Photovoltage Effect Research Articles

On the Bulk Photovoltaic Effect in the Characterization of Strained Germanium Microstructures

Strain engineering serves as an effective method for optimizing electronic and optical properties in semiconductor devices, with applications including the enhancement of optical emission in Ge and GeSn‐based devices, improvement of carrier mobility, and second harmonic generation in silicon photonics structures. Current methods for deformation characterization in semiconductors, such as X‐ray diffraction and Raman spectroscopy, often require bulky and expensive setups and are limited in vertical resolution. Consequently, techniques capable of measuring lattice strain while overcoming these drawbacks are highly desirable. This study proposes a proof of concept for a cost‐effective, compact, fast, and non‐destructive approach to probe non‐uniform strain fields and additional material properties by exploiting the bulk photovoltage effect. The method is benchmarked with an array of silicon nitride stripes deposited under varying pressure conditions on a germanium substrate. Initially, their surface strains are verified through Raman spectroscopy. The deformations are replicated in a finite element method platform by integrating mechanical simulations with deformation potential theory, thereby estimating the band edge energy landscape. Finally, the study discusses the theoretical behavior of the photovoltage signal, considering semiconductor properties, defects, doping, and deformation. The findings offer insights into the development of advanced techniques for strain and transport analysis in semiconductor materials.

Characterization of surface electric field in β-FeSi2 by Franz–Keldysh oscillations

The surface electric field (F) of β-FeSi2 has been investigated by Franz–Keldysh oscillations (FKOs) observed in photoreflectance spectra. The FKO signals were observed in an undoped β-FeSi2 epitaxial layer (3 nm) grown on p+-type β-FeSi2 layers (UP+ structure) by molecular beam epitaxy. The surface electric field obtained from the FKO at 11 K was F = 220 kV/cm. The surface electric field was almost independent of the excitation light power and temperature, showing that the surface electric field was not affected by the surface photovoltage effect. In the dependence of F on the thickness of the undoped layer (d), F was nearly constant at d = 2–56 nm. The result showed that the surface electric field of β-FeSi2 was applied to a thin region (<2 nm) at the surface.

Interaction and surface photovoltage effect of MoS2 with Na deposition

Interaction and surface photovoltage effect of MoS2 with Na deposition

Response to VOCs stimuli by triphenylamine derivatives functionalized zinc oxide nanorods: A promising material for food freshness monitoring

In this work, we have examined the photo-induced volatile organic compounds (VOCs) sensing ability of triphenylamine (TPA) derivatives functionalized zinc oxide nanorods (ZnO NRs) using the scanning Kelvin probe (SKP). We have explored the effect of contact potential difference variance and surface photovoltage in both dark and visible light illumination under different VOCs with reference to the ambient conditions. The ZnO NRs are synthesized by hydrothermal method followed by functionalization with three different TPA organic molecules namely (i) 4-formyltriphenylamine-acetophenone, (ii) 4,4’-diformyltriphenylamine-acetophenone, and (iii) 4,4’,4’’-triformyltriphenylamine-acetophenone (TFTPA). The pure and functionalized ZnO NRs are characterized by XRD, FESEM, HR-TEM, UV-visible absorption spectroscopy, Raman spectroscopy, XPS, and, SKP system. Three different VOCs such as ethanol, nonanal, and triethylamine are exposed on pure and functionalized ZnO NRs. In dark condition, high surface potential changes have been observed for nonanal in all the samples. Noteworthy, TFTPA_ZnO NRs show high adsorption towards nonanal during visible light illumination too. The irradiation of light has tuned the energy levels favorable for enhanced charge transfer between nonanal and TFTPA_ZnO. In parallel, the VOCs adsorption mechanisms are understood through density functional theory calculations. The computational adsorption energy and Mulliken charge analysis results are in accordance with the experimental ones. Overall, this combined study suggests that the ZnO NRs functionalized with the TPA derivatives are highly sensitive to nonanal. This can be used to monitor the freshness of edible oils (Peanut, soybean, and linseed), virgin olive oil, yak meat, etc. under visible light illumination.

Exciton formation dynamics at the SiO2/Si interface

Excitons can operate as carriers for energy transduction in optoelectronics, and engineering their dynamics is of great interest. Here, we employ time-resolved terahertz spectroscopy to analyze exciton formation dynamics as a function of temperature for a (100) N-type silicon substrate passivated by native SiO2. By analyzing the frequency-resolved complex conductivity as a function of temperature we resolve the photophysics for the formation of free carriers into excitons. Notably, we observe a relatively long-lived ~300 ps transient population of free carriers at temperatures well below the Mott transition (4 K). We rationalize this by transient photophysics at the SiO2/N-type-Si surface, where holes localize and release under high injection conditions due to a transient surface photovoltage effect. We believe our results have implications for the design of excitonic-based electronic applications operating at cryogenic temperatures and accessed optically.

