Dependence of Molecular Beam Epitaxy Grown GaN Nanowire Arrays with Various Si Doping Concentrations on Performance of Nanopiezotronics and Nanogenerators

Abstract

The impact of carrier concentration in MBE-grown GaN nanowire (NW) arrays on semiconducting piezoelectric direct-current single-nanowire nanogenerators (DC-SNWNGs) piezo-tronic devices and alternating-current (AC) vertical integrated nanogenerators (VINGs) is investigated in this study In the case of DC-SNWNGs and piezo-tronic devices unintentionally doped and Si-doped GaN NW arrays with various carrier concentrations ranging from 1017 (unintentionally doped) to 1019 cm-3 (heavily doped) are synthesized For DC-SNWNGs the output current of individual NWs starts from a negligible level and rises to the maximum of ~50 nA at a doping concentration of 5 63×1018 cm-3 and then falls off with further increases in carrier concentration due to the competition between the reduction of inner resistance and the screening effect on piezoelectric potential For piezo-tronic applications the force sensitivity based on the change of the Schottky barrier height works best for unintentionally doped NWs reaching 26 20 ± 1 82 meV nN-1 and then decreases with carrier concentration Although both types of devices share the same Schottky diode they involve with different characteristics in that the slope of the current-voltage characteristics governs DC-SNWNG devices while the turn-on voltage determines piezo-tronic devices Free carriers in piezo-tronic materials can influence the slope and turn-on voltage of the diode characteristics concurrently when subjected to strain A design guideline for the optimum doping concentration for obtaining the best performance in piezo-tronic devices and SNWNGs is provided in this work As for AC VINGs the carrier concentration enhancement with increasing Si doping is reflected by a blue shift of the near-band-edge optical emission of GaN NW arrays The effects of the protection layer substrate and carrier concentration of GaN NW arrays on the output performance of VINGs are evaluated of which carrier concentration is found to be dominant The output voltage and current density of AC VINGs made of GaN NW arrays strongly decrease with increasing doping concentration because of the enhanced carrier-screening effect to the piezoelectric polarization charges Consequently AC VINGs should be composed of piezo-tronic materials with the lowest possible carrier concentration to prevent the screening effect

Date of Award	2015 Jan 12
Original language	English
Supervisor	Chuan-Pu Liu (Supervisor)