Spinodal nanodecomposition in semiconductors doped with transition metals

Abstract

This review presents the recent progress in computational materials design, experimental realization, and control methods of spinodal nanodecomposition under three-and two-dimensional crystal-growth conditions in spintronic materials, such as magnetically doped semiconductors. The computational description of nanodecomposition, performed by combining first-principles calculations with kinetic Monte Carlo simulations, is discussed together with extensive electron microscopy, synchrotron radiation, scanning probe, and ion beam methods that have been employed to visualize binodal and spinodal nanodecomposition (chemical phase separation) as well as nanoprecipitation (crystallographic phase separation) in a range of semiconductor compounds with a concentration of transition metal (TM) impurities beyond the solubility limit. The role of growth conditions, codoping by shallow impurities, kinetic barriers, and surface reactions in controlling the aggregation of magnetic cations is highlighted. According to theoretical simulations and experimental results the TM-rich regions appear in the form of either nanodots (the dairiseki phase) or nanocolumns (the konbu phase) buried in the host semiconductor. Particular attention is paid to Mn-doped group III arsenides and antimonides, TM-doped group III nitrides, Mn-and Fe-doped Ge, and Cr-doped group II chalcogenides, in which ferromagnetic features persisting up to above room temperature correlate with the presence of nanodecomposition and account for the application-relevant magnetooptical and magnetotransport properties of these compounds. Finally, it is pointed out that spinodal nanodecomposition can be viewed as a new class of bottom-up approach to nanofabrication.

Fe dopant in ZnO: 2+ versus 3+ valency and ion-carrier s,p−d exchange interaction

“…A careful analysis of the data reveals the absence of ferromagnetic secondary phases (e.g., Fe-rich aggregates) in all of the studied samples. This is in contrast to what was reported previously for the (Zn,Fe)O 93 and other Fe-doped wide band gap semiconductors, e.g., for (Ga,Fe)N. 94,95 Consequently, the term C in the Eq. 5 will be neglected.…”

Two-Probe Measurements of Electron Transport in GaN:Si/(Ga,Mn)N/GaN:Si Spin Filter Structures

“…The obtained samples are systematically characterized by atomic force microscope (AFM), high resolution X-ray diffraction (HRXRD), and high resolution transmission electron microscopy (HRTEM). The AFM micrographs reveal a flat surface (rms roughness ∼ = 1 nm) while HRXRD and HRTEM confirm the high crystallinity of the samples without phase separation (precipitates) which are present under different growth conditions [12].…”

Фазовое разделение в слоях GaMnAs, сформированных импульсным лазерным осаждением

“…1, b, и низкую концентрацию дырок (из холловских измерений p ∼ 2 · 10 19 cm −3 при T = 295 K). Такую совокупность магнитооптических и электрических свойств можно объ-яснить в предположении, что в образце № 1 имеет место " химическое фазовое разделение" [26], т. е. рас-пределение Mn в нем существенно неоднородно, и в от-носительно слабо легированной (или сильно компенси-рованной) парамагнитной матрице имеются локальные ферромагнитные области (Ga, Mn)As с повышенной кон-центрацией Mn и дырок. В этом случае ЭЭК зондирует ферромагнитные области (Ga, Mn)As, а из транспортных измерений мы получаем характеристики парамагнитной матрицы образца № 1.…”