Photocapacitive Response Research Articles

Conformal Broad‐Spectra Laser Sensing Array from Ferroelectric Polymer Composites

AbstractPhotoelectric sensors based on charge‐coupled device (CCD) and complementary‐metal‐oxide‐semiconductor (CMOS) used to be planar image sensors due to the rigidity of the base materials. Moreover, they are limited to a narrow reaction wavelength range. Here, a conformal broad‐spectra laser sensor based on a flexible metal‐ferroelectric‐metal photocapacitor is promoted. The photocapacitance signal is attributed to the photothermal effect of copper (Cu) electrode and gold nanoparticles (Au NP), and the temperature‐dependent property of the dielectric constant of poly(vinylidene fluoride‐trifluoroethylene) (PVDF‐TrFE). Cu/PVDF‐TrFE/Cu and Cu/Au NP@PVDF‐TrFE/Cu flexible photocapacitors have a reliable photocapacitive response from −60 to 60 °C. Meanwhile, both photocapacitors respond from 265 to 980 nm due to the absorption of light by the composite structure, which can be used for broad‐spectra photodetection. The addition of a small amount of Au NP (0.05 vol%) effectively improves the photoresponsiveness of the device. Real‐time photodetection is realized on a hemispherical surface, and these photocapacitors with conformal characteristics are expected to gain application in an omnidirectional broad‐spectra laser alarming system.

Photo-induced defects in MAPbBr3 single crystals

Single crystals of hybrid organic–inorganic halide perovskite have exhibited significantly good stability and a low trap density, leading to advantageous applications in optoelectronics. Even with recent development of high-quality perovskite single crystals, a defect analysis should be addressed to improve device performance in addition to understand the interaction between photo-generated carriers and defects. In this paper, we present a photo-induced defect characterization of CH3NH3PbBr3 (MAPbBr3) perovskite single crystals using an interpretation of photo-current and photo-capacitance measurement. The bulk and the interfacial defect densities of MAPbBr3 crystals with a gold electrode are examined by the characterization of photo-capacitive response under three different wavelengths of light. The transient photo-response of the single crystals reveals the occurrence of carrier trapping and a recombination process. The photo-response under the various light conditions provides a possible origin of defects in MAPbBr3 single crystals. Our comprehensive optoelectronic analysis provides the establishment of the link between the carrier transport and device performance depending on the illuminations. The fundamental understanding of photo-induced defects in perovskites can be helpful to realize the origin of electrical loss and develop highly efficient optoelectronic devices.

Organic Semiconductors for Optically Triggered Neural Interfacing: The Impact of Device Architecture in Determining Response Magnitude and Polarity

The use of organic semiconductor devices as photocapacitors is an innovation with promising applications in neural interface technologies, particularly for retinal prosthetics. Here we report the characterization of four distinct photocapacitor device architectures that were fabricated by depositing ultra-thin layers of poly-3-hexylthiophene and C60 fullerene in various combinations on tin-doped indium oxide (ITO) electrodes. We used electrophysiological recordings to measure the intrinsic photoresponse at 470 nm, and also to determine light-induced voltage perturbations in electrolyte solutions interfaced with these semiconductors. We also determined the light-induced intracellular voltage changes in co-cultured sensory neurons. Electrochemical impedance spectroscopy was used to establish the photocapacitive response mechanism of the intracellular changes upon illumination. The largest amplitude photocapacitive response was elicited from a neuron/acceptor-donor bilayer/ITO device architecture, whilst reversing the donor and acceptor layer order enabled a neuron response of the opposite polarity. The photoresponse in the neuron/acceptor/donor/ITO bilayer device configuration was significantly enhanced in both amplitude and time duration by electrical grounding of the indium tin oxide layer. We describe the advantages and limitations of each configuration of these device and discuss pathways towards the creation of optically triggered neural interfaces that do not require an external electrical power supply.

