Studies of lowhyphen;surface 2hyphen;kT recombination current of the emitterhyphen;base heterojunction of heterojunction bipolar transistors

摘要

The 2hyphen;kT current at the emitterhyphen;base heterojunction of AlGaAs/GaAs heterojunction bipolar transistor grown by liquid phase epitaxy is found to be much lower than that of a GaAs homojunction diode. By measuring spectral response and currenthyphen;voltage characteristics of (n)AlxGa1minus;xAshyphen;(p)Al0.05Ga0.95As diodes having a similar structure to the emitterhyphen;base heterojunction, it is found that the 2hyphen;kT surface recombination current is determined by the lower doped side of the heterojunction. Therefore, a higher 1hyphen; to 2hyphen;kT current ratio and thus higher current gain can be obtained when a highhyphen;bandhyphen;gap emitter with lower doping concentration is used. It is also found that by inserting an undoped AlGaAs spacer layer in between the emitterhyphen;base heterojunction and applying an edgehyphen;thinning design, a highhyphen;gain heterojunction bipolar transistor can be routinely obtained.