Modulation of Surface Barrier in AlGaN/GaN Heterostructures

Large modulation of the surface barrier height in AlGaN/GaN heterostructures has been observed under different perturbations. Exposure to UV illumination results in large reduction of the surface barrier height. This is caused by the screening of the built-in electric field in the AlGaN barrier layer by the photogenerated carriers, lowering the surface barrier height. After the UV illumination is switched off, the reduced surface barrier returns very slowly to the equilibrium value. The recovery transient is modeled by thermionic emission of electrons from the quantum well, which recombine with the holes trapped at the surface. On the other hand, after applying high negative bias on the gate and positive bias on the drain of a transistor, large increase in surface barrier is observed near the gate. Such an increase in surface barrier reduces the 2DEG at the interface. It is proposed that under high bias stress, electrons tunnel from the gate and get trapped at the surface states near the gate increasing the barrier height.