Lateral Voltage Research Articles

Analysing the lateral series resistance of high-performance metal wrap through solar cells

In back-contact solar cells, both external polarities are located at the back surface of the device, which allows for higher photocurrent generation on cell level and reduced series resistance on module level, leading to higher energy conversion efficiencies compared to conventional solar cells and modules. However, the majority charge carriers, which are generated near the back emitter, have to flow laterally e.g. through the base in order to reach the external majority carrier contact. In the present work, we analyse the lateral series resistance by means of measurement and simulation for high-performance metal wrap through (HIP-MWT) solar cells. We compare theoretical models and experimental methods to extract the effective series resistance from simulated and measured current–voltage characteristics and show that lateral voltage variations significantly increase the local recombination current. If the width of the gap between the external majority carrier contacts is reduced from the typical value of 3.5mm to ideally 0mm, we expect an increase of the energy conversion efficiency of approximately 0.1%abs. for cells with three continuous rear emitter contacts on 125mm×125mm large silicon wafers. In a simulation study, the bulk doping concentration NA and the bulk lifetime are varied yielding an optimal base resistivity of 0.6Ωcm–1.5Ωcm for HIP-MWT solar cells based on Czochralski-grown silicon in the degraded state of the boron–oxygen defect and an optimal resistivity of less than 1.0Ωcm for the case of bulk lifetimes larger than ~300µs.

New super junction lateral double-diffused MOSFET with electric field modulation by differently doping the buffered layer

In order to break through the limit relationship between the breakdown voltage and specific on-resistance for LDMOS (lateral double-diffused MOSFET), a new super junction LDMOS is proposed with the electric field modulation by differently doping the buffered layer in this paper for the first time based on the buffered SJ-LDMOS. The new electric field introduced by the differently doping buffered layer, owing to the electric field modulation, is brought to the surface electric field of SJ-LDMOS, which alleviates a low lateral breakdown voltage due to the uneven electric field distribution for the LDMOS affected by the vertical electric field. Through the ISE simulation, the results are obtained that the surface electric field is optimized for the proposed SJ-LDMOS when the number of differently doping buffered layers is three. The saturated breakdown voltage for the new SJ-LDMOS is increased by about 50% compared with that for conventional LDMOS, and improved by about 32% compared with that for buffered SJ-LDMOS. The lateral breakdown voltage for unit length is increased to 18.48 V/μm. For the proposed SJ-LDMOS, the specific on-resistance is 25.6 mΩ· cm2 with a breakdown voltage of 382 V, which already breaks the limit relationship of 71.8 mΩ·cm2 with a breakdown voltage of 254 V in the conventional LDMOS.

Spatially Resolved Determination of Junction Voltage of Silicon Solar Cells

For the extraction of spatially resolved solar cell parameters, a variety of methods has been introduced in the past years. Nearly all methods use the fact that the local luminescence intensity can be calibrated to local junction voltage. The different methods however use different approaches for the calibration. In this work we discuss the different approaches used throughout literature. We investigate the key assumption of two approaches which assumes that there are no lateral junction voltage gradients at sufficiently low excitation conditions. Our investigation is based on circuit simulations and experimental results on an example cell. We give an explanation for the remaining contrasts in luminescence images taken at these low excitation conditions. A third approach which does not rely on the key assumption is discussed with respect to measurement time in comparison to the other approaches. Finally the role of the short circuit current is discussed and a modification to the approach as known from literature is proposed.

Correlation Between Lateral Photovoltaic Effect and Conductivity in p-type Silicon Substrates

