jap banner
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

Flickr Twitter iResearch App Facebook

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Next Issue

1 Jul 2000

Volume 88, Issue 1, pp. 1-602

Return to All Sections
back to top
RSS Feeds

Thermoelectric properties of Si1−xGex(x⩽0.10) with alloy and dopant segregations

Osamu Yamashita and Nobuhiro Sadatomi

J. Appl. Phys. 88, 245 (2000); http://dx.doi.org/10.1063/1.373648 (7 pages) | Cited 16 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The thermal conductivity κ and the thermoelectric properties of Si1−xGex(x⩽0.10) samples doped with B or P which were prepared by arc melting were measured as functions of carrier concentration n and temperature T in the range from 298 to 1273 K. The Si1−xGex(0.03⩽x⩽0.10) samples, doped with a small amount of B or P, have a significantly low κ value, less than one tenth that of pure Si, despite the presence of strong alloy and dopant segregations. The Seebeck coefficients S of the Si0.97Ge0.03 samples over the entire n range from 1018 to 1021 cm−3 were higher than the corresponding values of Si0.7Ge0.3 alloys with little segregation, although the difference between the electrical resistivities ρ of our samples and their alloys is very small. The optimum n value giving the largest thermoelectric figures of merit (ZT=S2T/κρ) for n- and p-type Si0.97Ge0.03 samples was about 2×1020 cm−3, which is almost the same as that for Si0.7Ge0.3 alloys. At n≒2×1020 cm−3 the ZT values of n- and p-type Si0.95Ge0.05 samples with segregation increase linearly with temperature, and become 0.90 and 0.57 at 1073 K, respectively, which corresponds to 92% and 81% of the ZT values for Si0.7Ge0.3 alloys with little segregation. © 2000 American Institute of Physics.
Show PACS
72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Jc Other crystalline inorganic semiconductors
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
64.75.-g Phase equilibria

Localized-state distributions in molecularly doped polymers determined from time-of-flight transient photocurrent

Takashi Nagase and Hiroyoshi Naito

J. Appl. Phys. 88, 252 (2000); http://dx.doi.org/10.1063/1.373649 (8 pages) | Cited 10 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Localized-state distributions have been studied in a molecularly doped polymer (MDP) system of a polymer binder (polycarbonate) doped with charge-transporting [N,N′-diphenyl-N, N′-bis(3-methylphenyl)(1,1′-biphenyl)-4,4′-diamine (TPD)] and trap-forming molecules [1-phenyl-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline (PRA)] simultaneously by means of the conventional time-of-flight (TOF) transient photocurrent measurements. The existence of a transport energy in the MDP system is experimentally shown by comparing Gaussian distributions of localized states deduced by the Gaussian disorder model, due to Bässler and co-workers [H. Bässler, Phys. Status Solidi B 175, 15 (1993)], with localized-state distributions determined from the analysis of the TOF transient photocurrent data, based on the trap-controlled band transport [H. Naito, J. Ding, and M. Okuda, Appl. Phys. Lett. 64, 1830 (1994)]. The transport energy is found to be located at the center of the Gaussian distribution due to the host TPD molecules. It is also found that at 0.1 mol % PRA addition, the Gaussian distribution of localized states due to TPD molecules is broadened through the random electrostatic potential generated by dipoles of PRA, and at 1 mol % PRA addition, the localized-state structure due to PRA molecules, as well as the further broadening of the Gaussian distribution, are observed. The energy level of the structure is determined to be 0.54 eV above the transport energy, which is almost equal to the difference in the ionization potential between PRA and TPD. © 2000 American Institute of Physics.
Show PACS
71.55.Jv Disordered structures; amorphous and glassy solids
72.40.+w Photoconduction and photovoltaic effects
79.60.Fr Polymers; organic compounds

Below band-gap optical absorption in semiconductor alloys

Srinivasan Krishnamurthy, A. Sher, and A.-B. Chen

J. Appl. Phys. 88, 260 (2000); http://dx.doi.org/10.1063/1.373650 (5 pages) | Cited 8 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We have used accurate Hamiltonians and resulting wave functions to calculate the two-photon absorption coefficient and the free-carrier absorption coefficient in InAs and a HgCdTe alloy with the same band gap. Detailed results are obtained for the dependencies of the absorption on photon energy and incident intensity. Optical matrix elements are calculated from the wave number dependent wave functions. We have further solved the appropriate steady-state differential equation, with the calculated values of absorption coefficients, for depth dependence of the intensity in the material. We find that the nonlinear absorption in a HgCdTe alloy is about 100% larger than that in InAs of the same band gap and window thickness. © 2000 American Institute of Physics.
Show PACS
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.65.-k Nonlinear optics

