The self-aligned GaAs metal-semiconductor field-effect transistor technology requires that the gate material maintains a good rectifying contact with the GaAs substrate when subjected to high-temperature annealing around 800–900° C. ZrN Schottky contacts to GaAs were previously shown to have excellent electrical properties at high tempratures. An increase of barrier height and a decrease in the reverse breakdown voltage with rapid thermal annealing at temperatures up to 900° C has been observed. The ideality factor increases after rapid thermal annealing at 900° C.
In an attempt to explain the above observations, we investigated the interface structure of such contacts under as-deposited and annealed conditions. By high resolution TEM it was found that the interface of as-deposited samples is fairly flat but protrusions form after rapid thermal annealing treatment at 850 and 900° C. The selected area diffraction analysis shows the presence of ZrO2 near the interface.
It is therefore likely that protrusions are the cause of the degradation of electrical properties of the contacts. These protrusions may be caused by the presence of a residual oxide layer before deposition. Indeed, a deposition of ZrN after sputter cleaning the substrates before deposition procedure resulted in an abrupt interface even after annealing at 900° C.