Top gates for InAs/InAlGaAs heterostructures

The intrinsic spin-Hall effect allows filtering of the electron spins in quasi one-dimensional electron systems. However the spin-Hall effect is only effective when the occupation of the transport modes is restricted to a small number. Hence control of the electron density is decisive. At the same time it is mandatory to keep the electron mobility high and to leave the spin-orbit coupling constant or to tune it in a precise and reproducible way. At liquid helium temperatures we determine from the Shubnikov-de Haas effect and the Hall effect the densities, the mobilities and the Rashba spin-orbit parameters of electrons in InAs/InAlGaAs heterostructures with metallic top gates. The top gates are evaporated on insulating hydrogen silsesquioxane layers spun before onto the semiconductors. Our investigation includes InAs/InAlGaAs heterostructures with different innate electron densities and mobilities. The thickness of the InAlAs capping layer above the conducting InAs channel and the thickness of the insulating layer are also varied.