The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
D Qiao - One of the best experts on this subject based on the ideXlab platform.
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Microstructure of Ti/Al Ohmic Contacts for n-AlGaN
Applied Physics Letters, 1998Co-Authors: S. S. Ruvimov, J. Washburn, Zuzanna Liliental-weber, D QiaoAbstract:Transmission electron microscopy was employed to evaluate the microstructure of Al/Ti Ohmic Contacts to AlGaN/GaN heterostructure field-effect transistor structures. Contact resistance was found to depend on the structure and composition of the metal and AlGaN layers, and on atomic structure of the interface. A 15–25-nm-thick interfacial AlTi2N layer was observed at the contact-AlGaN interface. Formation of such nitrogen-containing layers appears to be essential for Ohmic behavior on n-type III-nitride materials suggesting a tunneling contact mechanism. Contact resistivity was found to increase with Al fraction in the AlGaN layer.
S. S. Ruvimov - One of the best experts on this subject based on the ideXlab platform.
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Microstructure of Ti/Al Ohmic Contacts for n-AlGaN
Applied Physics Letters, 1998Co-Authors: S. S. Ruvimov, J. Washburn, Zuzanna Liliental-weber, D QiaoAbstract:Transmission electron microscopy was employed to evaluate the microstructure of Al/Ti Ohmic Contacts to AlGaN/GaN heterostructure field-effect transistor structures. Contact resistance was found to depend on the structure and composition of the metal and AlGaN layers, and on atomic structure of the interface. A 15–25-nm-thick interfacial AlTi2N layer was observed at the contact-AlGaN interface. Formation of such nitrogen-containing layers appears to be essential for Ohmic behavior on n-type III-nitride materials suggesting a tunneling contact mechanism. Contact resistivity was found to increase with Al fraction in the AlGaN layer.
Hongjie Dai - One of the best experts on this subject based on the ideXlab platform.
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ballistic transport in metallic nanotubes with reliable pd Ohmic Contacts
Nano Letters, 2003Co-Authors: David G J Mann, Ali Javey, Jing Kong, Qian Wang, Hongjie DaiAbstract:Contacting metallic single-walled carbon nanotubes by palladium (Pd) affords highly reproducible Ohmic Contacts and allows for the detailed elucidation of ballistic transport in metallic nanotubes. The Pd Ohmic Contacts are more reliable than the titanium (Ti) previously used for ballistic nanotube devices. In contrast, Pt Contacts appear to give nonOhmic Contacts to metallic nanotubes. For both Ohmic and nonOhmic Contacts, the length of the nanotube under the metal contact area is electrically turned off. Transport occurs from metal to nanotube at the edges of the Contacts. Measurements with large numbers of Pd-contacted nanotube samples reveal that the mean free path for defect scattering in SWNTs grown by chemical vapor deposition can be up to 4 Im. The mean free paths for acoustic phonon scattering are on the order of 500 nm at room temperature and .4 Im at low temperatures. Ohmic Contacts with minimum contact resistance are important to the fundamental characterization and realization of high-performance devices of electronic materials. Ohmic Contacts to individual metallic single-walled carbon nanotubes (m-SWNTs) by Cr and Ti have enabled the observation
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ballistic transport in metallic nanotubes with reliable pd Ohmic Contacts
arXiv: Condensed Matter, 2003Co-Authors: David G J Mann, Ali Javey, Jing Kong, Qian Wang, Hongjie DaiAbstract:Contacting metallic single-walled carbon nanotubes by palladium (Pd) affords highly reproducible Ohmic Contacts and allows for detailed elucidation of ballistic transport in metallic nanotubes. The Pd Ohmic Contacts are more reliable than titanium (Ti) previously used for ballistic nanotube devices. In contrast, Pt Contacts appear to give non-Ohmic Contacts to metallic nanotubes. For both Ohmic and non-Ohmic Contacts, the length of the nanotube under the metal contact area is electrically turned off. Transport occurs from metal to nanotube at the edges of the Contacts. Measurements with large numbers of Pd contacted nanotube samples reveal that the mean free path for defect scattering in SWNTs grown by chemical vapor deposition can be up to 4 microns. The mean free paths for acoustic phonon scattering are on the order of 500 nm at room temperature and >> 4 microns at low temperatures.
Paul H. Holloway - One of the best experts on this subject based on the ideXlab platform.
