Dark Current Analysis Research Articles

Growth and Dark Current Analysis of GaSb- and InP-Based Metamorphic In0.8Ga0.2As Photodetectors.

Short-wavelength infrared photodetectors based on metamorphic InGaAs grown on GaSb substrates and InP substrates are demonstrated. The devices have a pBn structure that employs an AlGaAsSb thin layer as the electron barrier to suppress dark current density. The strain effect on the electrical performance of the devices was specifically studied through the growth of the pBn structure on different substrates, e.g., InP and GaSb, via a specific buffering technique to optimize material properties and minimize dark current. A lower device dark current density, down to 1 × 10-2 A/cm2 at room temperature (295 K), was achieved for the devices grown on the GaSb substrate compared to that of the devices on the InP substrate (8.6 × 10-2 A/cm2). The improved properties of the high-In component InGaAs layer and the AlGaAsSb electron barrier give rise to the low dark current of the photodetector device.

Analysis of dark current and detectivity of CdS/ZnSe Based multiple quantum well photodetector for mid-infrared applications

Analysis of dark current and detectivity of CdS/ZnSe Based multiple quantum well photodetector for mid-infrared applications

Theoretical and Experimental Investigation of Barrier‐Energy‐Dependent Charge Injection Mechanisms in Organic Photodetectors

AbstractCharge injection is known as the major source of dark current under an applied reverse bias, which directly influences the performance of organic photodetectors with diode architecture. However, it is unclear which of various contributions, such as electron flow through the junction, shunt leakage, thermionic emission, and tunnelling, are dominant. This study investigates the thermionic emission and tunneling models to describe the origin of experimentally measured dark current generated in an organic photodetector. To elucidate the dominant mechanism, the barrier energies at anodic contacts are set from 0.6 to 1.0 eV using photosensitive layers composed of different acceptors. A linear relation is found between the natural logarithm of the dark current density under reverse bias and the square root of the barrier height, which strongly suggests direct tunneling as dominant mechanism for dark current injection. This conclusion is strengthened by temperature dependent dark current analysis. Further knowledge of the dominant mechanism by charge injection can help devise an effective strategy to suppress dark current for effective organic photodetector device implementation.

Physical engineering of anti‐solvents in perovskite precipitation for enhanced photosensitive affinity

For the development of the perovskite formation process, it is necessary to explore the principle of fabricating the photosensitive layer. Herein, a novel perspective on the physical properties of anti-solvents is proposed, which is related to perovskite crystallization. Specifically, we focus on aromatic solvents with different functional groups as anti-solvents (methylbenzene (MB) and chlorobenzene (CB)). This is because the precursor solubility depends on the interactions with each solvent, which is closely observed via FT-IR. In this context, the interfacial affinity of thin perovskite layer induced uniform morphology of electron transport layer (ETL). This phenomenon is characterized by FE-SEM, AFM, and XRD in detail. Based on these data, CB-treated perovskite photodetector exhibits superior detectivity and fast response speed owing to better interfacial affinity between perovskite and ETL. Also, improved charge dynamic behavior (dark current and impedance analysis) was observed in CB-treated condition. Therefore, it is demonstrated that the selection of anti-solvent is important to optimize morphological affinity between perovskite and interlayer in fabricating thin photosensitive layer, which contributes to realization of fast and highly sensitive photodetector.

Dark current simulation and analysis for InAs/GaSb long wavelength infrared barrier detectors

The authors reported a heterojunction dark current simulation method for InAs/GaSb long wavelength infrared barrier detectors. Calculations using the dark current model with energy band offset have shown that the theoretical and experimental data of the model are highly consistent. The energy band offsets of absorption and barrier region in the detectors were calculated by the 8-band k·p method. Then, the dark current model of heterojunction was established and compared with the homojunction model previously adopted. The agreement between the theoretical predictions and the experimental measurement led us to propose a barrier device structure with low dark current in long wavelength infrared domain. The results show that under a small reverse bias (V < -100 mV), the G-R and surface leakage current dominate, while the tunneling dark current occupies a leading position with a large bias (V > -320 mV) at 77 K. The dark current density under −10 mV bias voltage is 1.16 × 10-4A/cm2.

The Role of Noise in Specific Detectivity of InAs/GaSb Superlattice MWIR Bariodes.

