Growth kinetics of GaxIn(1-x)P nanowires using triethylgallium as Ga precursor

GaxIn(1-x)P nanowire arrays are promising for various optoelectronic applications with a tunable band-gap over a wide range. In particular, they are well suited as the top cell in tandem junction solar cell devices. So far, most GaxIn(1-x)P nanowires have been synthesized by the use of trimethylgallium (TMGa). However, particle assisted nanowire growth in metal organic vapor phase epitaxy is typically carried out at relatively low temperatures, where TMGa is not fully pyrolysed. In this work, we developed the growth of GaxIn(1-x)P nanowires using triethylgallium (TEGa) as the Ga precursor, which reduced Ga precursor consumption by about five times compared to TMGa due to the lower homogeneous pyrolysis temperature of TEGa. The versatility of TEGa is shown by synthesis of high yield GaxIn(1-x)P nanowire arrays, with a material composition tunable by the group III input flows, as verified by x-ray diffraction measurements and photoluminescence characterization. The growth dynamics of GaxIn(1-x)P nanowires was assessed by varying the input growth precursor molar fractions and growth temperature, using hydrogen-chloride as in situ etchant. We observed a complex interplay between the precursors. First, trimethylindium (TMIn) inhibits Ga incorporation into the nanowires, resulting in higher In composition in the grown nanowires than in the vapor. Second, the growth rate increases with temperature, indicating a kinetically limited growth, which from nanowire effective binary volume growth rates of InP and GaP can be attributed to the synthesis of GaP in GaxIn(1-x)P. We observed that phosphine has a strong effect on the nanowire growth rate with behavior expected for a unimolecular Langmuir-Hinshelwood mechanism of pyrolysis on a catalytic surface. However, growth rates increase strongly with both TEGa and TMIn precursors as well, indicating the complexity of vapor-liquid-solid growth for ternary materials. One precursor can affect the decomposition of another, and each precursor can affect the wetting properties and catalytic activity of the metal particle.