摘要:

The energetics of self‐compensation through atomic relaxation around acceptor impurities in ZnSe were examined via first principles total energy calculations. We find large charge state and impurity‐dependent lattice relaxations for As and P acceptors which can account for the experimentally observed difficulties in obtaining low‐resistivityp‐type ZnSe from these dopants. A much smaller relaxation is found for Li.

ISSN:0003-6951    

DOI:10.1063/1.101837

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

We have grown homogeneous alloys of Sn1−xGexwith 0.01<x<0.1 by molecular beam epitaxy on ⟨100⟩ InSb substrates. The Sn‐Ge system is immiscible due to differing equilibrium crystal structures at the growth temperature. By stabilizing the diamond cubic &agr;‐Sn with the InSb template, we have created a metastable miscibility region for alloying Sn and Ge. Pure &agr;‐Sn grown on ⟨100⟩ InSb shows a tetragonal expansion perpendicular to the substrate because of the slightly larger lattice parameter of &agr;‐Sn. As the smaller Ge atom is added, the strain converts from compressive to tension resulting in an effective 1.66% tetragonal contraction in the growth direction for Sn0.92Ge0.08.

ISSN:0003-6951    

DOI:10.1063/1.101838

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

A pulsed XeCl excimer laser (&lgr;=308 nm) is used to meltn‐ andp‐type GaAs samples. Melt‐induced defects shift the surface Fermi level to anewpinning position at 0.58±0.04 eV below the conduction‐band minimum forbothn‐ andp‐type samples. The Schottky barrier height of Au, deposited on the GaAs after laser irradiation, is increased by 0.38 eV (from 0.43 to 0.81 eV) forp‐type, and decreased by 0.30 eV (from 0.84 to 0.54 eV) forn‐type samples. In the post‐melted GaAs near‐surface region, four deep levels are found using deep level transient spectroscopy. The observation of minority‐carrier traps in the Schottky diode structures suggests the existence of minority‐carrier source. We speculate a compensated region forms near the GaAs surface. A bulk Fermi level stabilization model is used to explain the changes observed in the Schottky barrier heights.

ISSN:0003-6951    

DOI:10.1063/1.101839

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

We present a novel heterostructure that exhibits large electroabsorption and refraction. The structure is periodic with a stackable building block, thus it allows large contrast and waveguide operation. The mechanism used is the quenching of absorption produced by transfer of electrons from a reservoir into a quantum well. We demonstrate the principle by presenting differential absorption and refraction spectra on a ten‐period device.

ISSN:0003-6951    

DOI:10.1063/1.101840

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

In this work the role of extended defects on the electrical performance of epitaxial silicon on substrates containing an insulating SiO2layer has been examined. The buried SiO2layers in the substrates were obtained by two techniques: implantation of oxygen and zone melt recrystallization. In order to make a thorough structural and electrical evaluation of silicon on the insulator substrates, 5‐&mgr;m‐thick epitaxial capping layers have been simultaneously deposited via chemical vapor deposition on representative insulating substrates and reference wafers. The average minority‐carrier lifetime was found to vary from 2.5 to 242 &mgr;s depending on the density and distribution of dislocations emerging from the capping epitaxial layer.

ISSN:0003-6951    

DOI:10.1063/1.101841

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

We report on electron transport measurements in a planar resonant tunneling field‐effect transistor (PRESTFET) on a modulation‐doped GaAs/AlGaAs heterostructure. The PRESTFET is created by defining two independently biased, 60‐nm‐long Schottky gates separated by 60 nm, on top of the AlGaAs layer, which presents a tunable double‐barrier potential modulation to the electrons traveling from source to drain. Current measurements 4.2 K, as a function of gate bias, with both gates connected, exhibit strong multiple negative transconductance swings at a fixed drain bias below 5 mV, providing evidence of resonant tunneling through quantized states between the two barriers. Fixing the bias on one of the gates and scanning the second, or fixing the bias on both and varying the light intensity of a light‐emitting diode confirms this observation. In addition, a structure in the output conductance as a function of drain voltage at a fixed gate bias is clearly observed.

ISSN:0003-6951    

DOI:10.1063/1.102267

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

We have fabricated a GaAs diode sampling head which has a bandwidth of 130 GHz, which is a five times improvement over previous room‐temperature designs. This speed is attained with a monolithic sampling head design integrated with two nonlinear transmission lines which serve as the strobe pulse and test signal generators. A 4 ps transition time has been measured with the sampler. We have also measured sinusoidal waveforms to 120 GHz.

ISSN:0003-6951    

DOI:10.1063/1.101842

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Using single‐target off‐axis sputter deposition, high quality superconducting films of YBa2Cu3O7−&dgr;were madeinsitu. These films have properties which are distinctly different from those of bulk ceramics and of post‐deposition annealed films. Their superconducting resistive transitions remain sharp regardless of the value ofTcbetween 75 and 86 K. Normal‐state conductivities are as high or higher than the best single crystals. Critical current densities as high as 6×107A/cm2at 4.2 K.Tc(R=0) falls off with film thickness down to 10 K for 35–40 A˚ films. All of the above properties are relatively insensitive to compositional variation. The results can be explained if theinsitugrowth results in well‐formed CuO2planes with defects occurring elsewhere.

ISSN:0003-6951    

DOI:10.1063/1.102436

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

We demonstrate a photothermal method for making point measurements of the thermal conductivities of highTcsuperconductors. Images made at room temperature on polycrystalline materials show the thermal inhomogeneities. Measurements on single‐crystal Bi2Sr2CaCu2Oxcompounds reveal a very large anisotropy of about 7:1 in the thermal conductivity.

ISSN:0003-6951    

DOI:10.1063/1.101843

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The kinetics of crystallization in the BixCaSrCu2Ow(x=1.5, 2.7) glasses prepared by twin‐roller and metal‐plate quenching methods have been studied by a nonisothermal method using differential scanning calorimetry. Scanning electron microscopy studies suggest surface crystallization as the dominant mechanism. The activation energy for crystal growth calculated from modified Kissinger plots assuming surface nucleation decreased with an increase in the Bi content. Such a composition dependence is consistent with that of the activation energy for viscous flow in the glass transformation range.

ISSN:0003-6951    

DOI:10.1063/1.101844

出版商:AIP    

年代:1989

数据来源: AIP