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Journal of Applied Physics

Issue 12 • Date Jun 1990

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Displaying Results 1 - 25 of 70
  • Comparison of the χ(3) values of crystalline and amorphous thin films of 4‐butoxy‐carbonyl‐methyl‐urethane polydiacetylene at 1.06 and 1.3 μm

    Page(s): 7199 - 7203
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    The third‐order optical nonlinear susceptibilities of single‐crystalline and spin‐coated amorphous 4‐butoxy‐carbonyl‐methyl‐urethane polydiacetylene (red form) thin films were measured by third‐harmonic generation. The third‐harmonic intensities were calculated as a function of incident angle by solving the propagation equation of the electromagnetic field for a two‐layer system with one nonlinear media. From the best fit of the calculated and experimental data, the ( χ(3)) values of the spin‐coated amorphous film (χ(3)p) were found to be (9.6±1.0)×10-12 esu and (2.0±0.2)×10-11 esu at 1.064 and 1.319 μm, respectively, while the χ(3) values of the crystalline ( χ(3)pc) were (4.9±0.5)×10-11 esu and (1.0±0.07)×10-10 esu at 1.064 and 1.319 μm, respectively. A factor of five increase in the χ(3) of the crystalline film is attributed to the orientation effect of the polymer chains. The enhancement of the nonlinearity at 1.319 μm may be due to either three‐photon or two‐photon resonant effects. View full abstract»

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  • Boron doping of silicon by ArF excimer laser irradiation in B2H6

    Page(s): 7204 - 7210
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    Boron doping of silicon using a pulsed ArF excimer laser (λ=193 nm, FWHM=17 ns) with B2H6 has been investigated. Doping atoms are supplied mainly from both thermal and photochemical decomposition of the adsorbed layers on the surface. UV laser irradiation realizes both high surface carrier concentration (1×1021 cm-3) and a very shallow junction (0.1 μm). Diodes fabricated by laser doping show good electrical characteristics (n factor=1.10, reverse current density=1×10-7 A/cm2 at -5 V). Thermal annealing improves the reverse current density (3×10-9 A/cm2 at -5 V). A numerical calculation of boron concentration profiles has been performed by solving the diffusion equation in the melted region, which is evaluated by the heat conduction equation. From this calculation the diffusion coefficient of boron in liquid phase silicon (3×10-4 cm2/s) is obtained. View full abstract»

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  • A study of Si implanted with oxygen using spectroscopic ellipsometry

    Page(s): 7211 - 7222
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    Si(100) wafers were implanted with O+ at an energy of 180 keV to a dose of 2.3×1018/cm2 in the separation by implanted oxygen process. Following implantation, one wafer was annealed at 1275 °C for 2 h. Spectroscopic ellipsometry measurements were then performed on these samples. Effective medium modeling of the measurements was used to nondestructively depth profile the samples. These results show that the superficial Si layer for the unannealed sample includes noncrystalline and crystalline components. In addition, the optical properties of the buried oxide for the unannealed sample were found to be different from those of bulk fused silica or thermal oxides of Si. The superficial Si layer for the annealed sample was crystalline Si, but the buried oxide consisted of a phase‐separated mixture of noncrystalline SiO2 and crystalline Si. These results were further substantiated by selective chemical etch‐back studies and additional spectroscopic ellipsometry measurements, and by other techniques, including Raman spectroscopy, infrared transmission measurements, sputter depth profiling using x‐ray photoelectron spectroscopy, and Nomarski microscopy. View full abstract»

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  • Bounds on the thermoelastic properties of suspensions of spheres

    Page(s): 7223 - 7227
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    Three‐point upper and lower bounds on the effective thermal expansion coefficient and specific heats of statistically isotropic suspensions of mutually impenetrable spheres are computed for the first time. The three‐point bounds depend upon the microstructure via a three‐point spatial correlation function of the medium. Both equisized and multisized spheres are considered, and hence the effect of polydispersivity in sphere size on the thermoelastic properties is determined. For reasons of mathematical analogy, the results of this study for the thermal expansion coefficient translate immediately into equivalent results for the hygroscopic expansion coefficient. View full abstract»

