Papers by Keyword: Contact Resistivity

Abstract: To ensure maximum device current is supplied through a vertical device having a backside ohmic contact, the specific contact resistivity, ρ_c, must be well characterized as it constitutes a portion of the device resistance. While there are multiple approaches to deduce ρ_c, the transmission line model (TLM) remains a convenient choice because of its simplicity in terms of fabrication, measurement, and analysis. For thick substrates where mesa isolation is impractical, the circular transmission line model (CTLM) is an attractive path. In this study we propose an additional restriction on the CTLM design such that the ρ_c is readily extracted from a simple linear regression just as is the case in a linear TLM. We demonstrate the simplified method by extracting ρ_c of an ohmic contact to the c-face of 4H-SiC substrate.

Abstract: We present results of epitaxial characterization and benchmarking of Silicon Carbide (SiC) epitaxial layers grown on both 6-inch commercially available SiC substrate and on SOITEC’s new generation SmartSiC^TM substrate. Multi wafer reactor was utilized to avoid run-to-run variation. Schottky Barrier Diodes (SBD) and electrical test vehicles were fabricated to extract ideality factor, barrier height and ohmic contact resistance for benchmarking.

Abstract: The microstructures of Co–GaSb junctions in samples annealed at 300, 400, 500, and 600°C in a N₂ atmosphere were characterized using transmission electron microscopy (TEM) in combination with energy-dispersive spectrometry (EDS), nanobeam electron diffraction (NBD), and the selected area diffraction patterns (SADPs). The isolated CoSb₃(Ga) phase started to form at the interface of Co/GaSb in the temperature of 400°C and then the CoSb₃(Ga) phase changed to a continues layer at the interface when the annealing temperature was increased to 500°C. Upon increasing the temperature to 600°C, a large amount of Ga from GaSb diffused out toward Co to form a CoGa layer. The specific contact resistivity of Co/GaSb contact was evaluated by circular transmission line model (CTLM) and indicated that the lowest value was 5.410^-4 Ω-cm at annealing temperature of 500°C and possessed high current density of 41.7 A/cm² at 1V. These results indicate that the annealing temperature of the Co/GaSb structure could be maintained below 500°C for the successful formation of low-resistance metal Co/GaSb contacts in GaSb-based p-type metal-oxide-semiconductor field-effect transistors.

Abstract: The electrical contact properties of silicon carbide (SiC) and carbon nanotubes (CNTs) were measured by conductive atomic force microscopy (C-AFM). A CNT forest was synthesized by SiC surface decomposition. Trenches, which electrically separate the conduction area, were fabricated using a focused ion beam (FIB) without a cover layer, and the resistance of each island was measured by C-AFM. From the dependence of the resistance on the CNT forest island size, the contact resistance between the CNTs and the SiC substrate was measured. By varying the dopant density in the SiC substrate, the Schottky barrier height was evaluated to be ~0.5 eV. This is slightly higher than a previously reported result obtained from a similar setup with a metal covering the CNT forest. We assumed that the damaged region existed in the islands, which is due to the trench formation by the FIB. The commensurate barrier height was obtained with the length of the damaged region assumed to be ~3 μm. Here, we could estimate the resistivity of a CNT/SiC interface without a cover layer. This indicates that a CNT forest on SiC is useful as a brief contact electrode.

Abstract: The samples of Ag/ITO multilayer films with different Ag insert layer thickness (0.5, 2, 4 nm) were prepared on sapphire and p-GaN substrates. The effects of the Ag layer thickness, annealing temperature and annealing time on the transmittance, sheet resistance and specific contact resistance of Ag/ITO films were investigated. The experiment results show that the transmittance is obviously affected by Ag insert layer thickness. The Current–voltage (I–V) measurements indicate that the sheet resistance and specific contact resistance of Ag/ITO film on p-GaN are lower than those of single ITO film. The samples with Ag(0.5nm)/ITO film on p-GaN produce the low specific contact resistance of ~1.386×10-4Ω•cm2 , low sheet resistance of ~11Ω/sq and high transmittance of ~ 90% at 455nm when the samples are annealed at 600°C for 10 minutes.

Abstract: Al-Free Nanolayered Metallizations Based on the Transition Metals Ti, Mo, Ni and Pd, with Varied Ti Content, Have Been Developed as an Alternative of the Al-Based Contacts for Sub-Micron Hemts. the Electrical, Morphological and Thermal Properties of the Metallization Schemes Have Been Studied with the Aim of Obtaining the Most Suitable Combination of Low Resistivity, a Smooth Surface and an Acute Edge. the Lowest Resistivity of 8.8x 10-6 Ω.cm2 Has Been Determined with the Ti/Mo/Ti/Au Contact, while the Lowest Surface Roughness of 6 Nm Has Been Measured for the Ti/Ni/Ti/Au Metallization. these Contact Schemes Have Shown much Better Edge Acuity in Comparison to the Al-Based Metallizations.

