摘要:

Threshold switching has been observed and studied in thin films of NbOx(x?2) in the sandwich configuration and in a single‐crystal device having both a gap and sandwich configuration. The recovery curve has been determined by measuring the reswitching voltage after a specific zero‐voltage interruption time. Data indicate a maximum allowable interruption time of about 200 ns without a switch‐off transition. This is interpreted as the distribution trapped‐carrier lifetime for polycrystalline NbO2.

ISSN:0021-8979    

DOI:10.1063/1.325730

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Single‐crystal GaSb films have been grown on semi‐insulating (100) GaAs substrates using multitarget sputtering to vary the Sb/Ga atomic flux ratiorimpinging on the growing film. The effects of systematic variations in growth variables (r, growth temperature, target voltage, and Ar sputtering gas pressure and purity) on the electrical properties of deposited films were evaluated. Temperature‐dependent (8–600 °K) Hall coefficient and resistivity measurements were carried out on all films in order to determine the concentration and ionization energies of impurity and point‐defect levels. In all cases the Hall‐coefficient measurements could be fitted with two acceptor levels and a net concentration of very shallow (<1 meV) acceptors. The deepest acceptor level occurred at 80 meV above the valence‐band edge and was associated with electrically active sites on dislocations originating at the film‐substrate interface. A second acceptor level occurred at 40 meV above the valence‐band edge and was directly related to Sb vacancies or equivalent point‐defect complexes. The net concentration of very shallow acceptors was related to both Sb vacancies and donor impurities, probably oxygen. The room‐temperature hole‐carrier concentration in these films ranged from 5×1015to 1×1018cm−3, while the hole mobility was between 1 and 100 cm2/V sec. Analysis of temperature‐dependent mobility data showed that the dominant charge‐carrier scattering sites were dislocations introduced due to the large film‐substrate lattice mismatch, ∼8%.

ISSN:0021-8979    

DOI:10.1063/1.325722

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The capacitance‐voltage characteristics of ap‐type (metalllike)/n‐type semiconductor junction are described in terms of a simple three‐region space charge in the semiconductor. The assumed space charge consists of a narrow (∼100 A˚) high‐density space charge at the interface, followed by an extended low‐density space charge (insulating layer), and finally the bulk space charge. The calculations assume that the equilibrium space‐charge density does not change with applied reverse voltage. The electric field at the junction is calculated analytically, and the electrostatic potential is calculated for the case of abrupt junctions between the various space‐charge regions. The results indicate effective barrier‐height lowering as a consequence of interface charges, even in the presence of the insulating layer which dominates capacitance‐voltage measurements. An interpretation is given to the slope and voltage‐axis intercept of (1/C)2‐vs‐Vplots for a variety of special cases of the general space‐charge distribution. Dark‐capacitance–voltage data gathered on Cu2−xS/CdS photovoltaic cells are interpreted in terms of the proposed space‐charge distribution. The change in junction capacitance with the air‐heat treatments of this heterojunction is qualitatively explained by this model.

ISSN:0021-8979    

DOI:10.1063/1.325731

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Liquid‐nitrogen‐temperature Hall mobilities of about 105 000 cm2/V sec have been achieved inn‐type epitaxial layers grown by molecular beam epitaxy (MBE). The Hall mobility of thep‐type epitaxial layers at 78 °K was about 8440 cm2/V sec. The net donor concentration and the net acceptor concentrations forn‐type andp‐type epitaxial layers were about 4×1014and 1×1014cm−3, respectively. The compensation ratio in then‐type epitaxial layers was about 0.4 as determined from the 78 °K electron mobility. Cr‐doped GaAs buffer layers for FET’s were grown in a substrate temperature range of 500–640 °C. Sheet resistances in excess of 109&OHgr;/ &laplac; were achieved when the substrate temperature during the growth was about 580 °C or higher. The amount of Cr that can be incorporated into the epitaxial layer showed a strong substrate temperature dependence.

ISSN:0021-8979    

DOI:10.1063/1.325732

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Experimental results on the temperature dependence of the internal voltage in aluminum/(alumina) ‐barium‐stearate/tin sandwich structure have been described in the temperature range 50–0 °C. It is observed that the internal voltage, which arises from the asymmetric nature of the electrodes and due to the dipole field in the alumina film, decreases with decrease of temperature. The observed temperature dependence of the internal voltage has been attributed mainly to the thermal excitation of impurities in the insulating alumina film.

ISSN:0021-8979    

DOI:10.1063/1.325733

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

An external controllable dc negative‐differential‐resistance (NDR) device is presented. The device structure is composed of a conventional MOST and two parasitic transistors, which are internally coupled together. The mechanism of NDR is found to be initiated by both the breakdown phenomena at the drain junction and the negative‐feedback circuit from the drain to the gate electrode through an externally connected resistor. Both the experimental observations and qualitative physical interpretations are given.

ISSN:0021-8979    

DOI:10.1063/1.325734

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Effects of plastic deformation on the normal, zero‐field, and mixed‐state specific heat of the type‐II superconductor niobium were experimentally investigated. A high‐resolution ac calorimetry technique was developed and used to study the effects of plastic deformation on the specific‐heat superconducting transition in fields up to 2750 Oe. A method for the analysis of high‐resolution specific‐heat data near the superconducting transition is presented and used to determine &kgr; variations (within a material) caused by plastic deformation. The effects of plastic deformation on the bulk superconducting transition temperature and width are also shown. Measurements of the zero‐field specific heat show a systematic increase in width of the specific‐heat transition with increasing deformation as well as a small increase inTc. Both &kgr; and the &kgr; variation increase with increasing plastic deformation. The analysis method allows the specific‐heat data of the mixed state to be decomposed in a way consistent with previously reported anisotropy data for niobium.

ISSN:0021-8979    

DOI:10.1063/1.325735

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Niobium superconducting bridges having a variable‐thickness geometry consisting of a thin narrow implanted region joining two much thicker bulk films have been fabricated. The temperature dependence of the critical current is described well by the static theory of Likharev and Yakobson. The direct current and alternate current Josephson effects were observed at temperatures above the transition temperatureT′cof the bridge. The magnetic field period of the ’’diffraction pattern’’ dependence on magnetic field is analyzed taking into account demagnetizing effects in an approximate way. This field periodHpis found as a function of the bridge widthwand the lengthLfor wide bridges (w/L≫1), i.e.,Hp= (&Fgr;0/&mgr;0)/ 22/3w5/3L1/3.

ISSN:0021-8979    

DOI:10.1063/1.325736

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The noise temperature and gain stability of the superconducting unbiased parametric amplifier (SUPARAMP) have been calculated. The results of the analysis suggest that extremely low‐noise amplification of signals from cryogenic sources may be achieved. It seems possible to obtain an effective input noise temperature of 1 K for signal frequencies up to 10 GHz, having a stable power gain of 20–30 dB. This paper provides the fundamental design specifications necessary for the construction of a low‐noise SUPARAMP.

ISSN:0021-8979    

DOI:10.1063/1.325737

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The interaction of a resistance‐shunted Josephson junction with a tightly coupled resonant circuit has been examined analytically and in simulation. Parametric dependences are developed and demonstrated for the size of resonance‐induced current steps in the device’sV‐Icurve and the corresponding level of excitation of the resonance.

ISSN:0021-8979    

DOI:10.1063/1.325738

出版商:AIP    

年代:1979

数据来源: AIP