Abstract
Monolayer (ML) hexagonal boron nitride (hBN) is an important material in making, e.g., deep ultraviolet optoelectronic and power devices and van der Waals heterojunctions in combination with other two-dimensional (2D) electronic systems such as graphene and ML MoS. In this work, we present a comparative study of the basic optoelectronic properties of low resistance ML hBN placed on different substrates such as SiO/Si, quartz, PET, and sapphire. The measurement is carried out by using terahertz (THz) time-domain spectroscopy (TDS) in a temperature regime from 80 to 280 K. We find that the real and imaginary parts of the optical conductivity obtained experimentally for low resistance ML hBN on different substrates can fit well to the Drude–Smith formula. Thus, we are able to determine optically the key sample and material parameters (e.g., the electronic relaxation time or mobility, the carrier density, the electronic localization factor, etc.) of ML hBN. The effect of temperature on these parameters is also examined and analyzed. The results obtained from this study enable us to suggest the appropriate substrate for ML hBN based electronic and optoelectronic devices. This work is relevant to the application to a newly developed 2D electronic system as advanced electronic and optoelectronic materials.
Highlights
Hexagonal boron nitride has emerged as a realm of great interest for advanced electronic and optoelectronic devices, because of its distinguishable characteristics such as high chemical and thermal stability, mechanical strength, low dielectric constant, and near-zero polarization [1]. hBN has a very wide band gap, which makes it important for ultraviolet (UV) and neutron detectors, transparent membranes, UV LEDs, dielectric layers, etc. [2]
Due to the presence of the N-vacancies, we found that the ML hBN films on the above-mentioned substrates were p-type, similar to ML hBN samples grown through the chemical vapor deposition (CVD) technique by other groups [5,29] and that the ML hBN films on these substrates had relatively low electric resistance
The optical conductivity of ML hBN can be attained by using the Tinkham relation [31]: Esam pl e+substr ate (ω ) Esam pl e (ω )
Summary
Hexagonal boron nitride (hBN) has emerged as a realm of great interest for advanced electronic and optoelectronic devices, because of its distinguishable characteristics such as high chemical and thermal stability, mechanical strength, low dielectric constant, and near-zero polarization [1]. hBN has a very wide band gap, which makes it important for ultraviolet (UV) and neutron detectors, transparent membranes, UV LEDs, dielectric layers, etc. [2]. It is found that the presence of the dielectric substrate can induce the van der Waals force and the exchange interaction in the heterostructure [21] It is of great importance and significance to examine the effect of the substrate on the key sample and material parameters of ML hBN, and this becomes the prime motivation of the present study. We measured the key sample and material parameters such as electronic relaxation time, carrier density and electronic localization factor in ML MoS2 placed on different commonly used substrates [23] and in La0.33Pr0.34Ca0.33MnO3 thin films [24] by using THz TDS measurements Using this technique, we have examined the Faraday rotation effect and obtained the effective electron masses in biand tri-layer graphene in the presence of a magnetic field [25]. We generalize the THz TDS technique we used previously to the investigation of the optoelectronic properties of ML hBN
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