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15 Jun 1994

Volume 75, Issue 12, pp. 7607-8246

Page 2 of 5 Pages Previous Page Next Page | Jump to Page

Single crystalline GaSe/WSe2 heterointerfaces grown by van der Waals epitaxy. I. Growth conditions

O. Lang, R. Schlaf, Y. Tomm, C. Pettenkofer, and W. Jaegermann

J. Appl. Phys. 75, 7805 (1994); http://dx.doi.org/10.1063/1.356562 (9 pages) | Cited 31 times

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Epitaxial GaSe films have been prepared on WSe2 (0001) substrates with 14% lattice mismatch and characterized by photoelectron spectroscopy, electron diffraction, and ex situ by tunneling microscopy. The films grow in the Frank–van der Merve growth mode. The best films with perfect azimuthal orientation are formed after an annealing step at 720 K. The basic mechanisms of this van der Waals epitaxy are qualitatively discussed in terms of thermodynamic and kinetic parameters.  
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Single crystalline GaSe/WSe2 heterointerfaces grown by van der Waals epitaxy. II. Junction characterization

O. Lang, Y. Tomm, R. Schlaf, C. Pettenkofer, and W. Jaegermann

J. Appl. Phys. 75, 7814 (1994); http://dx.doi.org/10.1063/1.356563 (7 pages) | Cited 16 times

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The junction properties of GaSe/WSe2 heterointerfaces grown by van der Waals epitaxy have been characterized by photoelectron spectroscopy and surface photovoltage measurements (SPV). The surfaces of p‐WSe2 substrates doped with Se excess convert to n doping during annealing at T≥720 K, leading to a SPV of 330 mV. Deposited p GaSe forms an n‐p heterodiode opposing the p‐n homodiode within the substrate. Promising results are obtained for n‐WSe2/p‐GaSe heterointerfaces with SPV of at least 0.3 eV. The valence band and conduction band offsets are 0.6 and 0.2±0.1 eV, respectively, in accordance with the Anderson model of heterojunction formation.  
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ga II-VI semiconductors
79.60.Dp Adsorbed layers and thin films

Nitrogen‐doped ZnSe with selenium‐rich growth by low‐pressure organometallic chemical vapor deposition

M. K. Lee, M. Y. Yeh, S. J. Guo, and H. D. Huang

J. Appl. Phys. 75, 7821 (1994); http://dx.doi.org/10.1063/1.357029 (4 pages)

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A high‐quality nitrogen‐doped p‐type ZnSe epilayer on (100) GaAs substrate was obtained under selenium‐rich growth conditions by low‐pressure organometallic chemical vapor deposition. Ammonia was used as the dopant source. The resistivity (0.5 Ω cm) and the free‐carrier concentration (p=8.8×1017 cm−3) of as‐grown ZnSe:N were derived from Hall measurements. With selenium‐rich growth conditions, we can reduce the concentration of compensation defects (VSe‐Zn‐NSe which acts as a donor in ZnSe). Nitrogen is found to incorporate in ZnSe as a shallow level, which is examined by the dependence of free‐to‐acceptor emission on the NH3/H2Se molar ratio. The carrier concentration of as‐grown ZnSe:N seems to change insignificantly within a wide range of growth temperatures. That is thought to be useful for device fabrication due to uniformity considerations.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Study of interdiffusion in Pd/Cu multilayered films by Auger depth profiling

I. J. Jeon, J. H. Hong, and Y. P. Lee

J. Appl. Phys. 75, 7825 (1994); http://dx.doi.org/10.1063/1.356564 (4 pages) | Cited 5 times

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In thin films, diffusion phenomena play an important role for the growth process, and in the understanding of the mechanical, electrical and magnetic properties. The change in the concentration profile due to the interdiffusion by annealing was investigated using Auger electron spectroscopy depth‐profiling technique on Pd/Cu multilayered films. It was observed that the initial concentration distributions, which were almost rectangular in the unheated samples, were changed into sinusoidal ones in the annealed films at various temperatures. The concentration‐independent interdiffusion coefficients were calculated from the amplitudes of sinusoidal distributions. The activation energy was determined to be 1.66±0.23 eV from the Arrhenius plot. The concentration‐dependent interdiffusivity at 150 °C was also estimated using Boltzmann–Matano method.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
66.30.Ny Chemical interdiffusion; diffusion barriers
79.20.Fv Electron impact: Auger emission

