Two-dimensional electron gas structures with mobilities in excess of 3×106 cm2 V−1 s−1

Abstract

We have demonstrated that the mobility of two‐dimensional electron gas (2DEG) structures shows a gradual improvement with the number of uninterrupted growth runs in the molecular‐beam‐epitaxy system. Some, but not all, of this improvement can be attributed to the cleanup of the GaAs layers in the structure, and we suggest that there is a corresponding cleanup of the (Al,Ga)As which is also influencing the mobility. Once the system has passed the cleanup phase, a systematic trend of carrier density and mobility with undoped spacer thickness was observed, with a peak mobility at 4 K of 2.12×10⁶ cm² V⁻¹ s⁻¹ for a sheet carrier density of 2×10⁻¹¹ cm⁻² occurring at a spacer thickness of 800 Å. A further increase in mobility was achieved by using a thicker region of doped (Al,Ga)As, thereby moving the ionized centers in the surface depletion layer further away from the 2DEG. This has enabled us to produce a sample with mobility at 4 K of 3.1×10⁶ cm² V⁻¹ s⁻¹ (at a sheet charge of 3.1×10¹¹ cm⁻²)—the first time such a value, to our knowledge, has been reported.