Low-resistance nonspiking ohmic contact for AlGaAs/GaAs high electron mobility transistors using the Ge/Pd scheme

Nonspiking (nonalloyed) Ge/Pd ohmic contact formed via solid phase reaction on an AlGaAs/GaAs high electron mobility transistor (HEMT) was investigated. The surface morphology of the Ge/Pd contact is smooth and planar with a typical contact resistivity of about 3×10−7 Ω cm2. The current-voltage characteristics of the HEMTs with the Ge/Pd contacts are similar to those with the conventional AuGe/Ni spiking (alloyed) contacts. Since only a thin substrate surface layer of 100–200 Å was reacted with the Ge/Pd contact, we can conclude that ohmic contacts can be made to the two-dimensional electron gas without deep penetration of the metallization. This observation is in agreement with the concept that transport due to tunneling is significant across heterojunctions. The Ge/Pd contact may be potentially useful in HEMT integrated circuit technology.