Analysis of the temperature dependent thermal conductivity of silicon carbide for high temperature applications

R. P. Joshi, P. G. Neudeck, and C. Fazi

J. Appl. Phys. 88, 265 (2000); http://dx.doi.org/10.1063/1.373651 (5 pages) | Cited 10 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The temperature dependent thermal conductivity of silicon carbide has been calculated taking into account the various phonon scattering mechanisms. The results compared very well with available experimental data. The inclusion of four-phonon processes is shown to be necessary for obtaining a good match. Several important phonon scattering parameters have been extracted in this study. Dislocations are shown to have a strong effect at 300 K, but not as much at the higher temperatures. © 2000 American Institute of Physics.
Show PACS
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
61.72.Lk Linear defects: dislocations, disclinations
63.20.K- Phonon interactions

Electrode effect on photohole generation in smectic phenylnaphthalene liquid crystalline photoconductor

Hong Zhang and Jun-ichi Hanna

J. Appl. Phys. 88, 270 (2000); http://dx.doi.org/10.1063/1.373652 (8 pages) | Cited 7 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The photohole generation process in the smectic phases of a liquid crystalline photoconductor, 2-(4′-octylpheny)-6-dodecyoxylnaphthalene (8-PNP-O12) with different illuminated contact electrodes was investigated through steady-state and transient photocurrent measurements. It was revealed that the photogeneration of holes was governed by two different processes according to the electrode materials: the Onsager type of photocarrier generation in the bulk and the electrode-enhanced hole photoinjection with a delay of μs when Al, and either Pt or In2O3–SnO2 electrodes are applied, respectively. In the latter process, the photogeneration yield was one order of magnitude larger than that in the bulk generation process, but decreased as the molecular ordering degraded from the smectic B phase to the smectic A phase, then to the isotropic phase. According to the spectral response and the results of additional experiments on the effect of chemical doping with electron acceptors, the photohole injection was concluded to be attributed to the exciton decay at the interface of the electrode and liquid crystal, i.e., the charge transfer from photoexcited 8-PNP-O12 molecules to the electrode. The experimental results were analyzed according to a one-dimensional Onsager model and the diffusion length of excitons in the SmB phase was determined to be 30±10 nm. © 2000 American Institute of Physics.
Show PACS
72.40.+w Photoconduction and photovoltaic effects
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
64.70.M- Transitions in liquid crystals
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
73.20.At Surface states, band structure, electron density of states

Bandwidth considerations in modulated and transient photoconductivity measurements to determine localized state distributions

S. Reynolds, C. Main, D. P. Webb, and S. Grabtchak

J. Appl. Phys. 88, 278 (2000); http://dx.doi.org/10.1063/1.373653 (5 pages) | Cited 4 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
This work examines the influence of limited instrumental bandwidth on the accuracy of recovery of the density of localized states in semiconductors from transient and modulated photoconductivity data. Paradoxically, knowledge of the short-time transient photoresponse can be vital in the estimation, via a Fourier transform, of the density of deep-lying states. We demonstrate that retention of the natural response of a bandwidth limited system, although subject to distortion at short times, can lead to much improved accuracy in density of states determination than simple truncation of the short-time response. It is shown that this improvement arises simply from the integrating effect of a bandwidth limited system over short time intervals, which makes it possible to access and exploit information originating at times much shorter than the instrumentation rise time. These concepts are exemplified using computer simulated transient photoconductivity for several model systems including one which mimics the expected density of states in amorphous silicon. © 2000 American Institute of Physics.
Show PACS
72.40.+w Photoconduction and photovoltaic effects
71.55.Jv Disordered structures; amorphous and glassy solids

