Tunnel Junctions with a Doped ( In,Ga)N Quantum Well for Vertical Integration of III -Nitride Optoelectronic Devices

Properties of tunnel junctions (TJs) grown by plasma-assisted molecular beam epitaxy are investigated. Examined TJs consist of a ($\mathrm{In},\mathrm{Ga})\mathrm{N}$ quantum well (QW) sandwiched between ${\mathrm{In}}_{0.02}{\mathrm{Ga}}_{0.98}\mathrm{N}$ barriers. The influence of piezoelectric polarization, doping, and width of a TJ QW on resistivity of TJs is studied. A decrease of TJ resistivity is observed for high doping and high ($\mathrm{In},\mathrm{Ga})\mathrm{N}$ composition. Additionally, the crystal quality of TJs as a function of magnesium and silicon doping in a ($\mathrm{In},\mathrm{Ga})\mathrm{N}$ QW is discussed. Generation of defects in highly doped layers is observed in transmission electron microscopy and by defect selective etching. High doping leads to deterioration of surface morphology, which is corroborated by atomic force microscopy imaging. TJs with low resistance and high crystalline quality, without formation of structural defects, are demonstrated. A theoretical model for calculation of tunneling currents is proposed based on Kane tunneling theory, which considers a realistic electric field distribution in a TJ. A good agreement with the experimental data is obtained. The model is used to predict electrical parameters in a wide range of ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ compositions (x = 0--0.40), doping (${n}_{\mathrm{Mg},\mathrm{Si}}={10}^{17}\ensuremath{-}5\ifmmode\times\else\texttimes\fi{}{10}^{21}\phantom{\rule{0.25em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$), and TJ QW width (d = 2 -- 12 nm).