Experimental study of the kinetically-limited decomposition of ZnGeAs2 and its role in determining optimal conditions for thin film growth

To understand the thermochemistry and determine the rate limiting steps of ZnGeAs2 thin-film synthesis, experiments were performed to measure the (a) thermal decomposition rate and (b) elemental composition and deposition rate of films produced with pulsed laser deposition (PLD). The decomposition rate is kinetically limited with an activation energy of 1.08±0.05 eV and an evaporation coefficient of ∼10−3. We show that ZnGeAs2 thin film synthesis is a metastable process with the kinetically-limited decomposition rate playing a dominant role at the elevated temperatures needed to attain epitaxy. Our conclusions are in contrast to those of earlier reports that assumed the growth rate is limited by desorption and the resulting low reactant sticking coefficient. The thermochemical analysis presented here can be used to predict optimal conditions for ZnGeAs2 film physical vapor deposition and thermal processing.

► Temperature of ZnGeAs2 growth is limited by both desorption and decomposition. ► It has large kinetic barrier to decomposition with evaporation coefficient of 10−3. ► Decomposition rate is kinetically limited with an activation energy of 1.08±0.05 eV. ► High quality ZnGeAs2 films can be grown in the metastable regime.