V.N. Kulkarni

Synthesis and characterization of ZnO thin films for UV laser

We report on deposition of zinc oxide thin films on glass substrate at room temperature in ambient oxygen pressure ranging from 10 mTorr to 1 Torr by pulsed laser deposition. As grown polycrystalline thin films were optically pumped to investigate the dependence of laser action and photoluminescence (PL) on stoichiometry and microstrucure of the films. The intensity of the laser emission increases with thickness of the film and depends on the size of nano-crystallites. Films deposited at pressures lower than 300 mTorr showed better morphology, stoichiometry and adhesion quality. X-ray diffraction, atomic force microscopy, Rutherford back scattering and PL techniques were used to characterize as grown films.

Swift heavy ion induced modification of the Co/Si interface; cobalt silicide formation

Electron beam evaporated 60-nm Co films on Si (100) substrates were subjected to 120 MeV Au beam irradiation and subsequent thermal annealing to induce interdiffusion at the interface. Although low energy (keV/nucleon) ion beam induced mixing is known to produce cobalt silicides, the effect of MeV/nucleon radiation or swift heavy ions (SHIs), on the Co/Si system, has not been reported earlier. The irradiated and ex situ annealed samples were analyzed by Rutherford backscattering spectroscopy measurements. Respective crystalline cobalt silicide phases were identified by grazing incidence X-ray diffraction. Complete intermixing of Co and Si in the interfacial region to form CoSi was achieved following thermal annealing (at 400 °C) of the SHI irradiated Co/Si system. The radiation enhanced diffusion mechanism has been invoked to explain the SHI induced intermixing in the Co/Si system after annealing. Thermally assisted (ion generated) defect migration across the Co/Si interface enhanced defect mediated atomic mobility, which led to the formation of cobalt silicides, in accordance with the thermodynamically favored route. The post SHI irradiation annealing temperature required for the formation of crystalline phases (400 °C), is lower than that reported for low energy ion beam mixing cases where post irradiation annealing temperatures in excess of 700 °C are required for the occurrence of phases. Due to lower processing temperatures, SHI induced mixing may be considered as a promising silicidation technique in solid state technology.

Formation of Au0.6Ge0.4 alloy induced by Au-ion irradiation of Au/Ge bilayer

We report on the formation of a-axis oriented Au0.6Ge0.4 alloy on a Si(100) substrate on 120 MeV Au-ion irradiation of a Au/Ge bilayer and subsequent vacuum annealing at 360 °C. Irradiation-induced changes occurring across the Au/Ge interface were studied using Rutherford backscattering spectrometry. Phase identification was done by x-ray diffraction and the surface morphology of the samples was studied by scanning electron microscopy. Formation of oriented Au0.6Ge0.4 alloy was confirmed by transmission electron microscopy and discussed on the basis of swift heavy ion induced effects followed by thermal annealing.

Room‐temperature synthesis of copper germanide phase by ion beam mixing

This letter reports room‐temperature synthesis by ion beam mixing of the e1‐Cu3Ge phase which is a promising candidate for interconnect and contact material in very large scale integrated circuit technology. The resistivity of the mixed sample was found to be nearly the same as the one obtained from thermally prepared films. We briefly discuss the likely mechanisms of phase formation and conclude that reaction kinetics dominates over thermodynamic forces during phase formation. The sequence of phase formation is explained by effective heat of formation rule.

Physico-chemical changes in ion-irradiated KDP

Abstract We report on Mev He+ ion-induced physico-chemical changes brought into single crystalline potassium dihydrogen phosphate (KDP). Fluence-dependent hydrogen concentration has been studied by on-line elastic recoil detection analysis technique at different temperatures. Room temperature measurements show significant hydrogen loss from the samples, while at low temperature, there is no loss of H (at low fluences) or a little loss (at higher fluences). Structural changes studied by micro-Raman measurements also confirm loss of H followed by amorphization of KDP. Hydrogen depletion from KDP has been addressed in terms of basic ion–solid interaction. A phenomenological model has been used which considers ion-induced bond-breaking, diffusion of H radical, formation of H2 molecules and its release.

Atomic transport in Cu/Ge and Co/Ge systems during ion-beam mixing

Abstract This paper reports on the atomic transport occurring across the interface of Cu/Ge and Co/Ge layers leading to the synthesis of Cu 3 Ge and Co 2 Ge phases under MeV Kr and Ar ion irradiations. These phases have potential applications in modern semiconductor device technology. The marker experiments show that in the case of Cu/Ge systems both Cu and Ge are mobile but Cu is the dominant moving species. On the other hand, in the case of the Co/Ge system only Ge atoms are mobile. The atomic movements during ion irradiation in these two systems have been explained on the basis of distribution of defect density and effects of thermodynamic forces.

Ion-induced room temperature synthesis of low resistive nickel germanide phase

Low resistivity Ni2Ge phase, a promising candidate as a contact and interconnect material for very large scale integrated circuit applications, has been synthesized by MeV ion beam mixing using Kr and Ar ions at and above room temperatures. Thin films of this phase produced by ion beam mixing show resistivity comparable to the one produced by thermal annealing and is much lower than that of many important silicides. The critical temperature which marks the beginning of the temperature dependent mixing is 326 K. The room temperature mixing efficiency for this system is found to be about an order of magnitude higher than the value predicted by any of the existing ballistic and spike models. The crystalline nature of the mixed region and the occurrence of the Ni2Ge phase have been discussed.

A study of hydrogen in diamond like carbon films

Abstract Diamond like carbon (DLC) films have been produced using dc glow discharge decomposition of acetylene. Information on hydrogen content and its bonding in the films has been obtained using elastic recoil detection analysis, infrared spectroscopy and mass resolved thermal effusion measurements. DLC films having high hardness show a low hydrogen content and higher thermal stability.

ERD facility for analysis of hydrogen and deuterium in solids

Hydrogen is the lightest element in nature, and so, its detection and quantitative analysis is difficult by the conventional methods utilized for other elements. In the recent years the technique of elastic recoil detection analysis (ERD) using 1–2 MeV He+ beam has been developed to quantitatively and simultaneously analyze hydrogen and its isotopes in solids. Such a facility has been set up using the 2 MeV Van-de-Graaff accelerator at IIT Kanpur. It facilitates H and D analysis in a material up to a depth of ∼ 1µm with a detection sensitivity of 0·1 at.% and depth resolution of about 300 Å. The application potential of this setup is illustrated by presenting the results of measurements performed on Al:H:D systems prepared by plasma source ion implantation and highTc YBCO pellets exposed to humid atmosphere.

HE+ ION INDUCED HYDROGEN DEPLETION FROM A-C:H FILMS

Abstract We report room temperature He+ ion-beam induced hydrogen depletion from a-C:H films having different microstructures and H concentrations. The films were deposited on crystalline silicon substrates in a parallel plate dc glow discharge plasma reactor. Hydrogen contents of the films were measured by elastic recoil detection analysis (ERDA) technique. The H-depletion data has been explained in terms of a phenomenological model. A strong dependence of H-depletion on the film microstructure and the hydrogen contents, has been observed.