摘要:

The real space transfer in depletion‐mode dipole heterostructure field‐effect transistors (HFETs) has been investigated both theoretically and experimentally. Theoretically, we demonstrate that parallel conduction will be substantially reduced in the dipole HFET and to a smaller extent in the planar‐doped HFET when compared to the conventional HFET due to the increased carrier confinement. By measuring the cutoff frequency at various dc biases, the experimental results indicate that a reduced real space transfer effect occurs in the depletion‐mode dipole HFETs.

ISSN:0003-6951    

DOI:10.1063/1.104887

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

It has been reported that there is a drastic increase of grain size in polycrystalline silicon because of secondary grain growth in ultrathin, heavilyn‐type doped films upon conventional furnace annealing. There has been very limited work on secondary grain growth during rapid thermal annealing (RTA). This letter presents for the first time extensive data on secondary grain growth in heavilyn‐type, P‐doped amorphous silicon‐on‐oxide films during RTA. Grains as large as 16 &mgr;m in diameter have been obtained in 160‐nm‐thick films which represent the largest secondary grains and largest grain size to film thickness reported in the literature. The role of charged silicon vacancies is invoked in a new way to explain the observed lower activation energy for grain boundary mobility during secondary grain growth than during normal grain growth.

ISSN:0003-6951    

DOI:10.1063/1.104888

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have reproduced and extended some recently reported electron spin resonance (ESR) measurements related to the nature of the dominant charge traps in silicon nitride. We detected defect centers at low temperatures using ESR, in both as‐deposited and ultraviolet‐irradiated silicon nitride powders and films prepared by low‐pressure chemical vapor deposition (LPCVD). Only two silicon dangling bond defects were observed in the silicon nitride, one atg=2.003 (⋅Si≡N3), and the other atg=2.005 (⋅Si≡Si3). The signal intensity atg=2.003 is by far the dominant signal in the LPCVD films and powders subjected to UV illumination; the signal atg=2.005 is only about 3% of its intensity. These results support the idea that there is just one dominant silicon paramagnetic center (⋅Si≡N3), which is responsible for charge trapping in silicon nitride.

ISSN:0003-6951    

DOI:10.1063/1.104889

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A very high electron mobility pseudomorphic In0.8Ga0.2As heterostructure is successfully grown on InP both by the elimination of the overshoot of flux densities and by the precise control of the flux ratio through a new calibration technique of reflection high‐energy electron diffraction oscillations in a molecular beam epitaxy system. The critical‐layer thickness for the pseudomorphic growth of InGaAs on InP is found to follow the energy balance model, and a very high 2DEG mobility of over 1.5 m2/V s and over 15 m2/V s at 293 and 10 K, respectively, is obtained.

ISSN:0003-6951    

DOI:10.1063/1.104890

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Using metalorganic vapor phase epitaxy to grow GaInAs/InP layers on masked InP substrates patterned with submicron square holes, we have fabricatedinsituburied quantum dot arrays for the first time. Starting with mask openings ≥150 nm × 150 nm and utilizing the natural crystal habits to form low‐index plane facetted pyramids inside the holes, <m1;&40q>highly regular GaInAs quantum dots embedded in InP are obtained in a single growth step. <m1;&40q>As verified by cathodoluminescence, the dots exhibit very high luminescence efficiencies, even at room temperature, owing to the absence of air‐exposed or etch‐damaged heterointerfaces.

ISSN:0003-6951    

DOI:10.1063/1.104891

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Sub‐micron homogeneous powders of YBa2Cu4O8havingTc∼80 K were synthesised from aqueous solutions containing Y, Ba, Cu salts, and oxalic acid as a precipitant via a chemical coprecipitation method using triethylamine as a base. An accelerated formation−within 24 h−of nearly single phase YBa2Cu4O8powders was achieved. The intragrain critical current density at 5 K andH=1 T was determined to be 3.9×107A/cm2. This process may have considerable potential in the large‐scale preparation of YBa2Cu4O8.

ISSN:0003-6951    

DOI:10.1063/1.104892

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The interface between laser deposited Y‐Ba‐Cu‐O thin films and yttria‐stabilized cubic zirconia substrates was studied using high‐resolution transmission electron microscopy andinsituresistivity measurements. It was found that a ∼5 nm layer of low resistivity compound was formed at the interface, at a substrate temperature of ∼650 °C. This result is qualitatively different from other substrates such as SrTiO3and MgO, where the interface compounds are high resistivity oxides. ThisinsituY‐Ba‐Cu‐O thin film is superconducting with aTcof 88 K and aJcof 2×106A/cm2at 77 K.

ISSN:0003-6951    

DOI:10.1063/1.104863

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The use of silicon on sapphire (SOS) as a substrate for YBa2Cu3O7−&dgr;allows the growth of thick (∼4000 A˚) films without the thermally induced cracking characteristic of epitaxial films on bulk Si substrate. Epitaxy is sustained and reaction is prevented by an intermediate buffer layer of yttria‐stabilized (YSZ). The transport critical current density is as high as 4.6×106A/cm2at 77 K, and surface resistance measurements at 4.2 K are reported. Microtwin propagation from Si into YSZ is shown not to occur.

ISSN:0003-6951    

DOI:10.1063/1.104864

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Because of the mixed metal valance state of thallium in a Tl‐based superconductor, a nearly single ‘‘1223’’ phase can be readily prepared by a modified Pechini method (US Patent 3 330 697). Tl2O3and other metal nitrates are dissolved in an aqueous solution plus a certain amount of oxalic acid for chelating the metal cations. The desired phase shows zero resistance at 114 K and the phase purity is identified by x‐ray diffraction. Characteristics of superconductivity also are evidenced by the Meissner effect. The preparation technique is considered valuable to purify multiphase superconductors for mass production.

ISSN:0003-6951    

DOI:10.1063/1.104865

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have developed a two‐step anisotropic etching process to fabricate thin silicon membranes, used to study supercurrent transport in semiconductor coupled weak links. The process uses a shallow BF+2implantation, and permits easy control of membrane thickness ≤100 nm. Preliminary measurements on membrane‐based Nb‐Si‐Nb junctions reveal the simultaneous occurrence of tunnel behavior and Josephson coupling.

ISSN:0003-6951    

DOI:10.1063/1.104866

出版商:AIP    

年代:1991

数据来源: AIP