摘要:

A simple method for the separation of bulk and surface recombination parameters, based on the simultaneous control of time and amplitude characteristics of carrier concentration decay, is presented. To enhance the precision of the parameter extraction procedure, the amplitude is determined using a wavelength resulting in near surface carrier excitation while the effective lifetime is measured for homogeneous bulk excitation. For the fast interpretation of experimental data, a technique using nomographs of amplitude–decay time correlated dependencies on modulation depth is proposed. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363705

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Current filaments formed in the parameter regime of the low‐temperature impurity impact ionization breakdown ofp‐germanium were investigated by measuring tunneling and point contact characteristics of a scanning tunneling microscope tip fixed at certain sample positions under variation of the sample voltage. The results clearly indicate that the tip current is determined by local potential variations which can be interpreted by a model for the filament taking into account the finite electric resistivity of the sample contacts. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363706

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have measured the transport properties of Ru0.5Pd0.5Sb3from 300 down to 4 K and compared them to those of the binary‐skutterudite antimonides. In particular, the lattice thermal conductivity of this compound is substantially lower than that of CoSb3and IrSb3. This is attributed to the mixed‐valency of ruthenium in this compound. Using near‐edge extended absorption fine structure analysis, it is observed that ruthenium in this compound is in the Ru4+‐ and Ru2+‐valence states in approximately equal proportions. The potential for thermoelectric applications of this material is also discussed. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363707

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have grown high‐electron mobility transistor structures in the Al0.3Ga0.7As/In0.25Ga0.75As/GaAs material system with In0.25Ga0.75As channel thicknesses in the range 40–200 A˚. We have monitored the onset of channel relaxation using Hall mobility measurements, polychromatic cathodoluminescence mapping, time‐resolved photoluminescence, transmission electron microscopy, low‐frequency noise, and deep‐level transient spectroscopy measurements. It appears that the first relaxation symptom, the Stransky–Krastanow growth mode, is observed only by the last three techniques. This shows that the onset of relaxation is not detected by characterization techniques which measure global properties of the material. On the other hand, it is detected by low‐frequency noise, deep‐level transient spectroscopy, and transmission electron microscopy measurements, which yield an estimation of the defect density in the material. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363708

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

It has been found from ac conductance measurement that two kinds of interface states are generated in the upper half of the gap when (100)n‐Si metal/oxide/semiconductor capacitors are subjected to Fowler‐Nordheim tunneling electron injection. The generation efficiency of these interface states varies in a quite similar fashion with the oxide voltage, although the magnitude is somewhat different from each other. The electron capture cross section for both interface states shows a curious behavior that its value decreases with increasing interface‐state density when exceeding about 1.5×1011cm−2eV−1. This behavior is explained in terms of the occurrence of additional tunneling to defect states in the oxide. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363709

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Self‐consistent tight‐binding total energy calculations are performed to study the deposition of a few layers of cubic GaN on (100) &bgr;‐SiC substrates. Cohesion energies, atomic displacements, dangling bond occupancies and surface reconstructions are calculated for a variety of epitaxial systems including monolayers of either Ga or N as well as single and double bilayers of GaN on either Si or C terminated substrates. The SiC substrates and Ga‐N epitaxial layers are represented by 2×2 supercells of 9 Si and C monolayers plus the respective number of monolayers of Ga and N atoms. Depending on the system, surface atoms dimerize either symmetrically or asymmetrically resulting in either 2×1, c‐2×2, or 2×2 surface reconstructions. At the substrate‐epitaxial‐layer interfaces, N binds stronger than Ga to either Si or C. Interface mixing is found to be energetically not advantageous for both C‐ and Si‐terminated substrates, although for the latter the obtained small energy differences may suggest the possibility of mixing. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363710

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report on resonant tunneling through ZnSe/BeTe double‐barrier, single‐quantum‐well structures. Negative differential resistance has been observed in the current–voltage characteristics up to room temperature. Due to a conduction‐band offset of more than 2 eV, four resonances with negative differential resistance could be detected for this semiconductor material combination at liquid‐helium temperature. The structures exhibit a peak‐to‐valley ratio up to 6:1 at 4.2 K. Current–voltage characteristics as a function of temperature have been studied and analyzed. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363711

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Electrical conduction characteristics in polyetherimide (PEI) have been investigated at electric fields of 0.9–27 MV/m over temperatures of 50–100 °C. It is found that the current density of PEI increases with the increase of electric field and temperature and that its conduction is governed by the thermally activated ion hopping process. The hopping distance of ions in the PEI decreases from 5.69 nm at 50 °C to 3.34 nm at 100 °C due to the increase of chain motion with the increase of temperature. The activation energy for the electrical conduction is 0.74 eV. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363650

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A method and theory presented earlier by the authors, for the straightforward measurement of resistivity in the surface region of charged insulators, in the initial phase of charge decay, is demonstrated also to be valid for much longer time scales. This is achieved with the use of a theoretical charge transport model, enabling a direct comparison between experimental and theoretical data. This comparison enabled the accurate determination of both the diffusion coefficient (D) and the layer of surface charge (&Dgr;z). Results are presented for glass, plexiglas (perspex), and polyethylene covering a useful resistivity range in the insulator class. The surface charge transport behavior of small rectangular samples is also studied using this computational model, focusing on the potential and charge distributions involved. From this study, some insight is gained into the way the charge in the surface region of insulators decays away with time when one end of a charged sample is earthed. The method provides a ready means of measuring the resistivity, carrier diffusion coefficient, and carrier occupancy depth in surface charged insulators. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363651

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

In a GaAs field effect transistor there are ungated sections of the channel between the gate and the source/drain. The static characteristics and the transients which occur in various parameters after a change in the bias voltages can be shown to be affected by the surface potential in this region. A model is proposed for these effects which involves a surface region with lower effective energy gap. The gate current leakage characteristics and conductance deep level transient spectroscopy measurements on single and dual gate devices are consistent with this model. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363652

出版商:AIP    

年代:1996

数据来源: AIP