Current Injection into Single-Crystalline h-BN Towards 2D Power Device Application

Hexagonal boron nitride (<i>h</i>-BN) is a promising material for the next-generation power device application owing to its various intriguing properties, including high breakdown field, high thermal conductivity, and high chemical-thermal stability. Moreover, its 2D structure makes the <i>h</i>-BN power device compatible with the intensively investigated 2D-electronic systems, and also offers the possibilities for miniaturization of modern electronic devices. Nevertheless, to date, only the studies on electrical properties of defective polycrystalline <i>h</i>-BN have been reported, while the studies on those properties of the high-quality single-crystalline <i>h</i>-BN and its applications as an active material in electronic devices are lacking. This implies that the actual performance of <i>h</i>-BN devices has not yet been demonstrated nor evaluated. To do so, it is necessary to overcome the major challenge, namely the current injection into the high-quality single-crystalline <i>h</i>-BN.<br/>Here, we report the first demonstration of current injection into the high-quality single-crystalline carbon-doped <i>h</i>-BN prepared under high pressure and high temperature (HPHT). The <i>h</i>-BN flake doped with carbon of 1.5x10¹⁹ cm^-3 was mechanically exfoliated from the bulk single crystal and transferred onto a quartz substrate. Thermal treatment and plasma application were employed to selectively introduce defects during the contact formation. The electrical measurements were conducted in vacuum at the temperature varied from 10 K to 623 K. The temperature-dependent current-voltage (<i>I</i>-<i>V</i>) characteristics reveal the non-linear relation over the whole range of the applied voltage and the measured temperature. At room temperature, the current starts to be observed at the applied filed of around 5x10^-3 V/nm, which is much smaller than the field required for the dielectric breakdown of <i>h</i>-BN (~0.31 V/nm) under the same measurement condition. These results confirm that the observed current is not due to the dielectric breakdown of <i>h</i>-BN. In addition, based on the temperature dependence of <i>I</i>-<i>V</i> characteristics, the activation energies (<i>E</i>_A) for carrier transport are extracted from the Arrhenius plot. Particularly at high temperature, <i>E</i>_A are highly dependent on the applied voltage. Therefore, Poole-Frenkel (PF) model is employed to identify the PF effect in these devices. The results at high temperatures and high fields show a straight line in the PF plot, indicating a good agreement with the PF model. Hence, PF emission is proposed to be the dominant mechanism for the current injection at the metal/<i>h</i>-BN contact. Besides, by combining the PF barrier reduction with <i>E</i>_A, PF emission gives the average energy of dominant trap state to be ~ 0.24 eV, which is consistent within the fabricated devices.<br/>This work has demonstrated the current injection into the HPHT <i>h</i>-BN, the widely-known electrical insulator, indicating that it can be electronically treated as a semiconductor. These findings will make a significant step closer to the realization of not only the <i>h</i>-BN power device, but also other electronic/optoelectronic devices based on the high-quality single-crystalline <i>h-</i>BN as an active material.