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  • A distributed parameter wire model for transient electrical discharges

    Page(s): 7228 - 7239
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    A model for freely propagating transient electrical discharges, such as lightning and punch‐through arcs, is developed in this paper. We describe the electromagnetic fields by Maxwell’s equations and we represent the interaction of electric fields with the medium to produce current by ∂J/∂t=ω2(E-E*Ĵ)/4π, where ω and E* are parameters characteristic of the medium, J≡current density, and Ĵ≡J/∥J∥. We illustrate the properties of this model for small‐diameter, guided, cylindrically symmetric discharges. Analytic, numerical, and approximate solutions are given for special cases. The model describes, in a new and comprehensive fashion, certain macroscopic discharge properties, such as threshold behavior, quenching and reignition, path tortuosity, discharge termination with nonzero charge density remaining along the discharge path, and other experimentally observed discharge phenomena. Fields, current densities, and charge densities are quantitatively determined from given boundary and initial conditions. We suggest that many macroscopic discharge properties are properly explained by the model as electromagnetic phenomena, and we discuss extensions of the model to include chemistry, principally ionization and recombination. View full abstract»

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  • Fast metastable argon atoms from a hot‐cathode discharge

    Page(s): 7240 - 7245
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    Metastable atoms emitted from the anode of a hot‐cathode low‐voltage Ar gas discharge produce two peaks in the time‐of‐flight distribution. The slow peak typifies atoms with a thermal velocity distribution in the discharge. The fast peak can be approximated by a Gaussian function, and its dependence on the discharge current, voltage, and pressure is presented. The origin of the fast peak is investigated experimentally and shown to represent fast Ar(3P2,0 ) from the discharge. View full abstract»

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  • Plasma waves in a bounded anisotropic plasma: Influence of the electron density inhomogeneity

    Page(s): 7246 - 7253
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    The influence of a radial electron density inhomogeneity on plasma modes propagating in a cylindrical bounded plasma immersed in an axial static magnetic field, and the variations of the wave characteristics induced by a dielectric layer surrounding the plasma have been studied. The computations show that the electromagnetic‐field radial distribution can be very sensitive to the electron density gradient, with or without the presence of the dielectric. View full abstract»

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  • Temperature and relative density of atomic hydrogen in a multicusp H- volume source

    Page(s): 7254 - 7264
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    The Balmer β and γ line shapes have been analyzed to determine the relative density and the temperature of hydrogen atoms in magnetic multicusp plasma generators. Results for a 90‐V, 4–40‐mTorr, 1–18‐A conventional multicusp plasma generator and a 50‐V, 4‐mTorr, 1–15‐A hybrid multicusp plasma generator are presented. The relative number density of hydrogen atoms increased smoothly with pressure and discharge current but never exceeded 10%. The absolute atomic number density in a 90‐V 10‐A discharge varied in proportion with pressure. The atomic temperature (in the 0.1–0.4‐eV range) decreased with pressure and slowly increased with the discharge current. The role of atoms in the processes determining the H- temperature and the H2 vibrational and rotational temperatures is discussed. The results confirm that in multicusp negative‐ion sources collisional excitation of ground state atoms and molecules by energetic electrons is the dominant process in Balmer‐β and ‐γ light emission. View full abstract»

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  • Investigation of copper electrodes for mercuric iodide detector applications

    Page(s): 7265 - 7267
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    Copper diffusion in mercuric iodide was studied by low‐temperature photoluminescence (PL) spectroscopy and Auger electron spectroscopy. A broad radiative emission band at a wavelength of about 6720 Å in the PL spectra was found to be related to Cu incorporation in the crystal. PL spectra obtained from surface doping experiments indicate that Cu is a rapid diffuser in HgI2 bulk material. Auger electron spectroscopy performed as a function of depth from the crystal surface confirms the rapid bulk diffusion process of Cu in HgI2. Fabrication of HgI2 nuclear detectors with Cu electrodes indicates that Cu is not acceptable as an electrode material, which is consistent with the fact that it diffuses easily into the bulk crystal and introduces new radiative recombination centers. View full abstract»

