The Effect of Chemical Treatment of the GaAs Surface on the Ohmic Contact Properties

Abstract

ABSTRACTElectrical properties of metal/GaAs system are known to be influenced very much by GaAs surface condition before the metal deposition. The surface condition of GaAs epitaxial layer can be affected by the wet chemical treatment of the surface. The influence of different processes were compared to choose the best technique for a high quality ohmic contact technology. Applying a chemical treatment which contains degreasing process, a light surface etching and a rinsing process, the carbon contaminations, 20-25 nm GaAs surface layer and the native oxide layer are removed from the GaAs surface. The benefit of the rinsing step is to produce a reproducible, stable surface condition before the metallization. Since the importance of the finishing step was assumed, the investigated processes differed in this step. The compared methods finished with either alkaline, like NH4OH, or acidic, like HCl, etchants resulted higher specific contact resistance than the process finished with neutral, high purity (18 MΩcm) water. In the latest case the obtained specific contact resistance was (6.4 ± 2.7) ×10−6 Ωcm2 on a GaAs epitaxial layer with the doping concentration 1.5 × 1017cm−3.