Department of Chemistry, Myongji University, Yongin 449-728, KoreaReceived March 11, 2013, Accepted March 26, 2013The lateral photovoltaic effect (LPE) can be observed in semiconductors by irradiating a light spot positionbetween electrodes on sample’s surface. Because lateral photovoltaic voltage (LPV) is sensitively changed bylight spot position, a LPE device has been tried as a position-sensitive detector. This study discusses thecorrelation between LPV and conductivity in p-type silicon and nano-structured Au deposited p-type silicon(nano-Au silicon), respectively. Conductivity measurement of the sample was carried out using the four-wiremethod to eliminate contact resistance, and conductivity dependence on LPV was simultaneously measured bychanging the light irradiation position. The result showed a strong correlation between conductivity and LPVin the p-type silicon sample. The correlation coefficient was 0.87. The correlation coefficient between LPV andconductivity for the nano-Au silicon sample was 0.41.Key Words : Lateral photovoltaic effect (LPE), Lateral photovoltaic voltage (LPV), Conductivity, Correlationcoefficient, Four-wire method IntroductionThe lateral photovoltaic effect (LPE) has been popularlyused in semiconductor systems

Analytical models of lateral power devices with arbitrary vertical doping profiles in the drift region

By solving the 2D Poisson's equation, analytical models are proposed to calculate the surface potential and electric field distributions of lateral power devices with arbitrary vertical doping profiles. The vertical and the lateral breakdown voltages are formulized to quantify the breakdown characteristic in completely-depleted and partially-depleted cases. A new reduced surface field (RESURF) criterion which can be used in various drift doping profiles is further derived for obtaining the optimal trade-off between the breakdown voltage and the on-resistance. Based on these models and the numerical simulation, the electric field modulation mechanism and the breakdown characteristics of lateral power devices are investigated in detail for the uniform, linear, Gaussian, and some discrete doping profiles along the vertical direction in the drift region. Then, the mentioned vertical doping profiles of these devices with the same geometric parameters are optimized, and the results show that the optimal breakdown voltages and the effective drift doping concentrations of these devices are identical, which are equal to those of the uniform-doped device, respectively. The analytical results of these proposed models are in good agreement with the numerical results and the previous experimental results, confirming the validity of the models presented here.

Laterally-biased quantum dot infrared photodetector

At the Air Force Research Laboratory, Space Vehicles Directorate, we are interested in improving the performance of or modifying the capabilities of infrared detectors in order to locate and identify dim and/or distant objects in space. One characteristic we are very interested in is multicolor detection. To this end, we have turned to a novel detector design that we have come to call a Lateral Quantum Dot Infrared Photodetector (LQDIP). In this design, InAs quantum dots are buried in a GaAs quantum well, which in turn is tunnel-coupled to another GaAs quantum well. Photoexcited electrons from the quantum dots tunnel over to the second well and are then swept out via a lateral (perpendicular to the growth direction) bias voltage. This architecture should exhibit the ability to tune to select infrared frequencies with reduced dark current and unity gain. The lateral photocurrent is directed by a vertical (parallel to the growth direction) gate voltage. We will discuss this detector architecture and the LQDIP operating principles and conditions, and we will present some preliminary results of current–voltage, photocurrent, differential conductance, and spectral measurements.

An Analytical Model of Triple RESURF Device with Linear P-layer Doping Profile

An analytical model of Triple RESURF device with linear P-layer doping profile is proposed in the paper. According to the analytical model and numerical simulation, the surface potential and electric field distributions of Single RESURF device, Double and Triple RESURF devices with linear-doped P-layer are investigated. The impacts of the P-layer doping profile on the breakdown voltage and specific on-resistance of Triple RESURF devices are discussed in detail, and the electric field modulation mechanism of the linear-doped P-layer is also described. In addition, the ideal P-layer doping profile, the maximum lateral breakdown voltage, and the optimal N-drift doping concentration are derived to guide the design of the Triple RESURF device. The analytical results are well supported by the simulation results, confirming the validity of the model presented here.

Highly Heat-Dissipating and High-Voltage SOI-LDMOS Power Device

A highly heat-dissipating and high-voltage SOI-LDMOS power device is proposed. Its substrate was selectively etched, like the Camsemi SOI, so breakdown voltage was decided only by lateral breakdown voltage. A p-type layer and a Si3N4 buried layers were introduced into the new structure for lowering specific on-resistance and temperature. The simulation results show that breakdown voltage is 747 V at the 37 μm length of the drift region, and specific on-resistance and maximum surface temperature are reduced by 94.48% and 15.43% than those of Camsemi SOI, respectively.

