Passivation of HgCdTe with CdS thin films: Correlation of device characteristics with surface spectroscopy

We present results on the passivation of HgCdTe with thin films of CdS grown anodically from nonaqueous polysulfide electrolytes. Electrochemical measurements have been carried out to develop an understanding of the film growth. Capacitance-voltage measurements on metal-insulator-semiconductor (MIS) device structures that incorporated a ZnS cap and Pd gate metal over the CdS are used to compare electrical properties of the interface with Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) depth profiles. The surface spectroscopies were carried out using a sample temperature of 170 K, which allowed us to easily observe Hg by Auger electron spectroscopy. XPS and AES results show that Hg and Te are partially incorporated into the CdS layer, as sulfides that did not completely dissolve during the film growth. The interdiffusion of Zn into the interface resulted in large hysteresis in the C-V data. By minimizing the Zn interdiffusion, MIS devices with low hysteresis (∼0.25 V) that are bake stable to ∼95 °C have been fabricated and analyzed.