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Ohmic Contacts (ohmic + contact)
Selected AbstractsTransparent Ohmic Contacts on p-GaN Using an Indium Tin Oxide OverlayerPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2003Soo Young Kim Abstract We report a low-resistant, thermally stable ohmic contact on p-GaN using a promising contact scheme of Ni/Au/ITO. Ni/Au contact on p-GaN was annealed at 500 °C under an oxidizing atmosphere before ITO deposition, forming a NiO layer acting as a diffusion barrier of In atoms from ITO. Specific contact resistivity as low as 4.8 × 10,4 ,cm2 was obtained from the Ni (20 Å)/Au (30 Å)/ITO (1000 Å) contact annealed at 500 °C under an oxidizing atmosphere. Contact resistivity is decreased due to crystallization of ITO and Au indiffusion through the NiO layer after annealing at 500 °C under an oxidizing ambient. Also, under this condition, the measured optical transmittance of Ni/Au/ITO was above 80% at a wavelength of 470 nm. [source] High Productive Deposited Mo Layers for Back Ohmic Contacts of Solar CellsPLASMA PROCESSES AND POLYMERS, Issue S1 2009Jens-Peter Heinß Abstract In the paper, thin molybdenum (Mo) layers produced by magnetron sputtering [state of the art in production for photovoltaic applications (PV)] are compared with those produced by high-rate electron beam (EB) deposition technology. Stainless steel and borofloat glass served as substrate materials. Mo layers deposited by DC-magnetron sputtering were produced as a reference and investigated by analysis of structure and specific electrical resistance. Alternative layers prepared by high-rate EB-deposition with a rate up to 240,nm·s,1 were characterised by inquests of mechanical properties, sheet resistance and cell efficiency. A strong dependency of specific electrical resistance on residual gas conditions was determined. The specific electrical resistance dropped from 18 to 11,µ,·cm. Compactness of Mo layers increased with implementation of plasma activation. The layer formation became denser and comparable to the magnetron sputtered Mo layers. [source] Interface Atomic-Scale Structure and its Impact on Quantum Electron TransportADVANCED MATERIALS, Issue 48 2009Zhongchang Wang Local structure, chemistry, and bonding at interfaces often radically affect the properties of materials. A combination of scanning transmission electron microscopy and density functional theory calculations reveals an atomic layer of carbon at a SiC/Ti3SiC2 interface in Ohmic contact to p-type SiC (see image), which results in stronger adhesion, a lowered Schottky barrier, and enhanced transport. This is a key factor to understanding the origin of the Ohmic nature. [source] On the mechanism of conductivity enhancement and work function control in PEDOT:PSS film through UV-light treatmentPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2010Abderrafia Moujoud Abstract In this work, we study the effect of UV light on the work function of PEDOT:PSS films. The authors found that UV irradiation lead to an increase in the work function. Several devices with UV exposed and unexposed PEDOT:PSS were fabricated and measured. The current,voltage characteristics have been obtained for ITO/PEDOT:PSS/InZnO samples. We found that UV irradiated devices show better electrical characteristics and lead to Ohmic contact. The trend in device performance was explained by the observed changes in the work function of the PEDOT:PSS layer. The change in the work function was measured by ultraviolet photoelectron spectroscopy. The structural and morphological properties of PEDOT:PSS films with and without UV treatment were investigated by X-ray photoelectron spectroscopy and atomic force microscopy techniques. The change in the work function of PEDOT:PSS is mainly due to the surface conformational change. The stability of devices with and without UV treatment has been investigated under normal environmental conditions. Electrical properties of the devices have been studied over a period of 30 and 60 days. The stability tests show that devices with UV treatment are more stable that those without UV treatment. [source] Selective-area growth and fabrication of recessed-gate GaN MESFET using plasma-assisted molecular beam epitaxyPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2006Seung Jae Hong Abstract For the first time, selective-area growth (SAG) technique has been developed using plasma-assisted molecular beam epitaxy (PAMBE), enabling fabrication of a recessed-gate structure for the metal-semiconductor field-effect transistor (MESFET) without etching. On patterned SiO2 samples, polycrystalline GaN and single crystal n+ -GaN were observed to grow in the masked and unmasked regions, respectively. The regrown layers were analyzed using AFM. Ohmic contact formed on the n+ -GaN exhibited a vastly improved contact resistivity of 1.8 × 10,8 , cm2, giving rise to excellent device characteristics including a peak drain current of 360 mA/mm and a maximum transconductance of 46 mS/mm. The advantages of SAG were further investigated by comparing the dc characteristics of recessed-gate and unrecessed MESFET. