摘要:

The dopant and compound forming behavior of As and Au impurities in Ga2Te3is investigated by the combined application of Mo¨ssbauer spectroscopy, x‐ray diffraction, optical transmission, and electrical measurements. Arsenic is shown to act as an‐type dopant in Ga2Te3, and a ternary semiconductor AuGa2Te3is identified. The results allow for a concise description of the ohmic contact formation mechanism in alloyed Au/Te/Au/GaAs and related structures.

ISSN:0021-8979    

DOI:10.1063/1.351337

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

An increase in surface voltage decay time has been noted in corona‐charged polyvinylidene fluoride films solution cast on silicon, once these films have been charged a number of times and annealed. A re‐examination of the fundamental equations that describe these surface voltage decays shows that the relaxation of the electric field inside the polymer may be considerably lengthened, when the trapped charge density is comparable to the thermal free‐ carrier density.

ISSN:0021-8979    

DOI:10.1063/1.351338

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Open‐circuit dark‐surface potential measurements on corona‐charged solution cast films of polyvinylidene fluoride and a copolymer of vinylidene fluoride and trifluoroethylene show a slower decay after these films have been mechanically peeled from their silicon substrates. It is proposed that peeling produces a thin region of high trap density in the interface layer close to the peeled surface. A simple model of surface voltage decay is presented which accounts for near‐surface trapping due to peeling as well as bulk trapping. Practical ranges for the interface layer thickness and trapping density are discussed.

ISSN:0021-8979    

DOI:10.1063/1.351339

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Both ac and dc conduction processes through thin Langmuir–Blodgett (LB) films of the dodecyloxyphenylurethane of 2‐bromo‐5 (2’‐hydroxyethoxy) tetracyanoquinodimethan (DDOP‐C‐TCNQ, a redox‐active molecule) sandwiched between dissimilar metal (Pt and Mg) electrodes have been studied. The dc conduction changed from a linearI/Vcharacteristic for the lowest applied voltages (±20 mV) to a symmetric nonlinear characteristic obeying a ln I∝V1/4dependence for voltages up to ±1.5 V, in as‐prepared samples. For larger positive voltages, a large increase in current was observed with the dependence changing to a ln I∝V3law, a dependence not reported previously for metal/LB film/metal systems. For increased negative voltages, the ln I∝V1/4was again observed. For low applied ac fields, the conductance was found to follow a &ohgr;nlaw with a value ofnclose to 0.8. The effect of heat annealing the samples was also studied with significant differences in the observed changes in conductance between bilayer and monolayer structures. Emphasis was placed on understanding the conduction process through the single DDOP‐C‐BHTCNQ layer film. For the monolayer device, hysteresis is observed in the positive bias, and both as‐prepared and annealed samples exhibit ln I∝V3behavior. Such behavior was not observed for the corresponding negative voltages, indicating rectification across a distance approximated by the length of an individual molecule. Possible models of the three‐dimensional arrays for both monolayer and multilayer metal/LB film/Mg structures are presented. The weight of existing experimental results does not support the Aviram–Ratner ‘‘molecular rectifier’’ concept for presently known Pt/LB monolayer/Mg devices.  

ISSN:0021-8979    

DOI:10.1063/1.351340

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A new approach for enhancing the exciton absorption and increasing the saturation limit in quantum wells (QWs), using tensile strain, is proposed. Because of the valence‐band mixing in a strained QW, the in‐plane hole mass can become very large or negative. This leads to a heavy electron‐hole reduced mass (exciton mass), and therefore to a small exciton radius. Exciton absorption is substantially increased because of the increased electron‐hole overlap probability in these small‐radius excitons. The effects of saturation are also substantially reduced because of decreased charge‐screening effects for small‐radius excitons and because the rapid dispersal of the photon‐generated excitons reduces the Pauli exclusion effect.

