Comprehensive study of InGaP/AlxGa1-xAs/GaAs heterojunction bipolar transistors with doping concentrations of AlxGa1-xAs graded layers

The performances of InGaP/AlxGa1-xAs/GaAs heterojunction bipolar transistors (HBTs) with different doping concentrations of AlxGa1-xAs graded layers are theoretically studied. The use of the AlxGa1-xAs graded layer plays a key role in affecting the direct current and radio frequency performances of the studied HBTs. It is found that the studied devices with suitable doping concentrations of AlxGa1-xAs graded layers exhibit lower offset voltages, saturation voltages, and base and collector current ideality factors. Furthermore, due to the use of proper doping concentrations of AlxGa1-xAs graded layers, the studied devices show high values of the unity current gain cut-off frequency (f(T)) and maximum oscillation frequency (f(max)). It is known that, from the theoretical analysis, the appropriate doping concentration of the AlxGa1-xAs graded layer is 1 x 10(16) to 1 x 10(18) cm(-3). Consequently, this work is promising for device engineers to design high-performance HBT structures.