Showing papers on "Diffusion current published in 2015"

Electrical and photovoltaic characteristics of MoS2/Si p-n junctions

Abstract: Bulk-like molybdenum disulfide (MoS2) thin films were deposited on the surface of p-type Si substrates using dc magnetron sputtering technique and MoS2/Si p-n junctions were formed. The vibrating modes of E12g and A1g were observed from the Raman spectrum of the MoS2 films. The current density versus voltage (J-V) characteristics of the junction were investigated. A typical J-V rectifying effect with a turn-on voltage of 0.2 V was shown. In different voltage range, the electrical transporting of the junction was dominated by diffusion current and recombination current, respectively. Under the light illumination of 15 mW cm−2, the p-n junction exhibited obvious photovoltaic characteristics with a short-circuit current density of 3.2 mA cm−2 and open-circuit voltage of 0.14 V. The fill factor and energy conversion efficiency were 42.4% and 1.3%, respectively. According to the determination of the Fermi-energy level (∼4.65 eV) and energy-band gap (∼1.45 eV) of the MoS2 films by capacitance-voltage curve and ...

Modelling current efficiency in an electrochemical hypochlorite reactor

Abstract: A mathematical model was set up for anodic, cathodic and overall current efficiencies of an electrochemical cell for hypochlorite production acting as an ideal stirred reactor. A 0.06–0.20 mol dm −3 NaClO hypochlorite solution was obtained in the cell by the electrolysis of 0.25–0.50 mol dm −3 sodium chloride solution at a temperature of 20 °C, at a current density of 100 mA cm −2 and at 8.3 Theoretical dependences of the anodic current efficiency on the overall anodic current density, hypochlorite concentration and partial current density for water oxidation were established. Theoretically derived relations and the corresponding experimental results showed that oxygen evolution due to water and hypochlorite oxidation leads to reduced thickness of the anodic diffusion layer and increases the limiting diffusion current for hypochlorite oxidation. Mathematical models for the dependence of the cathodic current efficiency on the cathodic current density and hypochlorite concentration in the bulk solution were also established. The expression for the overall current efficiency of the electrochemical cell for hypochlorite production was derived on the basis of both the anodic and the cathodic current efficiency. The good agreement between experimental results and the values provided by the mathematical models has confirmed the correctness of the proposed models, suggesting that the model can be used to optimise electrolysis parameters. (The term hypochlorite is used to include both hypochlorite and undissociated hypochlorous acid.) The concentration of dissolved elementary chlorine in the slightly alkaline environment is negligible compared to hypochlorite concentration.

Electro-Optical Characteristics of P + n In 0.53 Ga 0.47 As Hetero-Junction Photodiodes in Large Format Dense Focal Plane Arrays

Abstract: This paper is concerned with focal plane array (FPA) data and use of analytical and three-dimensional numerical simulation methods to determine the physical effects and processes limiting performance. For shallow homojunction P+n designs the temperature dependence of dark current for T < 300 K depends on the intrinsic carrier concentration of the In0.53Ga0.47As material, implying that the dominant dark currents are generation and recombination (G–R) currents originating in the depletion regions of the double layer planar heterostructure (DLPH) photodiode. In the analytical model differences from bulk G–R behavior are modeled with a G–R like perimeter-dependent shunt current conjectured to originate at the InP/InGaAs interface. In this description the fitting property is the effective conductivity, σ eff(T), in mho cm−1. Variation in the data suggests σ eff (300 K) values of 1.2 × 10−11–4.6 × 10−11 mho cm−1). Substrate removal extends the quantum efficiency (QE) spectral band into the visible region. However, dead-layer effects limit the QE to 10% at a wavelength of 0.5 μm. For starlight–no moon illumination conditions, the signal-to-noise ratio is estimated to be 50 at an operating temperature of 300 K. A major result of the 3D numerical simulation of the device is the prediction of a perimeter G–R current not associated with the properties of the metallurgical interface. Another is the prediction that for a junction positioned in the larger band gap InP cap layer the QE is bias-dependent and that a relatively large reverse bias ≥0.9 V is needed for the QE to saturate to the shallow homojunction value. At this higher bias the dark current is larger than the shallow homojunction value. The 3D numerical model and the analytical model agree in predicting and explaining the measured radiatively limited diffusion current originating at the n-side of the junction. The calculations of the area-dependent G–R current for the condition studied are also in agreement. Unique advantages of the 3D numerical simulation are the ability to mimic real device structures, achieve deeper understanding of the real physical effects associated with the various methods of junction formation, and predict how device designs will function.

