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We present a straightforward approach to develop a high-detectivity silicon (Si) sub-bandgap near-infrared (NIR) photodetector (PD) based on textured Si/Au nanoparticle (NP) Schottky junctions coated with graphene film. This is a photovoltaic-type PD that operates at 0 V bias. The texturing of Si is to trap light for NIR absorption enhancement, and Schottky junctions facilitate sub-bandgap NIR absorption and internal photoemission. Both Au NPs and the texturing of Si were made in self-organized processes. Graphene offers additional pathways for hot electron transport and to increase photocurrent. Under 1319 nm illumination at room temperature, a responsivity of 3.9 mA/W and detectivity of 7.2 × 1010 cm × (Hz)1/2/W were obtained. Additionally, at −60 °C, the detectivity increased to 1.5 × 1011 cm × (Hz)1/2/W, with the dark current density reduced and responsivity unchanged. The result of this work demonstrates a facile method to create high-performance Si sub-bandgap NIR PDs for promising applications at ambient temperatures. [ABSTRACT FROM AUTHOR]

Metal-semiconductor-metal (MSM) architectures are popular for achieving high-responsivity Ga2O3 solar-blind photodetectors (SBPDs), however, the hot-electron-induced internal photoemission (IPE) effect restricts their detecting performance. Herein, we demonstrate the rational design of an Al/Al2O3/Ga2O3 metal–insulator-semiconductor (MIS) SBPD that has merits of enhanced responsivity, suppressed sub-gap response and ultralow dark current based on the simulation results obtained using Lumerical software. For the cylindrical patterned detectors with Al/Al2O3/Ga2O3 MIS structures, the optimized dimensions of Al electrodes with a conformed ultra-thin (2 nm) Al2O3 layer support the surface plasmon polariton resonances at 250 nm, thus improving the photoresponsivity to 74 mA W−1. Furthermore, the sandwiched Al2O3 layer lifts the barrier for hot electrons in electrodes, which significantly suppresses the IPE-induced sub-gap photoresponse by more than 105 in magnitude with respect to the Al/Ga2O3 MSM counterpart. Optical and electrical field distributions are overlapped in cylindrically patterned MIS detectors, simultaneously improving the excitation and collection efficiencies of excess carriers and resulting in the 103-boosted rejection ratio. [ABSTRACT FROM AUTHOR]

Silicon sub-bandgap near-infrared (NIR) (λ > 1100 nm) photovoltaic (PV) response by plasmon-enhanced internal photoemission was investigated. The Si sub-bandgap NIR PV response, which remains unexploited in Schottky junction-like solar cell device, was examined using nanometer sized Au/Al2O3/n-Si junction arrays. This kind of metal–insulator–semiconductor structure was similar in functionality to Schottky junction in NIR absorption, photo-induced charge separation and collection. It showed that NIR absorption increased steadily with increasing volume of Au nanoparticles (NPs) till a saturation was reached. Simulation results indicated the formation of localized surface plasmon on the surfaces of Au NPs, which was correlated well with the observed NIR absorption. On the other hand, the NIR PV response was found sensitive to the amount and size of Au NPs and thickness of Al2O3. Chemical and field-effect passivation of n-Si by using Al2O3 and SiO2 were used to optimize the NIR PV response. In the current configuration, the best PV conversion efficiency was 0.034% at λ = 1319 nm under illumination power of 0.1 W/cm2. [ABSTRACT FROM AUTHOR]

Internal photoemission-based hot electron generation at metal-semiconductor junctions holds significant potential for silicon-based sub-bandgap NIR photodetectors. In this work, we designed a simple nickel-silicon Schottky junction using the pulsed laser deposition technique and performed both experimental and theoretical analyses. To reduce the complexity of fabrication and lower costs, we used a planar nickel thin film on top of n-type silicon. The thickness of the nickel thin film was optimized to improve absorption and hot electron generation near the Ni/Si interface. We measured and calculated reflectance using the transfer matrix approach to quantify the effect of thickness on EQE. We also calculated the thickness-dependent absorption profile to estimate hot electron production near the junction. The current-voltage characterization of Ni/n-Si Schottky photodetector was investigated under the dark conditions as well under 1200 nm and 1300 nm light illumination. Under self-bias conditions, a photodiode with a 12 nm Ni thickness exhibits responsivity of 0.124 mA/W and 0.069 mA/W under illumination from 1200 nm and 1300 nm LED light, respectively. Furthermore, we used a comprehensive theoretical model to quantify the planar Ni/Si hot carrier generation and emission efficiency. and experimentally validated the calculated EQEs with the fabricated device. We believe the proposed complementary metal-oxide-semiconductor-compatible and simply structured Ni/Si Schottky photodetector will have potential applications in the silicon-based optoelectronics market. [ABSTRACT FROM AUTHOR]

