Phosphorus doped ZnO nanowires: acceptor-related cathodoluminescence and p-type conducting FET-characteristics

摘要

Phosphorous-doped ZnO (ZnO:P) nanowires were prepared by a high-pressure pulsed laser deposition process. To extend the size range of available wires, um-thick ZnO:P microwires were grown additionally by a direct carbothermal deposition process. Low-temperature cathodoluminescence of single ZnO:P nanowires grown by both processes exhibit characteristic phosphorus acceptor-related peaks: neutral acceptor-bound exciton emission ((A~0, X), 3.356 eV), free-electron to neutral-acceptor emission ((e, A~0), 3.314 eV), and donor-to-acceptor pair emission (DAP, ～3.24 and ～3.04 eV). This proves that stable phosphorus acceptor levels have been induced into the ZnO:P nano- and microwires. From the quantitative evaluation of the spectroscopic features we deduct an acceptor binding energy of 122 meV. The ZnO:P microwires were used as channels in bottom-gate field effect transistors (FET) built on Si substrates with SiO_2 gate oxide. The electrical FET-characteristics of several wires show reproducibly clear qualitative indication for p-type conductivity for variation of gate voltage. This behavior is opposite to that of nominally undoped, n-type conducting wires investigated for comparison. The p-type conductivity was found to be stable over more than six months.