Accumulation mode GaAs/AlGaAs 2D electron system with independent control of the channel and contact resistance

Semiconductor-insulator-semiconductor FETs (SISFETs) are an attractive alternative to modulation doped (MD) GaAs/AlGaAs systems. GaAs SISFETs consist of epitaxially grown layers of GaAs then AlGaAs capped with a degenerately doped GaAs layer. The cap acts as an in situ, over-all top-gate which attracts carriers to the GaAs/AlGaAs interface. The MBE grown top-gate eliminates scattering and charge-noise from surface states and unlike Schottky gates, there is no strain between the gate and insulating AlGaAs layer due to similar thermal expansion rates. The absence of a doping layer improves carrier mobility ($\mu$) at low densities ($n_s$) since in shallow MD devices the doping layer creates an additional long-range random impurity potential. For this reason SISFET devices improve $\mu$ at low $n_s$. However in the low $n_s$ regime the high contact resistance dominates the device resistance, which can limit electrical transport measurements. We fabricate a GaAs 2D electron SISFET with dual-gate architecture to independently control the contact and channel resistance. We characterize our device using standard low-temperature electrical transport measurements. The 2D $n_s$ could be varied from $0.1-3\times 10^{11}\,cm^{-2}$ with a $\mu$ of up to $9\times 10^{6}\,cm^{2}V^{-1}s^{-1}$.