Conductivity Measurements on Cubic Boron Nitride Kareem Hamdy and Athith Krishna School of Electrical and Computer Engineering, Cornell University May 8, 2015 I. Introduction Studies show that the synthetically formed cubic boron nitride (c-BN) is the 2nd hardest material af- ter natural diamond[1]. Since its first documented synthesis in 1957[2], this material has been of inter- est to researchers and industrialists alike for its novel electrical, mechanical, thermal and optical proper- ties. Because of its wide band gap and good thermal conductivity, c-BN has the potential to be used in high temperature and high power electronics with the added advantage of being dopable by both p- and n- type substances. In this experiment, we characterize and determine the resistivity of n-doped c-BN parti- cles.We also use two-probe measurements to find the double breakdown voltage of the c-BN particles. II. Theory Cubic boron nitride has a zincblende crystal struc- ture with a tetrahedral symmetry. In the work by Wang et al., it is stated that silicon doping of c- BN under certain conditions could tremendously re- duce the resistivity of the material[4]. Keeping in mind that this silicon doping happens by diffusion[5], one main question that arises would be the extent to which silicon is diffused in the c-BN particles. The reference to literature led us to a value from the fol- low up by the authors of the original experiment be- ing replicated; they suggested a value of about 10 μm as the depth that silicon diffuses.[4] The breakdown voltage of a solid insulator can be defined as the minimum voltage at which the insula- tor no longer insulates but instead shows conductive properties. For our measurements we make use of the method of “double breakdown voltage where we ap- ply both negative and positive voltage values across the material, thus making sure, to some extent, that the values that we obtain for the breakdown voltage is indeed the one at which the insulating property of the material fails. Here, we consider the particle as a double Schot- tky diode. We apply a voltage across it and measure the electrical breakdown of the particle as (pictured in Figure 2). For a diode, the breakdown voltage can Figure 1: A cartoon of the zincblende crystal structure of c-BN[3]. Figure 2: An equivalent circuit for the cBN IV testing system. The probe contact points effectively function as Schottky diodes. be defined as the maximum reverse bias that can be applied to that diode without causing an exponen- tial increase in current across it. Here, since we are making a double breakdown measurement, we can measure the breakdown voltage as both maximum forward and reverse bias that can be applied without causing an exponential increase in current across the diode. III. Experimental Procedure For this experiment we obtained amber c-BN single crystals (pictured in Figure 3) of average size of about 0.5 × 0.5 × 0.2 mm 3 . We followed the procedure of a similar experiment carried out by Wang et al.[6]. This experiment had 3 main steps: cleaning, annealing, collection. 1