Dielectric breakdown has historically been of great interest from theperspectives of fundamental physics and electrical reliability. However, todate, the anisotropy in the dielectric breakdown has not been discussed. Here,we report an anisotropic dielectric breakdown strength (EBD) for h-BN, which isused as an ideal substrate for two-dimensional (2D) material devices. Under awell-controlled relative humidity, EBD values in the directions both normal andparallel to the c axis (EBD+c & EBD//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, EBD+c for h-BN becomes smaller than that for c-BN, while EBD//cfor h-BN drastically increases. Therefore, h-BN can possess a relatively highEBD concentrated only in the direction parallel to the c axis by conceding aweak bonding direction in the highly anisotropic crystal structure. Thisexplains why the EBD//c for h-BN is higher than that for diamond. Moreover, thepresented EBD value obtained from the high quality bulk h-BN crystal can beregarded as the standard for qualifying the crystallinity of h-BN layers grownvia chemical vapor deposition for future electronic applications.
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