn-doped CIGS layer without a buffer layer and by the formation of a pn homojunction in the CIGS absorber.

High-rate deposition of silicon thin-film solar cells by the hot-wire cell method

Abstract The hot-wire cell method has been developed to grow polycrystalline and amorphous Si thin films with relatively high growth rates of 0.4–3.0 nm s −1 . It was found that polycrystalline Si films can be obtained at substrate temperatures of 175–400°C without hydrogen dilution when the filament temperature is 2000–2100°C. Valency control has been carried out using PH 3 and B 2 H 6 . Up to now, high conductivities of 13 and 4 S cm −1 have been achieved for n- and p-type polycrystalline Si thin films, respectively. Superstrate-type polycrystalline Si and amorphous Si solar cells prepared with deposition rates of 0.4–1.0 nm s −1 showed efficiencies of 1.6 and 4.3% under AM1.5 illumination, respectively. We found by SIMS analysis that a high concentration of O and C atoms, of the order of 10 20 –10 21 cm −3 , is incorporated into the film, which limits the performance of the present cell.

Bim+ ion beam patterning of germanium surfaces at different temperatures and ion fluence

Studies of pattern formation on variable-temperature Ge targets by ion beam sputtering are presented. A high-energy heavy polyatomic bismuth ion beam was used to reveal the effect of thermal spikes in the dynamics of pattern formation. By varying the target temperature in the range from 123 to 773 K, different morphologies of the irradiated surfaces were obtained. A smooth surface was observed for a target temperature of 123 K. Sputtering at a target temperature between 300 and 573 K gave rise to poorly oriented dot patterns and resulted in a checkerboard pattern at a target temperature of 773 K. Mechanisms of surface patterning under ion irradiation are discussed.

Phosphorous and Boron Incorporation and Its Effect on Electronic and Optical Properties of Ge:H Films Deposited by LF Plasma

In a previous work [1], the deposition conditions that provided low optical absorption related to both band tail and deep localized states have been found for both materials Ge: H and Si1-YGeY: H. In this work phosphorous and boron doping of Ge: H films have been systematically studied. These films were deposited by low frequency (LF) plasma under the conditions for low density of localized states whit optimal hydrogen dilution. The deposition parameters were as follow: substrate temperature Ts= 300 °C, discharge frequency f= 110 kHz, pressure P= 0.6 Torr, power W= 300 W, and the flow gas for the films of Ge: H was, germane flow QGeH4= 50 sccm, hydrogen flow QH2=2500 sccm, the phosphine flow was varied in the range of QPH3 = 20 to 100 sccm providing phosphorous concentration in gas phase in the range of XP= 4 to 20 %. For boron we used the same conditions as before, but the B2H6 flow was varied in the range of QB2H6 = 3 to 20 sccm providing concentration in gas phase in the range of XB = 0.3 to 4 %. SIMS profiling was used for determining the composition of the doped films. The hydrogen bonding was studied by FTIR. The temperature dependence of conductivity measured in DC regime was performed in a vacuum thermostat in order to study carrier transport. Optical measurements provided optical gap, absorption and refraction index. The Phosphorous incorporation to the solid film demonstrated that for the doping conditions used in this work, we obtained a constant P concentratio. But for boron incorporation, the concentration of it in the solid films increases linearly with its concentration in the gas phase. The influence of the P and B doping on the hydrogen concentration, activation energy and conductivity of the films is also studied and presented.

SIMS Study of Modern Semiconductor Heterostructures.

In this presentation we considered difficulties and perspective technique for SIMS depth profiling analysis of modern semiconductor heterostructures. Experimental measurements were performed with specially prepared samples: MBE grown delta AlGaAs layers in GaAs. It was found that primary ion induced atomic mixing in a near surface layer, and surface roughness, formed under ion irradiation, defines the final depth resolution. We performed an experimental study of parameters of the noticed physical phenomenon and found their dependence on the primary ion energy. The found results make it possible to perform deconvolution of experimental profiles and reproduce the original elemental distribution in these and similar heterostructures

Structural characterization of semi-strained layer (GaAs)1−x(Si2)x/GaAs multilayers grown by magnetron sputtering

Abstract Typical multilayers structures consisting of 3 periods with layers of GaAs and (GaAs) 1− x (Si 2 ) x were grown using magnetron sputtering. Although these multilayers are not properly superlattices because of the reduced number of layers grown, the structures grown show multiple X-ray reflections, characteristic of superlattices. A group of samples where the GaAs intermediate nominal layer thickness was kept at 810 A, and the alloy layer thickness was varied from 260 to 645 A, was grown. In all samples the nominal concentration x =0.06 for alloys layers was maintained constant. Secondary ion mass spectroscopy (SIMS), Raman spectroscopy and high-resolution X-ray diffraction (HRXRD) have been used to characterize these structures. X-ray rocking curves show interference peaks that can be attributed to a good periodicity of the layers and the comparison between experimental and simulated results shows that x value is in reality 0.085. The a ‖ and a ⊥ lattice parameters were obtained and a 12% average relaxation is deduced for the alloy layers. From Raman spectroscopy measurements the atomic concentration obtained is approximately x =0.07 which is within the experimental variation of the concentration. SIMS measurements show good layer periodicity and a x =0.075 value for alloy layer that compares well with the results of the other techniques.