  We investigate background charge fluctuation in a GaAs quantum dot device by
measuring 1/f noise in the single-electron tunneling current through the dot.
The current noise is understood as fluctuations of the confinement potential
and tunneling barriers. The estimated potential fluctuation increases almost
linearly with temperature, which is consistent with a simple model of the 1/f
noise. We find that the fluctuation increases very slightly when electrons are
injected into excited states of the quantum dot.
