Surface and Interface Studies of GaN Epitaxy on Si(111) via ${\mathrm{ZrB}}_2$ Buffer Layers

Gallium nitride films, epitaxially grown on Si(111) via a lattice-matched ${\mathrm{ZrB}}_2$ buffer layer by plasma-assisted molecular beam epitaxy, have been studied in situ by noncontact atomic force microscopy and also in real time by reflection high-energy electron diffraction. The grown films were determined to be always N-polar. First-principles theoretical calculations modeling the interface structure between GaN(0001) and ${\mathrm{ZrB}}_2(0001)$ clarify the origin of the N polarity.

Figure 1

(a) XPS spectra of as-loaded ${\mathrm{ZrB}}_2$ film (blue) and annealed film (red) in B $1s$ and Zr $3d$ regions. Oxide-related peaks disappeared after annealing at 760 °C overnight under UHV. (b) RHEED pattern of oxide-free ${\mathrm{ZrB}}_2(0001)$ film showing $2\times$ streaks at RT. The electron beam is parallel to ${\mathrm{ZrB}}_2⟨11\overline{2}0⟩$. STM images of the ${\mathrm{ZrB}}_2(0001)\mathrm{\text{−}}(2\times 2)$ surface (c) $100\times 100{\mathrm{nm}}^2$ ($+0.9\mathrm{V}$, 0.15 nA), showing terraces with narrow antiphase domains and step heights of about 0.34 nm, similar to the $c$ lattice constant of ${\mathrm{ZrB}}_2$, and (d) $10\times 10{\mathrm{nm}}^2$ ($+0.1\mathrm{V}$, 1.5 nA), showing atomically resolved ($2\times 2$) reconstruction with antiphase domain boundaries in brighter contrast.

Figure 2

NC-AFM images of a GaN film surface grown on ${\mathrm{ZrB}}_2/\mathrm{Si}(111)$. (a) Scan size $100\times 100{\mathrm{nm}}^2$, showing part of a spiral dislocation structure on an atomically flat $\mathrm{GaN}(000\overline{1})$ surface. Scan size $10\times 10{\mathrm{nm}}^2$, showing (b) ($3\times 3$), (c) ($6\times 6$), and (d) $c(6\times 12)$ reconstructions. (b), (c), and (d) are surface reconstructions all related to the N-polar $\mathrm{GaN}(000\overline{1})$ surface.

Figure 3

Atomistic representations of the six $\mathrm{GaN}(0001)\mathrm{\text{−}}{\mathrm{ZrB}}_2(0001)$ interface models. The atoms are represented by spheres: Ga (brown), N (dark blue), Zr (light blue), and B (pink). Models 1, 4, and 6 are N-polar, while models 2, 3, and 5 are Ga-polar.