Harmonic Content of Strain-induced Potential Modulation in Unidirectional Lateral Superlattices

TL;DR

This study analyzes the harmonic content of strain-induced potential modulation in unidirectional lateral superlattices, revealing significant higher harmonics that originate from subsurface strain effects and can be used to engineer small-scale modulations.

Contribution

It provides detailed Fourier analysis of potential modulation harmonics in superlattices, highlighting their origin and potential for nanoscale control in high-mobility 2DEGs.

Findings

Higher harmonics up to 30% of fundamental amplitude detected

Harmonics originate from subsurface strain effects

Potential modulation can be engineered for nanoscale applications

Abstract

Detailed analysis of the commensurability oscillation (CO) has been performed on unidirectional lateral superlattices with periods ranging from a=92 to 184 nm. Fourier analysis reveals the second (and the third) harmonics along with the fundamental oscillation for a>=138 nm (184 nm) at low-enough temperature, evincing the presence of corresponding harmonics in the profile of the potential modulation. The harmonics manifest themselves in CO with demagnified amplitude due to the low-pass filtering action of the thermal damping factor; with a suitable consideration of the damping effect, the harmonics of the modulation potential are found to have the amplitudes V_2 and V_3 up to roughly 30% of that of the fundamental component V_1, despite the small ratio of the period a to the depth d = 99 nm of the two-dimensional electron gas (2DEG) from the surface. The dependence of V_n on a indicates that the fundamental component originates at the surface, while the higher harmonics arise from the effect of the strain that penetrates down into subsurface. The manipulation of high harmonics thus provides a useful technique to introduce small length-scale modulation into high-mobility 2DEGs located deep inside the wafer.