THE EFFECTS OF GE CONTENT ON THE MICROSTRUCTURE AND SPECIFIC CONTACT RESISTANCE OF SOLID-STATE NIAUGE ZRB2/AU OHMIC CONTACTS TO N-INGAAS/

The Ge thickness, x, of NiAuGe(5 nm/45 nm Ix nm)/ZrB2(50 nm)/Au(20 nm) ohmic contacts to n-InGaAs was varied between 0 and 20 nm. The micros tructures of these contacts, after annealing at 270-degrees-C, were in vestigated using transmission electron microscopy (TEM) and correlated with the respective specific contact resistances. In the absence of G e, a Ni-Ga-As phase was formed at the metal-semiconductor interface an d the specific contact resistance was high (0.63 OMEGA mm). When thick nesses of x = 1 0 nm or x = 15 nm of Ge were added, Ni-Ge-As phases we re observed, but they were replaced by AuGeAs and NiGe when x = 20 nm. The specific contact resistance was a minimum (0.11 OMEGA mm) for thi s composition. Ge was clearly beneficial for ohmic-contact formation. The low-temperature I-V characteristics of the contact containing the largest amount of Ge (that is, x = 20 nm) indicated that electron tunn elling through degenerately-Ge-doped regions was not the dominant ohmi c mechanism in these contacts.