Doctor of Philosophy / Department of Chemical Engineering / James H. Edgar / The semiconductor boron phosphide (BP) has many outstanding features making it attractive for developing various electronic devices, including neutron detectors. In order to improve the efficiency of these devices, BP must have high crystal quality along with the best possible electrical properties. This research is focused on growing high quality crystalline BP films on a variety of superior substrates like AIN, 4H-SiC, 3C-SiC and ZrB₂ by chemical vapor deposition. In particular, the influence of various parameters such as temperature, reactant flow rates, and substrate type and its crystalline orientation on the properties of BP films were studied in detail. Twin-free BP films were produced by depositing on off-axis 4H-SiC(0001) substrate tilted 4° toward [1-100] and crystal symmetry matched zincblende 3C-SiC. BP crystalline quality improved at higher deposition temperature (1200°C) when deposited on AlN, 4H-SiC, whereas increased strain in 3C-SiC and increased boron segregation in ZrB₂ at higher temperatures limited the best deposition temperature to below 1200°C. In addition, higher flow ratios of PH₃ to B₂H₆ resulted in smoother films and improved quality of BP on all substrates. The FWHM of the Raman peak (6.1 cm⁻¹), XRD BP(111) peak FWHM (0.18°) and peak ratios of BP(111)/(200) = 5157 and BP(111)/(220) = 7226 measured on AlN/sapphire were the best values reported in the literature for BP epitaxial films. The undoped films on AlN/sapphire were n-type with a highest electron mobility of 37.8 cm²/V·s and a lowest carrier concentration of 3.15x1018 cm⁻ᶟ. Raman imaging had lower values of FWHM (4.8 cm⁻¹) and a standard deviation (0.56 cm⁻¹) for BP films on AlN/sapphire compared to 4H-SiC, 3C-SiC substrates. X-ray diffraction and Raman spectroscopy revealed residual tensile strain in BP on 4H-SiC, 3C-SiC, ZrB₂/4H-SiC, bulk AlN substrates while compressive strain was evident on AlN/sapphire and bulk ZrB₂ substrates. Among the substrates studied, AlN/sapphire proved to be the best choice for BP epitaxy, even though it did not eliminate rotational twinning in BP. The substrates investigated in this work were found to be viable for BP epitaxy and show promising potential for further enhancement of BP properties.

In this study unintentionally doped GaN grown by hydride vapor phase epitaxy that exhibits a sharply delimited region of green color was investigated. Optical analysis was performed by absorption and photoluminescence spectroscopy. An absorption band between 1.5 and 2.0 eV was found to be responsible for the green color and was related to a sharp emission at 1.193 eV by luminescence and excitation spectroscopy. The appearance of both optical signatures in the region of green color was related to an increase of Cr contamination detected by secondary ion mass spectrometry. We propose that the origin of green color as well as the emission line at 1.193 eV is attributed to internal transitions of Cr⁴⁺.

Silicon based solar cells have been used as photovoltaic devices for decades due to reasonable cost and environment- friendly nature of silicon. But the conversion efficiency of silicon solar cell is limited; for instance, the maximum conversion efficiency of a crystalline silicon solar cell available in the market developed by Kaneka Corporation is 26 % [1]. In comparison, III-V compound semiconductor multi-junction solar cells are the most efficient solar cells with efficiency of 47.1% [2]. However, due to high-cost substrate materials, III-V solar cells are not the best option for large scale production in real life. Therefore, integration of III-V compound semiconductors on silicon substrate has been studied to obtain III-V/Si multi junction solar cells with high conversion efficiency with reasonable price. To this end, we studied epitaxial growth of on GaAs deposited on Si.This thesis presents the characterization results of the above epitaxial layer and fabrication of a single junction solar cell on GaAs coated Si substrate and its performance.In the first part of the project, epitaxial layer grown by Hydride Vapor Phase Epitaxy (HVPE) on different kinds of substrates at different growth conditions are characterized to identify the optimized growth conditions and a suitable substrate. Samples are characterized by High Resolution X-ray Diffraction (HRXRD) and photoluminescence (PL) to determine the composition of and its crystalline quality and by optical microscope to assess the surface morphology. Scanning Electron Microscope (SEM) is used to study the depth of the dry etched structures.The second part of the project deals with the fabrication process consisting of 21 steps to obtain a single junction solar cell structure on GaAs/Si. This process flow will be explained in some detail along with a brief description of several tools in cleanroom that have been used for this purpose.Finally, in the third part, devices are characterized to investigate their performance. Transmission Line Method (TLM) is used to obtain important parameters such as specific contact resistance. Current- voltage (I-V) relation of solar cell is investigated to acquire its efficiency. The lowest specific contact resistance measured in this project is for p-contact (for 4041DV- cell 8) and the highest efficiency measured is 1.64% (for 4041DV- cell 6).In conclusion, although the results obtained are far from the state-of-the art results, this work has laid the foundation for future work that can lead to a breakthrough in fabricating multi-junction tandem solar cell on silicon. / Kiselbaserade solceller har använts i årtionden på grund av dess rimliga kostnad och miljövänliga natur. Omvandlingseffektiviteten för kiselsolcell är begränsad; till exempel är den maximala omvandlingseffektiviteten för solceller av kristallin kisel utvecklad av Kaneka Corporation 26 % [1]. Som jämförelse är III-V sammansatta halvledare multi-junction solceller de mest effektiva solcellerna med en effektivitet på 47,1 % [2]. På grund av de höga substratmaterialen är III-V-solceller i realiteter inte det bästa alternativet för storskalig produktion. Därför har integration av III-V sammansatta halvledare på kiselsubstrat studerats för att erhålla III-V/Si multi junction solceller med hög omvandlingseffektivitet till rimligt pris. För detta ändamål studerade vi epitaxiell tillväxt av på GaAs avsatt på Si.Denna avhandling presenterar karaktäriseringsresultaten av ovanstående epitaxiella skikt och tillverkning av en enkel förbindelse solcell på GaAs-belagt Si-substrat och dess prestanda.I den första delen av projektet karaktäriseras epitaxiallager odlat med Hydride Vapor Phase Epitaxy (HVPE) på olika typer av substrat vid olika tillväxtförhållanden för att identifiera de optimerade tillväxtförhållandena och ett lämpligt substrat. Prover kännetecknas av högupplöst röntgendiffraktion (HRXRD) och fotoluminescens (PL) för att bestämma sammansättningen av och dess kristallina kvalitet och med optiskt mikroskop för att bedöma morfologin. Scanning Electron Microscope (SEM) används för att studera djupet av de torretsade strukturerna.Den andra delen av projektet behandlar tillverkningsprocessen som består av 21 steg för att erhålla en enda förbindelse solcellsstruktur på GaAs/Si. Detta processflöde kommer att förklaras i detalj tillsammans med en kort beskrivning av flera verktyg i renrum som har använts för detta ändamål.Slutligen, i den tredje delen, karaktäriseras enheter för att frilägga dess prestanda. Transmission Line Method (TLM) används för att erhålla viktiga parametrar som specifikt kontaktmotstånd. Förhållandet mellan ström och spänning (I-V) hos solcellen undersöks för att uppnå optimal effektivitet. Den lägsta specifikt kontaktmotstånd som uppmätts i detta projekt är för p-kontakt (för 4041DV-cell 8) och den högsta uppmätta effektiviteten är 1,64% (för 4041DV-cell 6).Sammanfattningsvis, även om de erhållna resultaten är långt ifrån de senaste resultaten inom forskning, lägger detta arbete grunden för framtida arbete som kan leda till ett genombrott i tillverkningen av multi-junction tandemsolcell på kisel.