Superjunction Power Transistors With Interface Charges: A Case Study for GaN

Abstract

Recent progress in p-GaN trench-filling epitaxy has shown promise for the demonstration of GaN superjunction (SJ) devices. However, the presence of n-type interface charges at the regrowth interfaces has been widely observed. These interface charges pose great challenges to the design and performance evaluation of SJ devices. This work presents an analytical model for SJ devices with interface charges for the first time. In our model, two approaches are proposed to compensate interface charges, by the modulation of the SJ doping or the SJ geometry. Based on our model, an analytical study is conducted for GaN SJ transistors, revealing the design windows and optimal values of doping concentration and pillar width as a function of interface charge density. Finally, TCAD simulation is performed for vertical GaN SJ transistors, which validated our analytical model. Our results show that, with optimal designs, interface charges would only induce small degradation in the performance of GaN SJ devices. However, with the increased interface charge density, the design windows for pillar width and doping concentration become increasingly narrow and the upper limit in the pillar width window reduces quickly. When the interface charge density exceeds ∼3×10 12 cm −2 , the design window of pillar width completely falls into the sub-micron range, indicating significant difficulties in fabrication. Vertical GaN SJ transistors with interface charges retain great advantages over conventional GaN power transistors, but have narrower design windows and require different design rules compared to ideal GaN SJ devices.

Power device breakdown mechanism and characterization: review and perspective

“…Heterogeneous p-n junctions have been recently applied to a few WBG/UWBG systems to address the challenges of forming native p-n junctions 10,109) or forming them in selective areas. [109][110][111] High-performance devices have been demonstrated on the p-NiO/n-GaN junction, 45,47,112,113) p-NiO/n-Ga 2 O 3 junction, [114][115][116][117][118] p-GaN/n-Ga 2 O 3 junction, 119,120) p-diamond/n-GaN junction, 121,122) and p-diamond/ n-Ga 2 O 3 junction. 123) With various band alignments and carrier transport mechanisms, it is still unknown if heterogeneous p-n junctions can enable the avalanche capability.…”

(Invited) Multi-Channel AlGaN/GaN Power Rectifiers: Breakthrough Performance up to 10 kV

“…Superjunction is one of the most successful concepts in the history of power device development, which relies on alternative n-and p-doped pillars and can break the theoretical trade-off between RON and BV of 1-D drift regions (21). In GaN, the vertical superjunction like that in Si and SiC has not been experimentally demonstrated (22,23). An alternative superjunction in lateral GaN relying on the natural balance in polarization charges, which is referred to as "polarization superjunction" or "natural superjunction", has been experimentally demonstrated on single-or double-channels (10,24).…”

(Invited) A Path Toward Vertical GaN Superjunction Devices

“…Many efforts were taken to develop analytical models for Si (11,26), and SiC (27) SJ devices. Similar efforts are ongoing to develop a model for III-Nitridebased SJ devices (28)(29)(30)(31)(32)(33)(34)(35). Amongst those reports, only a few present a model for the GaN SJ, and those models are based on complicated infinite series to solve the electric field, which require substantial computation and time.…”