Formation of a two-dimensional electron gas in an inverted undoped heterostructure with a shallow channel depth

We investigated the dependence of transport characteristics of a two-dimensional electron gas (2DEG) on channel depth in an inverted undoped GaAs/AlGaAs heterostructure. We succeeded in forming a high-mobility 2DEG in a sample with 70 nm channel depth. We controlled the carrier density by varying the back-gate bias over a wide range. The highest mobility reached 2.3 × 10⁶ cm²/Vs at 3.4 × 10¹¹ cm^-2. The relation between mobility and carrier density is determined: the mobility decreases in a low-carrier-density region as the channel depth decreases. This result suggests that the scattering due to the remote surface charges plays a more significant role.