NC STATE UNIVERSITY

Manipulation of Room Temperature Ferromagnetic Behavior of GaMnN Epilayers.

Our work at NCSU on GaMnN

DMS device fabrication and testing

*GaMnN i-p-n structures with different Xp were fabricated

*I-V curve for Xp=0.17m is almost flat due to an almost fully depleted p-GaN

*As Xp increases, I-V curves of device rectifying p-n junctions are more evident

* Our experimental results are consistent with a simple estimate of carrier

depletion solving 1-D poison’s Eqn.

DMS device fabrication and testing

*For VR ≤ 3V, the Ms is independent of applied voltage

*Ms starts to decrease at VR =4V

*For VR=5V the p-layer is fully depleted and the GaMnN film is almost paramagnetic

Contact for Hallmeasurement

Sapphire

GaN template (0.75m)n-GaN (0.5m)

p-GaN (Xp)

34

1Va

Wp

GaMnN (0.5m) 2

Contact for Hallmeasurement

Sapphire

GaN template (0.75m)n-GaN (0.5m)

p-GaN (Xp)

34

1Va1Va

Wp

GaMnN (0.5m) 2

*Demonstration of the first electric field controlled room temperature DMS-based devices

GaMnN heterostructures on GaN:Mg/GaN:si/GaN stacks were grown by MOCVD. The

RT FM of these multilayer structures increases with Xp in the range 0.16 m ≤ Xp ≤ 0.25

m. These heterostructure based devices were fabricated and studied by AGM

measurement. AGM measurement shows decrease in Ms with reverse bias due to

depletion of p-GaN. The FM of these multilayer with undepleted p-GaN layer is

independent on the top GaMnN for tGaMnN >200 nm and decreases for tGaMnN < 200 nm.

Thus the RT FM of GaMn i-p-n structure based devices can be changed by manipulating

hole concentration in the p-GaN layer and tGaMnN, which would have application in room

temperature spin electronic components.

Conclusions:* We found that the ferromagnetism in GaMnN is carrier mediated

* GaMnN i-p-n devices were designed and fabricated for RT FM

* GaMnN i-p-n devices show electric field controlled FM at RT

* Demonstrated manipulation of RT FM in GaMnN based DMS devices

Magnetoresistance of GaMnN i-p-n devices

Summary

This work was supported by U. S. Army Research Office

Ferromagnetic semiconductor based devices that utilize both the charge and spin of

electrons to process and store information can have higher speed and efficiency, as well

as reduced size and power consumption. Most recent studies on dilute magnetic

semiconductor (DMS) materials have been focused on GaMnAs and InMnAs.

* Enhancement of FM by activating more

holes in p-GaN/GaMnN/p-GaN

heterostructures.

* Annealing activates more holes from the

* The starting film is Paramagnetic, where the Mn energy band is completely filled with electrons.

Structure GaMnN/GaN:Mg

Ec

Ev

EF

Ec

Ev

GaMnN GaN:Mg

Mn Mg

PM

GaN:Mg; 0.15 m

GaMnN; 0.375 mGaMnN; 0.375 m

GaN:Mg; 0.35 m

FM

N. Nepal1, M. Oliver Luen1, P. Frajtag2, J. M. Zavada1, S. M. Bedair1, and N. A. El-Masry2

1Electrical and Computer Engineering, North Carolina State University, Raleigh, NC 27695 USA2Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695 USA

Introduction

Motivation

Magnetic random access memories (MRAM)

Europhysics News (2003) Vol. 34 No. 6

DMS: offers a multifunctional device that could replace several components.

FM Semiconductor

Current injection

Suffers with interface scattering

Solution

Using dilute magnetic semiconductor (DMS)

Ref. H. Ohno et al., Nature 408, 944 (2000).

Metal gateInsulatorInMnAsInAs(AI,Ga)SbAISbGaAs substrate

RHall was measured at 22.5 K

VG>0 VG=0 VG<0

Ref. Fukuda et al., Appl. Phys. Lett. 91, 052503 (2007).

GaAs

InAlAs

GaMnAs

GaAs

AlAs

GaMnAs

(a)Schematic view of the device and microscope image of the channel region of the device. (b) Setup for TMR measurement. (c) TMR of MTJ-A measured at temperatures between 50 and 60 K.

Ga(In)MnAs based spin electronic devices work at low temperatures only!

SiGe

AlPAlAs

GaNGaP

GaAsGaSb

InPInAs

ZnOZnSe

ZnTe

10 100 1000Curie Temperature (K)

Computed Values of the Curie Temperature (using the Zener model description) for various p-type semiconductors containing 5% of Mn and 3.5 X 10 20 holes/cm3.

Ref: Dietl, et. al., Science, Vol. 287, 1019 (2000).

* According to Zener model, predicted Tc for GaMnN is above room temperature

* Highest reported Tc for Ga(In)MnAs

material system =185 K

* Tc (GaMnN) > 300 K (RT)

Ref. National Laboratory for Advanced Tecnology and nano Science, Nottingham Univ.

GaMnN could be the potential DMS to manipulate FM at room temperature

Previous work on III-V DMS

Variation of Ms with Xp and tGaMnN

A strong dependence of the GaMnN film ferromagnetism on p-GaN thickness was observed

Our work at NCSU on GaMnN

Heterostructure design and MOCVD growth

Magnetic measurement on heterostructures

* GaMnN layer on top of n-GaNparamagnetic

* GaMnN layer on top of p-GaNferromagnetic

* Annealing GaMnN/p-GaN doubles Ms

FM is hole mediated

*For Xp = 0.17 m, GaMnN i-p-n structure is

PM due to fully depleted p-GaN

* For Xp=0.25 and 33 m, it is FM

*By changing thickness of p-GaN layer in GaMnN i-p-n structure we can manipulate FM

FM of GaMnN i-p-n structures can be manipulated by varying the p-GaN or GaMnN layer thickness

*Ms increases with Xp and saturates for Xp ≥

0.25 m

*For Xp ~ 66 nm the GaMnN structure is PM

*No effect of tGaMnN on Ms for Xp=0.17 m

*For Xp = 0.25 m, MS decrease for tGaMnN

< 200 nm

Variation of Ms with Xp Variation of Ms with tGaMnN

Sapphire

GaN template (0.75m)

n-GaN (0.5m)

p-GaN (Xp)

i-GaMnN (0.5m)

,0 Md

RB

d

RR s

Hall

*VR increases the depletion width at the p-n junction by depleting the holes at the

junction that interact with the localized Mn ion spins.

* Only the holes near the GaMnN/p-GaN interface interact with localized Mn ion spins

Ref. NCSU- Nepal et al., Appl. Phys. Lett. 94, 132505 (2009).

OHE AHE

FM of GaMnN i-p-n structures can be manipulated by biasing p-n junction

Ref. NCSU-Reed et al., Appl. Phys. Lett. 86, 102504 (2005).

Si-

dop

ing

CB

VB

t2 Mn3+

0.3 eVe

1.7. eV

Mg-d

opin

g

* Si-doping moves the fermi level “Ef” up completely filled Mn band

* Mg-doping moves the fermi level “Ef” down empty Mn band

* Since Mn forms deep level in GaN, Si and Mg doped GaMnN films are insulating.

)exp(KT

Ep A∝

Loss of the ferromagnetism (FM)

Gain of the ferromagnetism (FM)

Ref. Arkun et al., Appl. Phys. Lett. 85, 3809 (2004).

GaMnN heterostructures were grown by metal organic chemical vapor deposition (MOCVD) and studied by alternating gradient magnetometer (AGM) and Hall measurements.