5350. Thermal redistribution of indium in amorphous silicon layers

Classified abstracts 5342-5350 ccollection methodology was developed to minimize errors resulting from Changes in flame ionization detector sensitivity at different altitudes (pressures). Selected aircraft data acquired during the 1979 Southeastern Virginia Urban Plume Study are presented to illustrate,instrument performance. W R Cofer, HI and G C Purgold, Rev Sci Instrum;52 (10), 1981, 1560-1564. 35. PROCESSING O F MATERIALS 35 5342. Annealing of zin,~-diffused GaAs. (GB) Experiments are described in which radioactive zinc was diffused into ntype GaAs at temperatures of 700, 900 and 1000°(3. Diffusion profiles were plotted. For certain of the experiments the external zinc vapour source was removed after diffusion had proceeded for 15 rain and the experiment was continued as a simple annealing stage for a further 15 min. Remarkably little further movement of the profile was found during this second stage. This effect is considered in the paper and an attempt is made to explain the results in terms of the kinetic processes involved in diffusion from a vapour source. In addition, the profiles permit an accurate value to be obtained for the diffusion coefficient of zinc in GaAs at 700°C and a concentration of 5 × 1019 cm -3. Brian Tuck and A J N Houghton, J Phys: Appl Phys, 14 (11), 1981, 2147-2152.. 35 5343. Pulsed lasex annealing of selenium implanted InP. (GB) Rutherford back-scattering (RBS), Hall effect and Nomarski interference microscopy have been used to study 200 keV selenium ions implanted into lnP in the dose range 1 × 1014 to 1 × 10Is cm -2. Samples were irradiated with single pulses from a Q-switched ruby laser in the energy range 0.2 to 2.2 J cm -2. It was found that capless laser irradiation does not allow complete recrystailization of damaged InP, and an energy density of 0.3 J cm -2 causes surface decomposition, thus producing indium-rich surface layers. To ensure that the measured electrical properties were due to the implanted atoms alone it was found necessary to thermally anneal samples at 400°C for 5 min after the laser irradiation. The activity was 26% and the mobility 300 cm z V- l s- t for a dose of 1 x 101 s SC+ cm - 2 irradiated at 0.5 J cm -2. S S Gill et al, J Phys D: Appl Phys, 14 (12). 1981, 2333-2339. 35 5344. The effect of annealing on the properties of silicidized molybdenum thin films. (USA) The effect of isothermal and isochronal anne.aling on the structural and electrical properties of silicidized Mo thin films is reported. The silicidation of Mo with Sill4 resulted in Mo films with increasing hexagonal MoSi 2 content as the reaction time increased. Post-reaction annealing was performed in various ambients (hydrogen, nitrogen and vacuum) at temperatures from 800 to 1000°C for times up to 1 h. Annealing in H 2 at 1000°C for only 5 rain results in the virtual disappearance of the original components and the formation of intermediate silicide phases (MosSi 3 and Mo3Si ) and the tetragonal MoSi 2 phase. This structural transformation leads to a significant increase in i'esistivity. The reaction kinetics are considerably slower in the case ofN 2 ambient where even after a 60-rain anneal at 1000°C a substantial percentage of Mo remains. This slower rate of phase change is reflected in a more gradual increase in the sheet resistance. The characteristics of vacuum-annealed films followed the N 2 case for short-term anneals (t ~<10 rain) but resembled the H2 case longer-term anneals it ~<15 rain). The dependence of reaction mechanisms on various ambients is discussed. T P Chow et al, J Appl Phys, 52 (10), 1981, 6331-6336. 35

5345. Thermal cycling-induced changes in the electrical transport properties of (111) epitaxial, n-type PbTe films. (USA) Weak-field magnetoresistance measurements at 297 K were used in conjunction with an appropriate band structure model to detect the substrate-induced strain in n-type PbTe epitaxial films grown on BaF2. Evidence of strain in as-grown films was found. The temperature of the sample was repeatedly cycled from 297 to 4.2 K and back, and the 297-K strain was found to decrease. At the same time, Hall effect and resistivity measurements show that the 4.2-K mobility dropped and the 297- and 4.2-K carder concentrations increased. The observed effects are ascribed to an extended defect density which grows larger as the number of tbermal cycles increases. J a Restorff et al, J Appl Phys, 52 (10), 1981, 6185-6189..

