Formation of Magnetic Nanostructures after Low Energy Ion Implantation'

1
Formation of Magnetic Nanostructures after Low
Energy Ion Implantation.
Mr. Dipak Paramanik Doctoral scholar
Institute of Physics, Bhubaneswar
Collaborator Dr. D. Kanjilal Nuclear Science
Centre, Delhi
Research Advisor Dr. S. Varma Institute of
Physics, Bhubaneswar
2
Motivation

• Incorporation of ferromagnetic nanostructure into
• semiconductor is of great scientific and
  technological
• interest as they can be used to produce and
  manipulate
• both charge and the spin of the carriers
• Or more generally called Spintronics.

• Diluted magnetic semiconductors based on III-V
  compounds have attracted lots of interest
  Integrating magnetism into opto electronic device
  technology.

3
Devlopement in semiconductor technology

• First came solid state electronics, producing the
  field effect
• transistor (FET), in which a tiny voltage applied
  to a gate enables
• a much larger Current to flow through a circuits.

• Next came optoelectronics, producing the light
  emitting diode
• (LED), in which the electrons and holes are made
  to combine and
• produce useful light .

• Then came spintronics, producing circiuit
  elements such as
• Magnetoresistive sensors, in which an electron
  polarization
• ( the direction of an electron magnetic moment)
  is an important
• variable.

• Now scientist would like to combine optical and
  magnetic features
• in a single technology.

4
Some steps have already been taken on Dilute
Magnetic Semiconductor (DMS) Material doped
with magentic metal atoms, can be made
ferromagnetic that is they can be magnetized and
will stay magnetic providing you stay below the
Curie temperature.
Ferromagnetism has recently been reported in
several classes of semiconductors including
II-VI, III-V,IV, and II-IV-V2 materials. To,
date the low solubility of magnetic ions in
non-magnetic semiconductors hosts and/or a low
Currie temperature tended to limit the
opportunities.
5
(No Transcript)
6
V
VI
IV
III
B
C
N
O
Al
Si
P
S
II
Ga
Ge
As
Se
III-V Ga-As In-As Ga-Sb
In
Sn
Sb
Te
7

• Spin Injection
• Heterostructures III-V (III,Mn)-V

• BUT
• Working at low temperature
• Small effects
• Curie Temperature lt 150 Kelvin

• Magnetic control of transport

• Electric control of Magnetism

8
Present International Status

• There are lot of work on dilute magnetic
  semiconductors.

• The ferromagnetic Curie temperature of the
  magnetic structures
• depend on the substrate ( semiconductor),
  implanted ion and the
• dose of the ion .

• Shi et al J. Appl. Phys. 79, 5296 (1996)
  have shown the formation MnGa ferromagnets
  imbedded in GaAs using Mn ion implantaion and
  subsequent heat treatment.

• GaAs(100) implanted with Mn ion of energy
  200KeV and
• dose 5x1016 ions/cm2 shows Tc 300º K.
• 1. Chenija Chen et al, J. Appl. Phys. 87,
  5636 (2000).
• 2. Jing Shi et al, , J. Appl. Phys. 79,
  5296 (1996).

9
They had shown that

• Unimplanted and annealed
• Implanted and unannealed
• Implanted and annealed at
• lower temp (600 ºC-700 ºC)

Nonferromagnet
Ferromagnetic domains of different sizes and
shapes.

• Implanted and annealed
• at temp. from 750 ºC 900 ºC

Most of the current studies deal with (Ga,Mn)As
diluted phases grown by molecular beam epitaxy .
M. Moreno et al, J. Appl. Phys. 92, 4672
(2002) This class of materials displays Curie
temperatures ( Tc) in the range 80 ºK- 110 ºK
10
Mn 2x1016/ cm2
Annealed at 830 ºC For 60 s.

• Topography and MFM images of the same area
• 3-D image of the same area.

Chenija Chen et al, J. Appl. Phys. 87, 5636
(2000).
11
Formation of magnetic domains
MFM images at different lift height of Fe
Pt co-implanetd Al2O3 , Annealed at 200 ºC
Vallet et al. J. Appl. Phys 92,6200(2002).
12
Origin of Ferromagnetism ?

