PdGe-based ohmic contacts to high-low doped n-GaAs with and without undoped cap layer

We report the ohmic contact formation mechanism for a low-contact resistanc e PdGe-based system on high-low doped GaAs with and without undoped cap lay er annealed in the temperature range of 380-450 degrees C. The lowest avera ge specific contact resistances of the Pd/Ge/Ti/Pt ohmic contacts with and without undoped cap layer after annealing at 400 degrees C were 5.3 x 10(-6 ) Omega cm(2) and 2.4 x 10(-6) Omega cm(2), respectively. And the lowest av erage specific contact resistances of the Pd/Ge/Ti/Pt/Au ohmic contacts wit h and without undoped cap layer after annealing at 380 degrees C were 3.5 x 10(-6) Omega cm(2) and 3.4 x 10(-6) Omega cm(2), respectively. For the Pd/ Ge/Ti/Pt contact without undoped cap layer, the x-ray diffraction, cross-se ctional scanning electron microscopy and Auger electron spectroscopy were u tilized in this study. The Pd/Ge/Ti/Pt ohmic contact without undoped cap la yer was thermally stable after isothermal annealing at 400 degrees C for 6 h.