High-voltage polarization-induced vertical heterostructure p-n junction diodes on bulk GaN substrates

Summary form only given. In this work, RF plasma-Molecular Beam Epitaxy (MBE) grown polarization-induced AlGaN (Pi-AlGaN) p-n vertical diodes are demonstrated on Ammono single-crystal bulk GaN substrates. A highest breakdown voltage (BV) of 120 V has been achieved on a Pi-AlGaN p-n diode with a 400-nm thick ndrift region, corresponding to an Ebr of 3.3 MV/cm. The diode structures are sketched in Figure 1. As shown in Figure 1(b), the n-region of Pi-AlGaN p-n diodes consists of a 200-nm-thick nGaN layer with doping ND~1.8x1016 cm-3, followed by a 200-nm-thick n-type linearly graded AlGaN layer with the Al composition graded up from 2% to 14.5%. The effective polarization-induced doping is this layer is measured to be ND,eff~9.1x1016 cm-3. Then a 200-nm-thick linear p-type linear graded AlGaN layer with the opposite Al composition gradient from 14.5% to 2% forms the p-region of the p-n junction. As a control sample, an impurity-doped GaN p-n diode is also realized (Fig 1a) with the same thickness of nregion, but using a Si-doped GaN layer with ND~1.7x1017 cm-3. A 100-nm-thick Mg-doped GaN layer forms the p-region. P-regions of both Pi-AlGaN p-n diodes and impurity-doped GaN p-n diodes have the same Mg concentration of NA~2x1019 cm-3. Since the NA/ND~100, the depletion region is mainly in the nside for all junctions. The doping concentrations in the n-region are verified by C-V measurements (not shown). The calculated energy band diagram of Pi-AlGaN p-n diodes at zero bias is shown in Figure 2. X-ray diffraction (not shown) and transmission electron microscopy (TEM, figure 3) verify the successful realization of the layer structures and thicknesses.