Operando x-ray photoelectron emission microscopy for studying forward and reverse biased silicon p-n junctions

Abstract

Significant progress in the understanding of surfaces and interfaces of materials for new technologies requires operando studies, i.e., measurement of chemical, electronic, and magnetic properties under external stimulus (such as mechanical strain, optical illumination, or electric fields) applied in situ in order to approach real operating conditions. Electron microscopy attracts much interest, thanks to its ability to determine semiconductor doping at various scales in devices. Spectroscopic photoelectron emission microscopy (PEEM) is particularly powerful since it combines high spatial and energy resolution, allowing a comprehensive analysis of local work function, chemistry, and electronic structure using secondary, core level, and valence band electrons, respectively. Here we present the first operando spectroscopic PEEM study of a planar Si p-n junction under forward and reverse bias. The method can be used to characterize a vast range of materials at near device scales such as resistive oxides, conducting bridge memories and domain wall arrays in ferroelectrics photovoltaic devices.

Electronic Structure Tunability of Diamonds by Surface Functionalization

“…The range of surface science techniques used here allowed us to visualize step-by-step changes in the electronic and morphologic structure of the samples, and thus measure the intermediate stages of termination from hydrogen to oxygen termination. We proved the tunability of the sample electronic properties by establishing the relation between oxygen coverage and electronic properties of diamonds, taking a fundamental step forward from previous literature works. − Our findings are also a stepping stone for future EF-PEEM in-operando studies where semiconductors are investigated as functions of time, position, and applied electric field. − The possibility to tune the electronic properties of diamonds by modifying the surface functionalization is also a proof-of-concept demonstration applicable to other wide-bandgap materials. − …”

Experimental Determination of the Ionization Energies of MoSe2, WS2, and MoS2 on SiO2 Using Photoemission Electron Microscopy

“…Fitting the leading (lower relative electron kinetic energy side) and trailing (higher relative electron kinetic energy side) edges of the photoemission spectra yields variations of the vacuum level ( E vac ) and the highest occupied states near Γ-point (near the BZ center because of the low photon energy used for the measurements) . The energies of the fitted edges are indicated in Figure by red dots for E vac and by blue dots for the highest occupied states.…”

“…The emergence of metallic edge states and the associated edge band bending are observed for the MoS 2 flakes using scanning tunneling microscopy. , The reported band bending induced by metallic edge states appears at a length scale of a few nanometers, suggesting a different physical origin from the ones we observed in MoSe 2 and WS 2 flakes. We can also exclude the possible influence of stray built-in fields affecting the PEEM images, which would skew the trajectory of photoemitted electrons because the band bending was absent at the edges of MoS 2 flakes. In the end, we surmise that the electrical transport of air-exposed TMDs could be significantly influenced by conductance through the edges and the overall aging.…”

“…The relative intensity of the bare SiO 2 maximizes at 260−280 nm (hν = 4.43−4.77 eV, data not shown) consistent with previous reports on the low photon energy photoemission of glassy SiO 2 and quartz implanted with metals ions. 28,29 Fitting the leading (lower relative electron kinetic energy side) and trailing (higher relative electron kinetic energy side) edges of the photoemission spectra yields variations of the vacuum level (E vac ) 30 and the highest occupied states near Γpoint (near the BZ center because of the low photon energy used for the measurements). 31 The energies of the fitted edges are indicated in Figure 2 by red dots for E vac and by blue dots for the highest occupied states.…”

Time-Resolved Operando Spectroscopic Measurements for Organic Field-Effect Transistors

“…However, since the semiconductors actually operate via microscopic processes of carrier injection, carrier transport, and carrier relaxation, device evaluation from a microscopic viewpoint should be employed in parallel with the electrical signal evaluation. As examples of such evaluation, spectroscopic measurements combined with semiconductor operation have recently been reported and they are often called operando measurements. − The main point of the measurement is to perform in situ spectroscopy during semiconductor operation under real operating conditions and attempt to draw information from working semiconductors . Such measurements were actually applied to organic FETs (OFETs), , where X-ray photoemission spectroscopy or X-ray diffraction spectroscopy was combined with OFET operation.…”