Ideal electronic properties of a p-Ge/p-Al0.85Ga0.15As interface
The isotype p+-Ge/p-Al0.85Ga0.15As interface is examined in this study. It is shown that a lattice-matched epitaxial layer of p-Al0.85Ga0.15 on p+-Ge acts like a minority-carrier mirror. Evidence for this action comes from improved short-wavelength response of a p+-n Ge solar cell and from a tenfold reduction in the dark saturation current of a p+-n Ge junction. At the same time, the p+-Ge/p-Al0.85Ga0.15As interface is electrically transparent to majority-carrier hole transport. Similarity of measured specific resistivities of Ti/Au ohmic contacts directly to Ge and through a p-Al0.85Ga0.15As layer to p+ Ge leads to this conclusion in spite of about 1 eV valence-band offset at the Ge-Al0.85Ga0.15As heterojunction interface. A possible mechanism for the hole transport through such an interface is discussed. Applied Physics Letters is copyrighted by The American Institute of Physics.