Electric and dielectric properties of Bi12TiO20 single crystals

S. Lanfredi, J. F. Carvalho, and A. C. Hernandes

J. Appl. Phys. 88, 283 (2000); http://dx.doi.org/10.1063/1.373654 (5 pages) | Cited 29 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The frequency dependence of the electrical properties of the Bi12TiO20 single crystal was investigated by impedance spectroscopy. The data were presented in the Nyquist diagram form, from which electrical resistivity was determined. Values ranged from 1.93×105 and 1.07×103 Ω cm in the temperature range of 400–700 °C. The electrical conductivity followed the Arrhenius law, with an activation energy of 0.99 eV. The dielectric behavior was investigated from room temperature to 700 °C. Permittivity was calculated based on the relaxation frequency, using an alternative approach based on the variation of the imaginary impedance component as a function of reciprocal angular frequency. The permittivity values obtained by means of these two methods showed good agreement up to 600 °C. The frequency dependence of real and imaginary permittivities from room temperature to 700 °C was also investigated. © 2000 American Institute of Physics.
Show PACS
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
72.20.Fr Low-field transport and mobility; piezoresistance

Alloy scattering in GaAs/AlGaAs quantum well infrared photodetector

Y. Fu and M. Willander

J. Appl. Phys. 88, 288 (2000); http://dx.doi.org/10.1063/1.373655 (5 pages) | Cited 5 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Surface kinetic processes and postgrowth treatments make the vertical and lateral interdiffusions of the Al atoms across GaAs/AlGaAs heterointerfaces inevitable. The increased degree of the Al interdiffusion has been clearly reflected in the spectra of dark current and photocurrent from postgrowth-treated GaAs/AlGaAs multiple-quantum-well-based infrared photodetectors. The Al diffusion length can be characterized from the cutoff wavelength of the photodetector. It has been shown that by including only the increased density of thermal-excited carriers, the theoretical expectation of the dark current enhancement due to the Al diffusion is more than what was observed experimentally. The discrepancy between carrier-density consideration and measurements about the dark current is explained by further considering the enhanced alloy scattering due to the Al interdiffusion and thus the reduced mobility of carriers at excited states. Furthermore, the reduced carrier mobility explains the decreased photocurrent while theoretically the absorption coefficient increases following the increases of the Al diffusion length. © 2000 American Institute of Physics.
Show PACS
73.61.Ey III-V semiconductors
81.05.Ea III-V semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.60.Gz Photodetectors (including infrared and CCD detectors)
72.80.Ey III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
73.50.Dn Low-field transport and mobility; piezoresistance

Role of the buffer layer in the active junction in amorphous-crystalline silicon heterojunction solar cells

J. Pallarès and R. E. I. Schropp

J. Appl. Phys. 88, 293 (2000); http://dx.doi.org/10.1063/1.373656 (7 pages) | Cited 14 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We fabricated pn and pin a-SiC:H/c-Si heterojunction solar cells following two different processes. In the first approach, wafers were subjected to an extra atomic hydrogen (produced by hot wire chemical vapor deposition) prior to the deposition of the amorphous layer. A reduction in the open-circuit voltage was observed for the passivated cells due to their higher leakage current. In the second process, pin solar cells with two different quality intrinsic a-Si:H buffer layers were fabricated using plasma enhanced chemical vapor deposition. The cells with a device quality buffer layer (deposited at higher temperature) showed better performance than those with a buffer layer with high hydrogen content and higher defect density (deposited at lower temperatures). © 2000 American Institute of Physics.
Show PACS
84.60.Jt Photoelectric conversion
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.61.Cw Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.-a Thin film structure and morphology

Electron transport across one-dimensional modulated superlattices in a quantum waveguide in magnetic fields

Ben-Yuan Gu, Yan Zhang, and Xue-Hua Wang

J. Appl. Phys. 88, 300 (2000); http://dx.doi.org/10.1063/1.373657 (9 pages) | Cited 2 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Electron transport in a quantum waveguide containing a finite length superlattice (SL) with periodically modulated potentials or Gaussian envelope modulation in magnetic fields is investigated with use of the scattering matrix method. When the modulated potential of the SL takes a Gaussian function, we found that the resonant peaks in conductance at zero field are prominently smoothed out and the conductance spectrum exhibits a monotonically increasing line with a finite rise at the beginning. The corresponding one-dimensional structure presents flat minibands and minigaps. When electron energy is aligned with the miniband, electrons are allowed to pass through the SL to be nearly unscattered. When applying magnetic fields, the conductance plateaus are observed again. From the analyses of the individual modal transmission probabilities, the conductance spectra can be understood well. It is expected that implanting a finite length SL with different modulation potentials may provide a way to tailor conductance spectrum to match the practical demands in devices. © 2000 American Institute of Physics.
Show PACS
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.23.-b Electronic transport in mesoscopic systems
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

