AlP sacrificial layer for GaP NW growth

Sammanfattning: III-V semiconductor nanowires (NWs) display outstanding potential for many technological applications, but their implementation into devices is restricted due to high material and fabrication costs. Common techniques for NW synthesis rely on single crystalline substrates, which are single-use and have large costs associated to them. In this project a method for substrate reuse was designed and investigated. An aluminum phosphide (AlP) segment was grown as the base of gallium phosphide (GaP) NWs. The AlP segment was used as a sacrificial layer, allowing for separation of the GaP NWs from the GaP substrates used, thereby allowing for several uses of a substrate. These axial AlP/GaP NWs were synthesized with the vapor-liquid-solid growth mode, using metal organic vapor phase epitaxy. During the project, the combination of the AlP and GaP compound materials was investigated regarding epitaxial growth, chemical etch characteristics and potential for substrate reuse. As a reference to the approach with an AlP sacrificial layer it was investigated if reuse of a GaP wafer was possible after standard GaP NW growth. The wafer surface was planarized by wet chemical etching, before processing was performed. Regrowth of GaP NWs was possible with a yield of 50 %. The highest yields obtained for GaP, AlP and axial AlP/GaP NW growth were 96 %, 96 % and 97 % respectively. For the regrowth experiments axial AlP/GaP NWs were grown with a 80 % yield on 1x1 cm^2 substrates. This project reports on two cycles of reuse using this approach. For the first cycle an overall yield of 82 % could be achieved, during the given time of this project, and in the second cycle the yield was slightly lower at 75 %. The substrates were still intact after the second regrowth and it should be possible to further reuse them.