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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|Zusammenfassung:||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.|