Scanned electron beam alloyed ohmic contacts to n-GaAs

Abstract

Scanned electron beam (SEB) is used for the alloying of evaporated AuGe-Ni metallisation on n-type GaAs so as to realise high quality ohmic contacts to n-GaAs. The contact quality is studied for various incident beam energy, scanning time and metallisation thickness. The electrical properties of the contacts are characterised by contact resistivity measurements and it is found that the contact resistivity for SEB alloyed contacts is lower than furnace alloyed contacts and it is independent of metallisation thickness. The optical and Scanning Electron Microscopic observation of surface and subsurface morphology establishes that SEB alloyed contacts have smooth and uniform morphology compared to furnace alloyed contacts. The electron microprobe analysis confirms that the contact constituents are uniformly distributed over the entire contact area. Penetration depth of gold in GaAs is studied by Rutherford Backscattering Techniques which shows that the penetration of gold for SEB contact is far less than furnace alloyed contacts and is independent of metallisation thickness. High temperature ageing tests confirm that SEB alloyed contacts undergo less ageing degradation compared to furnace alloyed contacts.