Structural Sources of Electronic Disorder in GaAs Quantum Devices

The fabrication of quantum dots in GaAs/AlGaAs heterostructures involves the formation of metallic gate electrodes lithographically patterned on their surfaces. The gates are used for the definition and tuning of the electrostatic potential of the dot via applied voltages. We show using synchrotron x-ray nanobeam diffraction that the gates generate significant stresses that influence the operation of quantum devices. The stress is transferred through the metal/semiconductor interface to the depth where a two-dimensional electron gas (2DEG) forms, inducing unintentional lattice distortions to the active region of the device. The x-ray diffraction studies reveal lattice tilts on the order of 0.04° in the quantum dot region and strain up to 4×10^-5 at the depth of the 2DEG. The piezoelectric effect in zinc-blende structures is the main source of electronic disorder with respect to the deformation potential which is an order of magnitude smaller. We estimate the piezoelectric potential induced by the lattice distortions to be approximately 10 mV. The strain leads to an energy shift of the minimum of the conduction band near the Γ point of GaAs due to the deformation potential by only 0.4 meV. The results indicate that such effects should be considered in the design of quantum devices.