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N-type ohmic contacts to undoped GaAs/AlGaAs quantum wells using only front-sided processing: Application to ambipolar FETs

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Taneja, D 
Sfigakis, F 
Croxall, AF 
Gupta, KD 


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 low-temperature (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.



undoped, GaAs/AlGaAs, quantum wells, ohmic contacts, etching, etch profiles

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Semiconductor Science and Technology

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Engineering and Physical Sciences Research Council (EP/J003417/1)
Engineering and Physical Sciences Research Council (EP/K004077/1)
Engineering and Physical Sciences Research Council (EP/H017720/1)
This work was funded by the Engineering and Physical Sciences Research Council (EPSRC), UK. DT acknowledges funding from St. Catharine's College, Cambridge, AFC from Trinity College, Cambridge and IF from Toshiba Research Europe Limited.