Interesting trends in direct current electrical conductivity of chemical vapor deposited diamond sheets

Self-supported diamond sheets of the thickness ranging from 15 to 30 mum we re prepared using hot filament chemical vapor deposition technique. The con trolled variation of the deposition parameters resulted in the sheets with varying amount of nondiamond impurities. Routine characterization of the sh eets was carried out using scanning electron microscopy, x-ray diffractomet ry, Raman spectroscopy, Fourier transform infrared spectroscopy, and Positr on annihilation spectroscopy techniques. Detailed measurements of room temp erature electrical conductivity (sigma (300)), current-voltage (I-V) charac teristics, and annealing studies on the sheets deposited with various struc tural disorder have yielded useful information about the electrical conduct ion in this interesting material. sigma (300) and I-V characteristic measur ements were done in sandwiched configuration taking care off the surface ef fects. The diamond sheets deposited at low deposition pressure (P-d< 60 Tor r) contain negligible nondiamond impurities and show sigma (300)congruent t o 10(-6)-10(-7) S.cm(-1). The I-V characteristics in these sheets show spac e charge limited conduction behavior with I proportional toV(n) and n >1, i n high voltage range. In contrast the sheets deposited at higher pressure ( 60 Torr and higher), containing high concentration of nondiamond impurities , show a sharp reduction in the values of sigma (300). Interestingly, the c onduction in these sheets is ohmic with n values nearly equal to unity. Sim ilarly the sheets deposited with nitrogen also show a sharp reduction in si gma (300). Annealing of all types of diamond sheets results in a decrease i n sigma (300) values by several orders of magnitude. In the sheets deposite d at low P-d, the n values increase sharply with annealing. On the other ha nd the values of n in the sheets deposited at higher pressure remain consta nt with annealing. The above results are explained in terms of hydrogen abs traction from the traps and compensation of donor-acceptor pairs. (C) 2001 American Institute of Physics.