Scanning tunneling microscopy/spectroscopy study of self-organized quantum dot structures formed in GaP/InP short-period superlattices

Self-organized quantum dot (QD) structures formed in (GaP)(n)(InP)(n) short-period superlattices (SLs) grown on GaAs (N11) substrates by gas source MBE (molecular beam epitaxy) are studied by scanning tunneling microscopy (STM)/scanning tunneling spectroscopy (STS). STM images show high density QD structures as bright areas. The dot size of these structures ranges from 15 nm to 25 nm with a dispersion of +/-10% depending on the n and m of the SLs. In the STS measurement, the voltage width for dI/dV = 0 varies along the lateral direction on the sample surface. This voltage width variation corresponds to the lateral variation of the band-gap energy and of the tunneling probability by the lateral composition modulation.