Identification by deuterium diffusion of a nitrogen-related deep donor preventing the p-type doping of ZnO

TL;DR

This study investigates how deuterium diffuses in nitrogen-doped ZnO layers, revealing a nitrogen-related deep donor that traps deuterium and prevents effective p-type doping.

Contribution

It identifies the (N2)O deep donor as a key nitrogen-related trap affecting deuterium diffusion in ZnO, providing insights into doping limitations.

Findings

Deuterium diffusion depth decreases with higher nitrogen concentration.

The nitrogen-related trap has a capture radius 20 times smaller than expected for D+ and nitrogen pairs.

The (N2)O defect is the dominant nitrogen-related deep donor in the samples.

Abstract

Deuterium diffusion is investigated in nitrogen-doped homoepitaxial ZnO layers. The samples were grown under slightly Zn-rich growth conditions by plasma-assisted molecular beam epitaxy on m-plane ZnO substrates and have a nitrogen content [N] varied up to 5x1018 at.cm-3 as measured by secondary ion mass spectrometry (SIMS). All were exposed to a radio-frequency deuterium plasma during 1h at room temperature. Deuterium diffusion is observed in all epilayers while its penetration depth decreases as the nitrogen concentration increases. This is a strong evidence of a diffusion mechanism limited by the trapping of deuterium on a nitrogen-related trap. The SIMS profiles are analyzed using a two-trap model including a shallow trap, associated with a fast diffusion, and a deep trap, related to nitrogen. The capture radius of the nitrogen-related trap is determined to be 20 times smaller than the value expected for nitrogen-deuterium pairs formed by coulombic attraction between D+ and nitrogen-related acceptors. The (N2)O deep donor is proposed as the deep trapping site for deuterium and accounts well for the small capture radius and the observed photoluminescence quenching and recovery after deuteration of the ZnO:N epilayers. It is also found that this defect is by far the N-related defect with the highest concentration in the studied samples.