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  • Application of the charged point‐defect model to diffusion and interdiffusion in GaAs

    Page(s): 7268 - 7273
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    Diffusion and interdiffusion in GaAs and GaAs/AlGaAs superlattices are shown to be consistent with the charged point‐defect model. The charged Ga vacancies V3-Ga and interstitials I2+Ga appear to control group II, III, and probably V element diffusion. After adjustment for carrier concentration and As pressure, these elements are found to have a nearly identical intrinsic diffusivity and activation energy over a wide range of temperature. A natural consequence of Ga diffusion via negative or positive point defects is that enhanced group‐III interdiffusion is expected with either n‐ or p‐type doping. Anomalous enhancements in group‐II dopant diffusivity have been related to the supersaturation of Ga interstitials. View full abstract»

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  • Strain relaxation of Ge films grown on a Si(001)‐2×1 surface by molecular beam epitaxy

    Page(s): 7274 - 7277
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    The crystalline quality of Ge films grown on a Si(100)‐2×1 substrate by molecular beam epitaxy has been studied by means of in situ reflection high‐energy electron diffraction, x‐ray diffraction, and Raman scattering spectroscopy. The Ge layers of thickness up to 4000 Å were deposited at 400 °C with and without thin (200 Å) Ge buffer layers predeposited at 200 °C. It was found that the buffer layers were effective in improving the quality of the thin Ge overlayers, while they had no noticeable effect on the thick layers whose x‐ray and Raman spectra were comparable to that of bulk Ge. It was also found that, even after the Ge films became relaxed with a generation of dislocations, they were not free from strain due to the lattice mismatch. This finding is supported by the quantitative estimate of the Raman frequency shift in terms of the uniaxial strain model. View full abstract»

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  • Separation of magnetic and topographic effects in force microscopy

    Page(s): 7278 - 7280
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    Several techniques are presented which allow magnetic force microscopy to be performed while simultaneously mapping the surface topographic features of a magnetic sample. The separation of magnetic and topographic features measured simultaneously with a scanning force microscope is made possible by an instrument based on a differential interferometer that can detect cantilever deflections of 0.005 nm at a frequency as low as 1 Hz. Two different applications are presented. View full abstract»

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  • Characterization of ion‐implanted and rapidly thermal annealed GaAs by Raman scattering and van der Pauw measurement

    Page(s): 7281 - 7286
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    The structures of microcrystalline or amorphous gallium arsenide (GaAs) introduced by 120‐keV Si+‐ or P+‐ion implantation with a dose of 1×1016 atoms/cm2 and the subsequent regrowth properties annealed by rapid thermal annealing in the range from 300 to 900 °C have been investigated by Raman scattering (RS) and by the van der Pauw measurement (sheet carrier concentration and sheet resistivity) [Phillips Res. Rep. 13, (1958)]. Raman spectra of the LO‐phonon mode observed for 514.5‐ and 457.9‐nm excitation of an Ar+ laser have been analyzed on the basis of a spatial correlation model [H. Richter et al., Solid State Commun. 39, 625 (1981); K. K. Tiong et al., Appl. Phys. Lett. 44, 122 (1984)]. The results show that the regrowth stages and the regrowth rates of the disordered GaAs in the annealing process depend on the excitation wavelength and annealing temperature, and the damaged layer regrows epitaxially toward the surface. Sheet carrier concentration was observed to increase steeply, and sheet resistivity decreased rapidly when the annealing temperature was raised from 600 to 700 °C. These results are consistent with the RS result of the 514.5‐nm excitation in the same temperature range. The above results indicate that the implanted silicon atoms replace the GaAs lattice sites and the recrystallization of the microcrystalline GaAs substrate occurs in this temperature range. On the other hand, the sheet resistivities were observed to increase from about 5×104 to 5×106 (Ω/⧠), when the annealing temperature was raised from room temperature to 500 °C, contrary to the 600–700 °C case. From these facts, it is concluded that the regrowth process originates principally from the recrystallization of the ion‐implantation‐i- nduced damaged GaAs substrate. View full abstract»