ISSN:0021-8979    

DOI:10.1063/1.351341

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The photoincrement of admittance (photoadmittance) of merocyanine‐arachidic acid mixed Langmuir–Blodgett films sandwiched between aluminium electrodes has been measured for frequencies &ohgr;/(2&pgr;)<1 Hz at room temperature using the monochromatized visible incident. The number of monolayers of the films was 3–19. The photoadmittance is ascribed to photoelectrons from the dye chromophores. The light‐intensity dependence obeys a square‐root law for thicker films, approaching a linear law as the film thickness decreases. The frequency dependence is found to originate from the dispersive component proportional to &ohgr;1−s, which predominates over the d.c. component for thicker films. The value ofs≊0.5 is evaluated with a critical length of about 30 nm as characterizing the crossover between the thin‐film and the thick‐film cases.

ISSN:0021-8979    

DOI:10.1063/1.351342

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A GaAs delta‐doped tunneling diode having a &dgr;n+‐i‐&dgr;p+‐i‐&dgr;n+structure is investigated. A negative differential resistance behavior with peak‐to‐valley ratio as high as 3.1 and a peak current density of 3 kA/cm2is exhibited when the device is operated at room temperature. It becomes resistor‐like at the temperature of 77 K. Theoretical analysis, based on envelope wave function approximation, indicates that the resonant interband tunneling process is responsible for room‐temperature characteristics, while the band‐gap widening effect is responsible for low‐temperature behavior. Furthermore, the dependence of device performance on such structure parameters as doping level, and the physical dimension of the delta‐doped region, etc., is discussed, and found to agree well with experimental results.

ISSN:0021-8979    

DOI:10.1063/1.351343

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Surfaces made of the nonreactive materials Au and graphite exhibit low surface potential variations after a low‐temperature ultrahigh vacuum bake. The variations (due to the finite size crystallites of these materials) may be reduced to a minimum by using Au surfaces of grain size less than 10 nm and graphite surfaces with highly alignedc‐axis orientation. Procedures where this may be accomplished are described. Application to the Los Alamos antiproton gravity experiment is presented.

ISSN:0021-8979    

DOI:10.1063/1.351358

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Al‐Ta‐O composite dielectric thin films prepared by rf plasma sputtering under various conditions have been used for gate insulators of CdSe thin‐film transistors. The hot electron injection method has been used for investigation of the electron trap properties in these thin‐film transistors. It shows clearly that the traps are mainly due to Coulomb attractive centers, i.e., oxygen vacancies. In the best films prepared in this work, capture cross sections of 3.8×10−13cm2and trap densities of 1.0 ×1017cm−3are obtained. The relationships between gate insulator preparation conditions and the traps of the Al‐Ta‐O/CdSe thin‐film transistors are precisely described in this paper.

ISSN:0021-8979    

DOI:10.1063/1.351344

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The mobility‐lifetime products of electrons and holes [(&mgr;&tgr;)eand (&mgr;&tgr;)h] in undoped hydrogenated amorphous silicon samples have been studied by photoconductivity and ambipolar diffusion length measurements. The density of dangling bondsNdin the samples is changed over a range of 3×1015–2×1018cm−3by annealing at high temperatures.Ndand the Urbach tail slopeEovhave been determined by the constant photocurrent method. In addition, the optical gap, the activation energy of dark conductivity, and the exponent governing the intensity dependence of &sgr;pchave been measured. The results show that there is a correlation betweenNdandEovwhich is consistent with equilibrium theory. (&mgr;&tgr;)eand (&mgr;&tgr;)hchange in quite different ways asNdincreases, namely, (&mgr;&tgr;)edecreases as a linear function of the inverse ofNd. However, (&mgr;&tgr;)hremains almost constant whenNd≤5×1016cm−3, then decreases fast for higherNd. The asymmetric dependence of transport properties of electrons and holes onNdsuggests that for electrons recombination through dangling bond states is dominant; but, for holes, recombination mainly proceeds through deep band tail states, especially whenNdis relatively low.

ISSN:0021-8979    

DOI:10.1063/1.351345

出版商:AIP    

年代:1992

数据来源: AIP