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

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 (10(11)-10(12) cm(-2)) QD structures periodically aligned along the [(2) over bar 33] and [0 (1) over bar 1] 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 [0 (1) over bar 1] 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 (Delta V) 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.