Gate-tunable carbon nanotube–MoS ₂ heterojunction p-n diode

Abstract

The p-n junction diode and field-effect transistor are the two most ubiquitous building blocks of modern electronics and optoelectronics. In recent years, the emergence of reduced dimensionality materials has suggested that these components can be scaled down to atomic thicknesses. Although high-performance fieldeffect devices have been achieved from monolayered materials and their heterostructures, a p-n heterojunction diode derived from ultrathin materials is notably absent and constrains the fabrication of complex electronic and optoelectronic circuits. Here we demonstrate a gate-tunable p-n heterojunction diode using semiconducting single-walled carbon nanotubes (SWCNTs) and single-layer molybdenum disulfide as p-type and n-type semiconductors, respectively. The vertical stacking of these two direct band gap semiconductors forms a heterojunction with electrical characteristics that can be tuned with an applied gate bias to achieve a wide range of charge transport behavior ranging from insulating to rectifying with forward-to-reverse bias current ratios exceeding 10 4 . This heterojunction diode also responds strongly to optical irradiation with an external quantum efficiency of 25% and fast photoresponse <15 μs. Because SWCNTs have a diverse range of electrical properties as a function of chirality and an increasing number of atomically thin 2D nanomaterials are being isolated, the gate-tunable p-n heterojunction concept presented here should be widely generalizable to realize diverse ultrathin, highperformance electronics and optoelectronics.2D transition metal dichalcogenide | single layer MoS 2 | van der Waals heterostructure | rectifier | photodetector

Self-Aligned van der Waals Heterojunction Diodes and Transistors

“…1 In contrast, while two-dimensional (2D) materials have shown significant potential for digital and analog electronics due to their high mobilities, ultrathin geometry, and broad range of permutations in van der Waals heterojunctions (vdWHs), [2][3][4][5][6][7][8][9] 2D material devices have not yet exploited parallel self-aligned fabrication to achieve both short channels and large area fabrication. Thus far, short-channel 2D material transistors and vdWHs have been achieved using serial processing methods such as electron-beam lithography or mechanical placement on nanotube or nanowire gates.…”

“…With previously reported fabrication methods, p-n vdWHs, whether lateral or vertical, consisted of a p-n heterojunction connected by two lateral p-type and n-type extensions (acting as FETs in series) or Schottky diodes with graphene, with the overall stack being coupled to one or two gates with alignment errors increasing with each component. [7][8][9][26][27][28][29][30][31] In the lateral geometry, p-n vdWHs offer electrostatically controlled doping in the constituent semiconductors but suffer from large parasitic resistance from the lateral extensions beyond the junction region. [7][8][9][28][29][30] On the other hand, vertical p-n vdWHs that employ a graphene electrode can achieve larger current density at the cost of defect-induced leakage currents, extraneous Schottky barriers, and electrode screening issues.…”

“…[7][8][9][26][27][28][29][30][31] In the lateral geometry, p-n vdWHs offer electrostatically controlled doping in the constituent semiconductors but suffer from large parasitic resistance from the lateral extensions beyond the junction region. [7][8][9][28][29][30] On the other hand, vertical p-n vdWHs that employ a graphene electrode can achieve larger current density at the cost of defect-induced leakage currents, extraneous Schottky barriers, and electrode screening issues. 27,30,31 For example, fully 8 vertical BP-MoS2 and WSe2-MoS2 p-n vdWHs using graphene contacts show poor electrostatic control of ID-VTG characteristics (Supporting Fig.…”

“…3g) as uniquely enabled by the self-aligned, semivertical architecture. [7][8][9] Finite-element simulations elucidate how this unique vdWH geometry improves current rectification and enables tunable anti-ambipolar behavior (Fig. 4).…”

Seeded growth of highly crystalline molybdenum disulphide monolayers at controlled locations

“…T he presence of an intrinsic direct energy bandgap in molybdenum disulphide (MoS 2 ) monolayers makes this two-dimensional material of both fundamental and technological interest [1][2][3][4][5][6][7][8][9][10] . Several synthetic methods have been reported, including sulphiding of Mo thin film 11 , and annealing of ammonium tetrathiomolybdate, which has both Mo and S components 12 .…”