Gibbs Free Energy Assisted Passivation Layers

Abstract

Reduction of surface leakage is a major challenge in most photodetectors that requires the elimination of surface oxides on etched mesas during passivation. Engineering the passivation requires close attention to chemical reactions that take place at the interface during the process. In particular, removal of surface oxides may be controlled via Gibbs reactivity. We have compared electrical performance of type-II superlattice photodetectors, designed for MWIR operation, passivated by different passivation techniques. We have used ALD deposited Al2O3, HfO2, TiO2, ZnO, PECVD deposited SiO2, Si3N4 and sulphur containing octadecanethiol (ODT) self-assembled monolayers (SAM) passivation layers on InAs/GaSb p-i-n superlattice photodetectors with cutoff wavelength at 5.1 mu m. In this work, we have compared the result of different passivation techniques which are done under same conditions, same epitaxial structure and same fabrication processes. We have found that ALD deposited passivation is directly related to the Gibbs free energy of the passivation material. Gibbs free energies of the passivation layer can directly be compared with native surface oxides to check the effectiveness of the passivation layer before the experimental study.