Modulation Doping of Si using Al-induced Acceptor States in SiO2 (talk)

Modulation Doping of Si using Al-induced Acceptor States in SiO2 — DIRK
KÖNIG1, •DANIEL HILLER2, SEBASTIAN GUTSCH2, MARGIT ZACHARIAS2, and SEAN SMITH1 —
1University of New South Wales (UNSW), Sydney, Australia — 2Laboratory for
Nanotechnology, IMTEK, University of Freiburg, Germany
Silicon nanovolumes suffer from effects that impede conventional doping due to
fundamental physical principles such as out-diffusion, statistics of small numbers,
quantum- or dielectric confinement. Efficient and reliable control over the majority
charge carriers by impurity doping is infeasible for ultra-small Si crystals [1].
In this work, we demonstrate a heterostructure modulation doping method for Si,
similar to the concept of modulation doping originally invented for III-V
semiconductors [2]. Our approach utilizes a specific acceptor state of Al-atoms in
SiO2, which is located 0.5 eV below the Si valence band, to generate holes as
majority carriers in adjacent Si [3]. The relocation of the impurity dopants from Si
to SiO2 circumvents all nanoscale doping problems. We present successful Si
modulation doping from the theoretical background (density functional theory
simulations, DFT) to experimental evidence by capacitance-voltage (C-V),
Hall-measurements and deep level transient spectroscopy (DLTS). In addition, we
demonstrate how modulation doping of bulk-Si enables passivating hole selective
tunnelling contacts as required for high-efficiency photovoltaics [3].
[1] Sci. Rep. 5, 09702 (2015) [2] Appl. Phys. Lett. 33, 665 (1978) [3] D. König &
D. Hiller et al., Sci. Rep., under review (2016)