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Nitrogen and iodine doping in amorphous diamond-like carbon films
DI ©ND AND NN TN© TNNIAL$ ELSEVIER
Diamond and Related Malcrizds 611q97)555 558
Nitrogen and iodine dopiag in amorphous diamond-like carbon films M. Allon-Alaluf *~ N. Croitoru Facuhy O/'Engi~weriltg, D,:tmrtmen; q/'Eleclrical E;2gi;weriny-Physical Electronics, Tel-Aviv UniversiO,, Ramat Aviv 69978, Israel
Abstracl Thin lihns of amorl)hous diamondlike carbon (a:DLCt were deposited by pl'-asma decomposition of hydrocarbon gas, such as
methane gas (CH4). The plasma was produced using a r.f. generator. "lhese thin films of a:DLC were doped by incorporation of nitrogen (a:N-DLC) and iodine (a:I-DLC) gases during the deposition process. Microhardness tests shox~,ed high hardness of about 4700-4900 kg mm-z for a:DLC fiims. The microhardness of the fihns was reduced by the doping process (3400 kg mm-' for 10% nitrogen and 3200 kg mm 2 for 10~k iodine partial pressure~. From optical measurements at visible light (400 800 nm), optical energy band gaps of about 1.1 eV for a:DLC lilm, 1.39 eV I\)r ~:N-DLC and (I.78 eV for a:I-DLC were determined. From measurements of d.c. conductivity as a function of temperature, the electrical activation energies were determined and found to be 0.34 eV for undoped a:DLC films, 0.20 eV lbr mtrogen-doped films and 0.23 eV for iodine-doped films. The electrical resistivity at room temperature was reduced by almost three and two orders of magnitude with the doping processes, t'rom 108W'cm for undoped fihn to 5.10SW'cm for nitrogen- and iodine-doped films. ~; 1997 Elsevier Science S.A. Kevwords." Amorphous; Microhardness: Optical: Electrical: Doping
1. |ntroduetion
Diamond-like carbon fihn in its amorphous form (a:DLC) was lound to be a hard material, with a low band gap (!.1 eV) and high resistivity ( l0 s f~.cm) [1 3]. These properties provide to these fihns advantages over other types of materials used for optical and electrical applications. Fabrication of electronic devices made of a: DLC films were reported [4,5]. There have been previous reports on electronic doping of a:DLC films with various elements [6-11]. Electrical resistivity reduction, which was reported, was achieved by: phosphine or diborate doping [6], incorporation of metals [9,10] and incorporation of nitrogen during the film decomposition [7,8,11 ]. Crystalline materials are being doped by using atoms which may change the local structure of bonding by introducing these atoms interstitially or substitutionally. In amorphous materials these types of coping can be made by addition of large concentrations of doping elements, to compensate the existing traps and dangling bonds. In this paper we examine the possibility of doping of a:DLC films which were grown with incorporation of * Corres ?onding author. 0925-9635/97/$17.00 © 1997 Elsevier Science S.A. All rights reserved. PII S0925-9635 (96) 00736-4
nitrogen and iodine during the deposition process. Tile hardness, optical energy gap and tile electrical conductivity of nitrogen- and iodine-incorporated a:DLC fihns (a:N DLC and a:l DLC, respectively) were measurcd It) determine the element incorporation influence on these properties.
