摘要:

A new technique is introduced to analyze digitally recorded capacitive transients in order to determine the properties of deep states. Using a nonlinear double exponential fitting routine, it is shown that a two‐trap model can be applied to the transient data. We determine the individual trap concentrations and produce two Arrhenius plots. The latter yields the thermal activation energies and capture cross sections of closely spaced traps. The excellent agreement between the new technique and the standard rate window technique is shown via a simulation deep‐level transient spectroscopy spectrum. The new method is applied to Se‐doped AlxGa1−xAs (x=0.19 and 0.27) grown by metal‐organic chemical vapor deposition. The measured results for all deep states including theDXcenters agree well with the values published in the literature.

ISSN:0021-8979    

DOI:10.1063/1.344973

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

TheE0exciton splitting intoEv10andEv20excitons (due to lattice mismatch), their energy shift and the lifetime broadening are obtained in the GaAs/AlxGa1−xAs alloy system grown by liquid‐phase epitaxy from the analysis of spectroscopic ellipsometry measurements in the temperature range between 12 and 800 K. The lifetime broadenings of these excitons at low temperature is shown to be described well by the statistical fluctuations of the alloy composition caused by the random distribution of Al and Ga on the cation sites (Schubert’s model). TheEv10exciton lifetime broadening was found to be larger in the Ga‐rich region as compared to the corresponding one of theEv20exciton and smaller in the Al‐rich region. The former broadening is explained qualitatively by the different effective masses (mv1&Ggr;>mv2&Ggr;), whereas the latter is produced in terms of the increase in the density of states of the holes in theV2valence band by the increasing energy splitting &dgr;Eswithx.

ISSN:0021-8979    

DOI:10.1063/1.344974

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Studies have been made of the macroscopic and microscopic electrical inhomogeneity in undoped bulk GaAs single crystals grown from As/As+Ga melt ratios of 0.48–0.45. Microscopic inhomogeneity was characterized by contact resistance line scans and whole wafer anodization, which gives high‐resolution two‐dimensional images of the low‐resistivityp‐type regions within the wafers. The resistivity was nonuniform in wafers from 0.48 As/As+Ga crystals, having a W‐shaped radial dependence with minima in the ⟨110⟩ directions and varying by six orders of magnitude across a wafer, whereas it was uniform in low‐resistivity wafers from 0.45 As/As+Ga crystals at fractions of melt solidified,g>0.4. Precise correlation of microscopic inhomogeneity with grown‐in linear and cellular arrays of dislocations was obtained in nonuniform wafers, but no correlation with slip dislocations was observed. Anodization images show that the carrier concentration is quantitatively in agreement with a uniform acceptor background compensated by EL2 concentration fluctuations of factors of 2–3 at the dislocation networks. Inhomogeneity variation withgand As/As+Ga ratio is consistent with macroscopic and microscopic decrease in EL2 with melt stoichiometry.

ISSN:0021-8979    

DOI:10.1063/1.344975

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We investigate &dgr;‐doped GaAs samples grown by molecular‐beam epitaxy with different silicon areal concentration and cap layer thickness, using photoreflectance spectroscopy. The features observed on the high‐energy side of the fundamental gap are attributed to transitions involving electronic sub‐bands in the &dgr;‐doped potential well that take into account the diffusion of the dopants.

ISSN:0021-8979    

DOI:10.1063/1.344976

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Charge trapping in layered organic photoconductors consisting of a charge generation layer (CGL) and a charge transport layer (CTL) was studied by xerographic residual potential measurements. The residual potential builds up during repeated corona charging and light exposure cycles of photoconductors. The negative residual potential is proportional to the square of the CGL thickness and is linearly proportional to the CTL thickness. The square dependence is caused by the bulk trapping of electrons in the CGL, and the linear dependence is due to the negative charges on the CTL surface. From experimental results, it is concluded that the electron trapping in the CGL enhances the trapping of holes at the CGL/CTL interface, and consequently a fraction of negative corona charges remains on the CTL surface even after light exposure. The buildup of the residual potential during xerographic cycling is initiated by the electron trapping in the CGL. On the other hand, the decay rate of the residual potential after xerographic cycling depends on hole transport properties in the CTL. The activation energy for the decay of the residual potential is in good agreement with that for the drifting of holes through the CTL obtained from thermally stimulated current measurements. The decay rate of the residual potential is controlled by the surface charge neutralization process which involves the release of holes trapped at the CGL/CTL interface and the subsequent drifting of holes to the surface.

