Semimagnetic heterostructures for spintronics [Elektronische Ressource] / vorgelegt von Taras Slobodskyy

Sujets

• Physik

Informations

• Publié par: julius-maximilians-universitat_wurzburg
• Publié le: 01 janvier 2006
• Nombre de lectures: 23
• Poids de l'ouvrage: 2 Mo

Extrait

Semimagneticheterostructures
forspintronics
DissertationzurErlangungdes
naturwissenschaftlichenDoktorgrades
derJulius–Maximilians–Universitat¨
Wurzb¨ urg
vorgelegtvon
TarasSlobodskyy
Wurzb¨ urg,2006Eingereichtam: ..........
beiderFakultatfurPhysikundAstronomie
1.Gutachter: Prof.Dr.L.W.Molenkamp
2. Priv.Doz.Dr.L.Worschech
derDissertation.
1.Prufer:¨ Prof.Dr.L.W.Molenkamp
2.Prufer:¨ Priv.Doz.Dr.L.Worschech
2.Prufer:¨ .........................................
imPromotionskolloquium
TagdesPromotionskolloquiums: ..........
Doktorurkundeausgehandigt¨ am: ..........Contents
Introduction 1
1 Growthandpropertiesofdilutedmagneticsemiconductors 3
1.1 Dilutedmagneticsemiconductor(Zn,Cd,Be,Mn)Se . . . . . . . . . . . . . . . 3
1.1.1 Crystallographicpropertiesof . . . . . . . . . . . . 3
1.1.2 Bandstructureof(Zn,Cd,Be,Mn)Se . . . . . . . . . . . . . . . . . . . 5
1.1.3 GiantZeemansplitting . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.2 Molecularbeamepitaxy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.3 GaAs-(Zn,Cd,Be,Mn)Seheterointerface . . . . . . . . . . . . . . . . . . . . 12
1.4 Reflectionhigh energyelectrondiffractiongrowthmonitoring . . . . . . . . . 15
1.5 HighresolutionX raysamplecharacterization . . . . . . . . . . . . . . . . . . 16
2 Semimagnetictunnelingstructures 19
2.1 Tunnelbarrierforspintronicsandbasicsofresonanttunneling . . . . . . . . . 19
2.2 Growthandcharacterizationofall II VImagneticRTDs . . . . . . . . . . . . 23
2.2.1 Superlatticeapproachtoscreeningoftheinterfacefield . . . . . . . . . 23
2.2.2 BigandNanoRTDstructureprocessing . . . . . . . . . . . . . . . . . 25
2.2.3 ContactingRTDdevices . . . . . . . . . . . . . . . . . . . . . . . . . 26iv CONTENTS
2.2.4 Current voltagecharacteristicofaRTD . . . . . . . . . . . . . . . . . 27
2.2.5 Collectorandinjectorbandprofile . . . . . . . . . . . . . . . . . . . . 29
2.2.6 Quantumwellpreparationandanalysis . . . . . . . . . . . . . . . . . 31
2.2.7 Straininthebarriersandthequantumwell . . . . . . . . . . . . . . . 32
2.3 Magneto transportinvestigationsofall II VImagneticRTDs . . . . . . . . . . 35
2.3.1 MagneticRTDwithmagneticimpuritiesintheQuantumWell . . . . . 35
2.3.2 MagneticRTDwithmagneticimpuritiesintheInjector,Collector . . . 39
2.3.3 MagneticRTDwithmagneticimpuritiesintheBarriers . . . . . . . . . 41
2.3.4 DoublequantumwelltriplebarriermagneticRTDs . . . . . . . . . . . 43
2.3.5 MagneticRTDsinseries . . . . . . . . . . . . . . . . . . . . . . . . . 47
2.3.6 GatedmagneticRTDs . . . . . . . . . . . . . . . . . . . . . . . . . . 49
2.4 Resonanttunnelingthroughquantumdotsinmagneticmedia . . . . . . . . . . 49
2.4.1 Growthofself organizedsemimagneticstructures . . . . . . . . . . . 49
2.4.2 Opticalinvestigationofquantumdots . . . . . . . . . . 53
2.4.3 Transportinvestigationofquantumdotsbymeansofresonanttunneling 56
3 (Zn,Mn)Seonsilicon 59
3.1 Comparisonof(Zn,Mn)SeandSilicon . . . . . . . . . . . . . . . . . . . . . . 60
3.1.1 Surfacemorphologyof(Zn,Mn)Se(100)andSi(100) . . . . . . . . . 61
3.2 Si(100)surfacepreparationandcharacterization . . . . . . . . . . . . . . . . 64
3.2.1 ModifiedRCASi(100)surfacepreparation . . . . . . . . . . . . . . . 64
3.2.2 Si(100):Hsurface . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
3.3 Growthof(Zn,Mn)SeonSi(100)surface . . . . . . . . . . . . . . . . . . . . 68CONTENTS v
3.3.1 HydrogendesorptionandarsenicpassivationofSi(100)surface . . . . 68
3.3.2 Si(100) (Zn,Mn)Seinterface . . . . . . . . . . . . . . . . . . . . . . . 70
3.3.3 GrowthstartandMBEgrowth . . . . . . . . . . . . . . . . . . . . . . 71
3.4 (Zn,Mn)Selayercharacterization . . . . . . . . . . . . . . . . . . . . . . . . . 74
3.4.1 Nomarskidifferentialinterferencecontrastmicroscopy . . . . . . . . . 74
3.4.2 HRXRDanalysisof(Zn,Mn)Selayers . . . . . . . . . . . . . . . . . . 75
3.4.3 Layerrelaxation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
3.4.4 SQUIDmeasurements . . . . . . . . . . . . . . . . . . . . . . . . . . 79
3.4.5 Magnetoopticalmeasurements. . . . . . . . . . . . . . . . . . . . . . 80
3.5 ElectricalpropertiesofSi(100) (Zn,Mn)Seinterface . . . . . . . . . . . . . . 81
3.5.1 Bandoffset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
3.5.2 I Vcharacteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Summary 87
Zusammenfassung 91
Bibliograhy 105vi CONTENTSIntroduction
The recent remarkable progress in the electronic industry is governed by the dictum known as