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Oxidation treatment on Ni/Au Ohmic contacts to p-type GaNPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003Z. Z. Chen Abstract Current,voltage (I,V) characteristics, transmission line method (TLM), and optical transmittance measurements are performed to investigate the effects of thermal oxidation and plasma-induced oxidation treatments on Ni/Au contacts to p-type GaN. Whether oxidation and thermal annealing are performed simultaneously or in succession, the specific contact resistances of Au/Ni/p-GaN are reduced. As to plasma-induced oxidation, neither no-oxidation nor long-time oxidation treatments on Ni/Au layers are suitable for obtaining a low-resistance Ohmic contact. The roles of oxidation are believed to activate the Mg acceptor in p-GaN and to form an oxygenous intermediate semiconductor layer, which may lower the Schottky barrier height between the metal layer and p-GaN. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Off-state breakdown in InAlN/AlN/GaN high electron mobility transistorsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009J. Kuzmik Abstract Unpassivated InAlN/AlN/GaN high electron mobility transistors off-state breakdown is analyzed for different gate-to-drain distances. The breakdown voltage linearly increases with the gate to drain distance reaching 350 V for a 10 ,m contact separation; the sub-threshold leakage current is < 10,5 A/mm. Similar breakdown voltages and leakage current are obtained on GaN buffer for two Ohmic contacts if their distance is the same. It is suggested that the breakdown is governed by injection/avalanche processes in the GaN buffer layer and is basically not affected by InAlN barrier. Our conclusions are further supported by measuring all currents in the three-terminal configuration of the transistors before and during the breakdown and by using a drain current injection technique. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Oxidation treatment on Ni/Au Ohmic contacts to p-type GaNPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003Z. Z. Chen Abstract Current,voltage (I,V) characteristics, transmission line method (TLM), and optical transmittance measurements are performed to investigate the effects of thermal oxidation and plasma-induced oxidation treatments on Ni/Au contacts to p-type GaN. Whether oxidation and thermal annealing are performed simultaneously or in succession, the specific contact resistances of Au/Ni/p-GaN are reduced. As to plasma-induced oxidation, neither no-oxidation nor long-time oxidation treatments on Ni/Au layers are suitable for obtaining a low-resistance Ohmic contact. The roles of oxidation are believed to activate the Mg acceptor in p-GaN and to form an oxygenous intermediate semiconductor layer, which may lower the Schottky barrier height between the metal layer and p-GaN. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Schottky-Gated Probe-Free ZnO Nanowire BiosensorADVANCED MATERIALS, Issue 48 2009Ping-Hung Yeh A nanowire-based nanosensor for detecting biologically and chemically charged molecules that is probe-free and highly sensitive is demonstrated. The device relies on the nonsymmetrical Schottky contact under reverse bias (see figure), and is much more sensitive than the device based on the symmetric ohmic contact. This approach serves as a guideline for designing more practical chemical and biochemical sensors. [source] Electrical and microstructural properties of low-resistance Ti/Re/Au ohmic contacts to n-type GaNPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2007V. Rajagopal Reddy Abstract The microstructural and electrical properties of Ti/Re/Au (10 nm/10 nm/50 nm) ohmic contacts to moderately doped n-type GaN (4.0 × 1018 cm,3) have been investigated by current,voltage (I ,V), Auger electron microscopy (AES) and transmission electron microscopy (TEM). The electrical characteristics of as-deposited and annealing at temperatures below 800 °C samples exhibit non-linear behaviour. However, the sample showed ohmic behaviour when the contact is annealed at 900 °C for 1 min in nitrogen ambient. The Ti/Re/Au contacts give specific contact resistance as low as 8.6 × 10,6 , cm2 after annealing at 900 °C. It is shown that the surface of the as-deposited contact is fairly