Investigation of Au–CdZnTe contacts using photovoltaic measurement

It is well known that a pure Au–CdZnTe contact will produce a Schottky barrier of height 0.7–0.8 eV depending on the Zn concentration. However, the actual barrier height in detector grade material has been measured to be around 0.9 eV. We have developed a model that explains the additional 0.2 eV barrier in terms of Au diffusion between the contact and the intrinsic CdZnTe bulk material. In this work, we have also analysed this contact structure to provide additional validation of our contact model. In this context, we operated the crystal in photovoltaic mode with illumination by a sub-bandgap (850 nm) IR laser point beam through the contact region. The photogenerated potential was measured using a constant current supply to null the photocurrent, and the corresponding potential across the current source was recorded by a digital voltmeter. By illuminating at varying depths into the crystal and with carefully controlled light intensities, we have produced further evidence for the lightly doped region just below the metal contact that is required by our model.