Main Objectives

Research package WP2 focuses on the development of advanced vertical power diodes in a GaN-on-GaN architecture. The use of native, highly crystalline gallium nitride substrates dramatically reduces dislocation density, which is critical for attaining ultra-high breakdown voltages and minimizing reverse leakage currents.

The scope of work encompasses:

• Optimizing epitaxial growth of thick, ultra-pure drift layers using MOVPE and HVPE techniques.
• Precise acceptor doping (Mg) and dopant activation via Ultra-High Pressure Annealing (UHPA).
• Establishing reproducible fabrication processes for p- and n-type ohmic and Schottky barrier contacts.
• Designing and fabricating edge-termination structures and JBS (Junction Barrier Schottky) diodes.

Investigated Device Architectures

Within the package, three primary diode configurations sharing a common n-type substrate and drift layer are developed and benchmarked:

1. Schottky Barrier Diodes (SBD): providing ultra-fast switching speeds and low forward voltage drop.
2. p-n Junction Diodes: offering superior high-voltage reverse blocking capabilities.
3. p-i-n Diodes: optimized for tailored electric field management within the intrinsic region.

Fig. 1. Architecture of test structures: Schottky, p-n, and p-i-n diodes sharing a common native substrate and drift layer.

Results and Progress

• Characterization of Am-GaN Substrates: A comprehensive electrical characterization suite was performed on 2-inch ammonothermal substrates (Hg-probe C-V, microwave resonators, SiPDR resistivity mapping). A clear correlation between decreasing resistivity and increasing net donor concentration ($N_D - N_A$) was confirmed.
• Fabrication of Test Structures: MOVPE epitaxy on Am-GaN substrates and HVPE on dedicated carriers were successfully executed, producing series of test diode structures for transport parameter calibration.
• Passivation Dielectric Evaluation: Nine dielectric variations deposited via PECVD and ALD were evaluated for dielectric breakdown strength. PECVD-grown SiN layers exhibited the highest breakdown voltages (53–89 V) and were selected for uniformity validation.

Fig. 2. Resistivity of Am-GaN substrates as a function of net donor concentration ($N_D - N_A$), measured by SiPDR and Hg-probe C-V at 295 K.

Upcoming Milestones

• Precision dicing of 2-inch substrates into $11 \times 11\text{ mm}$ working dies from qualified uniform zones.
• Implementation of ion implantation and dopant activation runs in high-pressure UHPA reactors.
• Experimental evaluation of dynamic and high-temperature performance metrics of prototype vertical power diodes.