The reverse-voltage dependence of a photocurrent in a Ni/ β -Ga _2 O _3 Schottky barrier diode was investigated under sub-bandgap monochromatic illumination with wavelengths ranging from 275 to 1200 nm. Under low reverse bias conditions, a photocurrent induced by internal photoemission was observed. However, under high reverse bias conditions, the photocurrent near the absorption edge increased significantly with reverse voltage, and the increase was more pronounced for wavelengths closer to the absorption edge. Numerical calculations based on direct optical absorption induced by the Franz–Keldysh (FK) effect showed excellent agreement with the experimental data.

Barrier height ( $\phi _{b}$ ), trap state, bandgap ( $E_{g}$ ), and band alignment information of the metal–ZrO2–metal capacitor have been extracted using internal photoemission (IPE) system. By correlating the IPE analysis with I-V and C-V characteristics obtained before and after rapid thermal annealing, origin and transformation of defect states have been successfully investigated. Our analysis revealed that deep-level defects originating from oxygen vacancies near the top electrode are causing of leakage current in MIM capacitor and these defects can be effectively reduced by a proper thermal annealing.

2D transition metal dichalcogenides (TMDs) have been widely investigated for possible application in field‐effect transistors and optoelectronic devices. However, due to the wide band gap of most TMDs, photoresponse to infrared wavelength is still a big challenge. Here, a lateral molybdenum disulfide (MoS2)‐on‐metal Schottky photodetector operating in internal photoemission mode for near‐infrared wavelength with high responsivity is reported. With moderate Schottky barrier height, a low dark current of 0.12 nA at −0.5 V and a remarkable rectification ratio of 103 at ±0.8 V are realized in the MoS2‐on‐Au Schottky photodetector. The maximum responsivity of 1.9 A W−1 at −1 V is achieved at 1310 nm due to the photoemission from the underlayering Au electrode, which absorbs most of the incident light through the transparent MoS2 layers, and the generated photocurrent gain in MoS2 layers. Furthermore, the MoS2 Schottky photodetectors are self‐powered. The high responsivity of 0.68 A W−1 and the excellent specific detectivity of 1.89 × 1012 Jones at 1310 nm are obtained under 0 V. The excellent performance demonstrates that internal photoemission mechanism can be well applied in 2D material Schottky photodetectors for infrared wavelengths. [ABSTRACT FROM AUTHOR]

Sub-bandgap photodetection with two-dimensional electron-confinement in CdZnO-MgZnO heterojunction is realized. The reported photodetection is based on metal-less internal photoemission via optical excitation in 2D electron gas (2DEG) present at the bottom of the conduction band offset in the heterojunction. A physical model is also employed to explain the underlying mechanism of transmission of electrons across the heterojunction. The rib structure of CdZnO waveguide provides strong optical confinement which leads to an improved electro-optic coupling. A high density of 2DEG, uniform momentum distribution across heterojunction and improved electro-optic coupling result in a responsivity of 8.5 mA/W at a wavelength of 532 nm. [ABSTRACT FROM AUTHOR]

Characteristic improvements of photon/plasmon detectors have been the subject of several investigations in the area of plasmonic integrated circuits. Among different suggestions, silicon-based metal-semiconductor-metal (MSM) waveguides are one of the most popular structures for the implementation of high-quality photon/plasmon detectors in infrared wavelengths. In this paper, an integrated silicon-germanium (SiGe) core MSM plasmon detector is proposed to detect λ = 1550 nm with internal photoemission mechanism. Performance characteristics of the new sub-micron device are simulated with a simplified hydrodynamic model. In a specific bias point (V = 3 V and the incident optical power of 0.31 mW), the output current is 404.3 μA (276 μA detection current and 128.3 μA dark current), responsivity is 0.89 A/W, and the 3-dB electrical bandwidth is 120 GHz. Simulation results for the proposed plasmon detector, in comparison with the empirical results of a reported Si-based MSM device, demonstrate considerable responsivity enhancement. [ABSTRACT FROM AUTHOR]

