Abstract
We have investigated the temperature-dependent photoluminescence (TDPL) profiles of Eu3+ ions implanted in an HVPE-grown bulk GaN sample doped with Mg and of donor–acceptor pairs (DAP) involving the shallow Mg acceptor in GaN(Mg) (unimplanted) and GaN(Mg):Eu samples. Below 125 K, the TDPL of Eu3+ in GaN(Mg):Eu correlates with that of the DAP. Below 75 K, the intensity of Eu3+ emission saturates, indicating a limitation to the numbers of Eu–Mg defects available to receive excitation transferred from the host, while the DAP continues to increase, albeit more slowly in the implanted than the unimplanted sample. Prolonged exposure to UV light at low temperature results in the photodissociation of Eu–Mg defects in their Eu1(Mg) configuration, with a corresponding increase in shallow DAP emission and the emergence of emission from unassociated EuGa (Eu2) defects.
Highlights
Rare-earth (RE)-doped wide bandgap semiconductors have potential applications in light emitting diodes and display devices [1,2,3,4]
In previous publications [9, 16, 25], we have reported that switching between Eu0 and Eu1(Mg) demonstrates the structural instability of GaN(Mg) at low temperature, with Eu ions acting as sensitive nanoprobes of the local environment
At higher temperatures, where donor–acceptor pairs (DAP) emission is absent, we must look for another process to increase the Eu3+ signal; this may be due to reduced competition from non-radiative processes [27, 28]
Summary
Rare-earth (RE)-doped wide bandgap semiconductors have potential applications in light emitting diodes and display devices [1,2,3,4]. When incorporated in III-nitride semiconductors, RE3+ ions exhibit characteristic sets of sharp intra-4f shell emission lines; Eu-doped GaN attracts special attention for intense red emission near 621 nm, due to 5D0 → 7F2 multiplet transitions [5,6,7,8,9,10]. Increases the luminescence intensity of samples measured at room temperature [11, 12]. In contrast to GaN:Eu, which shows Eu3+ emission from many different ‘RE sites’ [15], the photoluminescence (PL) spectrum of ion-implanted GaN(Mg):Eu is apparently dominated by emission from a single, albeit photochromic centre with a unique set of emission lines at room temperature, labelled Eu0 [9]; a variety of experimental results indicates that the Eu0
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