768

35 5346. An investigation into silicon doping of MBE (100) GaAs. (GB) A study of the silicon doping of MBE (molecular beam epitaxy) (100) GaAs is presented. The effects of the various growth parameters on the electrical properties of the layers have been investigated. In particular the influence of the As4 :Ga flux ratio on the Si incorporation is considered. A model based on the site occupancy of the Si dopant and an As-induced defect/Si-impurity complex is invoked to account for the observed electrical properties. E H C Parker et al, J Phys D: Appl Phys, 14 (10), 1981, 1853-1865. 35 5347. A photoluminescence study of beryllium-doped GaAs grown by molecular beam epitaxy. (USA) The 300-g photoluminescence internal quantum efficiency of berylliumdoped GaAs grown by molecular beam epitaxy at 580°C from As4 under arsenic stable conditions is limited by nonradiative recombination with zNs=3.5 to 5.6x10 -1° s. zsR remains in this range while 1.3 x 101S 0.69 % and > 7.6 %, respectively. The 6.5-K photoluminescence spectra of layers grown at 580, 620 and 660°C showed no significant differences and exhibited none of the new bound exciton lines reported by Kunzel and PIoog to be present in molecular beam epitaxial GaAs grown from As4 below 610°C. (GB) G B Scott et al, J Appl Phys, 52 (11), 1981, 6888-6894. 35 5348. Laser implantation of impurity atoms into silicon and galliamarsenide single crystals. (USA) Sn and Fe have been incorporated into the bulk of silicon single crystals by means of an irradiation of thin metallic surface layers of these elements with light pulses from a Nd-glass laser. Analogously, Sn has been implanted into gallium-arsenide single crystals and furthermore, a successful implantation of Sn into GaAs has been achieved by an irradiation from the backside of the sample. Depth profiles of the implants have been determined by Rutherford backscattering analysis. The state of the impurity atoms has been studied by conversion-electron M6ssbauer spectroscopy. The surface topography of Sn-implanted silicon was analysed by scanning electron microscopy. The dependence of the number of implanted impurity atoms and their depth profiles on the laser power density and the thickness of the deposited surface layer has been investigated. The fraction of atoms implanted from the surface layer decreases with increasing layer thickness. For a given layer thickness, the implanted fraction reaches a maximum for a certain laser power density. The impurity atoms can be implanted to a depth of several thousand angstroms with nearly homogeneous depth profiles for suitably chosen conditions. The concentrations exceed the solid solubilities by orders of magnitude. These findings are consistent with a qualitative model for the implantation process assuming a detailed balance between an evaporation of the metallic surface layers and the incorporation of the impurity atoms into the bulk by diffusion in a molten substrate layer. After the' recrystallization, as inferred from the M6ssbauer spectra, Sn is found on substitutional lattice sites in silicon and on substitutional Ga sites in GaAs, whereas Fe in silicon precipitates in agglomerates. Upon thermal annealing, the depth profiles relax towards more homoheneous distributions. No segregation of Sn from the supersaturated solution is indicated; however, drastic changes in the Fe M6ssbauer spectra after annealing indicate that a fraction of these atoms may occupy well-defined lattice sites, whereas the majority remains in agglomerates. (Denmark) S Damgaard et al, J Appl Phys, 52 (11), 1981, 6907-6916. 35 5349. Ion beam induced atomic distribution of implanted range profiles (the system Ne-,Ge/Si). (USA) The redistribution of Germanium atoms previously implanted at 40 keV in Si was investigated after bombardment with various fluences (10Is-10 x7 cm -2) of 20 keV Ne + ions. High resolution RBS was used for the depth analysis. The observed redistribution of the Germanium profile is discussed in terms of the Ne energy deposition distribution, and some preliminary theoretical estimates are given. (GB) N P Toguctti et al, Rad Effects Letters, 63 (3), 1981, 69-72. 35 5350. Thermal redistribution of indium in amorphous silicon layers. (USA) A new impurity redistribution mechanism is reported for low temperature annealing (525°C) of (100) Si samples implanted with high indium doses.

