Effects of thermal annealing on structural and electrical properties of surface-activated n-GaSb/n-GaInP direct wafer bonds
A study on the microstructure of argon-beam activated n-GaSb/n-Ga0.32In0.68P bond interfaces is presented, focusing on the behavior of the bond upon thermal annealing and the relationship with electrical bond properties. Structural investigations of annealed samples utilizing high-resolution transmission electron microscopy combined with energy dispersive x-ray spectroscopy are discussed and compared with electrical current-voltage measurements. An amorphous interlayer of ∼1.4 nm thickness between the n-GaSb and n-Ga0.32In0.68P originates from the argon sputtering process. This layer continuously recrystallizes upon thermal annealing, creating a mostly crystalline interface at an annealing temperature of 500 °C. Additionally at 400 °C, In enrichment is observed in the near-surface regions of GaSb and pores are generated at the interface. At 500 °C, larger pores are observed and the In enrichment continues, leading to the formation of crystalline In precipitates within the GaSb crystal. The observed changes in the interfacial microstructure upon annealing correlate with variations in the electrical bond resistances. All bonds show ohmic IV-characteristics with resistances in the range of few mOcm2. However, the bond resistance decreases after annealing at temperatures up to 350 °C but increases after annealing at higher temperatures. This behaviour agrees with the observation of reduced amorphous layer thickness upon annealing and with the formation of new induced interfacial defects for annealing temperatures above 350 °C.