Structural analysis of dilute bismide alloys by means of high resolution scanning transmission electron microscopy
Energy efficiency plays a key role in the development of new industrial as well as daily life applications. There exists a strong demand for a new energy efficient generation of optoelectronic devices, especially in the growing market of internet data transfer where devices operate in the 1.55 µm...
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|Summary:||Energy efficiency plays a key role in the development of new industrial as well as daily
life applications. There exists a strong demand for a new energy efficient generation of
optoelectronic devices, especially in the growing market of internet data transfer where
devices operate in the 1.55 µm wavelength regime. A promising material system that
could face the challenge of efficient devices is the dilute Bi containing Ga(AsBi) and
the dilute bismides in general. The novel material system Ga(AsBi) has been proven
that the incorporation of dilute Bi amounts reduces the bandgap energy. Furthermore, a
suppression of non-radiative loss mechanisms and a decreased temperature-dependency of
the emission wavelength could be verified which can be described by the valence band anti
crossing model. Moreover, first electrically pumped Ga(AsBi) based laser devices could be
fabricated which reveal once more the huge potential of dilute bismides.
In this work structural analysis of MOVPE grown Ga(AsBi), Ga(PAsBi) and Ga(NAsBi)
on GaAs substrates were carried out by means of spherical aberration corrected STEM. In
addition to STEM ADF measurements, ADF image simulations of Ga(AsBi) supercells
were performed which allowed the interpretation of the measurements as well as the Bi
quantification in Ga(AsBi)-QWs. Despite STEM measurements, image processing was
applied for further analysis, i.e., determination and separation of the crystal sublattices
in HR measurements via the MATLAB software. Image processing is mandatory since it
allows on the one hand a quantification of the Bi fraction in Ga(AsBi), and on the other
hand a further statistical evaluation of the atomic column intensities is possible.
The results of this work show that STEM is inevitable
for the characterization of novel semiconductors as well as for the detection of atomic
ordering. Finally, Bi has the ability to distribute homogeneously in dilute Bi-containing
materials, when MOVPE takes place under optimized growth conditions which is very
promising for the realization and fabrication of new energy efficient semiconductor devices.|
|Physical Description:||120 Pages|