Direct Optoelectronic Imaging of 2D Semiconductor–3D Metal Buried Interfaces

Abstract

The semiconductor-metal junction is one of the most critical factors for high performance electronic devices. In two-dimensional (2D) semiconductor devices, minimizing the voltage drop at this junction is particularly challenging and important. Despite numerous studies 2 concerning contact resistance in 2D semiconductors, the exact nature of the buried interface under a three-dimensional (3D) metal remains unclear. Herein, we report the direct measurement of electrical and optical responses of 2D semiconductor-metal buried interfaces using a recently developed metal-assisted transfer technique to expose the buried interface which is then directly investigated using scanning probe techniques. We characterize the spatially varying electronic and optical properties of this buried interface with < 20 nm resolution. To be specific, potential, conductance and photoluminescence at the buried metal/MoS2 interface are correlated as a function of a variety of metal deposition conditions as well as the type of metal contacts. We observe that direct evaporation of Au on MoS2 induces a large strain of ~5% in the MoS2 which, coupled with charge transfer, leads to degenerate doping of the MoS2 underneath the contact. These factors lead to improvement of contact resistance to record values of 138 kΩ µm, as measured using local conductance probes. This approach was adopted to characterize MoS2-In/Au alloy interfaces, demonstrating contact resistance as low as 63 kΩ µm. Our results highlight that the MoS2/Metal interface is sensitive to device fabrication methods, and provides a universal strategy to characterize buried contact interfaces involving 2D semiconductors.

Exciton–Photonics: From Fundamental Science to Applications

“…This has not only allowed comparison of TMDC−metal contacts that are formed via different evaporation/exfoliation schemes but also allowed investigation of different TMDC/metal combinations in determining the lowest resistance contact making schemes. 218 Near-field Raman spectroscopy is also an important spectroscopy mode for studying 2D TMDCs since it provides complementary information as compared to PL, such as nanoscale inhomogeneities in charge doping, stoichiometry, and strain. For instance, TERS measured from polycrystalline MoSe 2 transferred on a Au substrate showed nanoscale variance in A 1 ′ and E′ mode intensity at the basal plane and grain boundaries.…”

Tip-Enhanced Raman Spectroscopy of 2D Semiconductors

“…large tensile strain induced at the interface in this process reduces the bandgap of MoS 2 and thus influences the contact resistance as a consequence [68].…”

Covalent Patterning of 2D MoS2

“…The dramatic variation of surface potential (Figure S5b) can be attributed to significant change of electronic properties caused by the intercalation and chemical functionalization. [35][36][37] The SEM image of the patterned MoS 2 surface (Figure 3a and b) displays clear boundaries between functionalized and pristine MoS 2 regions. Elemental mapping of the patterned MoS 2 surface using EDS shows discernible C and Br signals (Figure 3c), originated from the introduced bromophenyl functional groups.…”

“…The surface potential map (Figure S5a) displays an alternately distributed ribbon pattern, suggesting a clear surface potential variation between the functionalized and pristine MoS 2 regions. The dramatic variation of surface potential (Figure S5b) can be attributed to significant change of electronic properties caused by the intercalation and chemical functionalization [35–37] …”

“…The dramatic variation of surface potential (Figure S5b) can be attributed to significant change of electronic properties caused by the intercalation and chemical functionalization. [ 35 , 36 , 37 ]…”