Reverse Bias Conditions Research Articles

Facile assembly of SnO2 thin film-based Al/SnO2/Al device for sensing of 260 nm UVC and 365 nm UVA radiation

An Al/SnO2/Al metal-semiconductor-metal (MSM) device was formed by depositing a ~55nm thin film of SnO2 on Si substrate. Structural, surface morphology and optical properties of the SnO2 film were studied. The current-voltage (I-V) characteristics of the device were recorded under the dark condition followed by 260 nm-UVC and 365 nm-UVA illumination conditions. Under the dark condition, the device shows a resistivity of 8.05 Ωcm at V=1.5V bias voltage. The device produces nearly symmetric rectifying-type I-V characteristics under forward and reverse bias conditions. The electrical properties of the device were explained using back-to-back Schottky diode model. Under the dark condition, the ideality factor of the junction under forward and reverse bias were estimated to be 1.08 and 1.72 respectively. The external quantum efficiency of the device under UVC was found to be ~518.72% and specific detectivity reached as high as 1.03×109 Jones at 2.0V with a response time of ~1s. The device showed a high signal-to-noise ratio between 0.5 and 1.5V bias voltages. The values of the ideality factor being greater than 1 was attributed to the presence of point defects in the SnO2 layer as verified by photoluminescence study. This study reveals that the device could be used as a UVC and UVA sensor at a relatively low bias voltage of ~1.5V.

Design strategies and systematic analysis of GaN vertical MPS diodes with T-shaped shielding rings

Abstract We report gallium nitride (GaN) vertical merged pn-Schottky (MPS) diodes with T-shaped p-GaN shielding rings (SRs). The embedded T-shaped SR features an overlapped depletion region by the lateral and vertical p n junctions under reverse bias condition, which can effectively enhance the charge coupling effect and homogenize the 2-D electric field distribution. In the meantime, the incorporation of the T-shaped SRs can minimize unnecessary depletion of the vertical conduction channel and guarantee a decent current spreading through the drift region. The impact of the key design parameters on the reverse breakdown and forward conduction performance are investigated systematically. We found that the doping concentration and the geomatical shape of the T-shaped p-GaN SRs are closed related to the electric field distribution and forward current conduction behavior, which determines the reverse breakdown and forward conduction performance. With optimum design parameters of the T-shaped SRs, the breakdown voltage of the MPS diodes features a dramatic improvement to 2749 V from 1123 V in conventional MPS diodes. The results can provide a design strategy for high performance vertical GaN power diodes towards high-power and high-frequency applications.

On analysis of structural and optical absorption characterization of Bi35Sb5Se60 nanostructured thin films for photosensing application

In this extensive study, the primary focus is directed towards the intricate exploration of the optical absorption characteristics inherent in nanostructured Bi35Sb5Se60 thin films, prepared by thermal evaporation under a vacuum of 10−5 Torr, ensuring high purity and uniformity for optoelectronic applications. With a particular emphasis on their prospective application in photosensing devices. The research employs a comprehensive approach, integrating various spectrophotometric measurements that encompass both transmission and reflection analyses. The meticulous examination of the absorption edge characteristics reveals a direct energy gap of 1.82 eV, providing a foundational understanding of the material's electronic structure. The determination of the dispersion energy at 6.35 eV and the oscillator energy at 2.96 eV further enriches the understanding of the material's optical behavior, shedding light on its capacity to interact with incident light. A noteworthy highlight emerges with the identification of high photosensitivity exhibited by the heterojunction, particularly under lower reverse bias conditions, underscoring its potential utility in photosensing applications. The PL spectra reveal a highly broadened defect emission band with peaks at 475 nm, 490 nm, and 540 nm, providing insights into the recombination processes within the material. The identification of emission peaks related to the conduction band edge and acceptor levels further enhances the comprehension of the material's optical and electronic characteristics. underscores the potential of these nanostructured thin films for efficient photosensing devices. The findings presented in this research not only advance the understanding of the material's properties but also lay a robust foundation for further research and development in the design and optimization of photoresponsive devices within the realm of optoelectronic technologies.

