Magnetic properties of (III,Mn)As diluted magnetic semiconductors Katarzyna Kluczyk Supervisor: Dr. Shengqiang Zhou Institute of ion beam physic and material research, HZDR Dresden

Outline Introduction Diluted magnetic semiconductors Preparation of DMS Origin of ferromagnetism Electrically control the ferromagnetism in DMS HZDR project Samples First results Summary

+ Future of spintronics Spintronics: Electronics: applications: memories, higher speed, lower power, tunable ,detectors and lasers manipulate: spin of electrons material: ferromagnetic Electronics: applications: diodes, transistors, detectors, lasers, solar cells manipulate: charge of electrons material: semiconductors + Usage both charge and spin of electrons Mass storage and processing information at the some time Heterostructures with nonmagnetic semiconductors ( store information, amplify spin current, process information, initialize and read-out spin quantum states ) Diluted magnetic semiconductors : charge and spin manipulation storage and processing information at the same time heterostructures with nonmagnetic semiconductors ( spin based optoelectronic, quantum computation)

Diluted magnetic semiconductors ( DMS) Ohno, H., Science. 281, 951 (1998). Aim: combine magnetic properties of ferromagnetics with electrical properties of the semiconductors alloy between nonmagnetic semiconductor and magnetic element What we want: no strong disturbed electric band structure of host semiconductor could be doped to type p and n Curie temperature above room temperature Combine electric properties of semiconductors and magnetic properties of ferromagnetics Alloys of nonmagnetic semiconductors and magnetic elements ( mostly transition elements, due to not fully occupied d shell ) Non disturbed energetic band structure E(k) of the host semiconductor ( theoretical description of band structure in semiconductors could be applied) Could be doped to type n and p Curie temperature Tc above room temperature Figure 1: Three types of semiconductor: (a) a magnetic semiconductor exhibiting ferromagnetism due to carrier mediated alignment of a periodic array of impurity transition metal dopants, (b) a non-magnetic semiconductor which contains no magnetic ions, and (c) a dilute magnetic oxide where only a small fraction of the host semiconductor sites are substituted for by transition metal dopants. Adapted from ref.2.

Preparation of DMS Main problems: low solubility of magnetic elements ( e.g. Mn ) compounds ( much below 0.1% ) Magnetic effect proportional to magnetic element concentration Low temperature molecular beam epitaxy ( LT-MBE ): kinetically suppressed formation of second phases ( low temperature) H. Ohno , J. of Magnetism and Magnetic Materials 200 (1999) Mn composition x Substrate temperature (oC) 0.02 0.04 0.06 100 200 300 Insulating (GaMn)As Roughness MnAs Precipitates Polycrystalline Metallic (GaMn)As 0.08 Wady i zalety obu metod wytwarzania DMS, najwyzsze osiagniete temperatury curie dla obu metod ( porownanie ) Main problem in preparation DMS materials is the low solubility of transition elements ( occuring strong magnetic magnetisation, due to not fully occupied d,f shell ) in solid semiconductor materials combine with proportional dependence of occuring magnetic effects and magnetic elemetns concentration. For GaMnAs for occuring magnetisation one need concentration two – three ordes of magnitude grather then solubility limit. To produce DMS one need then to work far from equilibrium. In case to do thies, two methods was developed : lower temperature beam epitaxy and ion implantation with annealing. First of them use thin film grow technique in vacuum in low temperatures, that do not allow to second phase to appear. Second method, used by our institute, is ion implantation followed by annealing. In thies method we use fact that for liquid phase in III-V semiconductors solubility limit for transitions elements is much higher and allow of formation DMS to ~10% off magnetic elements concentration. Ion beam implantation and annealing: higher solubility limit in liquid phase of host semiconductor

Ga1-xMnxAs, In1-xMnxAs Mn ion substitute Ga, In currier concentration = Mn concentration ~ 1020 (cm-2) Exchange interaction between curries and localized spins Curie temperature Tc1: 90-170 K for Ga1-xMnxAs x=5-9% 46 K for In1-xMnxAs x=4-5% Wang H L, Chen L, Zhao J H. Sci China-Phys Mech Astron, 2013 Crystal structure of (Ga,Mn)As Most investigated (III,Mn)As DMS are GaMnAs and InMnAs. In thies materials Mn ios substitute Ga atom or In atom thies materials. Mn: [Ar] 3d54s2 Ga: [Ar] 3d104s2p1 In: [Kr]4d105s25p1 Mn(Ga,In): acceptor ( provides hole) local spin moment Mn (I) : double donor ( provides 2 electrons) 1 S.Zhou et al., Appl. Phys. Express 5 (2012) 093007

Origin of ferromagnetism exchange interaction between carries and localized spins curried mediated ferromagnetism RKKY theory RKKY interaction ferromagnetic Paramagnetic Curie temperature ( a.u.) Interplay between the electronic spin degree of freedom, repulsive Culomb interactions between electrons and Fermi-Diracs statistics of electrons. Transfer of spin exchange interaction with free curries. RKKY ( Ruderman, Kittel, Kasuya,Yosida ) theory 50‘s Hm =ΣkJ(r-Rk)σSk n/N n – carries concentration N – concentration of localized spins antiferromagnetic R.Galazka, Semimagnetic semicondiuctors,(1977)