Moore’s law [Moo65], which predicts that the density of transistors on an integrated circuit
doubles about once every two years. Since the transistor density is a rough measure of the
attainableprocessingpower,theconsumersgainhigherprocessingcapabilities,smallerdevices,
andsmallerpricesperunit.
Sofar,manufacturershavebeenabletokeepupwiththedictumandincreasetransistordensity
byreducingelementsizeinaplanarlithographyprocess. Currentdevelopmentsshowthatwith
lithographical processes, it will be possible to decrease structure sizes to the scale of a few
nanometers. Soon, the dimensions of an individual device will reach a limit where quantum
mechanical processes start to dominate carrier transport. Even now, as a result of interface
quality and quantum mechanical effects (such as tunneling), most of the power consumed by
modernelectronicsiswastedonparasiticcurrents.
IntegratedcircuitmanufacturingisalmostexclusivelybasedonSilicon,andthematerialprop
ertiesofthissemiconductorhavebeenwellestablished. Manufacturingtechniquesareprecisely
controlled and employed in large scale productions. Technologies like the silicon on insulator
andstrainedSiGeallowforanadditionaltimeshiftofthesizelimitforconventionalelectronics.
For manufacturers, it would be desirable to use elements of standard electronic circuits and
extendthemforperformingnovelfunctionswithquantummechanicaleffectsinmind. Thefield
ofspintronicspresentsamodernanswertothischallenge;itcoversawideareaofinvestigations
using the spin degree of freedom. The searchfor novel magnetic materials, the optimization of
existing paramagnetic and ferromagnetic semiconductors and metals, and the study of carrier
transport through domain walls and interfaces are only a fraction of the activities in the field
of spintronics. Spin polarized transport through interfaces is a very crucial topic, since spin
related computations may require the spin to be transferred from magnetic into nonmagnetic
semiconductors which in long time scale preserve the spin orientation and in some cases the
spincoherence.
II/VIdilutedmagneticsemiconductorsareabletoproduceupto100%carrierspinpolarization
when an external magnetic field is applied. This property allows for the generation of spin
polarized carriers and, using electric fields, their transfer into a nonmagnetic semiconductor.2 INTRODUCTION
Injection of spin polarized carriers from (Zn,Mn)Se into GaAs light emitting diodes demon
+stratesthatthecanbetransferredthroughtheheterointerface[FKR 99].
Intheseexperimentsupto90%ofthecarrierspreservetheirspinpolarization.
In this work, diluted magnetic (Zn,Mn)Se layers grown on Si (100) for the very first time are
presented. These layers exhibit very good structural, optical, magnetic and electrical proper-
ties which indicate their superior quality. Results of initial transport measurements through
(Zn,Mn)Se/Siinterfacewillbediscussed.
In addition we used (Zn,Mn)Se in all II VI magnetic resonant tunneling diodes (RTDs) to
achieve spin filtering as current was passed through spin split levels in a magnetic quantum
+well [SGS 03]. The RTDs present a very interesting system for investigation of spin related
phenomena. Theirspin filteringpropertymaybeusedtogeneratespincurrentandtodetectthe
spinpolarizationofincomingcurrents.
In this work, the world’s first observation of spin splitting of resonances in all II VI magnetic
RTDs is presented. In the RTDs, magnetic layers lead to spin selective transport. Growth,
electrical and structural properties of all II VI magnetic RTDs will be discussed, together with
tunnelingbarriersforspintronics,spin filteringindoubleandtriplequantumwellRTDs.
Most of the devices used in spin transport experiments are grown on almost lattice matched
substrates. For example, the lattice mismatch between (Zn,Mn)Se and GaAs can be accounted
for by growing films below the critical relaxation thickness (∼100 nm for a (Zn,Mn)Se layer
containing3%Mn)orcompensatedbyaddingacertainfractionofBetothecompound.
However the lattice mismatch between different layers during epitaxial growth may be used to
produce self organized structures (e.g. quantum dots). By means of resonant tunneling an in
+dividual CdSe quantum dot embedded into a (Zn,Be,Mn)Se matrix was accessed [GSS 06].
Observation of carrier mediated local ferromagnetic interaction between magnetic atoms in
vicinityofthedotwillbediscussedinthiswork.Chapter1
Growthandpropertiesofdilutedmagnetic
semiconductors
Crystal-abodythatisformedbythesolidificationofachemicalelement,acom
pound,oramixtureandhasaregularlyrepeatinginternalarrangementofitsatoms
andoftenexternalplanefaces[MWD03].
1.1 Dilutedmagneticsemiconductor(Zn,Cd,Be,Mn)Se
In Diluted Magnetic Semiconductors (DMS’s), like (Zn,Mn)Se, a fraction of the atoms is re
placed by magnetic ions. The ions contribute