Surface Morphology and Mobility Anisotropy in GaAs(001): Linking Molecular Beam Epitaxy Interface Structures to Electrical Transport

Abstract

The performance of GaAs-based electronic and optoelectronic devices is critically shaped by surface morphology and interface roughness—both of which are strongly influenced by Molecular Beam Epitaxy (MBE) growth conditions. This project investigates two key questions: (1) how specific MBE parameters—including step-flow growth and native oxide desorption— influence surface features; and (2) how these features impact directional electrical transport, particularly mobility anisotropy. Atomic Force Microscopy (AFM) was used to characterize roughness, step orientation, mounding behavior, and pit formation on GaAs(001) surfaces. We find that well-controlled vicinal growth produces uniform step-flow terraces when angled toward (111)A, with more ragged steps when angled toward (111)B. We demonstrate that poor oxide desorption, arsenic deficiencies, or excess gallium leads to substantially rougher surfaces. A ramped preheat protocol was developed to balance oxide removal with minimal surface damage. We correlated AFM surface metrics with transport properties in quantum well heterostructures, demonstrating the influence of interface roughness on mobility anisotropy. Additionally, spatial frequency anisotropy in AFM scans correlated with directionally dependent carrier mobility. Together, these results clarify how surface features arise from MBE conditions and directly impact transport behavior, offering a pathway toward more precise engineering of GaAs.