InP-based heterostructure bipolar transistors

Bipolar transistors that are believed to be the fastest ever reported have been fabricated using a technology which exploits extreme nonequilibrium electron transport in In/sub 0.53/Ga/sub 0.47/As. High base doping with a low base sheet resistance has been achieved by growing the base region at temperatures (425-450 degrees C) lower than is usual for beam epitaxy. A typical layer structure is shown. The 350-AA-thick Be-doped InGaAs base (p=1*10/sup 20/ cm/sup -3/) has a base sheet resistance of 400 Omega / Square Operator . Although a 150-AA undoped setback was used, Be diffusion during growth reduced this to about 75 AA. Hole concentrations in InGaAs up to 5.6*10/sup 20/ cm/sup -3/ have been achieved at a growth temperature as low as 365 degrees C. The dependence of the Hall mobility on carrier concentration does not exhibit any unusual features at these low growth temperatures. High n-type doping is also required in the emitter and collector contact regions to reduce series resistance. A Sn-doped InGaAs contact layer with n=7*10/sup 19/ cm/sup -3/ has a sheet resistance less than 5 Omega / Square Operator , and contact resistances as low as 10/sup -8/ Omega -cm/sup 2/ have been achieved. The ability to significantly outperform ultra-high-speed Si electronics has been demonstrated.<>