Hydrothermal Growth of ZnO Single Crystals with High Carrier Mobility

Abstract

Thirty millimeter ZnO single crystals have been grown by the hydrothermal method with new mineralizers and a low-cost liner. A sharp X-ray rocking curve with the full width at half-maximum of 36 arcsec has been obtained for the (002) reflection, indicating a good crystallinity of the crystal. Low temperature photoluminescence spectrum revealed the crystal has a narrow and strong free exciton emission band (3.359 eV) at 10 K, with the absence of a green-yellow emission band that generally is induced by the impurities or lattice vacancies. Compared to ZnO crystals hydrothermally grown from conventional mineralizers (LiOH and KOH), this crystal has a unique feature that the room-temperature carrier mobility is close to the intrinsic value, with the carrier concentration maintained as high as 4.09 × 1016 cm−3. Two main donors which may relate to the H impurity were indicated. Analysis revealed that the diffusion of H in the ZnO lattice might be responsible for the decrease in conductivity of the ZnO crystal after annealing. The reason why the new hydrothermal method yielded low-resistance ZnO crystals could be interpreted as a much higher concentration of H impurity and much lower concentration of Li impurity incorporated into the ZnO lattice, compared with samples yielded by the conventional hydrothermal method. We anticipate the reported high-quality ZnO single crystals can not only be suitable objects for studying the intrinsic properties of ZnO, but also be potential substrates for fabricating ZnO light emitting diodes devices.