Effects of rapid thermal annealing on the structural and electrical properties of Na-doped ZnMgO films

Rapid thermal annealing (RTA) is a general approach to improve the crystallinity of thin solid films. In this study, we investigated the effects of RTA on the structural and electrical properties of Na-doped ZnMgO films grown by pulsed laser deposition. X-ray diffraction (XRD) results showed that the crystallinity of the Na-doped ZnMgO films was improved with RTA at 400-700 °C, and the grain size became larger as the annealing temperature increased. Moreover, room-temperature photoluminescence (PL) measurements demonstrated decent optical quality of the as-deposited and annealed Na-doped ZnMgO films. Hall-effect measurements showed that the hole concentration increased from 4.9 × 1014 to 6.6 × 1015 cm−3 to 1.9 × 1017 to 8.3 × 1017 cm−3 while the resistivity and the Hall mobility decreased after the RTA treatments. The conduction type of the films converted from p to n when the annealing temperature is higher than 800 °C. Therefore a wide temperature window to obtain reasonable p-type Na-doped ZnMgO films by RTA is achieved. It is important because RTA is generally needed to obtain p-type Ohmic contact in the fabrication processes of light-emitting diodes (LEDs).

Research highlights► It has been reported that the Na-doped ZnMgO films show p-type conductivity. However, the effect of annealing temperature on the p-type ZnMgO conductivity is not well understood. In this study, we demonstrate that the electrical properties of the p-type ZnMgO are strongly dependent on annealing temperature. ► The crystallinities of the Na doped ZnMgO films were improved with RTA at 400-700 °C, the crystal size get larger as the annealing temperature growed. The as-deposited and annealed Na-doped ZnMgO films showed great optical efficiency from the PL measurements. The hole concentration increased while the resistivity and the Hall mobility decreased after annealed at 400-700 °C. The carrier type converted from p to n at an annealing temperature higher than 800 °C. ► From our experiments, we can find a wide temperature window for achieving reasonable p-type by RTA, which is important because RTA is generally needed to get p-type Ohmic contact when fabricating LED.