Electric-field control of ferromagnetic properties Electric control of ferromegnetic phase In DMS it is possible to control a considerable portion of curries by external electric field and by this control theirs magnetic properties. we show electric field control of ferromagnetism in a semiconducting alloy (In,Mn)As thin film using an insulating gate field-effect transistor (FET) structure. By applying electric fields, we demonstrate that the transition temperature of hole-induced ferromagnetism in (In,Mn)As can be varied isothermally in a reversible way. Field effect control of hole induced ferromagnetism in magnetic semiconductor (In,Mn)As field-effect transistors. Shown are the cross-sections of a metal-insulator-semiconductor structure under gate biases VG, which controls the hole concentration in the magnetic semiconductor channel (schematically shown in red circles). Negative VG (gate bias) increases hole concentration resulting in enhancement of the ferromagnetic interaction among magnetic Mn ions, whereas positive VG has an opposite effect. The thickness of channel layer and insulator are 5 nm and 0.8 µm, respectively. RHall versus field curves under three different gate biases. Application of VG = 0, +125, and -125 V results in qualitatively different field dependence of RHall measured at 22.5 K. RHall is proportional to M due to anomalous Hall effect. When holes are partially depleted from the channel (VG = +125V), a paramagnetic response is observed (blue dash-dotted line), whereas a clear hysteresis at low fields (< 0.7 mT) appears as holes are accumulated in the channel (VG = -125 V, red dashed line). Two RHall curves measured at VG = 0 V before and after application of ±125 V (black solid line and green dotted line, respectively) are virtually identical. Inset, the same curves shown to higher magnetic fields. a) Schematic view of the effect b) magnetization curves obtained through a measure of the Hall resistivity in (In,Mn)As at different gate voltages H.Ohno, Nature materials, vol. 9, 952-54,2010

Outline Introduction Diluted magnetic semiconductors Preparation of DMS Origin of ferromagnetism Selected electrical properties of DMS HZDR project Samples First results Summary

Schematic view of samples Lattice constant equal lattice constant in InP („ferro diods” on (InGa,Mn)As/InP ) During summer student program at HZDR I will be investigate magnetic properties of GaAs/InAs ( gallium arsenide/ indium arsenide ) alloys implanted by Mn ( manganese ) ions and annealed by pulsed laser. I study two samples with different amount of indium arsenide and one heterostructure GaAs/InGaAs. All samples was implanted with dose of ten to sixteen Mn ions, with ions energy equal 90 keV and then annealed by single laser pulse with different values of energy densities. Implanted by Mn ions , dose φ = 1016 (cm-2), ion beam energy 90 keV Annealed with single laser pulse and energy density 0.25, 0.3, 0.35, 0.4 ( J/cm2) XeCl excimer laser ( Coherent COMPexPRO201, λ=398 nm, 30 ns , full width at half maximum )

Monte Carlo simulation of Mn distribution with program SRIM Rp – ion range of max concentration ΔRp – ion range straggling Rp =567Å ΔRp=294Å Rp =506Å ΔRp=274Å By using program SRIM (The Stopping and Range of Ions in Matter) I simulate distribution of Mn ions concentration in dependence of depth. For each sample I calculate 10000 single ion matter events. As we can see at the plot, concentration of Mn ions is similar for all samples with maximum circa 6,5%. The maximum range of Mn ions is also similar and equal 130 nm. We see that indium presence does not strongly change the ion stopping efficiency in the samples. But one can notice that with increase of indium concentration increase the ion range. Rp =550Å ΔRp=283Å Deph (Å)

Magnetic moment measurements by SQUID magnetometer as a function of applied magnetic field in temperature 5K After preparation magnetic properties of each sample was measured via SQUID – semiconducting quantum interface device magnetometer in case to investigate whether the sample exhibits ferromagnetic properties or not. As we expected at this temperature, for each sample we saw magnetization hysteresis loop, which proof ferromagnetic properties of the samples. „Soft“ shape of measured hysteretic loops indicate that measurement was provided in magnetic field applied along hard axis. By comparing hysteresis loops for In0.53Ga0.47As and In0.1Ga0.9As we can see that

Magnetic moment as a function of temperature measured in magnetic field 20 Oe Curie temperature in the range 40-55 K. The highest Tc for GaAs/InGaAs multilayer. Lower temperature for grater In concentration, but this could be, due lower energy density applied during laser annealing and lower Mn ions activation ( more interatomic defects, which decrease number of free curries and also localized spins ).

Summary Both GaAs/InGaAs superlattice and InGaAs can be prepared to be DMS Ion implantation and PLA: an effective method to synthesis DMS Directions for further research: Measurements of magnetization response along perpendicular direction ( to investigate magnetic anisotropy ) Measurements of samples annealed with different energy density (investigation of proper annealing conditions ) Investigation of Tc dependence on In concentration Measurements of magnetization dependence on temperature for InGaAs/GaAs multilayer. Looking for two magnetic phases.

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