Visible-light photodetection and interface-limited transport in Pd/n-GaP schottky diodes

A Pd/n-GaP Schottky diode was fabricated by thermal evaporation and comprehensively characterised through dark/illuminated I–V, C–V, Cheung, Norde, photovoltaic and photodetector analyses. The device exhibits stable rectifying behaviour (RR = 11.45 at ± 2 V) and low reverse saturation current (I₀ = 2.41 × 10⁻¹⁰ A), with barrier heights extracted from independent methods (I–V, Cheung, Norde, C–V) showing strong mutual consistency (Φb ≈ 0.84–0.90 eV). The high ideality factor (n > 6) and illumination-dependent barrier modulation are attributed to native-oxide-induced inhomogeneity, interface-state activation and partial Fermi-level pinning—mechanisms characteristic of wide-bandgap III–V Schottky contacts. Under 550 nm illumination (2–8 mW/cm⁻²), the diode demonstrates simultaneous photovoltaic and photodetector operation. Jsc increases linearly with illumination, while Voc decreases due to enhanced trap-assisted recombination, yielding a peak PCE of 0.031% at 4 mW cm⁻². Photodetector measurements reveal strong weak-light sensitivity, with maximum responsivity of 2.68 mAW⁻¹, detectivity up to 2.37 × 10¹⁰ Jones and EQE of 6.06%. A detectable zero-bias photocurrent confirms true self-powered behaviour. Illumination-dependent C–V analysis shows marked increases in donor concentration and reductions in Vbi and Φb, consistent with activation of interface traps. The interface-state density rises from 8.46 × 10¹⁵ to 2.15 × 10¹⁶ eV⁻¹ cm⁻² across the studied intensity range, correlating directly with the degradation of Voc, responsivity and detectivity. The findings identify Pd/n-GaP as a promising platform for low-power optoelectronic sensing and highlight clear opportunities for optimisation via interface passivation, oxide control and optical-coupling enhancement.