Internal Diode Research Articles

A novel SiC superjunction MOSFET with three-level buffer and unipolar channel diode

A novel SiC trench superjunction MOSFET with an integrated unipolar channel diode and three-level buffer (DioSJ-MOS) is proposed, which features an additional planar channel and a three-level buffer (TLB). The planar channel brings the effect of dual-channel forward conduction and unipolar reverse conduction, reducing specific on-resistance and improving third quadrant performance. The TLB composed of P-pillar, P + body and thickened oxide layer optimizes the in-body and gate-oxide electric field, improving gate oxide reliability, enhancing device breakdown voltage and lessening the gate-drain coupling. Furthermore, an embedded channel diode with low potential barrier for electrons transport replaces internal parasitic diode successfully. Compared with conventional MOSFET (SF-MOS) and trench/planar MOSFET (TP-MOS), DioSJ-MOS exhibits a lower specific on-resistance (1.08 mΩ cm2), an improved gate oxide electric field (2.6 MV/cm) and a better third quadrant performance （1.56 V） due to TLB structure and unipolar channel diode. Meanwhile, the gate to drain charge (QGD) and capacitance (CGD) of DioSJ-MOS are significantly reduced by about 3 × and 4 × in comparison with TP-MOSFET. Therefore, the overall enhanced performance indicates that DioSJ-MOS is more attractive device in high-voltage, high-reliability and high-frequency applications.

High performance SiC trench-type MOSFET with an integrated MOS-channel diode

A novel SiC double-trench metal-oxide-semiconductor field effect transistor (MOSFET) with integrated MOS-channel diode is proposed and investigated by Sentaurus TCAD simulation. The new SiC MOSFET has a trench gate and a stepped-trench source, and features an integrated MOS-channel diode on the top sidewall of the source trench (MT MOS). In the reverse conduction state, the MOS-channel diode turns on firstly to prevent the internal parasitic body diode being activated, and thus reduces the turn-on voltage V F and suppresses the bipolar degradation phenomena. The V F of 1.70 V (@I ds = –100 A/cm2) for the SiC MT MOS is 38.2% lower than that of SiC double-trench MOSFET (DT MOS). Meanwhile, the reverse recovery charge Q rr of the MT MOS is 58.7% lower than that of the DT MOS at I load = 700 A/cm2, and thus the reverse recovery loss is reduced. Furthermore, owing to the modulation effect induced by the double trenches, the MT MOS preserves the same superior forward conduction and blocking performance as those of DT MOS, with 22.9% and 18.2% improvement on breakdown voltage and R ON,sp compared to the trench gate MOSFET with planar integrated SBD (ST MOS).

Optimization of the Cryogenic Light-Emitting Diodes for High-Performance Broadband Terahertz Upconversion Imaging

High-performance terahertz (THz) imaging devices have drawn wide attention due to their significant application in a variety of application fields. Recently, the upconversion device based on the integrated homo-junction interfacial workfunction internal photoemission detector and light-emitting diode (HIWIP-LED) has emerged as a promising candidate for broadband THz upconversion pixelless imaging device. In this paper, systematical investigations on the cryogenic-temperature performances of the LED part in HIWIP-LED devices, including electroluminescence (EL) spectra and the EL efficiency, have been carried out by elaborating the radiative recombination mechanism in the quantum well, internal quantum efficiency, and the light extraction efficiency (LEE) both experimentally and theoretically. On this basis, we have further studied the operation mode of the HIWIP-LED and concluded that the LEE could directly determine the upconversion efficiency. A numerical simulation has been performed to optimize the LEE. Numerical results show that the device with a micro-lens geometry structure could significantly improve the LEE of the LED thereby increasing the upconversion efficiency. An optimal upconversion efficiency value of 0.12 W/W and a minimum noise equivalent power (NEP) of 14 pW/Hz1/2 are achieved using the micro-lens structure together with anti-reflection coating. This work gives a precise description of cryogenic LED performance in the HIWIP-LED device and provides an optimization method for the broadband HIWIP-LED THz upconversion pixelless imaging device.