Temperature dependent ARPES of the metallic-like bands in Si(553)-Au

We conducted a thorough investigation into the temperature dependence of the metallic-like bands of Si(553)-Au using angular-resolved photoemission spectroscopy (ARPES). Our study addresses the challenges posed by the short-term stability of the surface and photo-voltage effects, which we overcame to extract changes in the band-filling and Fermi-velocity. Our findings shed light on the low-temperature phase of the step edge in Si(553)-Au, which has been a topic of ongoing debate regarding its structural or electronic nature. Through comparison with theoretical predictions of a structural-related low-temperature to high-temperature phase transition, we discovered that the band-filling and Fermi-velocity do not change accordingly, thereby ruling out this scenario. Our study contributes to a better understanding of this material system and provides an important reference for future research.

Photothermoelectric AZO/SiO2/NiO Device

AbstractTransparent‐conductive‐oxide (TCO) materials and transparent devices combining photovoltage and thermoelectric effects are still scarce. Hence, a new transparent‐conductive‐oxide/insulating/transparent‐semiconductor‐oxide (TCO‐I‐TSO) structure combining such effects is developed. It is made of aluminum‐doped zinc oxide (AZO)/SiO2/NiO thin films sequentially deposited on glass substrates. AZO exhibits thermo and photovoltage in response to gradient temperature and absorption of UV photons, while NIR photons absorption in the NiO layer. Photovoltage appears in the plane between the AZO and NiO layer when the whole sample is irradiated with near infrared light, and it also depends on the thickness of the SiO2 layer. This photovoltage is continuously monitored on samples placed in a glass window facing south. Throughout the day, the photovoltage varies from 0 to 300 µV proportionally to the light intensity.

Impact of photoexcitation on secondary electron emission: A Monte Carlo study

Understanding the transport of photogenerated charge carriers in semiconductors is crucial for applications in photovoltaics, optoelectronics, and photo-detectors. While recent experimental studies using scanning ultrafast electron microscopy (SUEM) have demonstrated that the local change in the secondary electron emission induced by photoexcitation enables direct visualization of the photocarrier dynamics in space and time, the origin of the corresponding image contrast still remains unclear. Here, we investigate the impact of photoexcitation on secondary electron emissions from semiconductors using a Monte Carlo simulation aided by time-dependent density functional theory. Particularly, we examine two photoinduced effects: the generation of photocarriers in the sample bulk and the surface photovoltage (SPV) effect. Using doped silicon as a model system and focusing on primary electron energies below 1 keV, we found that both the hot photocarrier effect immediately after photoexcitation and the SPV effect play dominant roles in changing the secondary electron yield (SEY), while the distribution of photocarriers in the bulk leads to a negligible change in SEY. Our work provides insights into electron–matter interaction under photo-illumination and paves the way toward a quantitative interpretation of the SUEM contrasts.

Utilizing Angle‐Dependent Photovoltage Effect in a CH3NH3PbCl3/Si Heterojunction toward High‐Performance Polarized Light Detection in Ultraviolet Region

AbstractOrganic–inorganic hybrid MAPbCl3 perovskite (MA+ = CH3NH3+) in UV photodetection is drawing interest due to its superior semiconductor properties and UV‐matchable optical bandgap. However, MAPbCl3‐based photodetector targeting high‐performance polarized light detection has remained unexplored due to the isotropic structure of MAPbCl3. The photovoltaic effect in the heterojunction, which shows an angle dependence on light polarization, provides opportunities to break the restriction of intrinsic structure for realizing polarization‐sensitive photodetection. Herein, an effective strategy is reported to realize high‐performance polarization‐sensitive UV photodetection by constructing a heterojunction with two isotropic materials MAPbCl3 and Silicon (Si). Emphatically, the photovoltage in MAPbCl3/Si heterojunction changes with the angle of polarized light with the maximum (minimum) value of 0.15 V (0.05 V), originating from the built‐in electric field. More interestingly, driven by the photovoltage, the device thus exhibits a large polarization ratio (Imax/Imin) of 2.9 at 377 nm under the self‐driven mode. Besides, the present device also delivers high‐performance photodetection in UV region owing to the superior photoresponse of MAPbCl3, including a high detectivity (D*) of 2.93 × 1011 Jones, a superior responsibility of 8 mA W–1, a substantial switching ratio of 900, and an ultrafast response speed of 40/98 µs at 0 V bias. This work opens a new avenue for high‐performance polarization‐sensitive photodetection by utilizing angle‐dependent photovoltage effect.