A New Slope SOI-LDMOS High-Voltage Power Device

A slope SOI-LDMOS power device is proposed for high-voltage. When a positive bais is applied to the drain electrode, holes are induced and astricted by the slope buried oxide layer. So a high density positive charge layer is formed on the buried oxide layer. The electrical field in the buried oxide is improved as well as vertical breakdown voltage by the layer. Because the thickness of the drift region linearly increases from the source to the drain, the surface electric field is optimized, resulting in increase of lateral breakdown voltage. In this paper, the electric characteristics of the new device are simulated by Medici softerware. The result is shown that above 600 V breakdown voltage is obtained at 1μm thick buried oxide layer. The breakdown voltage is higher by three times than that of conventional SOI LDMOS.

I–V and Differential Conduction Characteristics of an AlGaAs/GaAs Lateral Quantum Dot Infrared Photodetector

A new infrared detector design, henceforth referred to as a lateral quantum dot infrared photodetector (LQDIP), with the potential for a tunable internal spectral response was investigated. In this design, InAs quantum dots are buried in a GaAs quantum well, which is in turn tunnel-coupled to a second GaAs quantum well. Photoexcited electrons from the quantum dots are expected to tunnel over to the second well, where they are then swept out via a lateral (perpendicular to the growth direction) bias voltage. The lateral photocurrent is in part directed to tunnel into the second quantum well by the depletion field of a narrow pinch-off gate, applied vertically (parallel to the growth direction). Under a proper biasing arrangement, this detector architecture is expected to exhibit the ability to tune to select infrared frequencies as well as operate with reduced dark currents and unity gain in the second well. The LQDIP detector architecture, operating principles and conditions, and preliminary results of I–V, photocurrent, and differential conductance measurements are all discussed.

A 2-D Analytical Model of Soi High-Voltage Devices with Dual Conduction Layers

By solving 2-D Poisson’s equation, a new analytical model to calculate the electric field distribution of a SOI RESURF device with Dual Conduction Layers (Dual-CL) is firstly proposed. The proposed model is also available for the single RESURF and triple RESURF SOI devices without any modification. A matrix equation is developed for the determination of the lateral and vertical breakdown voltages, in which the influences of the N-top layer, P-top layer, and the N-drift region are all considered. A unified RESURF criterion of single RESURF, triple RESURF, and Dual-CL SOI devices is further derived for optimizing the structure parameters. A good agreement between the analytical results and the numerical results shows that the N-top layer and P-top layer have opposite impacts on the breakdown performance of Dual-CL SOI devices. In addition, an optimal trade-off between the breakdown voltage and the specific on-resistance for the triple RESURF and Dual-CL SOI devices is obtained due to the incorporation of the P-top layer.

An L-Shaped Trench SOI-LDMOS With Vertical and Lateral Dielectric Field Enhancement

For the first time, we report a novel L-shaped trench LDMOS on silicon-on-insulator with double (lateral and vertical) enhanced dielectric field (ENDIF) (DENDIF) effect. This device features an L-shaped trench for accumulating charges (mainly, ionized charges) to enhance lateral breakdown voltage (BV). Then, the vertical ENDIF can be self-adaptive to the lateral ENDIF due to the lumped charges (mainly, inversion charges) at the interface of the buried oxide/silicon. The L-shaped trench makes the potential contours as tree roots, which can spread into the folded drift region to prevent premature breakdown in silicon. The simulated results of the DENDIF LDMOS show that the electric field in the dielectric layer is >; 200 V/μm, the gate-drain charge density (Qgd) is 0.39 nC/mm2, and the Baliga's figure of merit [(FOM); FOM = BV2/RON,sp] is 11.9 MW/cm2.

