Optical properties of GaN-rich side of GaNP and GaNAs alloys grown by gas-source molecular beam epitaxy

GaN-rich side of GaNP and GaNAs layers is grown at 750 °C by gas-source molecular beam epitaxy. Phase separation is observed for the layers with P and As composition of over 1.5% and 1%, respectively. Photoluminescence (PL) spectra for the non-phase-separated GaNP (P composition: 0.37%) and GaNAs (As composition: 0.26%) show redshift of 50 and 40 meV, respectively, from that of GaN, and exhibit Stokes shift of about 80 meV which is smaller than that of GaN (100 meV). On the other hand, the PL spectrum for the phase-separated GaNP shows a large redshift peaking at 2.101 eV. This peak is considered to be an emission from the phase-separated GaP-rich GaPN region. PL excitation spectrum shows two large broad peaks. One at 2.982 eV corresponds to the absorption at the Γ point of GaP-rich region, and the other at 2.308 eV corresponds to the absorption at the isoelectronic band edge of GaP-rich GaPN alloy originated from the X point of GaP. In the case of phase-separated GaNAs, no PL is observed, suggesting that the optical properties are much more sensitive to crystalline quality in GaAs-rich GaAsN than in GaP-rich GaPN.