A homogeneous and reproducible large-area, low dispersion GaN-on-Si normally-off 600 V transistor technology using selective GaN etching

The epitaxial structures are grown by metal-organic chemical vapor deposition on 4-inch Si(lll) substrates. First, a graded AlGaN buffer is deposited to mitigate lattice and thermal coefficient mismatches. Second, a thick GaN layer with an AIN interlayer is grown, followed by the AIGaN/GaN heterojunction. The structure is capped by a p-doped GaN layer. Mg is used as acceptor with a concentration around 3-4×10
¹⁹
cm
^-3
according to secondary ion mass spectrometry. The structural properties of the samples are investigated using high-resolution X-ray diffraction, see Figure 1. The thickness (approx. 15 nm) and composition (around 20% Aluminum) of the AlGaN barrier are well within the parameter space to obtain normally-off devices [1]. The p-doped GaN cap has a thickness around 53 nm. A two-step dry-etch process based on a Cl
₂
/N
₂
/O
₂
plasma [2] has been adapted in order to remove the p-doped GaN cap, see Figure 2. The process is characterized by a large process window in order to provide high reproducibility.