1.1 kV vertical p-i-n GaN-on-sapphire diodes

Abstract

Gallium nitride (GaN) has excellent material properties for power switching applications. The availability of low-defect density bulk GaN substrates has generated increased interest in vertically-structured devices [1]-[2]. By defining the electric field vertically, devices can sustain higher voltages within a smaller device footprint when compared to lateral topologies [2]. Despite record performance in vertical bulk-based devices, vertical heteroepitaxial devices remain attractive as a low-cost alternative [3]-[7]. A key design parameter is the drift layer thickness which, to first order, determines the maximum achievable breakdown voltage. For GaN-on-Si, drift layers have been limited to ~ 3 μm due to film quality issues from lattice and thermal mismatches [4], [6]. For growth on sapphire, films can be achieved. To date, drift layers ≤ 7 μm -thick and hard breakdown voltages have been reported for p-i-n GaN-on-sapphire [3], [5]. This may be due to difficulties with high-quality deep mesa etching. Recently, we reported exceptionally smooth -deep GaN etching which enables the use of thicker drift layers and simplified processing [8]. Here, vertical p-i-n GaN-on-sapphire diodes with a 10 μm -thick drift layer are demonstrated with 1.1 kV soft breakdown (defined at 0.1 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) and irreversible hard breakdown . These results are, to our knowledge, the highest breakdown voltage reported for GaN diodes on foreign substrates and were achieved without edge termination techniques due to our high-quality mesa isolation etch.