Impact of GaAs(100) surface preparation on EQE of AZO/Al2O3/p-GaAs photovoltaic structures.

Piotr Caban,Katarzyna Gwóźdź,Ewa Płaczek-Popko,Krzysztof Kopalko,Piotr Kuźmiuk,Jarosław Kaszewski,Rafał Pietruszka,Bartłomiej S Witkowski,Monika Ożga,Marek Godlewski,Krystyna Lawniczak-Jablonska

doi:10.3762/bjnano.12.48

Abstract

In order to effectively utilize the photovoltaic properties of gallium arsenide, its surface/interface needs to be properly prepared. In the experiments described here we examined eight different paths of GaAs surface treatment (cleaning, etching, passivation) which resulted in different external quantum efficiency (EQE) values of the tested photovoltaic (PV) cells. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) examinations were conducted to obtain structural details of the devices. X-ray photoelectron spectroscopy (XPS) with depth profiling was used to examine interface structure and changes in the elemental content and chemical bonds. The photoluminescence (PL) properties and bandgap measurements of the deposited layers were also reported. The highest EQE value was obtained for the samples initially etched with a citric acid-based etchant and, in the last preparation step, either passivated with ammonium sulfide aqueous solution or treated with ammonium hydroxide solution with no final passivation. Subsequent I–V measurements, however, confirmed that from these samples, only the sulfur-passivated ones provided the highest current density. The tested devices were fabricated by using the ALD method.

Highlights

The atomic layer deposition (ALD) method is used for silicon passivation in photovoltaics
In this work we examine the influence of the surface treatment of GaAs on the external quantum efficiency (EQE) results of the AZO/Al2O3/p-GaAs PV structures
We initially determined two paths of GaAs surface treatment that were best for a maximum EQE yield of the PV devices fabricated by ALD

Summary

Introduction

The atomic layer deposition (ALD) method is used for silicon passivation in photovoltaics. In this work we examine the influence of the surface treatment of GaAs (cleaning, etching, and passivation) on the external quantum efficiency (EQE) results of the AZO/Al2O3/p-GaAs PV structures (in which AZO stands for aluminum-doped zinc oxide). The samples prepared using the HCl solution bath (A3, B3) exhibit a predisposition to form crystallized oxide islands at the beginning of the stage of the ALD thin film covering GaAs. they show a very rugged surface of GaAs, which is seen on the SEM images of cross-sections and in the RMS values.

Results

Conclusion