An ultrahigh vacuum system for the fabrication and characterization of ultrathin metal–semiconductor films and sensors

Abstract

An ultrahigh vacuum system has been designed and built to study the magnetic and electrical behavior of ultrathin metal films deposited on semiconductors. The system allows variable temperature metal film deposition by electron beam evaporation onto an electrically active, low noise device structure. Significant features include, the use of microfabricated substrates to create reliable zero-force electrical contacts to ultrathin metal–semiconductor devices, a dark atomic beam source, and a compact magneto-optic Kerr effect (MOKE) magnetometer with an external electromagnet. A temperature controlled rotating sample manipulator allows the active metal surface to be deposited in one position and subsequently rotated between the poles of the electromagnet for simultaneous MOKE and electrical measurements while the surface undergoes controlled dosing from a molecular or atomic beam. Low-energy electron diffraction is available for sample characterization and a quadrupole mass spectrometer is used to monitor the beam. Results of iron on Si(111) show magnetic coercivity increasing approximately linearly with increasing film thickness to 6.4 kA/m at 100 Å. Current–voltage measurements of 50 Å iron and copper on Si(111) when fit to a thermionic emission model showed, respectively, ideality factors of approximately 4 and 1, and barrier heights of 0.45 and 0.65 eV after deposition at 160 K and annealing to room temperature. The use of the thin Cu film Schottky diode for atomic hydrogen detection is demonstrated.