NiAuGeAu ohmic contacts for a planar InP-based high electron mobility transistor structure with suppressed drain conductance frequency dispersion

Abstract

We have fabricated a thermally stable low-contact-resistance Ni/AuGe/Au contact metal for InP-based high electron mobility transistors (HEMTs) without a heavily doped cap layer. The contact resistance is strongly influenced by the amount of Ni. Minimum contact resistance of 0.19 Ω mm was obtained from a Ni (1 nm)/AuGe (50 nm)/Au (99 nm) contact annealed at 300 °C for 5 min in N2. A smooth surface was obtained after contact formation and excellent thermal stability was achieved during isothermal annealing at 350 °C for 1 h in a N2 ambient. This alloyed ohmic contact satisfies the requirements for device fabrication process steps after the ohmic contact formation. It prevents hole accumulation by eliminating the hole barrier at the carrier-supply layer/channel interface. It also suppresses the kink phenomena and drain conductance frequency dispersion of InP-based HEMTs, and therefore will greatly facilitate the fabrication of ultrahigh-speed integrated circuits.

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

“…Both the Pd/Ge/Ti/Pt and Ge/Ag/Ni contacts are alloyed. Arai et al 41 argued that alloying to place the metal/semiconductor interface in direct contact with the channel is needed to suppress hole accumulation in III-V HEMTs. Nevertheless, another frequently reported approach is the use of nonalloyed contacts.…”

“…The selected layer thicknesses and annealing conditions can greatly affect the morphology and contact resistance, as reported again in recent years, specifically for contacts to InAlAs/ InGaAs heterostructures. 40,41 For the III-V devices that are the subject of this issue, we can expect that the annealed Ni-Au-Ge contact has reacted partly or fully through any wider-gap semiconductor barrier layer, considering the depth of reaction typical for this contact, as illustrated schematically in Figure 9a. The overall morphology of this reaction, including any lateral diffusion, may prove challenging when devices are scaled to smaller feature sizes.…”

Thermal stability of Ti/Pt/Au ohmic contacts for cryogenically cooled InP-based HEMTs on (411)A-oriented substrates by MBE

“…Alloyed and non-alloyed ohmic contacts formed on a heavily Si-doped InGaAs cap layer are commonly used as source and drain electrodes of InP-based HEMTs [6,7]. In fact, a high f T of over 550 GHz was achieved using a non-alloyed Ti/Pt/Au ohmic contact [1,8].…”

RBS characterization on the PtSi-based ohmic contacts with n-InP

“…Au-Ge [1,2] based electrode to n-InP shows excellent ohmic behavior, however, which is not always stable for the heat excursion of the contacts because the reaction products at the contact interface change due to diffusion upon annealing. The diffusion of the dopant element deep into the substrate is also disadvantage of the electrode for the device applications.…”