The electron energy band alignment of the monolayer MoSe2/oxide/Si system is characterized by internal photoemission spectroscopy, where the oxide is Al2O3 or SiO2. Raman and photoluminescence spectroscopic measurements confirm the high quality of monolayer MoSe2 exfoliated with gold film as medium. At the oxide flat-band condition, the band offset from the monolayer MoSe2 valence band maximum to the Al2O3 and SiO2 conduction band minimum are measured to be (4.10 ± 0.05) eV and (4.80 ± 0.05) eV, respectively. By referencing the recently reported band gap value of 2.18 eV for monolayer MoSe2, we obtain the electron affinity of monolayer MoSe2 to be (3.8 ± 0.1) eV on Al2O3/Si and (3.5 ± 0.1) eV on SiO2/Si. It is believed that the results from this study will help accelerate the design of electronic and optoelectronic devices that employ this class of two-dimensional materials. [ABSTRACT FROM AUTHOR]

Abstract Internal photoemission of electrons from uncapped monolayer graphene to insulating SiO 2 has been observed in samples prepared by water-intercalation based graphene transfer. The barrier height between the graphene Fermi level and the oxide conduction band bottom was reproducibly found to be 4.1–4.2 eV. Moreover, this value was weakly sensitive to the contacting metal work function (Al, Cu, Au). This barrier height corresponds to an effective work function of graphene close to 5.0 eV, which is nearly 0.5 eV higher than the usually reported vacuum value. Highlights • Internal photoemission of electrons has been detected from uncapped monolayer graphene. • Effective work function (EWF) of graphene has been determined to be 5.0 eV. • EWF of graphene at the interface with SiO 2 is 0.5 eV higher than the vacuum value. [ABSTRACT FROM AUTHOR]

Abstract The ability to detect and determine a typically weak internal photoemission (IPE) signal from a usually strong photoconductivity (PC) signal within a spectral response (SR) measurement can be helpful in studying the interface properties of metal-semiconductor junctions, which are often critical for proper design and analysis of semiconductor electronic devices including organic photovoltaic devices. In this report, we propose a method to discern the voltage dependent IPE component from PC content in a measured SR of organic devices. The method is based on the ratio of SR measured at different voltage bias conditions in metal-organic semiconductor-metal devices. The separated IPE component, hence, can be used to estimate the associated interface barrier(s). The differentiation between IPE and PC is probably caused due to the barrier changing at the metal and organic semiconductor interface on the application of bias which causes a modulation in IPE signal with the applied bias. In this work, a theoretical basis for the method of characterisation has been developed. Based on the analysis, as an example, the barriers between [6,6] phenyl C61 butyric acid methyl ester (PCBM) and electrodes indium tin oxide and aluminium for different bias voltages have been evaluated. This simple and elegant method of studying metal and organic semiconductor barrier, when applicable, can be helpful in device design and characterisation. Graphical abstract Image 1 Highlights • Technique that identifies internal photoemission signal within spectral response. • Deviation in spectral response signal ratio at different biases modelled. • Multi-bias spectral response ratios analysed to estimate charge carrier barriers. [ABSTRACT FROM AUTHOR]

Interfaces of heterogeneous solids, ranging from polycrystalline materials to composites, are frequently encountered in nanotechnology. Electron transport in these materials and across their interfaces critically depends on the energy barriers electrons encounter on their way. Because of electrode structural heterogeneity, the barriers may exhibit significant spatial variations resulting in a broad distribution of barrier heights and built‐in potentials. Quantification of the distributed interface barriers represents a formidable experimental challenge since direct association of interface properties with those of an outer free surface is generally inaccurate. Here we present a methodology enabling quantification of electron barriers at interfaces of semiconductors and metals with insulators using the electric field‐dependent internal photo‐emission (IPE) of electrons. It is shown that practically relevant interfaces may contain “patches” with differences in barrier height (or the effective work function) of up to 1 eV, which makes the electrode heterogeneity a crucial factor in designing electron devices suitable for low‐voltage operation. [ABSTRACT FROM AUTHOR]

The energy barrier heights between an ultra‐smooth amorphous metal electrode, ZrCuAlNi, and several atomic layer deposited (ALD) insulators are measured using internal photoemission (IPE) spectroscopy. ZrCuAlNi–insulator barriers are characterized within metal–insulator–metal (MIM) stacks with Al top contacts and results are compared with the Al/insulator barrier heights. The measured barrier heights at the ZrCuAlNi interface are found to be 3.3, 3.2, 3.0, and 2.2 eV for SiO2, Al2O3, HfO2, and ZrO2, respectively. This barrier height trend is consistent with the electron affinity of the respective oxides. However, barriers for SiO2 and Al2O3 are smaller than that ideally expected based on the reported vacuum work function of ZrCuAlNi, indicating a smaller ZrCuAlNi effective work function in these device structures. The measured Al barrier height results confirm previous reports of a negative dipole at the Al–ALD insulator interface. [ABSTRACT FROM AUTHOR]