Diffusion current characteristics of defect-limited nBn mid-wave infrared detectors

Abstract: Mid-wave infrared, nBn detectors remain limited by diffusion current generated in the absorber region even when defect concentrations are elevated. In contrast, defect-limited conventional pn-junction based photodiodes are subject to Shockley-Read-Hall generation in the depletion region and subsequent carrier drift. Ideal nBn-architecture devices would be limited by Auger 1 generation; however, typical nBn detectors exhibit defect-dominated performance associated with Shockley-Read-Hall generation in the quasi-neutral absorbing region. Reverse saturation current density characteristics for defect-limited devices depend on the minority carrier diffusion length, absorbing layer thickness, and the dominant minority carrier generation mechanism. Unlike pn-based photodiodes, changes in nBn dark current due to elevated defect concentrations do not manifest at small biases, thus, the zero bias resistance area product, RoA, is not a useful parameter for characterizing nBn-architecture photodetector performance.

Latest Developments in Long-Wavelength and Very-Long-Wavelength Infrared Detection with p -on- n HgCdTe

Abstract: We report recent developments at Commissariat a l’Energie Atomique-Laboratoire d’Electronique des Technologies de l’Information Infrared Laboratory on the processing and characterization of p-on-n HgCdTe (MCT) planar infrared focal plane arrays (FPAs) operating in the long-wavelength infrared (LWIR) and very-long-wavelength infrared (VLWIR) spectral bands. The active layers in these FPAs were grown by liquid phase epitaxy (LPE) on a lattice-matched CdZnTe substrate. This technological process results in lower dark current and lower serial resistance than for n-on-p vacancy-doped architecture and thus is better adapted for lower flux detection or higher operating temperature. This architecture was evaluated for space applications in the LWIR and VLWIR spectral bands with cutoff wavelengths from 10 to 17 μm at 78 K. Innovations have been introduced to the technological process to form a heterojunction by use of an LPE growth technique. The initial objective was to reduce the dark current at low temperatures, by reducing the transition temperature from diffusion-limited to depletion-limited dark current. Another advantage is that the wider bandgap obtained in the vicinity of the junction ensures less sensitivity to the defects present at the interface between MCT and passivation layers. Electro-optical characterization of p-on-n photodiodes was performed on quarter video graphics array format FPAs with 25 and 30 μm pixel pitches. The results revealed excellent operabilities in current and responsivity, with low dispersion, and noise limited by current shot noise. Studies performed on the dark current show that dark current densities at 78 K are consistent with the heuristic prediction law “Rule 07”. Below this temperature, dark current varies as a pure diffusion current for a variety of devices from different manufacturers, introducing a temperature range limitation in the description of the “Rule 07” law.

Junction optimization in HgCdTe: Shockley-Read-Hall generation-recombination suppression

Abstract: Heterojunction device design concepts are leveraged to reduce depletion layer generation-recombination (G-R) dark current in planar P+-on-n SWIR HgCdTe infrared detectors. Shockley-Read-Hall (SRH) depletion dark current (when present) is expected to be the dominant dark current component at low temperatures, and in fact, it is beneficial for the transition from diffusion to G-R to be at such relatively low temperatures. However, it is empirically observed that even for relatively long values of the SRH lifetime ( 20 μs), the transition occurs at relatively high temperatures (>200 K) for material with a cut-off wavelength of 2.5 μm. A key device design parameter of P+-on-n photodiodes is the position of the electrical junction relative to the hetero-metallurgical interface. Junction formation via p-type arsenic implantation into the narrow-gap absorber layer is typically chosen for efficient collection of diffusion current, however, other configurations are possible as well. In this letter, we numerically ...