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Ohmic Contacts to ZnSe-Based Materials
Critical Reviews in Solid State and Materials Sciences, 1996Co-Authors: John F. Fijol, Paul H. HollowayAbstract:Abstract The formation of Ohmic Contacts to n- and p-type ZnSe is reviewed. The mechanisms for forming reasonable low-resistance Ohmic Contacts to n-ZnSe are well understood. This results from the fact that the Fermi energy level of ZnSe is unpinned and metals with sufficiently large work functions can make contact to n-type material. However, the situation is reversed for p-ZnSe where a large band gap and large electron affinity make it impossible to find metals with sufficiently large work functions to create an Ohmic contact. Instead, the use of HgSe to form low barrier height Schottky Contacts and of ZnSe/ZnTe multiple quantum wells (MQWs) to form Ohmic Contacts is reviewed. Although the MQWs can be used to form Ohmic Contacts to p-ZnSe, they degrade at high temperatures and high current densities. This is reviewed and shown to be a serious problem for applications to laser diodes.
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Ohmic Contacts to n-type GaN
Journal of Electronic Materials, 1996Co-Authors: Stephen A. Miller, Paul H. HollowayAbstract:Ohmic Contacts to n-GaN using Ag, Au, TiN, Au/Ti, Au/Mo/Ti, and Au/Si/Ti have been studied. The Fermi level of GaN appears to be unpinned, and metals and compounds with work functions less than the electron affinity resulted in Ohmic Contacts. Reactively sputter deposited TiN was Ohmic as deposited. However, Au/Ti, Au/Mo/Ti, and Au/Si/Ti required heat treatments to form Ohmic Contacts, with the best being an RTA at 900°C. Ag and Au were shown to diffuse across the GaN surface at T>500°C; therefore, they are unstable, poor Ohmic contact metallizations as single metals. The other contact schemes were thermally stable up to 500°C for times of 30 min.
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Indium Ohmic Contacts to n-ZnSe,
Vacuum, 1992Co-Authors: Y. X. Wang, Paul H. HollowayAbstract:The reaction between an indium over layer and high purity MBE grown n-ZnSe chlorine doped (2x 10(18) cm-3) epilayers has been investigated using X-ray diffraction, Rutherford backscattering spectroscopy, X-ray photoelectron and Auger electron spectroscopy, and by electrical function tests (I-V and C-V). Good Ohmic Contacts were formed after annealing at 250 or 300-degrees-C for a few minutes in forming gas. Annealing at lower or higher temperatures resulted in higher resistance or rectifying Contacts. The data show that no compounds were formed at the interface; instead In appeared to diffuse into the ZnSe. High surface doping densities appear to allow an Ohmic contact, but the electrical data suggest that compensation effects are also very significant in the formation of the contact. These effects must be considered for successful formation of the Ohmic contact.
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Mechanism of forming Ohmic Contacts to GaAs
Applied Physics Letters, 1991Co-Authors: Paul H. Holloway, Liu Lu‐min Yeh, David H. Powell, Alan Peter BrownAbstract:The distribution of Si dopant at the Au/GaAs interface after heat treatment has been studied using spatially resolved secondary‐ion mass spectrometry. Previously it has been shown that heat treatment changes as deposited Au thin film from Schottky Contacts to Ohmic Contacts. The present study shows that the transition to an Ohmic contact results from segregation of dopants in areas where GaAs is decomposed by reacting with the Au overlayer. Thus the Ohmic contact is spatially very inhomogeneous at the metal/semiconductor interface. The mechanism leading to concentrations of the Si and nonuniform Ohmic Contacts is discussed, and segregation to the solid during decomposition of the GaAs is the most likely mechanism.
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Indium Ohmic Contacts to n-ZnSe
AIP Conference Proceedings, 1991Co-Authors: Y. X. Wang, Paul H. HollowayAbstract:The reaction between an indium overlayer and high purity MBE grown n‐ZnSe chlorine doped (2×1018 cm−3) epilayers has been investigated using X‐ray diffraction, Rutherford backscattering spectroscopy, X‐ray photoelectron and Auger electron spectroscopy, and by electrical function tests (I‐V and C‐V). Good Ohmic Contacts were formed after annealing at 250 °C or 300 °C for a few minutes in forming gas. Annealing at lower or higher temperatures resulted in higher resistance or rectifying Contacts. The data show that no compounds were formed at the interface; instead In appeared to diffuse into the ZnSe. High surface doping densities appear to allow an Ohmic contact, but the electrical data suggest that compensation effects are also very significant in formation of the contact. These effects must be considered for successful formation of the Ohmic contact.
Suzanne E. Mohney - One of the best experts on this subject based on the ideXlab platform.
