Pronounced Photovoltaic Effect in Electrically Tunable Lateral Black‐Phosphorus Heterojunction Diode

Abstract

complicated split-gates structure and suffer from nonabrupt junction interface due to the divergence of static electric field, limiting their practical applications. 2D lateral homojunctions can be achieved by selective chemical doping as well, as in few-layer MoS 2 [7] and BP cases. [17,18] In addition to homojunctions, heterojunctions have recently been under intense study to extend further the frontiers of 2D materials for electronic and optoelectronics. Particularly, by vertically stacking together flakes of different 2D materials, the so-called van der Waals heterojunction is formed which gathered extensive attention by offering a vast number of candidate structures for high-performance optoelectronic applications. [3,8,11,15,19,20] Nevertheless, the construction of this structure usually requires a dry/wet transfer technique that complicates the fabrication process. [21] Besides, it also tends to suffer from contaminants and bubbles introduced during the transfer, resulting in unwanted defects at the interface. [11] In contrast to vertical heterojunctions, lateral heterojunctions composed of p-and n-type TMDCs semiconductors are also explored where disparate materials can be grown along the edges of the previously grown flakes in the epitaxy process. [22][23][24] Yet, this strategy is severely challenged by the control of large-area uniform growth and the high yield of clean junction interface. As well known, an inherent nature of 2D materials is their thickness-(or layer-number-) dependent bandgaps. [25] Such dependence implies energy bands discontinuities at the interface of different-layer-number films, forming spontaneously a lateral heterojunction distinct from the conventional ones. [26][27][28][29] The study on this kind of structure is likely to expand the realms of 2D materials diverse applications but few works have been done. [26,28,29] Recently, few-layer black phosphorus has been rediscovered as a novel promising 2D semiconductor for nextgeneration nanoelectronic and optoelectronic devices due to its direct bandgap, ambipolar conduction, anisotropic nature, and a high field-effect hole mobility. [30][31][32][33] Especially, BP has a largely adjustable direct thickness-dependent bandgap ranging from 2.0 eV for monolayer to 0.3 eV for its bulk form, [34] which bridges the bandgap space between gapless graphene and large gap TMDCs by covering the mid-infrared to near-infrared wavelengths, leading to new electronic and optoelectronic devices. [33] In this work, we experimentally demonstrate a gate-tunable all-BP lateral heterojunction diode with thickness-induced bandgap difference for high-performance photovoltaic application, Recently, both lateral and vertical p-n junctions have been realized in 2D materials using various strategies, with a number of works on exploring the potential of lateral heterojunctions resulting from thickness-modulated bandgaps at the interface. Here, electrically tunable all-black-phosphorus (BP) lateral heterojunction diodes, without the need of split-gating or sele...

2D Homojunctions for Electronics and Optoelectronics

“…The layer-engineered homojunctions may exhibit type-I or type-II band alignment [64][65][66][67][68] and thus demonstrate characteristics similar to the p-n junction, such as rectification behavior and photovoltaic effect. [46,69,70]…”

“…Meanwhile, reduced contact resistance and improved carrier mobility were also achieved in metallic 1T-MoS 2 /semiconducting 2H-MoS 2 [43] and metallic 1T′-MoTe 2 /semiconducting 2H-MoTe 2 . [44,45] Moreover, the thickness-modulated BP [46] and MoSe 2 [47] homojunctions were found to exhibit pronounced diode-like photovoltaic effects. These outstanding performances of 2D homojunctions are considered to attribute to the synergism of homogeneous components and fascinating properties at the interface, making them of great value in designing novel functional devices.Currently, the 2D homojunctions have become a state-of-the-art research topic for the development of electronic and optoelectronic devices (Figure 1).…”

2D Photovoltaic Devices: Progress and Prospects

“…Theoretical analysis has revealed that both type‐I and type‐II band alignments can possibly be formed at the BP monolayer–bilayer interfaces, depending on their orientation, hydrogen passivation, and also the width of the heterostructures, which is promising for diverse application purposes . Very recently, Wang et al experimentally demonstrated a gate‐tunable all‐BP lateral heterojunction diode for high‐performance photovoltaic application ( Figure ) . Thickness‐modulation gives rise to a bandgap difference and energy‐band misalignment between BP flakes, which eliminates the need of split‐gate structure or selective chemical doping or a transfer process.…”

“…d) Corresponding generated electrical power versus V d for different incident laser powers. Reproduced with permission . Copyright 2017, Wiley‐VCH.…”

Recent Advances in Black Phosphorus‐Based Electronic Devices

“…Table 1 shows the various field‐effect transistors with different metal contacts that have been reported in the literature. As can be seen in the table, the p‐type characteristic is prevalent with high work function metals such as nickel (Ni), palladium (Pd), and platinum (Pt); while low work function metals such as titanium (Ti), aluminium (Al), or scandium (Sc) resulted in n‐type behavior. Besides the work function of the metal contact, the thickness of the BP channel also plays a key role in deciding the final polarity of the transistor as the bandgap of BP is thickness dependent.…”