Low-dark current p-on-n MCT detector in long and very long-wavelength infrared

Abstract: This paper presents recent developments done at CEA-LETI Infrared Laboratory on processing and characterization of p-on-n HgCdTe (MCT) planar infrared focal plane arrays (FPAs) in LWIR and VLWIR spectral bands. These FPAs have been grown using liquid phase epitaxy (LPE) on a lattice matched CdZnTe substrate. This technology presents lower dark current and lower serial resistance in comparison with n-on-p vacancy doped architecture and is well adapted for low flux detection or high operating temperature. This architecture has been evaluated for space applications in LWIR and VLWIR spectral bands with cutoff wavelengths from 10μμm up to 17μm at 78K. Innovations have been introduced to the technological process to form a heterojunction with a LPE growth technique. The aim was to lower dark current at low temperature, by decreasing currents from the depletion region. Electro-optical characterizations on p-on-n photodiodes have been performed on QVGA format FPAs with 30μm pixel pitches. Results show excellent operabilities in current and responsivity, with low dispersion and noise limited by current shot-noise. Studies performed on dark current show that dark current densities are consistent with the heuristic prediction law "Rule07" at 78K. Below this temperature, dark current varies as a pure diffusion current.

1/ $f$ Noise in Mid-Wavelength Infrared Detectors With InAs/GaSb Superlattice Absorber

Abstract: The role of generation–recombination (g–r) and diffusion currents in the generation of 1/ $f$ noise was investigated in mid-wavelength infrared detectors with InAs/GaSb superlattice (SL) absorber. Modeling of the dark current reveals the region where g–r and/or diffusion currents dominate over the leakage current (shunt- and/or trap-assisted tunneling). Measurements of 1/ $f$ noise at constant reverse bias versus temperature show that noise intensity follows squared leakage current. There is no contribution to 1/ $f$ noise from g–r or diffusion currents or it is too small to be observed. This property should be attributed to InAs/GaSb SL material rather than to device specific features, since the batch of examined devices contained specimens with various architecture, passivation method, and substrate. Results for SL-based devices were compared with the state-of-the-art HgCdTe detectors. In these detectors, dedicated for high operating temperature, correlation between g–r/diffusion currents and 1/ $f$ noise is significant.

Proton radiation effect on performance of InAs/GaSb complementary barrier infrared detector

Abstract: In this work, we investigated the effect of proton irradiation on the performance of long wavelength infrared InAs/GaSb photodiodes (λc = 10.2 μm), based on the complementary barrier infrared detector design. We found that irradiation with 68 MeV protons causes a significant increase of the dark current from jd = 5 × 10−5 A/cm2 to jd = 6 × 10−3 A/cm2, at Vb = 0.1 V, T = 80 K and fluence 19.2 × 1011 H+/cm2. Analysis of the dark current as a function of temperature and bias showed that the dominant contributor to the dark current in these devices changes from diffusion current to tunneling current after proton irradiation. This change in the dark current mechanism can be attributed to the onset of surface leakage current, generated by trap-assisted tunneling processes in proton displacement damage areas located near the device sidewalls.

Diffusion Injection in a Buried Multiquantum Well Light-Emitting Diode Structure

Abstract: Devices based on nanostructures hold great potential to improve the performance of present light emitter technologies. In this paper, we examine a buried multiquantum well III-nitride diffusion injected light-emitting diode (DILED), where the active region is located outside the p-n junction and current injection to the active region takes place through bipolar diffusion. We study the current–voltage behavior and light emission characteristics of the DILED as a function of temperature experimentally and theoretically. We show that in contrast to conventional LEDs, the light output efficiency of the DILED increases when temperature is increased from 0 °C to 100 °C. This anomalous temperature behavior is shown to be linked to the strong temperature dependency of ionized acceptor density in the p-doped region, which increases the hole diffusion current into the active region. This highlights the fundamental difference in the operating principle of the DILED compared with conventional LEDs. In addition to optical and electrical characterization of a DILED, we also study the relation of the observed yellow-band luminescence to Shockley–Read–Hall recombination, compare the measurements to charge carrier transport simulations, and present an equivalent circuit model of the DILED structure for additional insight into the new current injection scheme.

Pulsed current signals in capacitor type particle detectors

Abstract: The problem of pulsed current signals in capacitor type sensors, due to drifting surface charge domain is considered for the analysis of the operational characteristics in photo- and particle-detectors. In this article, the models of the formation of the pulsed currents have been analyzed in vacuum and dielectric filled capacitor-like detectors. Injected charge drift regimes such as Shockley-Ramo's-type (large charge drift) and free flight within Coulomb's force field (small charge drift) are discussed. It has been shown that solutions of the injected charge drift in the vacuum gap capacitor can be employed to emulate charge drift over free path in dynamic solution of the problem with scattering. Pulsed current signals and charge drift in the detectors of the capacitor filled with dielectric type have been analyzed, where the bipolar charge injection and various drift regimes appear. The bipolar carrier drift transformation to a monopolar one is considered, after either electrons or holes, injected within the material, reach the external electrode. The impact of the dynamic capacitance and load resistance in the formation of drift current transients is highlighted. It has been illustrated that the synchronous action of carrier drift, trapping, generation and diffusion can lead to a vast variety of possible current pulse waveforms.

