Characteristics of mesa- and LOCOS-isolated molecular beam epitaxy SiGe diodes

Molecular beam epitaxy grown p+–n SiGe–Si heterojunction diodes with and without p+Si caps on top of the p+ SiGe have been fabricated on n-type Si<100> wafers with and without SiO2 LOCOS patterns. It is shown that the p+Si caps create p+–p+ Si–SiGe isotype heterojunctions in series with the p+–n SiGe–Si heterojunctions. Potential barriers and carrier depletion regions exist in the isotype heterojunction regions owing to the band-gap difference between the two materials. Effects of the LOCOS and the p+–p+ Si–SiGe isotype heterojunction in series with the p+–n SiGe–Si heterojunction on the characteristics of the diodes were studied experimentally and using simulation. The diodes fabricated exhibited I–V characteristics ideality factors between 1.05 and 1.20.