Direct observation of single InAs/GaAs quantum dot spectrum without mesa or mask

Photoluminescence spectra of single InAs/GaAs quantum dot are obtained on the crude surface of several low-dot-density samples, using a pinhole placed in the beam path. Considering the light diffraction, an optimal spectrum which corresponds to the least excited quantum dots can be detected as the pinhole size decreases. Cryostat temperature also influences quality of these spectra via shifting carrier diffusion length in wetting layer to change the number of quantum dots excited. With this method, intrinsic properties of individual quantum dot can be clearly studied because of the undamaged surface in contrast to the mesa or mask approach.