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High-temperature devices fabricated on silicon carbide and solid solution of silicon carbide - aluminium nitride

Due to its very attractive physical and electronic properties, silicon carbide (SiC) is a very promising semiconductor for high temperature and high voltage power devices applications. SiC wide bandgap, large critical electric field, high thermal conductivity and good carrier mobility theoretically push up limitations today imposed by silicon performance. The large markets of power electronics or more strategic fields like aerospace are closely concerned by SiC research.

High temperature field-effect transistors (FET's) of different modifications were made from 6H-SiC. But 4H-SiC is the most promising SiC polytype for power device applications because its electron mobility parallel to the c-axis is about twice that of 6H-SiC with low doping. Moreover, 6H-SiC exhibits a high degree of mobility anisotropy, having a mobility in the (0001) direction that is 1/5th that in the basal plane, yielding a 10x advantage for 4H-SiC for vertical power devices. In production of the 4h-SiC based FET's during this work it has obtained more fruitful results.

For more high frequency SiC based devices FET with Schottky diode gate (MESFET), usually using insulating of the FET channel from the substrates by p-n junction. This design, however, has certain disadvantages. For instance it is very hard to evaluate the capacitor recharge of the junction when a MESFET operates at high frequencies. In some cases the recharge may lead to I-V characteristic hysteresis.

MESFET based on seminsulating wafers do not suffer from this drawback, but the wafer fabrication presents much difficulty even for such conventional semiconductor materials as GaAS.

During this work we tried to use as growth of the SiC films on base of the other semiconductor semi-insulating wafer, as obtaining of the semi-insulating layers of the AIN (produced by implantation) inside the silicon carbide crystals.

On the other hand, electrophysical properties of the heterojunction (as between different SiC polytypes and also between AIN and SiC) are very interesting to our study. It must be very optimistic if we will achieve significant results in this field after a one year project. (Such good heterojunctions also not obtained anywhere in the world after many years of work.) This work was not successful in producing devices using any type of heterojunctions as active elements. But such investigations must be prolonged, may be using other growth methods (CVD for example) and after the determination of the one main aim.

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