Defect Characterization of the SiO₂/Si Interface Using Positron Spectroscopy #worldresearchawards


Introduction

This research explores drift-assisted positron annihilation lifetime spectroscopy (PALS) applied to a p-type (100) silicon substrate within a metal–oxide–silicon (MOS) capacitor. By employing an externally applied electric field, the study demonstrates precise control over the spatial distribution of positrons prior to annihilation. This approach enables deeper insight into interface-sensitive defect characterization, particularly at the technologically critical SiO₂/Si interface, which plays a central role in modern semiconductor device reliability and performance.

Electric-Field-Controlled Positron Drift in MOS Structures

The operation of the MOS capacitor under accumulation, depletion, and inversion regimes reveals that internal electric fields significantly influence positron drift transport. Depending on the bias condition, the electric field can either drive positrons toward the SiO₂/Si interface or repel them into the silicon bulk. This behavior effectively allows the interface to act as either a diffusion barrier or a diffusion support, providing a tunable mechanism for probing spatially resolved defect distributions.

Derivation of Positron Drift-Transport Parameters

From the measured positron lifetime spectra, key drift-transport parameters were extracted, offering quantitative insight into positron mobility and trapping efficiency under non-uniform electric fields. The analysis highlights how field strength and direction alter positron annihilation characteristics, enabling a more refined interpretation of lifetime components associated with bulk silicon, oxide regions, and interface-related defects.

Impact of Non-Linear Electric Fields on Positron Trapping

The study emphasizes the role of non-linear electric field profiles inherent to MOS operation in shaping positron trapping behavior. These fields modify the effective potential landscape experienced by positrons, influencing their interaction probability with defect states. As a result, variations in lifetime components reflect not only defect type but also the electrostatic environment, underscoring the need to consider device bias conditions in positron spectroscopy analyses.

Interface Defect Asymmetry: Oxide-Side vs Silicon-Side

Comparison with previous oxide-side drift experiments on the same MOS capacitor reveals that the SiO₂/Si interface exhibits asymmetrical defect characteristics. The oxide side is dominated by void-like defects, while the silicon side is characterized by vacancy-like Pb centers. This duality demonstrates that the interface cannot be treated as a uniform defect region and highlights the strength of drift-assisted PALS in resolving side-specific defect populations.

Charge State Modulation of Pb Centers

The positron data further suggest that the charge state of Pb centers varies with the operational mode of the MOS device. Changes in accumulation, depletion, and inversion conditions alter the electrostatic charge environment, which in turn affects positron trapping efficiency at these vacancy-like defects. This finding provides valuable insight into the dynamic nature of interface defects and their bias-dependent behavior, with implications for semiconductor device diagnostics and optimization.

Hashtags

#worldresearchawards #positronspectroscopy #semiconductorresearch #moscapacitor #siliconinterface #defectengineering #materialsphysics #nanotechnology #advancedcharacterization #solidstatephysics #microelectronics #interfacedefects #appliedphysics #researchinnovation #scientificdiscovery #devicephysics #vacancydefects #oxideinterfaces #palsresearch

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