2. Experimental details Thin films of a:DLC films were grown on several substrates, such as: silicon, germanium, several types of glasses and on several metals. The films were deposited by plasma decomposition of methane (CH4) using a r.f. generator (13.56 MHz) at room temperature substrates. The deposition conditions of the a:DLC films were: high vacuum (10-6Torr), generator power of 200W and CH4 pressure of 5 mTorr. The a:DLC films were found to be hard (4700 kg mm -2) with an optical band gap of 1.1 eV and electrical resistance of 10u f~. cm. The deposition apparatus and conditions, together with the mechanical, optical and electrical measurements have been described elsewhere [1-3]. Iodine-doped films were fabricated (a:I-DLC) [12]. Iodine in its crystalline form was stored in a vessel outside the deposition system for incorporation in the
556
.~I. :lth,n-Alahdl ,V ('roitortt Diam,mdw,t Rchm,d Mawr*aL~'(~i iooTi 555 55,~
films during the growing process, A heating element, in the temperature range of 30-60 C, heated the iodine crystal and transformed it in iodine gas that was admitted into the vacuum chamber. The total deposition gas pressure in the chamber was 5 mTorr and the partial pressure of the iodine was varied between 0 and 20% of it. Increasing the iodine partial pressure has increased the iodine incorporation in the films. Nitrogen-doped films (a:N-DLC) were also fabricated [ 13]. Nitrogen gas was added to the methane gas during the decomposition process to create nitrogen-doped films. The amount of the nitrogen during the incorporation process was controlled by the partial pressure in the chamber. Microhardness tests were conducted on doped and undoped films deposited (thickness, t =2000 2500 A) on silicon substrates. The tests x~,et'emade using Vickers method for thin films. Optical measurements were carried out on films deposited (t-,. 2500.&} on optical coming ghtss. The visible light measurements were performed by using a monochromator, at wavelengths of 400--800 nm, and a scanning detector. Electrical measurements were also performed on films that were deposited in a lateral MIM device. For the MIM device, the films were deposited on insulating substrates (coming glass}, and with thickness (t) of of about 3000,~. Top metal contacts were sputtered through a mask to obtam the I-cm wide lateral M IM device with 10-l.tm spacing between the contacts.
3, Results and discussion 3,1, X-ray pl~otoeh, ctron spectroscopic t XPS) am~ Auger e&ctron ,~pectroscopy ( A E S ) amdyses
For these analyses, nitrogen- and iodine-doped films (20% partial pressure), 450 A thickness, were grown on silicon substrates. The XPS analyses were performed using Ka radit~tion ( 1486.6 eV ) from an AI source. This analysis for a:N-DLC showed the existence of nitrogen atoms in the film together with the expected carbon atoms and ira.purities of oxygen atoms, which were adsorbed on the film surface. AES depth profile showed that the concentration of nitrogen in the film is constant along the film thickness. XPS analysis in a:I-DLC films showed the existence of iodine atoms together with nitrogen and oxygen atoms, and with the expected carbon atoms in the doped film, The presence of nitrogen and oxygen atoms in the doped film is not suppressed despite the high vacuum in the chamber before the deposition process. The iodine was admitted into the chamber from the outside vessel containing iodine crystals at low vacuum (10 -~ Torr). Atmospheric gases such as oxygen and nitrogen, which
are present in the vessel at this pressure, may penetrate together with the iodine gas into the vacuum chamber and incorporate in the films during the growth process. AES depth profile showed that the concentration of the iodine remains constant along the lilm thickness, the same result as in a:N-DLC. 3.2. Mh'rohar&wss tests
The microhardness test was conducted using the Vickers method for thin films. The hardness values of the films, grown on silicon substrates, were found by applying a determined load on the sample, by an diamond indenter and diagonally received patterns. The hardnesses of the films were calculated using the ,|onsson and Hogmark model [ 14] and compared to Ford's model [15]. The microhardness of the undoped a:DLC film was found to be high (4700-4900 kg mm z). The n~icrohardnesses of the undoped film and of a:N-DLC and a:I-DLC for dopir~g elements of 10 and 20% partial pressure, are shown in Fig. !. The incorporation of elements affects the fihn hardness, in both cases I nitrogen and iodine), and causes decrease in microhardness with increase of concentration of doping elements. 3.3. Optical properties
The optical properties of tile liims were determined by measuring the transmission iT) and reflection JR} of these films, in visible light. From the transmitted and lhe rellected light the complex refractive index { n - i k ) was determined. The absorption coefficient, ~, was estimated from the absorbence cocflicient, k, using the relation, :~--:4~kt~, where t and ~ are the liim thickness and the light wavelength, respectively. The optical absorption in the fiims was found to be high (:~>104cm ~m) for visible light [3]. Hence, for high absorption, the parabolic relation of Tauc is valid [16].
