X-Ray Diffraction and Photoluminescence Studies of InN Grown by Plasma-Assisted Molecular Beam Epitaxy with Low Free-Carrier Concentration

We report studies of InN grown by plasma-assisted molecular beam epitaxy. GaN templates were first grown on sapphire substrates followed by InN overgrown at 457A degrees C to 487A degrees C. Atomic force microscopy shows the best layers to exhibit step-flow growth mode of the InN, with a root-mean-square roughness of 0.7 nm for the 2 mu m x 2 mu m scan and 1.4 nm for the 5 mu m x 5 mu m scan. Measurements of the terrace edges indicate a step height of 0.28 nm. Hall measurements at room temperature give mobilities ranging from 1024 cm(2)/V s to 1904 cm(2)/V s and the electron concentrations are in the range of 5.9 x 10(17) cm(-3) to 4.2 x 10(18) cm(-3). Symmetric and asymmetric reflection x-ray diffraction measurements were performed to obtain lattice constants aa and c. The corresponding hydrostatic and biaxial stresses are found to range from -0.08 GPa to -0.29 GPa, and -0.05 GPa to -0.32 GPa, respectively. Low-temperature photoluminescence peak energies range from 0.67 eV to 0.70 eV, depending on residual biaxial stress, hydrostatic pressure, and electron concentrations. The electron concentration dependence of the estimated Fermi level is analyzed using Kane's two-band model and conduction-band renormalization effects.