Uniform Doping in Quantum-Dots-Based Dilute Magnetic Semiconductor

Abstract

Effective manipulation of magnetic spin within a semiconductor leading to a search for ferromagnets with semiconducting properties has evolved into an important field of dilute magnetic semiconductors (DMS). Although a lot of research is focused on understanding the still controversial origin of magnetism, efforts are also underway to develop new materials with higher magnetic temperatures for spintronics applications. However, so far, efforts toward quantum-dots(QDs)-based DMS materials are plagued with problems of phase separation, leading to nonuniform distribution of dopant ions. In this work, we have developed a strategy to synthesize highly crystalline, single-domain DMS system starting from a small magnetic core and allowing it to diffuse uniformly inside a thick CdS semiconductor matrix and achieve DMS QDs. X-ray absorption fine structure (XAFS) spectroscopy and energy-dispersive X-ray spectroscopy-scanning transmission electron microscopy (STEM-EDX) indicates the homogeneous distribution of magnetic impurities inside the semiconductor QDs leading to superior magnetic property. Further, the versatility of this technique was demonstrated by obtaining ultra large particles (∼60 nm) with uniform doping concentration as well as demonstrating the high quality magnetic response.

Dilute Magnetic Semiconducting Quantum Dots: Smart Materials for Spintronics

“…But, in co-doped ZnO with Cu and Fe, X-ray absorption spectroscopy (XAS) clearly showed the presence of both Fe +2 and Fe +3 and its relative percentage is dependent on the presence of Cu as a dopant. Another research revealed that the size of Fe doped CdS QD was responsible for the magnetic moment [57]. They have achieved a magnetic moment of 80 memu/g at RT for doped CdS and undoped CdS showed negligible amount of magnetic moment with the same scale reaction.…”

“…Clustering and surface doping are two main issues that are faced during the synthetic process for obtaining uniformed DMSQDs. To eliminate these key issues, one has to overcome selfpurification [57] of the materials and understand the reactivity between the host-guest materials [58,59]. The self-purification is a process where host molecule expels the guest molecule from the surface to attain a thermodynamically stable state by reducing its defect energy.…”

Recent Advances in Magnetic Ion-Doped Semiconductor Quantum Dots

“…Later Saha et al 47 showed in 2016 that self-purification of dopants, previously considered a bane, could be used as a boon for synthesis of uniformly doped QDs of required size. In this process, a small magnetic core was synthesized (demonstrated with the example of Fe 3 O 4 ) and was overcoated with a thick semiconducting shell (CdS).…”

“…It was demonstrated using X-ray absorption spectroscopy (XAS) that both Fe 2+ and Fe 3+ species were present and the relative percentage of the species was dependent on the presence of Cu as a dopant. More recently, it was observed that upon synthesis of DMS QDs using the insideout method 47 , it was possible to obtain much higher magnetic moment compared to earlier counterparts. In this work, it was shown that smaller QDs showed a moment of 80 memu/g at room temperature and the surface-only magnetism on undoped CdS also shown in the same scale was negligible.…”

“…In this work, it was shown that smaller QDs showed a moment of 80 memu/g at room temperature and the surface-only magnetism on undoped CdS also shown in the same scale was negligible. Recent reports 47,54 have used thermogravimetric analysis in these high quality uniformly doped QDs to realize the quantitative percentage of ligand weight and hence obtain the moment per magnetic ion. From these measurements, it can be observed that the magnetic moment per magnetic ion was found to be about 0.45  B /ion for smaller particles which increased to 1.6  B /ion for larger particles suggesting comparable values with that of the bulk Fe.…”