Hydrogen (H) is a ubiquitous and electrically active impurity in semiconductors, playing a decisive role in shaping their optical and electrical properties, particularly in wide band-gap materials such as gallium nitride (GaN). Although postgrowth activation dissociates Mg-N-H complexes, a substantial concentration of residual H remains in $p$-GaN, and its dominant atomic configurations and dynamic behavior under device-relevant operating conditions remain poorly understood. Here, we directly identify the nitrogen-vacancy-hydrogen $\left(V_{\mathrm{N}}\text{-H}\right)$ complex in $p$-GaN by combining polarization- and angle-resolved Fourier-transform infrared spectroscopy with first-principles phonon calculations. We observe a localized vibrational mode at $1727\mathrm{c}{\mathrm{m}}^{-1}$ that emerges under forward electrical bias and elevated temperature. The mode exhibits a nearly isotropic in-plane polarization response along with a pronounced out-of-plane component. The key experimental vibrational characteristics, including peak position, polarization dependence, and angle variation, are in good agreement with the first-principles calculations, providing a consistent vibrational fingerprint that supports the assignment of the mode to a $V_{\mathrm{N}}\text{-H}$ configuration. Building on this identification, we further propose a physically grounded kinetic picture in which electron injection under forward bias enables H released from the GaN lattice to participate in $V_{\mathrm{N}}\text{-H}$ formation. These findings resolve a long-standing question regarding residual H in $p$-GaN and offer critical insight into both H-related defect physics and device degradation mechanisms, with broad implications for the reliability of GaN-based electronic and optoelectronic devices.

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• Defects
• Hydrogen bonds
• Impurities
• Phonons
• Point defects
• III-V semiconductors
• Density functional calculations
• Fourier transform infrared spectroscopy