INVESTIGATION OF IN CONTACTS ON ATOMICALLY CLEAN GAAS(110) SURFACES

We have examined In-GaAs(liO) contacts fabricated in situ both by depositing In at room temperature followed with annealing and by depositing In on heated surfaces [n-and />-type GaAs(110) surfaces (250 and 300 °C, respectively) using synchrotron radiation photoemission. It is found that In deposition on GaAs(110) surfaces with temperature below room temperature does not induce measurable reaction, whereas reaction takes place with InAs as product when the room-temperature-formed interface is annealed or when In is deposited on the heated substrate. However, there is no evidence of InxGa1-xAs graded heterojunction formation at the interface in either case. Outdiffusion of the excess As from the substrate is suggested to provide a source for InAs formation instead of the previously proposed In-GaAs replacement reaction. Electrical measurements were also performed on in situ In/n-GaAs(110) contacts before and after annealing. Reproducible high-barrier heights were recorded (1.02 ± 0.02 eV) with good ideality factors (1.05 ± 0.01) for the unannealed contacts, which is significantly different from the previously published values (0.76 and 0.78 eV). No dramatic change has been recorded in terms of barrier height upon annealing up to 375 °C although the ideality factor increases to around 1.2±0.1. The implication of this study to ohmic contact formation mechanisms will be discussed. © 1990, American Vacuum Society. All rights reserved.