Bijoy K. Patnaik

Deposition of copper oxide thin films on different substrates by pulsed excimer laser ablation

Stoichiometric films of cupric and cuprous oxide are deposited on Si, MgO, and Y‐ZrO2 substrates by pulsed excimer laser ablation technique. It is found that the equilibrium phase diagram based considerations dictate the phase formation. The films are characterized by small‐angle x‐ray diffraction, infrared, and UV‐visible spectroscopies and Rutherford backscattering spectroscopy. It is shown that epitaxy of Cu2O films can be realized on single crystal MgO (100) substrates and the corresponding film resistivity is of the order of 40–60 Ω cm.

Transition between Ge segregation and trapping during high‐pressure oxidation of GexSi1−x/Si

A transition from Ge segregation to trapping during high‐pressure oxidation of GexSi1−x alloys has been observed. The atomic fraction x of Ge was varied from 0.4% to 26%, and oxidations were performed at 740 °C under 102 atm of dry O2. It was observed that the effect of oxidation on the Ge distribution could be divided into three stages. In the initial stage of the oxidation, Ge was segregated from the growing oxide and accumulated in a Ge‐rich layer at the oxide/alloy interface. For alloys with high Ge content this initial stage was very short. In the second stage of oxidation, after a critical quantity of Ge had accumulated at the interface, there was a transition from segregation to trapping of Ge in the oxide. In the third stage, the critical amount of Ge remained segregated at the interface, and the final oxide layer was Ge free. A kinetic model based on a steady‐state equilibrium between the diffusive flux of Si across the Ge‐rich layer and the rate of Si consumption by the oxidation reaction predic...

Purity and morphology of aluminium films

Abstract A continuous wire feed source of aluminium of 99.999% purity in conjunction with a composite ceramic boat has been used to deposit aluminium films of high purity in vacuum. The impurity content was analysed by proton-induced X-ray analysis with a Van de Graaff accelerator, supplemented by X-ray fluorescence, optical emission and Auger electron spectroscopy. The low impurity content achieved (∼ 50 atomic ppm) is attributed to the small quantity of molten aluminium maintained in the boat at one time. The morphology of the Al films was studied by reflection electron diffraction, X-ray diffraction and scanning electron microscopy. Thick Al films grew with {111} and {311} texture orientations. The grain size variation with thickness generally followed the known variation with the deposition rate.

Realization of Y1Ba2Cu3O7−δ/Y-ZrO2 epitaxial configuration on silicon (100) by pulsed laser ablation without chemical removal of native surface oxide

Abstract Epitaxial growth of Y-ZrO 2 buffer layer followed by that of the high- T c Y 1 Ba 2 Cu 3 O 7−δ on Si (100) substrate has been realized by pulsed excimer laser ( λ =248 nm ) ablation, without chemical removal of the native surface oxide on silicon. The influence of substrate surface preparation conditions and the substrate temperature on the crystallinity and quality of the Y-ZrO 2 buffer layers has been examined. it is observed that cubic Y-ZrO 2 films can be deposited epitaxially on Si (100) without chemical removal of the thin native oxide if the deposition is carried out at 800°C, initially at a reduced oxygen pressure (1 x 10 −6 Torr) followed by a deposition at higher pressure (5 x 10 −4 Torr). The crystalline qualities of the deposited films have been studied by X-ray diffraction, high resolution transmission electron microscopy (HREM) and Rutherford backscattering channeling techniques. The X-ray results reveal the high degree of c -axis orientation normal to the film surface. The χ min in the channeled RBS spectrum has been found to have values of 8% and 13% for Y-ZrO 2 and Y 1 Ba 2 Cu 3 O 7−δ films, respectively. The HREM results on the Y-ZrO 2 / Si interface show that the epitaxial layer of Y-ZrO 2 is separated from the crystalline silicon substrate by a few nanometer bridging layer of amorphous (or microcrystalline) SiO x . Typically, the superconducting films of thickness 5000 A deposited on silicon with a 1500 A epitaxial Y-ZrO 2 buffer layer have T c as high as 88 K and J c of more than 10 5 A/cm 2 at 77 K.

Determination of Si2p electron attenuation lengths in SiO2

Abstract Si2p electron attenuation lengths in SiO2 were measured at 1150 and 1380 eV using SiO2 films prepared by dry oxidation of 〈100〉 Si wafers. SiO2 thicknesses were determined using both ellipsometry and Rutherford backscattering spectrometry/channeling. Thicknesses determined by the two methods were within 3% for all but one sample. Electron attenuation lengths were calculated using three different methods, resulting in values of 3.0 nm for 1150 eV and 3.5 nm for 1380 eV.

