摘要:

The surface morphology of submonolayer coverages of platinum vapor deposited onto highly oriented pyrolytic graphite (HOPG) has been studied. With coverages of 5%–30% of a monolayer, we have observed both three‐dimensional clusters and two‐dimensional (2D) islands of Pt on the substrate. Our studies concentrated on the 2D islands of Pt, which exhibited several interesting features. Small islands exhibited epitaxial growth on the HOPG with markedly small Pt–Pt bond lengths, as well as occasional features of larger spacings. Similar larger structures on graphite islands and near graphite steps on the clean HOPG surface were observed. Results of scanning tunneling spectroscopy show that spectra on platinum deposits exhibit a broader character than those on clean graphite and show some structure consistent with bulk Pt.

ISSN:0734-211X    

DOI:10.1116/1.586691

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

The first observation of a surface reconstruction with an atomic force microscope (AFM) is reported. The Au(111)p×√3(p∼22–30) surface under electrochemical potential control has been studied. Values for the periodicities and corrugation of the reconstruction that are similar to those found with a scanning tunneling microscope (STM) are obtained. This is an important test of instrumental artifacts owing to the high electric field and uncontrolled contact force in the STM. The STM consistantly yields higher resolution of the reconstruction, although both techniques also consistantly show an ‘‘atomic’’ lattice at high magnification. This apparent contradiction suggests that the atomic resolution in the AFM may be caused by atomic‐scale periodicity in the tip–substrate interaction rather than by true single atom contact. This cannot be explained by tip geometry because the corrugation of thep×√3 reconstruction is much less (∼0.15 Å) than the height of a single atomic step on the Au(111) surface.

ISSN:0734-211X    

DOI:10.1116/1.586692

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

An ultrahigh vacuum (UHV) operating scanning tunneling microscope (STM) has been designed and built with the aim of studying surfaces irradiated with low energy ions. Because the low energy ion implanter was sited in a location remote from the STM laboratory, it was also necessary to design and build a portable vacuum system which was capable of interfacing with both the ion implanter and the STM chamber, and thus, effect a sample transfer under UHV. This article presents a description of the STM and a selection of recent research results which demonstrate the capabilities of the system. In particular, the article reports on the development of small‐scale structures on graphite, platinum, and copper surfaces after irradiation with low‐energy helium ions and on the growth of copper islands formed by ion beam deposition on graphite substrates.

ISSN:0734-211X    

DOI:10.1116/1.586693

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

The study of the crystal surface morphology of CdZnTe is important for the understanding of the fundamentals of crystal growth in order to improve the crystal quality which is essential in applications such as substrates for epitaxy or performance of devices, i.e., room temperature nuclear spectrometers. We present here a first atomic force microscopy study on CdZnTe. Cleaved (110) surfaces were imaged in the ambient and an atomic layer step structure was revealed. The effects of thermal annealing on the atomic steps together with Te precipitation along these steps are discussed in terms of deformation due to stress relief and the diffusion of tellurium precipitates.

ISSN:0734-211X    

DOI:10.1116/1.586694

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

The fabrication of through‐wafer via holes in GaAs substrates by plasma etching and laser drilling is reported. Using a low pressure (15–20 mTorr), low dc bias (−150 V) Cl2/BCl3discharge with Cl2‐to‐BCl3ratios ≤0.2, we are able to produce narrow (≤30 μm) via holes. This enables the use of a higher density of vias in closer proximity to the active GaAs power devices than can be achieved with normal diameter (100–150 μm) holes. Microwave enhancement of the plasma density using an electron cyclotron resonance source increases the GaAs vertical and lateral etch rates and requires use of low Cl2‐to‐BCl3ratios in order to retain the anisotropic nature of the vias. Multiple pass (∼100 per hole) drilling of vias with aQ‐switched Nd‐YAG frequency doubled (532 nm), 30 mW laser has also successfully produced through‐wafer connections. This provides a maskless, versatile method for producting vias customized for a particular wafer, but is less developed than plasma etching.