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  • Stable damping associated with linear viscous motion of the interface in a multiphase Al‐Zn alloy

    Page(s): 7287 - 7291
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    In the present paper, the characteristics of low‐frequency stable damping are studied in a multiphase eutectoid Al‐Zn alloy. Experimental results show that, within a low‐temperature and low‐strain‐amplitude range, the damping evidently manifests itself by linear viscous characteristics, namely, it obeys a law Q-1=(B/fn)exp(-nH/kT), where H is the real process activation energy, B and n (=0.21) are two experimental parameters, and k is the Boltzmann constant. A value of H=0.74 eV is obtained, which is closely related to the viscosity during interface motion. Accordingly, a linear viscous interface motion mode is put forward and can explain the experimental results as well. View full abstract»

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  • Microstructure and mechanical properties of ion‐beam‐produced Fe‐Ti‐(N), Fe‐Ti‐(C), and Fe‐Ti‐(C,N) surface films

    Page(s): 7292 - 7299
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    Ion‐mixed films of Fe53 Ti47 were produced by ion irradiating a Fe‐Ti multilayer structure on AISI 304 stainless steel. The ion‐mixed films were subsequently implanted with nitrogen, carbon, or both carbon and nitrogen. The microstructure following nitrogen implantation consisted of a bcc solid solution of iron and titanium and finely dispersed TiN precipitates. In the cases of carbon or carbon and nitrogen implantation, a two‐phase structure consisting of an amorphous matrix with TiC or Ti(C,N) precipitates was found. All these films initially possessed improved tribological properties as revealed by lowered friction and increased wear resistance. However, after an extended test of 1000 wear cycles, a reduced friction was only observed for the carbon or carbon and nitrogen implanted samples. The wear track on the dual implanted surface was extremely smooth, while the surface of the nitrogen‐implanted sample was partly worn through, causing the friction to increase to the level of the untreated sample. The improved tribological properties of the implanted films are attributed to an increase in surface hardness. However, the surface hardness is unable to explain differences between different implantations. In the case of the dual carbon and nitrogen implantation, improvements appear to be in part the result from an increased capability to accommodate plastic deformation. These conclusions are supported by transmission electron microscope studies of the wear tracks as well as by nanoindentation measurements. View full abstract»

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  • Saturation of the even‐order bounds on effective elastic moduli by finite‐rank laminates

    Page(s): 7300 - 7306
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    Sufficient conditions on the phase geometry for the reduction of even‐order bounds to bounds of second order are derived. It is found that finite‐rank laminates satisfy the sufficient conditions asymptotically as the length scale of the laminar microstructure goes to zero. This result is used to show that the effective elastic tensors of finite‐rank laminates saturate the even‐order bounds in the fine‐scale limit. View full abstract»

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  • Local mode spectroscopy and photo‐induced effects of oxygen‐related centers in semi‐insulating gallium arsenide