• CVD MoS2 growth from Vapor Phase Reaction (VPR) and Solid Precursor Film (SPF). • Determination of semiconductor valence band (VB) relative to the reference level of the insulator conduction band (CB) using Internal photoemission spectroscopy (IPE). • Found a significant enhancement of ≈ 600 meV in the electron barrier by changing different CVD chemistry. • Possible origin of interface dipole formation due to interaction of hydroxile groups from NaOH and AHM promoters. Reliable knowledge of energy alignment of electronic bands at interfaces of few layered Molybdenum Disulfide (MoS 2) is crucial for designing MoS 2 based electronic devices. In this work, we have applied internal photoemission spectroscopy (IPE) to characterize this band alignment. MoS 2 films grown on SiO 2 (50 nm)/Si using two different methods have been analyzed by IPE to determine the energy position of the semiconductor valence band (VB) relative to the reference level of the insulator conduction band (CB). We found that changing the MoS 2 growth method from Vapor Phase Reaction (VPR) of MoO 3 and sulfur, to Solid Precursor Film (SPF) of sulfurized AHM-NaOH spin coated MoS 2 film, results in significant (≈600 meV) enhancement in the electron barrier. Such effects are ascribed to the interaction of hydroxy groups from NaOH and AHM promoters with the SiO 2 surface leading to interface dipole modification. [ABSTRACT FROM AUTHOR]

Impact of deposition technique on the chemical bonding in low-κ organosilicate glass (OSG) films and on porogen residues was studied using near edge X-ray absorption fine structure (NEXAFS) and internal photoemission (IPE) spectroscopy. The carried analysis reveals that self-assembly technology (SAT) allows one to obtain OSG-films without carbon residues, i.e. with “a clean bandgap”. Conventional PECVD film contains appreciable amount of carbon clusters, which account for gap states responsible for charge trapping and leakage current. [ABSTRACT FROM AUTHOR]

Experiments on internal photoemission of electrons at interfaces of Si y Ge 1 − x − y Sn x binary and ternary alloys (0 ≤ x ≤ 0.11; 0 ≤ y ≤ 0.19) with amorphous insulating Al 2 O 3 reveal that the application of an additional oxidation step (5 min in dry O 3 at 300 °C) after atomic layer deposition of first ≈ 1 nm of alumina results in a significant increase of the electron barrier height (by ≈ 0.4–0.5 eV) as compared to the conventionally grown Al 2 O 3 layers. Furthermore, this supplemental oxidation step facilitates the removal of Ge sub-oxides from the interface. The observed electron barrier enhancement is suggested to be caused by formation of a wide gap germanate interlayer between the Ge-based semiconductors and alumina. [ABSTRACT FROM AUTHOR]

Such technologically abundant agent as hydrogen has a strong effect on the metal/oxide interface energy barrier. Internal photoemission analysis of electron barrier height variations at Pt/HfO 2 interfaces caused by annealing in hydrogen reveals the formation of a significant (≥ 0.4 eV) electrostatic dipole layer. The orientation of the H-induced dipole appears to be sensitive to the growth conditions and treatments, e.g., Hf precursor used in the atomic layer deposition (ALD) process: In the case of the HfCl 4 precursor, annealing in H 2 leads to barrier lowering, whereas the barrier becomes higher in samples grown by using tetrakis(dimethylamido)hafnium. These findings indicate that hydrogen may form dipoles of opposite orientation through two different mechanisms: The positive dipole is caused by H interaction with the metal surface, which can also be found at interfaces of Pt with other oxides such as SiO 2 and Al 2 O 3 . By contrast, the sensitivity of the negative dipole formation to the HfO 2 ALD chemistry suggests it to be related to a negatively charged bonded state of hydrogen in the near-interface oxide. Moreover, the formation of positive dipole is also observed after high temperature anneal in nitrogen suggesting the contribution of additional mechanisms of dipole formation. [ABSTRACT FROM AUTHOR]

This paper presents the design, fabrication, and characterization of Schottky erbium/silicon photodetectors working at 1.55 µm. These erbium/silicon junctions are carefully characterized using both electric and optical measurements at room temperature. A Schottky barrier ΦB of ~673 meV is extrapolated; the photodetectors show external responsivity of 0.55 mA/W at room temperature under an applied reverse bias of 8 V. In addition, the device performance is discussed in terms of normalized noise and noise-equivalent power. The proposed devices will pave the way towards the development of Er-based photodetectors and light sources to be monolithically integrated in the same silicon substrate, and both operating at 1.55 µm.

