Predeposition ultraviolet treatment for adhesion improvement of thin films on mercury cadmium telluride

Poor film adhesion to mercury cadmium telluride is a problem of general concern because of the low film deposition temperatures (<90 °C) necessary for this damage susceptible substrate material. Aluminum nitride is a wide band gap material with potential as a high quality dielectric which can be grown at room temperature for metal–insulator–semiconductor structures. Adhesion problems with aluminum nitride layers have been overcome by UV irradiation of the mercury cadmium telluride substrate prior to film growth. Chemical modification of the substrates due to the UV treatment was examined by x-ray photoelectron spectroscopy and secondary ion mass spectroscopy, which show that exposure to UV radiation from a mercury vapor lamp results in a reduction of weakly bound impurity absorbate species at the mercury cadmium telluride surface, particularly hydrogen and carbon (probably present as hydrocarbons). The improved film adhesion is therefore attributed to the desorption of these species by the ultraviolet light and the subsequent formation of high energy substrate–film bonds. Some change of surface stoichiometry compared to the bulk was also observed after the UV treatment, however this is shown not to adversely affect the electrical properties of the mercury cadmium telluride surface. Fixed interface charge densities of +2×1011 cm−2 and slow interface state densities of 4×1010 cm−2 were obtained at 100 K for aluminum nitiride/mercury cadmium telluride metal–insulator–semiconductor structures which had undergone the treatment.