Kyung Hoon Yoon

Optical and electrical properties of Ga2O3-doped ZnO films prepared by r.f. sputtering

Abstract Optical and electrical properties of Ga2O3doped ZnO films prepared by r.f. sputtering have been investigated as functions of preparation conditions and dopant concentration in an attempt to develop transparent films with low electrical resistivity and with good stability at higher temperatures. The electrical resistivity of the sputtered films depends strongly on the r.f. power density, the argon gas pressure, the Ga2O3 concentration and the thickness of the films when the thickness is less than about 2500 A. The optical transparency depends on the thickness and dopant concentration and is almost independent of the sputtering conditions. Ga2O3-doped ZnO films become degenerate semiconductors when the carrier concentration exceeds about 1019 cm−3 and the optical band gap increases with increasing electron concentration owing to the increase in the Fermi level in the conduction band. Ga2O3-doped ZnO films 3000 A thick with an optical transmission higher than 85% and with electrical resistivity lower than 10−3 ohmcm can be produced by sputtering a ZnO target containing 5 wt.% Ga2O3 with an r.f. power density of 0.84 W cm−2 and an argon gas pressure of 5 m Torr.

Growth of CuInSe2 thin films by high vapour Se treatment of co-sputtered Cu-In alloy in a graphite container

Abstract The crystallization of CuInSe 2 thin films by high Se vapour selenization of co-sputtered Cu-In alloy precursor within a partially closed graphite container is reported. X-ray diffusion (XRD) analysis of the Cu-In alloy films displayed mainly the CuIn 2 and Cu 11 In 9 phases. A three-fold volume expansion was recorded in all the selenized CuInSe 2 films at 500–550°C. Large and densely packed crystals with sizes of about 5 μm were exhibited by the films irrespective of whether they were Cu-rich or In-rich. Single phase chalcopyrite CuInSe 2 structure with preferential orientation in the (112) direction were obtained. Films with a wide range of compositions (Cu/In of 0.43–1.2 and Se/(Cu+In) of 0.92–1.47) were fabricated. All the films where Se rich, with the exception of samples with very high Cu content. The measured film resistivities varied from 10 −1 to 10 5 Ω-cm in consistence with the increasing Cu content of the alloy precursor during deposition. The alloy films with very high In content yielded the CuIn 2 Se 3.5 or CuIn 3 Se 5 compound as determined from XRD and EDX analyses. A study of the reaction mechanism performed between 250 and 550°C indicated that the crystal growth was assisted by the formation of the CuSe flux agent. The development of a suitable window layer to test the photovoltaic properties of these films is currently in progress.

Effects of Se Flux on the Microstructure of Cu ( In , Ga ) Se2 Thin Film Deposited by a Three-Stage Co-evaporation Process

This work was financially supported by the Ministry of Commerce,Industry and Energy in Korea.

Effects of selenization conditions on densification of Cu(In,Ga)Se2 (CIGS) thin films prepared by spray deposition of CIGS nanoparticles

Spray deposited porous CIGS nanoparticle-derivedthin films were selenized in a two zone rapid thermal annealing furnace and effects of various selenization parameters including Se evaporation temperature, flow rate of carrier gas, and substrate temperature on densification of the CIGS layers were investigated. It was found that higher Se supply to CIGS nanoparticles either by increasing Se evaporation temperature or by increasing the flow rate of carrier gas resulted in larger CIGS grains with higher degree of crystallinity, while it also induced formation of a thicker MoSe 2 layer in-between CIGS and Mo which resulted in partial detachment of CIGS / MoSe 2 / Mo layers from the glass substrate. Densification of CIGS layer by growth of nanoparticles and formation of thick MoSe 2 were explained by a liquid Se assisted reaction rather than by a vapor phase Se assisted reaction.

Growth of CuIn3Se5 layer on CuInSe2 films and its effect on the photovoltaic properties of In2Se3/CuInSe2 solar cells

Abstract The growth of CuIn3Se5 layer on bulk CuInSe2 films has been studied for the fabrication of CuInSe2 solar cells, using the three-stage process which involved the sequential evaporation of In–Se, Cu–Se, and In–Se elemental sources. After growing CuInSe2 films, the film surface was converted to a defect chalcopyrite (CuIn3Se5) compound. The X-ray diffraction and AES depth analysis indicated the formation of the CuIn3Se5 phase on the CuInSe2 surface. By the formation of the CuIn3Se5 phase, the absorption edge was shifted from 1200 to 1000 nm wavelength and the binding energies of Cu, In, and Se were shifted to higher energies. The current–voltage curves of In2Se3/CuInSe2 cells fabricated with a thick CuIn3Se5 layer on a CuInSe2 film displayed a kink effect which was possibly caused by the increase of series resistance and light absorption in the CuIn3Se5 layer instead of the junction region. The cells with a thin CuIn3Se5 layer at the In2Se3/CuInSe2 interface yielded solar efficiency of 8.46% with an active area of 0.2 cm2.