We report the systematic experimental studies demonstrating that a graphene layer inserted at metal/n-Si(001) interface is efficient to explore interface Fermi-level pinning effect. It is confirmed that an inserted graphene layer prevents atomic interdiffusion to form an atomically abrupt Schottky contact. The Schottky barriers of metal/graphene/n-Si(001) junctions show a very weak dependence on metal work-function, implying that the metal Fermi-level is almost completely pinned at charge neutrality level close to the valence band edge of Si. The atomically impermeable and electronically transparent properties of graphene can be used generally to form an intact Schottky contact for all semiconductors. [ABSTRACT FROM AUTHOR]

analyzing internal photoemission of electrons from Si/SiOx-passivated Ge into insulating HfO2 we found that insertion of additional La interlayer between SiOx and HfO2 leads to dramatic increase (more than by factor of 20) of the barrier transparency. However, no measurable variation of the interface barrier height is observed suggesting that La induces intermixing of near-interface oxide stack resulting in development of additional density of states corresponding to conduction band of LaOx and HfOx sub-networks. At the same time, photoemission results indicate the presence of discrete positive charges in the near-interface oxide layer which may explain the observed ∼1 V shift of capacitance-voltage curves. [ABSTRACT FROM AUTHOR]

analyzing internal photoemission of electrons from Si/SiOx-passivated Ge into insulating HfO2 we found that insertion of additional La interlayer between SiOx and HfO2 leads to dramatic increase (more than by factor of 20) of the barrier transparency. However, no measurable variation of the interface barrier height is observed suggesting that La induces intermixing of near-interface oxide stack resulting in development of additional density of states corresponding to conduction band of LaOx and HfOx sub-networks. At the same time, photoemission results indicate the presence of discrete positive charges in the near-interface oxide layer which may explain the observed ∼1 V shift of capacitance-voltage curves. [ABSTRACT FROM AUTHOR]

The band offset at the interface of a heterojunction is one of the most important parameters determining the characteristics of devices constructed from heterojunction. Accurate knowledge of band offsets and their temperature dependence will allow one to simulate and predict the device performances. We present a temperature-dependent internal-photoemission spectroscopy (TDIPS) for studying the band offsets. Applications of the TDIPS into III-V and II-VI materials are discussed. [ABSTRACT FROM AUTHOR]

Hot-electron devices are emerging as promising candidates for the transduction of optical radiation into electrical current, as they enable photodetection and solar/infrared energy harvesting at sub-bandgap wavelengths. Nevertheless, poor photoconversion quantum yields and low bandwidth pose fundamental challenges to fascinating applications of hot-electron optoelectronics. Based on a novel hyperbolic metamaterial (HMM) structure, we theoretically propose a vertically-integrated hot-electron device that can efficiently couple plasmonic excitations into electron flows, with an external quantum efficiency approaching the physical limit. Further, this metamaterial-based device can have a broadband and omnidirectional response at infrared and visible wavelengths. We believe that these findings may shed some light on designing practical devices for energy-efficient photodetection and energy harvesting beyond the bandgap spectral limit. [ABSTRACT FROM AUTHOR]

The interest in Infrared and Ultraviolet detectors has increased immensely due to the emergence of important applications over a wide range of activities. Detectors based on free carrier absorption known as Hetero-junction Interfacial Workfunction Internal Photoemission (HEIWIP) detectors and variations of these heterojunction structures to be used as intervalence band detectors for a wide wavelength region are presented. Although this internal photoemission concept is valid for all semiconductor materials systems, using a well-studied III–V system of GaAs/ Al x Ga 1 - x As to cover a wide wavelength range from UV to far-infrared (THz) is an important development in detector technology. Using the intervalence band (heavy hole, light hole and split off) transitions for high operating temperature detection of mid Infrared radiation is also discussed. A promising new way to extend the detection wavelength threshold beyond the standard threshold connected with the energy gap in a GaAs/ Al x Ga 1 - x As system is also presented. Superlattice detector technology, which is another promising detector architecture, can be optimized using both Type I and Type II heterostructures. Here the focus will be on Type II Strained Layer (T2SL) Superlattice detectors. T2SL Superlattices based on InAs/(In,GA)Sb have made significant improvements demonstrating focal plane arrays operating around 80 K and with multiple band detection capability. A novel spectroscopic method to evaluate the band offsets of both heterojunction and superlattice detectors is also discussed. [ABSTRACT FROM AUTHOR]