In this paper, the results of the electrical, noise, and optical characterization of p-i-n and p-B-i-n diodes with AlSb and 4 ML AlSb/8 ML GaSb superlattice barriers in High-Operating Temperature conditions, are presented. Experimental and theoretical noise parameters were compared. Both dark current and noise analysis showed that the p-Bp_bulk-i-n bariode had the best performance. P-i-n photodiodes had the highest experimental value of specific detectivity (D*) of 6.16 × 109 Jones at 210 K and zero bias. At about −1 V reverse bias, the bariode with AlSb/GaSb electron barrier caught up to it and both devices achieved D* = (1–1.1) × 108 Jones. Further optimization of the superlattice-based electron barrier should result in the improvement of bariode performance at a smaller bias, at which better noise performance is more pronounced. It was shown that neglecting the low-frequency noise component can lead to a significant overestimation of detectivity. The simple method of incorporation of low-frequency noise contribution in the detectivity calculation, without time-consuming measurements, has been proposed.

Substitutionally Doped MoSe2 for High-Performance Electronics and Optoelectronics.

2D materials, of which the carrier type and concentration are easily tuned, show tremendous superiority in electronic and optoelectronic applications. However, the achievements are still quite far away from practical applications. Much more effort should be made to further improve their performance. Here, p-type MoSe2 is successfully achieved via substitutional doping of Ta atoms, which is confirmed experimentally and theoretically, and outstanding homojunction photodetectors and inverters are fabricated. MoSe2 p-n homojunction device with a low reverse current (300 pA) exhibits a high rectification ratio (104 ). The analysis of dark current reveals the domination of the Shockley-Read-Hall (SRH) and band-to-band tunneling (BTB) current. The homojunction photodetector exhibits a large open-circuit voltage (0.68 V) and short-circuit currents (1 µA), which is suitable for micro-solar cells. Furthermore, it possesses outstanding responsivity (0.28 A W-1 ), large external quantum efficiency (42%), and a high signal-to-noise ratio (≈107 ). Benefiting from the continuous energy band of homojunction, the response speed reaches up to 20 µs. Besides, the Ta-doped MoSe2 inverter exhibits a high voltage gain (34) and low power consumption (127 nW). This work lays a foundation for the practical application of 2D material devices.

The optoelectronic behavior of reduce graphene oxide-carbon nanotube nanocomposites

Graphene-carbon nanotubes (CNTs) nanocomposites hold tremendous potential to offer more innovative and cost-effective electronic technologies. In this study, type of CNTs employed to form composites with reduced graphene oxide (rGO) were single walled carbon nanotubes (SWCNTs), multiwalled carbon nanotubes (MWCNTs), and mixed CNTs (blends of SWCNTs and MWCNTs). The composites were further utilized to fabricate the planar heterojunction devices. Field emission scanning electron microscopy, UV-Vis and Raman spectroscopy of the synthesized nanocomposites were performed to investigate the surface morphology, absorption behavior and structure, respectively. On comparing the optoelectronic performance of devices, we found that mixed CNTs-rGO nanocomposite-based devices exhibited greater responsivity and detectivity compared to those of SWCNTs and MWCNTs based devices. The superior performance is mainly ascribed to the better immunity of the mixed CNTs-rGO nanocomposite-based devices against the charge recombination due to the better interface quality and lesser interface defects, as inferred from the dark current analysis and impedance spectroscopy analysis. This work demonstrates the great potential of mixed CNTs-rGO composites as an active layer material for optoelectronic applications.

Dark current analysis of an InAs/GaSb type II superlattice infrared photodiode with SiO2 passivation

In this study, we present the current–voltage (I–V) characteristics of a 10 ML InAs/10 ML GaSb type-II superlattice (T2SL) with p-i-n structures for mid-infrared detection. At a negative bias and a temperature of 50 mV and 77 K, respectively, the cut-off wavelength of the fabricated T2SL photodiode with SiO2 passivation on the mesa side wall was approximately 5.6 μm, and the dark current density was found to be 1.9 × 10–5 A/cm2. The bulk dark current model was adopted in this study to obtain the measured values by modeling, assuming the generation-recombination lifetime of the carrier to be approximately 60 ns, and considering the surface leakage current, as well as the four dark current mechanisms. At low operating temperatures, we inferred that the T2SL photodiode was limited by the effects of surface leakage, whereas the effects of the band-to-band and diffusion components of the dark current were negligible. Therefore, reducing the surface leakage current to obtain high-performance detectors requires the development of advanced passivation materials and technology.

