Passivation effects of atomic-layer-deposited aluminum oxide

Abstract

Atomic-layer-deposited (ALD) aluminum oxide (Al2O3) has recently demonstrated an excellent surface passivation for both n-and p-type c-Si solar cells thanks to the presence of high negative fixed charges (Q f ∼ 10 12 −10 13 cm −2 ) in combination with a low density of interface states (Dit). This paper investigates the passivation quality of thin (15 nm) Al2O3 films deposited by two different techniques: plasmaenhanced atomic layer deposition (PE-ALD) and Thermal atomic layer deposition (T -ALD). Other dielectric materials taken into account for comparison include: thermally-grown silicon dioxide (SiO2) (20 nm), SiO2 (20 nm) deposited by plasma-enhanced chemical vapour deposition (PECVD) and hydrogenated amorphous silicon nitride (a-SiNx:H) (20 nm) also deposited by PECVD. With the above-mentioned dielectric layers, Metal Insulator Semiconductor (MIS) capacitors were fabricated for Q f and Dit extraction through Capacitance-Voltage-Conductance (C-V -G) measurements. In addition, lifetime measurements were carried out to evaluate the effective surface recombination velocity (SRV). The influence of extracted C-V -G parameters (Q f ,Dit) on the injection dependent lifetime measurements τ (Δn), and the dominant passivation mechanism involved have been discussed. Furthermore we have also studied the influence of the SiO2 interfacial layer thickness between the Al2O3 and silicon surface on the field-effect passivation mechanism. It is shown that the field effect passivation in accumulation mode is more predominant when compared to surface defect passivation.

Investigating the electronic properties of Al2O3/Cu(In,Ga)Se2 interface

“…These results reveal that the field-effect passivation due to negative fixed charges is activated only for post-deposition annealed Al 2 O 3 films, and that the extracted negative fixed charge density Q f is within a range similar to that observed on silicon surfaces. [9][10][11][12] This indicates that the field-effect passivation quality achieved by the PDA films on CIGS surfaces is comparable to that achieved by ALD Al 2 O 3 films on silicon surfaces. [9][10][11] Furthermore, due to the presence of highly negative Q f values in the PDA films, the net concentration of minority carriers (n s ) at the CIGS surface will be reduced, thereby satisfying one of the requirements to reduce the surface recombination rate (U s ) according to the Shockley-Read-Hall formalism.…”

“…The concept of passivating CIGS surfaces using ALD Al 2 O 3 films is based on previous experience gained from silicon solar cell technologies. [9][10][11][12] The surface passivation of silicon substrates using ALD Al 2 O 3 films has drawn intense attention from the silicon photovoltaic community because of these films' ability to passivate p-and n-type as well as highly doped p + silicon surfaces effectively. 9,10 This passivation ability is attributed to a high density of negative Q f (10 12 -10 13 cm −2 ) in the Al 2 O 3 bulk (field-effect passivation) in combination with a low interface-trap charge density D it (10 10 -10 12 eV −1 cm −2 ) at the Al 2 O 3 /Silicon interface (chemical passivation).…”

“…9,10 This passivation ability is attributed to a high density of negative Q f (10 12 -10 13 cm −2 ) in the Al 2 O 3 bulk (field-effect passivation) in combination with a low interface-trap charge density D it (10 10 -10 12 eV −1 cm −2 ) at the Al 2 O 3 /Silicon interface (chemical passivation). [9][10][11][12] Therefore, in the case of CIGS surface passivation by ALD Al 2 O 3 , experimentally extracting these electronic properties is important (i) to evaluate the passivation quality, and (ii) to understand the dominant passivation mechanism involved.…”

Interface-Dependent Effective Mobility in Graphene Field-Effect Transistors

“…It has been shown in several publications that ALD of Al 2 O 3 , when not deposited correctly, can result in a significant amount of trapped negative charge, resulting in a p-doping effect on the affected transistor. 13,14 When the top-gate metal was added, it balanced the intrinsic charge in the Al 2 O 3 and allowed the G-FET to act as if the charge had been removed.…”

Efficiency Enhancement of Multicrystalline Silicon Solar Cells by Inserting Two-Step Growth Thermal Oxide to the Surface Passivation Layer

“…Kotipallia et al [12] showed the D it reduction at the silicon/dielectric interface by using hydrogen gas annealing to reduce the dangling bonds. Schultz et al [13] showed the influence of thermal oxidation temperature on the D it of the interface.…”