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(a) Rocking curves (ω scans in HRXRD) of on-axis (0002) and off-axis ( and ( reflections measured with an open detector for a representative ∼0.6 -μm-thick InN film grown under N-rich conditions (TTC = 540 °C). FWHM values for the respective reflections are 0.15° for (0002), 0.3° for ( , and 0.4° for ( . (b) False color map illustrating the evolution of FWHM values of the dominant ( reflection (i.e., corresponding mixed edge-type TDs) as a function of substrate temperature and In flux under fixed N flux. Note the decrease in FWHM toward increased temperature and lower In flux, i.e., near-stoichiometric to N-rich conditions.
Cross-sectional TEM images ([ ] zone axis) at diffraction conditions of (a) g = (i.e., edge-type TD sensitive) and (b) g = 0002 (i.e., screw-type TD sensitive) for an InN film grown at TTC = 540 °C. The film was grown via a two-step process, i.e., a ∼0.75 -μm thick N-rich nucleation layer and subsequent ∼0.75-μm thick In-rich bulk layer to smoothen the top surface. Note the pronounced inclination and annihilation of edge-type TDs within the N-rich nucleation layer. (c) 5 × 5 μm2 and (d) 1 × 1 μm2 AFM surface morphologies with rms roughness of 6.0 nm and 0.5 nm, respectively. The image in (d) shows clear step-flow like terrace structure resulting from the two-step growth procedure.
Comparison of measured growth rate (SEM film thickness/growth time) for In-rich grown InN films (ΦIn = 8 nm/min) and slightly N-rich grown InN films (ΦIn = 6.5 nm/min) as a function of substrate temperature. The N flux was fixed at ΦN ∼ 7 nm/min for both growth series and the nominal film thickness was ∼0.75 μm (i.e., without thermal dissociation). A remarkable shift of the available growth temperature window towards higher temperature is found for N-rich conditions with respect to In-rich conditions.
AFM surface morphologies (5 × 5 μm2 and 1 × 1 μm2 -inset) of N-rich/high-T grown InN films (thickness ∼ 0.6–0.75 μm) at different temperatures (TTC) of (a) 480 °C, (b) 575 °C, (c) 585 °C, and (d) 600 °C. The height scales are 100 nm for the 5 × 5 μm2 images and 50 nm for the 1 × 1 μm2 images. Note the increased average grain size and trend towards smoother surfaces with increasing TTC; (e) Rocking curve FWHM values of the relevant ( reflection for the same N-rich/high-T film series in comparison with an In-rich film series films (at highest possible TTC, fixed ΦIn = 8 nm/min, thickness > 0.75 μm).
Rocking curve FWHM data for the on-axis (0002), as well as off-axis ( and ( reflections summarized for all InN films presented in Fig. 1(b) , listing also the measured film thickness d, supplied In flux ΦIn, growth temperature TTC, and room-temperature Hall effect mobility μ(RT) (experimental error < 10%). Note that sample growths marked with an asterisk had an In flux corresponding to nominally slightly In-rich conditions. However, their morphology showed no In droplets and resembled those grown under N-rich conditions, suggesting that the effective N flux was slightly higher for these two growths.
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