Oxygen incorporation and oxygen‐induced defect formation in thin Si and Si1−xGex layers on silicon grown by chemical vapor deposition at atmospheric pressure

D. Krüger, Th. Morgenstern, R. Kurps, E. Bugiel, Ch. Quick, and H. Kühne

J. Appl. Phys. 75, 7829 (1994); http://dx.doi.org/10.1063/1.356565 (6 pages) | Cited 1 time

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The incorporation of oxygen into thin epitaxial Si and heteroepitaxial Si1−xGex layers deposited, applying a conventional atmospheric pressure process, from silane, germane, hydrogen chloride, and hydrogen gas mixtures in a temperature range from 1070 to 720 °C is analyzed. The role of oxygen for defect formation has been shown by means of a correlation between high resolution defect analysis using transmission electron microscopy and quantitative oxygen depth profiling using Auger electron spectroscopy and secondary ion mass spectrometry. In the low‐temperature region traces of residual H2O vapor lead to oxygen precipitation. These precipitates are the origin of extended lattice defects such as stacking faults and microtwins and can result in highly defective films with polycrystalline inclusions and increased surface roughness. It was found that, in order to prevent the observed defects, it is necessary to keep the oxygen concentration below 3×1019 cm−3. However, by carefully controlling the experimental parameters it is also possible to realize nearly defect‐free structures with high oxygen concentrations up to 1020 cm−3.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.35.Dv Composition, segregation; defects and impurities

Effect of As4/Ga flux ratio on electrical and optical properties of low‐temperature GaAs grown by molecular beam epitaxy

S. O’Hagan and M. Missous

J. Appl. Phys. 75, 7835 (1994); http://dx.doi.org/10.1063/1.356566 (7 pages) | Cited 24 times

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Hall‐effect, near‐band‐edge infrared absorption, and photoluminescence measurements have been carried out on undoped and Si‐ and Be‐doped GaAs layers grown by molecular beam epitaxy at a substrate temperature of 250 °C, under As4/Ga flux ratios varying from As‐rich to stoichiometric growth conditions. Dopant concentrations at or above ∼1×1019 cm−3 appear to reduce the incorporation of excess arsenic as both antisite and interstitial defects at all flux ratios at this growth temperature, but only under stoichiometric conditions for Si doping of 1×1018 cm−3. The effect is attributed to dopant influencing the dissociation of the As4 molecule and the incorporation of excess As atoms into the crystal. Highly doped n‐type material with excellent electrical and optical properties, and high electrical quality p‐type material have been achieved by moving towards stoichiometric growth conditions. This is believed to be due to further reduction of formation of compensating defects, Ga vacancies in the n‐type case, As antisites in the p type. A photoluminescence peak at 1.24 eV suggests the formation of SiGa−VGa pair defects in the highly Si‐doped material.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Fd III-V semiconductors

Effect of anisotropy on the excess stress and critical thickness of capped Si1−xGex strained layers

K. Shintani and K. Fujita

J. Appl. Phys. 75, 7842 (1994); http://dx.doi.org/10.1063/1.356567 (5 pages) | Cited 3 times

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By using the anisotropic image force theorem of Barnett and Lothe, single‐ and double‐kink models for capped (buried) Si1−xGex strained layers are extended so as to take into account cubic anisotropy. The crystallographic configuration considered is such that the free surface is a (001) plane, misfit dislocation segments in the [110] direction and threading dislocations in the [011] direction lie within a (111) glide plane, and the Burgers vector is 1/2[101]. The results show that the effect of cubic anisotropy is significant and that it tends to decrease the excess stress and to increase the critical layer thickness in both of the single‐ and double‐kink models.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology

