Role of hole trapping in the unintentionally doped GaN layer in suppressing the two-dimensional electron gas degradation in AlGaN/GaN heterostructures on Si

We identify the spatially resolved trapping mechanism and clarify the role of the unintentionally doped (UID) GaN layer in suppressing the two-dimensional electron gas (2DEG) degradation in AlGaN/GaN heterostructures on Si. The trapping mechanism is characterized by measuring C-V dispersion after three different configurations of bias stress: high drain-substrate voltage stress, high drain-gate voltage stress and combined stress (with both high drain-gate voltage and drain-substrate voltage stress). Under the combined stress, the 2DEG degradation is the overall effect of electron trapping and hole trapping. By comparing samples with and without the UID GaN layer, we confirm the role of the UID layer in suppressing the 2DEG degradation by hole trapping in that layer. The electron and hole trap states are further identified by reversed vertical stress and current transient measurements. The electron trap with an activation energy of 0.53 eV and the hole trap with an activation energy of 0.81 eV are distinguished.