The low frequency noise was studied in 4H-SiC Metal Oxide Semiconductor Field Effect Transistors in the frequency range from 1 Hz to 100 kHz. The trap density responsible for the noise extracted using the McWhorter model increases approaching the conduction band edge, where it reaches the values up to similar to 10(20) cm(-3)eV(-1).

This paper presents the development of 1000 V, 30A bipolar junction transistor (BJT) with high dc current gain in 4H-SiC. BJT devices with an active area of 3/spl times/3 mm/sup 2/ showed a forward on-current of 30 A, which corresponds to a current density of 333 A/cm/sup 2/, at a forward voltage drop of 2 V. A common-emitter current gain of 40, along with a low specific on-resistance of 6.0m/spl Omega//spl middot/cm/sup 2/ was observed at room temperature. These results show significant improvement over state-of-the-art. High temperature current-voltage characteristics were also performed on the large-area bipolar junction transistor device. A collector current of 10A is observed at V/sub CE/=2 V and I/sub B/=600 mA at 225/spl deg/C. The on-resistance increases to 22.5 m/spl Omega//spl middot/cm/sup 2/ at higher temperatures, while the dc current gain decreases to 30 at 275/spl deg/C. A sharp avalanche behavior was observed at a collector voltage of 1000 V. Inductive switching measurements at room temperature with a power supply voltage of 500 V show fast switching with a turn-off time of about 60 ns and a turn-on time of 32 ns, which is a result of the low resistance in the base.

Due to the high critical field in 4 H - SiC , the drain charge and switching loss densities in a SiC power device are approximately 10X higher than that of a silicon device. However, for the same voltage and resistance ratings, the device area is much smaller for the 4 H - SiC device. Therefore, the total drain charge and switching losses are much lower for the 4 H - SiC power device. A 2.3 kV, 13.5 mΩ-cm2 4 H - SiC power DMOSFET with a device area of 2.1 mm × 2.1 mm has been demonstrated. The device showed a stable avalanche at a drain bias of 2.3 kV, and an on-current of 5 A with a VGS of 20 V and a VDS of 2.6 V. Approximately an order of magnitude lower parasitic capacitance values, as compared to those of commercially available silicon power MOSFETs, were measured for the 4 H - SiC power DMOSFET. This suggests that the 4 H - SiC DMOSFET can provide an order of magnitude improvement in switching performance in high speed switching applications.

This paper presents the reliability of MOS-based 4H-SiC devices. Recent high temperature gate oxide breakdown measurements on MOS capacitors reveal that the gate oxides on as-grown epi surface are more reliable than that grown on ion-implanted and activated surface. The reduction in the oxide reliability on implanted surface is primarily due to the deterioration of surface morphology as a result of implant damage. In addition, preliminary measurements on forward IN characteristics and threshold voltage of power MOSFETs under a constant applied gate voltage of +20 V show the devices to be stable up to 88 hrs of operation at room temperature.

Bipolar Junction Transistors (BJT) and integrated Darlington pairs have been developed in 4H-SiC. The 3 mm x 3 mm BJTs show an on-state current of 20 A at a forward drop of 1.2 V at room temperature. The smaller 2 mm x 2 mm devices were tested up to 325 degreesC. The on-resistance increases and the current gain reduces with increasing temperature. The reverse leakage current was measured to be less than 40 muA at 1000 V and 325 degreesC. Inductive switching at 1000 V, 5 A shows extremely fast turn-on and turn-off behavior.

10 kV, 123 mOmega(.)cm(2) Power DMOSFETs in 4H-SiC are demonstrated. A 42% reduction in R-on,R-sp, compared to a previously reported value, was achieved by using an 8 x 10(14) cm(-3) doped, 85-mum-thick drift epilayer. An effective channel mobility of 22 cm(2)/Vs was measured from a test MOSFET. A specific on-resistance of 123 mOmega(.)cm(2) were measured with a gate bias of 18 V, which corresponds to an E-ox of 3 MV/cm. A leakage current of 197 muA was measured at a drain bias of 10 kV from a 4H-SiC DMOSFET with an active area of 4.24 x 10(-3) cm(2). A switching time of 100 ns was measured in 4.6-kV, 1.3-A switching measurements. This shows that the 4H-SiC power DMOSFETS are ideal for high-voltage, high-speed switching applications.