Effect of CuIn3Se5 layer thickness on CuInSe2 thin films and devices

CuInSe 2 thin films were prepared by a three-stage sequential co-evaporation of In-Se, Cu-Se, and In-Se elements for photovoltaic application. After growing CuInSe 2 films, the film surface was converted to an ordered vacancy compound (CuIn 3 Se 3 ). The presence of a CuIn 3 Se 5 layer on the CuInSe 2 surface was confirmed by XRD and AES. By the formation of the CuIn 3 Se 5 phase on the CuInSe 2 surface, the absorption edge was shifted from 1200 A to a shorter wavelength. On the CIS films, an In 2 Se 3 buffer layer instead of the commonly known CdS layer was employed and deposited in the same evaporator without breaking the vacuum system. The ITO/ZnO/In 2 Se 3 /CuInSe 2 cells with a thin CuIn 3 Se 5 layer at the In 2 Se 3 /CuInSe 2 interface yielded a solar efficiency of 8.46% with an active area of 0.2 cm 2 which is considered high efficiency regarding no Ga in the CIS absorber layer.

Characterization of CuInS 2 Thin Films Grown by Close-spaced Vapor Sulfurization of Co-sputtered Cu?In Alloy Precursors

Cu–In alloy films were prepared on bare or Mo-coated glass by co-sputtering from Cu and In targets at ambient temperature. The formation of CuInS2 films was accomplished by sulfurization within a graphite container under high S vapor pressure. X-ray diffraction (XRD) analysis of the alloy films showed predominant variation of the phases from In→CuIn2→Cu11In9 as the Cu content in the films increased. The sulfurized In-rich films formed the CuIn5S8 phase that steadily transformed into CuInS2 as film composition changed toward the Cu-rich region. SEM analysis showed different morphologies for the CuIn5S8 and CuInS2 films. Cu-rich films exhibited very dense crystal structures. EDX composition measurements on the films showed Cu/(Cu+In) varying from 0.21 to 0.64 and S/(Cu+In) from 0.80 to 1.36. Resistivities in the range of 2.36 to 1.7×108 Ωcm were obtained. Studies of the growth mechanism indicated formation of CuIn5S8 as the main secondary phase in both Cu-rich and In-rich films at low temperatures before conversion into CuInS2 at temperatures >400°C.

Grain Growth Enhancement and Ga Distribution of Cu ( In0.7Ga0.3 ) Se2 Film Using Cu2Se Layer on Cu–In–Ga Metal Precursor

A precursor layer for Cu(In 0.7 Ga 0.3 )Se 2 (CIGS) was deposited by simultaneous sputtering of Cu 40 In 60 and Cu 50 Ga 50 and subsequent sputtering of Cu 2 Se. The Cu 2 Se/metal alloy-stacked precursor was selenized at 550°C in a Se vapor atmosphere to grow a CIGS film. The thickness of the Cu 2 Se layer was varied to control the Cu/(In + Ga) ratio and to study the grain growth behavior. A CIGS film with large grains can be achieved when the overall Cu/(In + Ga) ratio was above 0.92. With the existence of the Cu 2 Se layer, the Ga concentration was very low near the surface and it was accumulated near the CIGS/Mo interface. Also, the In concentration was very low near the CIGS/Mo interface. As a result, the CuInSe 2 phase was formed at the surface and the CuGaSe 2 phase was formed near the CIGS/Mo interface. The open-circuit voltage and fill factor were greatly reduced by the Ga segregation. Further supply of Ga on the selenized CIGS film reduced Ga segregation and improved the cell efficiency.

Preparation of CuInSe2 thin films by selenization of co-sputtered Cu–In precursors

CuInSe2 thin films have been prepared by high Se vapor selenization of co-sputtered Cu–In alloy precursors within a partially closed graphite container. Cu–In alloys with different compositions were investigated. X-ray diffraction (XRD) analysis of the films showed mainly CuIn2 and Cu11In9 phases and the Cu11In9 peak intensity was found to increase as the alloy composition tended towards Cu-rich. A linear dependence of the alloy composition on the Cu/In deposition power was observed from energy dispersive analysis by X-rays (EDX). A three-fold volume expansion was exhibited by all the CuInSe2 films after selenization at 500–550 °C. Scanning electron microscopy (SEM) analysis of the films showed large and densely packed crystal structures with sizes above 5 μm. The CuInSe2 films exhibited single phase chalcopyrite structure with preferential orientation in the (1 1 2) direction. The EDX composition analyses of the films showed Cu/In ratio ranging from 0.43 to 1.2, and Se/(Cu+In) ratios from 0.92 to 1.47. The measured film resistivities varied from 10-1 to 105 Ωcm. The Cu–In alloy precursors with Cu/In ratio less than 0.70 were found to form CuIn3Se5 a defect chalcopyrite compound. All films were Se rich, with the exception of samples with very high Cu content.© 1998 Kluwer Academic Publishers

Formation of CuIn1- xAlxSe2 thin films by selenization of metallic precursors in se vapor

CuIn1-xAxlSe2(CIAS) films were obtained by selenization process of metallic precursors. The metallic precursors were deposited sequentially by using sputtering system. As the ratio of Al/(Al+In) in the precursors increased, the chalcopyrite (112) peak shifted to high value and the band-gap of CIAS layer increased to 1.38 eV. However, the bi-layer morphology with well crystallized large grain on the surface and small grain thin bottom layer was observed. Although the sequences of precursors were changed in order to get uniform layer, no distinguishable difference was not observed.