Doping of ZnO

Further information on p-type doping of ZnO is given in other chapters of this book (2 and 7). 

Thus, to achieve p-t5q)e doping of ZnO a number of aspects have to be considered. First of all the formation of hydrogen shallow donors has to be prevented or their concentration has to be minimized. Recently it has been shown that a simple post anneal of state-of-the-art ZnO at 850 °C causes the dissociation of hydrogen shallow donors which results in a decrease of the free carrier concentration from 1x10 cm" to 6x10 cm". 

Solid-source chemical vapor deposition (SS-CVD) [131] was also used for nitrogen doping of ZnO. Zinc acetate dihydrate [Zn(CH3C00)2-2H20, solid] and ammonium acetate (CH3COONH4, solid) were used as the precursor and the nitrogen source, respectively. Samples showed p-type conductivity with a hole concentration of 9.8 x 10 cm, resistivity of 20 Q. cm, and hole mobility of 0.97 cm s . When... 

While most efforts on p-type doping of ZnO have focused on nitrogen doping with/without codopants because of its relatively shallow level, considerably fewer studies have considered other group V elements for substitutionally replacing O [98, 147, 150-154]. Only in some of these studies, inversion of the film s conductivity from n-type to p-type was observed. Even though hole concentrations above 10 cm and hole mobilities of 20 cm s have been reported, the reliability of the measurements is again questionable. 

Ryu et al. [151] employed GaAs substrates as an arsenic source for p-type doping of ZnO by PLD. In this case, a p-type ZnO layer was produced at the ZnO/GaAs interface after thermal armealing. The p-type ZnO films were grown on different substrates, ZnO, SiG, and sapphire, rather than on GaAs and As was supplied from an effusion cell in the PLD system. Thus, the postarmealing process was not deemed necessary to diffuse As into ZnO film [152, 153]. 

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