Abstract
The development of novel optoelectronic materials enabling advanced bandgap engineering and improved device performance is critical for the advancement of photonic technologies. To this end, this work concerns the fabrication and characterization of GaAs(N)Bi alloys, a novel type of semiconductor material system in which addition of both Bi and N to GaAs reduces the material band gap. This opens the potential for use in applications such as solar cells and other infrared optoelectronic devices.
To date, the application potential of this alloy system is hindered by the highly challenging nature of the epitaxial fabrication process, and the generally poor quality of the material. To this end, the main goal of this work was to investigate the relationship between the molecular beam epitaxial growth conditions and resulting material properties. In terms of applications, the aim was to utilize this knowledge in the development of low bandgap subjunctions in multi-junction solar cells.
Advanced methods enabling reproducible epitaxy and precise characterization of GaAs(N)Bi-based wafers were developed. Specifically, the stationary growth method was developed to enable controlled fabrication and characterization of GaAs(N)Bi samples with respect to source flux ratios. In addition, computational tools were developed for the analysis and exploration of data to enable efficient investigation of large data sets produced by experimental work.
Summarizing the main results, the systematic fabrication of GaAs(N)Bi samples with various growth parameters and investigation of the resulting material properties resulted in a comprehensive understanding of the aspects related to Bi incorporation. Various microstructural features, such as composition modulations and annealing- induced clustering were identified and their interplay with growth parameters investigated. To examine the application potential of the novel GaAsNBi alloy, solar cells with properties aimed to improve the efficiency of current multijunction solar cell designs were fabricated and characterized.
The results of the work serve as basis for further improvements in the control and optimization of the GaAs(N)Bi alloy system for optoelectronic applications and provide insight into the fundamental processes governing the growth of highly mismatched III-V alloys.
To date, the application potential of this alloy system is hindered by the highly challenging nature of the epitaxial fabrication process, and the generally poor quality of the material. To this end, the main goal of this work was to investigate the relationship between the molecular beam epitaxial growth conditions and resulting material properties. In terms of applications, the aim was to utilize this knowledge in the development of low bandgap subjunctions in multi-junction solar cells.
Advanced methods enabling reproducible epitaxy and precise characterization of GaAs(N)Bi-based wafers were developed. Specifically, the stationary growth method was developed to enable controlled fabrication and characterization of GaAs(N)Bi samples with respect to source flux ratios. In addition, computational tools were developed for the analysis and exploration of data to enable efficient investigation of large data sets produced by experimental work.
Summarizing the main results, the systematic fabrication of GaAs(N)Bi samples with various growth parameters and investigation of the resulting material properties resulted in a comprehensive understanding of the aspects related to Bi incorporation. Various microstructural features, such as composition modulations and annealing- induced clustering were identified and their interplay with growth parameters investigated. To examine the application potential of the novel GaAsNBi alloy, solar cells with properties aimed to improve the efficiency of current multijunction solar cell designs were fabricated and characterized.
The results of the work serve as basis for further improvements in the control and optimization of the GaAs(N)Bi alloy system for optoelectronic applications and provide insight into the fundamental processes governing the growth of highly mismatched III-V alloys.
| Original language | English |
|---|---|
| Place of Publication | Tampere |
| Publisher | Tampere University |
| ISBN (Electronic) | 978-952-03-3186-3 |
| ISBN (Print) | 978-952-03-3185-6 |
| Publication status | Published - 2023 |
| Publication type | G5 Doctoral dissertation (articles) |
Publication series
| Name | Tampere University Dissertations - Tampereen yliopiston väitöskirjat |
|---|---|
| Volume | 917 |
| ISSN (Print) | 2489-9860 |
| ISSN (Electronic) | 2490-0028 |