Thanks to its good thermal stability, including resistance to oxidation, platinum (Pt) is widely used in prototyping a wide spectrum of electron devices ranging from metal-oxide-semiconductor (MOS) transistors to resistive switching memory cells. In this work, the energy barriers for electrons between the Fermi level of Pt and the conduction band of several oxide insulators (SiO2, Al2O3, HfO2, Hf0.8Al0.2Ox, Sr0.53Ti0.47O3) were determined by using internal photoemission of electrons. By combining this barrier value with the electron affinity of the particular oxide, the effective work function (EWF) of Pt was determined for different interfaces. As studied over the reference Pt/oxide/Si stacks de-gassed in high vacuum at 400 °C, the EWF of Pt is found to differ significantly from the accepted vacuum WF value of 5.6 eV. The EWF is equal to 5.2 eV at the Pt/Al2O3 interface, 5.1 eV at Pt/HfO2, 5.3 eV at Pt/Hf0.8Al0.2Ox, 4.8 eV at Pt/SiO2, and 5.8 eV at the Pt/Sr0.53Ti0.47O3 interface indicating the presence of a polarization layer of which the contribution to the EWF depends on the oxide composition. Furthermore, annealing in H2 at 400 °C reduces the Pt EWF by ∼0.5 eV at all interfaces except for the Pt/Sr0.53Ti0.47O3 one. This observation indicates the formation of an additional H-related dipole at the Pt/oxide interfaces and suggests that the vacuum WF of Pt cannot be used as the value relevant for the MOS properties. [ABSTRACT FROM AUTHOR]

Internal photoemission of electrons from 4- and 2-monolayer thick MoS 2 films prepared by sulphurization of metallic Mo on top of SiO 2 or HfO 2 /SiO 2 insulating stacks is detected. This enables determination of the energy position of the MoS 2 valence band which is found to be at 4.1–4.2 eV below the SiO 2 conduction band. At the interface with HfO 2 , a barrier height of 3.7 eV is found, corresponding to an increase of the electron affinity of MoS 2 by ≈0.5 eV as compared to the SiO 2 case. This suggests the presence of interface charges (or dipoles) in the interfacial HfO 2 layer. [ABSTRACT FROM AUTHOR]

We have developed a new mapping technique, termed scanning internal-photoemission microscopy, to characterize the electrical inhomogeneity of metal-semiconductor interfaces. We characterized the initial stage of thermal degradation of Au/Ni/n-GaN Schottky contacts. We found that, upon 400 °C annealing, a partial thermal degradation occurred from a scratch on the dot, where Au atoms diffused to the interface and reacted with GaN. When the top Au layer was partially missing, upon annealing, the Ni surface was oxidized and NiOx/n-GaN with a small Schottky barrier height was formed. In addition, a thin contamination layer at the interface was clearly observed as a pattern. It was confirmed that this method is a powerful tool to map metal contacts for the investigations of partial thermal degradation, formation of parallel contacts, and inhomogeneity of surface chemistry. [ABSTRACT FROM AUTHOR]

Using a Z-transfer model applicable to a microring resonator enhanced internal photoemission-based photodetector (MRRE-IPE-PD); we develop a model for evaluating the effect of reflections in the microring resonator (MRR) on the quantum efficiency (QE). Simulations show that a 5% increase in the reflection from an ideal case QE and MRR quality factor reduces by ~30%. We also show that further increase in the reflection can result in a dramatic decrease in QE and break the degenerate resonant frequency down into two frequencies. Considering the detuning condition in an MRR, we extend an existing model suitable for the MRRE-IPE-PD. We evaluate the effect of this nonideality on the PD QE. A detuning equal to free spectral range (FSR)/3 reduces the QE to half of its value for an ideal case. Nonetheless, for a detuning equal to FSR/2, the QE of the ideal case is retained. We also evaluate the dependence of the QE bandwidth product (QE × BW) on the MRR radius in under-critical, critical, and over-critical coupling conditions. Simulations reveal that the latter is the optimized condition, wherein the QE × BW for a PD with 2-nm PtSi decreases from 32 to 30 GHz, when the radius is increased from 7 to 10 μm. [ABSTRACT FROM AUTHOR]