A Unique Failure Mode of SiC MOSFETs under Accelerated HTRB

Device lifetime under reverse bias conditions is an important reliability concern for SiC devices. Provided that the termination structure is well designed, device failure in the active cell is driven by gate oxide breakdown due to the high field in the semiconductor and gate dielectric. For planar MOSFETs, the largest field occurs in the JFET region [1,2]. Standard HTRB testing is insufficient to estimate failure rates under operating conditions and hence testing under accelerated off-state conditions (ALT-HTRB) is required. This paper provides data, statistical analysis, failure analysis and finally a Weibull statistics-based temperature, Vd and stress time dependent model.

Single Event Effects in 3.3 kV 4H-SiC MOSFETs due to MeV Ion Impact

In this work, MeV alpha particles generated from an accelerator are used to study single event breakdown (SEB) in 4H-SiC MOSFET samples, rated at 3.3 kV. The samples are exposed to bursts of alpha particles under reverse bias conditions to investigate the SEB sensitivity to ion energy and reverse bias. The energies of alpha particles are chosen to reach different depths in the drift region of the MOSFET devices, and also to penetrate the whole drift region. Forward and reverse characteristics are measured after each exposure, as long as no failures occur, to ensure that the device performance is maintained. The measurements show that no significant effects are observed on the drain-source leakage current, while minor effects on gate behavior can be seen as a function of accumulated fluence. Furthermore, SEB can only be triggered with a reverse bias larger than, or equal to 3 kV. A standard MOSFET cell with a similar rated voltage is also simulated in Sentaurus TCAD to study these effects, using two different models for the incident ion-induced ionization: the Alpha Particle and the Heavy Ion model. Simulations show that the Alpha Particle model cannot induce any device failures even with a 3.5 kV reverse bias, while it is possible to trigger a failure by the Heavy Ion model, where the ionization can be selected. Carrier plasma and internal electric field distributions of the two models are plotted and compared, showing that device failures triggered by a heavy ion are related to the hole injection at epi-substrate interface, in which linear energy transfer (LET) of the particle plays an important role.

High modulation efficiency sinusoidal vertical PN junction phase shifter in silicon-on-insulator

In this paper, a sinusoidal vertical PN junction phase shifter on a silicon waveguide is designed, and the results demonstrate that modifying the shape of the PN junction significantly increases the area of the depletion region within the standard waveguide width of 500 nm, thereby enhancing the overlap between the depletion region and optical waveguide modes under reverse bias conditions. Furthermore, by adjusting the sinusoidal amplitude (A) of the doping contact interface, it is observed that when A=0.065µm, the resulting sinusoidal PN junction most effectively enhances the interaction between carriers and photons, leading to the highest modulation efficiency and the lowest loss. Based on this, further adjustment of the doping concentration distribution in the waveguide was conducted using a doping compensation method. It is observed that setting the doping concentration at 3×1018cm−3 in the heavily doped region and at 1×1018cm−3 in the lightly doped region enables the phase shifter to achieve high modulation efficiency while maintaining low loss. This is attributed to the highest optical intensity being concentrated in the central region of the waveguide, as well as to the positive correlation between doping concentration and modulation efficiency. The final designed device with a length of 1.5 mm successfully attained a low V π L of 0.58V⋅cm, resulting in high modulation efficiency. By employing traveling wave electrodes and ensuring that the effective refractive index of the radio frequency (RF) matches the optical group index (OGI), circuit-level simulations were conducted. The device exhibited a 3 dB bandwidth of 8.85 GHz and eye diagrams of up to 40 Gbit/s, with a maximum extinction ratio (ER) of 8.27 dB and a bit error rate (BER) of 8.83×10−6, which can be widely used in the field of high-speed silicon optical modules.

