Ohmic contact diamond

While we have not yet carried out detailed kinetic measurements on the rate of photocorrosion, our impression is that the process is relatively insensitive to the specific composition of the strontium titanate. Trace element compositions, obtained by spark-source mass spectrometry, are presented in Table I for the four boules of n-SrTi03 from which electrodes have been cut. Photocorrosion has been observed in samples from all four boules. In all cases, the electrodes were cut to a thickness of 1-2 mm using a diamond saw, reduced under H2 at 800-1000 C for up to 16 hours, polished with a diamond paste cloth, and etched with either hot concentrated nitric acid or hot aqua regia. Ohmic contacts were then made with gallium-indium eutectic alloy, and a wire was attached using electrically conductive silver epoxy prior to mounting the electrode on a Pyrex support tube with either epoxy cement or heat-shrinkable Teflon tubing. 

Fig. 5. Complex-plane plot of impedance spectrum for a polycrystalline diamond film between two ohmic contacts. Frequency/kHz shown on the figure. Solid circles data obtained with ac bridge. Open circles data obtained with phase-sensitive analyzer. Top equivalent circuit [30].

Fig. 6. Top frequency dependence of the polycrystalline film active resistivity. Bottom model of the non-homogeneous film between two ohmic contacts (1) diamond crystallites (2) intercrystallite boundaries [30].

The diamond-deposited tungsten wire was then inserted into a pre pulled glass capillary (( )= 50-100 pm) and was sealed using epoxy. The ohmic contact to the diamond fiber was made using a copper wire with either mercury or silver paste. In the case of the microdisk electrode [22], the diamond fiber was preliminarily fully sealed by the use of epoxy, and the tip was then polished until the diamond was just exposed, while for the microfiber electrode [23], a 300-pm length of fiber was left exposed. 

Figure 2. Plots of the measured dc current density filled squares, steady state current density open circles, the current density computed from drift mobility measurements and Eq. 1 filled diamonds, the current density computed from the transient dark injection peak values. The contact under test is a carbon filled polymer coated with a transport layer (TPD/polycarbonate) that is known to support trap free hole transport. The insert shows a typical dark injection transient compared to a small signal TOF transient. Conformity of key features of the steady state and transient data with the theory of trap free space charge limited currents provides a self consistent demonstration of contact ohmicity.

Figure 6 Dependence of the contact resistance of Ti/Mo/Au ohmic metal on diamond on doping concentration. (From Ref. 42.)...

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