POx/Al2O3 stacks: Highly effective surface passivation of crystalline silicon with a large positive fixed charge

Abstract

Thin-film stacks of phosphorus oxide (POx) and aluminium oxide (Al2O3) are shown to provide highly effective passivation of crystalline silicon (c-Si) surfaces. Surface recombination velocities as low as 1.7 cm s−1 and saturation current densities J0s as low as 3.3 fA cm−2 are obtained on n-type (100) c-Si surfaces passivated by 6 nm/14 nm thick POx/Al2O3 stacks deposited in an atomic layer deposition system and annealed at 450 °C. This excellent passivation can be attributed in part to an unusually large positive fixed charge density of up to 4.7 × 1012 cm−2, which makes such stacks especially suitable for passivation of n-type Si surfaces.

Excellent Passivation of n‐Type Silicon Surfaces Enabled by Pulsed‐Flow Plasma‐Enhanced Chemical Vapor Deposition of Phosphorus Oxide Capped by Aluminum Oxide

“…[ 13 ] This layer stack can also provide excellent surface passivation on c‐Si, which is attributed to a low interface defect density (inferred from lifetime and high‐frequency parallel conductance data) in combination with a high positive fixed charge near the c‐Si surface. [ 14,15 ] In addition, there are also opportunities to achieve local contact formation by doping from the PO x /Al 2 O 3 layer stack. [ 16 ] The excellent surface passivation provided by PO x /Al 2 O 3 has so far been demonstrated on lightly doped planar n ‐FZ substrates, and the influence of the PO x film thickness as well as the annealing time and temperature on the passivation quality have been studied.…”

“…[ 16 ] The excellent surface passivation provided by PO x /Al 2 O 3 has so far been demonstrated on lightly doped planar n ‐FZ substrates, and the influence of the PO x film thickness as well as the annealing time and temperature on the passivation quality have been studied. [ 14,15 ] The PO x deposition has so far been achieved using a cyclical process flow typical of atomic layer deposition (ALD). As the reactions involved in this process are not strictly self‐limiting, it is labeled as an ALD‐like process in the remainder of this work, following previously used terminology.…”

“…In this contribution, we discuss a fast, pulsed‐flow plasma‐enhanced chemical vapor deposition (PECVD) process for the PO x layer, developed in the same ALD reactor used previously, [ 13–15 ] and we explore the passivation quality of the resulting PO x (5 nm)/Al 2 O 3 (10 nm) stacks deposited at a substrate temperature of 100 °C. This PECVD process is based on cycles, in analogy to the pulsed‐flow PECVD of Al 2 O 3 reported by Dingemans et al, [ 17 ] i.e., the precursor is briefly pulsed into the oxygen plasma during each cycle.…”

“…As PO x is known to be hygroscopic, it requires a capping layer to be stable in air, which in this study is a plasma ALD Al 2 O 3 layer, as also used previously. [ 13–15 ] An important advantage of the PECVD process with respect to the previously used ALD‐like process for the PO x layer is the fact that it is significantly faster, i.e., the deposition time is reduced by approximately a factor of 6. There would be opportunities to reduce the deposition time even further in a fully optimized continuous PECVD process.…”

Silicon surface passivation by transparent conductive zinc oxide

“…A highly transparent and conductive passivation layer would be ideal for the application at the front surface of solar cells, as it can, besides providing passivation, also assist in the current collection. Although in the last few years several new passivation materials have been discovered, 3 including AlN, 4 TiO x , 5 GaO x , 6 TaO x , 7 HfO x , 8 PO x , 9 NbO x , 10 and ZrO x , 11 sufficient passivation by a transparent conductive oxide (TCO) has not yet been achieved. In this work, we report on outstanding passivation of the c-Si surface by ZnO, a material that is widely used in the field of photovoltaics as TCO.…”