As a result of a relatively low E f s ( InAs ), applying a negative bias gate potential will create a conducting hole channel in GaSb and, hence, a separate Ohmic contact to the lower quantum well.
For the latter, the upper InAs quantum well is locally pinched off by top etched trenches capped with a remaining 2–3 nm InAs layer. In particular, separate Ohmic contacts to the upper InAs quantum well are achieved by selectively etching down to the InAs, while contacts to the lower GaSb quantum well are obtained by the depletion method. We report a nanofabrication technique that utilizes the surface Fermi level pinning position in InAs for realizing independent electric contacts to each well. InAs/GaSb double quantum wells separated by a 100 Å AlSb middle barrier are grown by molecular beam epitaxy.
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