In this thesis, the substitutional sites of $Mn^{2+}$, $Zn^{2+}$,and $Cd^{2+}$, ions in the $AgGaS_2$ single crystals were studied. The doped $AgGaS_2$ single crystals were synthesized by melt growth method and chemical transport reaction. The increase in the lattice constants of the Mn-doped polycrystals indicates that Mn substitute Ga sites in $AgGaS_2$, but the reduce in Cd-doped polycrystals's lattice constants shows Cd replace Ag sites. The ones with 0.68 mole % Zn exhibit nearly no change within the experimental error range. The $AgGaS_2$ single crystal of Mn doped one by nominally 1 mole % has the trend of increasing in $A_1$ Raman mode about $1.5 cm^{-1}$, but this value is cosiderably smaller than that of single crystal doped by the same mole % Co. It indicates Mn ions substitute Ga site. 0.68 mole % Zn doped single crystal has no shift in the $A_1$ raman mode. It shows Zn substitute Ga site in the crystal. The Raman modes of Cd doped crystals shift to high frequency about $0.5~2 cm^{-1}$. It denotes that Cd ions substitutes Ag site. If Cd substituted Ga site, $A_1$ mode would shift to lower frequency. X ray diffraction results agree with the Raman result.
