Low-temperature scanning tunneling microscopy of selfassembled inas quantum dots grown by droplet epitaxy

Using molecular beam epitaxy, we study self-assembled InAs quantum dots (QDs) grown on GaAs (001) substrates by lowtemperature scanning tunneling microscopy. We compare two different growth processes, the well-known Stranski-Krastanow mode and the more recently studied droplet epitaxy mode. We show that, for the same amount of deposited indium, the shape of the dots shows similar anisotropic tendency, but the InAs coverage dependence of the density shows that the growth mechanisms are different at the initial stage of the QD formation. By scanning tunneling spectroscopy at low temperature, we succeed in mapping the local density of states (LDOS) of a single quantum dot grown by the droplet epitaxy. Maps of LDOS are consistent with those previously reported for the Stranski–Krastanow mode; however, energy spectrum of our QDs shows different peak structures.