摘要:

Deep levels inn-type high-purity (HP) detector grade germanium are studied using optical deep level transient spectroscopy (ODLTS). In this technique, optical injection (using light of above band gap energy) from the back ohmic contact together with a suitable sample configuration results in the detection of centers in the minority half of the band gap. Six deep minority carrier traps are detected in typicaln-type HP germanium which turn out to be the same defects as found earlier in typicalp-type HP germanium as majority carrier traps. These deep defects are mainly copper related. A formula is deduced to calculate concentrations from the ODLTS spectra. It is shown that inn- andp-type HP germanium not only the same defects are present but that their concentrations are also comparable. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365219

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have applied a virtual crystal approximation to the linear combination of atomic orbitals method to calculate critical point energies of unstrainedSi1−x−yGexCyalloys spanning the composition parameter space. Additionally, we have calculated the band structure across the Brillouin zone for a series of alloy compositions. We found the band energies had significant bowing departures from linearity throughout the system. In some cases, the energy band gap was not monotonically dependent on composition. Our theoretical results are compared with recent experimental results, and good agreement was found overall. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365220

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Higher binding energies (30–60 meV) in II–VI wide-gap materials result in large exciton densities, making optical transitions due to excitons dominant over free electrons and holes. Optical gain and threshold current densities in ZnCdSe based multiple quantum wire lasers are computed including the effect of strain. It is found that the tensile-strained quantum wires yield lower threshold current densities than compressive strained or unstrained structures. The calculated threshold current density for a defect free tensile-strained ZnCdSe–ZnMgSSe quantum wire laser, realized on an InP substrate, has been computed to be58 A/cm2.The exciton transitions assist in lowering the threshold current density which is adversely affected by the presence of dislocations and surface states. It is found that the threshold current density would increase to435 A/cm2assuming1017 cm−3trapping levels due to dislocations and surface states. However, taking into account the exciton transitions, the threshold current density is reduced to79 A/cm2when assuming the same trapping level density. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365221

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The transition of materials from low resistivity to comparatively high resistivity can be utilized for current limitation, enabling permanent fuses that do not have to be replaced after an overload or short-circuit operation. An interesting class of materials for this purpose are particulate filled polymer composites with a strong positive temperature coefficient (PTC) of resistivity. If an applied current becomes too high, the PTC element is heated to its critical temperature and trips from the conducting into the insulating state. The dynamic heating of the composite upon current flow is described by a one-dimensional model. It is predicted that the heating of a composite depends on the size of the filler particles. Smaller filler particles should allow a faster heating and, hence, a better limitation of the current. Experimental verification is performed using composite ofTiB2particles in a polyethylene matrix. CommercialTiB2powders with different particle-size distributions between 1 and 200 &mgr;m were used. The specific resistivity of the composites is small, in the range of 0.01–0.02 &OHgr; cm. Around the melting temperature of the polymer, the resistivity increases within only 20 °C by seven orders of magnitude. In order to verify the expected dependence of the switching dynamic on the filler particle size, the tested elements had comparable electrical characteristics. Samples were prepared having, to a certain degree, the same specific resistivity, cross section, and total resistance. Free parameters were the length, and for some samples, the filler content. Short-circuit experiments show that for decreasing particle size the time until the material trips into the high-resistive state becomes shorter. The best current limitation occurs for composites containing particles in the range of 1–45 &mgr;m. Current limitation starts already after 150 &mgr;s, and a current density of up to10 kA/cm2can be switched off within a further 200 &mgr;s. The experiments are in excellent agreement with the predictions from theory. Due to the low resistance in the cold state and the very fast limitation of electrical currents, PTC elements based on conducting polymers can be highly attractive for power applications. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365222

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The constant photocurrent method has been widely used in hydrogenated amorphous silicon as an efficient way of determining the optical absorption coefficient in the low-absorption region, and of estimating the defect density in the band gap. However, while the analysis is generally carried out on the assumption of uniform material parameters throughout the sample the experimental situation may fail to approximate that model. We therefore examine the influence on the resolved defect density of an inhomogeneous spatial distribution of defects, and of surface recombination, by means of a steady-state diffusion equation for photoexcited carriers. Differences by as much as a factor of 2 are observed within the range of possible experimental circumstances. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365223

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Electrical current density expressions for electrons and holes for materials with position-dependent band structure are presented. This includes materials with nonuniform composition and devices with highly doped regions. Changes in the energy-band edges due to spatial variations in electron affinity and band gap, and spatial variations in the local kinetic energy produce terms in the current-density equations in addition to those for the homogeneous case. These new terms are derived and discussed. The development proceeds from the Boltzmann transport equation. The focus will be on the conceptual framework and the limitations in the underlying theory. Errors in the literature are noted where appropriate. The results are relevant to semiconductor device physics and analysis. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365224

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Thin polycrystalline films of perylenetetracarboxylic dianyhydride (PTCDA), an organic molecular solid, exhibits substantial anisotropies in its electronic transport properties. Only electrons transport in the directions along molecular planes, while mainly holes transport in the direction normal to molecular planes. A series of measurements on both field effect transistors with PTCDA active layers and light emitting diodes with PTCDA transport layers documents the anisotropy seen in the electronic transport in thin films of PTCDA. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365238

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

X-ray photoelectron spectra of 4,4′-bis(4 styryl-styryl) benzene oligomer (4PV) films metallized with chromium and aluminum films were used to investigate the nature of 4PV–metal interfacial reactions. The changes in the core level spectra of carbon, metal, and oxygen indicated the formation of a carbide in a chromium covered oligomer and a metal–oxide carbon and/or carbide in aluminum covered films. Yet no apparent reaction was observed in the interfacial layer when depositing the oligomer film on the chromium layer. These reactions are used as a possible explanation for the electrical characteristics of diodes made from these materials. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365239

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The carrier transport mechanism through thep-diamond/metal interface was studied by measuring specific contact resistances(&rgr;c)using a transmission line method for Ti, Mo, and Cr (carbide forming metals) and Pd and Co (carbon soluble metals) metals contacting to the boron-doped polycrystalline diamond films. Schottky barrier heights(&fgr;B)of around 0.5 eV were measured for the annealed contacts. The present result indicates that formation of thermally stable graphite layers at the diamond/metal interfaces upon annealing would pin the Fermi level of thep-diamond. This model led to the preparation ofin situOhmic contacts by depositing a thin diamondlike carbon on thep-diamond surface prior to metal deposition, and also to excellent Schottky contacts with breakdown voltages higher than 900 V. The present experiment concluded that the existence of a graphite layer at the diamond/metal interface controlled the electrical properties through thep-diamond/metal interface. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365240

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We demonstrate that hole trap densities and hole trapping inSiO2films on silicon can be predicted quantitatively using a physically based model of intrinsic oxide trapping centers. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365438

出版商:AIP    

年代:1997

数据来源: AIP