Impact of strain-induced cracking on the electrical performance of pseudo-vertical GaN-on-Si p–n diodes grown by selective area epitaxy

Selective-area growth (SAG) of gallium nitride (GaN)-on-silicon enables the growth of thick layers by elastically relaxing tensile stress during cooldown. However, the effects of strain-induced mechanical degradation on the performance of SAG-grown vertical devices remain poorly understood. In this work, pseudo-vertical GaN-on-Si p–n diodes were made by SAG on 200 mm Si (111) wafers to study how mesa geometry and drift-layer thickness affect performance. Devices with 9 μm-thick drift layers showed a strong dependence of specific on-resistance (Ron,sp) on mesa diameter, with 100 μm mesas showing lower Ron,sp than 200 μm ones. Structural analysis revealed greater degradation in mesa performance due to strain-induced cracking and delamination at the mesa base, disrupting conduction between the anode and the n+-GaN layer. Reducing the drift-layer thickness to 4 μm suppressed cracks and improved Ron,sp consistency. Devices without a p-GaN layer had even lower Ron,sp, indicating that the p-GaN layer and contact dominate resistance once cracks are mitigated. These findings highlight mechanical integrity as a key factor in the performance and uniformity of SAG-grown pseudo-vertical GaN-on-Si power devices.