Voltage bias controlled ferromagnetic, room temperature device in GaMnN.

1. 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 X p were fabricated *I-V curve for X p =0.17  m is almost flat due to an almost fully depleted p-GaN *As X p 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 V R ≤ 3V, the M s is independent of applied voltage *M s starts to decrease at V R =4V *For V R =5V the p-layer is fully depleted and the GaMnN film is almost paramagnetic *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 X p in the range 0.16  m ≤ X p ≤ 0.25  m. These heterostructure based devices were fabricated and studied by AGM measurement. AGM measurement shows decrease in M s 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 t GaMnN >200 nm and decreases for t GaMnN < 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 t GaMnN , 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 N. Nepal 1 , M. Oliver Luen 1 , P. Frajtag 2 , J. M. Zavada 1 , S. M. Bedair 1 , and N. A. El-Masry 2 1 Electrical and Computer Engineering, North Carolina State University, Raleigh, NC 27695 USA 2 Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695 USA Magnetic random access memories (MRAM) Europhysics News (2003) Vol. 34 No. 6 DMS: offers a multifunctional device that could replace several components. Suffers with interface scattering Soluti on Using dilute magnetic semiconductor (DMS) Ref. H. Ohno et al., Nature 408 , 944 (2000). Metal gate Insulator InMnAs InAs (AI,Ga)Sb AISb GaAs substrate R Hall was measured at 22.5 K V G >0 V G =0 V G <0 Ref. Fukuda et al., Appl. Phys. Lett. 91 , 052503 (2007). (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! 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/cm 3 . Ref: Dietl, et. al., Science, Vol. 287, 1019 (2000). * According to Zener model, predicted T c for GaMnN is above room temperature * Highest reported T c for Ga(In)MnAs material system =185 K * T c (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 M s with X p and t GaMnN 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-GaN paramagnetic * GaMnN layer on top of p-GaN ferromagnetic * Annealing GaMnN/p-GaN doubles M s FM is hole mediated *For X p = 0.17  m, GaMnN i-p-n structure is PM due to fully depleted p-GaN * For X p =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 *M s increases with X p and saturates for X p ≥ 0.25  m *For X p ~ 66 nm the GaMnN structure is PM *No effect of t GaMnN on M s for X p =0.17  m *For X p = 0.25  m, M S decrease for t GaMnN < 200 nm Variation of M s with X p Variation of M s with t GaMnN *V R 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-doping moves the fermi level “E f ” up completely filled Mn band * Mg-doping moves the fermi level “E f ” down empty Mn band * Since Mn forms deep level in GaN, Si and Mg doped GaMnN films are insulating. 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. Ec Ev E F Ec Ev GaMnN GaN:Mg Mn Mg PM GaN:Mg; 0.15  m GaMnN; 0.375  m GaMnN; 0.375  m GaN:Mg; 0.35  m FM Introduction Motivation FM Semiconductor Current injection GaAs InAlAs GaMnAs GaAs AlAs GaMnAs Sapphire GaN template (0.75  m) n -GaN (0.5  m) p -GaN (X p ) i -GaMnN (0.5  m) Si-doping CB VB t 2 Mn 3+ 0.3 eV e 1.7. eV Mg-doping ∝