Gas source molecular beam epitaxy growth of GaN-rich side of GaNP alloys and their observation by scanning tunneling microscopy

The GaN-rich side of a GaNP alloy exhibits a potentially large variation in band-gap energy with P content due to its large bowing. To study the phase separation observed in GaNP grown on a (0001) sapphire substrate with a P content larger than 0.015, GaNP layers are grown on (111)A substrates by electron cyclotron resonance molecular beam epitaxy (ECR-MBE). During the growth of GaNP layers, reflection high energy electron diffraction (RHEED) exhibits additional spotty patterns indicating phase separation as well as (1 x 1) streaks. Scanning tunneling microscopy (STM) images on the phase-separated samples show the bright clusters with about 3 nm in size, which correspond to the phase-separated GaP-rich region. I-V curves on the bright clusters are quite different from those on other areas indicating a lower band-gap energy.