R. P. S. Thakur
University of Oklahoma
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Featured researches published by R. P. S. Thakur.
Applied Physics Letters | 1991
R. Singh; S. Sinha; R. P. S. Thakur; P. Chou
When compared to furnace processing, for identical and lower substrate temperatures, more photons are available in the visible and ultraviolet regions for rapid isothermal processing (RIP) based on incoherent radiation as the energy source. In this letter, we provide experimental evidence for photoeffects in RIP for a wide variety of materials. As compared to furnace processed samples, rapid isothermal annealed phosphosilicate glass films on Si substrate show a higher value of refractive index, a lower flatband charge density, and a lower thermal stress. High‐temperature superconducting thin films on Y‐Ba‐Cu‐O deposited by RIP assisted metalorganic chemical vapor deposition on yttrium stabilized zirconia substrate show a larger grain size, a higher value of the transition temperature than their furnace counterpart. The microscopic understanding of a particular deposition or annealing process is necessary to take full advantage of photoeffects in RIP.
Journal of Applied Physics | 1991
R. P. S. Thakur; R. Singh; A. J. Nelson; H. S. Ullal; J. Chaudhuri; V. Gondhalekar
Annealing experiments were carried out on phosphosilicate glass (PSG) films deposited on (100) silicon substrates by using a low‐pressure chemical vapor deposition technique. Rapid isothermal processing and conventional furnace heating were used to study the electrical, structural, and mechanical characteristics of these films and the results of the two processes compared. A refractive index of 1.457 was obtained in the rapid isothermal annealing cycle of 800 °C/15S, but was 1.419 for the furnace annealing cycle (i.e., 800 °C/65S). Spreading resistance analysis has shown that the junction depth remains unchanged for an 800 °C/15S rapid isothermal annealing cycle. Stress measurements show that rapid isothermal annealing leads to less strain compared to furnance annealing. The x‐ray photoelectron spectroscopy analysis shows that as compared to furnance annealing, rapid isothermal annealing provides a chemically homogenous interface. High‐frequency capacitance voltage (C‐V) measurements show that furnance‐an...
Applied Physics Letters | 1989
F. Radpour; R. Singh; S. Sinha; A. M. Tulpule; P. Chou; R. P. S. Thakur; M. Rahmati; N. J. Hsu; A. Kumar
Thin films of barium fluoride (BaF2 ), used as a buffer layer between the substrate and the superconducting films, dramatically improve the properties of Y‐Ba‐Cu‐O (YBCO) superconducting films deposited by metalorganic chemical vapor deposition on yttrium‐stabilized zirconia (YSZ) substrates. For the as‐deposited films at a substrate temperature of 780 °C, the observed transition temperature Tc of 80 K on the BaF2 /YSZ structure represents the highest value reported to date. By using BaF2 buffer layers, superconducting films formed by using a paste of the YBCO powder and a binder, on BaF2 /Si provided a Tc of 80 K.
Journal of Applied Physics | 1991
R. Singh; S. Sinha; N. J. Hsu; J. T. C. Ng; P. Chou; R. P. S. Thakur; J. Narayan
Metalorganic chemical vapor deposition (MOCVD) has the potential of emerging as a viable technique to fabricate ribbons, tapes, coated wires, and the deposition of films of high‐temperature superconductors, and related materials. As a reduced thermal budget processing technique, rapid isothermal processing (RIP) based on incoherent radiation as the source of energy can be usefully coupled to conventional MOCVD. In this paper we report on the deposition and characterization of high quality superconducting thin films of Y‐Ba‐Cu‐O (YBCO) on yttrium stabilized zirconia substrates by RIP assisted MOCVD. Using O2 gas as the source of oxygen, YBCO films deposited initially at 600 °C for 1 min and at 745 °C for 25 min followed by deposition at 780 °C for 45 s are primarily c‐axis oriented and zero resistance is observed at 89–90 K. The zero magnetic field current density at 53 and 77 K are 1.2×106 and 3×105 A/cm2, respectively. By using a mixture of N2O and O2 as the oxygen source substrate temperature was furthe...
