It is shown that by using the forward current density-voltage (J-V) characteristics of a Schottky diode, a plot of d(V)/d(ln J) vs J and a plot of the function H(J) vs J, where H(J)≡V−n(kT/q)ln(J/A**T2), will each give a straight line. The ideality factor n, the barrier height φB, and the series resistance R of the Schottky diode can be determined with one single I-V measurement. This procedure has been used successfully to study thermal annealing effects of W/GaAs Schottky contacts.
W/GaAs diodes annealed at temperatures ranging from 100 to 900 °C were investigated with current voltage (I-V) and capacitance voltage (C-V) techniques, Rutherford backscattering spectrometry, scanning electron microscopy, and transmission electron microscopy. Improvements in the diode characteristics were observed after annealing at temperatures below 600 °C. Noticeable degradation in the rectifying behavior of the diodes occurred after annealing at temperatures >600 °C. Correlations between the electrical degradation and the interdiffusion of W and GaAs at the interface were found. Our results strongly suggest that the in-diffusion of W leads to the formation of a diffused, highly resistive region near the W/GaAs interface. The high resistance of this region is believed to be caused by the compensation of the substrate dopants by tungsten acceptors. Annealing the diodes at temperatures >850 °C resulted in reactions between W and GaAs. The W-GaAs reaction leads to islands of W2As3 at the W/GaAs interface, resulting in physical breakdown of the W/GaAs diode.
Influence of interfacial contamination on the structure and barrier height of Cr/GaAs Schottky contacts Appl.
Articles you may be interested inPlasma-induced damage of GaAs during etching of refractory metal contacts Thermal stability and barrier height enhancement for refractory metal nitride contacts on GaAs Appl. Phys. Lett. 50, 445 (1987); 10.1063/1.98169Refractory metal contacts to GaAs: Interface chemistry and Schottky-barrier formationThe electrical characteristics of reactive-sputtered refractory metal nitride contacts on GaAs are investigated for their high-temperature stability after rapid-thermal annealed up to 850·C for 10 s. It is observed that all the contacts studied, including ZrN/GaAs, TiN/GaAs, and NbN/GaAs systems, show improving rectifying characteristics with annealing temperatures up to 800-850 ·C. Not only do they maintain excellent thermal stability and have ideality factors very close to unity, these refractory metal nitride/GaAs contacts actually exhibit a barrier height enhancement ranging from O. 13 eV for NbN/GaAs to 0.30 eV for ZrN/GaAs when contacts are annealed from 500 to 850·C. Concomitantly, the small-signal capacitance of the contacts decreases with higher annealing temperature. The breakdown characteristics of these contacts become avalanche-like and the breakdown voltages increase by twofold. We have invoked the Shannon contact structure (I.e., metallp+ -GaAs/n-GaAs) to account for these hightemperature induced properties. The p -f -GaAs layer formation is attributed to the incorporation of nitrogen into GaAs substrate during sputtering deposition. Comparison between pure refractory metals and their nitride contacts on GaAs are also made with electrical techniques (I-V, c-V) and material characterization techniques (Rutherford backscattering, scanning electron microscopy). Our study suggests that refractory metal nitrides have several advantageous properties for self-aligned GaAs metal-semiconductor field-effect transistor processes.
Previous studies on acoustooptic hybrid bistable devices have been limited to the Bragg regime involving two diffracted orders, and no comparisons have been made between experimental results and theoretical predictions. In this paper, a model including both acoustooptic diffraction and a nonlinear feedback path is investigated. The Klein-Cook parameter Q has been brought into the investigation in that theoretical simulation results based on diffraction involving four diffracted orders are obtained. Experimental results are then presented and compared to theoretical predictions.
The solid-state reactions between (100) GaAs substrates and Rh films ∼150 Å and ∼600 Å thick, annealed at temperatures between 300 and 800 °C, are investigated with conventional and heavy ion Rutherford backscattering spectrometry, and x-ray diffraction. Initiation of interface reactions between the Rh films and the GaAs substrate is observed at ∼300 °C. Laterally segregated RhGa, RhAs, and RhAs2 phases are detected for the 150-Å Rh/GaAs contact annealed in the temperature range of 300–700 °C. For thick Rh film (∼600 Å) on GaAs, vertical phase separation between the RhGa and the Rh-As phases is observed after annealing. After annealing at 700 °C for 20 min, the reaction between the 600-Å Rh film and GaAs is complete and a layer sequence of RhGa/RhAs2/GaAs results. Electrical properties of Rh/n-GaAs diodes are measured using the current voltage dependence. A correlation between the electrical behavior and the metallurgical reaction is observed.
