Self-assembled InN quantum dots grown on AlN/Si(111) and GaN/Al ₂O₃(0001) by plasma-assisted molecular-beam epitaxy under Stranski-Krastanow mode

We demonstrate that InN quantum dots (QDs) can be spontaneously formed on AlN and GaN surfaces by plasma-assisted molecular-beam epitaxy under the Stranski-Krastanow (S-K) mode. Both Si(111) wafers and metal-organic chemical vapor deposition grown GaN/Al₂O₃(0001) templates were used as substrates in this work. Silicon is particularly interesting as a substrate for InN QD applications because of its electrical conductivity and transparency in the near-infrared. By using reflection high-energy electron diffraction (RHEED), the formation process of InN QDs can be monitored in situ. We observed the 2D-3D transition of S-K growth mode and the lattice constant varied dramatically at the 2D-3D transition point from AlN to InN lattice constant. Furthermore, from the ex situ atomic force microscopy and scanning electron microscopy measurements, we directly imaged InN QDs on the AlN surface with an average diameter of ∼ 14 nm and high areal density of ∼ 1.6 × 10¹¹ cm^{- 2}.