Simulated turn-off of 4H-SiC gate turn-off thyristors with gateelectrodes on the p-base or the n-base

Turn-off simulations of a 4H-SiC GTO thyristor structure having a gated p-base and p-type substrate are compared with that having a gated n-base and n-type substrate. Two gate drive circuits are considered, one with a voltage source and resistor between the gate and adjacent emitter region, and the other with a voltage source and resistor between the gate and farthest emitter region. The gated n-base thyristor's substrate current increases atypically before the device turns off. Also, the gated n-base structure turns off when the gate circuit is connected directly to the emitter region furthest from the gate region, but the gated p-base structure does not. Furthermore, turn-off gain is lower for the gated n-base structure due to mobility differences as demonstrated by current-voltage (I-V) and current versus time (I-t) curves     

A study on GTO turn-off failure mechanism—A time- and temperature-dependent 1-D model analysis

A 1-D model is presented for use in analyzing the GTO thyristor turn-off process, including the conduction region squeezing effects as well as the current due to temperature variation, i.e., thermal diffusion and the current due to bandgap variation with temperature change. The model simulates current-voltage characteristics for the current concentrated area, where the current density increases almost linearly with the anode voltage. It is found that the nonuniformity in the p-base sheet resistance is a significant cause for the current concentration because of the enhanceddv/dtcurrent due to the excess carrier removal from the highly injected n-base. The model also predicts the limitation to the anode voltage imposed on the device before the current is completely turned off.     

Electric characteristics of contact junctions between NbTimultifilamentary wires

Anomalous current-voltage characteristics have been found for a mechanical contact junction between NbTi superconducting multifilamentary wires. The pressure contact junctions between superconductors were created by either parallel-conductor contact or crossed-conductor contact. The junctions are superconductive over a limited current range. The current-voltage characteristics show switching phenomena, that are both large and very fast, at transitions between zero voltage and resistive states. The switching time is about 2 μs. A zero-voltage current of about 60 A was obtained for a 75-mm-long junction at zero applied magnetic field. The current-voltage curve of the junction shows hysteresis that varies with the contact junction's structure. It has been confirmed that mechanical pressure contact junctions can be used as persistent switches without heaters. Additionally, contact junctions may provide uniform current distribution for multistrand cables     

A New Emitter Switched Thyristor (EST) employing Trench Segmented p-base

A new emitter switched thyristor (EST) employing trench segmented p-base, which successfully improves the forward I-V and switching characteristics with decreasing the device active area, is proposed and verified experimentally with using shallow trench process of novel junction termination extension (JTE) method. The latching current of EST is determined by the p-base resistance of upper npn transistor. Floating n+emitter of conventional EST is enlarged to obtain large base resistance. However, the proposed EST increases the p-base resistance with shorter floating n+ emitter than that of conventional one. Shallow trench in floating emitter region forms the highly resistive p-base region under the bottom of trench. The experimental results show that the shortened floating n+ emitter and lowered latching current of proposed EST decrease experimentally the forward voltage drop by 17.7% and snap-back phenomenon with small active area. The breakdown voltage of series lateral MOSFET of proposed EST is increased from 7 to 14 V due to the trench filled with oxide which results in vertical redistribution of electric field, therefore current saturation capability and forward biased safe operating area (FBSOA) of proposed EST are enhanced. The simulation results show that the switching operation is performed successfully at the blocking voltage of 600 V and Eoff of the proposed one is reduced by 3.7%. The measured inductive load switching characteristics also shows that Eoff of proposed one is improved by 7.2%.     

A high-conductivity insulated gate bipolar transistor with Schottky hole barrier contact

This letter proposes a high-conductivity insulated gate bipolar transistor (HC-IGBT) with Schottky contact formed on the p-base, which forms a hole barrier at the p-base side to enhance the conductivity modulation effect. TCAD simulation shows that the HC-IGBT provides a current density increase by 53% and turn-off losses decrease by 27% when compared to a conventional field-stop IGBT (FS-IGBT). Hence, the proposed IGBT exhibits superior electrical performance for high-efficiency power electronic systems.     

High speed turn-on reverse conducting 4 kV static induction thyristors based on the buried gate type p-base n-emitter soft contact structure and anti-parallel diodes for solid-state power supplies in high energy accelerators

Buried gate type p-base n-emitter soft contact (PNSC) structure 4 kV static induction thyristors (SIThys) have been fabricated in order to make thyristors for high-speed turn-on applications to such as high energy accelerators. It was found that these static induction thyristors could be fabricated under the test pilot line with a good device production yield. The static characteristics and pulse switching characteristics of these static induction thyristors are examined. Several application examples of the present 4 kV static induction thyristors to power supplies for high energy accelerators are shown.     