Dark current analysis of p-i-n NiO/BiTiO3/ZnO thin film heterojunction diode

Dark current analysis of fabricated NiO/BiTiO3/ZnO heterojunction thin film p-i-n diode is demonstrated in this paper. The diodes layers; p-type NiO, i-type BiTiO3 and n-type ZnO were fabricated by using a sol-gel method on glass substrates. This method is the most practical techniques used for manufacturing the nanostructured thin films of metal oxide and perovskite semiconductors. The electrical characteristics of the vertical p-i-n diode were investigated using current-voltage characterization at room ambient in dark condition. The parameters, for example, threshold voltage, rectifying ratio, ideality factor, junction resistance and leakage current, were extracted from the measured data. The turn on voltage, ideality factor, saturation current, junction series resistance, and junction shunt resistance were estimated to be 0.6 V, 6.1, 8×10-7 A, 40 Ω and 760 Ω, respectively. The effect of post-fabrication heat treatments on electrical properties has been studied. The optimum temperature at 100°C that improves the device performance. The performance enhancement attributed to the interface improvement of the between the aluminum contact and p-i-n thin films. With respect as-deposited p-i-n devices, the heat-treated diodes performance parameters such as threshold voltage, ideality factor and leakage current of devices are found to improve by 5%, 47.3%, and 63.3%, respectively. The rectification performance of the device was 13.6 at 100°C and degrades after the temperature reached 125°C attributed to new material phases appears at interfaces.

UV–Visible photo sensing properties of CdS-porous silicon (PS): P-Si and ZnO-PS: p-Si heterostructures metal-semiconductor-metal (MSM) based devices

Present work reports fabrication of metal-semiconductor-metal (MSM) [1] devices based on CdS-PS: p-Si and ZnO-PS: p-Si heterostructures for photo sensing applications. Field Emission Scanning Electron Microscope (FESEM) analyses confirm growth of hierarchical flower like nanostructured CdS and spherical shaped nanostructured ZnO layers of uniform thicknesses ∼170 and 160 nm respectively on PS: p-Si substrate. UV–visible absorbance spectra for CdS and ZnO nanostructures provide optical band gap of 2.6 and 3.3 eV respectively. Photoluminescence (PL) spectra analyses of the heterostructures show near band edge (NBE) emissions of nanostructured CdS at ∼450–482 nm for CdS-PS: p-Si and at ∼378–398 nm of nanostructured ZnO for ZnO-PS: p-Si along with characteristic PL peaks of PS at ∼600 nm [2] and some trap/defect assisted luminescence bands. Dark current analyses of the heterostructures give values of ideality factors (n) of 3.4 and 4.4 respectively. Heterostructures under increasing illumination intensity (17–71 µW cm−2, 400 nm) show almost symmetric rectification enhancement for positive and negative bias condition with maximum photo to dark current ratio (Iph/Id) of 10.3 and 34.3 respectively at −2 V bias. ZnO-PS: p-Si heterostructure shows superiority for UV–Visible photo sensing application in terms of high responsivity ∼2.6 AW−1, high EQE ∼800% and response time of ∼1.12 sec compared to ∼0.6 AW−1, 180% and 0.16 sec of CdS-PS: p-Si respectively at biasing of −2 V.

Mid-wavelength interband cascade infrared photodetectors with two and three stages

In this paper, we report design, fabrication and characterization of mid-wavelength interband cascade infrared photodetectors (ICIP) with two- and three-stage. The effects of stage number and absorber thickness on the optical and electrical properties of the device are studied. Dark current analysis shows that the shunt current of the three-stage ICIP is lower than that of the two-stage ICIP. The temperature-dependent quantum efficiencies of the two devices are analyzed and the diffusion lengths are simulated. The optimal absorber thicknesses of the ICIP structure are calculated for the further improvement of the device performance.

Improved Efficiency of Perovskite Solar Cells Using a Nitrogen-Doped Graphene-Oxide-Treated Tin Oxide Layer.

