Structures and physical properties of sputtered amorphous SiC films

Optical and electrical properties have been measured for amorphous SiC films prepared by rf sputtering in a pure Ar atmosphere with a sintered 6H-SiC target. The absorption edge E₀ determined from the relation of αhΝ = B(hΝ-E₀)² ranged from 1.45 to 1.80 eV depending on the film thickness and the substrate temperature. The room temperature electrical conductivity is in the range of 5.4×10⁻¹¹ and 1.4×10⁻⁵ Ω⁻¹cm⁻¹. The absorption edge decreases and the conductivity increases with increasing film thickness. The absorption edge shifts to shorter wavelengths (blue shift) and the conductivity decreases during annealing below 400‡C for 60 min, whereas the absorption edge shifts to the longer wavelength side (red shift) and the conductivity increases during annealing at 800‡C It is proposed that the two annealing processes cause structural changes in amorphous SiC films, one of which involves removal of defects or voids while the other involves rearrangement or rebonding of the component atoms.     

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.     

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.     

The effect of annealing temperature on the carrier concentration OF Hg0.6Cd0.4Te

The carrier concentration dependence of Hg_0.6Cd_0.4Te on annealing temperature for the Hg and Te saturation condi-tions is presented in this paper. At low annealing tempera-tures, T_A < 350‡ C, residual donor impurities apparently limit the carrier concentration. In contrast, at higher annealing temperatures, 350‡ C < T < 700‡ C, the stoichio-metric acceptor density is increased such that the residual donors are compensated and the material is converted to p-type with an acceptor density as large as 10¹⁷ cm⁻³ . An empirical expression describing this dependence of the acceptors on annealing temperature is given for both the Hg and Te saturation condition: P (Hg saturation) = 1.46 × 10²² exp (−0.84/kT_A), P (Te saturation) = 1.90 × 10¹⁸ exp (−0.15/kT_A). Supported in part by Air Force Materials Laboratory, WPAFB, Ohio under Contract AF61533-C-74-5041.     

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.     

Recent status on high temperature superconducting Bi2Sr2CaCu2O8+x wire development at NYSIS: 1-90 meter length Jcs and 3 meter diameter ring furnace design

The status of long length, Bi₂Sr₂CaCu₂O_8+x (Bi-2212) wire development at the New York State Institute on Superconductivity (NYSIS) is reviewed and updated. Transport J_cs (4.2K, 0 T) of Bi-2212/Ag oxide powder-in-tube singlefilamentary tapes have reached 70,000-80,000, 50,000-60,000, and 30,000–40,000 A/cm² for 1, 4–15, and 40–90 meter length tapes, respectively. The decrease in J_c as the tape length was increased from 15 to 90 meters was attributed to the (measured) sensitivity of J_c to temperature nonuniformities (±3‡C) in the box-type furnace used for annealing. To reduce this problem, a ringtype high-temperature furnace (∼3 meter diameter) was designed and constructed which provides a large-volume (∼13^w × 10^h × 1000¹ cm) processing zone with expected excellent temperature uniformity (±0.5‡C). The advantages of the ring-type furnace for processing of kilometer-length conductors are described.     

Rapid capless annealing of28Si,64Zn,and9Be implants in GaAs

We report the use of tungsten-halogen lamps for rapid (−10 s) thermal annealing of ion-implanted (100) GaAs under AsH₃/Ar and N₂ atmospheres. Annealing under flowing AsH₃/Ar was carried out without wafer encapsulation. Rapid capless annealing activated implants in GaAs with good mobility and surface morphology. Typical mobilities were 3700–4500 cm²/V-s for n-layers with about 2×10¹⁷cm⁻³ carrier concentration and 50–150 cm²/v-s for 0.1–5xl0¹⁹ cm⁻³ doped p-layers. Rapid thermal annealing was performed in a vertical quartz tube where different gases (N₂, AsH₃/H₂, AsH₃/Ar) can be introduced. Samples were encapsulated with SiO when N₂ was used. Tungsten-halogen lamps of 600 or 1000 W were utilized for annealing GaAs wafers ranging from 1 to 10 cm² in area and 0.025 to 0.040 cm in thickness. The transient temperature at the wafer position was monitored using a fine thermocouple. We carried out experiments for energies of 30 to 200 keV, doses of 2×10¹² to 1×10¹⁵ cm⁻², and peak temperatures ranging from 600 to 1000‡C. Most results quoted are in the 700 to 870‡C temperature range. Data on implant conditions, optimum anneal conditions, electrical characteristics, carrier concentration profiles, and atomic profiles of the implanted layers are described. Presented at the 25th Electronic Materials Conference, Burlington, VT, June 22, 1983.     

