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Band bending analysis of charge characteristics at GeO <sub/>2</sub> /Ge interface by x-ray photoemission spectroscopy
摘要： Ge complementary metal oxide semiconductor (CMOS) is promising for scaling beyond the Si CMOS due to its higher carrier mobility than Si. Analogue to classical SiO2/Si system in the Si CMOS technology, various interface/bulk charges including interface traps (Qit), fixed surface state charges (Qf), trapped positive charges (Qpt) and negative charges ((Qnt) in GeO2/Ge system are also crucial both for the device performance and reliability. Because small amounts of charges would cause photoemission peak shift characterized by x-ray photoemission spectroscopy (XPS), it offers a feasible way to evaluate various charge densities by measuring the band bending in Ge substrate from Ge 3d core-level energy shift at GeO2/Ge interface. Moreover, photoemission peak shifts as a function of x-ray irradiation time have been widely accepted for characterization of charge trapping phenomena. Here, we report a band bending analysis at GeO2/Ge interface of featuring vital charge characteristics for diverse device applications by XPS. HF-last cleaned Ge surface was verified to tend to be p-type, irrespective of the bulk conductivity. The n-Ge/GeO2 interfaces exhibit a reduction of upward band bending evolution of Ge substrate, while p-type-Ge/GeO2 interfaces indicate a reduction of downward band bending evolution when comparing the different quality GeO2/Ge interfaces. Based on the requirement of surface charge neutrality, such observation has been attributed to a dominated passivation effect to negatively charged interface traps and the positive fixed surface state charges, respectively. Moreover, a time evolution of Ge 3d and O 1s signals reveals a progressive band bending modification at GeO2/Ge interface, clarifying the thermally-grown GeO2 also contains electron traps (Qnt). Ultimately, the four types of charges relying on the GeO2/Ge quality were modeled to correlate with the observed Ge band bending evolution, which would impact both the device operation and reliability.
关键词： band bending,x-ray photoemission spectroscopy,Ge-based electronics,charge characteristics
更新于2025-09-23 15:22:29
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Facet-Dependent Optical Properties of Semiconductor Nanocrystals
摘要： Recent observations of facet-dependent electrical conductivity and photocatalytic activity of various semiconductor crystals are presented. Then, the discovery of facet-dependent surface plasmon resonance absorption of metal–Cu2O core–shell nanocrystals with tunable sizes and shapes is discussed. The Cu2O shells also exhibit a facet-specific optical absorption feature. The facet-dependent electrical conductivity, photocatalytic activity, and optical properties are related phenomena, resulting from the presence of an ultrathin surface layer with different band structures and thus varying degrees of band bending for the {100}, {110}, and {111} faces of Cu2O to absorb light of somewhat different wavelengths. Recently, it is shown that the light absorption and photoluminescence properties of pure Cu2O cubes, octahedra, and rhombic dodecahedra also display size and facet effects because of their tunable band gaps. A modified band diagram of Cu2O can be constructed to incorporate these optical effects. Literature also provides examples of facet-dependent optical behaviors of semiconductor nanostructures, indicating that optical properties of nanoscale semiconductor materials are intrinsically facet-dependent. Some applications of semiconductor optical size and facet effects are considered.
关键词： surface band bending,semiconductors,facet-dependent properties,cuprous oxide,nanocrystals
更新于2025-09-19 17:15:36
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Direct Observation of Conductive Polymer Induced Inversion Layer in n‐Si and Correlation to Solar Cell Performance
摘要： Heterojunctions formed by ultrathin conductive polymer [poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)—PEDOT:PSS] films and n-type crystalline silicon are investigated by photoelectron spectroscopy. Large shifts of Si 2p core levels upon PEDOT:PSS deposition provide evidence that a dopant-free p–n junction, i.e., an inversion layer, is formed within Si. Among the investigated PEDOT:PSS formulations, the largest induced band bending within Si (0.71 eV) is found for PH1000 (high PEDOT content) combined with a wetting agent and the solvent additive dimethyl sulfoxide (DMSO). Without DMSO, the induced band bending is reduced, as is also the case with a PEDOT:PSS formulation with higher PSS content. The interfacial energy level alignment correlates well with the characteristics of PEDOT:PSS/n-Si solar cells, where high polymer conductivity and sufficient Si-passivation are also required to achieve high power conversion efficiency.
