Electrical characteristics of p+-Ge/(N-GaAs and N-AlGaAs) junctions and their applications to Ge base transistors

Electrical properties of p+-Ge/N-AlGaAs (and N-GaAs) are studied as a function of temperature and current conduction mechanisms are outlined. Junctions with Ge grown on GaAs and AlGaAs show ideality factors of unity and 1.03 at room temperature, respectively. Temperature-dependent current-voltage (I-V) and room-temperature capacitance-voltage (C-V) characterization are employed to determine the built-in voltage (Vbi) of the two diode structures. For Ge/GaAs, a valence-band discontinuity of 0.49±0.05 eV is measured which is in good agreement with the value deduced from photoemission studies. Implications of p+-Ge base in AlGaAs/Ge/GaAs double-heterojunction bipolar transistors (DHBTs) are discussed.