Oxidation through the zirconia substrates of heteroepitaxial silicon films Grown on yttria-stabilized cubic zirconia

We demonstrate the thermal oxidation of the Si side of the interface in epitaxial Si films grown on yttria-stabilized cubic zirconia, 〈Si〉/〈YSZ〉, to form a dual-layer structure of 〈Si〉 /amorphous SiO₂/〈YSZ〉. The SiO₂ films are formed in either dry oxygen (at 1100‡C) or in pyrogenic steam (at 925‡C) by the rapid diffusion of oxidizing species through the 425 Μm thick cubic zirconia substrate. For instance, a 0.17 Μm thick SiO₂ layer is obtained after 100 min in pyrogenic steam at 925‡C. This relatively easy transport of oxidants is unique to YSZ and other insulators which are also superionic oxygen conductors, and cannot be achieved in other existing Si/insulator systems, such as Si-on-sapphire. The present process eliminates the most     

Solution growth of Indium-Doped silicon

Indium-doped silicon has been grown from indium-rich solutions using a gradient-transport solution growth process. The growth temperatures were varied from 950‡ to 1300‡C to determine the solubility limits of indium in silicon. The maximum indium concentration obtained was 1.6×10¹⁸/cm³ at a growth temperature of 1300‡ but indications are that the maximum solubility is 2. 5×10¹⁸/cm³. The growth process is described by one-dimensional diffusion limited transport and predicts growth rates in excess of lcm/day at 1300‡C. Infrared absorption measurements were used to monitor the indium, oxygen and carbon concentrations, in addition to the shallower .indium: X defect found in the crystals. The solution-grown crystals were found to have a lower concentration of this shallower defect than melt grown crystals of the same indium concentration. The oxygen and carbon concentrations increased with the increased growth temperatures suggesting a solubility limited value. The shallower indium: X defect also increased with growth temperature, but the concentration was significantly lower than typically found in melt-grown crystals. The peak optical cross-section for indium was also determined to be 5.3×10^-17cm² from these measurements. This work was sponsored in part by the Defense Advanced Research Projects Agency under Order No. 3211, monitored by NV & EOL under Contract No. DAAK70-77-C-0194.     

Specific contact resistivity of indium contacts to n-type CdTe

Indium alloyed to n-type CdTe of about 10¹⁶ cm^-3 electron concentration provides a contact resistivity of about 7 x 10^-3 ohm cm². This is achieved by alloying for 10 minutes at 150-450‡C in a sealed ampoule with an overpressure of cadmium. If the alloying is done in an open tube H₂ flow without a Cd vapor overpressure, alloying temperatures above 250‡C cause the contact resistance to rise as cadmium vacancies increase the compensation in the CdTe. Further improvement of the contact resistivity to 1 x 10^-3 ohm cm is obtained by a 900‡C diffusion of In into the n-CdTe (electron concentration 10¹⁶ cm^-3 before the diffusion).     

Annealing studies of Be-implanted GaAs0.6P0.4

Differential resistivity and Hall effect measurements and secondary ion mass spectrometry (SIMS) are used to study the annealing behavior of Be-implanted GaAs_0.6P_0.4. Results similar to that previously reported for Be-implanted GaAs are observed, including outdiffusion of Be into the Si₃N₄ encapsulant during 900‡C annealing of high dose implants. Nearly all (85–100%) of the Be remaining after a 900‡C, 1/2 hr anneal is electrically active. However, the electrical activation at low annealing temperatures (600–700‡C) is much lower in GaAs_0.6P_0.4 than in GaAs. A substantial amount of diffusion is observed even for the low fluence Be implants in GaAs_0.6P_0.4 annealed at 900‡C, indicating a greater dependence of the diffusion on defect-related effects in the ternary. This work was supported by the Joint Services Electronics Program (U.S. Army, U.S. Navy, U.S. Air Force) under Contract DAAB-07-72-C-0259, by Monsanto Company, and by the Naval Electronic Systems Command. On leave at Cornell University, Department of Electrical Engineering, Ithaca, NY 14853.     

Growth-Temperature-Controlled Optical Properties of Textured MgxZn1?xO Thin Films

Pulsed laser deposition was used to grow magnesium zinc oxide thin films on amorphous fused silica substrates at several temperatures between room temperature and 750°C. In this study, the effect of growth temperature on the optical properties of textured Mg _x Zn_1−x O thin films was examined. The optical properties of the films were measured using absorption and photoluminescence spectrometry. Absorption spectra revealed that the bandgap values of textured Mg _x Zn_1−x O thin films were enhanced in films grown at higher temperatures. The absorption spectra near the absorption edge were fitted using the Urbach equation in order to investigate the effects of growth temperature on exponential band tail and bandgap. The photoluminescence spectra were measured for magnesium zinc oxide thin films deposited at 250°C, 350°C, 450°C, 550°C, and 650°C. The film grown at 350°C provided the highest excitonic peak intensity. On the other hand, the film grown at 250°C exhibited the lowest excitonic peak intensity. The excitonic peak intensity was considerably reduced in magnesium zinc oxide thin films grown at temperatures greater than 350°C. The ability to perform substrate-temperature-dependent bandgap engineering of Mg _x Zn_1−x O will enable use of this material in next-generation optical and optoelectronic devices.     

