The vacuum wafer bonding technique as an alternative method for the fabrication of metal/semiconductor heterostructures

The spin-valve transistor is a magneto-electronic semiconductor/ferromagnet/semiconductor heterostructure in which severe demands are put on the quality of materials and their interfaces. In this paper we discuss the vacuum bonding method as an alternative to heteroepitaxy for the fabrication of such complex devices. With this technique, bonding occurs by joining two substrates with a freshly deposited metal layer on top, in a UHV chamber. No high temperature nor high pressure steps are involved and the only requirement for successful vacuum bonding is the surface roughness. Using MBE techniques fairly complicated structures can be grown smooth enough to allow bonding. We show that UHV wafer bonding in combination with MBE grown semiconductor structures is a versatile technique to fabricate high quality hybrid structures with well controlled interfaces.