Electrical and Optical Properties of a Semiconducting Diamond

The electrical resistivity and Hall coefficient of a semiconducting diamond (Type IIb) have been measured between - 100°C and 600°C using standard d.c. methods. The diamond behaves like a normal p-type semiconductor. At 20°C its resistivity is 270 ohm cm and the Hall mobility of the holes is 1550±150 cm2 volt-1 sec-1. Near this temperature the mobility varies approximately as T-3/2. The activation energy of the acceptors is 0.38 eV. It is suggested that these acceptors are impurity atoms and that the total concentration of impurities is smaller in Type IIb diamonds than in other diamonds. The infra-red absorption spectrum of this diamond is typical of Type II diamonds but it shows an additional prominent peak at 3.57 μ, smaller peaks at 4.1 μ, 3.4 μ and 2.5 μ, and a continuum of absorption in the range 1 to 2.5 μ. This extra absorption is reversibly temperature dependent. The intensity decreases with increasing temperature and the peaks are undetectable above 300°C. At - 155°C, photocurrents of the order of 10-9 amp have been detected in the wavelength range 0.9 μ to 3.6 μ. A tentative model is proposed to relate this photoconductivity and the major absorption peak to the mechanism of conduction.