Effect of growth ambient on the structure and properties of MgxZn1-xO thin films prepared by radio-frequency magnetron sputtering

Mg(x)Zn(1-x)O thin films were grown by the radio-frequency magnetron sputtering technique in Ar + N(2) and O(2) + N(2) ambient with different nitrogen partial pressure ratios on quartz substrates at 773 K. The correlations between the growth ambient and the resultant films properties were discussed. It is found that Mg concentration, structure and band gap of the MgZnO film can be tuned by increasing the nitrogen partial pressure ratio of the Ar + N(2) ambient, but cannot be tailored by changing the nitrogen partial pressure ratio of the O(2) + N(2) ambient. X-ray diffraction shows that the Mg(x)Zn(1-x)O films grown in the Ar + N(2) ambient consist of wurtzite phase at the nitrogen partial pressure ratios from 0% to 50%, a mixture of wurtzite and cubic phases at the ratios of 78-83%, and a cubic phase at 100%, whereas such structure transformation did not exist in the Mg(x)Zn(1-x)O film deposited in the O(2) + N(2) ambient by changing the nitrogen partial pressure ratio. The Mg concentration increases linearly with the increasing nitrogen partial pressure ratio of Ar + N(2), but does not vary with the increasing nitrogen partial pressure ratio of O(2) + N(2). The band gap increases linearly from 3.64 to 4.02 eV for the wurtzite Mg(x)Zn(1-x)O deposited in the Ar + N(2) ambient as nitrogen partial pressure ratio increases from 0% to 50%, but the band gap of the Mg(x)Zn(1-x)O film deposited in the O(2) + N(2) ambient keeps a constant of 3.63 eV with oxygen gas and reaches 6.30 eV abruptly in pure nitrogen ambient (without oxygen gas). The Mg(x)Zn(1-x)O films, which are grown in the Ar + N(2) and O(2) + N(2) ambient at nitrogen partial pressure ratio from 50% to 100% and 83% to 100%, respectively, show p-type conduction after annealing.