Based on the first-principles pseudopotentials and the plane wave energy band method,the supercells of perfect crystal 4H-SiC and those with intrinsic defects VC,VSi,VC-C and VC-Si were calculated.Ignoring the atomic relaxations,the results show that the formation energy of intrinsic defects is ranked,from low to high,as VC,VC-C,VSi to VSi-Si at 0 K.The equilibrium concentration of each intrinsic defect can be deduced from the formation energy of each intrinsic defect.The concentration ranks,from high to low,as VC,VC-C,VSi,VSi-Si,which is in accordance with the ESR and PL results.The stabilizing process of metastable defects VSi converting to VC-C was explained by formation energy.
4H-SiC junction barrier Schottky（JBS）diodes with four kinds of design have been fabricated and characterized using two different processes in which one is fabricated by making the P-type ohmic contact of the anode independently,and the other is processed by depositing a Schottky metal multi-layer on the whole anode.The reverse performances are compared to find the influences of these factors.The results show that JBS diodes with field guard rings have a lower reverse current density and a higher breakdown voltage,and with independent P-type ohmic contact manufacturing,the reverse performance of 4H-SiC JBS diodes can be improved effectively. Furthermore,the P-type ohmic contact is studied in this work.
The current-voltage characteristics of 4H-SiC junction barrier Schottky （JBS） diodes terminated by an offset field plate have been measured in the temperature range of 25-300℃. An experimental barrier height value of about 0.5 eV is obtained for the Ti/4H-SiC JBS diodes at room temperature. A decrease in the experimental barrier height and an increase in the ideality factor with decreasing temperature are shown. Reverse recovery testing also shows the temperature dependence of the peak recovery current density and the reverse recovery time. Finally, a discussion of reducing the reverse recovery time is presented.
The 4H-SiC junction barrier Schottky （JBS） diodes terminated by field guard rings and offset field plate are designed, fabricated and characterized. It is shown experimentally that a 3-μm P-type implantation window spacing gives an optimum trade-off between forward drop voltage and leakage current density for these diodes, yielding a specific on-resistance of 8.3 mΩ-cm2. A JBS diode with a turn-on voltage of 0.65 V and a reverse current density less than 1 A/cm2 under 500 V is fabricated, and the reverse recovery time is tested to be 80 ns, and the peak reverse current is 28.1 mA. Temperature-dependent characteristics are also studied in a temperature range of 75 °C-200 °C. The diode shows a stable Schottky barrier height of up to 200°C and a stable operation under a continuous forward current of 100 A/cm2.
The current transport parameters of 4H-SiC merged PiN Schottky （MPS） diode are investigated in a temperature range of 300-520 K. Evaluation of the experimental current-voltage （I-V） data reveals the decrease in Schottky barrier height Φb but an increase in ideality factor n, with temperature decreasing, which suggests the presence of an inhomogeneous Schottky barrier. The current transport behaviours are analysed in detail using the Tung＇s model and the effective area of the low barrier patches is extracted. It is found that small low barrier patches, making only 4.3% of the total contact, may significantly influence the device electrical characteristics due to the fact that a barrier height of 0.968 eV is much lower than the average barrier height 1.39 eV. This shows that ion implantation in the Schottky contact region of MPS structure may result in a poor Ti/4H-SiC interface quality. In addition, the temperature dependence of the specific on-resistance （Ron-sp）, T^2.14, is determined between 300 K and 520 K, which is similar to that predicted by a reduction in electron mobility.
In this paper, a mixed terminal structure for the 4H-SiC merged PiN/Schottky diode （MPS） is investigated, which is a combination of a field plate, a junction termination extension and floating limiting rings. Optimization is performed on the terminal structure by using the ISE-TCAD. Further analysis shows that this structure can greatly reduce the sensitivity of the breakdown voltage to the doping concentration and can effectively suppress the effect of the interface charge compared with the structure of the junction termination extension. At the same time, the 4H-SiC MPS with this termination structure can reach a high and stable breakdown voltage.
