Infuence of surface and crystal structure on the conductivity of individual InAs and InP nanowires

Sammanfattning: To satisfy the great need for (opto-)electronic devices to become smaller and more efficient in energy and price, research is done on semiconducting III-V nanowires (NWs). Electrical devices using NWs show noteworthy assets being fast-paced with high-speed electronics and low power consumption, one of which are high-efficient solar cells at a moderate price. Developing electric devices it turns out to be of importance to measure individual NW conductivities for further improvements, if possible even in their upright standing growth geometry. Even though in the past this shaped up to be difficult, a new method was executed: utilizing scanning tunneling microscopy and a top contact method individual NWs are localized and contacted to finally be able to measure their individual conductance behavior. This new method was employed in this thesis by investigating two NW systems that are promising for application in high-speed electronics and energy harvesting. First the influence of boundary interfaces between wurtzite and zinc blende structures on the conductivity of InAs NWs was investigated. It is shown that these transitions play an important role in combination with the existence of oxides on the surface. Cleaning the NWs with hydrogen results in an unexpected consequence: The current rises significantly with almost two orders of magnitude, going hand in hand with a much larger conductivity. In addition one can observe the current-voltage behavior to become more homogeneous. Secondly, the influence of a passivation layer coating photovoltaic InP NWs is investigated. Determining an ideality factor of n = 2,4 ± 0,2 confirms the improvement of conductivity caused by the passivation layer. Lastly and contrary to expectations no photovoltaic response of the InP NW sample could be observed which is further discussed.