The chemical and electrical characteristics were measured of loo-keV Si+ -implanted GaAs at doses of(6-10) X 10 12 cm-2 after rapid thermal annealing (RTA) for times of 5-40 s at temperatures between 850 and 975°C. Optimal conditions were 5 s at 930°C in either Ar or Ar-H2 atmospheres. Purity of the gas ambient was critical at the higher temperatures. Surface degradation was minimal for face-to-face annealing, as compared to exposed Si0 2 encapsulated surfaces. Essentially identical electrical characteristics were obtained by the preferred RTA conditions as compared to 30-min conventional furnace annealing under optimum conditions at 850°C using the controlled atmosphere technique. The markedly different RTA annealing times with comparable electrical characteristics are attributed to the differences in the host lattice damage recovery resulting from heat transfer and the actual duration to reach the desired anneal temperature.
The redistribution of Cr in semi-insulating GaAs upon annealing at 860 °C can be greatly reduced by eliminating the use of a SiO2 encapsulant. The annealing schedule utilized a controlled atmosphere technique which insured the thermodynamic stability of the GaAs surfaces and had no tendency to getter Cr. The sample annealed with a SiO2 encapsulant showed a secondary-ion-mass-spectroscopy-measured minimum Cr concentration which was lower by a factor of 20–25 than the original, whereas the comparison of an annealed sample without the SiO2 cap had a minimum Cr concentration which was smaller by a factor of 2. The conversion near the surfaces of semi-insulating Cr-doped GaAs to moderately high-conductivity n type upon annealing can be minimized by using the above technique without an encapsulant.
Rapid thermal annealing (RTA) for the electrical activation of 300-keV Si+ implants in GaAs at doses of (6–8) ×1012 cm−2 is shown to be superior to conventional annealing. Higher gateless field-effect transistor saturation currents and greater uniformities of the saturation current were measured as well as higher peak electron concentrations and mobilities. The advantages of RTA for the removal of ion implantation damage in GaAs are attributed to the heating rate being two orders of magnitude greater than that for furnace annealing. Characteristics are given for single- and four-cell GaAs power metal-semiconductor field-effect transitions fabricated using the above implant and optimized RTA conditions. A 1-μm gate length by 2400-μm gate width device has demonstrated an output power of 1.73 W with 4.9 dB associated gain, 30% power-added efficiency, and 8.1 dB linear gain at 10 GHz.
Two calix [4]arene derivatives, in the partial cone conformation, with sulfur-containing functionalities, were tested as neutral carrier ionophores in potentiometric silver-selective electrodes of conventional membrane and membrane-coated glassy carbon electrode types. Comparison with a calix [4]arene in the cone conformation was made. The membranes were prepared using either 2-nitrophenyl octyl ether or bis(ethylhexyl)sebacate as plasticizers and potassium tetrakis(p-chloropheny1)borate as the lipophilic salt in a poly(viny1 chloride) matrix. Both calix[4]arenes yielded electrodes of good sensitivity (approx. 47 mV dec-') in the range lop4 -lo-' M and excellent selectivity [log KAg, Mn+ < -1.51 of transition, alkali and heavy metal cations, including sodium, mercury@) and lead(n) cations. Temperature effects and reproducibility of response were determined and the interfering effects of mercury(n) and lead(n) ions on the membranes were noted. The partial cone conformation allows improved selectivity over certain cations relative to calix [4]arenes in the cone conformation.
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