• Shi et al J. Appl. Phys. 79, 5296 (1996)
  have shown
• that ferromagnetism originates from GaMn
  precipetate.

• Ando et al Appl. Phys. Lett. 73,387(1998) ,
  there results
• shows that Ferromagentism comes from MnAs
  crystallites.

13

• It is generally belive that ferromagnetism
  in these system is carrier mediated. Currently
  there is no consensus on the gross features of
  the electronic structure of heavily doped
• Ga 1-x Mn x As, and therefore the details
  of the itinerent ferromagnetic state are
  unresolved .
• A common picture that has been used to
  interpret both transport and magnetoabsorption
  experiments is that Mn dopes a hole into the
  GaAs valence band and also act as a localized
  spin . Within this view, the hole promoting
  ferromagnetism via Ruderman-Kittel-Kasuya-Yosida
  (RKKY) interaction ought to be strongly
  influenced by the spin orbit interaction.
• J. B. Beschoten et al., Phys. Rev. Lett. 83, 3073
  (1999).
• Koning et al., Phys. Rev. Lett. 84, 5628 (2000).

14
The standard model

• Itinerant holes, effective mass approximation
• Localized d electrons
• Local hole-Mn exchange interaction
• Virtual Crystal approximation
• Mean Field approximation

• k.p Luttinger holes (SPIN-ORBIT)
• Spin wave fluctuations (beyond mean field theory)

15
Our Proposal
Although much attention has been focussed on the
(Ga,Mn)As and (In,Mn)As, There is realization
that any real break through with respect to
application will require dilute magnetic
semiconductor (DMS) that exhibit robust
ferromagnetism above room temperature.
Since MnAs precipetates is the origin of
Ferromagnetism we have planned to do
Mn As co-implantation in GaAs.
Fluence of Mn As will be 5x1016 ions/cm2
We want the formation of MnAs precipetate very
close to the surface. For getting MnAs
precipetate at 30 nm depth Energy of Mn 50
keV Energy of As 70 keV
16
TRIM calculation for the co-implatation of Mn and
As in GaAs.

• Beam 25Mn , 33As
• Energy 50 keV, 65 keV
• Fluence 5x1016 ions/cm2
• (dE/dx)e Se 13.6 eV/Ao, 16.2 eV/Ao
• (dE/dx)n Sn 105.4 eV/Ao, 158.1 eV/Ao
• Projected Range 306 Ao , 308 Ao
• Long. Straggling 179 Ao, 160 Ao
• Lat. Straggling 127 Ao , 114 Ao

17
Similar study we want to do for Mn Sb
co-implantationm in GaSb

• Beam 25Mn , 51Sb
• Energy 50 keV, 90 keV
• Fluence 5x1016 ions/cm2
• (dE/dx)e Se 13.3 eV/Ao, 15.8 eV/Ao
• (dE/dx)n Sn 96.9 eV/Ao, 263.3 eV/Ao
• Projected Range 294 Ao , 291 Ao
• Long. Straggling 199 Ao, 147 Ao
• Lat. Straggling 143 Ao , 107 Ao

18
Post irradiation measurements planned
After performing the above two experiment the
samples will be annealed in a Rapid Thermal
Annealing (RTA) system at temperatures 400 ºC
and 900 ºC for 60s under N2 atomosphere and
using a face to face configuration to avoid
surface degradation.
This annealing results in the regrowth of the
amorphous layer by solid phase epitaxy and the
diffusion of implanted species and the eventual
nucleation of MnAs precipitates which can grow
further as the annealing proceeds.
19

• Magnetic Force Microscopy (MFM) measurements
• will be performed to study the magnetic
  nanostructure
• on the surfaces of the samples. The size,shape
  and height
• of the particles as well as the distribution of
  the particles
• will be determined.

• X-ray Photoelectron Spectroscopy (XPS)
  measerment
• will be performed to find out the chemical
  composition
• of this magentic nanostructure on the surface.

20
(No Transcript)