Dilute nitrides (i.e. nitrogen-containing,
anion-mixed III-V ternary and quaternary alloys) have
recently attracted much attention due to their unusual
fundamental properties promising for device applications in
optoelectronics and photonics, such as highly efficient
and low cost near infrared lasers, efficient visible light
emitting diodes (LEDs), multi-junction solar cells, as well
as heterojunction bipolar transistors (HBTs). In order to
fully explore the potential of these new materials, detailed
knowledge on their fundamental and material-related
properties is required.The work presented in this thesis
focuses on optical studies of the electronic structure, radiative
recombination processes and also characterization of material
properties of several dilute nitrides systems that are relevant
to device applications, such as GaNP/GaP, GaNP/Si, GaNAs/GaAs
and GaInNP/GaAs. The thesis is divided into two parts. The
first part includes five chapters that give a general introduction
to the research field and also describes experimental methods
utilized in the research work. The second part contains seven
original scientific papers.Papers I and II report detailed studies
of effects of post-growth hydrogen incorporation on the
electronic structure of GaNAs and GaNP alloys by using
photoluminescence (PL), PL excitation (PLE), and Raman
spectroscopies, as well as high resolution X-ray diffraction
(HRXRD) measurements. Introduction of hydrogen in the
alloys was found to cause passivation of N-related localized
states. Additionally, profound and rather astonishing
changes in the band structure upon H incorporation were
observed, such as a recovery of the bandgap energies of the
parental GaAs and GaP, i.e. deactivation of the N-induced
bandgap bowing. In GaNP, this was accompanied by a reduction
in the N-induced coupling between the conduction band
states. Raman spectroscopy has showed that these effects
are related to hydrogeninduced breaking of the Ga-N bond.
Raman and HRXRD measurements have also shown that the
hydrogenation caused a strong expansion of the GaNP lattice,
which changes the sign of strain from tensile strain in the
as-grown GaNP epilayers to compressive strain after
hydrogenation, due to formation of complexes between
N and H.Paper III-IV discuss optical quality and defect
properties of GaNP/Si and GaNP /GaP alloys, as well as
effects of rapid thermal annealing (RTA). By employing a
variety of optical characterization techniques including
cathodoluminescence (CL), cwand time-resolved PL, PLE,
and optically detected magnetic resonance (ODMR), high
optical quality of the GaN0.018P0.982 epilayers lattice
matched to Si substrates was demonstrated and was
shown to be comparable to that of the "state-of-the-art"
GaNP alloys grown on GaP substrates. The growth of
GaNP on Si is, however, found to facilitate the formation
of several point defects, including complexes involving
Ga interstitials (Gai). A reduction and removal of
competing non-radiative point defects by RTA has been
concluded to be responsible for a substantial increase
in radiative efficiency of the GaNP epilayers subjected to
the post-growth annealing, evident from reduced thermal
quenching of the PL intensity as well as from a substantial
increase in carrier lifetime at room temperature.Papers
V-VII are devoted to detailed studies of Ga0.46In0.
54NxP1-x alloys lattice matched to GaAs, by using cw-
and time-resolved PL, PLE, and optically detected
cyclotron resonance (ODCR) measurements. The type-II
band alignment at the Ga0.46In0.54NxP1-x/GaAs interface
was concluded with x ? 0.5% based on (i) highly efficient
photoluminescence upconversion (PLU) observed in the N
containing alloys and (ii) appearance of a near-infrared PL
emission attributed to the spatially indirect type-II transitions.
Compositional dependence of the conduction band offset
at the GayIn1-yNxP1-x/GaAs interface was also estimated.
Origin of the PLU process was determined as being due to
two-step two-photon absorption (TS-TPA). Different from
other direct band gap dilute nitrides, the low temperature PL
emission was shown to largely arise from radiative transitions
involving spatially separated localized electronhole pairs.
The observed charge separation was tentatively attributed to
the long range CuPt ordering promoted by the presence
of nitrogen.
Ibañez Perez Jesus Oswaldo 18.353.376
CRF
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