Overcoming the Miscibility Gap of GaN/InN in MBE Growth of Cubic In x Ga1-x N

The lack of internal polarization fields in cubic group-IIInitridesmakes them promising arsenic-free contenders for next-generation high-performanceelectronic and optoelectronic applications. In particular, cubic In( x )Ga(1-x )Nsemiconductor alloys promise band gap tuning across and beyond thevisible spectrum, from the near-ultraviolet to the near-infrared.However, realization across the complete composition range has beendeemed impossible due to a miscibility gap corresponding to the amberspectral range. In this study, we use plasma-assisted molecular beamepitaxy (PAMBE) to fabricate cubic In x Ga1-x N films on c-GaN/AlN/3C-SiC/Sitemplate substrates that overcome this challenge by careful adjustmentof the growth conditions, conclusively closing the miscibility gap.X-ray diffraction reveals the composition, phase purity, and strainproperties of the In x Ga1-x N films. Scanning transmission electron microscopyreveals a CuPt-type ordering on the atomistic scale in highly alloyedfilms with x(In) & AP; 0.5. Layers with much lowerand much higher indium content exhibit statistical distributions ofthe cations Ga and In. Notably, this CuPt-type ordering results ina spectrally narrower emission compared to that of statistically disorderedzincblende materials. The emission energies of the films range from3.24 to 0.69 eV and feature a quadratic bowing parameter of b = 2.4 eV. In contrast, the LO-like phonon modes that areobserved by Raman spectroscopy exhibit a one-mode behavior and shiftlinearly from c-GaN to c-InN.