Determination of Lateral Extension of Extrinsic Photon Recycling in p-GaN by Using Transmission-Line-Model Patterns Formed with GaN p–n Junction Epitaxial Layers

The effect of extrinsic photon recycling (EPR) in p-type gallium nitride (p-GaN), namely, increased ionization ratio (R) of magnesium acceptors owing to radiative recombination, was quantitatively investigated. The lateral extension (L) of EPR was determined by using transmission-line-model (TLM) patterns, formed with GaN p–n junction epitaxial layers on free-standing substrates, as well as by using device simulation. With increasing vertical current (I V) of the p–n junction, lateral current (I L) in the p-GaN layer (magnesium concentration: N Mg = 5×1017 cm-3) was found to increase within L of 10 µm from the edge of the TLM electrodes; the measured I L corresponded to a large R, namely, 30%. This lateral extension will contribute to reducing base resistance and enhancing conductivity modulation of GaN bipolar power-switching devices for power-electronics applications.