基于硅堆的猝发高压脉冲源初步实验研究

为了产生驱动多幅闪光照相的高重频猝发高压电脉冲,开展了基于硅堆隔离的猝发高压脉冲发生装置的可行性研究。对普通整流硅堆脉冲条件的导通电流,反向关断时间进行了实验研究;采用脉冲形成线产生矩形脉冲,利用不同长度传输线的传输时延产生多脉冲,以硅堆隔离的方式实现多脉冲在负载的输出。研究表明:硅堆在500 ns脉宽条件下,其电流过载至少736倍,关断时间约200 ns,硅堆的绝缘恢复时间决定产生脉冲的最高重复频率。     

High performance of high-voltage 4H-SiC Schottky barrier diodes

High performance of high-voltage rectifiers could be realized utilizing 4H-SiC Schottky barrier diodes. A typical specific on-resistance (R_on) of these devices was 1.4×10³ Ω cm³ at 24°C (room temperature) with breakdown voltages as high as 800 V. These devices based on 4H-SiC had R _on's lower than 6H-SiC based high-power rectifiers with the same breakdown voltage. As for Schottky contact metals, Au, Ni, and Ti were employed in this study. The barrier heights of these metals for 4H-SiC were determined by the analysis of current-voltage characteristics, and the reduction of power loss could be achieved by controlling the barrier heights     

P-type 4H and 6H-SiC high-voltage Schottky barrier diodes

High-voltage Schottky barrier diodes have been successfully fabricated for the first time on p-type 4H- and 6H-SiC using Ti as the barrier metal. Good rectification was confirmed at temperatures as high as 250°C. The barrier heights were estimated to be 1.8-2.0 eV for 6H-SiC and 1.1-1.5 eV for 4H-SiC at room temperature using both I-V and C-V measurements. The specific on resistance (R_on,sp) for 4H- and 6H-SiC were found to be 25 mΩ cm^-2 and 70 mΩ cm^-2 at room temperature. A monotonic decrease in resistance occurs with increasing temperature for both polytypes due to increased ionization of dopants. An analytical model is presented to explain the decrease of R_on,sp with temperature for both 4H and 6H-SiC which fits the experimental data. Critical electric field strength for breakdown was extracted for the first time in both p-type 4H and 6H-SiC using the breakdown voltage and was found to be 2.9×10⁶ V/cm and 3.3×10⁶ V/cm, respectively. The breakdown voltage remained fairly constant with temperature for 4H-SiC while it was found to decrease with temperature for 6H-SiC     

I-V characteristics of high-voltage 4H-SiC diodes with a 1.1-eV Schottky barrier

The I-V characteristics of high-voltage 4H-SiC diodes with a Schottky barrier ∼1.1 eV in height are measured and analyzed. The forward I-V characteristics proved to be close to “ideal” in the temperature range of 295–470 K. The reverse I-V characteristics are adequately described by the model of thermionic emission at the voltages to 2 kV in the temperature range of 361–470 K if, additionally, a barrier lowering with an increase in the band bending in the semiconductor is taken into account.     

Characterization of hard- and soft-switching performance of high-voltage Si and 4H-SiC PiN diodes

This paper presents a study of the performance of high-voltage Si and 4H-SiC diodes in a DC-DC buck converter. Device operation in both hard- and zero-voltage switching conditions is presented with the help of measurements and two-dimensional (2-D) mixed device-circuit simulations. Experimental results show that SiC PiN diodes have a strong potential for use in high-speed high-voltage power electronics applications operating at high temperature. A combination of low excess carrier concentration and low carrier lifetime results in superior switching performance of the 4H-SiC diode over ultrafast Si diodes. Soft switching is shown to minimize the switching loss and allow operation at higher switching frequencies using Si diodes. The power loss of 4H-SiC diodes is dominated by conduction loss. Consequently, soft-switching techniques result in a marginal reduction in power loss. However, the low overall power loss implies that SiC diodes can be used at very high switching frequencies even in hard-switching configurations.     

Evaluation of high-voltage 4H-SiC switching devices

In this paper, the on-state and switching performance of 4H-SiC UMOSFETs, TIGBTs, BJTs, SIThs, and GTOs with voltage ratings from 1 to 10 kV are simulated at different temperatures. Comparison with silicon devices highlights the advantages of SiC technology. SiC BJTs suffer the same problem as Si BJTs, namely the degradation of current gain with increased voltage rating which makes them unsuitable for applications above 4 kV. SiC MOSFETs dominate applications below 4 kV for their attractive conduction performance and advantages such as ease of use. Above 3 kV, SiC MOSFETs are not as attractive as SiC bipolar devices because of their high on-state voltages. In the voltage range simulated, SiC IGBTs, SIThs, and GTOs have comparable current handling ability. Considering the GTOs slow switching speed and drive complexities, IGBTs and SIThs are a better choice in the voltage range 4-10 kV. Calculations based on conduction loss and switching loss indicate that SiC SIThs are superior to IGBTs except in high-temperature and high-frequency applications where IGBTs are better. The need to provide a large gate current during turnoff and turn-off failure caused by gate debiasing, decreases the attractiveness of the SITh     

