Optimization of metal-insulated-semiconductor field-effect-transistor for the formation of two-dimensional electron gas in dopant-free systems

We developed a geometry of metal-insulated-semiconductor field-effect-transistor for the formation of two-dimensional electron gas (2DEG) in dopant-free GaAs/AlGaAs heterostructures in which the conduction band can be modulated by external electric field. We showed two different kinds of device processes: for simple device fabrication and for the uniform 2DEG. We optimized the process of ohmic contacts and the gate geometry for the high quality 2DEG in a triangular quantum well formed at the GaAs/AlGaAs heterointerface. We use these two types of devices to perform a direct comparison of the magneto-transport properties at a low temperature (1.2 K) to get a relationship between the induced carrier density and external electric field. By using our developed fabrication process, the tunability of a high-quality 2DEG was obtained with a carrier density ranging from 0.8 to 2.3 × 10¹¹ cm⁻², for which the corresponding mobility ranged 1.5 to 3.3 × 10⁶ cm² V⁻¹ s⁻¹. Also, we demonstrated that the 2DEG is well established with a suitable depth, 120 nm below the surface (near the GaAs/AlGaAs heterointerface) which is calculated by the capacitance model.