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Ohmic Contacts for Technology for Frequency Agile Digitally Synthesized Transmitters
2007Co-Authors: Suzanne E. MohneyAbstract:Abstract : Ohmic Contacts to InAs and InGaAs have been investigated with the objective of providing low contact resistance, good thermal stability, and process compatibility for scaling lnP-based heterojunction bipolar transistors to smaller sizes. For p-type InAs, the combination of modest contact resistance and good thermal stability at 250 0 C was achieved with metallizations that had thin Pd layers deposited first, fol lowed by W or Ti/Pt barrier layers, then Au. For n-type InAs, however, Pd as a first metal layer provided a higher resistance than conventional Ti/Pt/Au Contacts. Ohmic Contacts to p-type InGaAs were also investigated. An electron-beam evaporated Pd/Ru/Au contact devel. oped at Penn State provided the minimum resistance of all Contacts tested as well as good thermal stability at 250 0 C, as demonstrated using contact resistances and cross-sectional transmission electron microscopy. However, Pt/Ti/Pt/Au Contacts provided better thermal stability at 350 0 C. Due to the possibility of electrochemically preparing Pd/Ru/Au Contacts, they were selected for further study, and electroless depo sition of successive Pd, Ru and Au layers on InGaAs was investigated.
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Ohmic Contacts to plasma etched n-Al0.58Ga0.42N
Applied Physics Letters, 2006Co-Authors: M. A. Miller, Suzanne E. Mohney, A. Nikiforov, G. S. Cargill, K. H. A. BogartAbstract:Plasma etching is required to expose n-AlxGa1−xN layers for bottom-emitting ultraviolet light emitting diodes grown on sapphire. However, etching can increase the difficulty of forming Ohmic Contacts. X-ray photoelectron spectroscopy and cathodoluminescence reveal how the semiconductor changes with etching and help explain why it becomes more difficult to form an Ohmic contact. A V∕Al∕V∕Au metallization has been investigated for Ohmic Contacts to n-Al0.58Ga0.42N etched with a BCl3∕Cl2∕Ar chemistry. Increased V thickness and higher annealing temperatures were required to obtain a specific contact resistance of 4.7×10−4Ωcm2 for etched n-Al0.58Ga0.42N compared to optimized Contacts on unetched films.
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Composite Ohmic Contacts to SiC
Materials Science Forum, 2006Co-Authors: A.v. Adedeji, Suzanne E. Mohney, Ayayi C. Ahyi, John R. Williams, Michael J. Bozack, B. Liu, James D. ScofieldAbstract:Composite Ohmic Contacts designed for SiC devices operating in air at 350°C have been studied. Ohmic Contacts to n- and p-4H-SiC were protected against inter-diffusion and oxidation by Ta-Si-N layers obtained by sputter deposition from a TaSi2 target in a mixture of Ar and N2. Platinum was sputter-deposited at 250°C to promote adhesion between the Ta-Si- N barrier layer and a thick Au cap layer. Platinum also acts as a barrier to the diffusion of Au. The electrical and mechanical characteristics of the composite Contacts were stable after hundreds of hours of annealing in air at 350°C. We report the effects of thermal aging on the specific contact resistance and the semiconductor sheet resistance, and the results of wire bond pull and shear tests following aging for Ta-Si-N / Pt / Au stacks deposited on both SiO2 dielectric layers and the Ohmic contact layers.
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Shallow Ohmic Contacts to p-type InAs
Electronics Letters, 2003Co-Authors: E. M. Lysczek, Suzanne E. Mohney, T.n. WittbergAbstract:A new Pd/Pt/Au Ohmic contact to p-InAs provides a lower specific contact resistance as deposited (9.6×10−7 Ω cm2) than Ti-based Ohmic Contacts prepared on the same epilayer (2.6×10−6 Ω cm2 or higher). The effect of the metal deposition method and annealing conditions on the resistance of the Contacts is also reported.
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Ohmic Contacts to P-Type SiC
2000Co-Authors: J. Crofton, Suzanne E. MohneyAbstract:Abstract : Alloys of aluminum (Al) have previously been used as Ohmic Contacts to p-type SiC, however the characteristics and performance of these Contacts is drastically affected by the type and composition of the Al alloy. This work examined alloys of Al and titanium (Ti) as a junction of alloy composition with the goal of determining the composition which would yield the best Ohmic contact to p-type SiC as characterized by a low specific contact resistance, a limited reaction between the metal alloy and the SiC, and reproducibility of contact parameters. After examining 4 Al-Ti alloys, it was determined that a 70/30 weight percent alloy composition of Al and Ti produced low resistance, reproducible Ohmic Contacts with minimal reaction to p-type SiC. It is further noted that a liquid phase of the alloy must be present during the anneal that forms the Ohmic contact. Although this work was performed on heavily doped 4H material, previous work done by the authors supports the conclusion that these results will be valid on all polytypes of SiC with a corresponding increase in specific contact resistance as the doping level of the semiconductor decreases.
