Design of I2-II-IV-VI4 Semiconductors through Element Substitution: The Thermodynamic Stability Limit and Chemical Trend

Through element substitution in Cu2ZnSnS4, a class of kesterite-structured I-2-II-IV-VI4 semiconductors can be designed as novel functional materials. Using the first-principles calculations, we show that this element-substitution design is thermodynamically limited, that is, although I-2-II-IV-VI4 with I = Cu, Ag II = Zn, Cd, Hg, IV = Si, Ge, Sn, and VI = S, Se, Te are stable quaternary compounds, those with II = Mg, Ca, Sr, Ba, IV =Ti, Zr, Hf, and VI = 0 are unstable against the phase-separation into the competing binary and ternary compounds. Three main phase-separation pathways are revealed. In general, we show that if the secondary II-VI or I-2-IV-VI3 phases prefer to have nontetrahedral structures, then the I-2-II-IV-VI4 semiconductors tend to phase separate. This finding can be used as a guideline for future design of new quaternary semiconductors.