Nanometer-scale studies of point defect distributions in GaMnAsGaMnAs alloys

Abstract

We have investigated the concentrations and distributions of point defects in GaMnAsGaMnAs alloys grown by low-temperature molecular-beam epitaxy, using ultrahigh-vacuum cross-sectional scanning tunneling microscopy (XSTM). High-resolution constant-current XSTM reveals “A,” “M,” and “V” defects, associated with AsGaAsGa, MnGaMnGa, and VAsVAs, respectively. A and V defects are present in all low-temperature-grown layers, while M defects are predominantly located within the GaMnAsGaMnAs alloy layers. In the GaMnAsGaMnAs layers, the concentration of V defects ([V])([V]) increases with the concentration of M defects ([M])([M]), consistent with a Fermi-level-dependent vacancy formation energy. Furthermore, [M][M] is typically two to three times [A][A] and [V][V], suggesting significant compensation of the free carriers associated with MnGaMnGa. A quantitative defect pair correlation analysis reveals clustering of nearest V–V pairs and anti-clustering of nearest M–M, M–V, and M–A pairs. For all pair separations greater than 2 nm2nm, random distributions of defects are apparent.