Multiple negative differential resistance devices with ultra-high peak-to-valley current ratio for practical multi-valued logic and memory applications

Abstract: In this paper, we propose a novel multiple negative differential resistance (NDR) device with ultra-high peak-to-valley current ratio (PVCR) over 106 by combining tunnel diode with a conventional MOSFET, which suppresses the valley current with transistor off-leakage level. Band-to-band tunneling (BTBT) in tunnel junction provides the first peak, and the second peak and valley are generated from the suppression of diffusion current in tunnel diode by the off-state MOSFET. The multiple NDR curves can be controlled by doping concentration of tunnel junction and the threshold voltage of MOSFET. By using complementary multiple NDR devices, five-state memory is demonstrated only with six transistors.

A Surface-Modified Hydrogen-Permeable Palladium-Silver Plate

Abstract: A composite target is developed for magnetron sputtering of alloys using silver and palladium with different area ratios. A process is proposed for modification of both surfaces of palladium-silver films formed by PVD and electroplating to improve hydrogen permeability of the amorphous palladium layer electrodeposited from a water solution of its salt at the current density exceeding the diffusion current density for these conditions. The modified palladium-silver membrane becomes hydrogen-permeable at room temperature at the overpressure values up to 0.3 MPa.

Possible theoretical models for carrier diffusion coefficient of one-dimensional Si wire devices

Abstract: We use the semi-microscopic theory to elucidate the effective diffusion coefficient of carriers in one-dimensional Si wire devices. In the theoretical model, it is assumed that the primary spectrum of the diffusion process of majority and minority carriers rules the diffusion process; a statistical assessment of the diffusion coefficient is performed using quantum-mechanical analysis. Here the model assumes that the thermalization of carrier transport is ruled by the specific characteristic length. The theory reveals that the diffusion coefficient drastically decreases as the wire width enters the sub-10-nm range. Although it is suggested that the behavior of the diffusion coefficient of such Si wires is related to phonon scattering events in narrow wires, it is not so clear whether it is the dominant mechanism ruling the diffusion coefficient of Si wires. A quantitative prediction of carrier mobility in Si wires is also made on the basis of Einstein's relation, and the model's validity is examined.

Mechanism of charge transfer in injection photodetectors based on the M(In)-n-CdS-p-Si-M(In) structure

Abstract: The mechanism of charge transfer in a new-type selective (with a tunable spectrum) injection photodetector based on the M(In)-n-CdS-p-Si-M(In) structure with the internal amplification has been analyzed. It has been shown that, in this structure, there is a mutual compensation of the drift and diffusion fluxes of charge carriers. The counter drift and diffusion fluxes of nonequilibrium carriers at reverse current densities I ∼ 10−8–10−7 A/cm2 lead to the appearance of sign-reversal points of the photosensitivity in the short-wavelength and long-wavelength regions of the spectrum. The mutual compensation of the counter drift and diffusion current fluxes at current densities of the order of ∼10−6 A/cm2 leads to the appearance of a sublinear section in the reverse current-voltage characteristic over a wide range of bias voltages. It has been found that the n-SdS-p-Si heterojunction has a low density of surface states at the interface. This makes it possible to develop an injection photodetector based on the considered structure with a high spectral sensitivity S λ = 5.0 × 104 A/W) and a high integrated sensitivity S int = 2.8 × 104 A/lm or 4.5 × 106 A/W in the for-ward direction of the current.

