Design of a shallow thermally stable ohmic contact to p-type InGaSb

Abstract

Ohmic contacts to p-type InGaSb have been investigated. The factors that influence the contact resistance, thermal stability, and shallowness of the contacts are examined. The most desirable contact studied in this work employs three layers. A very thin layer of palladium is deposited on the p-InGaSb first and is found to lower the resistance at the metal/semiconductor interface. The next layer is W, which is predicted to be in thermodynamic equilibrium with InGaSb and which serves as a diffusion barrier to protect the semiconductor from the reaction with the final capping layer. The final capping layer is a 100 or 150 nm Au layer. The Au lowers the metal sheet resistance, which we have found both experimentally and through modeling to influence the contact resistance measurements, and the Au layer provides a contact surface that does not oxidize. The contact resistance of the as-deposited Pd/W/Au (5/50/145 nm) contact is 0.08 Ω mm (corresponding to a specific contact resistance of <3×10−7 Ω cm2), while the more thermally stable Pd/W/Au (5/145/100 nm) contact exhibits a contact resistance of 0.08 Ω mm only after annealing at 250 °C for 3 h, in both cases on a p-In0.25Ga0.75Sb layer with a semiconductor sheet resistance of approximately 300 Ω/□. The thermal stability of the Pd/W/Au contacts was also examined. The Pd/W/Au (5/145/100 nm) contacts remained shallow and exhibited no measurable electrical degradation when aged at 250 °C in N2 for 100 h, while they survived at 250 °C for 14 days in sealed, evacuated, quartz tubes.

Low resistance, unannealed, Ohmic contacts to p-type In0.27Ga0.73Sb

“…4 Initial work on HEMTs and heterojunction bipolar transistors ͑HBTs͒ has been promising. [9][10][11] Specific contact resistances down to 2.8ϫ 10 −7 ⍀ cm 2 on 1.8ϫ 10 18 cm −3 p-type In 0.27 Ga 0.73 Sb for unannealed Pd/W/Au contacts were measured. 7 A critical aspect of low-power, high-speed HBT operation is a low base resistance and base contact resistance.…”

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

“…The test structures were filled circular contacts with gaps between the contacts and a large-area metal field. The gap spacings were nominally 4,8,14,20,30,50, and 75 µm. Prior to metal deposition, pre-metallization surface treatments were performed, as indicated in each of the following sections.…”

Source and Drain Contacts for Germanium and III–V FETs for Digital Logic

“…The latter can be detrimental for the formation of uniform, low-resistance ohmic contacts, and sulfur passivation has been used beneficially for some contacts to InGaSb and GaSb. [54][55][56] Boos et al 57 introduced the Pd/Pt/Au ohmic contact for AlSb/InAs, which, compared to AuGe/Ni/Pt/Au, provided a more controlled interfacial reaction and a lower contact resistance. They have continued to use this contact for both n-channel (InAs) and p-channel (InGaSb) devices.…”

“…For this reason, other refractory metal barrier layers also have been investigated between Pd and Au. 59,62 Summary Many challenges exist for developing ohmic contacts suitable for Ge and III-V channel field-effect transistors (FETs) for digital logic. One important requirement is that the resistance of the contact be very low.…”