Tin oxide (SnO2) is widely adopted as an electron transport layer in perovskite solar cells (PeSCs) because it has high electron mobility, excellent charge selective behavior owing to a large band gap of 3.76 eV, and low-temperature processibility. To achieve highly efficient SnO2-based PeSCs, it is necessary to control the oxygen vacancies in the SnO2 layer, since the electrical and optical properties vary depending on the oxidation state of Sn. This study demonstrates that the performance of PeSCs may be improved by using nitrogen-doped graphene oxide (NGO) as an oxidizing agent for SnO2. Since NGO changes the oxidation state of the Sn in SnO2 from Sn2+ to Sn4+, the oxygen vacancies in SnO2 can be reduced using NGO. Multiple devices are fabricated, and various techniques are used to assess their performance, including X-ray photoelectron spectroscopy, dark current analysis, and the dependence of the open-circuit voltage on light intensity. Compared with the average power conversion efficiency (PCE) of control devices, PeSCs with SnO2:NGO composite layers exhibit greater PCEs with less deviation. Therefore, the introduction of NGO in a SnO2 layer can be regarded as an effective method of controlling the oxidation state of SnO2 to improve the performance of PeSCs.

Investigation of performance of P3HT:PCBM organic photovoltaic module under real operating conditions

In this work the behavior of an organic solar module operating under real solar radiation conditions is presented. This allows to understand which parameters limit the efficiency of an organic device and their underlying mechanisms. The characterization of a module, produced by CSEM Brasil, with active layer P3HT:PCBM, is based on instantaneous voltage and current curves, dark current curves and analysis of the module operating continuously with fixed voltage. This allows to extract the parameters of the equivalent circuit of the module, such as diode saturation current (I0), series resistance (RS) and shunt resistance (RSH) as well as to understand the influence of different levels of radiation and temperature on such parameters. The work presented was performed by using a commercial organic solar module in extensive outdoor experiments. The results are based on continuous use and for several levels of radiation and temperature under real operating conditions in comparison with a theoretical model for the first time. With the continuous tests it was possible to demonstrate the average daily generation of the module in Wh/m2, and also to verify experimentally, that the module presents better efficiency for diffuse radiation.

Mid-Wave Infrared InAs/GaSb Type-II Superlattice Photodetector With n-B-p Design Grown on GaAs Substrate

In this paper, we report the direct growth and characterization of a mid-wave infrared InAs/GaSb type-II superlattice n-B-p photodetector on a GaAs substrate. The design consists of an n-doped contact, a wide bandgap unipolar barrier, and a p-doped absorber, which uses photogenerated electron as minority carriers to enjoy the longer electron diffusion length compared with hole diffusion length. At 77 K, the device exhibits a dark current density of $2.9\times 10^{-5}$ A/cm2 under −0.1 V and a zero-bias differential-resistance-area product (R0A) in excess of $8\times 10^{3}~ \Omega \cdot \text {cm}^{2}$ . Arrhenius analysis of dark current demonstrates that the dominant mechanism is diffusion at a temperature higher than 130 K. 50% cutoff wavelength of the detector is found at $6.4~\mu \text{m}$ at 77 K under zero bias, with a peak responsivity of 0.56 A/W. The corresponding specific detectivity is $7.6\times 10^{11}~\text {cm}\cdot \text {Hz}^{1/2}$ /W. The key device parameters which limit the further optimization of performance are discussed.

A comparative analysis of the optoelectronic performance of conventional and inverted design organic photodetectors

In this report, we present the comparison of the optoelectronic performance of conventional and inverted organic photodiodes (OPDs) based on the blended active layer of p-type poly (3-hexylthiphene) (P3HT) and n-type fullerene C70. The absorption and Raman studies of the blend film confirm the presence of both the constituents in prepared blends. The inverted design OPD demonstrates large photocurrent, responsivity, and detectivity than conventional OPD. The difference in the observed performances is explained by dark current and impedance spectroscopy (IS) analysis. The higher performance observed in inverted design is attributed to the improvement in charge extraction and collection, which is possibly resulting from the favorable vertical phase separation in the P3HT:C70 blends. Higher current levels under dark condition along with lesser ideality factor observed in the case of inverted OPD is in good agreement with the vertical morphology modification. The IS analysis also validate that the improved charge transport and collection enhances the performance of inverted design OPD.