Performance analysis of PIN photodiode under gamma radiation effects through modeling

Abstract: The main objective of this paper is to evaluate the p-i-n photodiode as a radiation detector for gamma ray spectroscopy. Therefore, the effect of incident gamma radiation on p-i-n photodiode performance characteristics is evaluated. The p-i-n photodiode is interesting from the point of view because it has numerous advantages over conventional semiconductor junction in terms of better long wavelength response, radiation hardness, high quantum efficiency, long lifetime and lower cost. Therefore, it is important to analyze and evaluate their characteristics. Models for this interesting type of detector were developed. These models describe a nontrivial evaluation of the most important characteristics. The minority carrier of the holes of the developed model is obtained by self-consistently solving the one-dimension diffusion equation. On other hand, it is used to calculate the diffusion length, diffusion current, drift current, total current, quantum efficiency and signals-to-noise ratio (SNR) as a function of the structural parameters. These parameters are the radiation fluence, photodiode area, bias voltage, spectral wavelength and the operating temperature. Also, optimization of various characteristics of p-i-n photodiode is of primary concern. A comparison between the results obtained by proposed models and that published are conducted and full agreement is observed. Therefore, it confirms our models and their validity on practical applications. The main strength of p-i-n photodiodes is that the gap between induced diffusion current and drift current is large. Moreover, the p-i-n photodiode has a comparable value of SNR accomplished with low values of corresponding bias voltage. The obtained results assure that p-i-n can be used as an efficient radiation detector.

A model to estimate QE/MTF of thinned, back-side illuminated image sensors

Abstract: An analytical model to estimate the quantum efficiency and the modulation transfer function of image sensors is proposed. Proposed approach follows similar prior studies, and tries to improve them in two directions: first, the impact of internal reflections on the optical generation profile is taken into account; second, the diffusion current calculations are extended for sensors utilizing graded-epi wafers and back-side passivation implants. A back-side illuminated photo diode sensor is used as a case study to demonstrate the model response.

Sorption-membrane system for deep deoxygenation of water

Abstract: We have studied the redox sorption of oxygen from flowing distilled water in a multistage sorptionmembrane cell with a metal (Cu)–sulfo cation exchanger (KU-23 in the H+ form) granular nanocomposite in the cathode compartment and a sulfo cation exchanger (KU-23 in the H+ form) in the anode compartments separated by a cation-exchange membrane (MC-40 in the H+ form). It is shown that the redox sorption of oxygen on the granular nanocomposite bed polarized with a current which is less than the limiting external diffusion one is complicated by internal steps (oxygen diffusion in the polymer matrix pores and the chemical oxidation of metal nanoparticles) and proceeds with a mixed diffusion-kinetic control. In the mode of limiting diffusion current polarization, the contribution of internal stages decreases and the process becomes steady due to the transition into the external diffusion region. A theoretical calculation shows that the process performed in series-connected multistage cells with polarization of each stage in the mode of limiting external diffusion current allows obtaining water with a dissolved oxygen content of <10 ppb.

Electric power system current quality assessment method

Abstract: The invention belongs to the electric energy quality analysis field, especially an electric power system current quality assessment method. The method comprises: firstly, performing Fourier decomposition on the voltage and current detected at a PCC, and dividing a voltage subset and a current subset obtained after decomposition into a harmonic portion and an interharmonic portion; secondly, for the harmonic portion, based on the harmonic wave power direction of each frequency, calculating harmonic voltages and harmonic current to obtain a current component under each frequency, and decomposing active current, diffusion current, reactive current, unbalanced current, zero sequence current and generation current; and finally, calculating each current component to obtain required current quality assessment indicators, i.e., a rate of equipment utilization, system operation efficiency, reactive current, zero sequence current, unbalanced current, reactive current fluctuation quantity and frequentness, generation current, diffusion current and interharmonic current. The assessment indicators are corresponding with real current quality phenomena one by one; an assessment system has clear concepts, and can effectively assess current quality in real engineering.

Analysis of Bohm Diffusions Based on the Ion-Neutral Collisions

Abstract: Three experimental cases of cross-field diffusions in the magnetized plasmas reported to be related with Bohm diffusion are investigated based on the ion current induced by the ion-neutral collisions. High diffusion coefficient for the original Bohm/Simon experiments and the recent experiments of strongly pulsed plasmas can be explained by the gyro-center shift current combined with the short circuit effect, which is different from the turbulence-induced transport of nuclear fusion devices. It can be deduced that Bohm’s interpretation of diffusion with $1/B$ dependence came from the fact that the short circuit effect of his experiment was limited by the parallel ion velocity. The ratio of azimuthal current density to the discharge current density measured in the pulsed magnetron experiments is analyzed to be constant and independent from the magnitude of magnetic field due to the maximum condition for the Pedersen conductivity.

