Anisotropic Charge Transport in HPHT Diamonds

A photovoltaic method is developed to determine the anisotropy of transport properties of the main charge carriers in HPHT diamonds with an electronic type of conductivity. The results of a comparative analysis of the mobility and lifetime of main charge carriers in the cubic {001} and octahedral {111} growth sectors of diamond samples cut from diamond single crystals grown in the Fe–Ni–C system are given. The mobility of most charge carriers is estimated from the experimentally measured dependence of the resistivity of a diamond sample on the voltage applied to the electrical contacts. When the electric field strength varied in the range from –1 to 1 V μm^–1, the resistivity of samples from the cubic and octahedral diamond growth sectors changed on average within the range of 0.15 × 10¹³–2.5 × 10¹³ and 0.1 × 10¹³–0.8 × 10¹³ Ω cm, respectively. The lifetime of most carriers is assessed by measuring the spectral current sensitivity under irradiation of diamond samples with ultraviolet light at a wavelength of 225 nm. It has been established that the best values of mobility and lifetime are achieved in the cubic crystal growth sector, in which the lifetime and mobility of the majority of charge carriers are greater than those in the octahedral sector by factors of 3.5–4.5 and 1.7–2.5, respectively. Our results demonstrate the suitability of the photovoltaic method for fast and efficient comparative analysis of the transport properties of charge carriers, which can be used in the technology of selecting diamond substrates in the production of devices of diamond based electronics.