Bulk Photovoltage Effect in Ferroelectric BaTiO3.

Due to the unusual charge separation mechanism and anomalous photovoltaic effects, the bulk photovoltage effect in ferroelectric semiconductors has attracted a great deal of attention in solar energy conversion, especially in attempts to utilize nonthermalized carriers. Among the various mechanisms that have been proposed for interpreting the photovoltaic effect, a shift mechanism was derived from quantum phenomena, which have been modeled and studied for many years. However, the concurrent shift and ballistic mechanism make investigating the ferroelectric bulk photovoltage effect complex and challenging. Here, taking a tetragonal ferroelectric BaTiO3 single crystal as a prototype, we report an approach for distinguishing the shift and ballistic mechanism-induced surface photovoltage. The results indicate different effects on the charge separation of the ballistic mechanism and shift mechanisms, as evidenced by surface photovoltage measurement. Interestingly, the shift and ballistic mechanisms afford charge separation in two opposite directions but on the same order of magnitude under monochromatic superband illumination. Our results provide facile and efficient methods for clarifying the shift and ballistic mechanisms in ferroelectrics.

Chain-to-Layer Dimensionality Engineering of Chiral Hybrid Perovskites to Realize Passive Highly Circular-Polarization-Sensitive Photodetection.

Chiral hybrid perovskites (CHPs), aggregating chirality and favorable semiconducting properties in one, have taken a prominent position in direct circularly polarized light detection (CPL). However, passive high circular polarization sensitivity (gres) photodetection in CHPs is still elusive and challenging. Benefitting from efficient control and turning of carrier transport of CHPs by dimensional engineering, here, we unprecedentedly proposed a chain-to-layer dimensionality engineering to realize high-gres passive photodetection. Two novel 2D layered CHPs (R/S-PPA)EAPbBr4 (2R/2S) (PPA = 1-phenylpropylamine, EA = ethylammonium) are successfully synthesized by alloying an EA cation with small steric hindrance into the chained CHPs (R/S-PPA)PbBr3 (1R/1S). Particularly, compared with the neglectable photoresponse in 1R, the obtained 2R by chain-to-layer dimensionality engineering gives rise to an excellent photoconductivity and robust polar photovoltage effect (PPE) with a giant open-circuit voltage of 2.5 V. Furthermore, such PPE promotes realizing an impressive gres in 2R up to 0.42 at zero bias because of the independent separation of photoexcited carriers, which is the highest value among the reported layered chiral perovskites. This work paves the way for the vigorous development of higher dimensional CHPs and will reveal their applications in the field of passive high-gres CPL detection.

Resistive switching and photovoltaic response characteristics for the BaTiO3/Nb:SrTiO3 heterostructure

Recently, perovskite compounds with ABX3 structures have been attracting increasing attention because of their excellent properties and their potential for applications in fields such as optoelectronics and memory devices. In this Letter, we introduce a BaTiO3/Nb:SrTiO3 (BTO/NSTO) heterostructure that displays both resistive switching and photovoltaic response characteristics. As a dual-function device, our heterostructure device not only exhibits bipolar resistive switching behavior with a switching ratio of up to 103 without any forming process but also shows a tunable photovoltage effect with an open-circuit voltage (Voc) of approximately 0.38 V. In addition, a high-resistance state and a low-resistance state of the device can be modulated by light illumination. This photo-modulation mechanism is revealed and shows that resistive switching can be attributed to migration of photogenerated carriers and charge trapping/detrapping caused by ferroelectric polarization reversal, which changes depletion layer characteristics at the BTO/NSTO interface. This work may help to provide an understanding of multifunctional characteristics of the BTO/NSTO heterostructure and will pave the way toward practical applications of this heterostructure in memory and optoelectronic devices.

Used for effect interpretation abnormal photo voltage

The paper presents the results of a study to identify the physical mechanism of anomalous photovoltage in polycrystalline structures. A qualitative theory of the effect of anomalous photovoltage is proposed on the basis of experimental results. In this work, the results an revealing the physical examination of the main photochemical polycrystalline structure's are brought. It is offered qualitative theory of the effect anomalous photochemical on base experimental result.

