Kyoo Ho Kim

Growth and Properties of Stannite-Quaternary Cu2ZnSnSe4 Thin Films Prepared by Selenization of Sputtered Binary Compound Precursors

Cu2ZnSnSe4 (CZTSe) thin films were grown on Corning glass 1737 by sequential methods of sputtering deposition and selenization process. As-grown films showed that elemental Cu, Zn, and Sn were in the nearly CZTSe stoichiometric ratio with Se-deficiency as detected by Energy Dispersive X-Ray spectrometry (EDX). In order to attain film stoichiometry, as-deposited films were subjected to selenization process in tube furnace under Ar ambient at different selenization temperatures for 10-60 min. It was found that compositions of binary compound in the sputtering target as well as selenization are critical for the growth of the CZTSe films. The structural characteristics of the selenized CZTSe films revealed a highly oriented stannite CZTSe phase with (112), (220/204) and (312/116) growth orientations and a CuSe secondary phase. By using 0.5% KCN solution, CuSe secondary phase could be totally etched from the CZTSe film surface.

Growth of Cu(In1-xAlx)Se2 Thin Films by Atmospheric Pressure Selenization of Sputtered Precursors

Cu(In1-xAlx)Se2 films were prepared using a two-stage process of sputtering and selenization. Stacked elemental layer precursors of Cu, In and Al were deposited onto corning glass substrates by RF magnetron sputtering. Precursors with different Cu/(In+Al) and In/Al ratio were selenized using elemental Se-vapor at atmospheric pressure in a commercial tube furnace under constant argon gas flow. Films with good adhesion to the substrate were grown successfully. All of the films show strong (112) and (220)/(204) CIS peaks. Addition of Al, at expense of In, shifts the peaks towards higher 2θ. This paper explores the possibility to use sputtering deposition and selenization process to grow Cu(InAl)Se2 thin films for solar cells applications.

Synthesis of Cu(In0.75Al0.25)Se2 Thin Films from Binary Selenides Powder Compacted Targets by Sputtering and Selenization

Cu(In0.75Al0.25)Se2 thin films were prepared using both one-step sputtering and two-stage process involving sputtering and selenization. Structure and properties of the films were analyzed and compared between the methods. All films had good adhesion to the substrate and showed strong (112), (220)/(204) peaks while minor secondary phase CuxSe was observed in the films from selenization. This paper compares the visibility of one step sputtering process and selenization of sputtered binary selenides layers to produce Cu(InAl)Se2 thin films (CIAS) for solar cell absorber applications. One step sputtering deposition from binary selenides powder compacted targets can produces CIAS films with better structural and optical properties compared to films produced by selenization of sputtered precursors.

The effect of gallium concentration and substrate temperature on the properties of Ga-Doped ZnO thin films sputtered from powder compacted target

Gallium-doped zinc oxide films with an average thickness of 300 nm were grown on corning glass 1737 substrate by radio frequency (RF) magnetron sputtering using powder compacted target with Ga concentrations of 0 wt.%, 2 wt.%, and 4 wt.%. The structural, optical and electrical properties of the films were investigated. During sputtering, deposition temperature was varied from room temperature to 200°C in 50°C intervals. All films were polycrystalline, having a preferred growth orientation with thec-axis perpendicular to the substrate. By increasing Ga concentration and substrate temperature, the peak height corresponding to the (002) plane was significantly increased. Columnar structure was clearly observed in the film deposited with a Ga concentration of 4 wt.% regardless of deposition temperature. The lowest resistivity achieved was 4×10−3 Ωcm at a Ga concentration of 4 wt.% grown at 200°C. All doped films showed an overall transmittance in the visible spectra of above 90%.

Highly c-Axis Oriented Al-Doped ZnO Thin Films Grown in Premixed H2/Ar Sputtering Gas

Al-doped ZnO (AZO) thin films were grown on Corning 1737 glass by RF Magnetron Sputtering under premixed hydrogen-argon (H2/Ar) sputtering gas. It is found that the introduction of various H2 concentrations during sputtering deposition altered the properties of Al-doped ZnO films. The presence of H2 during AZO growth at low deposition temperature leads to the growth of a-axis preferential orientation crystal whereas c-axis preferential orientation occurred only at higher deposition temperature. Highly oriented c-axis (002) crystal has been successfully grown under 3% H2 concentration at 200°C deposition temperature. Film’s resistivity is appeared to be a function of H2 concentration. Additional H2 concentration in sputtering gas increased of film’s transmittance up to 85% at visible-near infra red spectra while it caused the Burstein-Moss shift toward the blue region at 350 nm wavelength.

Highly Transparent and Low Resistivity Al-Doped ZnO Thin Films Grown by Pulsed Laser Deposition under Different Oxygen Flow Rates

Polycrystalline Al-doped ZnO (AZO) thin films with a thickness of 1300 Å were grown on Corning 1737 glass by pulsed laser deposition (PLD) at a low substrate temperature. The presence of oxygen gas during deposition led to a remarkable enhancement of the (002) c-axis preferential orientation as well as increased crystallite size. Highly transparent films with a transmittance of 85% could be obtained by controlling the oxygen flow rate, while causing a Burstein-Moss shift toward a shorter wavelength as well. The resistivities of the films were found to be functions of both the oxygen flow rate and substrate temperature, with the lowest value being 2.3 x 10-4 Ωcm (18Ω/sq sheet resistance). It was found that both the oxygen flow rate and substrate temperature are crucial in order to grow superior device quality films with an appropriate degree of crystallinity, less surface roughness, high transmittance and low resistivity, which are characteristics of great technological importance.

Cu 2 ZnSnSe 4 Thin Films Preparation by Pulsed Laser Deposition Using Powder Compacted Target

Cu 2 ZnSnSe 4 thin films for solar absorber application were prepared by pulsed laser deposition of a synthesized Cu 2 ZnSnSe 4 compound target. The film’s composition revealed that the deposited films possess an identical composition with the target material. Further film compositional control toward a stoichiometric composition was performed by optimizing substrate temperature, deposition time and target rotational speed. At the optimum condition, X-ray diffraction patterns of films showed that the films demonstrated polycrystalline stannite single phase with a high degree of (112) preferred orientation. The absorption coefficient of Cu 2 ZnSnSe 4 thin films were above 10 4 cm -1 with a band gap of 1.45 eV. At an optimum condition, films were identified as a p type semiconductor characteristic with a resistivity as low as 10 -1 Ωcm and a carrier concentration in the order of 10 17 cm -3 .

Preparation and characterization of sputtered CuInSe 2 thin films using a single target composed of a mixture CuSe and InSe binary selenides powders

In this study, the viability of growing a CuInSe2 thin film solar absorber by sputtering using a single target composed of CuSe and InSe powders was investigated. It was found that the ability to obtain a sputtered film with a stoichiometric composition was greatly dependent on the substrate temperature and that the optimum conditions could be obtained by adjusting the sputtering radio frequency power. A single phase chalcopyrite CuInSe2 film with a nearly stoichiometric composition and strong (112), (220/204) and (312/116) reflections was successfully grown under the optimized growth condition. The CuInSe2 films exhibit an absorption coefficient of 104 cm-1 and an optical band gap of 1.0 eV. According to the Hall measurements, the sputtered CuInSe2 film showed p-type semiconductor characteristics, which is in good agreement with the non-stoichiometry (Deltay>0) and non-molecularity (Deltax) model.