Junction Temperature Measurement Method for Thermal Resistance Testing of SiC MOSFET Module

The internal anti-parallel Schottky barrier diode threshold voltage of SiC metal-oxide-semiconductor field-effect transistor (MOSFET) modules is less than that of their body diodes, which prevents the use of the body diode voltage drop to measure junction temperature. In this paper, a thermal resistance test of the SiC MOSFET module is proposed based on the onstate voltage drop as a temperature-sensitive electrical parameter. Measurements are performed with the method and its feasibility evaluated. The on-state voltage drop temperature sensitivity under different gate voltages and the repeatability of the on-state voltage drop parameters before and after electric power heating in the thermal resistance tests are studied. The on-state voltage drop is measured under a high gate voltage and the accuracy of junction temperature measurement improves when the grid voltage remains the same during heating and measurement.

A Novel Non-Isolated Three-Port Bidirectional DC/DC Converter for Photovoltaic Electric Scooter Charging Stations

This paper proposes a novel non-isolated three-port bidirectional dc/dc converter for photovoltaic (PV) electric scooter (ES) charging stations. The proposed converter combines an improved boost converter and a bidirectional buck-boost converter. When the PV energy is sufficient, the PV module is stepped up to provide dc load energy to the ES through the improved boost converter in order to charge the ES battery. When the PV energy is insufficient, the storage battery is stepped up to provide energy to the ES load dc bus, and the ES load dc bus charges the battery if the battery energy is low. The proposed converter reduces the number of components and circuit cost by using a switch internal diode. Finally, a 400-W modified boost converter and a 120-W/60-W bidirectional boost-buck converter were implemented to verify the three operating modes of the proposed non-isolated dc/dc converter. The results revealed that the highest efficiency levels achieved under PV module step-up, storage battery step-up, and storage battery step-down operation were 97.5%, 96.6%, and 92%, respectively.

Investigation of the avalanche ruggedness of SiC MPS diodes under repetitive unclamped-inductive-switching stress

State of the art freewheeling diodes are connected antiparallel with a switch like IGBT or MOSFET and for latter also with the internal body diode. The diodes have to be rugged enough to overcome temporary overvoltage and overcurrent conditions during transient operation. SiC merged pin Schottky (MPS) diodes are one of the superior contenders and thus it is essential to make investigations under high avalanche energy. In this work, an avalanche ruggedness of 20 A/1.2 kV SiC MPS diodes was investigated far beyond the specified maximum ratings of the device under unclamped inductive switching (UIS) measurement. The function of avalanche energy versus applied inductance was investigated under single event avalanche stress. The reliability under high repetitive avalanche energy was studied in detail. A forward voltage drift, change in the Schottky junction voltage and increase in the leakage current was observed after the high repetitive avalanche stress far beyond the safe operating area. Detailed failure analysis was made, focusing on the degradation of the metallization and possible stacking faults (SFs) in the SiC bulk. Furthermore, the temperature was determined as a function of the blocking voltage during avalanche stress.

Failure of Switching Operation of SiC-MOSFETs and Effects of Stacking Faults on Safe Operation Area

When developing silicon carbide (SiC) devices, the reliability of the internal body diode is an important issue. Stacking faults (SFs) are expanded from basal plane defects by using a body diode. Although it is well known that ON-voltage degradation occurs due to SFs, their effects on dynamic reliability have not been studied well. Furthermore, including the effects of SFs, there are not many reports about the dynamic reliability of SiC-MOSFETs. In this paper, a double-pulse switching test using 3.3-kV SiC-MOSFETs was carried out to clarify the failure mechanism of the switching operation of SiC-MOSFETs and effects of SFs on the safe operation area (SOA). Before the switching test, current stress was applied to the body diode of the devices under test (DUTs) to expand the SFs. The circuit configuration was half-bridge type, and a double-pulse gate signal was applied to the lower arm DUT. The switching voltage was 1.8 kV, and the switching current increased at about 8-A steps to failure. As a result, reverse recovery SOA (RRSOA) reliability decreased depending on the amount of SFs in the SiC-MOSFET. Because RRSOA failure was caused by avalanche due to the hole concentration during reverse recovery and the SFs raised local current density, reverse bias SOA (RBSOA) hardly decreased even if SFs containing SiC-MOSFETs were used. This is because RBSOA failure was caused by degradation of the gate isolation layer due to overheating and the temperature coefficient of the SFs electric resistance indicated negative.

