Improving size distribution of InAs quantum dots for intersubband devices

We present the growth and characterization of InAs quantum dots on AlxGa1−xAs surfaces for intersubband devices. This requires the quantum dot energy levels in the AlxGa1−xAs matrix to be above the GaAs bandedge. Using standard As4 fluxes (beam equivalent pressure 8e−6 Torr), inhomogeneous broadening of the quantum dot size distribution increases with increasing Al content in the AlxGa1−xAs matrix. Reducing the As4 overpressure during In deposition is found to greatly improve the size distribution of the quantum dots, while producing slightly larger dots and a reduction in the density of small dots (h<1.3 nm). Annealing at the higher standard As4 flux for 30 s, after the reduced As4 In deposition, produced a negligible change in the quantum dot size distribution. Utilizing surface dots on top of 30 layers of self-assembled quantum dots, the maximum quantum dot height for ground state energies above the GaAs bandedge is determined to be 2 nm for Al0.30Ga0.7As and 3 nm for Al0.45Ga0.55As.