The morphology of thick evaporated aluminium films and their purity as determined by proton-induced x-ray analysis

Abstract Aluminium films of thickness 7–65 μm were vacuum deposited using a 99.999% purity aluminium wire, a composite ceramic boat and a continuous wire feed source. The morphology and the purity of the films were studied at various deposition and wire feed rates. X-ray diffraction and scanning electron microscopy investigations showed that the films grew mostly in a one-dimensional {311} texture orientation and that the surface grain size first increased with deposition rates up to about 100 kA min-1 and then decreased. The purity of the aluminium films was studied mainly by proton-induced X-ray analysis with a 4 MeV Van de Graaff accelerator. A total impurity content of about 10 atomic ppm, composed mainly of iron, copper and zinc and in some cases lead, was observed at low and medium wire feed rates. In addition, of the light elements, magnesium was qualitatively detected.

Trace element analysis in thick targets by charged particle induced X-rays

Abstract The quantitative determination of trace impurities in a thick target through detection of X-rays produced by an accelerated charged particle involves a continuous variation of energy of the charged particle, from the incident energy to a final minimum value. Hence the expression for the X-ray yield has to be summed over a continuous range of energies. A method is described to reduce this infinite sum into a finite sum.

Reassessment of the assignment of the InM2+3+VM2+ defect in CdTe and ternary II‐VI compounds

Previous perturbed angular correlation (PAC) spectroscopy measurements on the donor indium in CdTe and its alloys have revealed several defect complexes. One defect characterized by two sets of quadrupole interaction parameters, νQ=83 MHz, η=0.08 and νQ=92 MHz, η=0.08, was observed in Hg0.8Cd0.2Te (x=0.2 MCT) and attributed to the substitutional indium–metal vacancy complex InM2+3+VM2+. A defect characterized by νQ=61±1 MHz and asymmetry parameter η between 0 and 0.19 was seen in CdTe and widely attributed to the same complex. Both of these assignments were based mainly on an observed relationship between complex formation and the loss of metal ions. In this article we present PAC measurements on 111In‐doped x=0.45 MCT (Hg0.55Cd0.45Te). These measurements reveal defects having quadrupole interactions very similar to those seen previously in CdTe and in x=0.2 MCT. Two unique defect fractions f1 and f2, characterized by νQ1=60±3 MHz, η1≊0–0.2, and νQ2=87±4 MHz, η2≊0–0.15, were seen in x=0.45 MCT, in some ca...

Deposition of epitaxial Cu2O films on (100) MgO by laser ablation and their processing using ion beams

Epitaxial thin films of Cu 2 O have been deposited on (100) MgO substrates by pulsed excimer laser ablation technique. Chemical polishing of the substrates by etching them in hot phosphoric acid prior to film deposition is found to be a critical step in realizing epitaxy. A KrF excimer laser operating at 248 nm wavelengths was used for ablation. The depositions were carried out at the laser energy density of 2 J/cm 2 and the pulse repetition rate of 5 Hz. The substrate temperature was held at 700°C and the oxygen partial pressure during deposition and cooling was 10 −3 Torr. The epitaxial nature of the deposited films was established via X-ray diffraction (XRD) and Rutherford back-scattering (RBS) channelling measurements. The epitaxial films thus obtained were then subjected to ion bombardment for studies of damage formation. Implantations were carried out using 110 keV Ar + ions over a dose range between 5 x 10 14 and 1.5 x 10 16 ions/cmz. The as-grown and implanted samples were subjected to resistivity versus temperature measurements in view of the importance of the Cu-O system in the context of the phenomenon of high temperature superconductivity.

Channeling effect of P implantation in Si(100)

Abstract With the objective of obtaining shallow junctions, we have made a comparative study of the distribution profiles of phosphorus ions implanted into Si(100) at 5 to 200 keV, along different crystalline directions, viz. the [001] axis, the (310) plane with 7° tilt away from [001], and a random equivalent direction, defined by 5.2° tilt, and 7° rotation from the (100) plane. The P implants were also performed in amorphous Si, and through a thin SiO2 layer at the same energies for comparison. The P depth profiles in Si were measured by SIMS with 14.5 keV Cs ions. The damage profiles in Si(100) crystals were studied by RBS/channeling of 2 MeV He ions. The role of the implants along the selected orientations is discussed in light of the resulting depth of the tails of the implanted dopants distribution.