Thermal stability study of TiN/TiSi2 diffusion barrier between Cu and n+Si

Tzong‐Sheng Chang, Wen‐Chun Wang, Lih‐Ping Wang, Jenn‐Chang Hwang, and Fon‐Shan Huang

J. Appl. Phys. 75, 7847 (1994); http://dx.doi.org/10.1063/1.356568 (5 pages) | Cited 10 times

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The failure mechanism of the TiN/TiSi2 bilayers as diffusion barriers between Cu and n+Si was investigated. The TiN/TiSi2 bilayers were formed by either annealing Ti (50 nm)/n+Si via various rapid thermal processes or reactively sputtering TiN (50 nm) on TiSi2. The degradation study of the Cu/TiN/TiSi2/n+Si contact system was undertaken by scanning electron microscopy, cross‐section transmission electron microscopy (XTEM), secondary‐ion‐mass spectrometry (SIMS), and diode leakage current and contact resistance measurements. Leakage current measurements indicated no deterioration of n+‐p diode junctions up to 475 °C for 30 min in a N2 ambient. For the sintering temperature at 500 °C, the leakage current increased abruptly and SIMS profiles revealed a large amount of Cu atoms diffusing into the junctions of n+‐p diodes. XTEM showed that the small pyramidal‐shaped Cu3Si crystallite (with a size 0.25 μm) precipitated in the n+Si substrate. The formation of Cu3Si increased the occupied volume, then generated the gap between TiSi2 and n+Si, and gradually increased the specific contact resistance. The diffusion resistance, depending on the thickness of TiN film, was also observed.
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68.60.Dv Thermal stability; thermal effects
73.40.Cg Contact resistance, contact potential
85.40.Ls Metallization, contacts, interconnects; device isolation

Atomic ordering and domain structures in metal organic chemical vapor deposition grown InGaAs (001) layers

Tae‐Yeon Seong, A. G. Norman, G. R. Booker, and A. G. Cullis

J. Appl. Phys. 75, 7852 (1994); http://dx.doi.org/10.1063/1.356569 (14 pages) | Cited 28 times

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Transmission electron microscope, transmission electron diffraction, and high resolution electron microscope studies have been made of metal organic chemical vapor deposition In0.53Ga0.47As layers grown on (001) InP or GaAs substrates to investigate the CuPt‐type atomic ordering and associated microstructures present. The amount of ordering, the geometry of the (111) and (111) ordered domains, and the occurrence of anti‐phase boundaries (APBs) were determined as a function of the layer growth temperature and rate. The results are interpreted in terms of mechanisms involving ordering at the layer surface and disordering in a transition region below the surface. From a consideration of the former it is concluded that atomic steps associated with surface undulations have a major influence on the domain geometry and APBs. The different structures that occur, their dependence on growth conditions and their possible effects on the electrical and optical properties are discussed.
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68.55.-a Thin film structure and morphology
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Structural characterization of a bonded silicon‐on‐insulator layer with voids by micro‐Raman spectroscopy

Akira Usami, Masaya Ichimura, Takao Wada, and Shun‐ichiro Ishigami

J. Appl. Phys. 75, 7866 (1994); http://dx.doi.org/10.1063/1.356570 (3 pages) | Cited 1 time

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Crystalline quality in a void region of a bonded silicon‐on‐insulator (SOI) wafer is evaluated by micro‐Raman spectroscopy. Downshifting and broadening of the Si optical‐phonon peak are observed at the edge of the void, while spectra within the void are little different from those outside the void. Comparison with calculated results based on the theory of the phonon localization shows that both the shift and the broadening are mainly due to structural disorder and not strain. Electrical properties in a void region are also evaluated by a laser‐microwave method. The lifetime of excess carriers has its minimum value at the void edge. Those results consistently show that the SOI layer is deformed plastically rather than elastically at the boundary of the void.  
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68.55.-a Thin film structure and morphology
78.30.Hv Other nonmetallic inorganics

