Detection of Bi_Ga hetero-antisites at Ga(As,Bi)/(Al,Ga)As interfaces

In this work, we show how diffraction-based chemically sensitive dark-field transmission electron microscopy (DFTEM) reveals the presence of Bi hetero-antisites (Bi_Ga) at the interface of Ga(As,Bi)/(Al,Ga)As quantum well (QW) structures grown by molecular beam epitaxy on GaAs(001). The presence of Bi_Ga is demonstrated by the striking appearance of “dark-lines” at the interfaces under two-beam DFTEM imaging conditions using the (002) diffraction spot. Additional analytical scanning (S)TEM procedures reveal Ga depletion and Bi accumulation at the exact position of the dark-lines, consistent with Bi_Ga at this location. The precise location of the dark-lines agrees with the position of growth interruptions made to adjust substrate temperature and the As/Ga flux ratio and, most importantly, the realization of a Bi pre-treatment before QW growth. We believe the Bi pre-treatment may have favored formation of Bi_Ga hetero-antisites. We validate the use of g₀₀₂ DFTEM for further investigations of the intricate bismuth incorporation into the lattice and its dependence on the growth conditions. Finally, g₀₀₂ DFTEM imaging is positioned as a very powerful technique for the detection of point defects in general in materials with the zinc-blende crystal structure, beyond dilute bismide alloys.