In this paper, high performance, high voltage NPN bipolar junction transistors in 4H-SiC are presented for applications in low frequency (<5 MHz) power conversion systems. The power BJTs for low frequency switching applications were designed to block 1300 V and showed a specific on-resistance of 8.0 mohm-cm2, which outperforms all SiC power switching devices ever reported. Moreover, these transistors show a positive temperature coefficient in the on-resistance and a negative temperature coefficient in the current gain, which enable easy paralleling of the devices.

Various design issues pertaining to SiC-based IGBTs are described. A trench gate, p-channel IGBT was considered the most appropriate structure for fabrication in SiC. The fabrication and characterization of high temperature SiC IGBTs with high current levels are presented. Using optimized emitter processing, 6H-SiC p-IGBTs show a higher current capability than 4H-SiC p-IGBTs because of their lower emitter contact resistance and higher MOS channel mobility. Since IGBTs rely on minority carrier injection, the low bulk mobility parallel to the c-axis in 6H-SiC was not found to severely affect the current carrying capability as compared with 4H-SiC IGBTs in the present design. Measured results of these devices are described from room temperature to the 350-400/spl deg/C temperature range. For both polytypes, the current capability was found to be much larger when their MOS gates were fabricated in the 112~0 crystal direction compared with the 1100 crystal direction. The emitter (p-type) contact anneal was also found to significantly affect the performance of SiC IGBTs. 4H-SiC IGBTs showed a -85 V blocking capability (room temperature) and on-current of 100 mA at 350/spl deg/C. 6H-SiC IGBTs were demonstrated with -400 V blocking capability (at 25/spl deg/C) and 2 A at 400/spl deg/C.

We report on the characteristics of large area (3.3 x 3.3 mm(2)) high voltage 4H-SiC DiMOSFETs. The MOSFETs show a peak MOS channel mobility of 22 cm(2)/V(.)s and a threshold voltage of 8.5 V at room temperature. The DiMOSFETs exhibit an on-resistance of 27 mOmega(.)cm(2) at room temperature. The devices block approximately 1.6 kV at room temperature. Stable avalanche characteristics at approximately 2.4 kV are observed on smaller devices. An on-current of 20 A is measured on a 0.103 cm(2) device. High switching speed is also demonstrated. This suggests that the devices are ideal for high voltage, high frequency, low loss switching applications.

The dependence of the base current gain β on the collector current IC has been measured in high-voltage 4H-SiC bipolar junction transistors at collector current densities jC from 20 to 700 A/cm2. With increasing collector current, the β value grows, reaching a maximum βmax=23 at jCmax of about 250 A/cm2 and then decreasing sharply with further increase in current. The peculiarities of this dependence are analyzed in terms of a model taking into account the carrier recombination in the emitter space charge region (SCR), the surface recombination, and the emitter current crowding effect. It is shown that at relatively small jC the recombination in SCR plays a key role in limiting the β magnitudes. The decrease in β at high jC is mainly due to the surface recombination enhanced by the emitter current crowding effect. The effects of surface recombination and recombination in the SCR reduce the maximum current gain almost threefold: from 65 to 23.

High voltage npn bipolar junction transistors in 4H-SiC are presented in this paper. The BJTs were able to block 1800 V in common emitter mode and showed a peak current gain of 20 and an on-resistance of 10.8 m/spl Omega//spl middot/cm/sup 2/ at room temperature. Temperature-stable current gain was observed for these devices. This is due to the higher percent ionization of the deep level acceptor atoms in the base region at elevated temperatures, which offsets the effects of increased minority carrier lifetime at high temperatures. These transistors show a positive temperature coefficient in the on-resistance characteristics, which will enable easy paralleling of the devices.