Revealing Inclined Twin Related Defects in III-V Nanowires Grown in Popular Alternative Crystallographic Directions

Even after two decades of research, conventional ⟨111⟩ B oriented III-V nanowires are often perturbed by twins and stacking faults that form perpendicular to their growth direction and span the cross-section of the nanowire. Although not strong optical quenchers, these defects are known to result in undesirable effects, such as scattering charge carriers and altering band structure. One of the solutions brought forth to avoid the formation of such planar defects is to grow nanowires in alternative growth directions, such as [100] and ⟨111⟩ A, as they are often assumed to be inherently twin-free. These directions have recently gained popularity with the demonstration of increased yield of vertical growth. However, occasional twin defects can form also in nanowires of these orientations. These defects are inclined to the growth axis and have been attributed similar properties to those formed perpendicular to the growth direction in conventional ⟨111⟩ B nanowires. Here, by combining atomic resolution electron microscopy, simulations, and spatially resolved photoluminescence measurements on single nanowires, we show that inclined twins indeed form in both [100] and ⟨111⟩ A III-V nanowires and that their defect structure and resulting properties are more complex than previously thought; these defects can be trapped within the nanowire, bounded by partial dislocations, and when trapped also form detrimental nonradiative centers. Finally, by optimizing growth parameters, we have grown truly twin defect-free vertical InP and GaAs nanowires in [100] and ⟨111⟩ A directions, respectively.