• Không có kết quả nào được tìm thấy

S Y N T H E S IS A ND P R O P E R T IE S O F FE R R O M A G N E T IC M n -D O P E D AIN F ILM S

N/A
N/A
Protected

Academic year: 2022

Chia sẻ "S Y N T H E S IS A ND P R O P E R T IE S O F FE R R O M A G N E T IC M n -D O P E D AIN F ILM S"

Copied!
3
0
0

Loading.... (view fulltext now)

Văn bản

(1)

,VNU JOURNAL OF SCIENCE. M alhem atics - Physics, T.xx, N03AP. 2004

S Y N T H E S IS A ND P R O P E R T IE S O F FE R R O M A G N E T IC M n -D O P E D AIN F ILM S

P h a m H o n g Q u a n g '-2 , N g u y e n H u y S in h ', N g u y e n H u u D u e 1 a n d S e o n g C ho Yu*

'C ryogenic Laboratory, F aculty o f Physics, College o f N atural, V N U 2 D epartm ent o f Physics, C hungbuk N ational University, South Korea

A b s tr a c t: Mn-doped AIN semiconductor (AIMnN) films are a p ro m is in g m ate ria l fo r s p in tro n ic s b e c a u s e o f h ig h te m p erature fe rro m a g n e tism . A IM n N film s w ere s y n th e s iz e d b y D C s p u tte rin g te ch n iq u e . T h e crystal s tru c tu re o f s a m p le s w as c h a ra c te riz e d b y X R D . T h e c o n ce n tra tio n o f M n w a s de te rm in e d by E D S . U sing th e o p tim a l g ro w th p ro c e s s , w e h a v e ob ta in ed th e sing le p h a s e A IM n N film s w ith th e M n c o n te n t u p to 13.6 a t %. The s aturated m a g n e tiza tio n an d e n e rg y band g a p w e re fo u n d to d e c re a s e w ith incre a sin g M n con cen tratio n. T h e v a lu e s of a c tiv a tio n e n e rg y w e re d e riv e d from th e te m p erature d e p e n d e n c e o f re sista n ce , w h ic h e x h ib its c le a rly a se m ic o n d u c to r cha racte ristic.

1. I n t r o d u c t io n

T he com bination of several discoveries in m agnetic sem iconductors h a s opened up the possibility of a new re search field th a t is so-called spintronics. A s u b set of th is field involves diluted m agnetic sem iconductors (DMS). The m ain focus of th e DMS a re a is to effectively incorporate m agnetic ions in to a sem iconductor lattice and create a ferrom agnetic m aterial.

Since Dietl e t al. [1] predicted t h a t cubic GaN doped with 5 a t % of M n should exhibit a C urie te m p e ra tu re (Tc) exceeding room tem perature, a num ber of w orks have focused on wide ban d gap sem iconductors a s being the m ost prom ising ones for achieving high Tc.

Among them , th e w orks on M n-. o r Cr-doped AIN films [2,3] based on AIN sem iconductor with th e b an d gap of 6.2 eV a r e of partic u la r im portant. Room te m p e ra tu re m agnetism h as been reported for M n-doped film s grown by m olecular beam epitaxy [2].

T his p ap e r p re se n ts th e synthesis of Mn-doped AIN films usin g reactive DC sp u tte rin g technique, along w ith th e effect of M n concentration on th e properties such as crystal s tru c tu re , m agnetization, optical ban d gap, an d resistivity.

2. E x p e r i m e n t s

S am ples of com position A l|.xM nxN, w here X is the atom ic fraction of M n substituted for Al, w ere deposited sim ultaneously on q u artz s u b strates in a reactive DC m agnetron s p u tte rin g system . T he com posite ta rg e t includes a high p urity (99.999%) alum inum disk and a n u m b er o f s q u a re M n pieces 5x5 mm, which w ere placed sym m etrically on the surface of th e A1 disk. A n investigation of deposition process has been done on undoped films. T he deposition conditions w ere optimized and fixed a s following: th e partia l pressure of A r an d N., gas m ixture (67% Ar, 33% N,) w as 6 mTorr, the DC voltage w as 240V, the DC

10 6

(2)

S y n t h e s i s a n d p r o p e r tie s o f f e r r o m a g n e tic M n -doped. A I N fi l m s 1 0 7

c u rre n t w as 330mA, th e s u b s tra te tem p eratu re d u rin g deposition w as 300°c. The Mn contents w ere controlled by varying th e num ber of Mn pieces. T he XRD m ea su rem en ts were carried o u t in grazing mode using Cu-K„ radiation. T h e m ag n e tiz atio n of th e films w as m easured by a SQUID m agnetom eter. T he band gaps w ere o b tained from optical absorption m ea surem ent over th e w avelength from 200 to 900 nm in tra n s m itta n c e mode.

3. R e s u lts a n d d is c u s s io n

The atom ic concentrations of Mn determ ined by EDS w e re from X = 0.00 to 0.136, corresponding to th e num ber of Mn pieces varying from 0.0 to 3.0.

Fig. 1 show s XRD p a tte rn for one p artic u la r 0.40 ụm thick film w ith X = 0.075. All peaks are identified with th e hexagonal AIN stru ctu re . T he X-ray d a ta provide evidence th a t th e p re sen t M n-doped AIN film s are single phase. The second p h ase s w ere found by X- ra y for the film s with Mn content exceeding 0.136.