Cheung, S.K., SPE, Chevron Oil Field Research Co. Summary. The effects of acids on the integrity of gravels and proppants should be considered in acid treatments. This paper reports on the influence of acid type, acid concentration, and contact duration on the acid solubility of five sands and bauxitic materials. The effects of the acids on the mechanical strength and the size distribution of the solids are determined. We found that intermediate-density and low-density bauxites (IDB and LDB) are very soluble in HF acid and that sintered bauxite is weakened by HF acid. Introduction HCl and HF acids are pumped downhole to remove near-wellbore damage in many types of wells. The effects of acids on formation material have been studied extensively; however, the effects of acids on gravels and proppants should also be considered. Concerns about acid effects on formation materials differ from those about effects on gravels and proppants. For formation material, one must ensure that the acid can remove or bypass skin damage and does not cause further damage. For both gravels and proppants, one must ensure that the acid will not dissolve the solids significantly. The effects of the acids on size distribution and mechanical strength can also be important. API has prepared guidelines for testing gravel-packing materials and hydraulic fracture proppants. The acid-solubility testing procedure in the API guideline recommends acid contact of 1 hour at room temperature for gravels. This, however, is intended for quality-control purposes rather than for simulation of field operations. In actual field practices, the accumulated acid contact times are usually longer than 1 hour. In jobs with mechanical problems, acid contact time can be longer than planned. Furthermore, if an acid job with a 2-hour acid stage is performed annually, in 5 years the accumulated acid contact time is 10 hours. To simulate field operations, we determined acid solubilities at longer time intervals. Procedures and Tested Materials In this paper, we report the solubility of five different materials in HCl and HF acids. The effects of acid on the mechanical strength, bulk volume, and particle-size distribution of these solids were determined. All solids were sieved between 20- and 40-U.S.-mesh screens and then tested according to the procedures described in the Appendix. All five solids tested can be used as either fracture proppant or gravel-packing material. One difference is that the particle-size specification is tighter when the solids are used in gravel packs. The sands used were Ottawa and Heart of Texas sands. There are three types of bauxitic materials. Sintered bauxite in this study is dark gray and typically contains 87% aluminum oxide. Most of its aluminum oxide is in the form of corundum (Al2O3). IDB is usually dark brown and contains about 75% aluminum oxide, which has almost equal portions of corundum and mullite (Al6Si2O13). LDB has a bulk density almost equal to that of sands, is pale gray, and contains about 70% mullite and 30% cristobalite (SiO2). Test Results Dissolution in Acid. The acid solubilities in 15% HCl for all the solids tested for up to 24 hours were less than 2% (Tables 1 and 2). The resulting solids remained consolidated, and fines were not generated. In HF, all the solids tested have some solubility at 150F [66C]. Test results (Figs. 1 and 2) show that dissolution in HF generally increases with the concentration of HF and the length of acid exposure. Our study shows that the order of dissolution in HF, in increasing dissolution rates, is sands, sintered bauxite, IDB, and LDB. Sintered bauxite seems to dissolve quite rapidly during the first 6 hours of HF acid contact; then the dissolution rate tapers off. IDB and LDB dissolved alarmingly quickly in HF. After 24 hours, the HF acid solubility of IDB was 58% and that of LDB reached 97%. This means that for wells gravel packed with these two bauxitic materials, HF acid jobs may cause a loss of sand control. For wells propped with them, the HF acid job closes the fractures and causes a loss of fracture conductivity. Size Distribution. One concern about treating gravel packs and hydraulic fractures with acid is the reduction of particle size. For gravel packs, gravel-size reduction mayreduce the height of the gravel-packed interval and leave some zones without sand control,create voids within perforations and cause perforation collapse,change gravel-size distribution and decrease sand control efficiency, and/orgenerate fines and plug the gravel pack. For hydraulic fractures, proppant-size reduction may decrease fracture conductivity and generate fines. The loss of fracture conductivity near the wellbore can cause a dramatic reduction in well productivity. The particle-size distributions of 20/40-mesh solids treated with HF for 24 hours are listed in Table 3. For both sands, more than 90% of the resulting solids were within the 20/40-mesh size range after the HF acid exposure. Microscopic examination of HF-tested sintered bauxite showed pits in the particles (Fig. 3). For IDB and LDB, large amounts of fines were generated by the HF acid treatment. One interesting result of this study is that the particle-size distribution of sintered bauxite is not significantly affected by HF acid treatment. More than 99% of the HF-treated sintered bauxite remained within the 20/40-mesh range after 24 hours in HF (Table 4). Another interesting result is that the bulk volume of sintered bauxite is not affected by the HF acid treatment. After 24 hours in HF, the mass was reduced by 18.8% (acid solubility); the bulk density was also reduced by 17.3%. In terms of the definition of density (density equals mass divided by volume), the bulk volume of sintered bauxite remained essentially unchanged by HF. Because the particle-size distribution and bulk density are not affected, shallow wells gravel packed with sintered bauxite can be treated with moderate amounts of HF acid. Mechanical Strength. In hydraulic fracturing, the mechanical strength of the proppant is very important because proppants are sometimes used in deep zones where overburden pressure is large. If the proppants are crushed by this load, the fracture might close and lose its conductivity. SPEPE P. 201^
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