Effects of Drift Layer Thicknesses in Reverse Conduction Mechanism on Vertical GaN-on-GaN SBDs grown by MOCVD

Effect of drift layer thicknesses (DLT) (2, 15 and $30 \mu m)$ in reverse current conduction mechanisms of vertical GaN-on-GaN Schottky Barrier Diodes grown MOCVD has been investigated for the first time. The conduction mechanism is changing from thermionic field emission (TFE) to thermionic emission (TE) when the DLT of GaN increases. The SBDs with DLT of $2 \mu m$ and $30 \mu m$ exhibit TFE through PooleFrenkel emission and TE, respectively. However, the SBDs with DLT of $15 \mu m$ exhibit both TFE and TE. Activation energy $(E_{a})$ of traps was also calculated to be 0.69 eV for $2 \mu m$, 0.38 for $15 \mu m$ and 0.4 eV for $30 \mu m$ respectively. $E_{a}$ of 0.69 eV and 0.4 eV could be associated with screw threading dislocations and the presence of Mg in the grown drift layer, respectively.

Introduction

GaN is a promising material for particle detection on virtue of its high displacement energy (20 eV), which is twice of GaAs and other well-known semiconductors [1]. To enhance the sensitivity and resolution of the radiation detector, low reverse leakage current density based SBDs are required [2]. Researchers have realized low by the usage of reduced Threading Dislocation Density (TDD) grown free-standing GaN by HVPE for vertical GaNon-GaN SBDs. Recently we have demonstrated decrease of with the increase of Drift Layer Thickness (DLT) in vertical GaN-on-GaN SBDs [3]. So far, most of the researchers have reported Thermionic Field Emission (TFE) from vertical GaN SBDs both without drift layer [4] and with DLT of [5]. No reports have studied the effects of DLT in the reverse leakage current mechanisms of vertical GaN-on-GaN SBDs. In this work, we have observed two different current conduction mechanisms namely TFE through Poole-Frenkel (PF) and Thermionic Emission (TE), by measuring Current-VoltageTemperature (I-V-T) characteristics of the fabricated vertical GaN-on-GaN SBDs with different DLT. In addition, we have also discussed the extracted activation energies from the I-V-T measurements along with the effect of DLT on conduction mechanism.