Fig. 2, shows m agnetization versus field d ata for 0.4 Jim thick with X = 0.136. The values of sa tu ra te d m agnetization indicate th a t 20% of Mn is m agnetically active in AIN sam ples com pared with 4|V M n atom [4j. We found th a t Ms a t room tem p eratu re decreased w ith increasing M n concentration, nam ely, 9.6, 8.3 an d 7.7 em u/cm 3 for X = 0.045, 0.07Õ an d 0.136, respectively. The origin of th is behavior is unclear. I t m ay re su lt from the com pensation by in te rs titia l Mn donors and/or from changes in th e local spin configurations [5].

The u v optical absorption was perform ed on the films grown on q u artz su b s tra te s with the typical thickness of 400 nm . In se t in Fig. 3 shows a 2 vs hv plots (a is absorption coefficient) for a Al(i.95sMn00<(iN film s obtained by Tsuc’s m ethod. The band gap w as d eterm ined by extrapolating the lin ear portion of th e absorption edge to zero value.

The band gap w ith M n concentration is show n in m ain graph of Fig. 3. It is clear th a t th e band gap

decreases exponentially w ith increasing Mn concentration. T hese b an d gaps correspond to th e tran sitio n from th e top of th e im purity band to th e bottom of th e conduction band. We are un aw are of an electronic s tru c tu re calculation for tran sition-m etal-doped AIN system s.

Some recent re p o rts have theoretically produced th e electronic s tru c tu re of tran sitio n - m etal-doped GaN, w hich is ra th e r related to o u r cases [4,6], According to S an y al e t al. [6], the system behaviors like a ferrom agnetic m etal with a re duced m agnetic m om ent a t Mn concentration of 5 %. In th is point of view, th e exponential d ecrease of optical b and gap in Mn-doped is re la ted w ith band s tru ctu re change an d strongly co rrela te d w ith m agnetic behavior with M n concentration exceeding 5 %.

2 0 4 0 M SO

F ig .l. X-ray diffraction (xkỉ)) data for the 0.4 nm thick Al0»2jCr00T5N films.

H (kOe) Fig. 2: Magnetization M versus static external magnetic field H measured at 10 K and 300 K for the 0.40 nm thick

film. The field was applied in plane

(3)

108 P h a m H o n g Q u a n g , N g u y e n H u y S in h ,..

T ra n s p o rt p ro p e rty w a s m ea su red by four-probe m ethod. Fig. 4 show s the te m p e ra tu re dependence of re sistan c e, R(T), for th e 13.6 % M n-doped AIN film . R(T) plots follow th e expression R = R„Tl/2exp(En/k BT), which describes th e tr a n s p o r t p ro perty in a sem iconductor m ateria l. By fittin g th e R(T) plot, we could o b tain th e valu e of activation energy E„ = 145 meV. F u rth e r s tu d ie s have pointed o u t th a t tr a n s p o r t ch a rac teriza tio n depends n o t only on th e M n concentration but also on th e cry sta lin ity o f sam ples.

Fig.3. Optical band gap as a function of Mn concentration for Al,.,Mn,N (x = 0.0 - 0.136) films. Inset is a 2 vs photon energy plots at

X = 0.045 to get optical band gap

In sum m ary, we have obtained the single-phase A l|.vM nxN film s w ith th e Mn concentration up to a valu e of X = 0.136. The sa tu ra te d m ag netization a n d band gap decreased w ith in cre asin g M n concentration.

The exponential decrease of optical ban d gap in Mn- doped is strongly correlated with m agnetic behavior. T e m p e ra tu re dependence of re sistan c e exhibits clearly a sem iconductor characteristic,

Fig.4. R.TKi vs T plot und fitting curve for Al|JS(1Mn„ UN film

Acknow ledgem ents. T h e w ork a t Hanoi U niversity w as supported by the V ietnam ese-Italy cooperation program (8BS3). T he work in K orea w as supported by th e K orea Research F oundation G ra n t (K RF-2003-005-C00018).

R e fe re n c e s

1. T. Dietl, H. Ohno, F. M atsukura, J. Cibert, and D. Ferrand, Science 287(2002) 1019.

2. R. Frazier, G. T haler. M. Overberg, B. Gila, c . R. Abernathy, and s . J. Pearton. Appl.

Phys. Lett. 83(2003) 1758.

3. S. G. Yang, A. B. Pakhomov, s . T. Hung, and c . Y. Wong, Appl. Phys. Lett. 81(2002) 2418.

4. M ark van Schilfgaarde and o . N. Mryasov. Phys. Rev. B, 63(2001) 233205-1.

5. J . M asek and F. M ark. Acta Phys. Polon. A 100(2001) 319.

6. B. Sanyal, o . Bengone, and s . Mirbt. Phys. Rev. B, 68(2003) 20.

Tài liệu tham khảo

Tài liệu liên quan

W hen th e conditions of p aram etric resonance (PR) are satisfied, p aram etric interactions and transform ations (PIT) of sam e kin d s of excitations, such a s

In [1 2] the physics problem was restricted for degenerate semiconductors in the case of m onophoton ahsorptioii Tho rpsnlts of works [1,^] iìuliraí-o th at tho

Analytical expressions for the effective local force constants, correlated Einstein frequency and temperature, first cumulant or net thermal expansion, second

For saline soils with high enough salt levels to significantly damage plants and reduce growth, reclamation with excess water is recommended, provided there is enough good

cover will have a 50% reduction in soil loss compared to a bare field. This effect of residue cover on reducing soil loss occurs for a variety of reasons. As previously discussed,

It was shown th at for evaluation of LPS spectra we can consider the matrix eleiiK'nts to be constant and the intensity of angle-resolved LPS spectra is proportional

In this paper, the absolute efficiency of HPGe detector is surveyed and mearsured at different distances from detector and different gamma

[r]