Applied Physics Letters | 1990
R. Singh; R. P. S. Thakur; A. Kumar; P. Chou; J. Narayan
Rapid isothermal processing based on incoherent sources of light is emerging as a reduced thermal budget processing technique for the fabrication of next generation of semiconductor devices and circuits. In this letter, we show that integration of the rapid isothermal processing unit and the ultrahigh vacuum deposition system provides an in situ rapid isothermal processing capability for the solid phase epitaxial growth of SrF2 and BaF2 films on (100) and (111)InP. We also show that neither as‐deposited nor ex situ annealed films show solid phase epitaxial growth.
Applied Physics Letters | 1990
R. Singh; R. P. S. Thakur; A. Katz; A. J. Nelson; S. C. Gebhard; A. B. Swartzlander
The measurement of thermal stress of SrF2 films on InP as a function of temperature is presented. The in situ and ex situ rapid isothermal annealed films have different values of thermal stress at room temperature and show entirely different behavior of thermal stress during heating and cooling cycles. X‐ray photoelectron spectroscopy measurements were used to characterize the surface of the SrF2 films as well as the SrF2/InP interface for both the ex situ and in situ annealed films. It is shown that the difference in the microstructure of in situ and ex situ rapid isothermal annealed SrF2 films on InP is indeed reflected in the significant difference in the thermal stress.
Applied Physics Letters | 1990
R. Singh; A. Kumar; R. P. S. Thakur; P. Chou; J. Chaudhuri; V. Gondhalekar; J. Narayan
Planar strain in CaF2 films on (111) Si substrate has been measured by an x‐ray double‐crystal diffraction technique using rocking curves. The films grown by a solid phase epitaxial approach using in situ rapid isothermal processing are almost free of tensile planar strain, and free from defects as observed by the transmission electron microscope diffraction pattern.
Journal of Applied Physics | 1991
R. P. S. Thakur; R. Singh; A. J. Nelson; A. B. Swartzlander
Rapid isothermal processing (RIP) based on incoherent sources of light is emerging as a reduced thermal budget (product of processing time and temperature) processing technique. As compared to stand alone annealing unit, the in situ RIP unit is very attractive for the next generation of devices. A number of unwanted physical phenomena can be suppressed or completely eliminated in the in situ RIP case leading to improved quality of materials when compared to their ex situ rapid isothermal annealed and furnace annealed counterparts. We have used in situ rapid isothermal processor for the in situ rapid isothermal chemical cleaning of InP and GaAs substrates and in situ metallization of InP and GaAs Schottky diodes. As compared to ex situ annealing, the negligible oxygen content at the surface and interface of in situ RIP samples result in better current‐voltage characteristics, lower and compressive stress values, as well as smooth and continuous morphologies of the ohmic contact. In this paper, we have highlighted the role of in situ RIP in the metallization of InP and GaAs devices.
Journal of Vacuum Science and Technology | 1991
R. Singh; S. Sinha; N. J. Hsu; J. T. C. Ng; P. Chou; R. P. S. Thakur; J. Narayan
Metalorganic chemical vapor deposition (MOCVD) has the potential of emerging as a viable technique to fabricate ribbons, tapes, coated wires, and the deposition of films of high temperature superconductors, and related materials. As a reduced thermal budget processing technique, rapid isothermal processing (RIP) based on incoherent radiation as the source of energy can be usefully coupled to conventional MOCVD. In this paper we report on the deposition and characterization of high quality superconducting thin films of Y–Ba–Cu–O (YBCO) on MgO and SrTiO3 substrates by RIP assisted MOCVD. By using a mixture of N2O and O2 as the oxygen source films deposited initially at 600 °C for 1 min and then at 740 °C for 30 min are primarily c‐axis oriented and with zero resistance being observed at 84 and 89 K for MgO and SrTiO3 substrates, respectively. The zero magnetic field current densities at 77 K for MgO and SrTiO3 substrates are 1.2×106 and 1.5×106 A/cm2, respectively. It is envisaged that high energy photons f...
Journal of Electronic Materials | 1990
R. Singh; A. Kumar; R. P. S. Thakur; P. Chou; J. Narayan; A. J. Nelson; H. S. Ullal
In general, during the deposition of epitaxial dielectrics, the substrate is heated at elevated temperatures, which is undesirable for a number of applications. In this paper we report the use of in-situ rapid isothermal processing for the solid phase epitaxial growth of CaF2 on Si (111) and BaF2 and SrF2 on InP (100) substrates. X-ray diffraction, TEM, SEM, and XPS studies of grown films have clearly established the superiority of in-situ annealing over ex-situ annealing.