Probing the 2D to 3D growth transition dynamics in InAs/GaAs stacked submonolayer (SML) deposition by photoluminescence

The assembly of InAs/GaAs nanostructures using stacked submonolayer (SML) deposition by molecular beam epitaxy has been gaining interest. Compared to more conventional methods of nanostructure assembly, such as Stranski-Krastanov and droplet epitaxy, SML deposition provides higher controllability with the various growth parameters that can be independently tuned. It has been recently clarified that a transition in growth mode from 2D to 3D occurs during SML deposition, that leads to two distinct types of SML nanostructures: 2D islands and 3D structures. However, the detailed dynamics of the SML growth transition is yet to be understood. In the present work, photoluminescence (PL) spectroscopy is used to probe the detailed dynamics of the SML growth transition. Using SML samples with gradually varying In composition, the transition in the growth mode is observed by the PL spectra. Furthermore, the sequential phases of the growth transition are revealed. The stacked SML growth starts with predominantly 2D growth mode, as indicated by a single sharp PL peak. This is followed by a coexistence of 2D and 3D SML nanostructures, as evidenced by the emergence of a second, broader peak in the spectrum. Finally, the transition is concluded by a full conversion to 3D growth, as suggested by the quenching of the sharp 2D PL peak, and the enhancement and redshift of the broad 3D peak. The results elucidate the dynamics of 2D to 3D growth transition during stacked SML deposition, and provide essential understanding for future applications.