Dopant electrical activity of Si and Si1−xGex multilayer structures doped with δ‐like boron spikes at different temperatures

P. Gaworzewski, D. Krüger, R. Kurps, H. Rücker, and H. P. Zeindl

J. Appl. Phys. 75, 7869 (1994); http://dx.doi.org/10.1063/1.356571 (6 pages) | Cited 8 times

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Boron spikes within multilayer structures of Si and of Si1−xGex deposited by means of molecular‐beam epitaxy (MBE) at different temperatures have been investigated by secondary‐ion‐mass spectrometry (SIMS), spreading resistance, and Hall‐effect measurements. For a Ge amount of x=7% it is shown that segregation effects, electrical activity of B, steepness of B spikes, and solid solubility of B differ in Si and Si1−xGex at the same deposition temperatures. For Si1−xGex growth the surface segregation is significantly reduced in comparison to the growth of Si layers. Steeper B profiles can be obtained at same temperatures but the amount of electrically inactive B is higher. Calculations of the charge‐carrier distributions near the spikes have been performed using classical and quantum mechanical approaches to find out reasons for deviations of the concentration profiles of B and of holes obtained from SIMS and from spreading resistance measurements, respectively.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.61.Le Other inorganic semiconductors

Crystallization in fluorinated and hydrogenated amorphous silicon thin films

F. Edelman, C. Cytermann, R. Brener, M. Eizenberg, Yu. L. Khait, R. Weil, and W. Beyer

J. Appl. Phys. 75, 7875 (1994); http://dx.doi.org/10.1063/1.356572 (6 pages) | Cited 14 times

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The amorphous‐to‐crystalline (AC) transition of amorphous Si thin films containing fluorine or hydrogen is studied by transmission electron microscopy. The AC transition can be described quantitatively by the incubation time prior to the onset of crystallization t0. This parameter is found to decrease exponentially with temperature with an activation energy of 1.7 eV for a‐Si:F and 3.1 eV for a‐Si:H:D. It is found that during the crystallization process in a‐Si:F the crystallites organize as dendrite single crystals oriented along the 〈110〉 axis perpendicularly to the film surface. a‐Si samples that had been covered by Pd or Al crystallize at appreciably lower temperatures. In the case of Al lower activation energies of 0.7 eV for hydrogenated and 0.4 eV for fluorinated a‐Si are measured. In the case of Pd/a‐Si:H,F for both kinds of a‐Si an activation energy of 1.7 eV is found.
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68.55.-a Thin film structure and morphology
61.43.Dq Amorphous semiconductors, metals, and alloys
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Self‐induced laterally modulated GaInP/InAsP structure grown by metal‐organic vapor‐phase epitaxy

A. Ponchet, A. Rocher, A. Ougazzaden, and A. Mircea

J. Appl. Phys. 75, 7881 (1994); http://dx.doi.org/10.1063/1.356573 (3 pages) | Cited 37 times

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Zero‐net strained multilayer alternating tensile GaInP and compressive InAsP have been grown on (001)InP by metal‐organic vapor‐phase epitaxy. A structural analysis using transmission electron microscopy (TEM) is reported. A remarkably regular laterally modulated structure has been observed. GaInP‐ and InAsP‐rich vertical zones alternate with a periodicity of 0.28 μm along the lateral [110] direction, thus balancing the mismatch along the [110] rather than the [001] growth direction. TEM experiments suggest that each vertical zone is partially elastically relaxed.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Kk Vapor phase epitaxy; growth from vapor phase

A complete characterization of trapping levels in red mercuric iodide single crystals