Transient absorption spectroscopy of a single lateral InGaAs quantum dot molecule

AbstractLateral quantum dot molecules promise a scalable approach to quantum registers. The individual neutral exciton states can be controlled by a lateral bias voltage. In this way radiative emission of localized excitons can be switched between the two quantum dots in the molecule. Here, we report on coherent absorption spectroscopy of a single quantum dot molecule. By transient reflection spectroscopy we demonstrate that not only the emission but also the absorption switches from one dot to the other when varying the applied electric field. This result is consistent with Rabi flopping showing a radically suppressed dipole moment for the non‐emitting exciton transition

Quantitative analysis of electroluminescence images from polymer solar cells

We introduce the micro-diode-model (MDM) based on a discrete network of interconnected diodes, which allows for quantitative description of lateral electroluminescence emission images obtained from organic bulk heterojunction solar cells. Besides the distributed solar cell description, the equivalent circuit, respectively, network model considers interface and bulk resistances as well as the sheet resistance of the semitransparent electrode. The application of this model allows direct calculation of the lateral current and voltage distribution within the solar cell and thus accounts well for effects known as current crowding. In addition, network parameters such as internal resistances and the sheet-resistance of the higher resistive electrode can be determined. Furthermore, upon introduction of current sources the micro-diode-model also is able to describe and predict current-voltage characteristics for solar cell devices under illumination. The local nature of this description yields important conclusions concerning the geometry dependent performance and the validity of classical models and equivalent circuits describing thin film solar cells.

Analysing Solar Cells by Circuit Modelling

Solar cell models implemented in simulation packages (for example Sentaurus TCAD) are typically restricted either to only one or two dimensions, or to small scales. They therefore neglect effects of local inhomogeneities or large scale phenomena such as lateral transport to fingers or busbars. In this paper, we use a distributed circuit model to investigate lateral inhomogeneity effects on silicon wafer solar cells. The circuit is constructed of different unit elements based on the one-diode model. To calculate the characteristics of the circuit, we use the freely available software LTspice IV (Linear Technology Corp). The presented model is used to simulate the distributed current flow in a solar cell. First, the design of the distributed circuit model is described. Then, the current-voltage characteristics obtained by the distributed circuit model are compared with those obtained from measurements. Finally, one kind of large-scale lateral effect, the voltage distribution across the solar cell area, is analysed. Due to lateral ohmic voltage drops, the electric potential at the cell surface is shown to be higher in the middle between two busbars or fingers than close to them.

Electroluminescence as Characterization Tool for Polymer Solar Cells and Modules

We show that laterally resolved luminescence detection is a highly versatile measurement technique for the characterization of polymer solar cells and modules. Besides lock-in thermography also luminescence imaging is highly suitable for quality control of processing steps, especially the control of homogeneous layer deposition and the proper lateral function of polymer solar cells and modules, by identification of local defects. Furthermore the application of luminescence imaging allows discrimination between active layer and organic/electrode-interface degradation in stability experiments. By correlation with photovoltaic parameters important conclusions can be drawn with respect to the specific degradation mechanism. For quantitative interpretation of such electroluminescence images, we propose an equivalent circuit model in which local solar cells are interconnected by resistors representing the sheet resistance of the transparent electrode. In combination with the laterally resolved measurement of electroluminescence, the application of this model allows calculation of local photovoltaic parameters and quantification of the lateral current and voltage distribution.

Charge Collection Studies and Electrical Measurements of Heavily Irradiated 3D Double-Sided Sensors and Comparison to Planar Strip Detectors

Three-dimensional (3D) silicon detectors offer advantages over standard planar devices as more radiation hard sensors. These detectors and their applications in the upgrades of the LHC experiments are discussed. 3D detectors with a double-sided geometry have been fabricated as very short strip detectors with similar inter-column spacing as proposed for the ATLAS pixel detector and LHCb vertex locator upgrades. The detectors have been irradiated up to a fluence of 2 × 1016 cm-2 1 MeV equivalent neutrons, which is twice the expected dose of the inner pixel layer of the ATLAS detector and of the upgraded LHCb vertex locator for LHC high luminosity upgrade (HL-LHC) operation. Electrical measurements show a lateral depletion voltage of only 4 V for the device before irradiation which increases to 200 V after an irradiation to a fluence of 1 × 1016 cm-2 1 MeV equivalent neutrons. The strip isolation of the p-type detectors was robust to the maximum fluence. Charge collection studies have been performed with analogue readout with 25 ns shaping time, as required for LHC experiments. The response of the detectors to high energy electrons from a 90Sr source and a collimated pulsed laser light source are shown and compared with planar devices. The 3D detector, operated at no more than 350 V, is shown to have superior charge collection characteristics to planar devices for all the fluence range expected at HL-LHC even when compared to planar devices operating at 1000 V. When operated at a bias voltage of 350 V the 3D detector collects 2.8 times more charge than a p-type planar device operated at 1000 V after a fluence of 1016 cm-2 1 MeV equivalent neutrons. Charge multiplication in 3D detectors is also reported, in both 90Sr and laser tests, which leads to further enhancement in the charge collection and signal-to-noise ratio of the detector. The effect is demonstrated, through laser tests, to occur close to the junction electrode.