An efficient modeling workflow for high-performance nanowire single-photon avalanche detector

Single-photon detector (SPD), an essential building block of the quantum communication system, plays a fundamental role in developing next-generation quantum technologies. In this work, we propose an efficient modeling workflow of nanowire SPDs utilizing avalanche breakdown at reverse-biased conditions. The proposed workflow is explored to maximize computational efficiency and balance time-consuming drift-diffusion simulation with fast script-based post-processing. Without excessive computational effort, we could predict a suite of key device performance metrics, including breakdown voltage, dark/light avalanche built-up time, photon detection efficiency, dark count rate, and the deterministic part of timing jitter due to device structures. Implementing the proposed workflow onto a single InP nanowire and comparing it to the extensively studied planar devices and superconducting nanowire SPDs, we showed the great potential of nanowire avalanche SPD to outperform their planar counterparts and obtain as superior performance as superconducting nanowires, i.e. achieve a high photon detection efficiency of 70% with a dark count rate less than 20 Hz at non-cryogenic temperature. The proposed workflow is not limited to single-nanowire or nanowire-based device modeling and can be readily extended to more complicated two-/three dimensional structures.

Highly Responsive Switchable Broadband DUV-NIR Photodetector and Tunable Emitter Enabled by Uniform and Vertically Grown III-V Nanowire on Silicon Substrate for Integrated Photonics.

Low-dimensional semiconductor nanostructures, particularly in the form of nanowire configurations with large surface-to-volume-ratio, offer intriguing optoelectronic properties for the advancement of integrated photonic technologies. Here, a bias-controlled, superior dual-functional broadband light detecting/emitting diode enabled by constructing the aluminum-gallium-nitride-based nanowire on the silicon-platform is reported. Strikingly, the diode exhibits a stable and high responsivity (R) of over 200mAW-1 covering an extremely wide operation band under reverse bias conditions, ranging from deep ultraviolet (DUV: 254nm) to near-infrared (NIR: 1000nm) spectrum region. While at zero bias, it still possesses superior DUV light selectivity with a high off-rejection ratio of 106. When it comes to the operation of the light-emitting mode under forward bias, it can achieve large spectral changes from UV to red simply by coating colloid quantum dots on the nanowires. Based on the multifunctional features of the diodes, this study further employs them in various optoelectronic systems, demonstrating outstanding applications in multicolor imaging, filterless color discrimination, and DUV/NIR visualization. Such highly responsive broadband photodetector with a tunable emitter enabled by III-V nanowire on silicon provides a new avenue toward the realization of integrated photonics and holds great promise for future applications in communication, sensing, imaging, and visualization.

