摘要:

We employ the vibrating tip of an atomic force microscope as a lithographic tool to mechanically pattern a thin photoresist layer covering a GaAs–AlGaAs heterostructure. High aspect ratio electron beam deposited tips, additionally sharpened in an oxygen plasma, are used to minimize the dimensions of the fabricated quantum electronic devices. The fabrication parameters of the tips and the sharpening process are investigated. With these ultrasharp tips we are able to produce lines and holes with periods down to 9 nm in photoresist. In addition, the very sharp tips yield substantial improvements in the imaging mode. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115365

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The lattice location of three rare‐earth ions (Pr3+, Ho3+, Yb3+) in LiNbO3is investigated using Rutherford backscattering spectrometry/channeling techniques. All of them are found to occupy the Li+octahedron but shifted from the Li+regular position by different amounts (−0.45 A˚ for Pr3+, −0.38 A˚ for Ho3+, and −0.3 A˚ for Yb3+) as previously reported for other rare‐earth ions. The amount of displacement is directly related to the variation of the ionic radius of the rare‐earth ion, oppositely to transition metal ions which are not shifted. A simple model based on electronic configuration is given to account for this behavior. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115366

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A simple expression for the inverse subthreshold slope in polycrystalline silicon thin‐film transistors (TFTs) is derived as a function of the gate voltage and with parameters the trapping states at the grain boundaries, the grain size, and the gate oxide. Comparison with the experimental results verifies the validity of the derived expression. We show that in polysilicon TFTs, even with high trapping states density and small grain size, excellent subthreshold characteristics can be obtained by scaling down the SiO2thickness to 10 nm. Further improvement in the subthreshold characteristics can be achieved using as gate oxide a Si3N4/SiO2bilayer of thickness 10 nm which has higher dielectric constant, exhibits good interface properties with polysilicon and serves as a diffusion barrier to avoid penetration effects of impurities through the oxide. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115367

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Short‐period Ga0.51In0.49P/GaAsyP1−ystrained superlattices were grown, by organometallic vapor phase epitaxy, with periods around 70 A˚ and phosphorus compositions from 0.04 to 0.31. Ground state emission as high as 1.73 eV was observed. Model solid theory predictions fit this data well, particularly at lower P compositions. Type II structures were obtained for phosphorus compositions above 0.04. The introduction of phosphorus in the low bandgap regions of these superlattices was found to significantly improve their structural and optical quality. These superlattices provide, in many applications, a viable alternative to the quaternary alloy GaInAsP, which is required for obtaining these bandgaps in Al‐free systems lattice‐matched to GaAs. To our knowledge this is the first report on the growth and modeling of short‐period superlattices using this material system. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115368

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The relationship between the surface morphology and strain relaxation is explored in strained InxGa1−xAs layers grown on GaAs by molecular beam epitaxy.Insitulight scattering, detected simultaneously along [110] and [11¯0], reveals an asymmetric surface roughening which is consistent withexsituscanning force microscopy. Transmission electron microscopy shows that strain relaxation by misfit dislocation formation occurs before the surface roughening is detected, for In0.18Ga0.82As films grown at 490 °C. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115369

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The surface structure ofGa0.52In0.48Pwas studied by surface photoabsorption. An absorption peak due to P dimers onGa0.52In0.48Pwas observed at ∼400 nm, shorter than for InP (430 nm). From comparison with results for GaAs and InP, the data are interpreted to indicate that at a tertiarybutylphosphine (TBP) pressure of 50 Pa for temperatures below 670 °C, the P‐stabilized surface has P dimers aligned along the [1¯10] direction, i.e., it has a (2×4)‐like structure. Above 670 °C, the 400 nm peak due to the P‐dimer structure disappears because of P desorption from the surface at this TBP partial pressure. EpitaxialGa0.52In0.48Players grown using TBP, trimethylgallium and ethyldimethylindium are nearly disordered at 670 °C and highly ordered at 620 °C. These data suggest a correlation between surface structure and ordering. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115370

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An approach is presented which eliminates the problems caused by hydrocarbon polymer deposition in etching compound semiconductor with CH4/H2based plasmas. We find that atomic nitrogen, created by the addition of N2to the plasma, inhibits polymer deposition in the chamber and on the sample. Atomic nitrogen has several beneficial effects; the elimination of polymer precursors, the reduction of the atomic hydrogen concentration, and a potential increase of methyl radical concentration. It is also demonstrated that the addition of N2to CH4/H2based electrocyclotron resonance plasmas used to etch HgCdTe eliminates the roughness normally formed during etching. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115371

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Wide bandwidth AlAs/Al0.6Ga0.4As tandem Bragg reflectors were grown by organometallic vapor phase epitaxy. Quarter‐wave reflector stacks designed for different wavelengths were placed in cascade in epitaxially grown structures to expand the high reflectance bands. Intermediate low‐index layers were put in between every two stacks to suppress the transmission peaks in the centers of the combined high reflectance bands. While a single‐stack structure showed a full width half‐maximum bandwidth of 500 A˚, the two‐stack and the three‐stack structures effectively doubled and tripled this bandwidth to approximately 1000 and 1500 A˚, respectively. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115372

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Pump‐probe spectroscopy is used to determine the dynamics of carriers in thin films of Ga0.51In0.49P grown at temperatures of 500, 300, and 200 °C. The carrier trapping time &tgr;tr, is found to be ∼0.2 ps for the 200 °C sample and ∼0.9 ps for the 300 °C sample. Annealing of the 200 °C sample at 450 °C for 10 min causes the optical response to slow appreciably (&tgr;tr∼0.7 ps), indicating that the point defects are directly responsible for the ultrashort optical response observed in this material. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115373

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

GaN layers having the zinc blende and wurtzite structures can be selectively deposited on (111)A and (1¯1¯1¯)B GaAs substrates by varying the growth temperature. Using the growth temperature as a variable, layers having the two structures have been sequentially deposited. The as‐grown structures have been examined by cross‐sectional high resolution electron microscopy. Results indicate that the two phases once formed are structurally stable in the temperature range examined. Furthermore, the transition from GaN (zinc blende) to GaN (wurtzite) is sharp, whereas a faulted region is observed during the reverse transition. Arguments have been developed to rationalize these observations. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115374

出版商:AIP    

年代:1995

数据来源: AIP