Independent control of InAs quantum dot density and size on Al_xGa_(1-x)As surfaces

摘要

Decoupling of InAs quantum dot (QD) size and density on Al_xGa_(1-x)As surfaces (x = 0, 0.15, 0.30, and 0.45) is achieved by using a low growth rate and careful control of the temperature. The deposition rate of 0.01 μm/ h, instead of 0.05 μm/h, allows the QDs to ripen with additional InAs deposition while the substrate temperature (490-520 ℃) determines the QD density. On the GaAs surface, an increase of 10 ℃ results in an order of magnitude lower QD density. The increase of Al in the Al_xGa_(1-x)As surfaces results in a higher dot density, lower dot size, and an increased size distribution. All surfaces show reduced QD density with increasing temperature and an identical zero dot density temperature at 523 ℃. The GaAs surface shows increasing QD height with temperature while the Al_xGa_(1-x)As surfaces show the opposite trend, but the InAs volume fraction in QDs for all surfaces decreases with increasing temperature, implying a more stable wetting layer. Increasing Al content also increases the InAs volume fraction in QDs, implying the wetting layer for all but the 520 ℃ samples is less than one monolayer. Photolumi-nescence samples demonstrate ground state QD energies above the GaAs bandedge.