Electrical characterization and metallurgical analysis of Pd-containing multilayer contacts on GaN

Abstract

Ti(250 Å)/A1(2200 Å)/Pd(600 Å)/Au(1600 Å) contact on aqua-regia surface treated n-GaN (Si∼1.0 × 1019cm-3) has yielded a minimum specific contact resistance (ρc) of 4.21 × 10-8 Ω cm2, achieved after thermal annealing at 500 °C for 8 min. This is superior to the most common n-GaN contact, Ti/Al, which has also been studied in the current work and produced a lowest ρc of 4.63 × 10-6 Ω cm2, obtained after annealing at 700°C for 2 min. The long-term thermal stability analysis has also revealed that the Ti/Al/Pd/Au contact is more stable than Ti/Al on n-GaN. The projected mean time to 50% increase in ρc(μ50) at 150°C for the former is 1.22 × 1012 h, which is higher by about three orders of magnitude than that of the latter at 3.54 × 109 h. Pd(200 Å)/Ni(300 Å)/Au(2000 Å) contact on boiling aqua-regia surface treatedp-GaN (Mg∼1.0 × 1018 cm-3) has also been investigated and demonstrated a reasonable ohmic behavior with a ρc of 5.03 × 10-4 Ω cm2 after thermal annealing at 450 °C for 2 min. However, its thermal stability is mediocre with μ50 at 150°C of only 1.49 × 103 h. © 2001 American Institute of Physics.