摘要:

Selective epitaxial growth (SEG) of SiGe on patterned-oxide silicon substrates, using a tubular hot-wall low pressure chemical vapor deposition (LPCVD) system, has been demonstrated. This conventional LPCVD system was proposed as a low cost alternative for SiGe epitaxial growth. Dichlorosilane (SiH2Cl2)and germane (GeH4)were used as the reactant gases with hydrogen as a carrier gas, with no addition of HCl needed to achieve selectivity in quality epitaxial growth of SiGe. Nomarski microscopy showed good selectivity with no nucleation occurring on the SiO2areas. A low defect silicon buffer layer grown under SEG conditions was key in obtaining high-quality growth. Cross-sectional transmission electron microscopy showed that the SiGe strained layers grown at 700 °C, 750 °C, and 800 °C were of high quality.

ISSN:1071-1023    

DOI:10.1116/1.589239

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

Spatial selectivity of layer disordering induced in GaAs/AlGaAs quantum well heterostructures using SiO2and Si3N4capping and annealing was investigated using low temperature photoluminescence in conjunction with cross-sectional transmission electron microscopy. Comparative study reveals opposite behaviors for patterned Si3N4covered with SiO2and patterned SiO2covered with Si3N4. In the former, layer disordering occurs in the regions located under the SiO2strips and in the latter, layer disordering surprisingly occurs under the Si3N4strips while it is inhibited in the SiO2-capped areas. These results are in agreement with a proposed interdiffusion model based on the effect on Ga vacancy diffusion of the stress distribution generated in the heterostructure during annealing by the capping layers. This work clearly demonstrates that the diffusion of point defects, such as the Ga vacancies, which are responsible for the layer disordering, can be piloted by the stress field imposed to the semiconductor and opens new perspectives for defect engineering.

ISSN:1071-1023    

DOI:10.1116/1.589240

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

A novel selective etching method was employed to construct monolithic GaAs/AlGaAs microvacuum structures for transmission-mode photoemitters. These emitters consisted of a photon absorption layer with a window and top contact layers supported by micropillars of about 140 μm2in cross section areas, a 2-μm-wide vacuum space, and an electron collector. Part of the photoelectrons generated in the absorption layer were emitted into the vacuum space inside the microvacuum structure. They were subsequently accelerated by an applied reverse bias across the vacuum space and collected by a conductive GaAs substrate. The electron emitting surface was protected against contaminants from air by sulfur radicals by a H2SO4solution treatment. After thermal cleaning at 475 °C and activation with Cs, the microvacuum emitter exhibited an external quantum efficiency of 0.33% at 650 nm wavelength. Photocurrent was a linear function of the power of incident light, and the dark current of the microvacuum emitters remained below 90 pA/cm2at 20 °C. Experimentally observed spectral quantum efficiencies of the microvacuum and reflection-mode emitters are compared with theoretical diffusion model calculations.

ISSN:1071-1023    

DOI:10.1116/1.589241

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

Growth, doping, andin situetching of GaAs using cracked and uncracked tris-dimethylaminoarsenic (TDMAAs) in chemical beam epitaxy (CBE) have been studied. A reflection high-energy electron diffraction study indicates that the complete decomposition of TDMAAs occurs below370 °C. Possible TDMAAs decomposition pathways, which are consistent with experimental data, are presented. The carbon level in undoped GaAs films and the hole concentration in carbon-doped GaAs films using uncracked TDMAAs are much lower than those using cracked TDMAAs, which may be due to atomic hydrogen released from theβ-hydride elimination process of uncracked TDMAAs on the GaAs surface. Thein situGaAs etching effect was observed only when the substrate was exposed to uncracked TDMAAs. Possibly, reactive free radicals generated by uncracked TDMAAs on GaAs surfaces are responsible for the etching effect. Surface roughness in selective-area growth of GaAs and the poor interfaces in InGaAs/GaAs multiple quantum wells grown by CBE using uncracked TDMAAs may result from this etching effect.

ISSN:1071-1023    

DOI:10.1116/1.589242

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

We have developed a novel selective citric acid-based etchant used for GaAs over AlGaAs, which consists of citric acid,NH4OH,andH2O2. The etching rate ratio of GaAs toAl0.15Ga0.85Aswas as high as 80 by optimizing thepH and citric acid/H2O2ratio. The etch stop mechanism was investigated using x-ray photoelectron spectroscopy. The etching is stopped at the AlGaAs surface due toAl2O3formation, whose density is higher than that on a nonselectively etched surface. This selective citric acid-based etchant was applied to the fabrication of GaAs/AlGaAs heterostructure field effect transistors (HFETs). The threshold voltages of the HFETs exhibit excellent uniformity (the standard deviation of 32 mV across the 3 in. wafer), demonstrating the applicability of this selective etchant to the gate recess process.

ISSN:1071-1023    

DOI:10.1116/1.589243

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

A new analytical method for thin Si layer is proposed that uses low temperature oxidation and chemical analysis. The thin Si layer of silicon-on-insulator wafers is oxidized at a low temperature by electron cyclotron resonance oxygen plasma. The oxide is analyzed by vapor phase decomposition method and atomic absorption spectrometry. This approach makes it possible to analyze metallic impurities without the diffusion of contaminants because the oxidation is carried out at a low temperature. The results reveal that metallic impurity concentrations below 1010atoms/cm2can be detected with a depth resolution of 4 nm.

ISSN:1071-1023    

DOI:10.1116/1.589244

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

A dual tunneling-unit scanning tunneling microscope (DTU STM) was developed for nm order length measurement with wide scan range. The crystalline lattice of highly oriented pyrolitic graphite (HOPG) was used as reference scale. A reference unit was set up on top of a test unit. The reference sample holder and the probe tip of test unit were attached to one singleXYscanner on either surface, while the test sample holder was open. This enables simultaneous acquisition of wide images of HOPG and test sample. The length in test sample image was measured by counting the number of HOPG lattices. An inchworm actuator and an impact drive mechanism were introduced to roughly position probe tips. TheXYscanner was designed to be elastic to eliminate image distortion. Some comparison experiments using two HOPG chips were carried out in air. The DTU STM is confirmed to be a stable and more powerful device for length measurement which has nanometer accuracy when covering a wide scan range up to several micrometers, and is capable of measuring comparatively large and heavy samples.

ISSN:1071-1023    

DOI:10.1116/1.589245

出版商:American Vacuum Society    

年代:1997

数据来源: AIP

摘要:

A recently designed Langmuir trough using a steady-laminar flowing subphase is exploited to support polymer monolayers. The ultrathin poly(methyl methacrylate) (PMMA) films prepared by this technique have been explored as high-resolution electron beam resists. The lithographic exposure conditions of Langmuir–Blodgett PMMA films were investigated and the results of fabricating a 4 in. mask with 0.38μmin feature linewidth and 0.5μmin resolution were achieved by using the Jeoptic ZBA-23 electron-beam machine as the exposure tool.

ISSN:1071-1023    

DOI:10.1116/1.589246

出版商:American Vacuum Society    

年代:1997

数据来源: AIP