摘要:

Modeling the dark current in quantum well infrared photodetectors has been a topic of much recent research, but the implications of many of the underlying assumptions have not been clarified. We attempt to justify one such model and to provide physical insight for its success. We compare the dark current expression with experiments on several samples, and show that the model provides a good approximation for a wide range of device parameters including barrier thicknesses from 250 to 700 A˚ and number of wells from 4 to 32.

ISSN:0021-8979    

DOI:10.1063/1.353146

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We report on theinsitupreparation and characterization of thin YBa2Cu3O7−&dgr;films on various substrates. The films were grown by electron‐beam coevaporation of the pure metals Y, Ba, and Cu. A pressure stage is used to obtain high partial O2pressure close to the substrate and low pressure in the main vacuum system.Insituresistance measurements were performed to investigate growth dynamics during film formation, and temperature dependence during the cool down fromT≊1000 K toT≤Tc. The films were analyzed byR(T), ac susceptibility, x‐ray diffraction, and critical transport current measurements.

ISSN:0021-8979    

DOI:10.1063/1.353147

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We report attaining Ga‐terminated (4×2) surface reconstruction on virgin GaAs substrates using a completely dry process at temperatures below the oxide sublimation temperature and without group V overpressure. The native oxides are removed with an electron cyclotron resonance hydrogen plasma treatment, followed by annealing at 500 °C in ultrahigh vacuum, which yields a reconstructed surface suitable for epitaxial overgrowth. Characterization by secondary ion mass spectroscopy and transmission electron microscopy reveals the complete removal of O, reduced C, and high structural order at the epilayer/substrate interface when this preparation method is used before molecular beam epitaxy. Annealing the substrate at a lower temperature yields a nonreconstructed surface possessing significant impurity concentrations, and leads to dislocation defects at the epilayer/substrate interface.

ISSN:0021-8979    

DOI:10.1063/1.353148

出版商:AIP    

年代:1993

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.354098

出版商:AIP    

年代:1993

数据来源: AIP