Diffusion injected light emitting diode

Abstract: Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto.fi Author Lauri Riuttanen Name of the doctoral dissertation Diffusion injected light emitting diode Publisher School of Electrical Engineering Unit Department of Microand Nanosciences Series Aalto University publication series DOCTORAL DISSERTATIONS 213/2015 Field of research Optoelectronics Manuscript submitted 10 August 2015 Date of the defence 18 December 2015 Permission to publish granted (date) 17 November 2015 Language English Monograph Article dissertation (summary + original articles) Abstract Lighting plays a major role in consumption of electrical energy in the world. Thus, increasing the efficiency of light sources is one key element in reducing the green house gas emissions. Light emitting diodes (LEDs) are gaining a foothold in general lighting. Despite their rapid development in light output and their superior efficiency compared to other light sources, LEDs still need improvements in order to become the ultimate lighting technology. A typical LED is a double heterojunction (DHJ) structure, in which the active region fabricated from a lower band gap material is sandwiched between higher band gap pand n-doped regions. By biasing such a structure electrons and holes are transferred by current into the active region, where they recombine releasing energy as photons. The carrier injection in a conventional LED structure is typically efficient. However, in more exotic novel structures based on nanowires or near surface nanostructures, fabricating a DHJ becomes difficult. This thesis presents the experimental studies on a novel current injection method for light emitting applications. The method is based on bipolar diffusion of charge carriers. Unlike in the conventional method, the active region does not have to placed between the pand n-layers of the pn-junction. The diffusion injection method is experimentally demonstrated by two types of prototype structures. The first prototype was fabricated using a multi quantum well (MQW) stack buried under the pn-junction. The second prototype was fabricated using a near surface quantum well (QW) placed on top of the pn-junction. The first prototype showed that the diffusion current components can be used to excite an active region outside of the pn-junction. The second prototype showed a large improvement in injection efficiency as well as the suitability of the method for exciting surface structures. The applications of diffusion injection can be found in blue galliun nitride based LEDs studied in this thesis as well as in green solid-state light sources, light sources integrated into silicon technology and devices based on nanostructures and plasmonics.Lighting plays a major role in consumption of electrical energy in the world. Thus, increasing the efficiency of light sources is one key element in reducing the green house gas emissions. Light emitting diodes (LEDs) are gaining a foothold in general lighting. Despite their rapid development in light output and their superior efficiency compared to other light sources, LEDs still need improvements in order to become the ultimate lighting technology. A typical LED is a double heterojunction (DHJ) structure, in which the active region fabricated from a lower band gap material is sandwiched between higher band gap pand n-doped regions. By biasing such a structure electrons and holes are transferred by current into the active region, where they recombine releasing energy as photons. The carrier injection in a conventional LED structure is typically efficient. However, in more exotic novel structures based on nanowires or near surface nanostructures, fabricating a DHJ becomes difficult. This thesis presents the experimental studies on a novel current injection method for light emitting applications. The method is based on bipolar diffusion of charge carriers. Unlike in the conventional method, the active region does not have to placed between the pand n-layers of the pn-junction. The diffusion injection method is experimentally demonstrated by two types of prototype structures. The first prototype was fabricated using a multi quantum well (MQW) stack buried under the pn-junction. The second prototype was fabricated using a near surface quantum well (QW) placed on top of the pn-junction. The first prototype showed that the diffusion current components can be used to excite an active region outside of the pn-junction. The second prototype showed a large improvement in injection efficiency as well as the suitability of the method for exciting surface structures. The applications of diffusion injection can be found in blue galliun nitride based LEDs studied in this thesis as well as in green solid-state light sources, light sources integrated into silicon technology and devices based on nanostructures and plasmonics.

Enhancement of Oxygen Vacancies Induced Photovoltaic Effects in Bi0.9La0.1FeO3 Thin Films

Abstract: The photovoltaic effect in Ag/Bi0.9La0.1FeO3/La0.7Sr0.3MnO3 heterostructures was investigated and the short circuit photocurrent was found to be strongly dependent on the polarization orientation and oxygen vacancies (VOs) distribution. The photocurrent direction was switched accompanying polarization switching. Besides, according to manipulate the VOs accumulated at either the Ag/Bi0.9La0.1FeO3 or the Bi0.9La0.1FeO3/La0.7Sr0.3MnO3 interface by electric pulses, obvious enhancement of photovoltaic effects was obtained. These results can be explained well using the concepts of drift current and diffusion current controlled by the combination of oxygen vacancies and polarization. This work provides deep insights into the nature of photovoltaic effects in ferroelectric films, and will facilitate the advanced design devices combining spintronic, electronic, and optical functionalities.

