NiZnAl-based p-type ohmic contacts on AlGaAs/InGaAs heterostructures

p-type ohmic contacts based on Ni/Zn/Al/TiWN metallization were evaluated for application to self-aligned p-channel heterostructure FETs. Low-resistance, stable ohmic contacts were achieved on Al_x Ga_1-xAs/InGaAs heterostructures with aluminum composition (x) as high as 0.75. Following short-term annealing of 30 s in the temperature range of 500°C to 600°C, contact resistances less than 0.6 Ω-mm and specific resistivities under 5×10^-6 Ω-cm² were achieved. Further anneal at 500°C for 10 min resulted in a minimum contact resistance of 0.06 Ω-mm and a specific resistivity of 3.2×10^-8 Ω-cm². Contact morphology was mirror-smooth and specular and the contacts were found to be stable at 500°C for anneal times as long as 40 min, with contact resistance remaining below 1 Ω-mm