S. L. Sharma, T. Pal, and H. N. Acharya

J. Appl. Phys. 75, 7884 (1994); http://dx.doi.org/10.1063/1.356574 (10 pages) | Cited 2 times

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Photon stimulated current measurements have been performed on red mercuric iodide single crystals in order to determine the trap energy, trap density, and capture cross section for different trapping levels that may be present in the platelet‐shaped single crystals of red mercuric iodide grown by polymer controlled growth technique in vapor phase. The procedure of analysis of these measurements is outlined in brief. The analysis has shown that these crystals in general possess four trapping levels: two electron trapping levels with energies 0.10 and 0.31 eV and two hole trapping levels with energies 0.15 and 0.59 eV. The analysis has further shown that the total trap density is only of the order of 1013/cm3, indicating the superiority of this growth technique over other techniques. The analysis has also shown that all four trapping levels are of retrapping type. Finally, the possible mechanisms of formation of these trapping levels and the ways in which these trapping levels will influence the detector operation at room temperature are discussed.
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71.55.Ht Other nonmetals
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.40.+w Photoconduction and photovoltaic effects

New insights into the compensation mechanism of Fe‐doped InP

F. X. Zach

J. Appl. Phys. 75, 7894 (1994); http://dx.doi.org/10.1063/1.356575 (10 pages) | Cited 17 times

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We have investigated iron‐doped semi‐insulating and conducting InP using a variety of characterization techniques. The occupation of the iron acceptor level was determined from measurements of the Fe2+ intracenter absorption and the Fe3+ electron paramagnetic resonance signal. These iron concentrations were then related to the total iron content, the free carrier concentration, and the net donor concentration as determined from an impurity analysis. When comparing the sum [Fe2+]+[Fe3+] with the total iron content of the samples measured by glow discharge mass spectroscopy we find that below about 1×1017 cm−3 no significant formation of precipitates occurs. Analysis of the free carrier concentration in semi‐insulating crystals allows us to determine the temperature shift of the iron acceptor level with respect to the conduction band. We obtain a value of 4.7×10−4 eV/K somewhat larger than the band‐gap shift of InP (3.8×10−4 eV/K). Due to this temperature shift the thermodynamic position of the iron acceptor level at room temperature is about 0.49 eV below the conduction band. This value is significantly smaller than the low temperature value of 0.63 eV. We believe that the temperature shift of deep electronic levels provides insight into the local electron‐phonon coupling. Finally we find that the net donor concentration determined by an impurity analysis appears to be too low to account for the observed [Fe2+] concentrations. We present evidence that the missing donor is related to the well‐known hydrogen related local vibrational mode at 2315 cm−1. These results indicate that both hydrogen passivation and native defects are necessary for a quantitative understanding of the compensation mechanism in semi‐insulating InP.
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71.55.Eq III-V semiconductors
61.72.uj III-V and II-VI semiconductors
76.30.Fc Iron group (3d) ions and impurities (Ti-Cu)

Electron mobility in Hg0.78Cd0.22Te alloy

Srinivasan Krishnamurthy and Arden Sher

J. Appl. Phys. 75, 7904 (1994); http://dx.doi.org/10.1063/1.356576 (6 pages) | Cited 5 times

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The electron mobility in Hg0.78Cd0.22Te is calculated by solving the Boltzmann transport equation with Fermi–Dirac statistics and a full band structure. The calculated values are in excellent agreement with experiments, and effects of various traditional approximations are discussed.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.10.Bg General formulation of transport theory

Evidence for field enhanced electron capture by EL2 centers in semi‐insulating GaAs and the effect on GaAs radiation detectors

Douglas S. McGregor, Ronald A. Rojeski, Glenn F. Knoll, Fred L. Terry, Jack East, and Yosef Eisen