smooth and slightly degraded when the contact is annealed at 900 °C. The Ti/Re/Au ohmic contact showed good edge acuity after annealing at 900 °C for 1 min. Based on the Auger electron microscopy and transmission electron microscopy results, possible ohmic formation mechanisms for the Ti/Re/Au contacts to the n-type GaN are described and discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Mg-doped AlGaN grown on an AlN/sapphire template by metalorganic chemical vapour depositionPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2006Hongbo Yu Abstract The growth of high-performance Mg-doped p-type AlxGa1,xN (x = 0.35) layers using low-pressure metalorganic chemical vapour deposition on an AlN/sapphire template is reported. The influence of growth conditions on the p-type conductivity of the AlxGa1,xN (x = 0.35) alloy was investigated. It was found that the p-type resistivity of the AlGaN alloy demonstrates a marked dependence on the Mg concentration, V/III ratio and group III element flow rate. A minimum p-type resistivity of 3.5 , cm for AlxGa1,xN (x = 0.35) epilayers was achieved. A Ni/Au (10 nm/100 nm) ohmic contact was also fabricated and a specific contact resistivity of 8.1 × 10,2 , cm2 was measured. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optimization of the ohmic contact processing in InAlN//GaN high electron mobility transistors for lower temperature of annealingPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2010Karol Abstract In this article, we optimized the ohmic contact processing in InAlN/GaN high electron mobility transistors for the lower temperature of annealing by recessing of metalliza-tion to approach the 2DEG at the InAlN/GaN interface. The ohmic contacts which were recessed down to 5 nm depth and annealed at 700 °C 2 min. exhibited the contact resistance of 0,39 ,mm while the channel sheet resistance was 210 ,/square. These values are comparative to values of contacts processed at more conventional an-nealing conditions (800 °C, 2 min). Moreover we applied the recessed ohmic contact technology to fabricate Schottky barrier (SB) HEMTs and MOSHEMTs with Al2O3 dielectric film. For MOSHEMTs, we measured the maximal reduction of the gate leakage current by about 6 orders of magnitude if compared with SB HEMTs. The maximal drain current of MOSHEMTs was about 750 mA/mm at VGS = 0 V and the maximal extrinsic transconductance (gme) reached 101 mS/mm. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] On dot and out of dot electrical characteristics of silicon oxide nanodots patterned by scanning probe lithographyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2009Sabar D. Hutagalung Abstract Silicon oxide nanodot arrays were grown on pre-cleaned silicon (100) substrate by scanning probe nanolithography. In this study, a conductive AFM was used to fabricate nanoscale oxide dots in humidity controlled environment. The AFM is equipped with a nanotechnology software package providing the control of tip-sample voltage and tip motion according to pre-designed patterns. The surface topography and size of obtained patterns (diameter and height) were investigated by a noncontact AFM mode. A series of five silicon oxide nanodot array with diameter in the range of 146.05-247.65 nm and height 2.14-4.87 nm had been successfully fabricated. Meanwhile, a contact AFM mode was used to investigate the localized I-V characteristics on the dots and out of dot position. It was found, the on dot characteristics are highly nonohmic due to potential barrier interface between silicon oxide and silicon substrate. However, the out of dot characteristic is linear indicates an ohmic contact between AFM tip and sample. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Transparent Ohmic Contacts on p-GaN Using an Indium Tin Oxide OverlayerPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2003Soo Young Kim Abstract We report a low-resistant, thermally stable ohmic contact on p-GaN using a promising contact scheme of Ni/Au/ITO. Ni/Au contact on p-GaN was annealed at 500 °C under an oxidizing atmosphere before ITO deposition, forming a NiO layer acting as a diffusion barrier of In atoms from ITO. Specific contact resistivity as low as 4.8 × 10,4 ,cm2 was obtained from the Ni (20 Å)/Au (30 Å)/ITO (1000 Å) contact annealed at 500 °C under an oxidizing atmosphere. Contact resistivity is decreased due to crystallization of ITO and Au indiffusion through the NiO layer after annealing at 500 °C under an oxidizing ambient. Also, under this condition, the measured optical transmittance of Ni/Au/ITO was above 80% at a wavelength of 470 nm. [source] Effect of 1,1,-dibenzyl-4,4,-bipyridyl dichloride (DBD) on charge-conduction process and photovoltaic