Gate-controlled subband structure and dimensionality of the electron system in a wide parabolic quantum well

Remotely doped parabolic quantum wells have been used to produce thick (>2000 Å) layers of high-mobility electron systems. Using a front gate electrode we are able to simultaneously deplete the well and change the actual thickness of this quasi-three-dimensional system. Thus, we can successively depopulate the elecrical subbands in the well, leading to step-like changes in the gate to channel capacitance. This yields direct insight into the subband structure of the electron system and allows its spectroscopy without the need of a magnetic field. The experimental results are compared with those of a self-consistent subband calculation and we obtain a qualitative agreement.