Enhancing the luminescence yield of Cr3+ in β -Ga2O3 by proton irradiation

Abstract

In situ ion-beam-induced luminescence measurements reveal a strong enhancement of the Cr3+ emission yield in electrically conductive chromium doped β-Ga2O3 single crystals upon proton irradiation. The observed effect can be explained based on the Fermi-level pinning caused by radiation defects. This pinning of the Fermi level activates deep carrier traps that can act as sensitizers of the Cr3+ emission. In agreement with this model, in semi-insulating samples, where the Fermi level lies deep in the bandgap, the Cr3+ emission is present already in as-grown samples, and no enhancement of its intensity is observed upon proton irradiation. The boost of the Cr3+ emission yield by irradiation, observed in conductive samples, is reversed by thermal annealing in argon at temperatures above 550 °C for 30 s. The results reveal a high potential of Cr-doped β-Ga2O3 for in situ and ex situ optical radiation detection and dosimetry.

Probing the Cr3+ luminescence sensitization in β-Ga2O3 with ion-beam-induced luminescence and thermoluminescence

“…Moreover, the sample was observed by particle-induced X-ray emission (PIXE) to contain trace amounts of Fe, which is a common contaminant in the context of the EFG method. Further information on this sample and preliminary IBIL results have been published elsewhere 23 , 36 .…”

“…Such processes include energy or charge transfer between traps in β -Ga 2 O 3 and Cr 3+ ions 22 – 25 . Recent IBIL measurements monitored at the Cr 3+ emission wavelengths show a strong enhancement of the emission intensity as a function of the irradiation fluence in a conductive sample, thus suggesting that irradiation-induced defects play a major role in the activation of this luminescence 23 . Moreover, several works show a clear dependence of the Cr 3+ luminescence yield on the electrical conductivity of the sample, with insulating samples showing higher yields than conductive ones 23 , 26 , 27 .…”

“…Recent IBIL measurements monitored at the Cr 3+ emission wavelengths show a strong enhancement of the emission intensity as a function of the irradiation fluence in a conductive sample, thus suggesting that irradiation-induced defects play a major role in the activation of this luminescence 23 . Moreover, several works show a clear dependence of the Cr 3+ luminescence yield on the electrical conductivity of the sample, with insulating samples showing higher yields than conductive ones 23 , 26 , 27 . While this dependence has been suggested to be related with different Cr 2+ /Cr 3+ concentrations, due to different Fermi level positions inside the bandgap, there is no direct experimental evidence of Cr 2+ ions in β -Ga 2 O 3 23 , 27 , 28 .…”

“…Moreover, several works show a clear dependence of the Cr 3+ luminescence yield on the electrical conductivity of the sample, with insulating samples showing higher yields than conductive ones 23 , 26 , 27 . While this dependence has been suggested to be related with different Cr 2+ /Cr 3+ concentrations, due to different Fermi level positions inside the bandgap, there is no direct experimental evidence of Cr 2+ ions in β -Ga 2 O 3 23 , 27 , 28 . In fact, recent works found no changes in the Cr 3+ charge state irrespective of ion irradiation and irrespective of co-doping with Mg, both of which may pin the Fermi level by introducing deep defect levels within the bandgap 23 .…”

“…Therefore, while the Cr 3+ emission has been shown to depend on the electrical conductivity 23 , 26 , 27 and on the presence of certain defect levels within the band gap 22 , the full excitation processes are still unclear. In this context, this paper presents a detailed IBIL study performed on Cr-doped β -Ga 2 O 3 using two different ions (H + and He + ) in order to assess the evolution of the IBIL intensity associated with the Cr 3+ ions with the irradiation fluence.…”