| AVS 54th International Symposium | |
| Electronic Materials and Processing | Wednesday Sessions |
| Session EM-WeM |
| Session: | Contacts, Interfaces and Defects in Semiconductors |
| Presenter: | L. Wang, University of Illinois at Urbana-Champaign |
| Authors: | L. Wang, University of Illinois at Urbana-Champaign I. Adesida, University of Illinois at Urbana-Champaign |
| Correspondent: | Click to Email |
InAlAs/InGaAs HEMTs are promising devices for high speed circuits, millimeter-, and sub-millimeter-wave applications. Selection of gate metallizations plays a significant role in the performance, operation mode, stability, and manufacturability of these devices. Two factors need to be considered in choosing gate metals, namely, work function and reactivity with InAlAs during fabrication and operation. Electrically, metal work function determines Schottky barrier height (φB) which in turn decides key device operation parameters such as threshold voltage, transconductance, gate capacitance, etc. Structurally, reactivities or diffusivities of metals/InAlAs control the final gate-channel distance and thermal stability of the transistors. However, a thorough correlation of electrical and structural characterizations of metal/InAlAs contacts at various annealing conditions is still lacking. In this study, we examined the relationship between the φB characteristics and interfacial reactions of Ti/InAlAs and Ir/InAlAs. I-V characteristics of Schottky diodes were used for φB and ideality factors characterizations. Cross-sectional transmission electron microscopy is utilized to elucidate the microstructural evolution occurred at the metal/semiconductor interfaces. For Ir/InAlAs, φB decreased slightly compared to the as-deposited value when annealed at 250 °C. Beyond that φB increased monotonically until it reached the peak value of 825 meV at 400 - 425 °C. Further increasing the temperature led to φB degradation. Over a wide temperature range from ~375 to 450 °C, φB of over 800 meV could be achieved. XTEM studies showed that enhancement in φB is due to the formation of amorphous layer at the interface. Annealing above 455 °C led to the nucleation of IrAs2 crystals. For Ti/InAlAs, as-deposited diodes had a typical φB of 668 meV and an ideality factor of 1.0. Two maxima in φB were observed for samples annealed at temperatures above 300 °C. The first set of maxima had values between 748 and 726 meV. The second set of maxima had higher φB of over 760 meV after prolonged annealing. Similar to Ir/InAlAs, an amorphous mixture between Ti and InAlAs formed for samples annealed at short durations. Prolonged thermal treatment resulted in aggressive reaction leading to Kirkendall voids formation, deformation of InAlAs, and TiAs crystal growth. Such aggressive reaction and thus defects formation led to higher diode ideality factors.