Engineering Interface Composition for Passivation of HgCdTe Photodiodes

A compositionally graded surface layer has been created for the passivation of
$ Hg_1 - x Cd_x Te$
photodiodes. The graded
$ CdTe- Hg_1 - x Cd_x Te$
interface was created by deposition of CdTe and subsequent annealing. It was found that the composition gradient and width of the graded region could be tailored by adopting a suitable annealing procedure. The effect of grading on the interface electrical properties and photoelectrical properties was studied by X-ray photoelectron spectroscopy (XPS), photoconductive decay, and
$C-V$
measurements. Insulator fixed-charge density and interface-trap density could be reduced to
$3 times 10^10 hboxcm^-2$
and
$2 times 10^10 hboxcm^-2cdothboxeV^-1$
, respectively, by creating a graded interfacial composition. The interface conditions so engineered led to a low surface recombination velocity
$sim$
3000 cm/s. A direct correlation has been established between the process conditions, interfacial composition, and the electrical/photoelectrical properties of the
$ CdTe- Hg_1-x Cd_x Te$
heterostructures. The passivation layer formed by this method is shown to be suitable for the fabrication of high-performance infrared detectors.