(Invited) Recent Progress in Medium-Voltage Vertical GaN Power Devices

Vertical gallium nitride (GaN) power devices continue to garner interest in multiple power conversion applications requiring a medium-voltage (1.2 – 20 kV) capability. Currently, silicon carbide (SiC) is addressing this voltage range, however, with a comparable critical electric field and superior mobility, GaN is expected to offer advantages in applications where fast switching and avalanche breakdown response times are desired. While uses in electric vehicles, solid-state transformers, and renewable energy conversion are being actively explored, the potential of a vertical GaN device for electric grid protection in the form of an electromagnetic pulse arrestor is a unique proposition that requires very fast transient capabilities (<1 µs pulse widths with rise-times on the order of 10 ns). However, vertical GaN devices are significantly less mature than present SiC offerings. Specifically, low-doped, thick epitaxial growth of GaN via metal-organic chemical vapor deposition (MOCVD) still presents many challenges, and advancements in processing, manufacturability, and failure analysis are needed.In this work, we describe our efforts to address the above issues and advance the state-of-the-art in vertical GaN PN diode development. We have successfully demonstrated an MOCVD-grown, 50 µm thick, low-doped (<1015 cm-3) drift region on a GaN substrate that was processed into relatively large-area (1 mm2) PN diodes capable of achieving a 6.7 kV breakdown. Temperature-dependent breakdown was observed, consistent with the avalanche process. The devices consisted of a 4-zone step-etched junction termination extension (JTE), where the breakdown region was visualized via electroluminescence (EL) imaging. Ongoing work aims to scale the current capability of the medium-voltage diodes through a parallel interconnect design that negates defective or poor performing diodes. Further investigation of edge termination structures was explored using a bevel approach, where we studied the relationship between the bevel angle and p-doping. It was found that a very shallow angle of only 5° accompanied by a 500 nm p-region consisting of 3×1017 cm-3 Mg concentration resulted in a consistent 1.2 kV breakdown for an 8 µm thick, 1.6×1016 cm-3 doped drift region. EL imaging confirmed uniform breakdown, and temperature dependence was demonstrated. The bevel approach was then implemented on a diode structure with a 20 µm thick drift region capable of 3.3 kV breakdown, where an unclamped inductive switching (UIS) test was performed to evaluate the impact of a field plate design on avalanche uniformity and ruggedness.A parallel effort to establish a foundry process for vertical GaN devices has been underway. Initially, this focus was on comprehensive studies of GaN wafer metrology using capacitance-voltage (C-V) mapping, optical profilometry, and x-ray diffraction (XRD) mapping. A machine learning algorithm was implemented to identify defective regions and produce a yield prediction for each GaN wafer prior to processing. A hybrid edge termination structure consisting of implanted guard rings (GR) and JTEs was developed in coordination with a controlled experiment that varied the anode thickness, and therefore the remaining p-GaN after implantation. It was observed that thinner p-GaN regions under the JTE/GR region resulted in a significant (>100x) reduction in leakage current under reverse-bias conditions. This process has resulted in 1.2-kV-class devices with up to 18 A forward current for a 1 mm2 device with a specific on-resistance of 1.2 mOhm-cm2. The foundry effort has since been extended to 3.3-kV-class devices that utilize 25 µm thick drift layers with ~2-4×1015 cm-3 doping. These devices have demonstrated up to 3.8 kV breakdown with leakage currents <1 nA up to 3 kV. More than 40 wafers have been processed to date, resulting in >20,000 devices. Statistical variations in I-V and C-V characteristics will be discussed. Packaging process development and analysis are underway to develop electrical stress procedures and identify fundamental failure mechanisms. Finally, a pulse arrested spark discharge (PASD) setup, capable of up to 15 kV pulsed operation in 100 V steps, was implemented to quantify the time response of avalanche breakdown. Initial results on a packaged 800 V device showed a ~1 ns response time during breakdown, which reinforces the potential EMP grid protection applicability. This work was supported by the ARPA-E OPEN+ Kilovolt Devices Cohort directed by Dr.Isik Kizilyalli. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy of the United States Government.

Ultra-low reverse leakage in large area kilo-volt class β-Ga2O3 trench Schottky barrier diode with high-k dielectric RESURF

We introduce vertical Schottky barrier diodes (SBDs) based on β-Ga2O3 with trench architecture, featuring a high-permittivity dielectric RESURF structure. These diodes are designed for application demanding high voltage and current capacities while maintaining ultra-low reverse leakage currents. The trench design plays a pivotal role in reducing the electric field at the metal–semiconductor junction, thereby yielding minimal reverse leakage attributed to field emission under high reverse bias conditions. Additionally, the incorporation of a high-k dielectric helps to suppress leakage through the trench bottom corner dielectric layer. The small area trench SBD (200 × 200 μm2) demonstrates a breakdown voltage exceeding 3 kV, accompanied by a reverse leakage current of less than 1 μA/cm2 at 3 kV. Moving on to larger area devices, the 1 × 1 and 2 × 2 mm2 devices exhibit breakdown voltages of 1.8 and 1.4 kV, while accommodating pulsed forward currents of 3.5 and 15 A, respectively. The capacitance, stored charge, and switching energy of the trench SBDs are also found to be less than the similarly rated commercial SiC SBDs, reinforcing their potential for enhanced switching efficiency.

