Transport properties of h-BN lateral devices

One of the well-established and significant applications of hexagonal boron nitride (h-BN) is in solid-state neutron detectors, which necessitate the development of quasi-bulk h-BN crystals. To advance the material and device development of h-BN, it is essential to characterize its bulk electrical transport properties. However, this task is challenging due to h-BN's ultrawide bandgap (UWBG) of approximately 6.1 eV, which results in an extremely high electrical resistivity, typically exceeding 1012 Ω⋅cm. On the other hand, the mobility-lifetime (μτ) product, a key figure of merit for determining the overall device performance, is more readily accessible through the characterization of the I-V characteristics under illumination. In this study, we investigate the in-plane μτ products of lateral devices fabricated from freestanding quasi-bulk h-BN wafers synthesized by hydride vapor phase epitaxy. Our results reveal an unexpected decrease in the in-plane μτ product as the device width decreases. Utilizing a simple two-region carrier transport model, where the central region of the device represents the bulk h-BN material free from metal contacts and the two edge regions are influenced by metal contacts, we demonstrate that the μτ product in the edge areas covered by metal contacts decreases by nearly two orders of magnitude compared to the bulk value. We attribute this significant reduction in μτ product to the layered crystalline structure of h-BN, which permits metal atoms to infiltrate into the interlayer spacings. As a result, the measured μτ product is significantly lower than the true bulk value. These findings provide valuable insights into the design and fabrication of high-performance h-BN devices, which typically leverage its exceptional in-plane transport properties.