Light-extraction efficiency and forward voltage in GaN-based light-emitting diodes with different patterns of V-shaped pits

We present a new method of making a textured V-pit surface for improving the light extraction efficiency in GaN- based light-emitting diodes and compare it with the usual low-temperature method for p-GaN V-pits. Three types of GaNbased light-emitting diodes （LEDs） with surface V-pits in different densities and regions were grown by metal-organic chemical vapor deposition. We achieved the highest output power and lowest forward voltage values with the p-InGaN V-pit LED. The V-pits enhanced the light output power values by 1.45 times the values of the conventional LED owing to an enhancement of the light scattering probability and an effective reduction of Mg-acceptor activation energy. Moreover, this new technique effectively solved the higher forward voltage problem of the usual V-pit LED.

Mechanism of improving forward and reverse blocking voltages in AlGaN/GaN HEMTs by using Schottky drain

In this paper, we demonstrate that a Schottky drain can improve the forward and reverse blocking voltages （BVs） simultaneously in A1GaN/GaN high-electron mobility transistors （HEMTs）. The mechanism of improving the two BVs is investigated by analysing the leakage current components and by software simulation. The forward BV increases from 72 V to 149 V due to the good Schottky contact morphology. During the reverse bias, the buffer leakage in the Ohmic- drain HEMT increases significantly with the increase of the negative drain bias. For the Schottky-drain HEMT, the buffer leakage is suppressed effectively by the formation of the depletion region at the drain terminal. As a result, the reverse BV is enhanced from -5 V to -49 V by using a Schottky drain. Experiments and the simulation indicate that a Schottky drain is desirable for power electronic applications.

Influence of a drain field plate on the forward blocking characteristics of an AlGaN/GaN high electron mobility transistor

In this paper, the influence of a drain field plate （FP） on the forward blocking characteristics of an AlGaN/GaN high electron mobility transistor （HEMT） is investigated. The HEMT with only a gate FP is optimized, and breakdown voltage VBR is saturated at 1085 V for gate–drain spacing LGD ≥ 8 μm. On the basis of the HEMT with a gate FP, a drain FP is added with LGD=10 μm. For the length of the drain FP LDF ≤ 2 μm, VBR is almost kept at 1085 V, showing no degradation. When LDF exceeds 2 μm, VBR decreases obviously as LDF increases. Moreover, the larger the LDF, the larger the decrease of VBR. It is concluded that the distance between the gate edge and the drain FP edge should be larger than a certain value to prevent the drain FP from affecting the forward blocking voltage and the value should be equal to the LGD at which VBR begins to saturate in the first structure. The electric field and potential distribution are simulated and analyzed to account for the decrease of VBR.

A High Speed IGBT Based on Dynamic Controlled Anode-Short

IGBT with high switching speed is described based on the dynamic controlled anode- short,which incorpo- rates a normally- on,p- MOSFET controlled by the anode voltage indirectly.This device works just as normal when it is in on- state since the channel of the p- MOSFET is pinched- off.During the course of turning off,the channel of the p- MOSFET will prevent the injection of m inorities and introduce an extra access for the carriers to flow to the anode directly,which m akes the IGBT reach its off- state in a shorter time.The simulation results prove that the new structure can reduce the turn- off time by m ore than75 % compared with the normal one under the same break- down voltage and on- state perform ance.Only two more resistors are needed when using this structure,and the re- quirement of the drive circuits is just the sam e as normal.

Improvement of Electrical Performance of SOI-LIGBT by Resistive Field Plate

The electrical performance including breakdown voltage and turn-off speed of SOI-LIGBT is improved by incorporating a resistive field plate (RFP) and a p-MOSFET.The p-MOSFET is controlled by a signal detected from a point of the RFP.During the turning-off of the IGBT,the p-MOSFET is turned on,which provides a channel for the excessive carriers to flow out of the drift region and prevents the carriers from being injected into the drift region.At the same time,the electric field affected by the RFP makes the excessive carriers flow through a wider region,which almost eliminates the second phase of the turning-off of the SOI-LIGBT caused by the substrate bias.Faster turn-off speed is achieved by above two factors.During the on state of the IGBT,the p-MOSFET is off,which leads to an on-state performance like normal one.At least,the increase of the breakdown voltage for 25% and the decrease of the turn-off time for 65% can be achieved by this structure as can be verified by the numerical simulation results.

