Mesoscopic Elastic Distortions in GaAs Quantum Dot Heterostructures

Abstract

Quantum devices formed in high-electron-mobility semiconductor heterostructures provide a route through which quantum mechanical effects can be exploited on length scales accessible to lithography and integrated electronics. The electrostatic definition of quantum dots in semiconductor heterostructure devices intrinsically involves the lithographic fabrication of intricate patterns of metallic electrodes. The formation of metal/semiconductor interfaces, growth processes associated with polycrystalline metallic layers, and differential thermal expansion produce elastic distortion in the active areas of quantum devices. Understanding and controlling these distortions present a significant challenge in quantum device development. We report synchrotron X-ray nanodiffraction measurements combined with dynamical X-ray diffraction modeling that reveal lattice tilts with a depth-averaged value up to 0.04° and strain on the order of 10 in the two-dimensional electron gas (2DEG) in a GaAs/AlGaAs heterostructure. Elastic distortions in GaAs/AlGaAs heterostructures modify the potential energy landscape in the 2DEG due to the generation of a deformation potential and an electric field through the piezoelectric effect. The stress induced by metal electrodes directly impacts the ability to control the positions of the potential minima where quantum dots form and the coupling between neighboring quantum dots.

Electrode-induced lattice distortions in GaAs multi-quantum-dot arrays

“…One particular issue arises from the mechanical stress imposed on devices The magnitude of the residual stress in the metallic gates, the gate-induced lattice distortions, and their impact to the electronic properties of double-dot quantum devices have been measured and modeled quantitatively in both Si-based and GaAs-based heterostructures. 12,13 Here we show that there is an additional series of structural issues that arises in devices incorporating many quantum dots because these multi-dot devices occupy large, micron-scale areas and thus pose significant is formed, is shown in Fig. 1(a…”

“…3(c) has been previously observed and can be attributed to the strain gradient within the volume underneath the electrodes that change the effective angle of incidence of the x-ray nanobeam with respect to the lattice planes. 13 The magnitude of the vertical tilts varies along the length of the linear electrodes. The variation of the tilt is apparent in effect is apparent as differences in the vertical tilt at different positions along the horizontal direction of the tilt image in Fig.…”

“…In the case of Au and GaAs, the difference of the thermal expansion coefficients acts to reduce the magnitude of the stress between low temperature and room temperature. 13 A quantitative estimate for a single metal electrode indicates that the strain at low temperature is reduced by approximately a factor of two. 13 Previous work in Si devices showed that when cooling to cryogenic temperatures the strain in the semiconducting layers is compressive.…”

Heterointerface‐Driven Band Alignment Engineering and its Impact on Macro‐Performance in Semiconductor Multilayer Nanostructures

“…Among all factors, with its inherent determination on actual band alignment, heterointerface is at the heart. It could be effectively regulated by strain, charge, distortion, and defect, which alter macro‐performance and even induce an emergent phenomenon . For instance, in AlGaAs/GaAs heterostructures, nearly impurity‐free interfaces could be formed with a concerted growth sequence, achieving electron mobility as unprecedentedly high as >35 million cm 2 V −1 s −1 .…”

Combining Laue diffraction with Bragg coherent diffraction imaging at 34-ID-C

“…The reconstructed slices show in general the presence of small strain fields inside the crystal on the order of 10 À4 , except in the case of the " yy component, for which the bottom part of the Au particle reaches values up to 8 Â 10 À4 . This is likely due to stress transmitting through the interface of the Au particle with the silicon substrate (Pfeifer et al, 2006;Pateras et al, 2018). In comparison with other optical methods for measuring fullfield displacements and strains, such as digital image correlation, BCDI provides strain information in 3D allowing the investigation of defects or other nanoscale phenomena inside a single grain (Miao et al, 2015;Hung Lo et al, 2018).…”