Gallium (Ga, atomic number 31) and nitrogen (N, 7) combine into a semiconductor material – gallium nitride (GaN) - like Silicon (Si, 14). GaN is a ‘wide band-gap’ material because it offers an electron band-gap that is 3x larger than silicon, which means it can handle large electric fields with dramatically smaller chips.
With much smaller transistors and shorter current paths, ultra-low resistance & capacitance is achieved, while enabling up to 100x faster switching speeds. Low resistance and low capacitance translate to higher charging efficiencies, so more of the power is delivered to the battery, charging it faster instead of burning up that energy as heat which warms the charger in your hand.
Faster switching means that the charger can deliver more power to the battery with a dramatically smaller size & weight as the energy-storing passive components can shrink dramatically as they store much less energy in each switching cycle.