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5Duality of Au-dopant forms in laser hyperdoping of Si surface
V. Pryakhina1*, S. Kudryashov12, I. Gordeev3, M. Kovalev12, S. Starikov4, A. Akhmatkhanov1
1- Ural Federal University, Ekaterinburg, Russia 2- Lebedev Physical Institute, Moscow, Russia 3- Joint Institute for High Temperatures of RAS, Moscow, Russia 4- Interdisciplinary Centre for Advanced Materials Simulation, Ruhr-University, Germany
The hyperdoping technology, material saturation with dopants at the concentration higher than the equilibrium solubility level, extends the spectral response of silicon to near- and mid-infrared range and increase impurity absorption [1]. Laser hyperdoping can be naturally combined with laser annealing which restores doped layer crystallinity, while preserving the non-equilibrium dopant state. Chemically-inert gold is a promising doping candidate for Si-based near-infrared photo-detectors, exhibiting both donor and acceptor states, high trapping efficiency with low carrier lifetime and poor transport characteristics. Tuning laser processing parameters could facilitate obtaining dopant concentrations, doped layer thicknesses and doping/annealing conditions for specific applications.
In this work, Au-dopant distribution and chemical state in the Si surface layer, hyperdoped from the pre-deposited Au film and annealed by non-ablative nanosecond laser treatment, were studied by cross-sectional X-ray photoelectron spectroscopy and scanning electron microscopy imaging.
Au-coated initially undoped Si(100) wafers had been irradiated in the ambient atmosphere by 100-ns laser pulses at 1064-nm wavelength using a MiniMarker-2 M20 marking system (LTC, Russia) equipped with Yb fiber laser (IPG Photonics, IRE-Polus, Russia). The used fluence of 8 J/cm2 was lower, than the ablation threshold of gold, but close to the one of silicon.
Partial ablation of the gold film on the wafer surface, gold nanocrystallites precipitated on the Si nanograins inside the recrystallized layer and small gold clusters sedimented in the hyperdoped layer Si over the gold diffusion length (~ 1 ^m) were observed. The hyperdoping process crystallization characteristics studied at the atomic level by the molecular dynamics simulation were in good agreement with those experimental results. The laser-hyperdoped Si samples with removed residual gold have shown lower transmittance in the intra-gap spectral range (> 1.1 ^m) comparing to the highly transmissive Si wafer which implies the impurity absorption.
These findings shed the light on ambiguity of previously reported electrical characteristics of gold-hyperdoped Si and pave the way toward controllable fabrication of Au-Si based optoelectronic devices.
The research funding from the Ministry of Science and Higher Education of the Russian Federation (Ural Federal University Program of Development within the Priority-2030 Program) is gratefully acknowledged.
[1] M. Kovalev, et al, Au-hyperdoped Si nanolayer: laser processing techniques and corresponding material properties, Materials, vol. 16,
pp. 4439, (2023).