Mechanistic exploration of charge transport and photosensitivity of metal/polymer/semiconductor (MPS) junction for sensitive light detection applications

Herein, PVA: PVP@Ni(OAc)2 nanocomposite spin-coated thin films have been fabricated as a barrier modifier interlayer in a metal/polymer/semiconductor configuration for light detection applications. The nanostructure, as well as the surface roughness profile of the deposited thin films, have been inspected using a high-resolution transmission electron microscope (HR-TEM) and field emission scan electron microscope (FE-SEM). The obtained results showed nanoplatelet architecture films with smooth surfaces of average roughness of ~ 7.08 nm. The optical absorption, reflection, and transmission spectra have been analyzed and the value of the fabricated film’s energy gap has been confirmed with several analytical approaches. Furthermore, the DC electrical properties of Ag/Si (n-type and p-type), as well as Ag/polymer nanocomposite/Si (n-type and p-type), have been investigated under dark conditions. The microelectronic properties have been estimated using thermionic emission, Norde’s, and Cheung-Cheung’s models. Besides, the mechanistic details of charge transport have been explored under forward and reverse bias conditions. The photoresponsive features of the designed Ag/ PVA/PVP@Ni(OAc)2 /p-Si junction have been evaluated under different illumination intensities. The current device achieved superior photodetection capability with high responsivity, detectivity, and fast switching behavior.

High-performance blue light photodetector based on PANI/CdS heterojunction

The pursuit of innovative and enhanced p-n junction photo-diodes for application in optical, optoelectronic, and microelectronic devices has become a global research focus. These diodes' fundamental operation hinges on exploiting disparities in band gaps and electronic structures of constituent materials, thereby enabling the rectification of electrical current, permitting it to flow in a single direction. In this study, we present the design and fabrication of a high-performance blue light photodetector, which uses an n-type cadmium sulfide (CdS) thin film and a p-type polyaniline (PANI). The PANI/CdS heterojunction photodetector demonstrates exceptional performance characteristics, achieving a responsivity of approximately 32 mA/W, a detectivity of approximately 4 × 1010 Jones, and a sensitivity of 5.9 × 104 % under blue light illumination at an applied bias of 30 V. Furthermore, this photodetector exhibits a remarkable rectification ratio of 78 and an impressively short response time of 60 μs. The outstanding performance attributes, including rapid response speed and rectification behavior, are attributed to the surface passivation of the CdS material and PANI chain and CdS linkage mediated states, which effectively reduces the dark current. This process enhances the efficient and rapid transport of photo-generated carriers, whereas, the interfacial nature concurrently reducing photocurrent during reverse bias conditions, thus facilitating the observed rectification effect. This research presents a significant advancement in the area of high-performance photodetectors, holding promise for a multitude of applications across optical, optoelectronic, and microelectronic devices.

The Correlation between Surface V-Shaped Defects and Local Breakdown Phenomena in GaN-Based LEDs

This paper investigates the intriguing impact of surface V-shaped defects on the electrical and optical characteristics of GaN-based LEDs, particularly under reverse bias conditions. These defects introduce unique luminescence phenomena, notably giant dot-like luminescence (GDL), and exert significant influence on device performance. The size of these V-shaped defects plays a critical role: larger defects generate more indium-rich regions at their base, resulting in elevated tensile stress. This heightened stress promotes carrier tunneling, increasing reverse leakage current and leads to GDL formation. However, even with multiple V-shaped defects present, localized failure predominantly occurs at the defect experiencing the highest tensile stress, substantially reducing the breakdown voltage. Micro-Raman analysis further reveals distinct Raman shifts and increased tensile stress in these regions. These findings underscore the complexity of V-shaped defects’ effects, highlighting their importance in GaN-based LED design and optimization. Recognizing their influence on electrical and optical properties can significantly impact device reliability and performance, particularly in reverse bias conditions.

