We show evidence that tunnel junctions (TJs) in GaN grown by metal-organic vapor phase epitaxy are dominated by trap-assisted (Poole-Frenkel) tunneling. This stems from observations of the careful optimized doping for the TJs. Especially the p$^{++}$ and the n$^{++}$ layers are far from ideal. The n$^{++}$ layer induces 3D growth, which can be seen by a rising oxygen signal in Secondary Ions Mass Spectroscopy (SIMS). Furthermore, Mg segregation observed by SIMS indicates a depletion region of more than 10 nm. Still, we could realize TJ based LEDs with a low penalty voltage of 1.1 V and a specific differential resistance of about 10$^{-2}$ $\Omega$.cm$^2$ at 20 mA without using an InGaN interlayer.

中文翻译：

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MOVPE 生长的基于 np-n 隧道结的简单 LED 的局限性

我们证明了通过金属有机气相外延生长的 GaN 中的隧道结 (TJ) 受陷阱辅助 (Poole-Frenkel) 隧道效应支配。这源于对 TJ 的仔细优化掺杂的观察。特别是 p$^{++}$ 和 n$^{++}$ 层远非理想。n$^{++}$ 层诱导 3D 生长，这可以通过二次离子质谱 (SIMS) 中上升的氧信号看到。此外，通过 SIMS 观察到的 Mg 偏析表明耗尽区超过 10 nm。尽管如此，我们仍然可以实现基于 TJ 的 LED，其具有 1.1 V 的低惩罚电压和约 10$^{-2}$ $\Omega$.cm$^2$ 在 20 mA 时的特定差分电阻，而无需使用 InGaN 中间层。