Influence of Highly Efficient Carbon Doping on Al x Ga 1− x As Layers with Different Al Compositions ( x ) Grown by MOVPE

Carbon (C)-doped aluminum gallium arsenide (Al x Ga 1− x As) epitaxial layers with different aluminum (Al) concentrations have been grown on gallium arsenide (GaAs) substrates by metalorganic vapor phase epitaxy (MOVPE) technique. The impact of varying carbon tetrabromide (CBr 4 ) flow rates on the electrical properties of Al x Ga 1− x As materials with different Al compositions has been investigated. High-resolution x-ray diffraction (HRXRD) measurement and a Hall effect measurement system have been used to determine the Al compositions and to evaluate the electrical properties. It has been found that the carrier density increases and the mobility decreases by increasing the flow rate of CBr 4 and changing Al compositions up to a certain point. In contrast, at higher Al compositions, a decrease in carrier density and an increase in mobility have been observed with increasing CBr 4 flow rate. Since these observed trends require to be analyzed in more detail, x-ray photoelectron spectroscopy (XPS) has been used to analyze the elements in the structure. From the XPS results, it has been shown that the atomic concentration of the arsenic in the structure decreased with the increase in CBr 4 flow rates. In addition, it has been shown that the Al composition in the Al x Ga 1− x As material obtained from the XRD results increases with the increase in the atomic concentration of the arsenic. Accordingly, a linear increase in carrier concentration is shown with increasing Al composition. This increase is explained by the effect of the Al–C bond content on the electrical properties of Al x Ga 1− x As.