What can be a possible explanation for observing increasing oxygen vacancies in a metal oxide film (eg: Cu2O) deposited using ALD or CVD when the deposition temperature is increased?
As I understand, greater reactivity with water at higher deposition temperatures should result in fewer oxygen vacancies.
Thank you.
If all the experimental conditions remain the same and the only variable is temperature, then the increased defect concentration (assuming Schottky type) with increase in the temperature is explained by the relation:
ns = N exp(-Es/2kBT), where ns = concentration of oxygen vacancy, N = possible oxygen sites per unit volume, Es = defect formation energy, kB = Boltzmann constant, T = temperature.
It is well known that presence of moisture (water vapor) or higher oxygen partial pressure will decrease the oxygen vacancies.
Perhaps, with the example given, the oxidation state of the Copper varies.
CuO, CuO2, and Cu2O3 should be considered.
Not only Cu other metals also, it may due to thermal to binding energy unbalance so vacancy may occur. Some cases Si also incorporates
Agree with Krishnan Raja and Bablu K. Ghos. Lattice oxygen balance (and concentration of oxygen vacancies) depends on temperature and oxygen partial pressure over the surface. This is by the way one of the working mechanisms for oxygen sensors production. To decrease oxygen vacancies at certain temperature you may increase oxygen partial pressure at ALD (CVD) process.
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