Epitaxial Growth of Bismuth-Modified III-V Systems on 001 GaAs

Bandgap engineering of III-Vs with Bi has been a promising candidate for next generation infrared
detectors and avalanche photo diode devices (APD). The large, induced change in bandgap, up to 78
meV per % Bi incorporated and the surfactant effect of Bi on the surface during epitaxial growth make
it an attractive option. However, the application of Bi to III-V growth I nontrivial with low miscibility
necessitating significantly reduced growth temperatures and narrow viable flux III-V flux windows.
This necessitates careful optimisation and growth studies to produces device quality material with
significant remaining challenges in the growth of Bi containing alloys.
The first chapter focuses on the surfactant effect of Bi on InAs quantum dot (QD) formation for infrared
emission and detection in the O and C fibre communication attenuation windows. Bi fluxes between 0
to 3.5 nA were supplied to the surface during InAs QD formation at 480 °C at a rate of 0.01 atomic
monolayers per second (MLs-1
). The QDs were capped with 50 nm of GaAs and a further surface layer
grown atop. The morphological changes and optical characteristics assessed by atomic force
microscopy (AFM) and photoluminescence measurements (PL). QD height was found to vary between
3.8 to 10.1 nm in non-trivial relationship with supplied Bi flux. A critical threshold was observed were
Bi initially enhanced QD formation up to 1.2 nA before the trend reversed and the level of enhanced
QD height reduced. Supply at 3.5 nA was found to hinder the QD formation relative to no supplied Bi
flux. The lowest energy emission was observed at 1.049 eV and 0.971 eV for PL measurements at 20
and 297 K respectively.
The second and third chapters investigate the growth and post-processing respectively of the quaternary
alloy AlxGa1-xAs1-yBiy. Of interest owing to the potential application as a next generation avalanche
region in APD devices. Growth starts from optimised GaAsBi growth conditions with contents of Al
between 0 to 15 at% grown. Further exploration of key growth parameters was conducted with Bi flux
varied between 0.8 to 2.8 nA and growth temperatures between 280 to 340 ºC. Sample were the analysed
by XRD, PL and ion beam analysis to quantify crystalline, optical and compositional properties of the
samples. The substitution of Ga for Al was found to introduce significant quantities of defects which
acted as non-radiative recombination centres with 2-3 orders of magnitude decrease in PL brightness
observed. Once Al was present the impact remained stable and insensitive to further increases in content
between 2.5 to 15 at% Al. There was no indication the Al content affected the incorporation of Bi. Bi
contents between 1.4 to 4.6 at% Bi and 0.9 to 6.2 at% for Bi flux and growth temperature control
respectively with 5 at% Al. Sample grown for the ex-situ annealing suffered from degraded quality due
to the cold capping layers. This overshadowed any indication that the material was degraded by the
capping process or that it could be improved in quality by ex-situ annealing at temperatures between
400 to 650 ºC for 30s. The viability of synthesis of this alloy was confirmed However there remains an
elevated quantity of unidentified compensation complexes within the material that degrade the optical
quality.