V. Venkatesan

Evaluation of ohmic contacts formed by B+ implantation and Ti-Au metallization on diamond

Low‐resistance ohmic contacts have been fabricated on a naturally occurring B‐doped diamond crystal and on polycrystalline diamond films by B ion implantation and subsequent Ti/Au bilayer metallization. A high B concentration was obtained at the surface by ion implantation, a post‐implant anneal, and a subsequent chemical removal of the graphite layer. A bilayer metallization of Ti followed by Au, annealed at 850 °C, yielded specific contact resistance (ρc) values of the order of 10−5 Ω cm2 for chemical vapor deposition grown polycrystalline films and the natural IIb crystal. The ρc values from transmission line model measurements on three different contact configurations, namely, standard rectangular pads, rectangular pads on diamond mesas, and three‐ring circular structures have been compared. These contacts were stable to a measurement temperature of ∼400 °C and no degradation due to temperature cycling was observed. Chemical analysis by x‐ray photoelectron spectroscopy (XPS) in conjunction with Ar+ sp...

Electrical characterization of semiconducting diamond thin films and single crystals

Naturally occurring semiconducting single crystal (type IIb) diamonds and boron doped polycrystalline thin films were characterized by differential capacitance-voltage and Hall effect measurements, as well as secondary ion mass spectroscopy (SIMS). Results for natural diamonds indicated that the average compensation for a type IIb diamond was >17%. Mobilities for the natural crystals varied between 130 and 564 cm2/V·s at room temperature. The uncompensated dopant concentration obtained by C-V measurements (2.8 ± 0.1 × 1016 cm−3) was consistent with the atomic B concentration measured by SIMS performed on similar samples (3.0 ± 1.5 x 1016 cm−3). Measurement of barrier heights for three different metals (platinum, gold, and aluminum) found essentially the same value of 2.3 ± 0.1 eV in each case, indicating that the Fermi level was pinned at the diamond surface. Polycrystalline semiconducting diamond thin films demonstrated a complex carrier concentration behavior as a function of dopant density. This behavior may be understood in terms of a grain boundary model previously developed for polycrystalline silicon, or by considering a combination of compensation and impurity band conduction effects. The highest mobility measured for a polycrystalline sample was 10 cm2/V·s, indicating that electrical transport in the polycrystalline material was significantly degraded relative to the single crystal samples.

Effect of back contact impedance on frequency dependence of capacitance‐voltage measurements on metal/diamond diodes

Differential capacitance‐voltage (C‐V) measurements were performed on Al and Pt rectifying contacts fabricated on natural (type IIb) diamonds. The C‐V data showed frequency dependence, which decreased significantly after reducing the back contact impedance. The frequency dependence seems primarily to be an effect of the contact capacitance, contact resistance, and bulk resistance of diamond. A model which includes these variables has been proposed to explain this frequency dependence using both large and small back contact impedances.

Comparison of the electric properties of single-crystal and polycrystalline diamond by hall effect and capacitance-voltage measurements

Abstract The transport properties of type IIb (naturally B-doped), single-crystal diamond were investigated by differential capacitance-voltage ( C - V ) measurements, Hall effect measurements and resistivity measurements. The results for the Hall effect and resistivity measurements on single-crystal samples were compared with similar measurements on polycrystalline samples grown by microwave-assisted chemical vapor deposition. The C - V and Hall effect measurements on single crystal, type IIb diamond samples showed consistent results. Temperature-dependent resistivity measurements verified an activation energy of 0.36 eV, while room temperature Hall effect measurements on a (100)-oriented, type IIb single crystal indicated that the active carrier concentration was 2.1 × 10 13 cm −3 . This result was consistent with total B concentrations measured by both C - V and secondary ion mass spectroscopy (SIMS). The transport properties for polycrystalline samples were not as good as those for single-crystal samples. At room temperature, the mobilities were 3 and 10 cm 2 V −1 s −1 for two in situ doped polycrystalline thin films, as compared with 325 cm 2 V −1 s −1 for the single-crystal sample. For one in situ doped sample, the activation energy was measured to be 0.05 eV and the room temperature carrier concentration was 1.8 × 10 16 cm −3 , while SIMS indicated that the total atomic B concentration was 5 × 10 18 cm −3 . The relatively low carrier concentrations measured in the polycrystalline samples may be indicative of a high level of compensation (about 65%) or trapping of charge at the grain boundaries, leading to a depletion of carriers in the crystallites.

Deep-level effects on forward characteristics of rectifying contacts on semiconducting diamond

Current-voltage characteristics of P-doped polycrystalline Si, Au, and Pt contacts on naturally occurring semiconducting

Application of ion-assited electron beam metallization to diamond electronics

Abstract The application of the ion-assisted electron beam deposition technique for the fabrication of contacts on diamond has been evaluated by studying the adhesion of metal films as well as by performing electrical measurements on metal/diamond structures. Metal films were deposited on naturally occuring B-doped diamond crystals (type IIb) and on polycrystalline diamond films using an electron beam deposition technique with and without ion assist. A marked improvement in adhesion was observed for the films deposited with ion-assisted deposition compared to those deposited by non-ion-assisted electron beam technique. The metal contacts fabricated on a natural diamond (type IIb) exhibited excellent rectifying characteristics with low reverse leakage current densities. No apparent difference in the reverse leakage current densities could be detected for the contacts deposited by ion-assisted electron beam deposition as compared to the contacts deposited by non-ion-assisted electron beam.

High Temperature Rectifying Contacts on Semiconducting Diamond Using Doped Silicon

High temperature rectifying contacts have been fabricated on naturally occurring lib semiconducting diamond crystals using highly doped Si. Polycrystalline Si deposited by low pressure chemical vapor deposition (LPCVD) and amorphous Si deposited by sputtering were investigated. Following LPCVD deposition, the polycrystalline Si filn was doped with P by solid state diffusion at a temperature of 900°C using a POCI 3 source. Boron doped and As doped Si films were deposited by sputtering from highly doped Si targets. Current-voltage measurements were performed on the fabricated P doped, B doped and As doped Si contacts from room temperature up to ∼400∼C. In all cases, the contacts yielded excellent rectification in the temperature range investigated. Current conduction in doped Si/diamond systems appears to be space charge limited. The position and concentration of deep levels in a natural lib diamond crystal have been determined from an analysis of space charge limited current-voltage (I-V) characteristics.

Formation and Characterization of Ohmic Contacts on Diamond

Low resistance ohmic contacts have been fabricated on a naturally occurring lib diamond crystal and on polycrystalline diamond films by B ion-implantation and subsequent Ti/Au bilayer metallization. A high B concentration was obtained at the surface by ion implantation, a postimplant anneal and a subsequent chemical removal of the graphite layer. A bilayer metallization of Ti followed by Au, annealed at 850°C, yielded specific contact resistance values (as measured using a standard transmission line model (TLM) pattern) of the order of 10 -5 Ω cm 2 for chemical vapor deposition (CVD) grown polycrystalline films and the natural lib crystal. Specific contact resistance values have also been determined from circular TLM measurements on CVD films and the values compared to those from standard TLM measurements. These contacts were stable to a measurement temperature of ∼400°C and no degradation due to temperature cycling was observed.