Probing the Surface Photovoltage Effect by Imaging Photo-assisted Secondary Electron Emission

Probing the Surface Photovoltage Effect by Imaging Photo-assisted Secondary Electron Emission

Impact of surface photovoltage on photoemission from Ni/p-GaN

Surface studies on the Ni films on p-GaN concentrated on photoelectron spectroscopies are presented. We found the surface condition on which the surface photovoltage (SPV) effect, caused by an excitation source, leads to the appearance of a quasi-Fermi level located above the Fermi level of the electron energy analyzer. The energy shifts of core-level lines were also noted due to this. This means that for meta/semiconductor systems some energy shifts of peaks observed do not have to result from a chemical reaction and may be done through SPV effects. The formation of the interface, as well as its physicochemical and structural analysis, were carried out in situ under ultrahigh vacuum. Ni films were vapour deposited onto the Mg-doped GaN, (0 0 0 1)-oriented. X-ray and ultraviolet light sources were applied in photoemission experiments. The low-energy electron diffraction technique was employed for surface structure investigation.

Studies of NO2 Gas-Sensing Characteristics of a Novel Room-Temperature Surface-Photovoltage Gas Sensor Device.

In this work the characteristics of a novel type of room temperature NO2 gas sensor device based on the surface photovoltage effect are described. It was shown that for our SPV gas sensor device, using porous sputtered ZnO nanostructured thin films as the active gas sensing electrode material, the basic gas sensor characteristics in a toxic NO2 gas atmosphere are strongly dependent on the target NO2 gas flow rate. Moreover, it was also confirmed that our SPV gas sensor device is able to detect the lowest NO2 relative concentration at the level of 125 ppb, with respect to the commonly assumed signal-to-noise (S/N) ratio, as for the commercial devices.

Bidirectional surface photovoltage on a topological insulator

Controlled extraction of spin-polarized currents from the surface of topological insulators (TIs) would be an important step to use TIs as spin-electronic device materials. One way is to utilize the surface photovoltage (SPV) effect, by which the surface current may flow upon irradiation of light. To date, unipolar SPV has been observed on TIs, while the realization of ambipolar SPV is crucial for taking control over the direction of the flow. By using time-resolved photoemission, we demonstrate the ambipolar SPV realized on the TI ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$. The topological surface states showed downward and upward photovoltaic shifts for the $n$- and $p$-type samples, respectively. We also discerned the photogenerated carriers accumulated in the surface states for $g4\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{s}$. We provide the keys besides the in-gap Fermi level to engineer the SPV on TIs.

A Novel Type Room Temperature Surface Photovoltage Gas Sensor Device.

In this paper a novel type of a highly sensitive gas sensor device based on the surface photovoltage effect is described. It is based on the Kelvin probe approach. Porous ZnO nanostructured thin films deposited by the direct current (DC) reactive magnetron sputtering method are used as the active gas sensing electrode material. Crucially, the obtained gas sensing material exhibited a nanocoral surface morphology and surface Zn to O non-stoichiometry with respect to its bulk mass. Among other responses, the demonstrated SPV gas sensor device exhibits a high response to an NO2 concentration as low as 1 ppm, with a signal to noise ratio of about 50 and a fast response time of several seconds under room temperature conditions.

Interfacial carrier dynamics of graphene on SiC, traced by the full-range time-resolved core-level photoemission spectroscopy

Carrier dynamics through a heterointerface of a Dirac material and a semiconductor was studied by the measurement of the full-range time-resolved core-level photoemission spectroscopy using synchrotron radiation. The electron-hole recombination process during relaxation of the surface photovoltage effect was delayed in a graphene layer due to the bottleneck effect of Dirac cones. When an intermediate buffer layer exists, the recombination mainly takes place at the interfacial Si dangling-bond sites and the relaxation time shortens by one-order of magnitude. The present result demonstrates unusual carrier dynamics at a semiconductor surface, terminated by a layer of the Dirac material.

Controlling the surface photovoltage on WSe2 by surface chemical modification

The surface photovoltage (SPV) effect is key to the development of opto-electronic devices such as solar-cells and photo-detectors. For the prototypical transition metal dichalcogenide WSe2, core level and valence band photoemission measurements show that the surface band bending of pristine cleaved surfaces can be readily modified by adsorption with K (an electron donor) or C60 (an electron acceptor). Time-resolved pump-probe photoemission measurements reveal that the SPV for pristine cleaved surfaces is enhanced by K adsorption, but suppressed by C60 adsorption, and yet the SPV relaxation time is substantially shortened in both cases. Evidently, adsorbate-induced electronic states act as electron-hole recombination centers that shorten the carrier lifetime.