A perspective on the doping of transition metal dichalcogenides for ultra-scaled transistors: Challenges and opportunities

Abstract

To support the ever-growing demand for faster, energy-efficient computation, more aggressive scaling of the transistor is required. Two-dimensional (2D) transition metal dichalcogenides (TMDs), with their ultra-thin body, excellent electrostatic gate control, and absence of surface dangling bonds, allow for extreme scaling of the channel region without compromising the mobility. New device geometries, such as stacked nanosheets with multiple parallel channels for carrier flow, can facilitate higher drive currents to enable ultra-fast switches, and TMDs are an ideal candidate for that type of next generation front-end-of-line field effect transistor (FET). TMDs are also promising for monolithic 3D (M3D) integrated back-end-of-line FETs due to their ability to be grown at low temperature and with less regard to lattice matching through van der Waals (vdW) epitaxy. To achieve TMD FETs with superior performance, two important challenges must be addressed: (1) complementary n- and p-type FETs with small and reliable threshold voltages are required for the reduction of dynamic and static power consumption per logic operation, and (2) contact resistance must be reduced significantly. We present here the underlying strengths and weaknesses of the wide variety of methods under investigation to provide scalable, stable, and controllable doping. It is our Perspective that of all the available doping methods, substitutional doping offers the ultimate solution for TMD-based transistors.

Hybrid Integrated Silicon Photonics Based on Nanomaterials

“…The integration of TMDs in integrated photonic platforms has been investigated in order to develop photonic circuitry exploiting the aforementioned promising features of this material class [119], enabling the development of essential photonic devices such as Mach-Zehnder interferometers [120]. Additionally, the possibility to tune the effective refractive index of TMDs by means of bandgap engineering [116] or by exploiting electrostatic doping via ionic liquid gating [121,122] enabled the realization of photonic modulators [123,124]. For instance, Joshi et al [125] have realized electro-optical modulators with different TMDs integrated in silicon nitride waveguides, investigating their performance in terms of modulation strength and finding that in their device geometry WS 2 resulted in the strongest modulation (19.88%), followed by WSe 2 (9.48%), MoS 2 (3.72%) and MoSe 2 (2.95%).…”

Engineered Two-Dimensional Transition Metal Dichalcogenides for Energy Conversion and Storage

“…Moreover, high contact resistance (R C ) stands out as a major bottleneck in TMD-based nano-electronics. 84 Doping, has been extensively used as a primary technique to alter semiconductor transport and for decades has been the pillar of modern electronic technologies by enabling the modulation between p-and n-type by the addition of boron and phosphorus to Si. The above-mentioned challenges for TMDs can be addressed by using various doping methods, including electrostatic doping, 85 conventional substitutional doping, 86 intercalation, and surface charge-transfer doping 87 .…”

“…Due to weak screening and the band gap increase with decreasing layer number in 2D materials, dopant energy levels in monolayer TMDs are typically deep levels, leading to high ionization energies and low thermal activation rates of dopants. 84 For instance, even relatively shallow-level dopants in monolayer TMDs have ionization energies ranging between 100 and 200 meV, 91 resulting in a minimal conductivity increase at room temperature under normal doping concentrations. To offset this high ionization energy of dopants, high impurity densities, sometimes approaching the alloying limits (>5%), may be necessary.…”

“…However, a significant challenge in optimizing TMD performance at device levels is the current difficulty in precisely controlling carrier concentration, electrical conductivity, and threshold voltages. Moreover, high contact resistance ( R C ) stands out as a major bottleneck in TMD-based nanoelectronics . Doping, has been extensively used as a primary technique to alter semiconductor transport and for decades has been the pillar of modern electronic technologies by enabling the modulation between p - and n -type by the addition of boron and phosphorus to Si.…”

Ferroelectric Polarization‐Mediated Modulation of Optical Properties in 2D van der Waals Architectures

“…[3,4] Typically, it is necessary to perform controlled doping and defect modulation on TMDs, manage the type and concentration of carriers, and ultimately realize material functionalization and device integration. [7][8][9][10] While advancements have been made in exploring doping methodologies for TMDs, the currently employed approaches present multiple challenges. These include achieving stable, long-term doping under ambient conditions, producing high-resolution graphical representations of doped structures, and implementing reversible doping processes.…”