Influence of V/III Flow Ratio on Growth of InN on GaN by PA-MOMBE

InN epilayers were prepared on c-GaN/sapphire substrates by plasma-assisted metal-organic molecular beam epitaxy using N2 and trimethylindium precursor as the V/III sources. We studied the influence of the V/III flow ratio on the film structure, surface morphology, film compositions, and optical and electrical properties using scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray diffraction, X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), photoluminescence (PL) measurement and Hall effect. The results show that epitaxial InN films can be obtained with the V/III ratio in the range between 1.81 and 4 at 500°C. The InN growth rate decreases from 1.9 to 1.4 μm/h when the ratio increases from 1.81 to 4. The surfaces of the InN films are not smooth in the V/III range used. Cross-sectional TEM revealed that the planar defect density in InN is as high as ∼ 1.5 × 106 cm−1 at a V/III ratio of ∼1.81. XPS and SIMS results show that the film surface contains oxygen, which is found to affect the measured carrier mobility and concentration.