    Page(s): 7307 - 7312
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    Vibrational absorption of semi‐insulating O‐containing GaAs samples has been investigated under high‐resolution spectroscopy at low temperature and many sharp lines due to localized modes have been observed. Some of them, between 714 and 730 cm-1 had already been ascribed to some (Ga,O)‐related center having features common with the vacancy‐oxygen defect in silicon, but a new state related to this center, giving a local mode near 713 cm-1 is reported here for the first time. Another new low‐frequency mode at 604 cm-1 is also reported, involving probably nitrogen or more likely oxygen bonded to two next‐nearest‐neighbor Ga atoms. The attribution of new modes in the 950–1400 cm-1 spectral region to complexes involving oxygen, arsenic, and eventually impurities with 100% isotopic abundance is discussed. The effects of near‐infrared illumination on the observation of the (Ga,O)‐related modes between 713 and 730 cm-1 and on a new mode at 983 cm-1 have been studied. Tentative explanations based either on metastability or on photo‐induced changes of the charge states of the centers are proposed. These results seem to show that in GaAs, oxygen decorates native centers and that this kind of study could provide a clue to their understanding. View full abstract»

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  • Phase formation sequence for the reaction of multilayer thin films of Nb/Al

    Page(s): 7313 - 7322
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    We have investigated the phase formation sequence for the reaction of Nb and Al in multilayer films using cross‐sectional transmission electron microscopy and x‐ray diffraction. NbAl3 is the first intermetallic phase to form. Contrary to previous reports, we find evidence from cross‐sectional transmission electron microscopy that the sigma phase, Nb2Al, is not bypassed in the reaction sequence. Instead, its formation is concurrent with the formation of the superconducting A15 phase, Nb3Al. However, depending on the periodicity and the composition of the film, the Nb2Al phase can be consumed by the Nb3Al phase for long annealing times. The significance of this phase formation sequence to powder metallurgically processed magnet wire is discussed. View full abstract»

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  • Hugoniot of amorphous metallic ribbon Metglas 2605CO for stresses of 0–38 kbars

    Page(s): 7323 - 7328
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    A light gas gun has been used to measure the Hugoniot of Metglass 2605CO ribbon. Quartz gauges were used to measure stress. Both front‐ and rear‐surface measurements were done. Front‐surface experiments impacted the ribbon onto quartz gauges, while back‐ surface experiments impacted an aluminum plate into the ribbon which was backed by a quartz gauge. Single layers and composite layers of the ribbon were used. Two single‐layer front‐surface experiments provided the most accurate data. View full abstract»

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  • Selected‐area deposition of diamond films

    Page(s): 7329 - 7336
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    Selected‐area deposition of diamond film has been accomplished on Si substrates prepared by two different methods: reactive‐ion etching (RIE) and amorphous‐Si masking (ASM). In the RIE method, a Si substrate polished by a diamond paste was patterned with a photoresist mask, and the unprotected areas were etched by RIE, followed by a complete removal of the photoresist films. The diamond deposition was done by electron‐assisted chemical‐vapor deposition (CVD), and diamond films grew only in the areas once covered with the photoresist films and not etched by RIE. In the ASM method, a polished Si substrate was also photolithographically masked with photoresist, followed by a uniform deposition of a hydrogenated amorphous silicon (a‐Si:H) film. The photoresist film was then lifted off together with the overlay of deposited a‐Si:H, leaving the polished Si surface patterned with an a‐Si:H mask. In this case, the diamond deposition was done by microwave plasma CVD, and diamond films grew only in the areas not covered with a‐Si:H. In both cases, well‐defined diamond patterns with line/space dimensions of a few micrometers were formed on the substrates. View full abstract»

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  • Oxygen distribution in silicon‐on‐insulator layers obtained by zone melting recrystallization

    Page(s): 7337 - 7347
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    The oxygen content in zone melting recrystallization silicon‐on‐insulator (ZMR SOI) layers with thicknesses ranging between 0.5 and 25 μm obtained with a movable lampheater is studied. Secondary‐ion‐mass spectrometry profiling as well as numerical calculations are presented. The simulations are based on oxygen redistribution during cooling down. In the model it is assumed that the interface reaction is fast enough to be not the rate‐limiting step in the redistribution process. Consequently, the oxygen transport was considered to be entirely diffusion limited. Good agreement was found between the measurements and calculated values. The profiles show a maximum at the center of the layer and symmetrically depleted regions in the top and bottom of the silicon film. It has been generally accepted that ZMR SOI layers have a high oxygen concentration corresponding to the saturation level at melting point. In the present study, however, we show that in the 0.5‐μm layers the oxygen concentration is as low as 1×1017(O atoms)/cm3. View full abstract»