J. Appl. Phys. 75, 7910 (1994); http://dx.doi.org/10.1063/1.356577 (6 pages) | Cited 32 times

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The performance of Schottky contact semiconductor radiation detectors fabricated from semi‐insulating GaAs is highly sensitive to charged impurities and defects in the material. The observed behavior of semi‐insulating GaAs Schottky barrier alpha particle detectors does not match well with models that treat the semi‐insulating material as either perfectly intrinsic or as material with deep donors (EL2) of constant capture cross section compensated with shallow acceptors. We propose an explanation for the discrepancy based on enhanced capture of electrons by EL2 centers at high electric fields and the resulting formation of a quasineutral region in the GaAs. Presented is a simple model including field enhanced electron capture which shows good agreement with experimental alpha particle pulse height measurements.
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29.40.Wk Solid-state detectors
71.55.Eq III-V semiconductors
73.30.+y Surface double layers, Schottky barriers, and work functions

Annealing effects on the electrical properties and microscopic structure of semi‐insulating polycrystalline silicon films

Wonju Cho, Yuji Takeuchi, and Hiroshi Kuwano

J. Appl. Phys. 75, 7916 (1994); http://dx.doi.org/10.1063/1.356578 (6 pages) | Cited 2 times

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The dependence of the electrical properties and microscopic structure of semi‐insulating polycrystalline silicon (SIPOS) films prepared by low‐pressure chemical‐vapor deposition on annealing temperature has been investigated, and the electrical conduction mechanisms have been clarified. As‐deposited SIPOS films were crystallized from an amorphous matrix by annealing, which changes the structure to polycrystalline films at annealing temperatures above 1100 °C. The electrical conduction mechanisms in films annealed at temperatures above 1000 °C can be explained by thermionic emission theory over a wide range of temperatures from high temperatures to those below room temperature, and by hopping conduction through the trap states at the grain boundaries at sufficiently low temperatures. For films annealed below 1000 °C, the electrical conduction mechanisms can be explained by conduction in the extended states over the high‐temperature range, and by hopping conduction through the localized states below room temperature. Undoped and lightly doped SIPOS films exhibit p‐type properties for annealing temperature above 1000 °C, but display an n‐type property when annealed at temperatures below 1000 °C. The dependence of the density of localized states and the band‐gap width on annealing temperature were also investigated.
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73.61.Cw Elemental semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance

High frequency capacitance behavior of metal‐oxide‐semiconductor tunnel structures

Vassiliki Bredimas

J. Appl. Phys. 75, 7922 (1994); http://dx.doi.org/10.1063/1.356579 (9 pages) | Cited 3 times

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We use a simple model based on the steady‐state balance of current flowing by tunneling across a Si‐SiO2‐metal structure. The recombination current is not taken into account. This model yields analytical expressions for the positions of the quasi‐Fermi levels at the Si‐SiO2 interface which govern the shape of current‐voltage and capacitance‐voltage characteristics. In particular, the knee which appears in the capacitance‐voltage curves of inverse‐biased structures and the corresponding plateau or the break in the slope of the 1/C2 versus applied voltage curve is correctly described. Measuring the slopes before and after the plateau or breaking, which marks the boundary of the tunneling domain, could provide information on the surface states when the surface parameters are known or vice versa. The main feature in the interpretation of the curves obtained is the degree of communication between metal and semiconductor, which is dominated by the tunnel transmission coefficient. The main parameters are therefore the oxide thickness and the minority barrier height for reverse polarization and the majority barrier height for forward bias polarization. It turns out that actual structures never have the predicted values for these barriers but notably lower ones when one assumes a perfect oxide layer. This fact may be due to defects in the oxide layer.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.40.Gk Tunneling