Demonstration of Si based InAs/GaSb type-II superlattice p-i-n photodetector

In this paper, mid-wave infrared photodetection based on an InAs/GaSb type-II superlattice p-i-n photodetector grown directly on Si substrate is demonstrated and characterized. Excitation power dependence on integrated intensity from the photoluminescence measurements reveals a power coefficient of P ∼ I0.74, indicating that defects related process is playing an important role in the predominant recombination channel for photogenerated carriers. At 70 K, the device exhibits a dark current density of 2.3 A/cm2 under −0.1 V bias. Arrhenius analysis of dark current shows activation energies much less than half of the active layer bandgap, which suggests that the device is mainly limited by surface leakage and defect-related generation-recombination, consistent with the photoluminescence analysis. The detector shows 50% cutoff wavelength at ∼5.5 µm at 70 K under bias of −0.1 V. The corresponding peak responsivity and specific detectivity are 1.2 A/W and 1.3 × 109 cm∙Hz1/2/W, respectively. Based on these optoelectronics characterization results, reduction of defects by optimizing the III/V-Si interface and material growth quality are argued to be the main factors for performance improvement in this Si-based T2SL detector towards low cost, large-format MWIR detection system on Si photonics platform.

Photo sensing property of nanostructured CdS-porous silicon (PS):p-Si based MSM hetero-structure

Present work reports light sensing property of metal–semiconductor–metal device based on nanostructured CdS-PS:p-Si hetero-structure. PS with thickness of ~ 1500 nm is prepared on p-Si (100) oriented wafer using electrochemical anodization method. Thin nanostructured n-CdS layer of ~ 170 nm is deposited on PS:p-Si substrate by vacuum evaporation. FESEM observation confirms growth of hierarchical flower like CdS nanostructure on PS:p-Si substrate. UV–Vis absorption spectrum gives bandgap of CdS nanostructure to be 2.6 eV. Reflectance measurement of CdS-PS:p-Si hetero-structure shows multiple interference pattern within the spectral range of 200–800 nm, with remarkable blue shift of the pattern compared to that of PS:p-Si structure. Photoluminescence study of the hetero-structure reveals presence of various luminescence bands peaked at ~ 450, 460, 468, 482, 560, and 590 nm. Dark current (Id) analysis shows low leakage current ~ 32 nA at − 2 V with ideality factor (n) and reverse saturation current (Is) values of 1.57 and 0.2 nA respectively. Spectral response of the hetero-structure at a bias voltage of − 2 V and irradiation wavelength of 400 nm shows maximum responsivity (Rλ) value of ~ 0.6 AW−1 and external quantum efficiency of ~ 180%. Response and recovery times of the device are ~ 160 and ~ 350 ms respectively. The prepared hetero-structure has been compared with other silicon based optoelectronic switching devices to find suitability of an alternate choice.

High performance CdSe quantum dot sensitized ZnO solar cell fabricated from ion exchange

We report on a facile and efficient way to prepare CdSe/ZnO photoanode for quantum dot sensitized solar cell (QDSSC). CdSe/ZnO is achieved through a two-step ion exchange process in aqueous solution at lower temperature. SEM, light absorption, dark current and impedance spectroscopy analyses revealed that this process of ion exchange can form not only higher amount and larger sized QDs on ZnO that lead to the enhancement of light harvesting, but also full coverage of QDs on ZnO as well as excellent QD/ZnO interfaces that contribute to the suppression of charge recombination. In combination with ZnSe overcoating, QDSSC assembled with the CdSe/ZnO photoanode exhibits high cell efficiency of 5.08%.

Room temperature operation of mid-infrared InAs081Sb019 based photovoltaic detectors with an In02Al08Sb barrier layer grown on GaAs substrates

In this paper, InAs0.81Sb0.19-based hetero-junction photovoltaic detector (HJPD) with an In0.2Al0.8Sb barrier layer was grown on GaAs substrates. By using technology computer aided design (TCAD), a design of a barrier layer that can achieve nearly zero valance band offsets was accomplished. A high quality InAs0.81Sb0.19 epitaxial layer was obtained with relatively low threading dislocation density (TDD), calculated from a high-resolution X-ray diffraction (XRD) measurement. This layer showed a Hall mobility of 15,000 cm2/V⋅s, which is the highest mobility among InAsSb layers with an Sb composition of around 20% grown on GaAs substrates. Temperature dependence of dark current, photocurrent response and responsivity were measured and analyzed for fabricated HJPD. HJPD showed the clear photocurrent response having a long cutoff wavelength of 5.35 μm at room temperature. It was observed that the dark current of HJPDs is dominated by the diffusion limited current at temperatures ranging from 200K to room temperature from the dark current analysis. Peak responsivity of HJPDs exhibited the 1.18 A/W and 15 mA/W for 83K and a room temperature under zero bias condition even without anti-reflection coating (ARC). From these results, we believe that HJPDs could be an appropriate PD device for future compact and low power dissipation mid-infrared on-chip sensors and imaging devices.