Investigation of lateral gated quantum devices in Si/SiGe heterostructures

Abstract

Quantum dots in Si/SiGe have long spin decoherence times, due to the low density of nuclear spins and weak coupling between nuclear and electronic spins. Because of this, they are excellent candidates for use as solid state qubits. The initial approach towards creating controllable Si/SiGe quantum dots was to fabricate them in delta doped heterostructures. We provide evidence that the delta doping layer in these heterostructures provides a parallel conduction path, which prevents one from creating controllable quantum dots. Instead, it may be more favorable to supply electrons in the 2DEG through capactive gating, instead of a delta doping layer. We therefore discuss efforts to fabricate Si/SiGe quantum dots from undoped heterostructures and the difficulties encountered. A new method for fabricating ohmics in undoped heterostructures is discussed. We also discuss parallel conduction which occurs in the Si cap layer of these undoped heterostructures, which appears to be a major obstacle towards achieving workable devices in undoped Si/SiGe heterostructures.