Evolution of arsenic and phosphorus during heat treatment of unprotected and encapsulated Au, AuZn and AuGeNi contacts on GaAs and InP has been examined and correlated with their ohmic behavior.
The interaction between CdTe and In during the formation of an ohmic contact has been investigated. Emphasis is placed on the study of the effect of thermally induced sublimation of cadmium on electrical properties of contacts. Presented results prove the effectiveness of cap annealing and rapid thermal processing in fabrication of improved ohmic contacts with limited Cd losses during the contacting procedure.
Reactively sputtered TiN films were evaluated as annealing cap improving the formation of Au(Zn) ohmic contact and as antidiffusion barrier protecting contact metallization and underlying GaAs against reaction with Au overlayers.
Low resistance (Au)GeNi ohmic contacts to n-GaAs with smooth morphology and restricted penetration into the substrate have been fabricated. Rapid thermally nitrided tungsten has been demonstrated to be an effective capping layer during the contact processing.
General behavior of In/GaAs couple heat-treated at 570°C for 2 hours was studied with secondary-ion-mass spectrometry, scanning electron microscopy, Rutherford backscattering spectroscopy and Nomarski microscopy. It is shown that, besides the well-known InGaAs crystallites which epitaxially grow upon dissolution of the substrate, In interacts with the substrate dislocations to form In(Ga)As dendrites. The driving force for this process is presumably excess arsenic reported to be present in the vicinity of the individual dislocations.
Recent advances in the technology and understanding of ohmic contacts to GaAs are presented. The paper emphasizes the reactions at the metal/GaAs interface and the structural factors which govern its electrical behavior and long-term stability. Results on the optimization of conventional gold-based ohmic contacts together with recent achievements in the technology of non-alloyed contacts are overviewed.
Interfacial reactions between thin films of Zn and GaAs were studied by means of transmission electron microscopy. Low-temperature interaction is governed by the penetration of Zn into the native oxide layer at the metal/GaAs interface. At 360°C the formation of Zn_{3}As_{2} phase, highly oriented with respect to the (100) substrate takes place.
Interfacial reactions between GaSb and Au were studied by Rutherford backscattering, X-ray diffraction, and cross-sectional transmission electron microscopy. Evaluation of the extent to which the GaSb substrate decomposes was of primary concern. The results give evidence that the reaction takes place even at temperatures as low as 180°C. High reactivity of gold towards GaSb revealed by this study demonstrates that Au-based metallization is not a good candidate for device quality ohmic contacts to GaSb-based devices.
Very thin Au(Zn) contacts to p-GaAs were studied by means of transmission electron microscopy and secondary ion mass spectrometry. It was found that such contacts when cap annealed became ohmic, even though the reaction between the metallization and GaAs is confined to a very close vicinity of the interface.
The effects of interaction between thin films of Zn and (100)InP were studied with secondary ion mass spectrometry, X-ray diffraction and transmission electron microscopy. Zn was found to penetrate the native oxide on InP surface during deposition and to form an ohmic contact when deposited on highly doped n-type InP. Heat treatment causes the formation of Zn_{3}P_{2} phase lattice matched to InP.
The analysis of phosphorus release from Au/InP contacts heat treated at temperature from the range 360-480°C showed that P evaporation accompanies any stage of contact reaction. The use of encapsulating layer during contact annealing suppresses the loss of phosphorus and changes the kinetics of thermally activated interfacial reaction.
The relationship between electrical properties and microstructure of pure Zn and AuZn contacts to p-GaAs has been studied. The obtained results prove that mechanism responsible for the ohmic behaviour of these contacts is associated with the lowering of the potential barrier at metal/semiconductor interface, resulting from the phase transformations in the metallization.
Ni/Si-based contact schemes based on the solid-phase regrowth process have been developed to form low-resistance ohmic contacts to GaN with a minimum contact resistivity of 1×10^{-3} Ωcm^{2} and ≈1×10^{-2} Ωcm^{2} to GaN:Si (n ≈ 2×10^{17} cm^{-3}) and GaN:Mg (p ≈ 3×10^{17} cm^{-3}). The solid-phase regrowth process responsible for the ohmic contact formation was studied using X-ray diffraction, secondary ion mass spectrometry and Rutherford backscattering spectrometry.
The microstructure of Ni/Si-based contacts to GaN has been studied using transmission electron microscopy methods. The transition from non-ohmic to ohmic behavior appears to correlate with the initial limited reaction of GaN with Ni and further Si-Ni reaction-driven decomposition of the interfacial GaN-Ni phase.
Thanks to its outstanding electronic properties, like very high mobility of carriers, graphene has emerged in recent years as exciting candidate for use in new electronic devices. When it is patterned in the form of ribbons with widths in the range of nanometers, its transport properties become strongly influenced by the presence of the states localized at the edges of the ribbon. Using first principles calculations we study the properties of these states for both isolated ribbons and in the presence of metallic electrodes. The calculations were performed for end contacted geometry i.e. for graphene sheets at right angle to the electrodes. Both para- and ferromagnetic electrodes were considered.
A qualitative discussion of the simple interface barrier defect-type model (Bardeen-like) trying to explain the metal-polymer-vacuum interface formation in the high static electric field (field emission microscopy) is presented.
A study is made of surface preparation, metallization, patterning and dielectric deposition with the aim of developing process technology for GaSb-based photonic devices.
Autocorrelation functions for rough (random, quasiperiodical and deterministicperiodical) surfaces are deduced from the surface profiles determined by using the line-by-line analysis of atomic force microscopy images. It is shown that the initial parts of autocorrelation functions have a Gaussian form. An attempt to use the concept of fractal as a bridge between deterministic periodic and random (spontaneous) surfaces including quasiperiodic ones have been made.
In this work we studied the influence of an external electric voltage on spatial dimensions of CdZnTe mixed crystals. In order to get an absolute magnitude of the sample thickness and to gain insight to the changes of lateral dimension, in quasi-bulk 3 μm thick CdZnTe layers grown by molecular beam epitaxy square craters were formed by ion sputtering in a secondary ion mass spectrometer. The vertical and lateral dimensions of the craters were studied by the atomic force microscopy. The atomic force microscopy measurement revealed that the thickness of the CdZnTe layer increases in a result of applying a single voltage pulse to the sample surface and decreases reversibly after applying reversely biased voltage. The voltage triggering was high enough to switch the conductivity state of the sample i.e., the effect of thickness change is accompanied by the effect of conductivity switching. The thickness change is significant, reaching several percents of the entire layer thickness.
The optical properties (infrared reflectance) and the photoemission current for the surface-barrier structures of metal-semiconductor type with microrelief interface have been investigated. The participation of surface plasmon polaritons in internal photoemission of the Au-GaAs Schottky barriers has been observed.
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