We studied the electrical properties of Cd0.9Zn0.1Te:In (CZT) single crystals with [In]=3*1015 at/cm3 at its high-temperature point-defect (PD) equilibrium state under a Cd overpressure (PCd). We detailed the influence of thermal treatment and the deviation of stoichiometry on the electron concentration, observing unexpectedly high conductivity and an increase in free-electron density ( ~ 1.5-2 orders of magnitude) when annealing the sample at 770 K under a Cd vapor pressure (0.01 atm.). Prolonged exposure of the samples under these conditions lowered the electron density by two approximately orders-of-magnitude until it approached the intrinsic value. The electron mobility after such treatment increased to CZT's maximal values at ~ 460 K (650-700 cm2/(V*s)). Therefore, such annealing can be effective in assuring high-resistive CZT detectors after crystal growth, or by special treatment, thereby eliminating the inclusions. We analyzed these data in the framework of Kröger's theory of quasi-chemical reactions, and compared the findings to those obtained for undoped CdTe.