6000 i,
•
doped Nitrogendoped Undoped
.ILI~T._IIodine
i/.SZTZI
5000
-
'
E
E
4000
v 3000 ........
lo
.......
t--2~00
1000
0
i.........l .........! 1u
20
Partial presure of I and N
Fig. I. The microhardness of undoped and nitrogen- and iodinedoped films
.~t. ..t//on-.4/alu/i N. ('t'oiror,
Dimn,md ,m,t Rclatc¢l Materials 6 i 1997 555 55,~'
Using the Tauc relation: {:X" E ) t'2 = B 12 • ( E - - Eg )
{ ~}
the optical band gap of the films was determined. Fig. 2 presents ~he Tauc pJot ~k~r the undoped film and !i)r :,;N-DLC a~d a:l-DJ C fihns !by inc(,rporadon of N ~:nd I elements of 20% partial pressure), tn conclusion, our study shows that nitrogen and iodine incorporation affects the optical band gap of the a:DLC films. Nitrogen increases the optical band gap from 1.I tv 1.39eV, whereas iodine causes a decrease in the E e to 0.78 eV. However, the refractive index, n, was unchanged by the doping, and was found to be n =2.4 for undoped and doped films.
3.4. Eh,ctrical properties The d.c. conductivity (~r) dependence on temperature (T) were measured using lateral MIM devices in the temperature range of 150-300 K. The experimental semilog plots for a:DLC, a:N-DLC and a:I-DLC fihns arc shown on Fig. 3. The electrical field for these measurements was about 10-' V c m 700
557
The conductivity in a : D L ( tibias, whk.h decreases as a function ot" l / 7 l a - e x p ~ - - f / k T~) only a', high temperature ~F>275 K ~, suggests a thermally activated conduction for these values of T. At Ro~er temperatures the variation of cr as a function of T was different, ~hich suggests that other processes have an influence on the conductivity. However, the conductivity in a:N-DLC and a:[-DLC varied with 1/T for all measured temperatures. The value of o was determined and it was found that nitrogen (20% partial pressure) and iodine (10% partial pressure) caused an increase in the value of conductivity of more than three orders of magnitude for nitrogen-doped films and two orders of magnitude for iodine-doped film. Furthermore, it was also shown that p = t.4. [0 s f2.cm at 300 K with an activation energy of 0.34 eV, whereas for a:N-DLC, p=5.10 s f~.cm with an activation energy of 0.20eV, and p = 5 . 1 0 s f ~ . c m with an activation energy of 0.23 eV for a:I-DLC. a:DLC fihns deposited on glass at higher concentration of iodine (20% and more) cracked after a short period of time Ca few hours), which made electrical measurements difficult to perform.
-
4. Conclusions 600
'/3¢" a:DLC '#-" 500
~/¢! ~" .
~
f,
,
~.'-
,4> ~
400,
,,.W~... /
,,~?,,f' g~ a.N-DLC
://., /
Eo i 2" :,0o
~,-o,.c/;,/ / ; # = ,re
2
..¢
,
100
^/
I 1
2
21
Photon energy (eV) Fig. 2. Tauc plot tbr the undoped and doped lihns. 10-~
\
10.~
\,)'\
'E I0~ L)
\
I~ 10 "8
10~
a:N-DLC \\
NN~
a:I-DLC i
a:DLC 10 lo
-* . . . .
2
r
,
. . . . . . . . . . . . . . .
3
4
Amorphous diamond-like carbon lilms were deposited using r.f. plasma decomposition of metl,a;:e gas. Incorporation of nitrogen or iodine into a:DLC fihns, during the film deposition, produced doped a:DLC lilms. XPS analysis of a:N-DLC showed the presence of nitrogen in tile film, and analysis of a:I-DLC showed tile presence of iodine atoms together with carbon, n i l r o g e n ;.ind oxygen atoms. Microhardness tests showed a decrease m microhardhess after nitrogen and iodine doping. Optical measure° ments in visible light showed a reduction of optical energy band in a:I-DLC films, from !.i eV in a:DLC films to 0.78 eV, and an increase of the optical energy band gap in a:N-DLC fihns~ to 1.39 eV. Iodine doping also affects the electrical conductivity. The conductivity increased by more than two orders of magnitude in a:I-DLC films (10% partial pressure) as compared to a:DLC films, and three orders of magnitude in a:N-DLC films (20% martial pressure). Iodine and nitrogen reduce the electrical activation energy of the fihns from 0.34eV for a:DLC to 0.23 and 0.20eV. respectively.
"
T . . . . . .
r
5
6
"
r
,
Acknowledgemen~
,
7
1000/T (K "1)
Fig. 3. The conductivity versus temperature in doped and undoped films.