Depth profile of thermal donor in boron‐doped Czochralski‐grown silicon

Edward M. Filangeri and Toshikazu Nishida

J. Appl. Phys. 75, 7931 (1994); http://dx.doi.org/10.1063/1.356580 (4 pages) | Cited 2 times

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Near‐complete suppression of thermal donor formation is observed at the silicon surface independent of annealing time. Schottky barrier capacitance‐voltage profiling of p‐type Czochralski silicon following heat treatment at 200–450 °C in N2 indicates thermal donor depletion near the surface consistent with earlier reports. Analysis of the capacitance‐voltage method indicates that series resistance effects on the depth profile are negligible. Possible mechanisms for the thermal donor depletion at the silicon surface are discussed.
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71.55.Cn Elemental semiconductors
73.30.+y Surface double layers, Schottky barriers, and work functions
61.72.S- Impurities in crystals

An analytical saturation region model for amorphous silicon thin film transistors using a quasi‐two‐dimensional and an effective temperature approach

S. S. Chen and J. B. Kuo

J. Appl. Phys. 75, 7935 (1994); http://dx.doi.org/10.1063/1.356581 (7 pages)

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This paper reports an analytical saturation region model for amorphous silicon thin film transistors using a quasi‐two‐dimensional and an effective temperature approach. As verified by the published data, this analytical saturation region model provides an accurate prediction on the drain current characteristics of an amorphous silicon thin film transistor.
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85.30.De Semiconductor-device characterization, design, and modeling
73.61.Jc Amorphous semiconductors; glasses

Many‐body effects on temperature dependence of the interband absorption in quantum wells

Godfrey Gumbs, Danhong Huang, and Vassilios Fessatidis

J. Appl. Phys. 75, 7942 (1994); http://dx.doi.org/10.1063/1.356582 (7 pages) | Cited 1 time

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A theory, which includes many‐body effects, is presented for the interband absorption in a pseudomorphic Ga1−yAlyAs/InxGa1−xAs/GaAs modulation‐doped quantum well. The electron‐electron interaction in a degenerate Fermi sea is calculated in the self‐consistent Hartree approximation. In addition, the binding energy within an electron‐hole pair is included in the ladder approximation as a vertex correction to the response function. Due to the subband structure arising from the quantization by the quantum well, there are different types of excitons associated with the electrons and holes in different subbands. In the theory, the coupling between excitons is calculated in the random‐phase approximation. The numerical results for the temperature dependence of the absorption peaks at the Fermi edge (low temperature) and the band edge (room temperature) compare well with available experimental data which was obtained in electric‐field modulated photoreflectance experiments. At low temperatures, the theory shows that there are important modifications to the single‐particle model. The Fermi energy is extracted by fitting the calculated results to the thermally broadened line shape of the absorption spectrum. As a consequence, the electron density of the quantum wells can be accurately determined by means of this contactless, nondestructive, rapid and simple characterization method. Moreover, information on the alloy composition, built‐in electric field, and the interface stress can also be obtained.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.Fd III-V semiconductors

Measurement of n‐type dry thermally oxidized 6H‐SiC metal‐oxide‐semiconductor diodes by quasistatic and high‐frequency capacitance versus voltage and capacitance transient techniques

P. Neudeck, S. Kang, J. Petit, and M. Tabib‐Azar

J. Appl. Phys. 75, 7949 (1994); http://dx.doi.org/10.1063/1.356583 (5 pages) | Cited 22 times

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Dry‐oxidized n‐type 6H‐SiC metal‐oxide‐semiconductor capacitors are investigated using quasistatic capacitance versus voltage (C‐V), high‐frequency C‐V, and pulsed high‐frequency capacitance transient (C‐t) analysis over the temperature range from 297 to 573 K. The quasistatic C‐V characteristics presented are the first reported for 6H‐SiC MOS capacitors, and exhibit startling nonidealities due to nonequilibrium conditions that arise from the fact that the recombination/generation process in 6H‐SiC is extraordinarily slow even at the highest measurement temperature employed. The high‐frequency dark C‐V characteristics all showed deep depletion with no observable hysteresis. The recovery of the high‐frequency capacitance from deep depletion to inversion was used to characterize the minority‐carrier generation process as a function of temperature. Zerbst analysis conducted on the resulting C‐t transients, which were longer than 1000 s at 573 K, showed a generation lifetime thermal activation energy of 0.49 eV.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.20.Hb Impurity and defect levels; energy states of adsorbed species
81.65.-b Surface treatments

