About nature of the effective surface charge on InAs crystals transformation during anode oxide layer growing

Abstract

Dynamics of changes in fluorine atoms distribution through grown anodic oxide layer thickness and the effective surface charge on InAs crystals under such layers has been studied. Anodic oxidation was performed in alkaline electrolyte with fluorochemical additive component in galvanostatic mode at anode current densities 0.05 or 0.5 mA·cm⁻². The layers thickness in boundes 32—51 nm varied by electrodes final voltage setting in range 15—25 V. The layer thickness and refractive index was measured by ellipsometric method, and distribution of fluorine atoms through thickness — by photoelectron−spectroscopy method, combined with ion etching. At the same time, based on grown layers there were produced MIS structures, and from calculation of theirs capacitance−voltage characteristics are determined effective surface charge and surface states density, corresponding to different layer thicknesses.Main results are reduced to the facts during layers growing despite of anodizing current density comes their sealing, the profile of fluorine atoms distribution shifts towards InAs, positive effective surface charge gradually decreases from 3.6 · 10¹¹ to 2.0 · 10¹¹ cm⁻² at surface states density in (6—7) · 1011 eV·cm⁻² range for all cases. Based on comparison of these data and theoretical concepts of MIS structure charge construction, there was made a conclusion about gradual built−in charge distancing from the border with InAs in the process of growing anodic oxide layer, which explains observed effective surface charge decrease during layer thickness increasing. This results indicates that the layer growth rate exceeds the built−in charge displacement rate towards InAs.