Metallization options and annealing temperatures for low contact resistance ohmic contacts to n-type GaSb

Abstract

With GaSb emerging as one of the crucial material for 6.1 Å based electronic devices, low contact resistivity ohmic contacts suitable for nano-electronic and high-speed device operation are desirable. The surface of GaSb is believed to exhibit Fermi level pinning near the valence band making ohmic contact formation to n-type GaSb challenging. MBE GaSb, doped n-type with GaTe and grown on semi-insulating GaAs, is examined. The semi-insulating substrate allows mesa isolation and accurate ohmic contact evaluation by Transmission Line Model (TLM) measurements. A variety of metallization schemes and alloy temperatures are examined with lowest contact resistances observed for Pd containing ohmic contacts. A Pd/Ge/Pd/In/Pd metallization on GaSb:Te doped to 5.6×10 17 cm −3 alloyed at 350 °C for 60 s exhibited a specific contact resistivity as low as 1.4×10 −6 Ω-cm 2 and contact resistance of 0.068 Ω-mm. Pd/Ge/Pd metallization on GaSb:Te doped at 1.8×10 18 cm −3 exhibited specific contact resistivities of 3.8×10 −6 Ω-cm 2 and contact resistances of 0.058 Ω-mm after a 400 °C/60 s alloy. During the alloy cycle a solid phase reaction and regrowth is taking place forming a new interface compound responsible for the low contact resistances. At this time these results represent the lowest reported contact resistivity ohmic contacts to n-type GaSb.