摘要:

We report the measurement of the x‐ray power from four transition radiators. The average power from a 44 &mgr;A, 104 MeV electron beam penetrating a stack of fifteen 1.5‐&mgr;m‐thick aluminum foils was 0.7 mW at a peak photon energy of 1.56 keV with an approximate bandwidth of 40%. The peak power from the same stack in a 17 ns pulse was 58 W. Foil stacks constructed of Mylar, parylene, or boron were either distorted or destroyed by exposure to the high average current electron beam.

ISSN:0003-6951    

DOI:10.1063/1.103179

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Plasma etching of InP in a microwave (2.45 GHz) electron cyclotron resonance (ECR) CH4/H2/Ar discharge has been investigated as a function of additional radio frequency (rf, 13.56 MHz) self‐biasing of the sample. The etch rate of InP in a 1 mTorr, 250 W CH4/H2/Ar (5/15/7) ECR discharge increases linearly with applied rf bias, from 50 A˚ min−1at 0 V to 350 A˚ min−1at 200 V. Etching under ECR conditions alone yields smooth surface morphologies, while additional rf biasing of the discharge leads to In droplets remaining on the surface. This appears to be a result of preferential removal of P by the high atomic hydrogen density in the discharge. The room‐temperature photoluminescence intensity from InP is reduced by approximately an order of magnitude after ECR etching, but is restored after removal of ∼20 A˚ from the surface by wet chemical etching. Gold Schottky contacts on InP samples etched under ECR conditions only yield barrier heights of 0.48 eV and ideality factors of 1.1, essentially identical to those on wet‐etched control samples. ECR etching performed with an additional 100 V rf bias yields diodes with barrier heights of 0.44 eV and ideality factors of 1.6. Removal of ∼20 A˚ of the surface on these samples restores the values to those obtained on the control material.

ISSN:0003-6951    

DOI:10.1063/1.102487

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Doping dependence of intersubband absorption in In0.53Ga0.47As/In0.52Al0.48As multiquantum wells (MQWs) grown by molecular beam epitaxy is investigated. The MQWs having a constant well width of 130 A˚ are uniformly doped to a sheet carrier concentration of 4×1011–1×1013cm−2. AboveNs=1.8×1012cm−2, the intersubband absorption from the second to the third subband is observed, as well as from the first to the second, which agrees well with theoretical calculations.

ISSN:0003-6951    

DOI:10.1063/1.102488

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A fluorinated thermal SiO2, grown after HF surface treatment without de‐ionized water rinse, was estimated to contain ∼3×1013cm−2of fluorine by the19F(p,&agr;&ggr;)16O reaction. Secondary‐ion mass spectrometry data indicate that the SiF distribution is peaked at the SiO2/Si interface in the fluorinated oxide. The time‐dependent change of the absolute amount of fluorine on the HF‐treated silicon surface as a function of storage time in air or in vacuum was also investigated by the19F(p,&agr;&ggr;)16O reaction. The initial number of fluorine atoms on the HF‐treated silicon surface was estimated to be ∼1015cm−2before substantial desorption took place. Fluorine atoms desorb from the silicon surface much more rapidly if the sample is stored in air than in vacuum. These results were also supported by the x‐ray photoelectron spectroscopy measurement.

ISSN:0003-6951    

DOI:10.1063/1.103206

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

GaAs was grown on a Si substrate by metalorganic chemical vapor deposition using GaAs/GaAsP strained‐layer superlattice (SLS) intermediate layers. The dislocation density decreases at the interface between GaAs and the SLS, but does not decrease in the SLS. When a GaAs/GaAsP SLS is used as the intermediate layer, part of the threading dislocation propagates into the top GaAs layer because of the lattice mismatch of GaAs and SLS. The low etch pit density of (3–5)×105cm−2was obtained by using the intermediate layer of a GaAs/GaAsP SLS and an AlAs/GaAs superlattice with thermal cycle annealing.

ISSN:0003-6951    

DOI:10.1063/1.102489

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We describe a plasma‐based dry etching procedure which permits selective etching of Si over Ge with a Si/Ge etch rate ratio of over 70 and negligible etching of the Ge underlayer. This is achieved in a SF6/H2/CF4gas mixture by the formation of a thin (&bartil;3 nm) involatile etch stop layer on the Ge surface which consists of Ge‐sulfide and carbonaceous material.

ISSN:0003-6951    

DOI:10.1063/1.102490

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

High quality long‐wavelength InGaAsP/InP lasers were grown by atmospheric organometallic vapor phase epitaxy using tertiarybutylarsine (TBA) as a substitute for AsH3. Electrical and photoluminescence measurements on InGaAs and InGaAsP showed that TBA‐grown material was at least as good as AsH3material in terms of suitability for lasers. From two wafers grown by TBA, current thresholdsIthas low as 11 mA were obtained for a 2‐&mgr;m‐wide semi‐insulating blocking planar buried heterostructure laser lasing near 1.3 &mgr;m wavelength. The differential quantum efficiencies &eegr;Dwere as high as 21%/facet with a low internal loss &agr;=21 cm−1. In additionIthas low as 18 mA and &eegr;Das high as 18% have been obtained for multiplequantum well lasers at 1.54 &mgr;m wavelength. These results show that TBA might be used to replace AsH3without compromising on laser performance.

ISSN:0003-6951    

DOI:10.1063/1.102491

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Previously reported growth of SiC films on SiC by chemical vapor deposition (CVD) used Acheson and Lely &agr;‐SiC crystal substrates. We report the CVD growth and evaluation of high quality 6H‐SiC films on 6H‐SiC wafers cut from large boules grown by the modified‐sublimation process. The single‐crystal 6H‐SiC films were grown on wafers oriented 3° to 4° off the (0001) plane toward the ⟨112¯0⟩ direction. The films, up to 12 &mgr;m thick, had surfaces that were smooth and featureless. The high quality of the films was demonstrated by optical and electron microscopy, and low‐temperature photoluminescence.

ISSN:0003-6951    

DOI:10.1063/1.102492

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Polycrystalline silicon has been grown by ArF excimer laser (193 nm) induced dissociation of Si2H6adsorbed on a quartz substrate cooled to −69 °C. Silicon atomic layer growth has also been achieved by controlling the Si2H6adsorbed layer thickness. It is found that the chemical reactivity of the first one monolayer of Si2H6in contact with the growing Si surface is extremely high compared to that of the second or third Si2H6layer. The effective photodissociation reaction rate at 193 nm for the first Si2H6layer is estimated to be more than 40 times faster than that of an isolated Si2H6molecule. Such high reactivity of the first monolayer is a possible mechanism of the self‐limiting process in the atomic layer growth.

ISSN:0003-6951    

DOI:10.1063/1.102493

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Thermally cracked tertiarybutylarsine and tertiarybutylphosphine were used to replace AsH3and PH3for the growth of Ga0.47In0.53As and InP by metalorganic molecular beam epitaxy. For both materials, carrier concentrationsn=(1–2)×1015cm−3were obtained at 300 and 77 K, with 77 K mobilities of 29 000 and 31 000 cm2 V−1 s−1. The GaAs wasp‐type withp=4×1015cm−3at both temperatures and a 77 K mobility of 2200 cm2 V−1 s−1. The lifetimes for carriers in 14–60 A˚ thick quantum wells were 3±1 ns. The reacting arsenic species for epitaxy were As2and As4. The reacting phosphorus species were PH2and possibly PH.

ISSN:0003-6951    

DOI:10.1063/1.102494

出版商:AIP    

年代:1990

数据来源: AIP