摘要:

We have discovered that a class of inorganic sulfides [Li2S, (NH4)2S, Na2S⋅9H2O, etc.] imparts excellent electronic properties to GaAs surfaces. The surface recombination velocity at the interface between Na2S⋅9H2O and GaAs begins to approach that of the nearly ideal AlGaAs/GaAs interface. We propose the formation of a robust covalently bonded sulfide layer to explain the favorable electronic quality of such interfaces.

ISSN:0003-6951    

DOI:10.1063/1.98415

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Metal‐semiconductor field‐effect transistors (MESFET’s) have been fabricated in an unintentionally doped,n‐type &bgr;‐SiC thin film grown by chemical vapor deposition (CVD). Thisn‐type layer was deposited on a monocrystallinep‐type &bgr;‐SiC (100) CVD layer previously grown on ap‐type Si (100) substrate. The buriedplayer allowed the devices to be fabricated several microns away from the SiC/Si interface region which contained numerous defects formed as a result of the poor lattice match and different coefficients of thermal expansion between SiC and Si. Thermally evaporated Au was utilized for the gate contact. Sputtered TaSi2was employed for the source and drain contacts. The gate lengths and channel depths of these MESFET’s were 3.5 and 0.60 &mgr;m, respectively. Saturation of the drain currents was achieved at room temperature. Furthermore, the current‐voltage characteristics, measured from 298 to 623 K for the first time, indicated that these MESFET’s performed reasonably well throughout this temperature range. The maximum transconductance obtained was 1.6 mS/mm; the value of this parameter decreased with temperature.

ISSN:0003-6951    

DOI:10.1063/1.98416

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Thermally stimulated resonant current peaks are observed in Al0.4Ga0.6As/GaAs triple barrier diodes. These current peaks are interpreted as resonant tunnelings from the first excited electron subband in the first well to the first excited subband and to the second excited subband in the second well. The activation energies for these resonance peaks are measured. The results imply that in the substrate‐side well there is a large amount of excess electrons to compensate the positive charge of silicon atoms segregated into the structure during the growth.

ISSN:0003-6951    

DOI:10.1063/1.98417

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The linear and lowest order nonlinear response of a quantum well resonant tunneling diode is evaluated using quantum transport theory. The calculations show that the negative conductance persists up to about 5 THz, although parasitic circuit elements will limit the maximum oscillation frequency to a much lower value. The nonlinear response (rectification) remains significant to frequencies near 10 THz and shows a resonant peak near 4 THz. These calculations support the interpretation of the experimental data of T. C. L. G. Sollner, W. D. Goodhue, P. E. Tannenwald, C. D. Parker, and D. D. Peck [Appl. Phys. Lett.43, 588 (1983)] that rectification at 2.5 THz was observed in their devices.

ISSN:0003-6951    

DOI:10.1063/1.98418

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Hydrogen neutralization of chalcogen (S, Se, and Te) double‐donor centers in single‐crystal silicon is demonstrated with deep level transient spectroscopy. The deep‐donor chalcogen concentration can be reduced by greater than a factor of 100, while in the same samples the phosphorus shallow‐donor concentration decreases by only a small percentage. Both electronic levels of the double donors were fully removed by hydrogenation and recovered with an anneal at 500 °C.

ISSN:0003-6951    

DOI:10.1063/1.98419

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We report fracture toughness measurements on single crystals of YBa2Cu3Ox, the phase responsible for superconductivity above liquid‐nitrogen temperatures. Indentation crack length measurements on the (010) orthorhombic crystal growth faces revealed the (100) and (001) planes as preferred fracture planes. The toughness of these planes isKc=1.1±0.3 MPa m1/2, and the hardnessH=8.7±2.4 GPa. The observed growth of both radial and lateral cracks in ambient air suggests that these crystals are susceptible to moisture‐enhanced nonequilibrium crack propagation.

ISSN:0003-6951    

DOI:10.1063/1.98420

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

An electron diffraction and microscopy study is presented of a variety of phases in the Y:Ba:Cu:O system in which superconductivity occurs. The superconducting phase is demonstrated by convergent beam electron diffraction to be centrosymmetric with space groupPmmm, in contrast to a previous determination ofPmm2. This discrepancy arises from local symmetry‐breaking defects. In addition to this phase and a cubic BaCuO2phase, we characterize two other phases. One is the Y‐rich orthorhombic phase:Pnmawitha=13.5 A˚,b=6.3 A˚, andc=7.6 A˚. The second occurs by a phase transition of the superconductingPmmmphase toP4/mmmwitha=3.85 A˚,c=11.7 A˚. The superconducting phase may now be described as either an ordered array of oxygen vacancies in the perovskite structure, or an ordered array of oxygen interstitials in the new tetragonal phase, which may explain how the material can lose oxygen reversibly.

ISSN:0003-6951    

DOI:10.1063/1.98421

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Critical currents of the new high‐temperature superconductor Y1Ba2Cu3O7have been measured in applied fields of up to 7 T and for temperatures down to 70 K. We find that the critical current is drastically reduced by the application of magnetic fields much smaller than the upper critical field of the samples,Hc2. This anomalous behavior might be due to very weak pinning, or to a very strong anisotropy ofHc2.Hc2is found to follow a linear temperature dependence that however extrapolates to a critical temperature higher than that measured directly. This might result from the existence of a percolative structure, or from the presence of a small volume fraction of high critical temperature, high critical field regions.

ISSN:0003-6951    

DOI:10.1063/1.98422

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

An improved trapping‐detrapping model is presented describing the effect of electron injection into the oxide of metal‐oxide‐silicon devices. The model covers both hot‐electron and tunneling injection. It takes into account the spatial variation of the oxide electric field due to the trapped charge as well as the effect of this variation on the trapping‐detrapping processes. The calculated results agree well with previously reported experimental results such as the field‐dependent steady‐state flatband voltage and the trapped charge centroid.

ISSN:0003-6951    

DOI:10.1063/1.98423

出版商:AIP    

年代:1987

数据来源: AIP