Scanning Tunneling Microscopy Study on Self-Formation Process of Quantum Dot Structures by the Growth of GaP/InP Short-Period Superlattices on GaAs (311)A Substrate

Abstract

Self-formation process of quantum dot (QD) structures in (GaP)1.5 (InP)1.88 short-period superlattices (SLs) grown on GaAs (311)A substrates by gas source MBE (molecular beam epitaxy) are studied by scanning tunneling microscopy (STM). STM images reveal high-density (1011–1012 cm-2) QD structures periodically aligned along the [233] and [011] directions. STM observations of the self-formed structures as a function of SL cycle number show that almost complete QD structures are formed only after the growth of 1 cycle of SL (1.5 monolayer GaP and 1.88 monolayer InP), although the periodic structures elongated only along the [011] direction are formed even after the growth of 0.5 cycle of SL (1.5 monolayer GaP). In the dI/dV vs. V measurement, the voltage width (ΔV) for the dI/dV=0 varies periodically along the lateral direction on the sample surface, and the amplitude of this periodic variation increases with the SL cycle number and saturates at 2 SL cycles.