Impact ionization and transport properties of hexagonal boron nitride in a constant-voltage measurement
Impact ionization and transport properties of hexagonal boron nitride in a constant-voltage measurement
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DOI：
10.1103/physrevb.97.045425
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发表时间：
2018-01-24
影响因子：
3.7
通讯作者：
Nagashio, Kosuke
中科院分区：
文献类型：
--
作者：
Hattori, Yoshiaki;Taniguchi, Takashi;Nagashio, Kosuke
尽管六方氮化硼（h - BN）作为二维范德华异质结构器件的衬底非常重要，但其结晶度的电学评估仍局限于介电击穿强度的测量。在这项研究中，利用恒压应力测试研究了剥离的单晶h - BN薄膜的退化和失效的物理现象。在低电场下，电流随时间逐渐减小并趋于饱和，而在高于约8MV/cm的电场下电流增大，并最终导致灾难性的介电击穿。这些瞬态行为可能是由于载流子被h - BN中的缺陷位点捕获，因为被捕获的载流子根据其极性降低或增强h - BN中的电场。关键发现是在高电场下电流随时间增强，这表明碰撞电离过程产生的电子的积累。因此，建立了一个包含碰撞电离过程中电子产生率的理论模型。实验数据支持了h - BN预期的退化机制。此外，成功提取了碰撞电离系数，其与SiO₂的相当，尽管h - BN的本征带隙比SiO₂的小。因此，h - BN中主要的碰撞电离可能是带间激发，而非缺陷辅助的碰撞电离。
The electrical evaluation of the crystallinity of hexagonal boron nitride (h-BN) is still limited to the measurement of dielectric breakdown strength, in spite of its importance as the substrate for two-dimensional van der Waals heterostructure devices. In this study, physical phenomena for degradation and failure in exfoliated single-crystal h-BN films were investigated using the constant-voltage stress test. At low electrical fields, the current gradually reduced and saturated with time, while the current increased at electrical fields higher than similar to 8MV/cm and finally resulted in the catastrophic dielectric breakdown. These transient behaviors may be due to carrier trapping to the defect sites in h-BN because trapped carriers lower or enhance the electrical fields in h-BN depending on their polarities. The key finding is the current enhancement with time at the high electrical field, suggesting the accumulation of electrons generated by the impact ionization process. Therefore, a theoretical model including the electron generation rate by an impact ionization process was developed. The experimental data support the expected degradation mechanism of h-BN. Moreover, the impact ionization coefficient was successfully extracted, which is comparable to that of SiO2, even though the fundamental band gap for h-BN is smaller than that for SiO2. Therefore, the dominant impact ionization in h-BN could be band-to-band excitation, not defect-assisted impact ionization.