Applied Science and Convergence Technology 2020; 29(6): 176-179
Published online November 30, 2020
Copyright © The Korean Vacuum Society.
Dae-Kyoung Kim, Seok-Bo Hong, and Mann-Ho Cho*
Department of Physics, Yonsei University, Seoul 03722, Republic of Korea
Correspondence to:E-mail: firstname.lastname@example.org
We investigated the control of the charge carrier density of black phosphorus (BP) 2D nanosheets in a rapid plasma doping process. The electronic structure of plasma boron-doped BP was investigated using X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. The characteristics of a doped BP device were evaluated by fabricating a field-effect transistor under spatially controlled doping in BP nanosheets. The results confirmed the incorporation of ionized boron through the plasma doping process, resulting in the donation of strongly electron dope (electron mobility: ~275 cm2/V·s) on the boron-doped BP switching device. In particular, the fabricated p–n homojunction of the BP device showed an excellent photodetection behavior. This work provides a rapid and stable plasma doping technique for two-dimensional nanosheets employed in next-generation electronic and optoelectronic devices.
Keywords: Black phosphorus, Plasma doping, Homojunction, Optoelectronic device
Two-dimensional (2D) layered materials with a heterojunction have attracted attention in recent years owing to their unique physical properties (high mobility and ultimate flexibility) and promising applications in new-generation electronic and optoelectronic devices [1–3]. Among the many 2D applications, photovoltaic-based 2D layered material devices exhibit both n- or p-type unipolar characteristics in semiconductors composed of the same material (i.e., homojunction). These homojunctions of the 2D materials can be formed stably and can help reduce the number of defect states in the interface region owing to their perfectly ordered microstructure. Thus, many 2D materials along with the modulation of the carrier-type method have been actively researched. However, controlling the carrier type in 2D materials for work function engineering or separated charge conversion remains difficult, and an unstable distribution is sometimes formed. Among 2D materials with unique physical properties, black phosphorus (BP) has shown a band gap ranging from 0.3 eV (for its bulk crystal) to 2.0 eV (for the monolayer) as the thickness is reduced up to the monolayer under direct energy band-gap [4–6]. The notable thickness-modulated energy gap and its characteristics have enabled the application of such materials to optoelectronic devices. Moreover, BP can exhibit a hole-dominated ambipolar carrier for a high hole mobility (~1000 cm2/V•s) at room temperature. However, the deviation in the characteristics of the carrier type has made it difficult to create complementary logic devices on a single BP semiconductor. Thus, controlling the charge carrier density is important to tune the n- or p-type energy level of the BP system and thereby improve the performance of BP-based electronic and optoelectronic devices.
In this work, we evaluated the control of the charge carrier density of 2D BP nanosheets in a rapid plasma boron doping process. The results confirm boron incorporation through the pulsed-plasma doping process, resulting in the donation of surface electron dope on BP. Furthermore, the fabricated p–n homojunction of the BP photovoltaic device showed an excellent photodetection behavior.
Exfoliated BP was prepared using the standard scotch tape method and transferred onto a 300 nm SiO2/Si think film containing Au electrode markers. The height and optical image contrast of the BP nanosheets were confirmed by atomic force microscopy, and metal (Ti/Au) electrodes were patterned by e-beam lithography. After exposing the BP flakes to the plasma doping process, we preserved the samples in a vacuum storage. The plasma-doped samples were investigated under vacuum conditions (X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) measurements). The plasma doping process was performed using BF3 (a dopant gas). As optimal process parameters, the plasma power, accelerating voltage, and working pressure were set to 100 W, 4000 V, and 1×10−2 Torr, respectively. The properties of the chemical bonding states of the plasma-processed BP were investigated using high-resolution XPS with a monochromatic Al
First, we evaluated the changes in the surface chemical bonds on the BP surface with the boron interaction process. Figure 1(a) presents the chemical bonding states of the 1
where the photocurrent
In summary, we investigated the control of the charge carrier density of black phosphorus (BP) 2D nanosheets in a rapid plasma boron doping process. We confirmed boron incorporation following the plasma boron doping process, resulting in the donation of strongly electron dope on BP. In particular, the plasma boron-doped BP p–n homojunction device showed an excellent rectification and photo-detection behavior. This work provides a rapid and stable plasma doping technique for 2D nanosheets employed in next-generation electronic and optoelectronic devices.
This research was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea governm nt (Grant No. 2017R1A5A1014862, SRC program vdWMRC center).