Master Defense: Alexander Whiticar – University of Copenhagen

Master Defense: Alexander Whiticar

Main supervisor: Jessica Bolinsson
Co-supervisor: Jesper Nygård
 
Censor: Prof. Anders Mikkelsen, Lund University

Title:

Alternative Seed Particles for III-V Nanowire Arrays

Towards seed particle engineering for tuneable crystal structure and growth direction

Abstract:

In my thesis I explore the engineering of alternative seed-metals for GaAs nanowire (NW) growth by electron beam lithography in both molecular beam epitaxy (MBE) and metal-organic chemical vapour deposition (MOCVD) systems.  The key findings of my thesis are that by tuning metal-seed composition stable particle arrays are possible and that by using Ag and AgAu alloyed nanoparticles (NPs) as seeds, state of the art GaAs NWs are obtained.

We conducted systematic annealing experiments to demonstrate that alternative metals could form the necessary NPs needed for growth. This revealed inherent differences between Au and Ag/AgAu NPs even during the annealing stage of NW growth.

A systematic study of MBE GaAs NW growth from Ag NPs formed by thin film annealing permits high quality NW growth with minimal defects.  An analogous study with a MOCVD growth system compares the systems and enhances the research into the nature of seeding material. An important finding is that pure Au and Ag seeded GaAs NWs grown in the <111>B direction, using the same growth conditions, have a random polytypic crystal structure, whereas the Ag-Au alloy seeded growth are observed to be pristine wurtzite structure with only rare occurrences of stacking faults.  In addition, alternative seeding in both systems allowed for a high yield of GaAs NWs grown in the <100> direction.