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     

Electrically active defects in shallow pre-amorphisedp + n junctions in silicon

An examination of shallow pre-amorphisedp ⁺ n junctions in silicon has revealed three distinct defect related phenomena determined largely by the annealing temperature and relative location of the junction and the amorphous-crystalline (α-c) boundary. For temperatures below 800‡ C all samples displayed leakage currents of ∼10⁻³ A/cm² irrespective of the amorphising atom (Si⁺, Ge⁺ or Sn⁺). The generation centres responsible were identified to be near mid-gap deep level donors lying beyond the α-c interface. For samples annealed above 800‡ C, the leakage current was determined by the interstitial dislocation loops at the α-c boundary. If these were deeper than the junction, a leakage current density of ∼10⁻⁵ A/cm² resulted. From the growth of these loops during furnace annealing it was concluded that the growth was supported by the influx of recoil implanted silicon interstitials initially positioned beyond the α-c boundary. In the case where the as-implanted junction was deeper than the α-c boundary, annealing above 800° C resulted in a transient enhancement in the boron diffusion coefficient. As with the dislocation loop growth, this was attributed to the presence of the recoil implanted silicon interstitials.     

Understanding the phase relations and cation disorder in LRE1+xBa2− xCu3O7+δ

Unlike Y123 which forms only a stochiometric compound, the light rare earth elements (LRE) form a solid solution LRE_1+xBa_2-xCu₃O_7+δ (LRE123ss), with increasing substitution of the LRE³⁺ for the Ba²⁺ with increasing ionic radii of the LRE. Charge balance is maintained by increasing oxygen occupation on the anti-chain sites. The range of solubility is partially controlled by the oxygen partial pressure (PO₂). The peritetic decomposition temperature also increases with increasing ionic radii. At doping levels of 0 > × > 0.1, there is an increase in T_c when the high temperature annealing (T ∼ 940‡C) is performed in low PO₂ (> 0.1 bar). The maximum T_c occurs at a doping level of ∼x < 0.05 for Nd and Gd. When annealing is performed in 1 bar PO₂, there is a gradual decrease in T_c with increasing x. These phenomenon can be understood in terms of the number and distribution of the LRE which substitute on the Ba site.     

Effect of Rapid Thermal Annealing on Sputtered CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> Thin Films

Calcium copper titanium oxide (CaCu₃Ti₄O₁₂, abbreviated to CCTO) films were deposited on Pt/Ti/SiO₂/Si substrates at room temperature (RT) by radiofrequency magnetron sputtering. As-deposited CCTO films were treated by rapid thermal annealing (RTA) at various temperatures and in various atmospheres. X-ray diffraction patterns and scanning electron microscope (SEM) images demonstrated that the crystalline structures and surface morphologies of CCTO thin films were sensitive to the annealing temperature and ambient atmosphere. Polycrystalline CCTO films could be obtained when the annealing temperature was 700°C in air, and the grain size increased signifi- cantly with annealing in O₂. The 0.8-μm CCTO thin film that was deposited at RT for 2 h and then annealed at 700°C in O₂ exhibited a high dielectric constant (ε′) of 410, a dielectric loss (tan δ) of 0.17 (at 10 kHz), and a leakage current density (J) of 1.28 × 10⁻⁵ A/cm² (at 25 kV/cm).     

Miscibility gap in the GaAsy Sb1−y system

Measurements have been made to determine accurately the solidus curve of the pseudobinary section GaAs_ySb_1−y, by annealing samples to equilibrium and determining compositions by x-ray powder photography. It is found that the equilibriui diagram shows a peritectic form with a peritectic temperature of 745 ± 1‡C and a miscibility gap at that temperature extending from y = 0.38 to y = 0.68. It is also shown that as the temperature is lowered the miscibility gap widens rapidly, being from y = 0.30 to y = 0.95 at 700‡C. The form of these phase boundaries is important when growth of GaAs_ySb_1−y alloys by liquid phase epitaxy or similar techniques is considered.     

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.     

Raman characterization of hydroxyl in fused silica and thermally grown SiO2

We developed Raman spectroscopy to characterize the hydroxyl (OH) solubility in fused silica and thermally grown steam SiO₂ from 695 to 1000‡C and 1–10 atm steam pressure. The technique was extended to measure the OH diffusion profiles in bulk v-SiO₂, and the derived diffusion coefficients supplement those published in the literature. Fused silicas processed with higner fictive temperatures display larger initial OH solubilities which decrease with time, but saturations at temperatures as low as 600‡C remove much of the prior thermal history as the glass structurally relaxes. The OH solubility appears to be proportional to the square root of external steam pressure; however, the quasiequilibrium temperature dependence is unresolved. The behavior of OH in fused silica and the thermally grown oxide is very similar when the two materials are identically processed.     