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  • Thermal stability of the Cu/Ta/PtSi structures

    Page(s): 7348 - 7350
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    Cu/Ta/PtSi structures are heated between 200 and 700 °C, with Ta as a barrier for improving the thermal stability of Cu/PtSi. A small amount of Cu silicides is observed after a 30‐min anneal in N2‐H2 at 300-400 °C. This is accompanied by an extensive mixing among the components present, and increasing sheet resistances. By comparing with the reactions of the Cu/Ta/Si, Al/Ta/PtSi, and Al/Ta/Si structures, the mechanisms suggested earlier are supported, with the high affinity of Cu toward Si playing a major role for the low thermal stability of the Cu/PtSi structures with and without various barrier layers. View full abstract»

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  • Defect identification in semiconductor alloys using deep level composition dependence. II. Application to GaAs1-xPx

    Page(s): 7351 - 7358
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    We predict the x dependencies of deep levels produced by vacancy‐impurity complexes in GaAs1-xPx. These predictions, along with those obtained earlier for the x dependencies of deep levels due to impurities, show that the slope of a deep level with x depends strongly on the site of the impurity atom for both complexes and isolated impurities. Furthermore, we find that the slopes of some of the levels produced by the vacancy complexes are very different than those associated with the corresponding point defects. We thus suggest that the theory can be used to obtain site information about the defect producing an observed level and, in favorable cases, to distinguish between levels produced by isolated impurities and those produced by complexes. We also present photoluminescence data on two unknown centers in GaAs1-xPx and compare some of our theoretical slopes with those of the levels extracted from the data. The results show that the theory can be useful as an aid to defect identification in GaAs1-xPxx. View full abstract»

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  • Rechargeable E’ centers in silicon‐implanted SiO2 films

    Page(s): 7359 - 7367
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    Implantation of Si in does of 1015–1016 cm-2 into dry thermal oxides on silicon wafers produces a three‐state MOS memory device. For both positive‐ and negative‐going traps, gate voltage stress up to ±10 MV/cm-1 generates stable (±) oxide charge near the gate and (∓) charge near the substrate. Electron paramagnetic resonance (EPR) measurement on corona‐field (≤11 MV/cm) stressed oxides reveals E’ centers in regions of positive charge, which may be recycled between the EPR‐visible (+) state and the invisible neutral state. The correspondence of charge and EPR indicates a composite or Feigl‐Fowloer‐Yip E’ center, O3 3/4 Si:...+Si 3/4 O3, arising from nonstoichiometric Si fused into the SiO2 lattice. Upon trapping an electron, the center rebonds to yield O3 3/4 SiSi 3/4 O3. The charging parameters of the E’ center suggest tunneling of an electron from the (0→+) state, and are consistent with the theoretical prediction of the energy level and Franck–Condon relaxation. The three types of E’ centers observed in this and related studies are compared with the Eα, Eβ and Eγ variants of bulk amorphous silica. View full abstract»

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  • Impact ionization of deep traps in semi‐insulating GaAs substrates

    Page(s): 7368 - 7372
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    The behavior of the leakage current in the semi‐insulating substrate of a GaAs device is more complicated than previously recognized. The voltage dependence of this current seen in a conventional voltage‐controlled experiment has hysteresis, which arises from an S‐type negative differential conductivity (S‐NDC). This is incompatible with the conventional trap‐fill‐limited model, and we propose an alternative explanation based on the impact ionization of deep‐level traps. We show how this simple model can account qualitatively for the S‐NDC and the associated current instability, and how it can be extended when the deep traps are photoexcitable. View full abstract»

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Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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Editor
P. James Viccaro
Argonne National Laboratory