Selective Galvanostatic Formation of Polyphosphazene Patterns for Chemical Passivation of n -InP Surfaces

Abstract

InP is among the most widely adopted direct-bandgap semiconductor materials for current and next-generation of optoelectronic devices. In this paper, highly doped n-InP substrates are employed as electrode materials for surface passivation purposes. The passivation is achieved via anodic treatment in a liquid ammonia (NH3 Liq) bath at −55 °C under a constant current density. As a main result, we demonstrated that selective passivation was possible on a patterned InP substrate (using SiO2 lines deposited under a clean room conditions as masks). X-ray Photoelectron Spectroscopy mapping confirms that both bare and exposed InP regions of SiO2-patterned surfaces are uniformly coated with a thin homogeneous polyphosphazene (PPP) layer. In addition, the electrochemical process provides a very high degree of InP surface coverage. The custom-developed setup enables passivation of large InP samples (nearly 4 cm2). The as-formed PPP film locally protects InP from air oxidation and remains chemically stable even after a wet chemical treatment with hydrofluoric acid (HF). This stability allows for the selective removal of the SiO2 mask, paving the way for the fabrication of PPP/InP surface networks. These results demonstrate the spatially selective formation of chemically passivating PPP layers on InP surfaces. Building on our previous studies, which established that PPP passivation preserves the electronic and optoelectronic properties of InP, this selective approach enables patterned surface engineering for advanced InP-based devices, while the impact on device performance remains to be investigated.