Analysis of bulk and surface components of leakage current in 4H-SiC PiN MESA diodes

The leakage current in circular- and ring-shaped epitaxial 4H-SiC PiN mesa diodes with different size and periphery to area ratios was evaluated under the influence of the UV irradiation and temperature in the range from room temperature (RT) to 250 °C. The surface leakage current component was found to dominate the reverse current characteristics and was found to be dependent on time and temperature both after reactive ion etching (RIE) of the diodes in the SF₆/Ar gas mixture and after the UV irradiation. Charging of the surface states is believed to be responsible for the observed behavior. The UV irradiation is believed to charge the surface positively. The drift of the I(V) characteristics is due to the trapping of the electrons neutralizing the positive donor states.     

A new, high-voltage 4H-SiC lateral dual sidewall Schottky (LDSS) rectifier: theoretical investigation and analysis

In this paper, we report a new 4 H-silicon carbide (SiC) lateral dual sidewall Schottky (LDSS) rectifier on a highly doped drift layer consisting of a high-barrier sidewall Schottky contact on top of the low-barrier Schottky contact. Using two-dimensional (2-D) device simulation, the performance of the proposed device has been evaluated in detail by comparing its characteristics with those of the compatible lateral conventional Schottky (LCS) and lateral trench sidewall Schottky (LTSS) rectifiers on 4H-SiC. From our simulation results, it is observed that the proposed LDSS rectifier acts as a low-barrier LTSS rectifier under forward-bias conditions, and as a high-barrier LTSS rectifier under reverse-bias conditions, making it an ideal rectifier. The LDSS rectifier exhibits an on/off current ratio (at 1 V/-500 V) of 5.5/spl times/10/sup 7/ for an epitaxial layer doping of 1/spl times/10/sup 17/ /cm/sup 3/. Further, the proposed LDSS structure exhibits a very sharp breakdown similar to that of a p-i-n diode in spite of using only Schottky junctions in the structure. We have analyzed the reasons for the improved performance of the LDSS.     

Threshold current characteristics of GaAs lasers under short pulse excitation

Measurements of the temperature dependence of threshold current using both short pulse and CW excitation of GaAs heterostructure lasers with multiquantum well and conventional active layers are presented. Our results show that the carrier density at threshold is weakly temperature-dependent in both types of lasers. This is consistent with the measured carrier lifetime at threshold.     

Stacking-fault formation and propagation in 4H-SiC PiN diodes

Stacking-fault growth in SiC PiN diodes has been examined using light-emission imaging and stressing at 80 A/cm² and 160 A/cm². Dark areas in the emission develop because of stacking faults and the current capability of the diode drops. More detailed images are produced by reducing the current by a factor of 1000. The low-current images are bright lines at dislocations bounding the stacking faults and at or near the stacking-fault intersection with the surface. Stacking faults nucleate 1–2 μm below the surface. Most, but not all, continue growing until they span the diode. Growth dynamics and their dependence on the current density are discussed. An erratum to this article is available at .     

Microwave p-i-n diodes and switches based on 4H-SiC

The 4H-SiC p-i-n diodes were designed, fabricated, and characterized for use in microwave applications. The diodes with mesa structure diameters between 80 and 150 /spl mu/m, exhibited a blocking voltage of 1100 V, a 100-mA differential resistance of 1-2 /spl Omega/, a capacitance below 0.5 pF at a punchthrough voltage of 100 V and a carrier effective lifetime between 15-27 ns. X-band microwave switches based on 4H-SiC p-i-n diodes are demonstrated for the first time. The switches exhibited insertion loss as low as 0.7 dB, isolation up to 25 dB and were able to handle microwave power up to 2.2 kW in isolation mode and up to 0.4 kW in insertion mode.     

