G. Braunstein

Epitaxial LiTaO3 thin films by pulsed laser deposition

Epitaxial LiTaO3 thin films having excellent crystalline properties have been achieved on (0001)‐sapphire substrates using the technique of pulsed laser deposition. X‐ray diffraction analysis revealed that completely single‐phase c‐oriented LiTaO3 films were produced. X‐ray rocking curve analysis showed that the range of misalignment of the c‐axis direction was about 0.2°. Ion channeling studies indicated a minimum backscattering yield of only 4.9%. Channeling also revealed an improvement in crystalline perfection as a function of distance above the interface with the sapphire substrate. Optical waveguiding with losses on the order of 1 dB/cm was demonstrated.

A model for pulsed laser melting of graphite

A model for laser melting of carbon at high temperatures to form liquid carbon has been developed. This model is solved numerically using experimental data from laser irradiation studies in graphite consistent with a melting temperature for graphite of 4300 K. The parameters for high‐temperature graphite are based on the extension of previously measured thermal properties into the high‐temperature regime. A simple classical free electron gas model is used to calculate the properties of liquid carbon. There is very good agreement between the model calculation and experimental results for laser pulse fluences below 2.0 J/cm2. Modifications to the model for larger laser pulse fluences are discussed.

Effective p‐type doping of diamond by boron ion implantation

Highly conducting p‐type diamond layers have been obtained by high‐dose boron implantation followed by annealing (1400 °C) and subsequent removal of the graphite‐like layer that is formed as a result of the heat treatment. Conductivity and Hall measurements showed transport features typical of heavily doped semiconductors. The fact that identical carbon implantations have yielded no measurable conductivity is taken as evidence that the highly conductive p‐type layer obtained by boron implantation is indeed due to effective doping.

Can n‐type doping of diamond be achieved by Li or Na ion implantation?

The electrical conductivity of Na‐ and Li‐implanted diamond is investigated. The highest conductivities are obtained for high dose implantations followed by thermal graphitization of the heavily damaged layer and chemical removal of the graphitized layer. The temperature dependence of the resistivity is measured, yielding activation energies of 0.2 eV for Li (400<T<680 K) and for Na 0.13 eV (220<T<400 K) and 0.21 eV (415<T<670 K). Analysis of the data shows that the conduction may be understood in terms of variable range hopping between implant sites in the crystal rather than due to thermal activation.

p type doping of zinc oxide by arsenic ion implantation

p type doping of polycrystalline ZnO thin films, by implantation of arsenic ions, is demonstrated. The approach consisted of carrying out the implantations at liquid-nitrogen temperature (∼−196°C), followed by a rapid in situ heating of the sample, at 560°C for 10min, and ex situ annealing at 900°C for 45min in flowing oxygen. p type conductivity with a hole concentration of 2.5×1013cm−2 was obtained using this approach, following implantation of 150keV 5×1014As∕cm2. A conventional room-temperature implantation of 1×1015As∕cm2, followed by the same ex situ annealing, resulted in n type conductivity with a carrier concentration of 1.7×1012cm−2.

Electric-pulse-induced reversible resistance in doped zinc oxide thin films

Nonvolatile, electric-pulse-induced resistance switching is reported on S and Co doped ZnO thin films deposited on different substrates using magnetron sputtering and laser ablation. Two resistance states were obtained by applying voltage pulses of different polarity. The switching was observed regardless of the substrate, dopant species, or microstructure of the samples. In the Co doped ZnO samples, the two resistance states are remarkably stable and uniform.

Heteroepitaxy of carbon on copper by high-temperature ion implantation

The recently reported carbon‐ion‐implantation‐outdiffusion method [J. F. Prins and H. L. Gaigher, Mater. Res. Soc. Sym. Proc. (to be published, 1991)] of growing epitaxial diamond layers on copper was carefully examined. X‐ray diffraction, Raman scattering, and transmission electron diffraction characterization of films prepared by implanting 200 keV carbon ions into (100), (110), (111), and (210) copper, held at temperatures of 850–1000 °C, showed that the films were invariably highly oriented crystalline graphite. No evidence has been found to support the claim that diamond was formed by this implantation‐outdiffusion method.

Damage and lattice location studies in high‐temperature ion‐implanted diamond

The results of implantation of various ions (Li,C,P,Ge, and Sb) into heated diamond (∼1000 °C) are studied by channeling techniques. The residual damage and the locations in the lattice, which the implants occupy, are determined. It is shown that by implanting into heated diamond (i) graphitization can be avoided and (ii) an appreciable fraction of Li ions can be driven into interstitial sites where they are expected to be electrically active donors.

Characterization of proton exchange lithium niobate waveguides

Proton exchanged samples of LiNbO3 have been profiled by micro‐Raman spectroscopy, secondary ion mass spectroscopy, Rutherford backscattering channeling, and by x‐ray diffraction (XRD). Following proton exchange (PE) there are two different phases in addition to pure LiNbO3 detected by XRD. After successive annealing steps the outermost phase disappears and an interfacial region forms progressively between PE and LiNbO3. Specific vibrational bands are correlated to electro‐optic and nonlinear optical properties of the system, and the recovery of these properties upon annealing is correlated to chemical bonding changes.

The processes of formation and epitaxial alignment of SrTiO3 thin films prepared by metallo-organic decomposition

The processes of formation and crystallization of thin films of SrTiO3 prepared by the method of metallo‐organic decomposition have been studied with particular emphasis on the relationship between the thermal decomposition of the metallo‐organic precursors and the eventual epitaxial alignment of the crystallized films. The films are deposited by spin coating onto single‐crystalline silicon and SrTiO3 substrates, pyrolyzed on a hot plate at temperatures ranging from 200 to 450 °C, and subsequently heat treated in a quartz tube furnace at temperatures ranging from 300 to 1200 °C. Heat treatment at temperatures up to 450–500 °C results in the evaporation of solvents and other organic addenda, thermal decomposition of the metallo‐organic (primarily metal‐carboxylates) precursors, and formation of a carbonate species. This carbonate appears to be an intermediate phase in the reaction of SrCO3 and TiO2 to form SrTiO3. Relevant to this work is the fact that the carbonate species exhibits diffraction lines, indi...