Ohmic Contacts to p-Type III-V Semiconductors for the Base of Heterojunction Bipolar Transistors

Abstract

Ohmic contacts to p-type In0.25Ga0.75Sb, InAs, and InAs0.8P0.2 have been investigated for the base of heterojunction bipolar transistors. On all these semiconductors, using Pd and/or Pt as the first layer in the metallization stack provided the lowest contact resistances. Specific contact resistances as low as 3 x 10-7 Ω-cm2 were measured for Au/W/Pd/p-InGaSb. Thin reactive layers of Pd or Pt were used beneath an unreactive W barrier to keep the contacts shallow, but contact resistance and thermal stability were sacrificed when 2 nm of Pd was used instead of 5 nm. The lowest contact resistance we measured on p-InAs was obtained with Pd/Pt/Au, but Pd/W/Au exhibited better thermal stability at 250 °C. For p-type InAsP, Pd/Ru/Au provided a specific contact resistance of 4 x 10-6 Ω-cm2 as deposited. The contact consumed only 4 {plus minus} 2 nm of InAsP after 3 days at 250 °C, and its resistance remained low.

Facile and Electrically Reliable Electroplated Gold Contacts to p-Type InAsSb Bulk-Like Epilayers

“…The contact resistance values for metallization schemes in Sb-containing InAs-based semiconductors have been limitedly reported. For instance, Mohney and co-workers presented an extended study on distinct three- and four-layered ohmic contact metallization with Au cap layer to maintain a low metal sheet resistance to highly Be-doped InAs (>10 19 cm −3 ) with ρ c at a level of 10 −6 Ω·cm 2 [ 17 , 18 ]. Guo et al conducted an analysis on highly Be-doped InAs/InAsSb cap structure, yielding an ultralow ohmic contact with ρ c of 1.3 × 10 −8 Ω·cm 2 [ 19 ].…”

“…The thermal stability studies conducted by Lee et al [16] on InAs/graded InGaAs structure revealed that the In atoms diffuse and penetrate into the 110 nm thick Ti layer, leading to InAs film decomposition at 350 • C. Other more complex Au-containing metallization schemes were tested as well on InAs-based structures using distinct adhesive/barrier layers such as Pd, Co, Ni, etc. [17][18][19]. Nevertheless, Au is normally the main constituent of metallization schemes due to high electrical conductivity and excellent corrosion resistance [20] and is vital in processing semiconductor devices.…”

“…Other more complex Au-containing metallization schemes were tested as well on InAs-based structures using distinct adhesive/barrier layers such as Pd, Co, Ni, etc. [ 17 , 18 , 19 ]. Nevertheless, Au is normally the main constituent of metallization schemes due to high electrical conductivity and excellent corrosion resistance [ 20 ] and is vital in processing semiconductor devices.…”