response of a polypyrrole (PPy) thin-film devicePOLYMER INTERNATIONAL, Issue 4 2002S Roy Abstract The present communication deals with analysing the effect of 1,1,-dibenzyl-4,4,-bipyridyl dichloride (DBD) substitution at the N -position of 2,5-polypyrrole (PPy), on electrical, impedance and photovoltaic properties. The thin-film device was fabricated by sandwiching DBD-substituted PPy between indium tin oxide (ITO) and aluminium (Al) electrodes. The formation of a Schottky barrier with Al and ohmic contact with ITO are explained in terms of p-type semiconducting behaviour of DBD-substituted PPy. In the low-voltage region, Ohm's law is followed, while in the high-voltage region, a space-charge-limited conduction (SCLC) controlled by the exponential-trap distribution was observed. DBD substitution causes shifting of the Fermi level towards the valence-band edge and an increase in charge-carrier mobility. A remarkable change in dark electrical conductivity of the order of five has been observed in DBD-substituted PPy. The electrical and impedance measurements of an ITO/PPy:DBD/Al device confirms the formation of a Schottky barrier at the DBD-substituted PPy/Al interface. Additionally, it can be modelled by a simple equivalent circuit of two resistance,capacitance (RC) elements in series representing the bulk and a junction-region. At low frequency, the device capacitance follows a pronounced voltage dependence. From a detailed analysis of the J,V and C,V characteristics, the ionized acceptor concentration (Na), width of depletion layer (W) and potential barrier height (,b) have been evaluated. We observed a significant enhancement in photocurrent on DBD substitution. The increase in photocurrent is explained by the efficient charge separation induced by the intermolecular transfer of photo-excited electrons from PPy to DBD. The substitution also causes a reduction in the trapping centres in the material. © 2002 Society of Chemical Industry [source] Hole Injection in a Model Fluorene,Triarylamine CopolymerADVANCED FUNCTIONAL MATERIALS, Issue 2 2009Hon Hang Fong Abstract Recent developments in synthesis and purification have yielded conjugated polymers with hole mobilities exceeding 0.01,cm2 V,1 s,1. Essential to harvesting the potential of these materials in organic light emitting diodes (OLEDs) is the identification of suitable ohmic contacts. Using a model fluorene copolymer that shows high-mobility, non-dispersive hole transport, it is demonstrated that electrodes commonly used as anodes in OLEDs are very poor hole injectors. Injection from Au and indium tin oxide anodes is limited by energy barriers of 0.75 and 0.65,eV, respectively, and the injected current is found to be temperature independent,a prediction that was not reproduced by the leading injection model for disordered organic semiconductors. Injection from a poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) anode, on the other hand, is found to become less efficient with electric field, a behavior which is currently not understood. In thinner poly[(9,9,-dioctylfluorenyl-2,7-diyl)- co -(4,4,-(N -(4- sec -butyl))diphenylamine)] films, which are of relevance to OLEDs, ohmic losses on the PEDOT:PSS layer are found to limit the flow of current. These results illustrate the opportunity to further improve the performance of OLEDs as well as the challenge posed by high mobility conjugated polymers for the design of hole injection layers. [source] Implementation of the GaN lateral polarity junction in a MESFET utilizing polar doping selectivityPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2010Ramón Collazo Abstract The difference in surface energies between the Ga-polar orientation and the N-polar orientation of GaN translates into a completely different behavior for the incorporation of intentional and unintentional impurities. Oxygen is found to be an impurity with higher concentration in the N-polar films than in Ga-polar films and is the cause of n-type conductivity observed in N-polar films. Utilizing this doping selectivity we fabricated a depletion-mode metal-semiconductor field effect transistor (MESFET) with n-type N-polar domains as source and drain and a Ga-polar channel on polarity-patterned wafers. The difference in the electronic properties of the different domains, i.e., as-grown N-polar domains are n-type conductive and Ga-polar domains are insulating, allows for laterally selective doped areas that can be realized for improving contact resistance to the n-type conduction channel. Basically, the N-polar domains acted as the ohmic contacts to the channel localized in a Ga-polar domain. A MESFET with a Schottky gate was fabricated as an example of implementation of this