ISSN:0021-8979    

DOI:10.1063/1.344977

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The temperature dependence of electrical resistivity of Nd1.85Ce0.15CuO4−ywas measured with oxygen partial pressure fixed at 2.08×10−1, 1.8×10−2, 8.1×10−4, and 3.3×10−6atm. The oxygen partial pressure dependence of resistivity indicated that the charge carriers in Nd1.85Ce0.15CuO4−ywere electrons. The temperature dependence of resistivity exhibited a linear metallic behavior at high temperatures and a semiconductorlike behavior at low temperatures, having a minimum at an intermediate temperature. Difficulties are pointed out in obtaining a unified view for the mechanism of normal electrical conduction in Nd1.85Ce0.15CuO4−y.

ISSN:0021-8979    

DOI:10.1063/1.344978

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

It is demonstrated that multijunctiona‐Si:H‐based solar cells are more stable than their single‐junction counterparts and that the stability improves as the number of junctions increases. It is further shown that the rate of degradation of multijunction devices can be explained in terms of the rates of degradation of their individualilayers. It is thus possible to predict the amount of photodegradation of multijunction devices after prolonged light soaking, knowing only the rates of degradation of single‐junction cells in terms of thei‐layer thicknesses and the intensity of the illumination to which they are exposed.

ISSN:0021-8979    

DOI:10.1063/1.344979

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Thin‐film polycrystalline CdTe was electrodeposited as described previously onto indium‐tin‐oxide coated glass under argon and then stored either under argon or air before and after the annealing step. Dopants were incorporated into films by several methods. Indium, Cadmium, and silver were introduced into the films either by codeposition or by electromigration techniques as described previously for copper, and the doping process was followed by heat treatment. Tellurium was introduced into two films by heating the samples in a tellurium atmosphere, and the effect of oxygen on the CdTe was investigated by a high‐temperature heat treatment in air. The effect of these doping procedures on the conductivity was investigated at various temperatures. For this purpose, a system was built to measure extremely high resistances (>1012) over a large and well‐controlled temperature range. Because of the polycrystalline nature of the films, the results are discussed in terms of a model in which the conducitivity is affected by the density of grain boundary states.

ISSN:0021-8979    

DOI:10.1063/1.344980

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A new approach is presented for the development of a metal‐insulator–semiconductor field‐effect transistor technology. It is applied to the optimization of Al2O3/InP structures prepared by the deposition of evaporated Al2O3on arsenic‐stabilized InP surfaces. Molecular beam epitaxy and surface‐science techniques (reflected high‐energy electron diffraction and x‐ray photoelectron spectroscopy are used to control step by step the fabrication of the structures and to describe the microscopic properties of the interfaces. The optimization of the fabrication process is based on correlations between interfacial physicochemical properties and metal–insulator‐semiconductor capacitor electrical properties. It is shown that an interfacial oxide buffer layer can favor crystallochemical matching between Al2O3and InP.

ISSN:0021-8979    

DOI:10.1063/1.346054

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The electrical properties and thermal stability of In/W Ohmic contacts inn‐type GaAs were studied by analyzing interfacial microstructure using cross‐sectional transmission electron microscopy and measuring the contact resistances by transmission line method. Indium layers with various thicknesses were deposited directly on GaAs substrates, which were kept at room or liquid‐nitrogen temperature. The lower contact resistances (Rc) were obtained when the contacts were prepared at liquid‐nitrogen temperature. These lowRcvalues were due to formation of large‐areal InxGa1−xAs phases on the GaAs substrate after annealing at temperatures higher than 600 °C. The In layer thicknesses of the In/W contacts prepared at liquid‐nitrogen temperature strongly affected the contact resistances as well as the thermal stability after contact formation. The optimum In layer thickness which provided the best electrical properties and thermal stability was determined to be 3 nm. The In(3 nm)/W contacts yieldedRcvalues less than 0.2 &OHgr; mm and theRcvalues did not deteriorate after annealing at 400 °C for more than 20 h. The contacts with In layer thicknesses thinner than 3 nm resulted in higherRcvalues due to insufficient InxGa1−xAs phases at the metal/GaAs interfaces. The contacts with In layer thicknesses thicker than 3 nm resulted in poor thermal stability due to formation of large amounts of In‐rich In(Ga,As) phases with low melting points. The present In(3 nm)/W Ohmic contacts are believed to be the simplest metallurgy with excellent electrical properties and thermal stability among In‐based Ohmic contacts.

ISSN:0021-8979    

DOI:10.1063/1.344955

出版商:AIP    

年代:1990

数据来源: AIP