Manipulating Mn–Mgk cation complexes to control the charge- and spin-state of Mn in GaN

Abstract

Owing to the variety of possible charge and spin states and to the different ways of coupling to the environment, paramagnetic centres in wide band-gap semiconductors and insulators exhibit a strikingly rich spectrum of properties and functionalities, exploited in commercial light emitters and proposed for applications in quantum information. Here we demonstrate, by combining synchrotron techniques with magnetic, optical and ab initio studies, that the codoping of GaN:Mn with Mg allows to control the Mnn+ charge and spin state in the range 3≤n≤5 and 2≥S≥1. According to our results, this outstanding degree of tunability arises from the formation of hitherto concealed cation complexes Mn-Mgk, where the number of ligands k is pre-defined by fabrication conditions. The properties of these complexes allow to extend towards the infrared the already remarkable optical capabilities of nitrides, open to solotronics functionalities, and generally represent a fresh perspective for magnetic semiconductors.

Functional Mn–Mgk cation complexes in GaN featured by Raman spectroscopy

“…We have recently demonstrated how the formation of Mn-Mg k complexes in (Ga,Mn)N:Mg substantially affects the behaviour of each dopant, resulting in remarkable and unforeseen material properties. 5 The interplay between the dopants, but also with the host lattice must be understood in order to ensure a controlled and effective functionality of these nano-objects in innovative devices. Raman spectroscopy is particularly suitable to investigate impurities and impurity complexes in semiconductors 6 due to its sensitivity to variations in the structural and electronic properties of the material under study.…”

“…In the case of doping of nitrides with Mg, this technique was decisive to identify the Mg-H complexes 7,8 responsible for the low efficiency of the Mg activation, and for the consequent poor p-type conductivity especially in GaN:Mg. [9][10][11] While Mg is the most relevant p-type dopant in GaN, and is employed in the majority of optoelectronic devices based on GaN, Mn generated interest lately for its potential in spintronics, and particularly in the perspective of turning p-type Mn-doped GaN (i.e., (Ga,Mn)N:Mg) into a ferromagnetic dilute magnetic semiconductor with a high Curie transition temperature. 12 Moreover, the recent demonstration of unexpected (infrared) optical and magnetic responses in (Ga,Mn)N:Mg, 5 has opened appealing fundamental and technological perspectives for this system.…”

“…Furthermore, synchrotron x-ray absorption fine structure (EXAFS) studies demonstrate that at least 95% of the Mn ions substitutes Ga cations, 14 and we have reported that in the case of Mn-Mg codoping, both Mn and Mg occupy Ga substitutional sites, and Mg tends to stay close to Mn, separated by one N atom, to form Mn-Mg k cation complexes, where k is the number of Mg ions in the first cation shell of a single Mn. 5 The Mn and Mg concentrations x Mn and x Mg are extracted from secondary ion mass spectroscopy (SIMS) and lie between 0% and 1%. The Raman spectra are acquired with a Jobin-Yvon LabRAM HTS confocal micro-Raman setup equipped with 532 nm, 633 nm, and 785 nm lasers with a spectral resolution of 1 cm À1 .…”

“…3 broad band (ABDE and to a lesser extent of C); (2) a shift in the position of the C peak; (3) the appearance of an additional sharp peak around 650 cm À1 ; (4) the presence of a specific broad peak around 688 cm À1 . In the following, we discuss these features in the frame of the recently demonstrated evidence of Mn-Mg k complexes in (Ga,Mn)N:Mg. 5 In order to provide a quantitative description, we deconvolute the spectra in a similar way as we did in the case of (Ga,Mn)N (without Mg). To take the influence of Mg into account, three Lorentzian contributions are added, one around 650 cm À1 to describe feature (3) and two between 680 cm À1 and 695 cm À1 to describe feature (4).…”

“…The saturation of these shifts reveals that for a high Mg/Mn ratio, the Mn environment is not perturbed anymore, as shown by synchrotron EXAFS measurements. 5 However, this simplified model does not account for the red shift of the C peak at low x Mg /x Mn . To understand this phenomenon, it is necessary to take into account the spin density calculations reported in Ref.…”