Survivability of microstructure semiconductor neutron detectors (MSND) in a thermal neutron radiation environment

The performance of five representative microstructured semiconductor neutron detectors (MSND) were investigated after exposure to varying magnitudes of thermal neutrons fluences ranging from 107 cm−2 to 1012 n cm−2. The devices have 95% enriched microparticulate 6LiF granules backfilled in microscopic trenches within a Si pvn diode. Neutron interactions in the 6Li causes the emission of reaction products which ionize the trenched Si diode depletion regions. The average intrinsic thermal-neutron detection efficiency (ϵtn) of the five devices before irradiation measured as 24.09% ± 0.35% with an operating leakage current below 11 nA at a −3 V reverse bias condition. The observed threshold of performance deterioration was approximately 1010 n cm−2, resulting in an spectral shift in the reaction product spectrum to lower energy channels and a general increase in leakage current. Although damage was observed beyond a thermal-neutron fluence of 1010 n cm−2, the devices remained operable. Beyond a thermal-neutron fluence of 1012 n cm−2, the devices experienced severe damage and demonstrated poor detector performance. At the highest thermal neutron fluences tested, near 1012 n cm−2, the average ϵtn of the five devices decreased to 4.42% ± 0.10% with an average operating leakage current of 300 nA at a −3 V reverse bias condition. Performance degradation was attributed to reaction-product damage in the MSND pvn diode structure.

Nanomanipulation of Functionalized Gold Nanoparticles on GaN

Gold nanoparticles (AuNPs) is known for its high surface area to volume ratio which acts as an excellent receptor when placed in between electrodes in sensors application. Microelectrodes which are bar and needle shape pointed ends with two arrangements; comb and castle wall configurations were designed to be used for fabrication of electrodes to observe the relation between geometry of electrodes and dielectrophoretic of AuNPs on p-gallium nitride (GaN) substrates. The dielectrophoretic behaviour and electrical properties were analysed before and after the drop cast of AuNPs using current-voltage (I-V) curve method with manual probing. Resistance values of each sample were calculated under reverse bias condition. The effect of design on the nanomanipulation of AuNPs will be discussed.

Heterostructure axial GaAsSb ensemble near-infrared p–i–n based axial configured nanowire photodetectors

In this work, we present a systematic design of growth experiments and subsequent characterization of self-catalyzed molecular beam epitaxially grown GaAsSb heterostructure axial p–i–n nanowires (NWs) on p-Si <111> for the ensemble photodetector (PD) application in the near-infrared region. Diverse growth methods have been explored to gain a better insight into mitigating several growth challenges by systematically studying their impact on the NW electrical and optical properties to realize a high-quality p–i–n heterostructure. The successful growth approaches are Te-dopant compensation to suppress the p-type nature of intrinsic GaAsSb segment, growth interruption for strain relaxation at the interface, decreased substrate temperature to enhance supersaturation and minimize the reservoir effect, higher bandgap compositions of the n-segment of the heterostructure relative to the intrinsic region for boosting the absorption, and the high-temperature ultra-high vacuum in situ annealing to reduce the parasitic radial overgrowth. The efficacy of these methods is supported by enhanced photoluminescence (PL) emission, suppressed dark current in the heterostructure p–i–n NWs accompanied by increased rectification ratio, photosensitivity, and a reduced low-frequency noise level. The PD fabricated utilizing the optimized GaAsSb axial p–i–n NWs exhibited the longer wavelength cutoff at ∼1.1 μm with a significantly higher responsivity of ∼120 A W−1 (@−3 V bias) and a detectivity of 1.1 × 1013 Jones operating at room temperature. Frequency and the bias independent capacitance in the pico-Farad (pF) range and substantially lower noise level at the reverse biased condition, show the prospects of p–i–n GaAsSb NWs PD for high-speed optoelectronic applications.