Optical Beam-Based Defect Localization Methodologies for Open and Short Failures in Micrometer-Scale 3-D TSV Interconnects

We report laser-based fault isolation methodologies for the localization of open and short failures in $1 \times 5\,\,\mu \text{m}$ via-last through-silicon via (TSV) structures for 3-D system-on-chip (SoC) integration. Due to the photosensitive TSV interconnect capacitance, observation of the photocapacitance response enables nondestructive localization of metallization ruptures. A light-induced capacitance alteration (LICA) measurement is demonstrated on an open failed $1 \times 5\,\,\mu \text{m}$ TSV chain structure with a manufacturing defect. We validate our measurements with active voltage contrast imaging in the scanning electron microscope (SEM) and focused-ion beam (FIB) cross sectioning. Second, TSV dielectric defects generating leakage current between TSV and substrate (i.e., short defects) are detected and localized by sensing the laser-induced TSV photocurrent. An optical beam-induced current (OBIC) measurement is demonstrated on electrically overstressed TSV array structures whereby multiple TSVs are configured in a parallel arrangement. By applying a selective substrate removal process, we can expose the full TSV array and perform optical and tilted SEM inspection and reveal pinhole defects in the TSV liner. We further investigate the effect of breakdown energy on the pinhole formation, relate electrical measurements to SEM inspection, and confirm our results by FIB cross sectioning.

Defect localization of metal interconnection lines in 3-dimensional through-silicon-via structures by differential scanning photocapacitance microscopy

We report a differential scanning photocapacitance microscopy technique based on the detection of light-induced capacitance changes allowing mapping of metal interconnection line defects in through-silicon-via (TSV) structures used in three-dimensional (3-D) integration technology. Due to the photosensitive silicon depletion capacitance, observation of the photocapacitance response enables non-destructive two-dimensional (2-D) visualization of metallization line ruptures in TSV structures. We demonstrate the application of the proposed method on a TSV chain structure and reveal the location of the open metallization rupture.

Photo-response of a P3HT:PCBM blend in metal-insulator-semiconductor capacitors

Metal-insulator-semiconductor capacitors are investigated, in which the insulator is cross-linked polyvinylphenol and the active layer a blend of poly(3-hexylthiophene), P3HT, and the electron acceptor [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Admittance spectra and capacitance-voltage measurements obtained in the dark both display similar behaviour to those previously observed in P3HT-only devices. However, the photo-capacitance response is significantly enhanced in the P3HT:PCBM case, where exciton dissociation leads to electron transfer into the PCBM component. The results are consistent with a network of PCBM aggregates that is continuous through the film but with no lateral interconnection between the aggregates at or near the blend/insulator interface.

Nickel Phthalocyanine-Based Sandwich-Type Photocapacitive Illumination Sensors for Environmental Monitoring

In this paper, the properties of organic semiconductor nickel phthalocyanine (NiPc)-based photocapacitive illumination sensors are reported. Thin films of NiPc and aluminum were deposited sequentially by vacuum evaporation on ITO-coated glass substrates to form ITO/NiPc/Al sensors with different thicknesses of NiPc, i.e., 50, 100 and 150 nm. The effective surface area of each cell was 80 mm2 (8 × 10 mm). The cells were then annealed at 150°C for 2 h under ambient conditions to improve the uniformity of the films. The effects of film thickness and illumination with a filament lamp on the capacitance of the sensors were studied. Under filament lamp illumination of up to 2,000 lx the relative photocapacitance of the sensors increased by 50%. It was assumed that the photocapacitive response of the sensors is associated with polarization caused by the transfer of photogenerated electrons and holes. The illumination-dependent capacitance properties of these sensors make them attractive for use in multimeters and instruments for environmental monitoring of illumination.

Optoelectronic Properties of <i>Vanadyl phthalocyanine</i> Based Organic-Inorganic Hybrid Devices

The Optoelectronic properties of organic-inorganic hybrid devices consisting of Ag/VOPc/n-Si/Ag structure have been investigated through analyzing the current-voltage characteristics. We have also studied the effect of illumination on the open circuit voltage, capacitance and reverse resistance with consideration of VOPc film thickness. The dark I-V characteristics display rectification behaviour of such hybrid structures and a very high photo-capacitive response under illumination of 200 lx is observed. Furthermore due to the generation of photo induced charges, under illumination, the decrease in reverse bias resistance to one third of its value is observed.