Improvement of qualitative indicators of LLC converter using the evaluation method FoM of perspective semiconductor and magnetic components

The paper deals with FoM parameter analysis of power semiconductor system’s components. This parameter can be used as optimization tool of quality indicators for power supply systems. The main advantage of using FoM assessment technique for certain system’s components is the elimination of simulation and physical experiments for efficiency evaluation. This paper consists of description of FoM assessment process for perspective converter topologies, for various operational conditions, while the appropriateness of using this method is verified by simulation experiments of proposed converter system with high degree of validity. Also in the paper, the experimental measurement of converter at various operational conditions is taken, where we find that it is necessary to modify the calculations of FoM parameter for transistors for the application using internal body diode. The relevancy of FoM parameter is finally evaluated in the way of efficiency (one of the qualitative indicators) investigation, where different materials of transformers are also considered within verification. At the end of the paper, analysis was conducted using a perspective semiconductor device and simulation analysis in the way of implementation of synchronous rectifier into the investigated converter.

Novel Snapback-Free Reverse-Conducting SOI-LIGBT With Dual Embedded Diodes

A novel 500 V reverse-conducting (RC) silicon-on-insulator lateral insulated gate bipolar transistor (SOI-LIGBT) with dual embedded diodes (DEDs) is proposed to eliminate the snapback, and its mechanism is investigated by simulation. The RC is realized by the internal diode, which consists of two p-i-n diodes (D1 and D2). The two diodes are connected in series. In the RC-state, the current flows through D1 first and then through D2. D2 is embedded in the anode region of the proposed DED-LIGBT and is fully isolated by the deep-oxide trench. In the forward conducting state, D2 is reverse biased and the electrons from the N+ cathode can only flow into the P+ anode. The DEDs reroute the electron current path, and thus, the snapback is avoided. Moreover, by adjusting the width of D2 ( ${W}_{b})$ , the internal diode of the DED structure achieves superior reverse recovery time ( ${t}_{\text {rr}})$ and reverse recovery peak current ( ${I}_{\text {rrm}})$ to the conventional SOI p-i-n diode.

A photobioreactor for microalgae cultivation with internal illumination considering flashing light effect and optimized light-source arrangement

In this study, a photobioreactor for mass-culturing microalgae was developed. Because of the optimized arrangement of internal light-emitting diode (LED) illumination, a major advantage to this reactor is that the volume of the reactor vessel is not limited. Using Dunaliella tertiolecta as the microalgae, the bioreactor displayed the flashing-light effect of the microalgae photosynthesis process. This phenomenon was achieved using a series of blue and red LEDs set at appropriate positions within the reactor to evenly distribute the light intensity. Our experimental results suggested that the maximum cell density in the culture experiment was 1.88×103cellsL−1, which is approximately 67% of the maximum density under ideal conditions. The harvest yield of the algae was estimated by a numerical model using measured parameters; it was predicted that the bioreactor developed in this study can attain a high growth rate of D. tertiolecta by controlling the distance between LEDs.