关键词： core level shifts,band bending,PEDOT:PSS/Si solar cell,energy level alignment,inversion layer
更新于2025-09-11 14:15:04
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Influence of Work Function of Carrier Transport Materials with Perovskite on Switchable Photovoltaic Phenomena
摘要： The hysteresis effect and switchable photovoltaic phenomena in organo-metal halide perovskite have been observed in perovskite solar cells with certain structures and under certain measure conditions. These phenomena were favorably applied to resistive random-access memory and human-brain-mimicking devices, especially using photons as a reading or stress probe apart from using electrical probe. However, the mechanisms causing these effects are not fully understood. In this paper, the perovskite devices with different hole transporting layers, which have the work functions ranging from 5.9 eV to 3.7 eV, were fabricated and systematically characterized by current-voltage measurements and time-resolved photo-response measurements. These measurements show that the switchable photovoltaic phenomena are highly related to the work function of the hole transporting layer. The interfacial electronic structures of perovskite and several materials were studied in details using X-ray and ultraviolet photoemission spectroscopy (XPS and UPS), suggesting that the switchable photovoltaic is extensively dependent on the strong band bending effect. Light-mediated XPS measurements reveals that the degree of band bending in the perovskite layer was manipulated by charge trapping/de-trapping and hole-carrier accumulation. Based on the electrical measurements and band diagram, we propose a model that combines ion migration and charge trapping/detrapping processes to explain the switchable photovoltaic phenomena.
关键词： work function,band bending,hole transporting layer,perovskite,ion migration,charge trapping,switchable photovoltaic
更新于2025-09-11 14:15:04
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Two-dimensional phosphorene/C3N p-n heterostructure: Effect of contact type on electronic and optical properties
摘要： p-n heterostructure (HTS) is a fundamental component for high-performance electronic and optoelectronic device. Vertical stacking through van der Waals (vdW) force is emerging as a feasible technique to construct p-n HTS. Herein, we designed a novel kind of direct-bandgap C3N monolayer, via adjusting the arrangement of C and N atoms in C3N hexagonal cell. On the basis of the density functional theory combined with the non-equilibrium Green’s function method, we built two-dimensional vdW-contact phosphorene (BP)/C3N p-n HTS, and analyzed its electronic and optical properties in comparison with the inplane-jointed ones. The strong charge transfer between BP and C3N segments results in a wide bandgap of 0.48 eV for joint-contact type BP/C3N HTS, whereas the effective interlayer coupling in vdW-contact type leads to an improved light adsorption as compared to the isolated C3N monolayer. By fabricating dual-gated BP/C3N HTS field-effect transistors (FETs), the dynamic transport behaviors demonstrated that the band bending under a lower threshold voltage makes band-to-band tunneling possible for vdW-contact type. Our work suggests that vdW-contact type is superior to joint-contact type in constructing p-n HTS for high-performance electronic and optoelectronic devices.
关键词： C3N,phosphorene,band bending,band-to-band tunneling,covalent joint,van der Waals
更新于2025-09-10 09:29:36
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Depth-resolved electronic structure measurements by hard X-ray photoemission combined with X-ray total reflection: Direct probing of surface band bending of polar GaN
摘要： We have developed high-throughput depth-resolved electronic structure measurements using hard X-ray photoelectron spectroscopy (HAXPES) combined with X-ray total reflection (TR). By utilizing a steep change of the X-ray attenuation length around the TR condition, we controlled the effective inelastic mean-free-path of photoelectrons from >2 to >12 nm in HAXPES. We applied this method to probe the surface band bending of n-type polar GaN and found the different band bending behaviors in the Ga- and N-polar surfaces. This result is related to the surface contaminations and crystal quality near the surfaces of polar GaN.
关键词： hard X-ray photoelectron spectroscopy,surface band bending,depth-resolved electronic structure,polar GaN,X-ray total reflection
更新于2025-09-04 15:30:14
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Electronic structure of the polymer-cathode interface of an organic electroluminescent device investigated using operando hard x-ray photoelectron spectroscopy
摘要： The electronic structure of a polymer-cathode interface of an operating organic light-emitting diode (OLED) was directly investigated using hard X-ray photoelectron spectroscopy (HAXPES). The potential distribution pro?le of the light-emitting copolymer layer as a function of the depth under the Al/Ba cathode layer in the OLED depended on the bias voltage. We found that band bending occurred in the copolymer of 9,9-dioctyl?uorene (50%) and N-(4-(2-butyl)-phenyl)diphenylamine (F8-PFB) layer near the cathode at 0 V bias, while a linear potential distribution formed in the F8-PFB when a bias voltage was applied to the OLED. Direct observation of the built-in potential and that band bending formed in the F8-PFB layer in the operating OLED suggested that charges moved in the F8-PFB layer before electron injection from the cathode.
关键词： polymer-cathode interface,band bending,organic light-emitting diode,electronic structure,hard X-ray photoelectron spectroscopy
更新于2025-09-04 15:30:14