摘要:

GaAsp/njunction solar cells, grown by vapor transport, frequently show a change in efficiency with light concentration that exceeds the predictions of the standard model based on diffusion limited and generation/recombination current‐voltage mechanisms. A cell was selected where the efficiency changed from 12 to 22% between 1 and 600 suns concentration or about four times that predicted by the standard model. The dark and light, current‐voltage characteristics of this cell were modeled with a trap controlled, space‐charge‐limited current diode model for the device leakage current. A good fit to the experimental data required a distribution density of electron traps, in the high‐resistancep/njunction interface region, on the order of 1018cm−3 eV−1with a minimum at 0.4 eV below the conduction‐band edge. Since the measured thickness of the high resistance region is 0.1 &mgr;m, the equivalent interface state density is on the order of 1013cm−2 eV−1.

ISSN:0003-6951    

DOI:10.1063/1.100811

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

A general expression based on the interfacial layer model is derived for the equilibrium Schottky barrer height, and it is applied to annealed Au‐GaAs contacts. Relations between the experimental barrier height, relative interfacial layer thickness and interface charge values, and the interface state energy distribution spectra are presented. The validity of the interfacial layer model is demonstrated. The obtained barrier height values and the near‐ohmic behavior after high‐temperature annealing are probably due to ionized donor type interface states in the upper half of the forbidden gap.

ISSN:0003-6951    

DOI:10.1063/1.101351

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

A new equivalent circuit is derived for the double‐barrier resonant tunneling diode. An essential feature of this circuit is the addition of an inductance in series with the differential conductanceGof the device. The magnitude of the inductance is &tgr;N/Gwhere &tgr;Nis the lifetime of the (Nth) quasibound state through which all of the conduction current is assumed to flow. This circuit model is used to derive values of theoretical oscillator power that are in much better agreement with experimental results than theoretical predictions made without the inductance. The conclusion is drawn that the response of the double‐barrier structure to a time varying potential is consistent with the coherent picture of resonant tunneling.

ISSN:0003-6951    

DOI:10.1063/1.100812

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

After reviewing the experimental data on the valence‐band offset for HgTe‐CdTe heterojunctions, we support previous suggestions of an extreme temperature dependence for this offset with a calculation based on a bond charge model. The model predicts theTdependence of the valence‐band offset to be 77% of the difference in the band‐gap temperature dependence of the heterojunction constituents. In the HgTe‐CdTe system, the opposite signs of the band gapTvariations yield an anomalously large increase in the offset of 213 meV between 0 and 300 K.

ISSN:0003-6951    

DOI:10.1063/1.100813

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

High‐density delta doping of semiconductors may result in partial ordering of dopant atoms. Under suitable circumstances, periodic delta doping leads to significant suppression of elastic scattering and a consequent enhancement in charge carrier mobility.

ISSN:0003-6951    

DOI:10.1063/1.100814

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Sidegating in GaAs integrated circuits can be eliminated in molecular beam epitaxially grown structure with the incorporation of a GaAs buffer layer grown at low substrate temperatures (200–300 °C). We have grown two films which were identical except one had the low‐temperature buffer layer included in the film structure. The films were modulation‐doped heterojunctions designed to produce a high‐mobility two‐dimensional electron gas. The electrical characteristics of the two‐dimensional electron gas were identical for the two samples. No deleterious effect on the mobility or carrier density was observed with the incorporation of the low‐temperature buffer layer. At 4.2 K both films exhibited carrier densities of 4×1011cm−2and mobilities of (1.4–1.7)×106cm2/V s in the dark. After a brief illumination at 4.2 K, the samples exhibited carrier densities of 5×1011cm−2and mobilities of (1.6–2.0)×106cm2/V s. These electron mobilities are comparable to the highest electron mobilities ever obtained at these electron densities.

ISSN:0003-6951    

DOI:10.1063/1.101358

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

We report the first observation of phonon density of states effects in a superconductor using a low‐temperature scanning tunneling microscope (STM). The phonon effects were observed using a STM spectroscopy method to measuredItunneling/dVvsVfor the tunnel junction formed by the Au STM probe and a superconducting Pb sample.

ISSN:0003-6951    

DOI:10.1063/1.100815

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

A jitter‐free, repetitive opening switch made of YBa2Cu3O7−xhigh‐temperature superconductor is demonstrated. The switch conducts electrical current at no loss when it is superconducting. A pulse or pulse train of magnetic field on the order of 100 G causes the transition of the switch from the superconducting state to the resistive normal state and forces current to flow through a load resistor that is connected in parallel with the switch. Repetitive operation of this switch at rep rates higher than 1 kHz has been demonstrated.

ISSN:0003-6951    

DOI:10.1063/1.100816

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

We have made a series of single‐level dc superconducting quantum interference devices (SQUIDs) from 4‐&mgr;m‐thick TlBaCaCuO films with large grain sizes and operated them in liquid nitrogen. Although device characteristics could not be precisely controlled, some devices had white‐noise levels that approached thermally limited noise above ∼1000 Hz. In addition, devices with 5 and 80 pH loop inductances had 1/ fnoise levels at 10 Hz of 2×10−29and 5×10−29J/Hz, respectively. The noise levels at these frequencies are comparable to commercial rf SQUIDs operating in liquid helium, but the hysteresis of the voltage‐flux characteristic of the highTcSQUIDs remains large.

ISSN:0003-6951    

DOI:10.1063/1.100817

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

An oxygen jet placed near the target during plasma‐assisted laser deposition produces a strong atomic oxygen beam with kinetic energies of 5.6 eV, simultaneous with the laser‐induced atomic beams of Ba, Cu, and Y from the target. All atomic beams can be well characterized by a supersonic expansion mechanism. The behavior of the velocity distributions was studied as a function of the distance from the target and laser energy fluence. A target‐substrate separation of 7 cm was found to be optimum in terms of producing the best as‐deposited films. At that distance, the velocity distributions of all atomic beams become nearly the same.

ISSN:0003-6951    

DOI:10.1063/1.100777

出版商:AIP    

年代:1989

数据来源: AIP