摘要:

The effect of polar additives is introduced into the theoretical model of charge carrier transport by hopping across disordered rigid polymer matrices. The electrostatic charge carrier–dipole interaction causes a broadening of the energy distribution of transport states which results in a decrease in the charge carrier mobility. The mobility depends on the dipole moment, the molecular dimensions of the additive, and the additive concentration. For geometrically similar additives, the mobility decreases with increasing dipole moment. The theory explains well the observed decrease in the mobility of holes in poly(methyl‐phenylsilylene) with increasing concentration of 1‐(benzamido)‐4‐nitronaphthalene. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360547

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Using a transmission probability formalism, we perform theoretical calculations for the current‐noise characteristics of a finite semiconductor superlattice with correlated thickness randomness in which the thicknesses of barriers are regular but those of wells are partially random. The transmission probability is calculated by the use of an exact Airy‐function formalism combined with a transfer matrix technique. We show that the tunneling resonance, owing to the existence of reflectionless electron waves in the absence of electric field, is sensitively suppressed by the applied field, leading to a special region of negative differential resistivity at low bias voltages in theI‐Vcurve. The current fluctuations near the peak of theI‐Vcurve are decreased from the usual shot‐noise values due to the large transmission of the reflectionless waves. The results may shed light on the possibility of exploiting the structure in designing resonant‐tunneling systems that require optimum sensitivity to applied electric field. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360548

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An analytical calculation scheme for the band profile in theiregion of a semi‐infinitep/iorn/ijunction with arbitrary thickness of the intrinsic top layer is presented. Using this algorithm the surface potential as a function ofi‐layer thickness as well as the band profile within the top layer can be calculated without mathematical approximations as long as the surface potential is held a fewkTaway from its intrinsic position by the doped sublayer, i.e., up to a critical thickness. Above that thickness the band profile can be approximated with sufficient accuracy by that of the corresponding infinite junction for which the exact solution will be also given in analytical terms. In a second step an arbitrary surface charge layer is incorporated into the algorithm which can modify the band profile considerably. The method whose mathematical derivation is presented in detail in this article was motivated by experiments on the surface‐near passivation of dopants in silicon by hydrogen but should be generally useful for the discussion ofp/iorn/ijunctions. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360730

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Computations of scattering rates from strain variations in high‐mobilityn‐channel Si/SiGe heterostructures are presented, and the results compared with experiment. Two sources of strain variation are considered—interface roughness and misfit dislocations—both of which form to relieve strain in the Si channel layer which is under tension. Strain variations induced by interface roughness are demonstrated to provide a source of scattering which, for highly strained systems of the type considered here, is significantly larger than conventional geometrical roughness scattering. Misfit dislocations provide a source of localized scattering centers, and an appropriate formalism is developed to describe this case. For both types of scattering, reasonable agreement with measured mobilities is found for various values of channel thickness. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360549

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Films of zinc sulfide (ZnS) have been grown on silicon (Si) substrates by sputtering in argon and either sulfur‐enriched or deficient‐gaseous environments. The density of electron traps at the ZnS/Si heterojunction is invariant with gas. However the photoluminescent intensity increases for films grown in argon enriched with hydrogen sulfide (Ar:H2S) compared with those grown in argon. Furthermore the density of sulfur vacancies is reduced by the presence of H2S, particularly compared with films grown in a mixture of argon and hydrogen (Ar:H). In these latter films sulfur vacancies increase the electrical conductivity by approximately three orders of magnitude. It is expected, therefore, that the high field condition essential for hot‐electron production in thin film electroluminescent devices is optimized in films with a reduced sulfur vacancy content, i.e., grown in Ar:H2S. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360550

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Phonon‐assisted tunneling (PAT) has been studied in detail for two similar GaAs/AlAs double‐barrier structures. Calculations of the PAT current—including effects of optical‐phonon localization—are in good agreement with experimental data, and the emission rate for certain phonon types is found to depend sensitively on GaAs well width. We find that GaAs‐like modes clearly dominate in structures with wider wells, while GaAs and AlAs‐like modes contribute equivalently in narrower well structures. A simple overlap integral—involving the phonon potential and electronic wave functions—provides an effective selection rule for determining which types of phonons are preferentially emitted. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360551

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A new ohmic contact system, Ge/Pt/Ge/Pt/n‐InP, was studied systematically by measuring its specific contact resistance and by using Auger electron spectroscopy, x‐ray‐diffraction analysis, Rutherford backscattering spectroscopy, and scanning electron microscopy. It was found that the system has a wide temperature range for annealing, i.e., 450–550 °C, to achieve the specific contact resistance of the order of 1.0×10−5&OHgr; cm2. It can achieve a low specific contact resistance of 7.71×10−6&OHgr; cm2when it is subjected to rapid thermal annealing at 500 °C for 30 s. The whole process is a solid phase reaction so that a smooth surface morphology is obtained. The ohmicity is due to the heavy doping of Ge in the regrown InP film. The contact system exhibits good thermal stability, being able to maintain a low specific contact resistance of 9.15×10−6&OHgr; cm2for 20 h, 400 °C aging, and 2.77×10−5&OHgr; cm2for 80 h aging. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360552

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The influence of the electrodes on the dielectric behavior and especially on the leakage behavior of SrTiO3thin films was investigated by impedance analysis. Based on measurements on thin films with different electrode materials the work function of these materials was found to determine the leakage currents. The main conduction mechanism is thermionic emission of electrons from the cathode into the SrTiO3thin film. The current–voltage characteristics are influenced by the Schottky effect. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360553

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We propose a simulation model to explain two‐dimensional field‐effect operation of undoped poly‐Si thin‐film transistors (TFTs) under small drain voltages. Our model includes both thermionic‐emission and drift‐diffusion conduction processes. We calculated grain‐boundary potential barriers, channel currents, and various device parameters depending on grain size and defect density. In order to validate our model, we compared calculated currents with experimental data for two types of poly‐Si TFTs. We could obtain good current fits simultaneously in both subthreshold and linear regions by adopting proper densities of states in the poly‐Si channels. We could also explain well the temperature‐dependent current changes and the current activation energy versus the gate voltage. Finally, we succeeded in modeling the drain current under small drain voltages by using the combined transport process in the two‐dimensional grain‐boundary structure. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360554

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The influence of plasma etching on the electrical properties ofn‐type gallium nitride (GaN) thin films has been investigated. Electron‐cyclotron‐resonance microwave plasma reactive ion etching in CH4/H2/Ar, in CH4/H2, and in H2results in an increase in the GaN layer’s sheet carrier concentration and a decrease in the effective Hall mobility. Neither wet chemical etching nor etching in Cl2or BCl3plasmas introduces similar changes. Therefore, the observed damage is considered to be related to the CH4/H2/Ar plasma chemistry. In particular, it suggests hydrogen influence on the defect generation. Subsequent annealing of the affected GaN layers at 800 °C removes the plasma damage.

ISSN:0021-8979    

DOI:10.1063/1.360555

出版商:AIP    

年代:1995

数据来源: AIP