Anisotropic Dielectric Breakdown Strength of Single Crystal Hexagonal Boron Nitride

Dielectric breakdown has historically been of great interest from the perspectives of fundamental physics and electrical reliability. However, to date, the anisotropy in the dielectric breakdown has not been discussed. Here, we report an anisotropic dielectric breakdown strength (E_BD) for h-BN, which is used as an ideal substrate for two-dimensional (2D) material devices. Under a well-controlled relative humidity, E_BD values in the directions both normal and parallel to the c axis (E_BD⊥c and E_BD∥c) were measured to be 3 and 12 MV/cm, respectively. When the crystal structure is changed from sp³ of cubic-BN (c-BN) to sp² of h-BN, E_BD⊥c for h-BN becomes smaller than that for c-BN, while E_BD∥c for h-BN drastically increases. Therefore, h-BN can possess a relatively high E_BD concentrated only in the direction parallel to the c axis by conceding a weak bonding direction in the highly anisotropic crystal structure. This explains why the E_BD∥c for h-BN is higher than that for diamond. Moreover, the presented E_BD value obtained from the high quality bulk h-BN crystal can be regarded as the standard for qualifying the crystallinity of h-BN layers grown via chemical vapor deposition for future electronic applications.