Eu3+ optical activation engineering in Al Ga1-N nanowires for red solid-state nano-emitters

Abstract

In this work, Eu 3+ -implanted and annealed AlxGa1-xN (0 ≤ x ≤ 1) nanowires (NWs) grown on GaN NW template on Si (111) substrates by plasma-assisted molecular beam epitaxy are studied by µ-Raman, cathodoluminescence (CL), nano-CL, and temperature-dependent steady-state photoluminescence. The preferential location of the Eu 3+ -implanted ions is found to be at the AlxGa1-xN top-section. The recovery of the as-grown crystalline properties is achieved after rapid thermal annealing (RTA). After RTA, the red emission of the Eu 3+ ions is attained for all the samples with below and above bandgap excitation. The 5 D0 → 7 F2 transition is the most intense one, experiencing a redshift with increasing AlN nominal content (x) from GaN to AlN NWs. Moreover, AlN nominal content and annealing temperature alters its spectral shape suggesting the presence of at least two distinct optically active Eu 3+ centers (Eu1 and Eu2). Thermal quenching of the Eu 3+ ion luminescence intensity, I, is found for all the samples from 14 K to 300 K, being the emission of Eu 3+ -implanted AlN NWs after RTA at 1200 ℃ the most stable (I300 K/I14 K ~80%). The GaN/AlN interface in this sample is also found to have a key role in the Eu 3+ optical activation.

Europium-Implanted AlN Nanowires for Red Light-Emitting Diodes

“…The most intense 5 D 0 → 7 F 2 transition is located at ∼624 nm, which corresponds to a red shift of ∼2 nm relative to the same transition in GaN hosts, in good agreement with previous reports. 18,47 This result confirms that the observed emission is mainly due to Eu 3+ implanted into the AlN host. In addition to the intra-4f 6 emissions, PL spectra reveal a green luminescence band (GB) centered at ∼530 nm (better detailed in the inset of Figure 4A).…”

“…Indeed, the optical properties of Eu-implanted AlGaN NWs are improved when the Al content increases: (i) the intensity of the Eu 3+ luminescence increases and (ii) the thermal quenching of the respective luminescence decreases. 18 This improvement may be related to the higher resistance of AlGaN hosts to implantation damage with increasing Al content, for the low fluences investigated here, as well as better thermal stability during annealing. 28,29 Thus, a lower defect density may contribute to a lower probability of unwanted recombination (radiative or nonradiative) at these defects.…”

“…Such differences might be due to the implantation geometry. In the previous study, 18 the implantation was performed at an angle of 45°to the NWs' growth axis (for the same fluence). The total defect density is expected to be lower when implantation is performed along the c-axis than for the implantation with a certain angle to the c-axis due to the reduced probability for direct collisions with the lattice atoms.…”

“…Assuming that the microscopic structure of Eu1 is similar in GaN and AlN and that charge compensation (with Mg doping) occurs at the expense of V N defects, 59 this could also help explain the increase in the PL intensity of Eu1 in the Eu-implanted AlN NW p−n junctions compared to that in unintentionally doped AlN NWs implanted with Eu. 18 Figure 4C shows temperature-dependent HR PL spectra of sample "NW-5e14" around the 5 D 0 → 7 F 2 transition from 14 to 300 K. The PL intensity of all the identified Eu 3+ -related peaks decreases when increasing the temperature, contributing to the reduction of the integrated PL intensity within this spectral region. Such behavior is due to competitive thermally activated nonradiative processes.…”

“…Moreover, the NW configuration allows higher incorporation of dopants and an expected increased light extraction than thin films . Doping of III-N NWs with Eu ions can be obtained either by in situ doping during growth , or by ion implantation. − Remarkably, the Eu 3+ luminescence was enhanced when incorporated into GaN NWs instead of GaN layers. , Recently, red LEDs based on in situ Eu-doped GaN NWs grown directly on Si were demonstrated, exhibiting rectifying characteristics and sharp Eu 3+ luminescence insensitive to charge injection …”