Spontaneous Oscillations and Waves during Chemical Vapor Deposition of InN

We report observations of self-sustaining spatiotemporal chemical oscillations during metal-organic chemical vapor deposition of InN onto GaN. Under constant supply of vapor precursors trimethylindium and ${\mathrm{NH}}_3$, the condensed-phase cycles between crystalline islands of InN and elemental In droplets. Propagating fronts between regions of InN and In occur with linear, circular, and spiral geometries. The results are described by a model in which the nitrogen activity produced by surface-catalyzed ${\mathrm{NH}}_3$ decomposition varies with the exposed surface areas of GaN, InN, and In.

Figure 1

Indium fluorescence and InN (110) diffraction intensities versus time after initial injection of $p(\mathrm{TMI})=1.22\times {10}^{-3}\mathrm{mbar}$ at 937 K, $p({\mathrm{NH}}_3)=40\mathrm{mbar}$.

Figure 2

Optical images of a $15\times 15\mathrm{mm}$ substrate during growth on its central area at 937 K. Regions of InN islands and In droplets correspond to dark and light contrast, respectively. (a) and (b) Recorded with Fig. 1 data at times 8262 and 8342 s, showing wave moving from right to left; $p(\mathrm{TMI})=1.22\times {10}^{-3}\mathrm{mbar}$, $p({\mathrm{NH}}_3)=40\mathrm{mbar}$. White outline shows x-ray illuminated area. (c) Expanding circular disk; $p(\mathrm{TMI})=0.92\times {10}^{-3}\mathrm{mbar}$, $p({\mathrm{NH}}_3)=40\mathrm{mbar}$. (d) Outwardly propagating spiral; $p(\mathrm{TMI})=1.22\times {10}^{-3}\mathrm{mbar}$, $p({\mathrm{NH}}_3)=57\mathrm{mbar}$.

Figure 3

Atomic force microscopy images of (a) hexagonal InN islands and (b) spherical elemental In droplets on a sample quenched after $\sim 5$ oscillation periods under the same conditions as data shown in Fig. 1. ($10\times 10\mu \mathrm{m}$ areas).

Figure 4

(a): Total ($\mathrm{InN}+\mathrm{In}$ Liquid) and InN curves are normalized fluorescence and diffraction data from Fig. 1; In Liquid curve is the difference. (b): Calculated Total, InN, and In Liquid evolution from reaction-diffusion model. Parameter values used are $q=0.5$, $r=1$, $k_1=0.05$, $k_2=0.40$, $k_3=2$, ${\gamma }_2/{\gamma }_1=2$, ${\gamma }_3/{\gamma }_1=0.08$, and ${\gamma }_1=0.0147{\mathrm{s}}^{-1}$.