Thorsten Krämer

(001)-Textured Cu2S Thin Films Deposited by RF Reactive Sputtering

Cu2S thin films were deposited on float glass substrates by radio frequency reactive sputtering. X-ray diffraction measurements, including grazing incidence geometry, showed that the sputtered Cu2S films had hexagonal structure with a strong (001) fiber texture. The thickness, surface density and roughness of the sputtered layers were characterized by X-ray reflectivity. Scanning electron microscopy from both top view and cross section revealed good morphology and uniform microstructure of the sputtered films. Rutherford backscattering spectroscopy and energy dispersive X-ray analysis were used to examine the composition of the films. By the optical transmission measurements, the indirect and direct band gaps of the films were estimated to be 1.19 and 1.82 eV, respectively.

Post-growth treatment effects on properties of CuInS2 thin films deposited by RF reactive sputtering

Post-growth treatments, such as annealing, sulfurization, etching as well as ageing, were performed on CuInS2 films prepared by RF reactive sputtering. Their effects on the structural, optical and electrical properties of the films were studied by means of x-ray diffraction (XRD) and scanning electron microscopy (SEM), optical transmission, and Hall effect measurement, respectively. Heating under vacuum at 500 °C for a certain duration causes recrystallization of the as-sputtered films. The secondary Cu–In phases coexisting in the films sputtered with an insufficient H2S flow during sputtering can be eliminated by annealing in H2S atmosphere at 500 °C for suitable duration. Meanwhile, the film structural as well as optical properties are enhanced. The electrical properties of the as-grown films changed dramatically with ageing in air, and annealing in vacuum or air. KCN etching removed CuxS segregations on the film surfaces and returned the film electrical property to its initial state.

Influence of the preparation conditions on the properties of CuInS2 films deposited by one-stage RF reactive sputtering

Abstract We investigated systematically the influence of the sputter parameters, such as substrate temperature, H 2 S flow, and sputter power on the structural, optical, and electrical properties of the sputtered CuInS 2 films, to optimize the parameters for the one-stage growth of CuInS 2 films by radio frequency (RF) reactive sputtering. When the H 2 S flow during sputtering is too low, there are mainly Cu–In secondary phases coexisting in the films. With a RF power of 200 W and a H 2 S flow in the range of 20–30 sccm (standard cubic centimeter per minute), high quality films with good adhesion can be sputtered on bare float glass at a substrate temperature of 400 °C or above. A higher substrate temperature (500 °C) resulted in bigger grain sizes of the films. Moreover, the films sputtered at 500 °C showed a sharper absorption edge than those sputtered at 400 °C, and the corresponding band gap shifted from approximately 1.27 to 1.44 eV. Mo- or ZnO-coatings of the substrates can help to reduce the substrate temperature to 200 °C, and work effectively as a barrier to prevent Na diffusion from the substrates into the sputtered CuInS 2 layers.

Highly (112)-Oriented CuInS2 Thin Films Deposited by a One-Stage RF Reactive Sputtering Process

We demonstrate the first one-stage growth of CuInS2 films by radio frequency (RF) reactive sputtering with a Cu–In alloy target and H2S gas. High quality films of good adhesion can be sputtered either on bare float glass at a minimum substrate temperature of 400°C or on Mo- or ZnO-coated float glass at a relatively low temperature of 200°C. X-ray diffraction results revealed that the films sputtered on the bare, Mo- or ZnO-coated float glass substrates are highly (112) oriented. Typically the as-deposited films are slightly Cu-rich as determined by Rutherford backscattering spectroscopy. The surface morphology and homogeneity of the layers were as well analyzed by atomic force microscopy and secondary ion mass spectroscopy.

SURFACE AND STRUCTURAL CHARACTERIZATION OF CuInS2 THIN FILMS DEPOSITED BY ONE-STAGE RF REACTIVE SPUTTERING

CuInS2 films were deposited on float glass substrates by a one-stage reactive RF sputter process using a Cu-In alloy target and H2S gas. The sputtered films generally have a (112) preferential orientation. X-ray reflectometry was used to measure the thickness, surface density as well as surface roughness of the sputtered films. The surface morphology of the films was studied by scanning electron microscopy. Energy-dispersive X-ray analysis was performed to determine the composition of the films. XPS revealed that the film surfaces remain In-rich with respect to the bulk.