MOCVD epitaxial growth of single crystal GaN,AlN and AlxGa1-xN

Ga begins to deposit from a stream of trimethylgallium (TMG) in H₂ at a minimum temperature of 475‡C. Addition of sufficient amounts of NH₂ results in the growth of textured polycrystalline GaN on basal plane sapphire substrates above 500‡C. A minimum temperature of 800‡C is required for the epitaxial growth of GaN on the substrate. Under similar conditions, but with the TMG replaced with trimethylaluminum (TMA), polycrystalline A1N begins forming at 400‡C (in the absence of NH₃,, the TMA starts pyrolyzing at 300‡C), but single crystal growth of A1N requires a temperature of at least 1200‡C. Epitaxial single crystal layers of Al_x Ga_1-x N can be grown in the temperature range 800−1200‡C, tne minimum temperature being approximately proportional to x, but preferential deposition of A1N on the hot walls of the reactor (>400‡C) precludes precise control of the alloy composition. This predeposition of A1N can be retarded by keeping the walls below 400‡C by using a water-cooled jacket, by rapid flow-rates, or by injecting the TMA through a nozzle close to the surface of the substrate.     

Liquidus isotherms,solidus lines and LPE growth in the Te-rich corner of the Hg-Cd-Te system

Liquidus isotherms for the Hg_1−xCd_xTe primary phase field in the Te-rich corner of the Hg-Cd-Te ternary system have been determined for temperatures from 425 to 600‡C by a modified direct observational technique. These isotherms were used to help establish conditions for the open-tube liquid phase epitaxial growth of Hg_1−xCd_xTe layers on CdTe_1−ySe_y substrates. Layers with x ranging from 0.1 to 0.8 have been grown from Te-rich HgCdTe solutions under flowing H₂ by means of a horizontal slider technique that prevents loss of Hg from the solutions by evaporation. Growth temperatures and times of 450–550‡C and 0.25–10 min, respectively, have been used. The growth solution equilibration time is typically 1 h at 550‡C. Source wafers, supercooled solutions, and (111)-oriented substrates were employed in growing the highest quality layers, which were between 3 and 15 Μm thick. Electron microprobe analysis was used to determine x for the epitaxial layers, and the resulting data, along with the liquidus isotherms, were used to obtain solidus lines. In addition to EMP data, optical transmission results are given. This work was sponsored by the Department of the Air Force and the U. S. Army Research Office.     

Au/Ge/Ni ohmic contacts to n-Type InP

The relationship between the electrical properties and microstructure for annealed Au/Ge/Ni contacts to n-type InP, with an initial doping level of 10¹⁷ cm^-3, have been studied. Metal layers were deposited by electron beam evaporation in the following sequence: 25 nm Ni, 50 nm Ge, and 40 nm Au. Annealing was done in a nitrogen atmosphere at 250-400‡C. The onset of ohmic behavior at 325‡C corresponded to the decomposition of a ternary Ni-In-P phase at the InP surface and the subsequent formation of Ni₂P plus Au₁₀In₃, producing a lower barrier height at the InP interface. This reaction was driven by the inward diffusion of Au and outward diffusion of In. Further annealing, up to 400‡C, resulted in a decrease in contact resistance, which corresponded to the formation of NiP and Au₉ln₄ from Ni₂P and Au₁₀In₃,respectively, with some Ge doping of InP also likely. A minimum contact resistance of 10^-7 Ω-cm² was achieved with a 10 s anneal at 400‡C.     

Stability of various doping species in trans-polyacetylene

Polyacetylene, a simple conjugated organic polymer, a material of strong interest if doped by various chemical species such as iodine or antimony pentafluoride : its electrical conductivity increases by more than twelve orders of magnitude. By increasing the dopant concentration one obtains a semiconductive or a metallic regime. Such properties allow us to make electronic material and then devices by convenient n or p type doping of polyacetylene. However,it is necessary to determine the thermal stability of the various dopant species. In this paper, we compared the stability of iodine, SbF₅ and CF₃SO₃H dopants by studying the mass loss and the electrical conductivity decrease at various temperatures from 20‡C up to 180‡C. It is shown that only SbF₅ is a relatively stable dopant up to 80‡C, a temperature which may be reached in some active electronic devices. Raman spectroscopy allowed us to measure the ratio of I₋₃ to I₋₅ ions during the desorption process and to propose a possible chemical reaction which produces gaseous iodine from the active dopant species.     

Phase relations and homogeneity region of the hightemperature superconducting phase (Bi,Pb)2Sr2Ca2Cu3O10+d

For the nominal composition of Bi_2.27−xPb_xSr₂Ca₂Cu₃O_10+d, the lead content was varied from x < 0.05 to 0.45. The compositions were examined between 800 and 890‡C which is supposed to be the temperatue range over which the so-called 2223 phase (Bi₂Sr₂Ca₂Cu₃O_10+d) is stable. Only compositions between x < 0.18 to 0.36 could be synthezised in a single phase state. For x <0.36, a lead-containing phase with a stoichiometry of Pb₄(Sr,Ca)₅CuO_d with a small solubiliy of Bi is formed, for x > 0.18 mainly Bi₂Sr₂CaCu₂O_8+d and cuprates are the equilibrium phases. The temperature range for the 2223 phase was found to be 800 to 890‡C but the 2223 phase has extremely varying cation ratios over this temperaure range. Former single phase 2223 samples turn to multiphase samples when annealed at slightly higher or lower temperaures. A decrease in the Pb solubility with increasing as well as decreasing temperature with a maximum at about 850‡C was found for the 2223 phase.