Abstract: The dependence of the structure and composition of nanolayered Au/Ti/Al ohmic contacts to p-type 4H-SiC on the initial Ti:Al ratio has been investigated. Two contact compositions, Au/Ti(70%)/Al(30%) and Au/Ti(30%)/Al(70%), have been studied regarding the electrical properties, structure, composition and annealing temperature in the interval 850 – 1000o C. The correlation between the electrical behaviour and structure of the annealed contacts is discussed. Very low resistivity of 1.42x10-5 .cm2 after annealing at 900o C has been obtained for the contact having an initial composition Ti:Al (30:70), while the lowest resistivity of 1.21x10-5 .cm2 has been measured for the contact with a composition Ti:Al (70:30) after annealing at 1000o C. Strong dependence of the contact structure on the Ti:Al ratio and annealing temperature, respectively, has been found out. A presence of two phases, Au2Ti and Al3Ti, in all contacts has been determined after annealing, despite the temperature value and Ti:Al ratio. The TEM analysis reveals that titanium and aluminum silicides and carbides are formed after annealing as the Ti:Al ratio affects the kind of silicides and carbides created. It is obtained that the initial composition of the deposited metal layers influences only the phase composition of the annealed contact but not the grain sizes of the dominant phases formed. The origin of the ohmic properties improvement is explained by the formation of Ti3SiC2 compound and/or enhanced carrier transport by the presence of metal spikes into SiC depending on the initial contact composition and as consequence the optimal annealing temperature.

Abstract: Three types of nanolayered Pd-based metal/p-4H SiC systems, Au/Pd, Au/Pd/Al and Au/Pd/Ti/Pd have been investigated and compared to Pd monolayered metallization regarding the electrical and thermal properties. The lowest contact resistivity of 2.8x10-5 .cm2 has been achieved with the Au/Pd/Ti/Pd contact. This contact exhibits excellent thermal stability during long-term heating at temperature of 700oC and at operating temperatures up to 450oC. The surface morphology investigation has shown that despite the observed decrease, the palladium agglomeration has been not avoided completely in the same contact. The dominated surface roughness was measured to be 75 nm. However, the formation of dendrites in certain places leads to increase the surface roughness to 125 nm. The structural analysis revealed that palladium silicides are formed at the interface metal/p-4H SiC which affects on decrease of the barrier height in more than two times and conversion of the contact from Schottky into ohmic.

Abstract: Electrical, morphological and chemical properties of nanolayered Au/Ti/Al ohmic contacts with different Ti:Al ratio are investigated. Contact resistivities of 1.42×10-5 ⋅cm2 and 1.21×10-5 ⋅cm2 are achieved for Au/Ti(70)/Al(30) and Au/Ti(30)/Al(70) contacts, respectively. It is found that the Ti:Al ratio does not affect the lowest resistivity value but influences on the optimal annealing temperature at which it is obtained. The different optimal annealing temperature provokes different element distributions and interface chemistry of the annealed contacts. An increase of the Al concentration in the contact composition causes essentially the surface morphology leading to an increase in surface roughness of the as-deposited and annealed contacts.

Abstract: Recently Ni/SiC contacts have been studied in order to achieve very low contact resistivity (rc) values on n-type SiC. In this work contact resistivity values of Ni-silicide contacts to n-type ion implanted 6H-SiC are analyzed aiming at extracting the Schottky Barrier Height (SBH). The n-type ion implanted 6H-SiC specimens were annealed at 1300, 1500, 1650°C for 20 min in a high purity Ar ambient. The rc values have been extracted from Transmission Line Method (TLM) measurements in the range of temperatures 25-290°C. The rc values are in the range 1-5×10-5 Wcm2 depending on the annealing temperature. The SBH fBn has been extracted by exploiting the dependence of the contact resistivity on the temperature. By using the field emission model, the value obtained for fBn on our samples is in the range 1.1-1.3 eV depending on the annealing temperature. The SBH on p-type 6H-SiC has been evaluated on Schottky diodes by means of both IV and C-V measurements. A value of qfBp= (1.75±0.05) eV has been obtained on p-type SiC through the C-V method. The average SBH extracted from I-V data collected at room temperature is (1.19±0.03) eV and this value increases as a function of the temperature until (1.50±0.01) eV at 290°C. Differences between values of SBH extracted from I−V and from C−V measurements are explained in terms of inhomogeneous barrier height