Shallow carrier traps in hydrothermal ZnO crystals

TL;DR

This study investigates shallow carrier traps in hydrothermal ZnO crystals, revealing how native and hydrogen-induced traps affect optical properties and excitonic behavior, with implications for optoelectronic applications.

Contribution

It provides new insights into the nature of shallow traps in hydrothermal ZnO and proposes a model explaining anomalous temperature-dependent luminescence in H-doped samples.

Findings

Native ZnO has a trap at 23 meV.

H-doped ZnO shows traps at 22 meV and 11 meV.

Anomalous increase in excitonic emission with temperature in H-doped ZnO.

Abstract

Native and hydrogen-plasma induced shallow traps in hydrothermally grown ZnO crystals have been investigated by charge-based deep level transient spectroscopy (Q-DLTS), photoluminescence and cathodoluminescence microanalysis. The as-grown ZnO exhibits a trap state at 23 meV, while H-doped ZnO produced by plasma doping shows two levels at 22 meV and 11 meV below the conduction band. As-grown ZnO displays the expected thermal decay of bound excitons with increasing temperature from 7 K, while we observed an anomalous behaviour of the excitonic emission in H-doped ZnO, in which its intensity increases with increasing temperature in the range 140-300 K. Based on a multitude of optical results, a qualitative model is developed which explains the Y line structural defects, which act as an electron trap with an activation energy of 11 meV, being responsible for the anomalous temperature-dependent cathodoluminescence of H-doped ZnO.