ISSN:0734-211X    

DOI:10.1116/1.586695

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

A fast, reproducible, and reliable via hole dry etching process for GaAs monolithic microwave integrated circuit (MMIC) fabrication is described. The etching process consists of two steps. During the first etching step, BCl3/Cl2/Ar gas mixture is used to achieve a high etch rate and small lateral etching. In the second etching step, CCl2F2gas is used to achieve a selective etching of the GaAs substrate with respect to the front side metal layer, which is 500 Å thick chromium. Via holes are formed from the back side of a 100 μm thick GaAs substrate and are electroplated with gold (∼20 μm thick). The resulting via hole profile and surface morphology are satisfactory for reproducible and reliable MMIC via groundings.

ISSN:0734-211X    

DOI:10.1116/1.586696

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

The stress distribution in a refractory gate GaAs substrate during annealing was calculated by computer simulation, using the finite element method. Simulations were used to investigate the correlation between the thermal expansion coefficient of the gate and the encapsulant internal stress. The condition in which minimum or no dislocations were induced into the GaAs substrate were studied. It was demonstrate that the best thermal expansion coefficient value of the gate was close to the value that was reported for tungsten. It was concluded that, by controlling the encapsulant thermal stress of SiO2or SiN encapsulant, during high temperature annealing, a dislocation‐free GaAs substrate could be obtained.

ISSN:0734-211X    

DOI:10.1116/1.586697

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

Previous measurements of the photoreflectance line shape of GaAs at theE1transition (2.9 eV) were extended. This study covers the combined effect of temperature and carrier concentration along with a discussion of the effect of the electric field intensity and the field inhomogeneity within a depth of 20 nm from the surface. A systematic study of changes in the line shape of the above band gap transition,E1as a function of temperature (80–400 K) and carrier concentration (CC) (2–200×1016cm−3) is presented and a model of the effect is discussed. It was found that as the carrier concentration increases beyond 1×1017cm−3, the line shape changes in phase and in broadening in a characteristic way which depends on CC and temperature. A simple correlation is established between both the broadening and the line shape rotation as a function of temperature and CC. Using the Schottky relation and Fermi‐level pinning, the observed effect qualitatively was explained. Also the effect of near‐surface electric field on the line shape is discussed. The observed effect may be applied as an optical measurement of the carrier concentration or possibly the electric field within a depth of ≂20 nm from the surface/interface.

ISSN:0734-211X    

DOI:10.1116/1.586698

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

Possible defects originating in the interface of GaAs Schottky barriers have been considered. Three types of imperfections, such as clusters, metal microphases, and extended dislocation defects, have been recognized after intentional thermal treatment of the samples. It has been shown that those defects may affect strongly the Schottky barrier height, and thus, the idea of an effective work function [J. M. Woodall and J. L. Freeout, J. Vac. Sci. Technol.21, 578 (1982)] has been supported. By deep‐level transient spectroscopy spectra simulation, characteristic broadening and shifting of the experimental spectra have been explained to be due to dislocation defects. A model has been proposed of defect formation which may act as a possible limit of metal–insulator semiconductor field effect transistor operation at high temperatures.  

ISSN:0734-211X    

DOI:10.1116/1.586699

出版商:American Vacuum Society    

年代:1993

数据来源: AIP

摘要:

We have investigated the feasibility of depositing InN from nitrogen plasmas by electron cyclotron resonance metalorganic molecular‐beam epitaxy (ECR MOMBE) for use in ohmic contact formation. Resistivity, growth rate, and morphology were evaluated as a function of microwave power, growth temperature, and trimethylindium flux. Fine‐grained polycrystalline films with N/In ratios of 1.15 and resistivities as low as 190 μΩ cm were obtained under optimized growth conditions and represent the first demonstration of nitride growth by ECR MOMBE. Carbon and oxygen backgrounds were below the detection level of Auger electron spectroscopy. Ti/Pt/Au contacts deposited on InN yielded contact resistances of 5–6×10−7Ω cm2and are thermally stable at normal alloying temperatures (∼380 °C).  

ISSN:0734-211X    

DOI:10.1116/1.586700

出版商:American Vacuum Society    

年代:1993

数据来源: AIP