Effect of deep levels on current excitation in 6H-SiC diodes

The results of an experimental study of deep levels in the p-base of 6H-SiC diodes are presented. A deep level of unknown origin, with ionization energy E _c -1.45 eV, acts as an effective recombination center for minority carriers, and controls recombination processes. A level with ionization energy E _c -0.16 eV is attributed to a nitrogen donor impurity. Electron capture and thermal activation processes associated with this level substantially extend the duration of current relaxation in the p-n junction. Fiz. Tekh. Poluprovodn. 31, 1220–1224 (October 1997)     

Characterization of Ti schottky diodes on epi-regrown 4H-SiC

The electrical characteristics of Schottky diodes fabricated on n-type epi layers regrown over an n-drift layer and regrown over a drift layer with selective boron-implanted p-type regions have been evaluated and compared to those on virgin, as-grown commercial epi-drift layers. Slightly lower (0.1–0.2 eV) Schottky barrier heights and larger ideality factors (1.2 vs. 1.03) were extracted for the regrown diodes from forward current-voltage and capacitance-voltage measurements. Although more than 1–2 orders higher reverse leakage current were also observed, our epi-regrowth process is still considered adequate for novel power device realization.     

漂移层经碳处理后的4H-SiC PiN 二极管的特性与分析

The characteristics of 4H-SiC PiN diodes with a carbon-implanted drift layer was investigated and the reason of characteristics improvement was analyzed. The forward voltage drops of the diodes with carbonimplanted drift layer were around 3.3 V, which is lower than that of devices without carbon implantation, the specific-on resistance was decreased from 9.35 to 4.38 mΩcm² at 100 A/cm², and the reverse leakage current was also decreased. The influence of carbon incorporation in the Si C crystalline grids was studied by using deep-level transient spectroscopy（DLTS）. The DLTS spectra revealed that the Z_1/2 traps, which were regarded as the main lifetime limiting defects, were dramatically reduced. It is proposed that the reduction of Z_1/2 traps can achieve longer carrier lifetime in the drift layer, which is beneficial to the performance of bipolar devices.     

Partial dislocations and stacking faults in 4H-SiC PiN diodes

Using plan-view transmission electron microscopy (TEM), we have identified stacking faults (SFs) in 4H-SiC PiN diodes subjected to both light and heavy electrical bias. Our observations suggest that the widely expanded SFs seen after heavy bias are faulted dislocation loops that have expanded in response to strain of the 4H-SiC film, while faulted screw or 60° threading dislocations do not give rise to widely expanded SFs. Theoretical calculations show that the expansion of SFs depends on the Peach-Koehler (PK) forces on the partial dislocations bounding the SFs, indicating that strain plays a critical role in SF expansion.     

Fabrication and characterization of heterojunction diodes withHVPE-grown GaN on 4H-SiC

GaN/SiC heterojunctions can improve the performance considerably for BJTs and FETs. In this work, heterojunction diodes have been manufactured and characterized. The fabricated diodes have a GaN n-type cathode region on top of a 4H-SiC p-type epi layer. The GaN layer was grown with HVPE directly on off-axis SIC without a buffer layer. Mesa structures were formed and a Ti metallization was used as cathode contact to GaN, and the anode contact was deposited on the backside using sputtered Al. Both current-voltage (I-V) and capacitance-voltage (C-V) measurements were performed on the diode structures. The ideality factor of the measured diodes was 1.1 and was constant with temperature. A built in potential of 2.06 V was extracted from I-V measurements and agrees well with the built in potential from C-V measurements. The conduction band offset was extracted to 1.1 eV and the heterojunction was of type II. The turn on voltage for the diodes is about 1 V lower than expected and a suggested mechanism for this effect is discussed     

Pulsed breakdown of 4H-SiC Schottky diodes terminated with a boron-implanted p-n junction

Pulsed reverse current-voltage characteristics have been measured in the breakdown region for 1-kV 4H-SiC Schottky diodes terminated with a boron-implanted p-n junction. It was shown that the dynamic breakdown voltage of the diodes increases as the pulses become shorter. Owing to the homogeneous avalanche formation at the edge of the guard p-n junction and to the high differential resistance in the breakdown region, the diodes sustain without degradation a pulsed reverse voltage substantially exceeding the static breakdown threshold. Characteristic features of the pulsed breakdown are considered in relation to the specific properties of the boron-implanted guard p-n junction.     

Self-heating and gate leakage current in a guarded MOSFET

Gate leakage current measurements of a guarded MOSFET show that device self-heating has a marked effect on the Schottky emission current. This effect can make the bias conditions for zero gate leakage current very sensitive to changes in drain voltage.     

Optimized design of 4H-SiC floating junction power Schottky barrier diodes

SiC floating junction Schottky barrier diodes were simulated with software MEDICI 4.0 and their device structures were optimized based on forward and reverse electrical characteristics.Compared with the conventional power Schottky barrier diode,the device structure is featured by a highly doped drift region and embedded floating junction region,which can ensure high breakdown voltage while keeping lower specific on-state resistance,solved the contradiction between forward voltage drop and breakdown voltage.The simulation results show that with optimized structure parameter,the breakdown voltage Can reach 4 kV and the specific on-resistance is 8.3 mΩ·cm2.