Electrical Characteristic Study of an SOI-LIGBT With Segmented Trenches in the Anode Region

This paper presents the electrical characteristic of a 500 V silicon-on-insulator (SOI) lateral insulated-gate bipolar transistor (LIGBT) with segmented trenches in the anode (STA) region. The STA-LIGBT features segmented n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> anodes and segmented trenches. The segmented n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> anodes are shorted to the p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> anode, which accelerates the extraction of stored electrons during the device turn-OFF. The segmented trenches are arranged between the p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> anode and the shorted n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> anode. The resistors between the adjacent segmented trenches and the adjacent segmented n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> anodes contribute to low snapback voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</sub> ) while maintain high current density. In addition, an internal diode is formed by introducing the shorted n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> anode. The 3-D simulations and the experiments are carried out to characterize the electrical performances of the STA-LIGBT and its internal diode. Compared with the conventional SOI-LIGBT, the STA device achieves a 73% improvement in turn-OFF time (t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> ) at the same current density. Correspondingly, the internal diode of the STA-LIGBT achieves a forward voltage drop (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</sub> ) of 1.32 V and a reverse recovery time (t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rr</sub> ) of 321 ns, which are superior to those of a conventional p-i-n SOI diode.

Analysis of different forward current–voltage behaviours of Al implanted 4H-SiC vertical p–i–n diodes

In this work different experimental current–voltage behaviours of several Al implanted 4H-SiC p–i–n diodes are investigated by means of numerical simulations in a wide range of currents and temperatures. Some devices for which recombination and tunneling are the dominant current processes at all biases are classified as “leaky” diodes. The well behaved diodes, instead, show good rectifying characteristics with a current conduction due to tunneling below 1.7V, recombination between 1.7V and 2.5V, and diffusion processes above 2.5V. At higher current regimes, a series resistance in excess of 1mΩcm2 becomes the main current limiting factor. Depending on the relative weight between the contact resistances and the internal diode resistance, different temperature dependencies of the current are obtained. A good agreement between numerical and measured data is achieved employing temperature-dependent carrier lifetime and mobility as fitting parameters.

Effect of conjugated polyelectrolyte interlayer at cathode in bulk heterojunction photocells based on neat C70 and low-energy-gap polymer prepared with halogen-free solvent

The effect of the insertion of a very thin layer of a conjugated polyelectrolyte poly[9,9-bis(3′-(N,N-dimethylamino)-propyl-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN) at the composite/cathode interface in bulk heterojunction photocells based on a low-energy-gap polymer PTB7 and neat C70 is studied. The device performance is sensitive to the deposition condition of the PFN layer. An analysis based on a simple one-diode equivalent circuit model reveals that the PFN interlayer deposited under an appropriate condition effectively reduces the saturation current of the internal diode as well as the series resistance, resulting in a power conversion efficiency (PCE) of over 4%.

Current and illumination dependent series resistance of solar cells

Precise knowledge of the series resistance is essential for failure and loss analysis as well as yield prediction of solar cell devices. In this work, a method which determines the current and photogeneration dependence of the series resistance without assuming any specific current-voltage characteristic for the internal diodes is presented. This approach is of particular interest for solar cells which cannot be described by the one- or two-diode model such as organic solar cells. Furthermore, it clarifies the difference in the series resistance values that are obtained from current-voltage curves in the dark and under illumination as well as short-circuit-current and open-circuit-voltage characteristics. Additionally, it is shown how other cell parameters, such as the shunt resistance or the current-voltage characteristic of the internal diode are determined in a consistent way. Finally, it is demonstrated that our approach can be easily implemented in a new generation of solar simulators that are based on light-emitting diodes instead of conventional light sources.

Development of 3.3 kV SiC-MOSFET: Suppression of Forward Voltage Degradation of the Body Diode

In order to achieve cost reduction or shrinkage of power devices, an internal body diode, which forms in a MOSFET parasitically, can be designed as a free-wheeling diode in substitution for an external Schottky barrier diode (SBD). However, in a SiC p-i-n diode, forward current stress causes reliability degradation due to expansion of the electron-hole recombination-induced stacking faults. Applying the process optimization of the epitaxial layer for the reduction of recombination-induced stacking faults and the body diode screening method to 3.3 kV SiC-MOSFETs, we obtained more stable devices under forward current operation.

