K. Rajeev Kumar

Effect of ZnO Buffer Layer on the Structural and Optical Properties of Zn2GeO4 : Mn2 + Thin Films

Mn 2+ -activated Zn 2 GeO 4 phosphor thin films were deposited on quartz substrates using the radio frequency magnetron sputtering technique. The crystallanity, composition ratio, and luminescent behavior of the films were highly sensitive to the deposition parameters. Zn 2 GeO 4 :Mn 2+ films grown on amorphous substrates were polycrystalline in nature, whereas those deposited on the ZnO buffer layer were highly oriented along the (220) plane under similar deposition conditions. Tauc plot analysis of the Zn 2 GeO 4 :Mn 2+ films grown on ZnO/quartz substrate exhibits strong subband absorption in comparison to the Zn 2 GeO 4 :Mn 2+ film deposited on quartz substrate. The spectral overlap between the subband states and excited levels of Mn 2+ is more favored with the buffer layer presence improving the resonant energy transfer from the host to the activator. The subsequent 4 T 1 - 6 A 1 transition in the Mn 2+ levels results in the green photoluminescent (PL) emission at 540 nm. The maximum PL emission is observed for the film deposited at 650°C. The photoluminescent excitation spectra of Zn 2 GeO 4 :Mn 2+ film on ZnO/quartz substrate showed a blueshift with substrate temperature.

Simple one step spray process for CuInS2 / In2S3 heterojunctions on flexible substrates for photovoltaic applications

Flexible semiconducting devices such as solar cells and displays have been a recent attraction. Unlike heavy, brittle glass substrates, plastics and metallic foils have advantage of flexibility. They also have added advantages like good thermal stability and high melting point. In this paper we present a very simple method for the growth of Copper Indium Sulphide (CIS) films by depositing merely Indium Sulphide (InS) directly over the Cu foil using simple and economical chemical spray pyrolysis technique. The effects of volume of precursor solution on structural and morphological properties of the films were studied. Finally trials on heterojunctions with a structure of Cu foil/CIS/InS/Ag were also employed. Further improvement on heterojunction is expected by optimizing the morphological and structural properties of the film.

Deposition and characterization of CuInS2 thin films deposited over copper thin films

Simple, cost effective and versatile spray pyrolysis method is effectively combined with vacuum evaporation for the deposition of CuIns2 thin films for photovoltaic applications. In the present study In2s3 was spray deposited over vacuum evaporated Cu thin films and Cu was allowed to diffuse in to the In2S3 layer to form CuInS2. To analyse the dependence of precursor volume on the formation of CuInS2 films structural, electrical and morphological analzes are carried out. Successful deposition of CuInS2thin films with good crystallinity and morphology with considerably low resistivity is reported in this paper.

Modification of opto-electronic properties of ZnO by incorporating metallic tin for buffer layer in thin film solar cells

In this report, the effect of incorporation of metallic tin (Sn) on opto-electronic properties of ZnO thin films is presented. ZnO thin films were deposited through ‘automated chemical spray pyrolysis’ (CSP) technique; later different quantities of ‘Sn’ were evaporated on it and subsequently annealed. Vacuum annealing showed a positive effect on crystallinity of films. Creation of sub band gap levels due to ‘Sn’ diffusion was evident from the absorption and PL spectra. The tin incorporated films showed good photo response in visible region. Tin incorporated ZnO thin films seem to satisfy the desirable criteria for buffer layer in thin film solar cells.

Compositional characterization of atomic layer deposited alumina

As the microelectronic industry demands feature size in the order of few and sub nanometer regime, the film composition and other film properties become critical issues and ALD has emerged as the choice of industry. Aluminum oxide is a material with wide applications in electronic & optoelectronic devices and protective & ion barrier layers. Al2O3 is an excellent dielectric because of its large band gap (8.7eV), large band offsets with silicon. We have deposited thin layers of alumina on silicon wafer (p-type) for gate dielectric applications by ALD technique and compositional characterizations of the deposited thin films were done using EDS, XPS and FTIR spectra.

Effect of power variation in a microwave film deposition unit with different loads

A microwave film deposition unit can be designed with the use of a domestic microwave oven with a quartz tube kept inside the chamber. Air is used as the medium for the formation of plasma. The plasma induced in the quartz tube is a medium for coating the nano particles in the glass substrate. Calorimetric calibration for various heating loads under standard conditions of supply voltage, time of heating, position and quantity were done. Parameters like position of the vessel in the chamber, supply voltages to magnetron, load volume and the heating time influence the load performance. The calorimetric calibrations were carried out with varying heating loads like coconut oil, engine oil, fruit juice and water. It was observed that coconut oil absorbed maximum microwave energy whereas engine oil absorbed minimum. The study points out the differences between coconut oil and engine oil with respect to their heating characteristics under exposure to microwave energy.