novel structure showing a lowering in the specific contact resistivity. [source] Electrical and microstructural properties of low-resistance Ti/Re/Au ohmic contacts to n-type GaNPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2007V. Rajagopal Reddy Abstract The microstructural and electrical properties of Ti/Re/Au (10 nm/10 nm/50 nm) ohmic contacts to moderately doped n-type GaN (4.0 × 1018 cm,3) have been investigated by current,voltage (I ,V), Auger electron microscopy (AES) and transmission electron microscopy (TEM). The electrical characteristics of as-deposited and annealing at temperatures below 800 °C samples exhibit non-linear behaviour. However, the sample showed ohmic behaviour when the contact is annealed at 900 °C for 1 min in nitrogen ambient. The Ti/Re/Au contacts give specific contact resistance as low as 8.6 × 10,6 , cm2 after annealing at 900 °C. It is shown that the surface of the as-deposited contact is fairly smooth and slightly degraded when the contact is annealed at 900 °C. The Ti/Re/Au ohmic contact showed good edge acuity after annealing at 900 °C for 1 min. Based on the Auger electron microscopy and transmission electron microscopy results, possible ohmic formation mechanisms for the Ti/Re/Au contacts to the n-type GaN are described and discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Transparent ohmic contacts to GaSb/In(Al)GaAsSb photovoltaic cellsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2007K. Golaszewska Abstract In this paper we present the results of study of thin oxide films: CdO, ZnO and RuSiO4 used as transparent ohmic contacts to GaSb/InGaAsSb/AlGaAsSb photodiodes. Thin oxide films with thickness of 50 nm were deposited by magnetron sputtering. CdO and RuSiO4 were formed in a reactive process in Ar,O2 atmosphere, from Cd and Ru1Si1 targets, respectively. ZnO films were deposited directly from ZnO target by rf sputtering. We have shown that application of CdO, ZnO and RuSiO4 transparent films instead of conventional metal-based contacts enables to improve of photodiode properties. As a result, GaSb/InGaAsSb/AlGaAsSb photodiodes with detectivity D * increased by factor of 2 and reduced by factor of 3 the series resistance were obtained. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Enhancement in electrical properties of GaN heterostructure field-effect transistor by Si atom deposition on AlGaN barrier surfacePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009Norio Onojima Abstract This study demonstrates that deposition of Si atoms on AlGaN barrier surfaces in GaN heterostructure field-effect transistors (HFETs) can modulate the electrical properties of the two-dimensional electron gas (2DEG). The results of Hall measurements performed using the eddy current and four-point van der Pauw methods showed that the sheet resistance of an AlGaN/GaN HFET sample without surface passivation increased from that of the unprocessed sample after post-metallization annealing at 820 °C for ohmic contacts. In contrast, the sheet resistance of the Si-deposited sample did not increase even after annealing. Furthermore, eddy current measurements for unprocessed wafers with and without Si deposition revealed that the sheet resistance can be reduced by depositing Si atoms, regardless of annealing. The effect of Si deposition on devices having a thin Al-rich barrier layer was found to be significant. The deposition of Si atoms (2 nm) on the AlN barrier surface in an AlN/GaN HFET (AlN 2 nm) resulted in a remarkable decrease in the sheet resistance from 60356 to 388 ,/sq. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Formation of ohmic contacts to ultra-thin channel AlN/GaN HEMTsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008Tom Zimmermann Abstract AlN/GaN-based high electron mobility transistors with ultra-thin AlN barriers of 2.3 - 5 nm are attractive candidates for very high speed applications owing to the aggressive scalability such structures afford. We report the first study on formation of ohmic contacts to these high quality ultra-thin channel heterostructures (ns > 1x1013 cm,2 and , > 900 cm2/Vs) with systematically varying barrier thicknesses. While the conventional ohmic contacts to AlGaN/GaN structures generally require high temperature annealing, these ohmic contacts were found to behave ohmic or near ohmic as-deposited. Annealing (400-860 0C) improves the contact resistance to a range of 0.8 - 2 ohm-mm but the annealing conditions strongly depend on the AlN thickness as well as the heterostructure quality (,). All alloyed contacts show smooth morphology, making them suitable for e-beam lithographically defined gate patterning. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||