Exactly at the end of 120 min of heating, the flow of reactant and carrier gases were stopped and the furnace was set to cool down to room temperature before NU7026 removing the sample. Once the furnace got cooled to near room temperature, the sample was removed from it. Grayish white
deposits were observed on the silicon substrate. The same procedure was repeated for all samples of different dopant concentrations. Doping mechanism of ZnO:Al Due to their confined electronic states to a very small volume in nanocrystals, doping leads to phenomena not found in the bulk counterparts. Although the underlying mechanism responsible for these observations are still under investigation, we believe that the following reactions spontaneously occur during the deposition of ZnO:Al NSs. (2.1) (2.2) It is expected that doubly charged donors including oxygen JQ-EZ-05 mouse vacancies (V o) and zinc interstitials (Zn i ) would be formed by the extrinsic doping check details of Al. This is possible if the incorporated Al atoms take oxygen from ZnO and form either or inside the ZnO matrix. As the standard Gibbs-free energy change of these reactions is largely negative (-618 kJ mole-1) , it is believed that the formation of m */m o is responsible for the extrinsic doping of ZnO:Al, which
is contrary to the conventional doping mechanism based on the substitution of foreign elements. Doping takes place by incorporating Al atoms in which charged donors would be formed at or near the Al2O3/ZnO interface in compensation for free electrons. The electrons around these donors could be localized within the Bohr radius (aH) of ZnO as stated below: (2.3) where a o = Bohr radius of H atom (0.53 Å), ϵ r = relative permittivity of ZnO (81), m * = effective mass of an electron in ZnO (0.318), m o = mass of an electron, and a H = Bohr radius of ZnO. Theory in reference  suggests that of ZnO in Equation (2.3) is approximately Unoprostone 14 Å. Since donated electrons orbit around charged donor with the radius, the repulsion force between electrons belonging to adjacent donors could suppress the donation of additional electrons. The Coulomb repulsion force between
adjacent charged donors may also cause decrease of carrier concentration in the same manner. Thus, these repulsion forces could cause the effective field for doping around each donor. These effective fields probably limit the doping efficiency of Al atoms within a single Al2O3 layer. Alloying evaporation method According to the self-catalytic growth mechanism proposed by Dang et al. , the process completes in four major steps. Figure 2 best explains the particular growth mechanism. It can be understood as follows: (A) As soon as the temperature of the furnace reaches the melting point of the Zn powder, it starts to melt and form a large quantity of melting liquid drops of size approximately identical to those of the original solid metal particles.