Quad Port Multipolarized Reconfigurable MIMO Antenna for Sub 6 GHz Applications

Recent reconfigurable technological advancements for wireless communication systems provide various global solutions. This research work presents a quad port multipolarized switchable multiple input multiple output (MIMO) antenna for sub 6 GHz applications. It covers the frequency range from 3.1 to 5.1 GHz, including the 5G NR band n78 (3.3 to 3.8 GHz) and 5G NR band n79 (4.4 to 5 GHz). The proposed antenna comprises four offset-fed monopole antenna elements with an overall dimension of 60 mm × 65 mm. To achieve circular polarization (CP), a parasitic meandering resonator is integrated with antenna elements using four PIN diodes. The polarization diversity is obtained by controlling the bias states of four PIN diodes. The radiating element −1/−3 offers left hand circular polarization (LHCP), while element −2/−4 procures right hand circular polarization (RHCP) when all diodes are ON. Consequently, the proposed antenna provides linear polarization (LP) under reverse bias conditions. Moreover, the designed antenna acquires a wide axial ratio bandwidth (ARBW) of 36.1%. In addition, the developed MIMO antenna exhibits isolation greater than 15 dB using the common ground plane, and the obtained ECC is less than 0.13. The prototype is fabricated, and the simulated responses are in good correlation with the measured results.

Enhanced performance of flexible quantum dot light-emitting diodes using a low-temperature processed PTAA hole transport layer

Low-temperature processing is important for improving the stability and performance of flexible quantum dot light-emitting diodes (QLEDs). In this study, QLEDs were fabricated using poly[bis(4-phenyl) (2,4,6-trimethylphenyl)amine] (PTAA) as a suitable hole transport layer (HTL) material owing to its low-temperature processability and vanadium oxide as the low-temperature solution-processable hole injection layer material. The maximum luminance and highest current efficiency of the QLEDs on a glass substrate with an optimal PTAA HTL was 8.9 × 104 Cd/m2 and 15.9 Cd/A, respectively, which was comparable to that of conventional devices. The QLEDs on a flexible substrate showed a maximum luminance of 5.4 × 104 Cd/m2 and highest current efficiency of 5.1 Cd/A. X-ray and ultraviolet photoelectron spectroscopies were used to investigate the chemical state and interfacial electronic structure according to the materials and the state changes of the HTL, respectively. The interfacial electronic structure showed that PTAA exhibited a better hole transport ability owing to its low hole injection barrier ({Phi }_{{text{h}}}). Moreover, QLEDs with a PTAA HTL could operate as photosensors under reverse bias conditions. These results indicate that the low-temperature-processed PTAA HTL is suitable for improving the performance of flexible QLEDs.

Voltage and frequency controlled Ge/SeO2 thin film transistors designed as rectifiers, negative capacitance and negative conductance sources

Herein voltage and frequency controlled thin film transistors fabricated by depositing SeO2 onto germanium thin crystals are reported. For these devices measurements of the current-voltage characteristics revealed a biasing dependent rectification ratios. The devices showed metal-oxide-semiconductor character under reverse biasing conditions. In addition, the biasing dependent capacitance and conductance spectral studies in the frequency domain of 20M-1000MHz has shown the possibility of switching the capacitance and negative conductance from negative mode to positive mode. The features of the Ge/SeO2 devices make them attractive for use in electronic circuits as parasitic capacitive circuit elements, noise reducers, signal amplifiers and microwave oscillators.

Improving Infrared Photodetection Performance by Ultraviolet-Ozone Treatment in Lead Sulfide Films

Lead sulfide (PbS) films are important infrared-active materials, and they are generally made by physical vapor deposition techniques such as magnetron sputtering. However, these deposition techniques are costly, and the PbS films need high-temperature oxygen-treatment to passivate sulfide vacancies and lead ion cluster defects. In this work, we report a facile chemical water bath to fabricate highly crystalline PbS films, where their defects were passivated by a controllable low-temperature ultraviolet-ozone (UVO) treatment, leading to a significantly reduced dark current and thus an improved room-temperature photodetectivity. The PbS photodetectors exhibited a specific detectivity increasing from 1.94 × 1010 to 4.40 × 1010 Jones under the reverse biased condition of −0.8 V after the UVO treatment. This work has demonstrated a low-cost production of high-quality PbS films and a low-temperature defect-passivation approach to improve infrared photodetection performance.