Critical thickness of β-InN/GaN/MgO structures

Abstract

InN films were grown on MgO substrates with a β-GaN buffer layer using the gas source molecular beam epitaxy technique. Initially, at typical growth rates from 0.09 to 0.28 ML/sec and at 500 °C substrate temperature, the growth was performed in a layer by layer way as revealed by in situ reflection high-energy electron diffraction (RHEED). In all samples studied, a critical thickness of ∼5 ML in InN pseudomorphic layer was measured with a frame by frame analysis of RHEED patterns recorded on video. After reaching critical thickness, the InN films undergo a relaxation process, going from two-dimensional growth to three-dimensional, as evidenced by the transformation of the RHEED patterns that change from streaky to spotty. Depending on the In cell temperature, either nanocolumnar InN or flat cubic final films are grown, as can be corroborated by scanning electron microscopy. The experimental critical thickness (hc) value of 5 ML is compared to values calculated from different critical thickness models.

Self‐organized growth of cubic InN dot arrays on cubic GaN using MgO (001) vicinal substrates

“…Similar structures are also observed for c‐GaN grown using Si (001) substrates . This is due to the existence of two orthogonal domains of c‐GaN: one domain is c‐GaN (001) of which the [110] direction is parallel to [110] of a substrate, while it is parallel to of the substrate in the other domain. The typical scale of the domain size is 300–500 nm, as shown in the image of a c‐GaN surface grown on a MgO (001) substrate taken by atomic force microscopy (AFM) in Fig.…”

“…MgO (001) substrates enable us to grow c‐GaN and c‐InN with very high phase purity . However, mosaic structures consisting of many grains are often observed on the surface of c‐GaN grown on MgO (001) substrates . Similar structures are also observed for c‐GaN grown using Si (001) substrates .…”