Junction barrier Schottky rectifier with an improved P-well region

A junction barrier Schottky （JBS） rectifier with an improved P-well on 4H-SiC is proposed to improve the VF-IR trade-off and the breakdown voltage. The reverse current density of the proposed JBS rectifier at 300 K and 800 V is about 3.3 × 10-s times that of the common JBS rectifier at no expense of the forward voltage drop. This is because the depletion layer thickness in the P-well region at the same reverse voltage is larger than in the P＋ grid, resulting in a lower spreading current and tunneling current. As a result, the breakdown voltage of the proposed JBS rectifier is over 1.6 kV, that is about 0.8 times more than that of the common JBS rectifier due to the uniform electric field. Although the series resistance of the proposed JBS rectifier is a little larger than that of the common JBS rectifier, the figure of merit （FOM） of the proposed JBS rectifier is about 2.9 times that of the common JBS rectifier. Based on simulating the values of susceptibility of the two JBS rectifiers to electrostatic discharge （ESD） in the human body model （HBM） circuits, the failure energy of the proposed JBS rectifier increases 17% compared with that of the common JBS rectifier.

Thin Emitter Structure Improved Turn-on Characteristics in RSD

The thin emitter structure was introduced into reversely switched dynistor（RSD） to improve its turn-on characteristics. According to the analysis of turn-on condition, thin emitter structure is capable of reducing the extraction action for the triggering plasma layer P1 during turn-on process, and satisfying the requirement that triggering electric charge cannot be exhausted and therefore enables RSD to turn on uniformly. The on-state thin emitter RSD was equivalent to an asymmetric pin diode model. The simulation result shows that the forward voltage drop of RSD falls with the decrease of doping dose in p^＋-emitter in a certain range, and when the doping concentration is extremely tow, the decrease of the width of p^＋-emitter can obtain a tow forward voltage drop. Thin emitter RSD chips were made by sintering AI on n-Si. The test result shows that their turn-on process is uniform and the voltage drop is 7.5 V when the peak conversion current is 5 500 A.

A new static induction thyristor with high forward blocking voltage and excellent switching performances

A new static induction thyristor （SITH） with a strip anode region and p- buffer layer structure （SAP-B） has been successfully designed and fabricated. This structure is composed of a p- buffer layer and lightly doped n- regions embedded in the p＋-emitter. Compared with the conventional structure of a buffed-gate with a diffused source region （DSR buffed-gate）, besides the simple fabrication process, the forward blocking voltage of this SITH has been increased to 1600 V from the previous value of 1000 V, the blocking gain increased from 40 to 70, and the turn-offtime decreased from 0.8 to 0.4μs.

Characteristics of high power LEDs at high and low temperature

The high power light emitting diodes（LEDs） based on InGaN and AlGaInP individually are tested on line at temperatures from -30 to 100℃.The data are fitted to measure the relationship between temperature and the properties of forward voltage,relative light intensity,wavelength,and spectral bandwidth of two different kinds of LEDs.Why these properties changed and how these changes reflected on applications are also analyzed and compared with each other.The results show that temperature has a great influence on the performance and application of power LEDs.For applications at low temperature,the forward voltage rising and the peak wavelength blue-shifting must be considered;and at high temperature,the relative light intensity decreasing and the peak wavelength red-shifting must be considered.

Insulated gate bipolar transistor with trench gate structure of accumulation channel

An accumulation channel trench gate insulated gate bipolar transistor （ACT-IGBT） is proposed. The simu- lation results show that for a blocking capability of 1200 V, the on-state voltage drops of ACT-IGBT are 1.5 and 2 V at a temperature of 300 and 400 K, respectively, at a collector current density of 100 A/cm2. In contrast, the on-state voltage drops of a conventional trench gate IGBT （CT-IGBT） are 1.7 and 2.4 V at a temperature of 300 and 400 K, respectively. Compared to the CT-IGBT, the ACT-IGBT has a lower on-state voltage drop and a larger forward bias safe operating area. Meanwhile, the forward blocking characteristics and turn-off performance of the ACT-IGBT are also analyzed.