Effects of order and disorder on field‐effect mobilities measured in conjugated polymer thin‐film transistors

E. R. Holland, D. Bloor, A. P. Monkman, A. Brown, D. De Leeuw, M. M. Bouman, and E. W. Meijer

J. Appl. Phys. 75, 7954 (1994); http://dx.doi.org/10.1063/1.356556 (4 pages) | Cited 8 times

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The morphology of conjugated polymer thin films has been controlled by exploiting the processes giving rise to solvatochromism in the initial polymer solutions from which the polymer films were deposited by spin coating. The material used was the substituted polythiophene, 3[2(S2‐methylbutoxy)ethyl]‐polythiophene. Starting with polymer dissolved in ‘‘good’’ solvent, various quantities of ‘‘bad’’ solvent when added lead to the reorganization of the solubilizing side chains attached to the conjugated polymer backbone. Ordering of these side chains increases with addition of bad solvent decreasing the flexibility of the backbone, yielding more rigid rodlike polymer chains. This in turn causes aggregation and finally precipitation. It is found that this molecular order can be transferred from solution to solid film during the spinning process, ascertained from optical spectroscopy. With these films acting as the active layer in a field‐effect transistor structure, the mobility of the carriers injected into the films can be measured. It is found that as the molecular order and aggregation increases, carrier mobility decreases from ∼10−5 cm2 V−1 s−1 to ≤10−8 cm2 V−1 s−1 in films displaying the highest degree of molecular order. This is ascribed to the increased interchain separation in the ordered systems along with effects due to macroscopic aggregate grain boundaries.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
73.61.Ph Polymers; organic compounds
85.30.Tv Field effect devices

YBa2Cu3O7−x films on yttria‐stabilized ZrO2 substrates: Influence of the substrate morphology

G. Brorsson, E. Olsson, Z. G. Ivanov, E. A. Stepantsov, J. A. Alarco, Yu. Boikov, T. Claeson, P. Berastegui, V. Langer, and M. Löfgren

J. Appl. Phys. 75, 7958 (1994); http://dx.doi.org/10.1063/1.356557 (8 pages) | Cited 11 times

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c‐axis‐oriented YBa2Cu3O7−x (YBCO) thin films were laser deposited on (001) yttria‐stabilized ZrO2 (YSZ) substrates with different surface morphologies. The in‐plane orientation of the films on smooth substrates was sensitive to the deposition conditions, often resulting in mixed orientations. However, a strongly dominating [110]YBCO//[110]YSZ orientation was obtained at a deposition temperature of 770 °C. Films on substrates with surface steps, induced by depositing a homoepitaxial buffer layer or by thermally annealing the substrate, had a [110]YBCO//[100]YSZ orientation when deposited at the same temperature. It was concluded that the [110]YBCO//[100]YSZ orientation was promoted by a graphoepitaxial mechanism. Films prepared under identical conditions on smooth and stepped substrates grew with extended c axes on the former. It is proposed that the extension can be induced by disorder, invoked by a low oxygen pressure and a low density of adsorption sites. The disorder may be eliminated by either an increase of the oxygen pressure or an increase of the density of adsorption sites in the form of steps. The film microstructure influenced the microwave surface resistance, which was similar for films with one exclusive in‐plane orientation and higher for films with mixed orientations. The films on the stepped surfaces had superior superconducting properties; inductive measurements gave a Tconset of 88 K, a ΔT(90%–10%)c of 0.2 K, and the transport jc was 1.5×106 A/cm2 at 83 K, for films on substrates with homoepitaxial buffer layers.
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74.78.-w Superconducting films and low-dimensional structures
74.25.N- Response to electromagnetic fields
81.15.Fg Pulsed laser ablation deposition
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