A physical model for the reverse leakage current in (In,Ga)N/GaN light-emitting diodes based on nanowires

TL;DR

This paper presents a physical model explaining the high reverse leakage current in (In,Ga)N/GaN nanowire LEDs, based on deep level traps and charge transport mechanisms, validated by experimental measurements and applicable to planar LEDs.

Contribution

A new quantitative physical model for reverse leakage current in nanowire LEDs, incorporating trap states and conduction mechanisms, with validation against experimental data.

Findings

Identification of two deep electron traps in the depletion region.

Development of a comprehensive model combining hopping and emission processes.

Model applicability to planar GaN-based LEDs and leakage current reduction strategies.

Abstract

We investigated the origin of the high reverse leakage current in light emitting diodes (LEDs) based on (In,Ga)N/GaN nanowire (NW) ensembles grown by molecular beam epitaxy on Si substrates. To this end, capacitance deep level transient spectroscopy (DLTS) and temperature-dependent current-voltage (I-V) measurements were performed on a fully processed NW-LED. The DLTS measurements reveal the presence of two distinct electron traps with high concentrations in the depletion region of the p-i-n junction. These band gap states are located at energies of $570\pm20$ and $840\pm30$ meV below the conduction band minimum. The physical origin of these deep level states is discussed. The temperature-dependent I-V characteristics, acquired between 83 and 403 K, show that different conduction mechanisms cause the observed leakage current. On the basis of all these results, we developed a quantitative physical model for charge transport in the reverse bias regime. By taking into account the mutual interaction of variable range hopping and electron emission from Coulombic trap states, with the latter being described by phonon-assisted tunnelling and the Poole-Frenkel effect, we can model the experimental I-V curves in the entire range of temperatures with a consistent set of parameters. Our model should be applicable to planar GaN-based LEDs as well. Furthermore, possible approaches to decrease the leakage current in NW-LEDs are proposed.