Electronic properties of unipolar heterostructures amorphous carbon diamond - amorphous carbon

Planar heterostructures (/spl alpha/C-i-/spl alpha/C have been made by fine focused 100 keV Ga/sup +/ ion beam implantation on polished surfaces of high quality free standing polycrystalline (5 to 20 /spl mu/m grains) CVD diamond films. The structures consist of two irradiated square areas (amorphous carbon regions /spl alpha/C; irradiation dose from 5.2/spl times/10/sup 14/ to 2.6/spl times/10/sup 16/ cm/sup -2/; size from 10/spl times/10 to 30/spl times/30 /spl mu/m/sup 2/) separated by nominally non-irradiated gap (i-region) of a width varying from 1.6 to 30 /spl mu/m. Micro-Raman topography and AFM characterization of the structures reveal full conversion of diamond into amorphous carbon for the doses above 10/sup 15/ cm/sup -2/. The structures with highly irradiated (/spl alpha/C regions and narrow i-regions exhibit almost Ohmic current-voltage characteristics whereas these with wide i-regions and irradiated with moderate doses show exponential I-V curves of a type I-exp(V/sup n/), where n, may vary from 0.2 to 2. The conductivity of structures with a strong nonlinear behavior reveals different activation energies E/sub a/ in low (10/sup 3/ V/cm) and high (10/sup 5/ V/cm) electrical fields: in the former case E/sub a/. varies from 0.04 to 0. 17 eV, whereas in the latter case it is of 0.3 eV. The mechanisms of the conductivity of the structures is believed to be (i) variable range hopping over the electronic states of the growth defects of polycrystalline diamond CVD and the radiation defects created in the /spl alpha/C-i junctions as well as (ii) electron injection into the intrinsic diamond from the /spl alpha/C regions.