Rapid synthesis of epitaxial ZnO films from aqueous solution using microwave heating

Abstract

Rapid deposition of epitaxial ZnO films has been demonstrated with a low temperature aqueous solution technique utilizing microwave heating. X-Ray diffraction analysis of films deposited on single crystal (111) MgAl₂O₄ substrates revealed the ZnO to deposit epitaxially with an orientational relationship of ZnO [110]‖MgAl₂O₄ [2] & ZnO [010]‖MgAl₂O₄ [10]. By altering conditions of solution pH, ammonia concentration, heating rate, and hold time, the growth rate and morphology of the ZnO films can be modified. Using a pH 11, 1 mol L⁻¹ammonia growth solution, an approximately 2 micron thick continuous ZnO film can be deposited in only 5 minutes at 90 °C. Compared to similar ZnO deposition conditions using conventional heating, the use of microwave heating resulted in substantially higher nucleation and growth rates. Using an explanation based on classical nucleation theory and predicted variations in ZnO solubility with temperature, the increase in nucleation and growth rate is attributed to the high heating rates achieved with microwave heating.