Thermodynamic Instability of InxGa1–xAs/GaAs Quantum Dots

A report describes experiments that generated evidence of thermodynamic instability of nanometer-size islands (quantum dots) in InxGa1–xAs grown on GaAs. InxGa1–xAs/GaAs specimens were grown by metal-organic chemical vapor deposition, using various partial pressures of AsH3. Examination of specimens by force microscopy, electron microscopy, and low-temperature photoluminescence spectroscopy revealed differences in island formation at different partial pressures of AsH3, including differences in (1) surface coverages of islands, (2) ratios between numbers of coherent and incoherent islands, (3) sizes and shapes of islands after annealing, and (4) thicknesses for the onset of the Stranski-Krastanow (S-K) transformation (in which quantum dots form spontaneously in a second semiconductor deposited on a lattice-mismatched first semiconductor once the second semiconductor reaches a critical thickness, which is typically a few molecular layers).