Real-time observation of self-interstitial reactions on an atomically smooth silicon surface

Abstract

Self-diffusion and impurity diffusion both play crucial roles in the fabrication of semiconductor nanostructures with high surface-to-volume ratios. However, experimental studies of bulk-surface reactions of point defects in semiconductors are strongly hampered by extremely low concentrations and difficulties in the visualization of single point defects in the crystal lattice.Herein we report the first real-time experimental observation of the self-interstitial reactions on a large atomically smooth silicon surface. We show that non-equilibrium self-interstitials generated in silicon bulk during gold diffusion in the temperature range 860-1000 o C are annihilated at the (111) surface, producing the net mass flux of silicon from the bulk to the surface. The kinetics of the two-dimensional islands formed by self-interstitials are dominated by the reactions at the atomic step edges. The activation energy for the interaction of self-interstitials with the surface and energy barrier for gold penetration into the silicon bulk through the surface are estimated.These results demonstrating that surface morphology can be profoundly affected by surface-bulk reactions should have important implications for the development of nanoscale fabrication techniques. 2 reactions of point defects at the surfaces and interfaces become predominant and may significantly modify the properties of fabricated nanostructures [8-11]. While the properties of point defects in bulk semiconductors have been extensively studied and are well understood, little is actually known about the point defect formation, reactions, and basic mechanisms of the diffusion in the vicinity of free surfaces. At the heart of the problem lies the need for direct visualization of the single point defect diffusion in crystal bulk, which is still lacking, especially at high temperatures, where diffusion is fast compared to the imaging rate of modern atomic-scale characterization techniques such as aberration-corrected high-resolution transmission electron microscopy (HRTEM). In addition, the extremely low concentrations of point defects in silicon make their observation quite difficult. On the other hand, the direct visualization of single atoms, vacancies, and their clusters on crystal surfaces has become routine with the development of surface-sensitive techniques such as scanning tunneling (STM), atomic force (AFM), low-energy (LEEM), and reflection electron microscopy (REM). However, atomic steps that are an inherent part of all crystalline surfaces, acting as sinks for adsorbed atoms and vacancies, hamper direct experimental studies of point defect properties.This study used high-temperature (860-1000 o C) submonolayer gold deposition onto an atomically smooth large size (up to 100 μm in diameter) step-free Si(111) surface to study the interaction of the native point defects (self-interstitials and vacancies) with the surface boundary, considering the finite efficiency for the penetration, annihilation, and creation of point defects at the surface.Since it is well ...

Subsurface diffusion in crystals and effect of surface permeability on the atomic step motion

“…Diffusion of the adsorbed interstitials and vacancies is described by corresponding subsurface diffusion coefficients which can differ from surface and bulk D i , v diffusion coefficients. Earlier it had been shown that an increase in the concentration of the self-interstitials in silicon during high-temperature submonolayer gold deposition results in the changing the kinetics of the atomic steps 22,23 . The later can be attributed to the change in the atomic step rate of advance as described by Eqs (3a) and (3b).…”