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

Abstract
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 (IV) and room‐temperature capacitance‐voltage (CV) 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.