Abstract
Silicon nanovolumes (nanowells, nanowires, nanocrystals – NWells, NWires, NCs) suffer from effects that impede conventional doping due to fundamental physical principles: out- diffusion [1,2], small number statistics [3], and quantum- or dielectric confinement [2,4-8]. For III-V semiconductors, modulation doping was discovered by Störmer & Dingle in 1978 [9], paving the way for loss-free and fast carrier transport as required for ultrafast VLSI electronics and lasing, and Störmer having been awarded the 1998 Physics Nobel Price.
In 2017, direct modulation doping of SiO2 with Al-induced acceptor states for introducing holes as majority carriers to adjacent Si was demonstrated in theory and experiment [10]. This approach offered a whole new vista on preventing problems in compound with impurity doping of nano-Si in VLSI, and also yielded highly conductive hole-selective contacts to Si solar cells with excellent field-effect passivation as a spin-off [10,11]. Recent work on intrinsic Si-NWires with ultrathin Al-doped SiO2 coatings demonstrated in experiment that the conductivity of such NWires rose by nearly seven orders of magnitude to p-type [12]. In addition, the Schottky barriers of NWire to Ni contacts were reduced from
0.45 to 0.09 eV, decreasing contact resistivity to exp(-5) = 0.67 % of its nominal value [13].
Here, we will focus on the fundamentals of direct modulation doping of Si: its principle (Why direct? What are the consequences?) [14], its quantum-chemical requirements, control of active dopant density [14,15] (Why/how do we defeat the ‘small number statistics’ problem?), modulation acceptor candidates [14] and similarities and differences to impurity acceptors in bulk Si (Al works, B does not – why?) [14,15], the structural properties of modulation acceptors in SiO2 [16], and its impact on the deactivation of interface trap states [17]. This fundamental part will be rendered by a glimpse on the numerous applications of direct modulation doping and corroborated with experimental data [10-13,17]. We will further discuss whether an antipolar counterpart to direct modulation acceptors in SiO2 – that is, an Si-based solid with direct modulation donors for adjacent Si – could exist and how such a material system would probably look like.
References:
[1] G.M. Dalpian et al., Phys. Rev. Lett., 2006, 96, 226802. [2] D. König et al., Sci. Rep., 2015, 5, 09702. [3]
D.J. Norris et al., Science, 2008, 319, 1776. [4] D. Hiller et al., Sci. Rep., 2017, 7, 863. [5] D. Hiller et al., Sci. Rep., 2017, 7, 8337. [6] D. Hiller et al., Beilstein J. Nanotech., 2018, 19, 1501. [7] D. Hiller et al., Phys. Stat. Sol. B, 2021, 258, 202000623. [8] M.T. Björk et al, Nature Nanotech., 2009, 4, 103. [9] R. Dingle et al., Appl. Phys. Lett., 1978, 33, 665. [10] D. König et al., Sci. Rep. 2017, 7, 46703. [11] D. Hiller et al., Solar Energy Mater. & Solar Cells 2020, 215, 110654. [12] S. Nagarajan et al., Phys. Stat. Sol. A 2023, 220, 2300068. [13]
S. Nagarajan et al., Adv. Mater. Interfaces 2024, 11, 2300600. [14] D. König et al., Phys. Rev. Appl. 2018, 10, 054034. [16] D. Hiller et al., ACS Appl. Mater. Interfaces 2018, 10, 30495. [15] D. Hiller et al., J. Phys. D: Appl. Phys. 2021, 54, 275304. [17] D. Hiller et al., J. Appl. Phys. 2019, 125, 015301.
In 2017, direct modulation doping of SiO2 with Al-induced acceptor states for introducing holes as majority carriers to adjacent Si was demonstrated in theory and experiment [10]. This approach offered a whole new vista on preventing problems in compound with impurity doping of nano-Si in VLSI, and also yielded highly conductive hole-selective contacts to Si solar cells with excellent field-effect passivation as a spin-off [10,11]. Recent work on intrinsic Si-NWires with ultrathin Al-doped SiO2 coatings demonstrated in experiment that the conductivity of such NWires rose by nearly seven orders of magnitude to p-type [12]. In addition, the Schottky barriers of NWire to Ni contacts were reduced from
0.45 to 0.09 eV, decreasing contact resistivity to exp(-5) = 0.67 % of its nominal value [13].
Here, we will focus on the fundamentals of direct modulation doping of Si: its principle (Why direct? What are the consequences?) [14], its quantum-chemical requirements, control of active dopant density [14,15] (Why/how do we defeat the ‘small number statistics’ problem?), modulation acceptor candidates [14] and similarities and differences to impurity acceptors in bulk Si (Al works, B does not – why?) [14,15], the structural properties of modulation acceptors in SiO2 [16], and its impact on the deactivation of interface trap states [17]. This fundamental part will be rendered by a glimpse on the numerous applications of direct modulation doping and corroborated with experimental data [10-13,17]. We will further discuss whether an antipolar counterpart to direct modulation acceptors in SiO2 – that is, an Si-based solid with direct modulation donors for adjacent Si – could exist and how such a material system would probably look like.
References:
[1] G.M. Dalpian et al., Phys. Rev. Lett., 2006, 96, 226802. [2] D. König et al., Sci. Rep., 2015, 5, 09702. [3]
D.J. Norris et al., Science, 2008, 319, 1776. [4] D. Hiller et al., Sci. Rep., 2017, 7, 863. [5] D. Hiller et al., Sci. Rep., 2017, 7, 8337. [6] D. Hiller et al., Beilstein J. Nanotech., 2018, 19, 1501. [7] D. Hiller et al., Phys. Stat. Sol. B, 2021, 258, 202000623. [8] M.T. Björk et al, Nature Nanotech., 2009, 4, 103. [9] R. Dingle et al., Appl. Phys. Lett., 1978, 33, 665. [10] D. König et al., Sci. Rep. 2017, 7, 46703. [11] D. Hiller et al., Solar Energy Mater. & Solar Cells 2020, 215, 110654. [12] S. Nagarajan et al., Phys. Stat. Sol. A 2023, 220, 2300068. [13]
S. Nagarajan et al., Adv. Mater. Interfaces 2024, 11, 2300600. [14] D. König et al., Phys. Rev. Appl. 2018, 10, 054034. [16] D. Hiller et al., ACS Appl. Mater. Interfaces 2018, 10, 30495. [15] D. Hiller et al., J. Phys. D: Appl. Phys. 2021, 54, 275304. [17] D. Hiller et al., J. Appl. Phys. 2019, 125, 015301.
Original language | English |
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Pages | 232 |
Number of pages | 233 |
Publication status | Published - 13 Sept 2024 |