VM
V. Mohammadi
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Stability, local structure and electronic properties of borane radicals on the Si(100) 2x1:H surface
A first-principles study
Abstract Deposition of a thin B layer via decomposition of B2H6 on Si (PureB process) produces B-Si junctions which exhibit unique electronic and optical properties. Here we present the results of our systematic first-principles study of BHn (n=0-3) radicals on Si(100)2x1:H surfaces, the initial stage of the PureB process. The calculations reveal an unexpectedly high stability of BH2 and BH3 radicals on the surface and a plausible atomic exchange mechanism of surface Si atoms with B atoms from absorbed BHn radicals. The calculations show strong local structural relaxation and reconstructions, as well as strong chemical bonding between the surface Si and the BHn radicals. Electronic structure calculations show various defect states in the energy gap of Si due to the BHn absorption. These results shed light on the initial stages of the complicated PureB process and also rationalize the unusual electronic, optical and electrical properties of the deposited Si surfaces.
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Abstract Deposition of a thin B layer via decomposition of B2H6 on Si (PureB process) produces B-Si junctions which exhibit unique electronic and optical properties. Here we present the results of our systematic first-principles study of BHn (n=0-3) radicals on Si(100)2x1:H surfaces, the initial stage of the PureB process. The calculations reveal an unexpectedly high stability of BH2 and BH3 radicals on the surface and a plausible atomic exchange mechanism of surface Si atoms with B atoms from absorbed BHn radicals. The calculations show strong local structural relaxation and reconstructions, as well as strong chemical bonding between the surface Si and the BHn radicals. Electronic structure calculations show various defect states in the energy gap of Si due to the BHn absorption. These results shed light on the initial stages of the complicated PureB process and also rationalize the unusual electronic, optical and electrical properties of the deposited Si surfaces.
The interest in nanostructures of silicon and its dopants has significantly increased. We report the creation of an ultimately-shallow junction at the surface of n-type silicon with excellent electrical and optical characteristics made by depositing an atomically thin boron layer at a relatively low temperature where no doping of silicon is expected. The presented experimental results and simulations of the ab initio quantum mechanics molecular dynamics prove that the structure of this new type of junction differs from all other known rectifying junctions at this time. An analysis of the junction formation has led to the conclusion that the chemical interaction between the surface atoms of crystalline silicon and the first atomic layer of the as-deposited amorphous boron is the dominant factor leading to the formation of a depletion zone in the crystalline silicon which originates from the surface. The simulation results show a very strong electric field across the c-Si/a-B interface systems where the charge transfer occurs mainly from the interface Si atoms to the neighboring B atoms. This electric field appears to be responsible for the creation of a depletion zone in the n-silicon resulting in a rectifying junction-formation between the n-silicon and the atomically thin boron layer.
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The interest in nanostructures of silicon and its dopants has significantly increased. We report the creation of an ultimately-shallow junction at the surface of n-type silicon with excellent electrical and optical characteristics made by depositing an atomically thin boron layer at a relatively low temperature where no doping of silicon is expected. The presented experimental results and simulations of the ab initio quantum mechanics molecular dynamics prove that the structure of this new type of junction differs from all other known rectifying junctions at this time. An analysis of the junction formation has led to the conclusion that the chemical interaction between the surface atoms of crystalline silicon and the first atomic layer of the as-deposited amorphous boron is the dominant factor leading to the formation of a depletion zone in the crystalline silicon which originates from the surface. The simulation results show a very strong electric field across the c-Si/a-B interface systems where the charge transfer occurs mainly from the interface Si atoms to the neighboring B atoms. This electric field appears to be responsible for the creation of a depletion zone in the n-silicon resulting in a rectifying junction-formation between the n-silicon and the atomically thin boron layer.
Conference paper
(2016)
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V. Mohammadi, R.W.E. van de Kruijs, Padmakumar Ramachandra Rao, J.M. Sturm, S. Nihtianov
This paper presents our latest results from the investigation of the surface oxide content in boron capped layers used as the entrance window in ultraviolet silicon (UV-Si) photodetectors. These photodetectors have been studied electrically and optically to define the correlation between oxide content and performance, i.e. the direct relationship between the amount of undesired surface oxide in the active region where the boron layer is deposited, and the detector stability to high UV exposure levels. The boron capping layers were deposited by either chemical or physical vapor based deposition techniques (CVD or PVD). Although these techniques provide photodetectors that are highly sensitive to UV radiation [1], the formation of surface oxide during deposition is a major concern, especially for stability. To analyze the oxide content, an XPS (X-ray photoelectron spectroscopy) analysis was performed on high-temperature (HT-CVD: 700 °C), low-temperature (LT-CVD: 400 °C), and room-temperature (RT-CVD: 25 °C) based pure boron (PureB) photodetectors. An inverse relationship between deposition temperature and oxide content was noticed. While the HT-CVD based photodetectors were found to contain 30% of oxide in its active region, this amount drops to less than 10% for LT-CVD, and to a few percent for RT-PVD based process.
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This paper presents our latest results from the investigation of the surface oxide content in boron capped layers used as the entrance window in ultraviolet silicon (UV-Si) photodetectors. These photodetectors have been studied electrically and optically to define the correlation between oxide content and performance, i.e. the direct relationship between the amount of undesired surface oxide in the active region where the boron layer is deposited, and the detector stability to high UV exposure levels. The boron capping layers were deposited by either chemical or physical vapor based deposition techniques (CVD or PVD). Although these techniques provide photodetectors that are highly sensitive to UV radiation [1], the formation of surface oxide during deposition is a major concern, especially for stability. To analyze the oxide content, an XPS (X-ray photoelectron spectroscopy) analysis was performed on high-temperature (HT-CVD: 700 °C), low-temperature (LT-CVD: 400 °C), and room-temperature (RT-CVD: 25 °C) based pure boron (PureB) photodetectors. An inverse relationship between deposition temperature and oxide content was noticed. While the HT-CVD based photodetectors were found to contain 30% of oxide in its active region, this amount drops to less than 10% for LT-CVD, and to a few percent for RT-PVD based process.
In this chapter, a new technology for low‐temperature (LT, 400°C) boron deposition is developed, which provides a smooth, uniform, closed LT boron layer. This technology is successfully employed to create near‐ideal LT PureB (pure boron) diodes with low, deep junction‐like saturation currents, allowing full integration of LT PureB photodiodes with electronic interface circuits and other sensors on a single chip. In this way, smart‐sensor systems or even charge‐coupled device (CCD) or complementary metal oxide semiconductor (CMOS) ultraviolet (UV) imagers can be realised.
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In this chapter, a new technology for low‐temperature (LT, 400°C) boron deposition is developed, which provides a smooth, uniform, closed LT boron layer. This technology is successfully employed to create near‐ideal LT PureB (pure boron) diodes with low, deep junction‐like saturation currents, allowing full integration of LT PureB photodiodes with electronic interface circuits and other sensors on a single chip. In this way, smart‐sensor systems or even charge‐coupled device (CCD) or complementary metal oxide semiconductor (CMOS) ultraviolet (UV) imagers can be realised.