High Internal Quantum Efficiency Blue-Green Light-Emitting Diode with Small Efficiency Droop Fabricated on Low Dislocation Density GaN Substrate

We fabricated blue (∼450 nm), blue-green (∼500 nm), and green (∼525 nm) light-emitting diodes (LEDs) of different dislocation densities (DD) and characterized their internal quantum efficiency (IQE). The IQE of the blue LEDs fabricated using GaN substrate exceeded 90% (DD: ∼106 cm-2), however, when we used a GaN-on-sapphire substrate (DD: ∼108 cm-2), IQE was limited to ∼60%. Droop was reduced by use of the GaN substrate. The junction temperature of the GaN-on-sapphire substrate was found to be ∼200 °C although the junction temperature of the GaN substrate was ∼50 °C when a forward current of 100 A/cm2 was driven. A lowering of IQE in green LEDs to ∼60% was observed, even though we used a low-dislocation-density substrate [DD: (1–2)×107 cm-2]. The junction temperature of blue-green and green LEDs was about 100 °C when a forward current of 177 A/cm2 was driven, which indicated that junction temperature is not a major factor for IQE suppression in green LEDs.

Silicon–carbide junction field effect transistor built-in diode: an experimentally verified electrical model

Wide band-gap semiconductor devices like silicon-carbide junction field effect transistor (SiC JFET) are being applied in several industrial applications. Converters using these advanced devices have been introduced. SiC JFETs from SiCED/Infineon enable design of diodeless inverters. This is a positive argument regarding reliability issues for a harsh environment. From a design point of view, primary circuit models of SiC JFET have already been published but the internal diode has not been addressed so far. There is thus an interest for an accurate model of the SiC JFET built-in diode. In this study, this internal diode is demonstrated to be a power PiN diode. A novel analytical state-space model of this diode is proposed and the design parameters are identified. It is important to note, that these parameters are crucial for the device behaviour, modelling and fabrication procedure. The proposed model and associated parameters are validated with built-in diodes of several SiC JFETs. The validity domains are discussed.

Study on the Output Characteristics of Organic Photovoltaic Cells

Based on the analysis of the equivalent circuit model of organic photovoltaic (OPV) cells, the explicit expression of current, short-circuit current and open-circuit voltage was obtained by means of W-function, and the effects of internal resistances and diode quality factor on the output characteristics of OPV cells were studied. The results demonstrate that the series resistance can effect short-circuit current but not open-circuit voltage, and the shunt resistance and diode quality factor can influence open-circuit voltage but short-circuit current unchanged. The decrease in series resistance and the increase in shunt resistance and diode quality factor can enhance the fill factor and energy conversion efficiency of OPV cells. This conclusion is essential in preparing OPV cells and improving device performance.

Improved Electrostatic Discharge Protection in GaN-Based Vertical Light-Emitting Diodes by an Internal Diode

We first fabricated GaN-based vertical light-emitting diodes (LEDs) with electrostatic discharge (ESD) protection internal diode. Despite the reduced emitting area due to the internal diode, the LEDs with the internal diode give a forward voltage of 3.42 V at 350 mA similar to that (3.40) of LEDs without the internal diode. It is shown that the output power of the LEDs with the internal diode is reduced by about 6% at 350 mA compared to reference LEDs without the internal diode. It is, however, further shown that the LEDs without the internal diode give a yield of 0% at the reverse voltages above 400 V, while the LEDs with the internal diode show a yield of ~ 90% at reverse voltages of 2-4 kV.

GaN-Based Power Flip-Chip LEDs With an Internal ESD Protection Diode on Cu Sub-Mount

The authors demonstrate the fabrication of 1 mm t 1 mm GaN-based power flip-chip light-emitting diodes (LEDs) with an internal electrostatic discharge (ESD) protection diode on Cu sub-mount. With the internal diode, it was found that forward voltage of the LED increased from 3.22 to 3.38 V while output power decreased from 366.5 to 273.9 mW when under 350 mA current injection due to the reduced light emitting area. It was also found that we can achieve a significantly better ESD robustness by building the internal diode inside the LED chip. Furthermore, It was found that 90% of the LEDs with internal diode survived with an applied reverse ESD surge of 12000 V and 25% of the LEDs can even endure 20000 V reverse ESD stressing.