Ohmic Contacts for Phosphorus-Doped n-Type Diamond

Abstract

Electric contacts for phosphorus (P)-doped n-type diamond films have been studied. The P-doped {111} homoepitaxial diamond thin films with n-type conduction are grown on high temperature high pressure diamond substrates by microwave-enhanced plasma chemical vapor deposition. The donor density and crystallinity of the phosphorus-doped diamond films were varied depending on the growth conditions. Metals with different work function and different reactivity to diamond films were deposited on the P-doped diamond films as electrodes. Ion implantation was also applied for introducing electrically active defects in diamond films. We found that n-type rectification properties with average Schottky barrier height of 2.4 eV were obtained from both Au and Cu contacts deposited on lightly doped diamond films with donor density N D of 5 Â 10 17 cm ±3 . Ohmic properties were obtained from electrodes on heavily doped layer with N D of over 1 Â 10 19 cm ±3 . Electrodes formed on the diamond film with electrically active defects also show Ohmic properties. These features indicate that the behavior of contacts formed on P-doped n-type diamond films is similar to those on typical n-type semiconductors.

Charge-based deep level transient spectroscopy of phosphorous-doped homoepitaxial diamond

“…Despite this, none of the contacts were found to give good rectification properties, even Au, which has been reported by others as yielding Schottky contacts when deposited onto high-quality P-doped diamond substrates. 29,30 In the present case, only a slight asymmetry in the I -V characteristic of sample No. 2, indeed pointing to a higher contact resistivity of the Au-P-doped diamond interface, was observed when the Au-P ϩ contact scheme was used.…”

“…1͒. This S-shaped behavior, which is often observed when common metals are evaporated to P-doped diamond, 29,30 clearly indicates that all the contact types used here ͑apart from the highly doped regions͒ differ significantly from ohmic contacts. Despite this, none of the contacts were found to give good rectification properties, even Au, which has been reported by others as yielding Schottky contacts when deposited onto high-quality P-doped diamond substrates.…”

“…The electronic properties of metal contacts to P-doped homoepitaxial diamond have been studied by Teraji et al 29,30 Their results indicate that ohmic contacts are difficult to form to P-doped diamond using common evaporated metals, except in the case of highly doped and defective samples. Here, it has been found that contacts consisting of highly doped regions lead to linear I -V characteristics at RT and somewhat above ͑see inset of Fig.…”

“…This has been explained either in terms of tunneling, when observed using highly doped films, or by a lower barrier for carrier injection, when observed in the case of lightly doped samples. 30 Some metals, like Au, can even lead to good rectification properties: Schottky contacts have been reported in the case of small area Au and Cu contacts to lightly doped films. 30 These observations strongly suggest that any contact to P-doped homoepitaxial diamond, including the P ϩ contacts, tend to show a certain level of rectification, the amount of leakage current being then responsible for the exact shape of the I -V characteristic.…”

Characterization of phosphorus-doped homoepitaxial (100) diamond films grown using high-power-density MWPCVD method with a conventional quartz-tube chamber

“…The morphology of Pdoped diamond films was studied using an atomic force microscope (AFM, Shimadzu Corp.: model SPM-9600). By using a Hall-effect measurement system (Toyo Corp.: model ResiTest 8300) with a 200 mHz AC magnetic field of 0.53 T, the electrical characterization of the P-doped diamond films was performed by means of van der Pauw method [8] in the temperature region from 313 to 673 K. In order to obtain the ohmic contacts (electrodes) to each P-doped sample, 20 nm thick Ti, 10 nm Pt and 20 nm Au multi-thin layers were evaporated in this sequence through a thin metal mask with four symmetrically located holes (300 mm diameter) using an electron beam (EB) evaporation apparatus with multi-evaporation sources (ULVAC: model UEP-3000) after 30 keVGa + beam irradiations to the four contact areas using a focused ion beam (FIB) apparatus (SII: model JFIB-2300) [9]. Subsequent annealing in vacuum at 700 8C was performed to achieve stable ohmic contacts.…”