Classified abstracts 5351-5361

The redistribution is a strong function of implant dose and is believed to be stress related. (GB) R G Elliman, Rad Effects Letters, 67 (3), 1981, 77-82. 35 5351. Formation of AI-nitride films at room temperature by nitrogen ion implantation into aluminium. (USA) A new method is demonstrated for the preparation of thin aluminium nitride layers using the direct nitridation of aluminium by low-energy nitrogen ion implantation in the ion energy range 0.5-5 keV. The AInitride films were obtained at room temperature without any thermal annealing. For the first time Al-nitride was studied with Auger electron spectroscopy (AES) and low-energy electron-loss spectroscopy (ELS) and the corresponding spectra, together with those of AI and Al203, are presented. An electron energy-level scheme for Al-nitride was derived from the AlLyv Auger spectra, from the valence electron excitation spectra, and from the AI (2p) and N (Is) core electron excitation spectra measured by ELS. (West Germany) N Lieske and R Hezel, J Appl Phys, 52 (9), 1981, 5806-5810. 35 5352. Molecular beam epitaxlal ZnSe:Mn de electroluminescent cell with very low threshold voltage. (USA) A Au/ZnSe:Mn/n-GaAs de-operated electroluminescent cell was prepared by molecular beam epitaxy. The lowest threshold voltage achieved was 3.8 V, and the highest power conversion efficiency and brightness were 7.6x 10 - s W[W(18 V, 0.027 A/cm 2) and 270 fL(16.8 V, 0.25 A/era2), respectively. These values are superior to any previously reported in ZnSe:Mn EL cells. (Japan) Tomoyoshi Mishima et al, J Appl Phys, 52 (9), 1981, 5797-5799. 35 5353. Photoluminescence of AIxGa t -x As grown by molecular beam epitaxy. (USA) Reduction of background oxygen containing species, higher substrate temperature, and low arsenic fluxes during growth have all been found critical to improve the luminescence of molecular beam epitaxy AlxGa t _ As alloys. Attention to these parameters has allowed greatly improved quality films to be grown which show strong exciton recombination for the first time. The main unintentional acceptor impurity was then found to be carbon. G Wicks et al, J Appl Phys, 52 (9), 1981, 5792-25796. 35 5354. The effect of thermal anneafing on the grain size and electrical characteristics of arsenic ion-implanted and laser-irradiated polyerystamne sificon films. (USA) Q-switched Nd: YAG laser irradiation and subsequent thermal anealing are carried out for arsenic ion-implanted polycrystalline silicon films. Crystallographical and electrical characteristics of polycrystalline silicon are studied by using transmission electron microscopy and Hall measurements. Almost all implanted arsenic ions are electrically activated on laser irradiation, but grain growth and crystalline recovery are not found. The crystalline recovery begins to occur and carrier mobility increases during subsequent thermal annealing at temperatures of 500°C and higher. The carrier concentration decreases due to the inactivation of the arsenic atoms with subsequent thermal annealing in the temperature range between 500 and 750°C. At temperatures above 750°C, grain growth and defect annihilation take place, and the carrier concentration per cm 2 increases due to the diffusion and reactivation of arsenic atoms. (Japan) Kenji Shihata and Shinji Onga, J Appl Phys, 52 (9), 1981, 5566-5574. 35 5355. Compensation in Go-doped p-type Ga t _rAIrAs grown by liquid phase epitaxy. (USA) The effect of compensation on the pair spectra from Ge-doped p-type Gao.6oAlo.+oAs grown by liquid-phase epitaxy under high-purity He ambient is investigated. It is found that when the amount of compensation is high, pair transitions occur mainly via the deep G e ~ acceptors at low excitation levels. The addition of oxygen (0.3-0.9 ppm) or H 2 (11 ~ ) to the He ambient during growth reduces the compensation, with hydrogen found to be more effective than 02. For reduced compensation, pair transitions via the shallow acceptors due to residual C and Si are favoured. The compensation is due to the presence of residual donors such as S whose concentration varies from wafer to wafer causing fluctuations in the relative intensities of pair transitions. Since strong pair transitions involving shallow acceptors reflect low concentration of compensating donors and thus improved conductivity in the p layers, the use ofH 2 in the

'~,

He ambient gas during the growth of (GaAl)As double-hetcrolaser structures should be advantageous. V Swaminathan et al, J Appl Phys, 52 (9), 1981, 5603-560?. 35

