NITRIDE/4H-SIC HETEROSTRUCTURES HEMTS

The military has a need for high power/high frequency electronics which can operate at high temperatures for applications such as radar and electronic warfare systems. While Si and GaAs are already being used near their limits of output power and operating temperature, the potential of SiC is just beginning to be realized. High frequency 4H-SiC MESFETs with an f(max) as high as 12.9 GHz, and RF output power at 1.8 GHz of 2.8 W/MM, have already been demonstrated. This power density is three times higher than that of Si or GaAs structures. However, the operating frequencies of SiC FETs are still limited by its relatively low electron mobility. The design that most ideally minimizes the effect of low electron mobility in SiC is a High Electron Mobility Transistor (HEMT). The use of a heterostructure gate (a wider bandgap layer on top of the lower bandgap SiC) allows the SiC channel region to be formed of low doped material, which has the highest mobility. For 4H-SiC, the electron mobility of low doped material is greater than 800 cm(2)/V-sec. In a HEMT, a two-dimensional electron gas is formed in the potential well of the lightly doped material underneath the heterojunction. Therefore it is proposed that nitride-based heterostructures on 4H-SiC (E(g)=3.26 eV) be investigated for their potential use in HEMTs. The three nitride systems to be investigated are GaN/SiC, and AlN/SiC alloys on SiC.