A back-gated high electron mobility transistor utilizing a p-type doped layer A C Churchill, M P Grimshaw, D A Ritchie et al. AlGaAs/GaAs modulation-doped structures grown on a Be-ion-implanted GaAs back gate Y Hirayama and T Saku Preparation of electron waveguide devices M Knop, M Richter, R Maßmann et al. Fabrication of quantum wires in thermally etched V-grooves by molecular beam epitaxy D Scheiner, Y Hanein and M Heiblum Linear non-hysteretic gating of a very high density 2DEG in an undoped

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... metal--semiconductor--metal sandwich structure Abstract We report the development of a simple and reliable, front-sided-only fabrication technique for n-type ohmic contacts to two-dimensional electron gases (2DEGs) in undoped GaAs/AlGaAs quantum wells. We have adapted the well-established recessed ohmic contacts/insulated metal gate technique for inducing a 2DEG in an undoped triangular well to also work reliably for undoped square quantum wells. Our adaptation involves a change in the procedure for etching the ohmic contact pits to optimise the etch side-wall profile and depth. As an application of our technique, we present a front-side-gated ambipolar field effect transistor (FET), where both 2D electron and hole gases can be induced in the same quantum well. We present results of lowtemperature (0.3 K -4 K) transport measurements of this device, including assessment of the n-type ohmic contact quality. On the basis of our findings, we discuss why the fabrication of these contacts is difficult and how our technique circumvents the challenges.