Cu(II) 5,10,15,20-tetrakis(4-isopropylphenyl) porphyrin based photo capacitive Detectors

Abstract:In this study a photosensitive organic semiconductor Cu(II) 5,10,15,20-tetrakis(4􀆍-isopropylphenyl) porphyrin (CuTIPP) was synthesized and investigated as an activematerial in photocapacitive detectors. Thin films of the CuTIPP were deposited bysublimation on a glass substrate with preliminary deposited metal electrodes andAl/CuTIPP/Al and Au/CuTIPP/Au surface type photocapacitive detectors werefabricated. Thickness of the CuTIPP films was equal to 100 nm in the Al/CuTIPP/Aland Au/CuTIPP/Au detectors. Length and width of the semiconducting channel betweenmetallic electrodes were equal to 40 􀈝m and 15 mm, respectively. It was observed thatunder filament lamp illumination of up to 4000 lx the capacitance of the Al/CuTIPP/Aland Au/CuTIPP/Au photocapacitive detectors increased by 2.6 and 2.2 times,respectively, with respect to the dark conditions. The photoconductivity of the detectorsincreased with illumination as well. It is assumed that the photocapacitive response ofthe detectors is associated with polarization occurring due to the transfer of photogeneratedelectrons and holes. The equivalent circuit of the photocapacitive detectors ispresented. Data obtained by simulation showed reasonable matching with experimentalresults.

Humidity and illumination organic semiconductor copper phthalocyanine sensor for environmental monitoring

In this investigation properties of organic semiconductor copper phthalocyanine (CuPc) capacitive humidity and illumination sensors were studied. Organic thin film was deposited by vacuum evaporation on a glass substrate with silver surface-type electrodes to form the Ag/CuPc/Ag sensor. The capacitance of the samples was evaluated at room temperature in the relative humidity range of 35-92%. It was observed that capacitance of the Ag/CuPc/Ag sensor increases with increase in humidity. The ratio of the relative capacitance to relative humidity was about 200. It is assumed that in general the capacitive response of the sensor is associated with polarization due to absorption of water molecules and transfer of charges (electrons and holes). It was observed that under filament lamp illumination of up to 1,000 lx the capacitance of the Ag/CuPc/Ag photo capacitive detectors increased continuously by 20% as compared to dark condition. It is assumed that photo capacitive response of the sensor is associated with polarization due to transfer of photo-generated electrons and holes. An equivalent circuit of the Ag/CuPc/Ag capacitive humidity and illumination sensor was developed. Humidity and illumination dependent capacitance properties of this sensor make it attractive for use in humidity and illumination multi-meters. The sensor may be used in instruments for environmental monitoring of humidity and illumination.

Photo-capacitance response of internal tunnelling coupling in quantum-dot-imbeddedheterostructures under selective photo-excitation

Under selective photo-excitation, the capacitance response of internal tunnellingcoupling in quantum-dots-imbedded heterostructures is studied to clarify theelectronic states and the number densities of electrons filling in the quantumdots (QDs). The random nature for both optical transitions and the fillingin a QD assembly makes highly resolved capacitance peaks appear in theC–V characteristic after turning off the photo-excitation.

Photocapacitance effect at low temperatures in a unipolar MIS capacitor with a semiconductor electrode doped with two different acceptor impurities

The photocapacitance effect at low temperatures in a unipolar MIS capacitor with a semiconductor electrode doped with two types of acceptor impurities characterized by different ionization energies E ia (deep-level acceptor) and E ib (shallow-level acceptor) is examined theoretically. It is shown that the photocapacitance response of such a capacitor arises in a relatively narrow range of bias voltages. The maximum of the response at a constant bias depends on the temperature as exp(E ia /kT). An infinite increase in the photocapacitance response is related to the singularity that appears with decreasing temperature in the bias-voltage dependence of the ionized acceptor concentration. The capacitance and photocapacitance characteristics for a structure with a silicon electrode doped with In and B are calculated.

Experimental evidence of boron induced charged defects in amorphous silicon materials

We present an experimental proof of the existence of charged defects related to boron diffusion at the p–i interface of single junction amorphous silicon solar cells. Two different test devices were manufactured substituting the intrinsic absorber layer of a standard p–i–n structure with a boron lightly doped layer or a microcompensated region. Presence of trap states lying around 0.3–0.4 eV above the valence band was demonstrated through spectral photocapacitance response under medium infrared radiation and through capacitance versus frequency measurements that show the typical response of trapping kinetics process. Differences in the experimental results between our test devices and standard p–i–n solar cells show that boron atoms are the main cause of charged defect formation.

Photocapacitive effects at silicon-collodion-gold contacts

The paper describes the photocapacitive response of silicon-collodion-gold contacts in the visible and near-infrared regions. The principal light effects are shown to be associated with the lateral diffusion of light-generated minority carriers under the gold electrode. They are therefore essentially edge effects. Factors governing spectral response and sensitivity are discussed.