Powder processing of high temperature ceramic superconductor Tl2Ba2Ca2Cu3O10

We have developed a technique to produce high quality Tl₂Ba₂Ca₂Cu₃O₁₀ powders used for making superconducting wire, tape, lead, shield, and other large scale bulk applications. Starting with T1₂O₃, BaO₂, CaO, and CuO, we mix and grind these chemicals with a machine ball mill and then press the ground mixture into pellets. The pellets are sintered at about 895‡C for at least 30 h in an oxygen atmosphere. The sintered material is mainly the Tl₂Ba₂Ca₂Cu₃O₁₀ compound. To get more homogeneous superconductor powders, we pulverize the sintered material and use a magnetic superconducting material selector to separate and grade the material. Finally, the top grade material has a phase purity of <98% and a T_c(r < 0) of 123–126K.     

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.     

The phase relations in the system Tl2Se-As2Se3 and the crystal growth of Tl3AsSe3

The phase diagram for the system T12Se-As2Se3 was studied by quenching and thermal analysis experiments, with emphasis on the composition range 15 to 35 mol % As₂Se₃, so as to determine the melting relations of Tl₃AsSe₃, a useful compound for optical and acousto-optical devices. Tl₃AsSe₃ melts congruently at 311 ± 2‡C, and the only other pseudobinary compound, TlAsSe₂, melts congruently at 272 ± 2‡C. Eutectics lie between Tl₂Se and Tl₃AsSe₃ (∿ 21 mol % As₂Se₃, 302 ± 2‡), between Tl₃AsSe₃ and TlAsSe₂ (∿ 32 mol % As₂Se₃, 238 ± 3‡), and between TlAsSe₂ and As₂Se₃ (∿ 72 mol % As₂Se₃, 249 ± 3‡). The maximum-melting Tl₃AsSe₃ composition lies at 24.62 + 0.13 mol % As₂Se₃. Crystals of Tl₃AsSe₃ were grown from three pseudobinary compositions with the best crystals obtained from melts containing 24.62 mol % As₂Se₃. This research was sponsored by the Advanced Research Projects Agency of the Department of Defense and was monitored by the Air Force Materials Laboratory, LP, under Contract No. F33615-72-C-1976     

Electron microscope studies of InxGav1−xAs/GaAs/Si grown by metalorganic chemical vapor deposition

The microstructure of In_xGa_1−xAs/GaAs (5 nm/5 nm, x < 0 to 1.0), as grown by a metalorganic chemical vapor deposition two-step growth technique on Si(100) at 450‡C, and subsequently annealed at 750‡C, is investigated using plan-view and cross-sectional transmission electron microscopy. The variations in resultant island morphology and strain as a function of the In content were examined through the comparison of the misfit dislocation arrays and moirés observed. The results are discussed in relation to the ways in which the island relaxation process changes for high In content.     

Effect of Ar annealing temperature on SiO2/4H-SiC interface studied by spectroscopic ellipsometry and atomic force microscopy

The authors have investigated the effects of different annealing temperatures in Ar atmosphere on the SiO₂/4H-SiC interfaces by spectroscopic ellipsometry (SE) and atomic force microscopy (AFM). There is a strong correlation between the annealing temperatures and the quality of SiO₂/4H-SiC interface. Annealing at 600 °C can significantly improve the quality of SiO₂/4H-SiC interface with no transition layer. The reasons for such improvement in the quality of the SiO₂/4H-SiC interface after moderate temperature annealing at 600 °C may be explained by the formation and consumption of carbon clusters and silicon oxycarbides during annealing.     

Thermally stable Ge/Cu/Ti ohmic contacts to n-type GaN

The performance of a novel Ge/Cu/Ti metallization scheme on n-type GaN has been investigated for obtaining thermally and electrically stable low-resistance ohmic contacts. Isochronal (2 min.) anneals in the 600–740°C temperature range and isothermal (690°C) anneals for 2–10 min. duration were performed in inert atmosphere. For the 690°C isothermal schedule, ohmic behavior was observed after annealing for 3 min. or longer with a lowest contact resistivity of 9.1 × 10⁻⁵ Ωcm² after the 10 min. anneal for a net donor doping concentration of 9.2 × 10¹⁷ cm^−Ω3. Mean roughness (R_a) for anneals at 690°C was almost constant at around 5 nm, up to an annealing duration of 10 min., which indicates a good thermal stability of the contact scheme.