Demonstration of a 4H-silicon carbide bipolar junction transistor with high current and power densities suitable for high frequency applications

Silicon carbide is a wide band gap semiconductor that has been identified as a potential candidate for its use in high power and high frequency devices due to its superior material parameters, primarily its large breakdown field and excellent thermal conductivity. To date there are only a few reports on SiC bipolar transistors and the few studies have primarily concentrated on power switching transistors. To the best of my knowledge there are no reports on the high frequency performance of these devices.; The objective of this thesis is to explore the suitability of 4H-SiC bipolar transistors for high frequency operation. Devices with an emitter stripe width of 2μm were fabricated on commercially available npn 4H-SiC epilayers using a double mesa structure patterned by reactive ion etching. A novel technique was developed to accurately monitor the etch rate of SiC. An innovative technique of successive sacrificial oxide growth and removal was introduced in order to obtain a reliable and repeatable way to reach the thin p-type base.; The observed DC characteristics of the fabricated transistors were used to develop a circuit model based on the Gummel-Poon model. This model includes a resistor-diode array added between the base and the collector as well as a base-emitter leakage resistor. Some of the experimentally determined DC characteristics are explained using this model.; The best DC devices obtained have a maximum common emitter current gain of 17.4, a maximum current density of 42 kA/cm2 and maximum DC power dissipation density of 1.67 MW/cm2. The highest current gain demonstrated is 32.4.; Small-signal high frequency characteristics are also reported. A cutoff frequency of 600MHz and a maximum oscillation frequency of 200MHz were measured at an emitter current density of 10kA/cm2. The measured transit frequency is only 3% of the expected cutoff frequency. Based on the same model developed for the DC devices, the high sheet resistance of the base is shown to be responsible for the limited high frequency characteristics.