摘要:

We compare the general Beran bounds on the effective electrical conductivity of a two‐phase composite to the bounds derived by Torquato for the specific model of spheres distributed throughout a matrix phase. For the case of impenetrable spheres, these bounds are shown to be identical and to depend on the microstructure through the sphere volume fraction &fgr;2and a three‐point parameter &zgr;2, which is an integral over a three‐point correlation function. We evaluate &zgr;2exactly through third order in &fgr;2for distributions of impenetrable spheres. This expansion is compared to the analogous results of Felderhof and of Torquato and Lado, all of whom employed the superposition approximation for the three‐particle distribution function involved in &zgr;2. The results indicate that the exact &zgr;2will be greater than the value calculated under the superposition approximation. For reasons of mathematical analogy, the results obtained here apply as well to the determination of the thermal conductivity, dielectric constant, and magnetic permeability of composite media and the diffusion coefficient of porous media.

ISSN:0021-8979    

DOI:10.1063/1.337614

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Ga0.96Al0.04Sb layers have been grown by liquid‐phase epitaxy on GaSb substrates at 400, 450, and 550 °C. The 450 °C growth leads to the best control of the layer’s quality. At 450 °C the naturalp‐type doping of the layers is limited by the thermal acceptors ( p∼4×1016cm−3) and the lowest reproducible uniform electron concentration obtained by Te compensation isn∼1016cm−3. Electrical and photoelectrical properties of Schottky diodes and mesa Zn‐diffused homojunctions realized on these layers are described. They are strongly affected by surface effects attributed to the band bending ofn‐type GaAlSb. Some parameters can be deduced from the various characterizations: the carrier lifetime in the space‐charge region of Zn‐diffusedp+/njunctions, &tgr;∼3×10−10s; electron diffusion lengths in the as‐grown Ga0.96Al0.04Sb layer,Ln=5 &mgr;m, and in the Zn‐diffused layer,Ln=1.5 &mgr;m; and the hole diffusion length in then‐compensated layers,Lp=1 &mgr;m.

ISSN:0021-8979    

DOI:10.1063/1.337615

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The interpretation of experimental results concerning insulator‐semiconductor interface states in metal‐insulator‐semiconductor structures obtained with the deep‐level transient spectroscopy (DLTS) techniques, particularly in the case of high‐density interface states continuously distributed in the energy band gap (larger than 5×1011eV−1 cm−2), is reconsidered. It is shown that the ‘‘saturating pulse’’ condition, which allows a classical treatment of the DLTS spectra, corresponds to a filling pulse amplitude which rapidly increases with the average density of the traps located at the interface. The use of large or small pulses is discussed. The determination of the profile of interface state densityNss(E) can only be derived for high densities from a simulation of the DLTS signal &Dgr;C(T), since the classical relation betweenNssand &Dgr;Cis no more valid in this case. A simplified simulation is proposed. It allows us to justify the results reported in this paper and to fit experimental results previously obtained on Al–Si3N4–GaAs structures with interface state densities about 1013eV−1 cm−2.

ISSN:0021-8979    

DOI:10.1063/1.337564

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The density of localized states at the interface between as‐deposited 51 at. % semi‐insulating polycrystalline silicon and silicon has been measured using the conductance technique. Aluminum‐gated metal‐insulator‐semiconductor structures were made onn‐n+andp‐p+epilayered silicon and full details of capacitance‐voltage and conductance‐voltage characteristics are given. The interface state response is shown to fit the statistical model and comparisons with the Si‐SiO2interface were made. The density of states is found to be between ∼6×1010cm−2 eV−1near midgap rising to ∼6×1011cm−2 eV−1at the band edges.

ISSN:0021-8979    

DOI:10.1063/1.337565

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The transport of charge carriers in a multijunction, consisting of alternating thinp‐ andn‐type sublayers of amorphous semiconductor, has been analyzed theoretically. It is shown that the multijunction behaves in the dark like apn‐junction diode, while it has an advantage in reducing range limitation of photogenerated carriers. These properties are realized when the sublayer thickness is of the order of 100 nm for realistic values of doping levels and localized state density.

ISSN:0021-8979    

DOI:10.1063/1.337566

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

In this paper we present the results of a forward‐biased capacitance measurement on palladium silicon Schottky diodes. The data are interpreted in terms of the interface state density by taking into account the effect of series resistance and using Shockley–Read–Hall statistics. Exchange of charge between the metal and the interface states is included in the model. For the as‐deposited sample, an effective state is postulated to lie opposite the metal Fermi level with a concentration of 1×1012/cm2. Upon annealing and formation of palladium silicide, the density of states decreases by a factor of 2 and changes occur in the capture and emission time constants.

