DIAMOND TRANSISTOR PERFORMANCE AND FABRICATION

This article reviews some of the device properties of diamond as well as recently developed diamond device fabrication techniques. Diamond as a semiconductor in high-frequency, high-power transistors has unique advantages and disadvantages. Two advantages of diamond over other semiconductors used for high-frequency, high-power devices are its high thermal conductivity and high electric-field breakdown. The high thermal conductivity allows for higher power dissipation over similar devices made in Si or GaAs and the higher electric-field breakdown field makes possible the production of substantially higher power, higher frequency devices than can be made with other commonly used semiconductors. The lack of large area single crystal diamond substrates is the one largest technical obstacles to the development of diamond transistors. Boron is the only known p-type diamond dopant and because of its high activation energy (0.37 eV), only a fraction of the boron atoms contribute carriers to the valance band at room temperature. This makes even moderately doped, 10(16) cm-3, diamond considerably more resistive, 10 to 100-OMEGA-cm, than Si, 0.5 OMEGA-cm, doped to the same level. However, even with these disadvantages, high voltage high power diamond transistors will still have lower on resistance than similar devices in Si or GaAs because of the diamond's high breakdown field. Much of the development necessary for the production of diamond devices already exists. Doping by homoepitaxy, diamond etching, device quality SiO2-diamond interface, and ohmic contact technology will be reviwed. The remaining problems are the development of large area single crystal diamond substrates, improvement of doping techniques, and refinement in ohmic contact technology.