In Situ Hydrodynamic Lateral Force Calibration of AFM Colloidal Probes

Lateral force microscopy (LFM) is an application of atomic force microscopy (AFM) to sense lateral forces applied to the AFM probe tip. Recent advances in tissue engineering and functional biomaterials have shown a need for the surface characterization of their material and biochemical properties under the application of lateral forces. LFM equipped with colloidal probes of well-defined tip geometries has been a natural fit to address these needs but has remained limited to provide primarily qualitative results. For quantitative measurements, LFM requires the successful determination of the lateral force or torque conversion factor of the probe. Usually, force calibration results obtained in air are used for force measurements in liquids, but refractive index differences between air and liquids induce changes in the conversion factor. Furthermore, in the case of biochemically functionalized tips, damage can occur during calibration because tip-surface contact is inevitable in most calibration methods. Therefore, a nondestructive in situ lateral force calibration is desirable for LFM applications in liquids. Here we present an in situ hydrodynamic lateral force calibration method for AFM colloidal probes. In this method, the laterally scanned substrate surface generated a creeping Couette flow, which deformed the probe under torsion. The spherical geometry of the tip enabled the calculation of tip drag forces, and the lateral torque conversion factor was calibrated from the lateral voltage change and estimated torque. Comparisons with lateral force calibrations performed in air show that the hydrodynamic lateral force calibration method enables quantitative lateral force measurements in liquid using colloidal probes.

High voltage buried step-doping p+ layer silicon-on-insulator lateral double diffused mosfet (SOI LDMOSI) with a back-gate

A high voltage buried step-doping p+layer (BSP+L) lateral double diffused mosfet (LDMOS) on silicon-on-insulator (SOI) with a back-gate is proposed. The new structure is characterized by a BSP+L on the buried oxide under the source. When a high positive bias is applied to the back-gate in the off-state, the depleted BSP+L greatly enhances the electric field in the buried oxide layer under the source. Compared with conventional SOI LDMOS, much higher vertical breakdown voltage is sustained by the buried oxide layer under the source. Moreover, the reduced surface electric field (RESURF) effect is enhanced by the BSP+L, resulting in improvement of lateral breakdown voltage. Simulation results show that breakdown voltage of the new structure is improved greatly while on-resistance is relatively low. Key words: Silicon-on-insulator, breakdown voltage, back-gate, buried step-doping p+ layer.

Controlling DNA Translocation through Gate Modulation of Nanopore Wall Surface Charges

One major challenge of nanopore-based DNA sequencing technology is to find an efficient way to reduce DNA translocation speed so that each nucleotide can reside long enough in the pore for interrogation. Here we report the electrical tuning of DNA translocation speed by gate modulation of nanopore wall surface charges. We find that native surface-charge-induced counterions in the electroosmotic layer substantially enhance advection flow of fluid, which exerts stronger dragging forces on the translocating DNA, and thereby lowering the DNA translocation speed. We propose a feedback device architecture to regulate DNA translocation by modulating the effective wall surface charge density σw*via lateral gate voltages--at the beginning, a positive gate bias is applied to weaken σw* in order to enhance the capture rate of DNA molecule; upon detection of ionic current variance indicating DNA has been driven into the nanopore, gate bias is turned to be negative so that σw* is reinforced and DNA translocation is retarded. We show that a gate electric field can dramatically decrease the DNA translocation speed at a rate about 55 μm/s per 1 mV/nm.