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0The influence of hyperdoping gold film thickness on the photoresponse of laser hyperdoped silicon
A. Akhmatkhanov1*, R. Saifetdinov1, V. Pryakhina1, A. Sherstobitov1, M. Kovalev1,2, S. Kudryashov1,2
1- Ural Federal University, Ekaterinburg, Russia 2- Lebedev Physical Institute, Moscow, Russia
* andrey.akhmatkhanov@urfu.ru
The working range of conventional Si-based photodetectors is limited by 1.1 ^m bandgap-related value thus excluding most of the telecommunication bands in the near-infrared region (NIR). This spectral range can be covered by alternative technologies, including InGaAs, HgCdTe and Ge-based detectors, however their integration with existing Si platform for efficient signal processing can be complicated and expensive. Alternative approach to this problem is related to the developing of hyperdoped Si NIR detectors, which implies doping of deep level impurities (such as gold) at concentrations above the equilibrium solubility level. An intermediate impurity band formed in this case enables efficient sub-bandgap light adsorption. Nanosecond laser hyperdoping through laser melting and dopant diffusion is one of the most widely used technique within this approach.
In this work we study the influence of hyperdoping gold film thickness on the photoresponse of Au-hyperdoped Si detectors.
Commercial 200-^m-thick nominally pure Si (100) wafers (resistivity > 1000 Ohm cm) were used. The 3x10 mm2 Si samples were covered by Au films with thickness from 20 to 100 nm by magnetron sputtering. The sample surface was single-pass scanned in the ambient atmosphere by 100-ns laser pulses at 1064-nm wavelength (repetition rate 80 kHz, scan speed 80 mm/s, filling 100 lines/mm, fluence 8 J/cm2, laser beam diameter 5 0 ^m) using a MiniMarker-2 M20 marking system (LTC, Russia). Residual metal film was removed after laser hyperdoping by chemical etching in HNO3 :HCl 1:3 mixture and HF aqueous solution. Ohmic indium contacts were soldered on obtained samples for further two-and four-probe resistivity and photoresponse measurements.
We have measured the change of sample's resistivity as a result of laser light irradiation at 1550 nm wavelength. The experimental setup was based on the continuous ELM-1550-5-LP fiber laser (IPG Photonics, IRE-Polus, Russia) and microscope stage THMS600 (Linkam Scientific Instruments, UK) with temperature control. Sample resistivity was measured using Keithley 6430 sub-femtoamp Remote SourceMeter (Keithley, USA). The measurements were carried out in the temperature range from -175°C to room temperature. Additional precautions were made to take into account the influence of sample heating during laser light irradiation on resistivity change. Preliminary measurements of temperature dependence of samples resistivity have revealed the appearance of dopant levels with depth about 0.15-0.2 eV.
We have revealed that laser light irradiation leads to up to 17% decrease of sample resistivity at room temperature. It should be noted that the highest resistivity change was observed for the samples hyperdoped using 20-nm-thick Au films. The decrease of sample temperature leads to strong increase of the photoresponse resulting in 20-fold decrease of sample resistivity for temperature -175°C.
The possible mechanisms of hyperdoping film thickness influence on the Au-hyperdoped Si are discussed. Obtained results pave the way towards reproducible creation of reliable and cost-effective Au-hyperdoped Si detectors for the near infrared range.
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.
