Hydrothermal growth and characterization of aluminum-doped ZnO bulk crystals

Bulk ZnO crystals were grown by the hydrothermal technique with Al 2 O 3 added to the solution in an attempt to obtain Al-doped ZnO crystals. Aluminum and indium co-doped ZnO were also grown by the same technique. Adding Al 2 O 3 to the growth solution has a significant impact on the ZnO growth ⎯ either preventing overgrowth and dissolving the seed growth or degrading the crystalline quality; nevertheless, the resulting crystals of both Al:ZnO and Al/In:ZnO are highly conductive, similar to In and Ga doped ZnO crystals, with a resistivity approaching 0.01 Ω cm, as revealed by temperature-dependent Hall-effect measurements. Photoluminescence spectra at 18 K show Al 0 -bound-exciton peak energies of 3.3604 eV on the Zn face and 3.3609 eV on the O face for the Al-doped ZnO crystals. Similarly both an Al 0 - bound-exciton peak at 3.3604 eV and an In 0 -bound-exciton peak at 3.3575 eV were found on the Al/In-co-doped crystals. The electrical properties of all group III doped ZnO crystals grown hydrothermally are compared with each other and with Al:ZnO obtained by other growth methods.