Carbon Doped HBT Development for Power Applications

Heterojunction bipolar transistor, HBT, technology offers an extremely attractive alternative to field effect transistors, FETs, for a variety of high speed applications. High p-type base doping levels (on the order of 1O 20 power cm-3) have allowed for the improvement of the maximum oscillation frequency, f max, as well as current gain cutoff frequency. Commonly used p-type dopants, Be and Zn, suffer from diffusion during the epitaxial growth process as well as during high current level operation resulting in decreased emitter injection efficiency. Carbon as a p-type dopant is attractive because of its low diffusion coefficient. The use of carbon in the base of an npn HBT increases the wafer yield and device reliably by eliminating dopant diffusion into the emitter during epitaxial growth and reducing the current induced degradation of the dc gain observed during operation. Pennsylvania State University has installed a gas source carbon cell on their existing Varian Gen II MBE and is currently using CBr4 as their source for carbon, while QED has installed an electron beam evaporation solid source carbon cell to one of their existing Varian Gen II MBEs. Phase I of this program will investigate the two most promising carbon doping techniques in order to establish the most viable.