ISSN:0021-8979    

DOI:10.1063/1.337567

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Electrical conduction in ultrathin nitrided oxide films on silicon has been investigated by comparing it with that in ultrathin oxide. Significant current enhancement in the nitrided oxide and partial recovery of the enhancement by O2annealing were observed, which can be satisfactorily explained by a two‐step tunneling via traps generated in the nitrided oxide during nitridation. From the comparison between theoretical calculations of tunneling current and experimental data for the nitrided oxide and the SiO2, it is found that the effective barrier height for electrons at an aluminum‐nitrided oxide interface decreases from 3.1 to 2.5 eV for an as‐grown nitrided oxide and to 2.75 eV for a nitrided oxide annealed in O2. The nitrogen‐related traps are estimated to be situated at the surface portion within 32–34 A˚ from the metal‐insulator interface with the energy level of 2.87 eV for the former and 3.32 eV for the latter below each conduction‐band edge.

ISSN:0021-8979    

DOI:10.1063/1.337568

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The optical and electrical properties of grain boundaries inn‐ andp‐type CdTe have been investigated by analysis of single boundaries within bicrystals and of polycrystalline thin films. The grain‐boundary parameters evaluated include the conductivity activation energy, the boundary diffusion potential, the energy distribution of grain‐boundary states, the minority‐carrier recombination velocity, the majority–carrier capture coefficient, and the optical cross section of grain‐boundary states. Passivation experiments indicate that heat treatment in H2or Li provide effective but temporary passivation inp‐type CdTe, and that similar effects are found for heat treatment in air forn‐type material.

ISSN:0021-8979    

DOI:10.1063/1.337569

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We have characterized the effects of Be+implantation and controlled‐atmosphere annealing on the structure of Ga(AsP)/GaP strained‐layer superlattices (SLSs). Damage and strain distributions within the implanted layers were examined by cantilever‐beam bending measurements, double‐crystal x‐ray rocking curves, and a variety of ion‐channeling techniques. Implantation‐induced displacement damage produces additional stress in the SLS, in this case reaching 4.5×109dyn/cm2, a value comparable to that of the built‐in stresses in these SLSs. The depth distribution of ion damage as measured by ion channeling agrees well with the predictions of thetrimcode, although substantial recovery occurs during the room‐temperature implant. Rocking curve analysis indicates that the interlayer strain in the SLS is retained despite the ion damage, and that the ion damage can be modelled as an independent additional source of strain in the as‐implanted structure. The linear expansion of the layers due to point defect generation for the 1×1015Be/cm2implant is determined to be approximately 0.3% by all three techniques. After controlled‐atmosphere annealing at the nominal SLS growth temperature, both the x‐ray and ion‐channeling measurements indicate removal of the implant damage with the as‐grown strain retained and no resolvable intermixing of the layers in the SLS. These results demonstrate that ion‐implantation technologies developed for bulk semiconductors can successfully be applied to strained‐layer superlattice systems.

ISSN:0021-8979    

DOI:10.1063/1.337570

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We have investigated the properties of Ga(AsP)/GaP strained‐layer superlattices (SLSs) that have been doped by implantation of 1×1015/cm2, 75 keV Be+followed by controlled‐atmosphere annealing at 825 °C for 10 min. Our results indicate that doping of these strained‐layer superlatticeswithoutdisordering is a viable process. Liquid‐helium temperature photoluminescence suggests a binding energy for the implanted acceptors of 50 meV, consistent with that of beryllium in GaP‐based alloys. The implantation‐doped regions exhibit room‐temperature electrical activation of 15% and hole mobilities of 20 cm2/V s, consistent with the values expected for type‐converted GaP‐based alloys. SLS diodes fabricated by this process exhibit excellent rectification properties, with a forward turn‐on voltage of approximately 1.8 V and low values of room‐temperature reverse leakage current densities. Diodes formed from SLSs with originaln‐type doping of 1×1017/cm3have typical reverse leakage current densities of 1×10−7A/cm2at −10 V, despite the depletion region penetrating approximately ten interfaces of the SLS at this bias. Deep‐level transient spectroscopy demonstrates the existence of defect centers, whose densities and signatures are similar to those found in ion‐implanted GaP. The implanted photodiodes exhibit a wavelength‐dependent photoresponse characteristic of grown‐junction SLS photodetectors in the same chemical system. Examination of the spatial response of the photodiodes to a tightly focussed (FWHM=2.45 &mgr;m) laser beam at a wavelength of 488 nm indicates that the photoresponse from the device is uniform to within 10% for regions away from the edges of the implanted regions. Modelling of the wavelength‐dependent and the spatially dependent photoresponse allows an estimate of minority‐carrier diffusion lengths for electrons and holes of 1.0 &mgr;m parallel to the SLS layers and 0.1 &mgr;m perpendicular to the SLS layers. The excellent electrical and optical properties of the implanted and annealed SLS materials implies additional device applications for these novel materials.

ISSN:0021-8979    

DOI:10.1063/1.337796

出版商:AIP    

年代:1986

数据来源: AIP