The effective work function (EWF) and the energy position of the valence band in 20-40-nm thick VO2and V2O5layers grown by atomic layer deposition (ALD) on top of insulating SiO2 and γ-Al2O3 films were evaluated using the comparison between capacitance-voltage and internal photoemission measurements. From the capacitance measured at different temperatures on the metal-VO2(V2O5)-insulator-silicon and metal-insulator-silicon diodes we found that the both studied vanadium oxides have the same EWF as gold electrodes evaporated on the same oxides. This result is further collaborated by the internal photoemission experiments at the VO2/SiO2 and V2O5/SiO2 interfaces which indicate the energy barrier between the top of the vanadium oxide valence band (in the insulating phase) and the insulator conduction band to be 4.1 ± 0.1 eV. Since the transition from the narrow-gap VO2 to the wide-gap V2O5 oxide causes no change in the WF or in the photoemission threshold, we conclude that the ALD-grown VO2 in its insulating phase represents a a heavily-doped semiconductor which becomes metallic upon metal-insulator transition without significant EWF change. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The effective work function (EWF) and the energy position of the valence band in 20-40-nm thick VO2and V2O5layers grown by atomic layer deposition (ALD) on top of insulating SiO2 and γ-Al2O3 films were evaluated using the comparison between capacitance-voltage and internal photoemission measurements. From the capacitance measured at different temperatures on the metal-VO2(V2O5)-insulator-silicon and metal-insulator-silicon diodes we found that the both studied vanadium oxides have the same EWF as gold electrodes evaporated on the same oxides. This result is further collaborated by the internal photoemission experiments at the VO2/SiO2 and V2O5/SiO2 interfaces which indicate the energy barrier between the top of the vanadium oxide valence band (in the insulating phase) and the insulator conduction band to be 4.1 ± 0.1 eV. Since the transition from the narrow-gap VO2 to the wide-gap V2O5 oxide causes no change in the WF or in the photoemission threshold, we conclude that the ALD-grown VO2 in its insulating phase represents a a heavily-doped semiconductor which becomes metallic upon metal-insulator transition without significant EWF change. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Current injection in organic semiconductors remains difficult to predict due in large part to the challenge of characterizing the contact energy barrier and interface density of states directly in organic electronic devices. Here, resonant coupling to surface plasmon polariton modes of a metal contact is demonstrated as a means to carry out internal photoemission (IPE) accurately in disordered organic semiconductor devices and enable direct measurement of the contact injection barrier by isolating true IPE from spurious sub-gap organic photoconductivity. The substantial increase in sensitivity afforded by resonant coupling enables measurement in the low-field injection regime where deviation from the standard Fowler prediction is explained quantitatively by the existence of a broad distribution of interface states. This technique is broadly applicable to metals and surface treatments commonly used in organic light emitting diodes, thin film transistors, and photovoltaics, and should therefore provide a quantitative basis to understand and model current injection in these devices over their entire operational lifetime. [ABSTRACT FROM AUTHOR]

Highlights: [•] Photoemission of electrons from Cu x Te1−x and Te into Al2O3 and SiO2 is observed. [•] The Cu x Te1−x stoichiometry has a marginal impact on the electron barrier height. [•] Application of Te electrodes leads to the increase of the barrier height. [•] EWF of Cu and Te on Al2O3 are considerably higher than vacuum WF. [•] Negative charges may be present at the Cu x Te1−x/Al2O3 interface. [ABSTRACT FROM AUTHOR]

The energy band alignments of Ni/AlO/GaN heterostructures have been explored by internal photoemission (IPE) and capacitance-voltage (CV) measurements. By performing IPE measurements at both reverse- and forward-bias conditions, the Ni/AlO Schottky barrier is found to be 2.9 ± 0.1 eV with the presence of a strong image force lowering effect, while the AlO/GaN conduction-band offset is determined to be 2.2 ± 0.1 eV and is insensitive to oxide electrical field. CV-based flat-band voltage analysis has further been performed on samples with different oxide thicknesses, not only confirming the IPE-measured band alignment but also revealing the presence of 3.0 × 10 cm net positive charge at the AlO/GaN interface. [ABSTRACT FROM AUTHOR]

Precise evaluation of the effective work function and the built-in voltage in metal-oxide-metal (MOS) or metal-insulator-metal (MIM) stacks is crucial for attaining the functionality of various oxide-based electron devices. We studied the impact of a low work function (WF) metal interlayer (IL), i.e. Ti, on the electron barrier height between the metal Fermi level and the conduction band of the oxide insulator. The experiments were performed on structures comprised of a layer of thermal SiO2 or an atomic layer deposited Al2O3 on heavily doped p- or n-Si substrates. In order to evaluate the impact of the Ti IL, 3, 6 or 10 nm thick Ti films have been deposited prior to TiN x sputtering. Spectral curves of electron photoemission from the metal layer into the oxide were analyzed in order to determine the energy barrier for electrons between the Fermi level of the metal and the conduction band of the insulator ( Φe). As expected, the insertion of the low WF metal shifts the barrier to lower energies, depending on the IL thickness. However, while a 3-nm thick Ti IL is sufficient to lower the barrier by 0.5 eV in the SiO2-based stack, it has no measurable impact on the barrier in the Al2O3/Ti/TiN x stack. For the latter structure, both Ti and the Al2O3 thicknesses influence the Φe lowering trend, suggesting that oxygen scavenging from Al2O3 by Ti and nitridation of the Ti IL by subsequent TiN deposition may affect the band alignment between the metal and the oxide. [ABSTRACT FROM AUTHOR]

