Abstract
The goal of the work presented here was to use cryogenic Scanning Near-field Optical Microscopy
(SNOM), an imaging technique that detects local changes to the dielectric function
of a sample surface, to locate and identify single dopants in silicon for quantum technologies.
SNOM imaging was performed on heavily doped Ga in Si at room and low (8K) temperatures
where free carriers donated by the Ga atoms caused changes in the samples dielectric function.
These investigations yielded a minimum number of observable dopants equal to an estimated
5000 Ga atoms per 1 μm^2. Lightly doped (2.5×1015 cm^−3) indium in silicon samples were also
studied as their transition lines lie within the SNOMs wavelength range and the local dielectric
function of the sample may be changed by moving the SNOM imaging wavelength on and off
the lines. No indium atoms were observed in these experiments.
Photonic Crystal Cavities (PCCs) in silicon were also investigated with an eventual aim of
coupling single donors / acceptors with a PCC and inffering the presence of the single dopant
by a shift in the cavities resonance. SNOM imaging was carried out on PCCs designed to
have cavity resonances within the SNOM wavelength range 7.6-8.6 μm, suitable for dopants in
silicon, and showed light confinement within the cavity. Also, THz – time domain spectroscopy
was performed on PCCs with cavity resonances between 1-4 THz, suitable for dopants in
germanium, and showed frequency dependent drops in transmission of the THz through the
PCCs.
Finally, characterisation techniques for determining the radiation pattern, absolute power
and frequency spectra of THz sources have been developed and implemented to evaluate sources
within the 1-4 THz range for possible coupling to the SNOM to study dopants in germanium.
Characterisation techniques have been demonstrated on two different emitters operating between
50 GHz to 1 THz.