On the Control of the Fixed Charge Densities in Al₂O₃-Based Silicon Surface Passivation Schemes

Abstract

A controlled field-effect passivation by a well-defined density of fixed charges is crucial for modern solar cell surface passivation schemes. Al2O3 nanolayers grown by atomic layer deposition contain negative fixed charges. Electrical measurements on slant-etched layers reveal that these charges are located within a 1 nm distance to the interface with the Si substrate. When inserting additional interface layers, the fixed charge density can be continuously adjusted from 3.5 × 10(12) cm(-2) (negative polarity) to 0.0 and up to 4.0 × 10(12) cm(-2) (positive polarity). A HfO2 interface layer of one or more monolayers reduces the negative fixed charges in Al2O3 to zero. The role of HfO2 is described as an inert spacer controlling the distance between Al2O3 and the Si substrate. It is suggested that this spacer alters the nonstoichiometric initial Al2O3 growth regime, which is responsible for the charge formation. On the basis of this charge-free HfO2/Al2O3 stack, negative or positive fixed charges can be formed by introducing additional thin Al2O3 or SiO2 layers between the Si substrate and this HfO2/Al2O3 capping layer. All stacks provide very good passivation of the silicon surface. The measured effective carrier lifetimes are between 1 and 30 ms. This charge control in Al2O3 nanolayers allows the construction of zero-fixed-charge passivation layers as well as layers with tailored fixed charge densities for future solar cell concepts and other field-effect based devices.

Plasma nitridation of atomic layer deposition (ALD) Al2O3 by NH3 in plasma-enhanced chemical vapor deposition (PECVD) for silicon solar cell

“…It was noted that in the Al 2 O 3 sample, the D it had decreased from 1.0 × 10 12 cm −2 eV −1 to 5.5 × 10 10 cm −2 eV −1 and Q f had increased from −3.5 × 10 12 cm −2 to 1.4 × 10 13 cm −2 after 400 W plasma nitridation. This clearly corroborates the formation of decreased interface defects and negative fixed charges [16,17].…”

Al2O3/HfO2 Multilayer High‐k Dielectric Stacks for Charge Trapping Flash Memories

“…It might be due to nonstoichiometric initial growth (increased O/Al ratio has been found within the first several Al 2 O 3 monolayers on Si) leading to formation of negatively charged defects (interstitial oxygen and Al vacancies). Simon, et al have suggested that the negative charge results from the tetrahedrally coordinated Al which is dominant at the interface. The present investigation reveals that negative charge is observed after high temperature treatment which implies that they are formed as a result of some intermixing at HfO 2 /Al 2 O 3 interface and breaking of bonds.…”

Absence of Evidence for Fixed Charge in Metal–Aluminum Oxide–Silicon Tunnel Diodes

“…The N F was quantified experimentally in MOSCAP structures by measuring the capacitance‐voltage ( C–V ) characteristics and relating V fb to fixed charge according to Equations and …”