5356. Sharp profiles with high and. low doping levels in silicon groWn by molecular beam epitaxy. (USA) We fincl mat heavy adsorbed dopant layers, up to several tens of equivalent monolayers, can be made to produce heavily doped n (Sb)and p (Ga) layers in molecular beam epitaxy grown silicon. By preadjustingtbe adiayer concentration to the required value while temporarily arresting silicon growth, arbitrarily sharp profiles of any sequence of dopant type with very high or low levels can be grown. Examples are given o f e + ip + and n + +p+ structures grown with transition thieknees 1<300 A, and with controlled layer thicknesses'of ~ 1000 A, Such structures, difficult to achieve otherwise, should be ideal for fabrication of high-frequency millimeter wave devices. S S l y e r et al, d Appl Phys, 52 (9), 1981, 5608-5613. 35 5357. Properties of nluminium epitaxlal growth on GaAs. (+USA) The structural perfection and epitaxial growth process of Ai films deposited by molecular beam epitaxy (MBE) on (100) GaAs substrates have been analysed by transmission electron microscopy (TEM) and Rutherford backscattering analysis (RBS). Two epitaxial relationships between the AI film and (100) GaAs are observed. In general, deposition on As-rich surfaces at room temperature and low deposition rates (200-750 ~ h - z) lead to < 110> oriented AI films. Higher deposition rates at room temperature yield a mixture of (110> and < 100> oriented fdms or completely (100> oriented films at the higher deposition rates. On Ga-rich surfaces, only (100> oriented AI films are observed. For both epitaxial orientations the misfit elastic strain at the interface is aecomodated by misfit dislocations localized in the AI film for film thickness of ~600 A,. Under these conditions the GaAs substrate at the interface is strain free and dislocation free. The presence of surface steps associated with surface reconstruction at the start of the epitaxial process is invoked to aecouqt for the existence of (110> oriented film growth on <100> substrates. P M Petroff et al, J Appl Phys, 52 (12), 1981, 7317-7320. 35 5358. Comparison of eharacterisation methods for As-doped silicon. (USA} Silicon wafers implanted with arsenic doses from I x l0 ts to 2 × 10 xe As/cm2 were characterized with the following methods: four point probe, bevel and stain, secondary ion mass spectroscopy, spreading resistance, incremental sheet resistance and infrared transmittance and reflectance. The results are compared and the capability of each method is discussed. (West Germany) Hans H Wagner et al, J Appl Phys, 52 (10), 1981, 6173-6177. 35 5359. Metastable honeycomb model of laser annealing. (USA) A model for microstructural double bifurcation following abrupt energy deposition by intense laser pulses to produce epitaxial regrowth of disordered Si surface layers can account for recent observations that indicate local heating far below the bulk melting point. The model also indentifies and explains anomalous functional behaviour in k'(o), the crystal impurity segregation coefficient, as a function of regrowth front velocity v. J C Phillips, J Appl Phys, 52 (12), 1981. 7397-7402. 35 5360. Growth of Sb and lnSb by molecular-beam epitaxy. (USA) The temperature dependence of the surface lifetime of free antimony on lnSb has been determined using 10-kV reflection electron diffraction (RHEED). A desorption activation energy was extracted from these data and found to have a value of 64.2+3 K cal/mole which is within experimental error of AH (sublimation) for monatomic Sb. At substrate temperatures of 280°C, it was possible to nucleate antimony in an epitaxial relationship with (111 )A- and (111 )B-oriented InSb surface; subsequent epitaxiai growth could continue at temperatures as low as 40°C. Films of InSb were grown bomoepitaxially on (11 I)A-, (111)B-, and (001)--oriented InSb substrates and heteroepitaxially on (001)-oriented lnAs and Ga~s over a wide temperature range, 280°< T<450°C. Surface-atom recon, structions for Sb-stahilized and In-stabilized films are +identified. A J Noreika et al, J Appl Phys, 52 (12), 1981, 7416-7420. 3+5 5361. The effect of substrate growth temperatm-e on deep levels in nAIxGa, _~As growth by molecular beam epitaxy, (USA) The deep level transient spectroscopy (DLTS) technique has:been used'to study changes in electron trapping centres as a function of substmte

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