Charge transport in III-V narrow bandgap semiconductor nanowires
Sammanfattning: This thesis describes charge transport in III-V narrow bandgap semiconductor nanowires. We are particularly interested in quantum transport in InSb, InAs and InP-InAs core-shell nanowires. According to the type of transport mechanism dominating in the devices, this thesis can be divided into four parts.In the first part of this thesis, we investigated the temperature dependent transport properties of InSb nanowires using field effect transistors made of InSb nanowires grown by chemical vapor deposition. Ambipolar transport is observed in measurements in a wide range of temperatures up to 300 K. A bandgap of 220 meV is extracted from the temperature dependent measurements. Hole and electron field effect mobility are determined and their temperature dependence studied. The off state current shows a strong dependence on the temperature and the channel lengths of the transistors. In the second part of this thesis, spin relaxation and quantum interference in InSb nanowires are explored. Low-field magneto-conductance measurements are performed and a crossover from weak antilocalization to weak localization is observed. The experimental results are well explained with quasi one dimensional weak localization theory. Spin relaxation length and phase coherence length are defined. A strong spin-orbit strength of αR = 0.4 eVÅ-0.87 eVÅ is extracted. In the third part of this thesis, electron transport in a single quantum dot is studied in the weak and strong dot coupling regimes. The single quantum dots are formed in InSb nanowires by side gates. Various transport features such as sequential tunneling, excited states, and cotunnelings are investigated. Low temperature transport properties of InP-InAs core-shell nanowires are also explored and the coulomb blockade effect is revealed from a quantum structure extending over the entire core-shell nanowire. In the last part of this thesis, we report on electron transport through double quantum dots in InSb and InAs nanowires defined by side gates. From the measurements in the weak inter dot coupling regime, Pauli spin blockade is observed. The evolutions of states in the Pauli spin-blockade region with magnetic field is also studied.
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