Discerning the piezoelectric quality of CdS and ZnO crystals and films from etch properties

Several tests have been used over the years to determine the quality of piezoelectric crystals and films. Chemical etching, (destructive to a portion of the crystal or film), reveals information which can be related to its piezoelectric properties. Acid etching of CdS and ZnO crystals and films is highly anisotropic depending upon whether the acid attacks the cadmium-zinc face or the sulfide-oxide face, or laterally to the c-axis. The etch pit density per unit area is a useful parameter for both crystals and films and can be used for comparison with piezoelectric related properties. By controlling the percentage of the acid etchant in water, direct comparisons can be made of film properties under different deposition conditions. This paper presents the results of etching studies on CdS and ZnO crystals and sputtered thin-films with comparisons to their crystalline, piezoelectric, and device properties.