Highlights: [•] Interface barriers for electrons at Al2O3/metal interfaces can be controlled by liners. [•] Tantalum and titanium liners allow for >1eV barrier lowering at Cu/Al2O3 interface. [•] Application of Hf liner is hindered by oxygen scavenging from Al2O3. [Copyright &y& Elsevier]

Abstract: We addressed the possible variation of the electron barrier at the Cu0.6Te0.4/Al2O3 interface as compared to the pure Cu electrode case. The experiments were performed using structures fabricated by atomic layer deposition of an Al2O3 insulator on (100)Si or thermally oxidized (100)Si, followed by sputtering of Cu or Cu0.6Te0.4 top electrodes. These structures were used to observe electron photoemission from the metal layer into the oxide in order to determine the energy barrier for electrons between the Fermi level of the metal and the conduction band of the insulating layer. The electron barrier height at interfaces of Cu and Cu0.6Te0.4 electrodes is found to be the same but appears to be sensitive to the oxide type which is ascribed to the formation of a polarization layer. [Copyright &y& Elsevier]

Metal-semiconductor interfaces are ubiquitous in modern electronics. These quantum-confined interfaces allow for the formation of atomically thin polarizable metals and feature rich optical and optoelectronic phenomena, including plasmon-induced hot-electron transfer from metal to semiconductors. Here, we report on the metal-semiconductor interface formed during the intercalation of zero-valent atomic layers of tin (Sn) between layers of MoS 2 , a van der Waals layered material. We demonstrate that Sn interaction leads to the emergence of gap states within the MoS 2 band gap and to corresponding plasmonic features between 1 and 2 eV (0.6-1.2 μm). The observed stimulation of the photoconductivity, as well as the extension of the spectral response from the visible regime toward the mid-infrared suggests that hot-carrier generation and internal photoemission take place.

We have shown that using focused UV laser beam in photoelectric methods it is possible to measure local φMS values over the gate area of a single MOS structure. The φMS distribution is such that its values are highest far away from the gate edges regions, lower in the vicinity of gate edges and still lower in the vicinity of gate corners. Examples of measurement results and description of the measurement system are presented. The dependence of the φMS value on the exposure time and the power density of UV light is discussed.

Abstract: This paper presents experimental evidence on effective work function tuning due to the presence of oxygen at the TiNx/LaLuO3 interface. Two complementary techniques, internal photoemission and X-ray photoelectron spectroscopy, show good agreement on the position of the metal gate Fermi level to conduction (2.79±0.25eV) and valence (2.65±0.08eV) band edge for TiNx/bulk LaLuO3 gate stacks. The chemical shifts of Ti2p and N1s core levels and different degree in ionicity of TiNx metal gates correlate with the observed valence band offset shifts. The results have significance for setting the band edge work function and resulting low threshold voltage for ultimately scaled LaLuO3-based p-metal oxide semiconductor field effect transistor devices. [Copyright &y& Elsevier]

We present measurements of band alignment of atomic layer deposited high- k dielectrics on Si(100) using linear internal photoemission (IPE), detected by measuring photocurrent from a biased MOS capacitor, and internal multi-photon photoemission (IMPE), detected by optical second-harmonic generation (SHG). In IPE, Band offsets are extracted from either the threshold of quantum yield; in IMPE, they are determined by detecting discrete increments in multi-photon order. IPE and IMPE yielded identical conduction band (CB) offsets (2.0 eV) for as-deposited Si/Al2O3 structures with 10 and 3 nm oxides, respectively, in excellent agreement with previous measurements of annealed structures. Band offset measurements for Si/HfO2, on the other hand, show a strong (0.3 eV) upshift of the oxide valence band (VB) maximum, and an equal decrease of the oxide band gap upon post-deposition annealing (PDA) at 600 °C, while the CB offset remains unchanged. We attribute the shift of the VB edge to thermally driven oxygen diffusion away from the Si/HfO2 interface. [ABSTRACT FROM AUTHOR]