Doping of Semiconductor Nanowires
Abstract: In this thesis, in situ doping during growth of III-V semiconductor nanowires, primarily for photovoltaic applications, is investigated. The nanowires were grown by metalorganic vapor phase epitaxy (MOVPE), with gold seed particles. After growth the nanowires were characterized using various techniques, including photoluminescence, transmission electron microscopy and electrical measurements of contacted nanowires. Different III-V materials were studed, both binary materials such as InP and GaAs, and ternary materials such as GaxIn1-xP. To achieve p- and n-doping, different precursors were employed. The results show that successful p- and n-doping can be achieved in many materials. The in situ doping is shown to affect the nanowire growth strongly, but differently depending on the combination of material and dopant. The main effects are related to the growth rate and the crystal structure. It is shown that the n-dopant H2S increases the growth rate and induces wurtzite crystal structure in InP nanowires, while the p-dopant DEZn gives an unchanged growth rate with zinc blende crystal structure. High doping and sharp doping profiles are demonstrated with interband tunneling in Esaki tunnel diodes. Finally, in situ doping is used to create p-i-n doped InP nanowire arrays which are processed into solar cells with 13.8% efficiency.
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