Investigation of the lateral turn-on process of thyristors with an epitaxial p-base

In this paper, the effect of the p-base doping concentration NAon the spreading velocity vsin power thyristors is examined. Chemical vapor deposition (CVD) techniques are used to produce the p-base layer, in order to change the p-base doping concentration and thickness independently. The results show a large reduction of vswith growing p-base doping concentration. At a doping concentration higher than 5 × 10¹⁶/cm³the spreading velocity follows a power law with an exponent of -0,9. The introduction of a sandwiched low-doped player between the p⁺-base and the n-emitter slows down the plasma propagation. The decrease of vs, in both cases, is attributed to the reduction of the current gain β2of the n-p-n transistor with doping concentration. In order to explain this behavior, a simple expression for the spreading velocity is derived, which relates the spreading velocity to the time constant of current rise trand consequently to the feedback loop gain (β1β2) of the two transistor components. In this derivation, only the lateral drift current in the p-base is taken into account. It was found that vsis given byv_{s} sim 1/t_{r} sim ln beta_{1}beta_{2}, in good agreement with the experiment.     

Theoretical and experimental characteristics of the base resistancecontrolled thyristor (BRT)

Described are the characteristics of a new MOS gated thyristor structure called the base resistance controlled thyristor (BRT), in which the turn-off of a thyristor built with an N drift region is achieved by reducing the resistance of the p-base region under MOS gate control. A p-channel MOSFET used to achieve turn-off is formed in the N drift region. The device is designed so that, when the p-channel MOSFET is switched on, holes are diverted from the p-base region of the thyristor into the adjacent p⁺ region, raising the holding current of the thyristor above the operating current level, and turning off the thyristor. Results of extensive 2-D numerical simulations that have been performed to demonstrate operation of this new device concept are discussed. Experimental results on 600-V devices fabricated with an IGBT process have corroborated theoretical predictions. Current densities above 900 A/cm² have been turned off at room temperature with a gate bias of -10 V     

A time- and temperature-dependent 2-D simulation of the GTO thyristor turn-off process

GTO thyristor turn-off process is analyzed for a resistive load case by performing an exact two-dimensional time- and temperature-dependent numerical simulation. A newly defined concept "on-region" is introduced to help understanding of the simulation results. Excess carrier plasma (on-region) in the p-base is squeezed finally to as narrow as 60 µm wide, accompanying a large current density increase at the center of the middle junction. The carriers in the n-base are found not to be greatly affected by the initial plasma squeezing in the p-base. After the on-region width in the p-base reaches its final limit, the excess carriers around the middle junction of the final on-region is rapidly reduced, resulting in complete anode current turn-off.     

The effects of finite contact energy barriers and traps on space-charge-limited currents in thin insulators

The effects of finite contact energy barriers and small insulator thickness on space-charge-limited currents are investigated. Diffusion effects are implicitly considered. The analysis is extended to include a variety of common trap distributions, and numerical results are given using zinc sulphide as the insulator. The concepts discussed are illustrated by current-voltage characteristics computed from the exact space-charge-limited theory.     

Energetic deposition,measurement and simulation of graphitic contacts to 6H-SiC

Junctions between energetically deposited graphitic carbon and n-type 6H-SiC have been fabricated. Their current-voltage characteristics have been measured and compared with simulations using Sentaurus TCAD finite element software. Agreement between the experimental and simulated current-voltage characteristics was achieved using parameters derived from electrical measurements and electron microscopy. Using the best-fit models, the effects of interfacial layers and contact work function variations were elucidated to provide guidance for improved device performance.     

The influence of high-temperature annealing on SiC schottky diode characteristics

The influence of high temperature (up to 800C) annealing on the current-voltage characteristics of n-type 6H-SiC Schottky diodes is presented. Our experimental results indicate that high-temperature annealing can result in the improvement of the forw ard and reverse electrical characteristics of SiC Schottky diodes by repairing any leaky low barrier secondary diode parallel to the primary diode that may be present due to the barrier inhomogeneities at the Schottky contact interface.     

Tunneling current of the contact between impurity-containing graphene nanoribbons

The current-voltage characteristics of a tunneling contact between two graphene nanoribbons containing impurity atoms are obtained based on the previously calculated density of states. The dependences on the nanoribbon geometrical and energy characteristics are calculated.     

