Thin films of Zn-compounds grown in a chemical bath have been studied by Elastic Recoil Detection Analysis (ERDA). The bath contained zinc acetate, thiourea and complexing agents such as ammonia and hydrazine. Large amounts of hydrogen and oxygen are detected within all samples. A strong effect of the pH of the solution is revealed: At high pH (>11.5) mainly ZnS growth takes place, while at lower pH Zn(OH)2 is the dominant product. Hence the pH of the solution can be used to adjust the film stoichiometry. Deposition of Zn-compound films is possible without ammonia in the solution while presence of hydroxide ions and hydrazine species is necessary. It is proposed that film formation takes place via a complex combining hydrazine and hydroxide ligands.