A quantitative conduction model for a low-resistance nonalloyed ohmic contact structure utilizing low-temperature-grown GaAs

Nien-Po Chen, H. J. Ueng, D. B. Janes, J. M. Woodall, and M. R. Melloch

J. Appl. Phys. 88, 309 (2000); http://dx.doi.org/10.1063/1.373658 (7 pages) | Cited 8 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present a quantitative conduction model for nonalloyed ohmic contacts to n-type GaAs (n:GaAs) which employ a surface layer of low-temperature-grown GaAs (LTG:GaAs). The energy band edge profile for the contact structure is calculated by solving Poisson’s equation and invoking Fermi statistics using deep donor band and acceptor state parameters for the LTG:GaAs which are consistent with measured bulk and surface electrical properties of this material. The specific contact resistance is then calculated using an analytic expression for tunneling conduction through an equivalent uniformly doped Schottky barrier. The model has been used to fit measured specific contact resistances versus LTG:GaAs layer thickness and versus measurement temperature. These comparisons provide insights into the contact mechanism (electron tunneling between metal states and conduction band states in n:GaAs) and indicate that low barrier heights (0.3–0.5 V) and high activated donor densities (∼1×1020 cm−3) have been achieved in these ex situ contacts. © 2000 American Institute of Physics.
Show PACS
73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
73.61.Ey III-V semiconductors

Current–voltage characteristics of Schottky barrier structures on porous silicon, and effect of an organic stabilizer film

W. Li, I. Andrienko, and D. Haneman

J. Appl. Phys. 88, 316 (2000); http://dx.doi.org/10.1063/1.373659 (5 pages) | Cited 4 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The stability and reproducibility of current–voltage curves of Schottky barrier structures on particular porous silicon surfaces used for obtaining electroluminescence is greatly improved by first coating the surface with a conducting polymer, poly-4-dicyanomethylene-4H-cyclopenta [2,1-b:3,4-b′] dithiophene. With such coated structures it is possible to fit the usual diode formula at room temperatures with a quality factor of 3.0, obviating the need for more complex theories. The stability of electroluminescence, which shows a redshift from 500 to 580 nm after coating, is also greatly improved. The coating appears to chemically react with the hydride surface and also mechanically strengthens the structure. © 2000 American Institute of Physics.
Show PACS
78.66.Db Elemental semiconductors and insulators
78.60.Fi Electroluminescence
73.40.Ns Metal-nonmetal contacts
73.61.Ph Polymers; organic compounds
73.61.Cw Elemental semiconductors

Increased mobility anisotropy in selectively doped AlxGa1−xAs/GaAs heterostructures with high electron densities

D. Reuter, M. Versen, M. D. Schneider, and A. D. Wieck

J. Appl. Phys. 88, 321 (2000); http://dx.doi.org/10.1063/1.373660 (5 pages) | Cited 2 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We have investigated the electron transport properties of a two-dimensional electron gas in a selectively doped AlxGa1−xAs/GaAs heterostructure with reduced Al content in the doped layer by recording the longitudinal resistance as a function of magnetic field and performing Hall measurements at low magnetic fields on the same sample. The electron density was varied by stepwise illumination and we observe a dip in the mobility versus density dependence around a density of 5.0×1011 cm−2. As a reason for this mobility decrease we identify by magnetotransport measurements the onset of parallel conductance in the Si-doped AlxGa1−xAl layer. With the onset of parallel conductance, the anisotropy in the electron mobility increases significantly. We attribute this to an increase of interface roughness scattering induced by the parallel conducting channel. © 2000 American Institute of Physics.
Show PACS
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.My Galvanomagnetic and other magnetotransport effects
73.43.-f Quantum Hall effects
Return to All Sections
Close

Google Calendar

ADVERTISEMENT

Go to AIP Home   © AIP Publishing LLC
close