Application of hydrogenation to low-temperature cleaning of the Si(001) surface in the processes of molecular-beam epitaxy: Investigation by STM, RHEED and HRTEM

TL;DR

This study investigates how hydrogenation and thermal desorption influence the structural quality of Si(001) surfaces during low-temperature cleaning in molecular-beam epitaxy, using STM, RHEED, and HRTEM techniques.

Contribution

It demonstrates that hydrogenation prior to annealing affects surface smoothness and reveals the role of temperature and chemical treatment in surface morphology control.

Findings

Smooth surfaces with wide terraces are achieved at >600°C dehydrogenation.

Clean surfaces at <600°C are rough due to dimer attachment/detachment dynamics.

Surface roughness depends on hydrogen desorption temperature and chemical pre-treatment.

Abstract

Structural properties of the clean Si(001) surface obtained as a result of low-temperature (470--650C) pre-growth annealings of silicon wafers in a molecular-beam epitaxy chamber have been investigated. To decrease the cleaning temperature, a silicon surface was hydrogenated in the process of a preliminary chemical treatment in HF and NH_4F aqueous solutions. It has been shown that smooth surfaces composed by wide terraces separated by monoatomic steps can be obtained by dehydrogenation at the temperatures > 600C, whereas clean surfaces obtained at the temperatures < 600C are rough. It has been found that there exists a dependence of structural properties of clean surfaces on the temperature of hydrogen thermal desorption and the process of the preliminary chemical treatment. The frequency of detachment/attachment of Si dimers from/to the steps and effect of the Ehrlich-Schwoebel barrier on ad-dimer migration across steps have been found to be the most probable factors determining a degree of the resultant surface roughness.