Inside a high-power transistor, heat escapes through junctions between different crystals, like water through narrow locks. For aluminum and gallium nitrides, key materials in power electronics, that lock is often a thin layer of their alloy. It is added deliberately or forms on its own during crystal growth. Until now, no one knew whether it helped or hindered heat dissipation.

Physicists built a computer model based on quantum calculations and tested it for all possible alloy compositions. They found that such a layer does not improve but noticeably worsens heat transfer — by up to a factor of two. The reason is that aluminum and gallium atoms in the alloy are arranged randomly, and thermal vibrations scatter on these irregularities, like waves on a rocky shoal.

But there is good news too. If the alloy composition is changed not abruptly and not uniformly, but along a smooth S-shaped curve (first slowly, then quickly, then slowly again) the heat flow crosses the interface almost without loss. Such a transition works like an acoustic horn: sound does not reflect off a step but gently flows into another medium. This discovery gives engineers a simple recipe: to keep a powerful chip from overheating, you need to properly "smear" the interface between materials.