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 variati on 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 subs trate with a P content larger than 0.015, GaNP layers are grown on (11 1)A substrates by electron cyclotron resonance molecular beam epitaxy (ECR-MBE). During the growth of GaNP layers, reflection high energy el ectron diffraction (RHEED) exhibits additional spotty patterns indicat ing phase separation as well as (1 x 1) streaks. Scanning tunneling mi croscopy (STM) images on the phase-separated samples show the bright c lusters with about 3 nm in size, which correspond to the phase-separat ed GaP-rich region. I-V curves on the bright clusters are quite differ ent from those on other areas indicating a lower band-gap energy.