摘要:

The photosensitivity of semiconducting polymers can be enhanced by blending donor and acceptor polymers to optimize photoinduced charge separation. We describe a novel phase‐separated polymer blend (composite) made with poly[2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐1,4‐phenylene vinylene], MEH‐PPV, as donor and cyano‐PPV, CN‐PPV, as acceptor. The photoluminescence and electroluminescence of both component polymers are quenched in the blend, indicative of rapid and efficient separation of photogenerated electron‐hole pairs with electrons on the acceptor and holes on the donor. Diodes made with such a composite semiconducting polymer as the photosensitive medium show promising photovoltaic characteristics with carrier collection efficiency of 5% electrons/photon and energy conversion efficiency of 0.9%, ∼20 times larger than in diodes made with pure MEH‐PPV and ∼100 times larger than in diodes made with CN‐PPV. The photosensitivity and the quantum yield increase with reverse bias voltage, to 0.3 A/W and 80% electrons/photon respectively at −10 V, comparable to results obtained from photodiodes made with inorganic semiconductors. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359792

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The electronegativity difference between silicon and SiO2produces a dipole layer at the Si–SiO2interface which determines the barrier height between the silicon and SiO2conduction bands. Because thermally grown SiO2is amorphous, the alignment of these dipoles with respect to each other fluctuates resulting in a barrier height distribution. Photon‐assisted injection of electrons into the thermally grown gate oxide of a metal‐oxide‐semiconductor field‐effect transistor is used to extract this distribution by experiment. The ratio of the injected gate current to the short‐circuit source–drain photocurrent collected under the gate is shown to be the Laplace transform of the barrier height distribution. By inverting the Laplace transform, measured under the specific experimental conditions described, the barrier height distribution is found to be Gaussian. The average zero‐field barrier height is found to be 3.5 eV with a standard deviation of 0.64 eV measured in the oxide over a plane parallel to the Si–SiO2interface. The relation is given between the average barrier height and the high‐field extrapolated barrier height of 3.1 eV, and it is argued that the standard deviation is a measure of the degree of disorder in the SiO2. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359793

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Using the Laplace transform method, the specific experimental conditions are given under which the extraction of a Gaussian distribution of barrier heights, in the Si–SiO2heterojunction, is based. Specifically described are: (1) the maintenance of a constant oxide field despite oxide charging; (2) the determination of the substrate field produced by the backgate bias; (3) the extraction of the short‐circuit source–drain photocurrent collected under the gate from the total short‐circuit photocurrent which is the sum of the photocurrents collected under the gate and by the source–drain junctions; (4) the minimization of inversion layer free‐carrier absorbtion to make the amount of incident light that penetrates the substrate independent of both the gate and backgate bias; and (5) the implementation of the measurement system to extract the barrier height distribution. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359794

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Transient photocurrents in amorphous selenium (a‐Se) and nematic liquid crystal (NLC) double layers have been investigated to elucidate the charge carrier transport process in NLC. It is shown that the transient photocurrents obtained in the experiment are space‐charge limited currents induced by the delayed charge injection from thea‐Se layer to the NLC layer. The mobile charge carriers are found to be positive ions with the drift mobility of 3.5×10−6cm2/V s at 303 K and the ionic radius of 0.32 nm in 4‐cyano‐4′‐alkyl‐biphenyl. The origin of the ions is briefly discussed. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359795

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Atmospheric degradation of unencapsulated CdS‐CdTe solar cells was modeled by assuming that the initial CdTe/electrode interface becomes a metal/insulator/semiconductor junction as oxygen diffuses through the metal to form a CdTeO3insulating layer. The doping concentration, barrier height, and oxide thickness were varied and the numerical calculations were compared with the experimental data on cells aged in a humidity chamber. The degradation was most severe when the cells were exposed to high humidity and high temperature. This degradation could be modeled in terms of the growth of the insulating CdTeO3layer from 20 A˚ to 80 A˚. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359796

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The down sizing of devices has been so rapidly promoted that the device and the circuit feature size will break into the nanometer range less than 1000 A˚ at the beginning of the next century. It is of critical importance to investigate the characteristics of microstructure capacitances for analysis of future devices and circuits. We analyze the general features of microstructure capacitance based on the self‐consistent field approximation, and clarify that it is decomposed into three components. One is the extension of the capacitance of classical perfect conductors discussed in electrostatics. The quantum‐mechanical effect plays an important role in the other two components; one of them is proportional to the electronic density of states at the Fermi potential of the conductor in low temperatures. At room temperature this portion is proportional to the electronic charge in the conductor. The other is due to the delocalization of electronic charge off the surface into the bulk of conductor. These two components have only self‐capacitance contributions. Various aspects of the microstructure capacitance, e.g., the order of magnitude, the diagrammatic expression, the charging energy, and the quantum dot charging are discussed. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.359797

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Ideal threshold current densities of 2.1–4.1 &mgr;m IR lasers are calculated for active layers composed of InAs/InGaSb superlattices, InGaAsSb quantum well quaternaries, InAsSb bulk ternaries, and HgCdTe superlattices. The fullyK‐dependent band structure and momentum matrix elements, obtained from a superlatticeK⋅pcalculation, are used to calculate the limiting Auger and radiative recombination rates and the threshold current density. InGaAsSb quantum wells and InAs/InGaSb superlattices are found to be more promising laser candidates than HgCdTe superlattices and InAsSb bulk ternaries. The calculated threshold current densities of InAs/InGaSb superlattices are similar to those of InGaAsSb active layers at 2.1 &mgr;m, but are significantly lower at longer wavelengths. Comparison with experiment indicates that the threshold current densities of InGaAsSb‐based devices are about three times greater than those calculated for 25 cm−1gain. The threshold current densities of present InAs/InGaSb superlattices are about 100 times above their theoretical limit. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359798

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Experiments on the controlled generation of up to 20 current filaments inn‐type GaAs have been performed in the electric field region, where impurity impact‐ionization avalanche breakdown takes place. This strongly nonlinear system is found to be very sensitive to small deviations of the technological parameters. In particular, we present the results of time‐resolved current measurements on two filaments connected in parallel, which compete for the impressed total current due to nonlocal coupling via a common load resistor. The observed switching time constants down to 100 ns make this system very interesting as a ‘‘winner takes all’’ element in synergetic computer applications. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359799

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We propose a simple potential model which reproduces the main properties of the electronic structure of a delta‐doped field‐effect transistor. On the basis of selfconsistent calculations we conclude that the energies, wavefunctions and other characteristic properties obtained with the proposed model are very close to the results of full selfconsistent calculations. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359800

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The quantum transport of electrons in a T‐shaped waveguide structure is investigated using the tight‐binding model. We take into account electron‐electron interaction in the resonator region within the mean‐field approximation. The scaling rule breaks down in the interacting system and the effect of the interaction is significant when the sample dimensions become large compared to the effective Bohr radius of electrons. The nearly perfect reflection due to the transmission resonances is shifted to higher energy as the repulsive interaction is increased. The interaction effect in the presence of short‐range disorder is also examined. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359801

出版商:AIP    

年代:1995

数据来源: AIP