The influence of thermal treatment on the passivation of SiNx film and the dark current of p-i-n InGaAs detector

Abstract: In this paper, we focus on the influence of thermal treatment on the passivation of silicon nitride (SiNx) film of p-i-n InGaAs detector. In our experiment, the perimeter/area (P/A) test diodes are fabricated by using two different device processes, and the relationship between the dark current density and P/A is investigated. The results indicate that the thermal treatment in the vacuum can be able to improve the passivation SiNx film effect and thus suppress the perimeterrelated current with the decrease of two orders of magnitude. Then the analysis of dark current source is carried out. The result shows that the sample with SiNx film through thermal treatment is composed of diffusion current and ohmic current, on the contrary, the other mainly consists of surface leakage current and diffusion current. It is illustrated that the passivation effect of SiNx was strengthened after thermal treatment and surface leakage current can be suppressed.

Vertical excitation profile in diffusion injected multi-quantum well light emitting diode structure

Abstract: Due to their potential to improve the performance of light-emitting diodes (LEDs), novel device structures based on nanowires, surface plasmons, and large-area high-power devices have received increasing amount of interest. These structures are almost exclusively based on the double hetero junction (DHJ) structure, that has remained essentially unchanged for decades. In this work we study a III-nitride diffusion injected light-emitting diode (DILED), in which the active region is located outside the pn-junction and the excitation of the active region is based on bipolar diffusion of charge carriers. This unorthodox approach removes the need of placing the active region in the conventional current path and thus enabling carrier injection in device structures, which would be challenging to realize with the conventional DHJ design. The structure studied in this work is has 3 indium gallium nitride / gallium nitride (InGaN/GaN) quantum wells (QWs) under a GaN pn-junction. The QWs are grown at diferent growth temperatures for obtaining distinctive luminescence peaks. This allows to obtain knowledge on the carrier diffusion in the structure. When the device is biased, all QWs emit light indicating a significant diffusion current into the QW stack.

High performance InAs/GaSb superlattice long wavelength photodetectors based on barrier enhanced structures

Abstract: The barrier enhanced InAs/GaSb long wavelength photodetectors were designed and demonstrated in this paper. A PBIN detector with an electron barrier inserted between P type contactor and absorption region show significantly improved electrical performances compared to a PIN structure. The RmaxA product of the PBIN detector was measured to be 104 Ωcm2 at 80K and 7360 Ωcm2 at 50K. Temperature dependent measurements show that the tunneling currents dominate the dark current below 50K, the generation-recombination (GR) currents dominate from 50K to 90K, and the diffusion current dominate over 90K. The PBIN structure benefits from a lower electric field in the absorption region and therefore, suppressed the tunnel currents and GR currents. To improve the quantum efficiency, Be-doping was employed to convert the conductivity of the long wavelength SL structure, the PN junction moves away from the B-I hetrostructure to the π-N interface, which loses the barrier effect. Therefore, the hole barrier was needed to form a PBπBN structure. In this paper, hole barrier was designed without Al element to form a PBπBN structure. The RmaxA product of the PBπBN detector was measured to be 77 Ωcm2 and the dark current density under -0.05V bias was measured to be 8.8×10-4A/cm2 at 80K. The peak current responsivity at 9.8 μm was 2.15A/W and the quantum efficiency was 26.7%.

Influence of Etching-Induced Surface Damage on Device Performance With Consideration of Minority Carriers Within Diffusion Length From Depletion Edge

Abstract: The influence of etching-induced damage outside the depletion edge on the electrical characteristics of device is investigated using p-type metal-oxide–semiconductor structure with 2.5-nm SiO2 dielectrics. It is found that surface defects act as generation centers when minority carrier concentration is below equilibrium, leading to the increase of diffusion current injecting into depletion region. The saturation current in inversion region is an order larger for damage located at 5 $\mu $ m from the gate edge than that for damage free. On the contrary, the defects act as recombination centers when given light illumination. The saturation current in inversion region under illumination is reduced to one-fifth by etching-induced traps located at 5 $\mu $ m from the gate edge with respect to that without etching due to the reduction of diffusion current. A semiempirical current model based on the lateral diffusion current due to the modulation of minority carrier concentration outside the depletion edge is in great agreement with the experimental results by quantitative simulation. The model is applicable to devices involving etching process or surface issues, especially for those in the submicrometer regime.