Flip Chip Bonding of 68 $times$ 68 MWIR LED Arrays

The flip chip bonding process is optimized by varying the bonding pressure, temperature, and time. The 68times68 mid wave infrared (MWIR) LED array was hybridized onto Si-CMOS driver array with same number of pixels. Each pixel has two indium bumps, one for cathode and another for anode. Both LED array and CMOS drivers have 15-mum-square Indium bump contact pads. We used Karl Suss FC150 flip chip machine for bonding of CMOS driver array onto LED array. From the LED current-voltage characteristics, it is concluded that the optimized flip chip bonding process results in uniform contact and very low contact resistance. Both electrical and optical characteristics of LED array after flip chip bonding are presented.     

IGBT dynamics for clamped inductive switching

Clamped inductive switching performance of insulated gate bipolar transistors (IGBTs) have been studied in detail with the aid of extensive measurements and numerical simulations. Internal dynamics of a latch-up free punch-through IGBT during clamped inductive switching is studied using two-dimensional (2-D) mixed device and circuit simulations incorporating the self-heating mechanism. Failure of IGBT during inductive load turn-off is shown to occur due to thermally assisted carrier multiplication at the reverse biased p-base n-drift region junction under the emitter contact     

Sources of spontaneous emission based on indium arsenide

The results obtained for light-emitting diodes based on heterostructures that contain InAs in the active region and are grown by the methods of liquid-phase, molecular-beam, and vapor-phase epitaxy from organometallic compounds are reviewed. The emission intensity, the near-field patterns, and the light-current and current-voltage characteristics of light-emitting diodes that have flip-chip structure or feature a point contact are analyzed.     

Effect of photovoltage on current flow in metal-semiconductor schottky-barrier contacts

It is shown that changes in device characteristics and an increase in the light-to-electrical energy conversion efficiency in metal-semiconductor Schottky barrier contacts are associated with a peripheral electric field built into the contact. For contacts with longer perimeters, variations in device characteristics and the light-to-electrical energy conversion efficiency are significantly larger. Since the photovoltage and peripheral electric fields in the contact region are codirected with the intrinsic electric field of the space-charge region, contact illumination results in a larger increase in the “dead” zone in forward portions of current-voltage characteristics, a larger decrease in the effective Schottky barrier height, and an increase in the field electron emission. An increase in the reverse field emission under photovoltage leads to an increase in the recombination current in the space-charge region, which provides dc photocurrent flow in the circuit.     

Novel lateral IGBT with n-region controlled anode on SOI substrate

A new lateral insulated-gate bipolar transistor (LIGBT) structure on SOI substrate, called an n-region controlled anode LIGBT (NCA-LIGBT), is proposed and discussed. The n-region controlled anode concept results in fast switch speeds, efficient area usage and effective suppression NDR in forward I-V characteristics. Simulation results of the key parameters (n-region doping concentration, length, thickness and p-base doping concentration) show that the NCA-LIGBT has a good tradeoff between turn-off time and on-state voltage drop. The proposed LIGBT is a novel device for power ICs such as PDP scan driver ICs.     

4H-SiC npn双极型晶体管的研制

采用国产的4H-SiC外延材料和自行开发的SiC双极晶体管的工艺技术,实现了4H-SiC npn双极晶体管特性。为避免二次外延或高温离子p+注入等操作,外延形成n+/p+/p/n-结构材料,然后根据版图设计进行相应的刻蚀,形成双台面结构。为保证p型基区能实现良好的欧姆接触,外延时在n+层和p层中间插入适当高掺杂的p+层外延,但也使双极晶体管发射效率降低,电流放大系数降低。为提高器件的击穿电压,在尽量实现低损伤刻蚀时,采用牺牲氧化等技术减少表面损伤及粗糙度,避免表面态及尖端电场集中,并利用SiC能形成稳定氧化层的优势来形成钝化保护。器件的集电结反向击穿电压达200 V,集电结在100 V下的反向截止漏电流小于0.05 mA,共发射极电流放大系数约为3。     

Charge carrier transport through the contact of metal with a superconducting semiconductor

Mechanisms controlling the charge carrier transport through the contact of a metal with a superconducting semiconductor were studied. The current-voltage characteristics of the contact was calculated for the thermionic, thermal-field, and tunnel emission currents. The dependences of the current transport conditions on the contact parameters and applied voltage were determined. The transition of the semiconductor to the superconducting state was shown to cause a decrease in the current through the contact in the voltage range controlled by the potential-barrier height and the energy band parameters of the superconductor.