Equilibrium compositon in II-VI telluride MOCVD systems

摘要

Thermodynamic calculations, or comptuer simulation of the equilibrium compostion, offer an excellent possibility to reduce drastically the elaborte trial-and-error experimental efforts of finding the optimal prepration conditons for MOCVD processes (temeprature T, pressure P initial compostion of the vapors X), to limit them only to the P-T-X field of existence of the solid to be preapred and an acceptable yield of the product. In this communication equilibrium composiotn was investigaed for MOCVD processes of CdTe, ZnTe, HgTe and slid solutions Cd_xZn_1-xTe and Hg_xCd_1-xTe. A number of volatile organometallic compounds have been used as precureors for MICVD growth. These are deimethylcadmium (CH_3)_2 Cd, DMCd; diethylizinc (C_2H_5)_2Zn, DEZn; diisopropylzinc [CH(CH_3)]_2An, DiPZn; diethyltellurium (C_2H_5)_2 Te, DETe; diisopropyltellium [CH(CH_3)_2Te, DiPTe; methylallytellurium CH_3TeCH_2CHCH_2, MATe. A choice of the particulr combinaiton of the precursors largely depends on the desired compostion of the film to kbe prepared, especially in case of solid soltuions Cd_xZn_1xTe and Hg_xCd_1-xTe where the avapor pressure of the precurors is instrumental of the compostion of the vapor in the reaction zone and, ultimately, for the compostion x of the solid solution. Equilibrium compsotion for II-VI telluride MOCVD systems was investigated at temepratures up to 873 K in hydrogen and inert gas atmospheres at pressures up to 1 atm. P-T--X regions of existence were outlined for each of the five materials.