The author would like to thank Mr. L. Kiibanov (Tei-Aviv University, Israel) for some of the conductivity measurements
558
M, ,qllon~:lhah~?i N, ()~oito~'l~ / DiamotM amt Rebated Matersals 6 t 1997) 5 5 : 5 5 8
Referenees
tSl A. Grill, V. Paid and S. Coheu, Dhmaond R¢,A~I, Mater., 3 ( 19941 281,
[ 1] M. Alaluf, D. Aizenman and N. Croitoru, lst~,el Ah~terhd Engineering Col!ference, IMEC 6, 1993. [2] M. Alalul\ J. Appelbaum, L. Klibanov, D. Brinker, D. Scheimar, and N. Croitoru, Thin Solid Films. 256 (1995) I. [3] M. Allon-Alaluf, L. Kiibanov, A. Seidman and N. Croitoru, Dhamond Relat, Mater,, 5(IO06) 1275, [4] G. Amaratunga, D, Segal and D, Mcknezie, Appl. Phys. Lett,, 59 ( 1991 )69. [5] V. Polyakov, P.I. Perov, M.G, Ermakov and O.N. Ermakova, Thin Solid Fibns, 212 (1992) 226. [6] B. Meyerson and F, Smith, Solid State Commun., 34 (1980) 531. [7] O. Amir and R, Kalish, J, Appl. Phys,, 7() ( 1991 ) 4958.
[91 H, Dimigen, H. Hubsch and R. Memmmg, AppL Phys. Lctt., 50 { 1987~ 1056,
li01 P. Kiages and R, Memmim, Mater, St'i. Forum, 52- 53 11989) 609. [!11 S. Silva and G. Aramatunga, Thin Solid Fibns, 2"PO{ 1995) 194, 1~21 M. Allon-Alaluf, L. Klibanov and N. Croitoru, Diamond Rehlt. Mater., { 1996) in press.
[131 L. Klibanov, M, Alaluf, A. Seidman and N. Croitoru, ,~ttt IEEE Cony. Tel-Aviv, Israel, 1995.
[14] B. Jonsson and S. Hogmark, Thhi Solid Fihns, 114 (1984) 257. [15] l.J. Ford, Thh, Solid Films, 245 (1994) 122. [16] N.F. Mort and E.A. Davis, Eh, ctronic Processes in Non-cr.vstallhze Materials, 2nd edn., Clarendon Press, 1979.
Diamond and Related Malcrizds 611q97)555 558
Nitrogen and iodine dopiag in amorphous diamond-like carbon films M. Allon-Alaluf *~ N. Croitoru Facuhy O/'Engi~weriltg, D,:tmrtmen; q/'Eleclrical E;2gi;weriny-Physical Electronics, Tel-Aviv UniversiO,, Ramat Aviv 69978, Israel
Abstracl Thin lihns of amorl)hous diamondlike carbon (a:DLCt were deposited by pl'-asma decomposition of hydrocarbon gas, such as
methane gas (CH4). The plasma was produced using a r.f. generator. "lhese thin films of a:DLC were doped by incorporation of nitrogen (a:N-DLC) and iodine (a:I-DLC) gases during the deposition process. Microhardness tests shox~,ed high hardness of about 4700-4900 kg mm-z for a:DLC fiims. The microhardness of the fihns was reduced by the doping process (3400 kg mm-' for 10% nitrogen and 3200 kg mm 2 for 10~k iodine partial pressure~. From optical measurements at visible light (400 800 nm), optical energy band gaps of about 1.1 eV for a:DLC lilm, 1.39 eV I\)r ~:N-DLC and (I.78 eV for a:I-DLC were determined. From measurements of d.c. conductivity as a function of temperature, the electrical activation energies were determined and found to be 0.34 eV for undoped a:DLC films, 0.20 eV lbr mtrogen-doped films and 0.23 eV for iodine-doped films. The electrical resistivity at room temperature was reduced by almost three and two orders of magnitude with the doping processes, t'rom 108W'cm for undoped fihn to 5.10SW'cm for nitrogen- and iodine-doped films. ~; 1997 Elsevier Science S.A. Kevwords." Amorphous; Microhardness: Optical: Electrical: Doping
1. |ntroduetion
Diamond-like carbon fihn in its amorphous form (a:DLC) was lound to be a hard material, with a low band gap (!.1 eV) and high resistivity ( l0 s f~.cm) [1 3]. These properties provide to these fihns advantages over other types of materials used for optical and electrical applications. Fabrication of electronic devices made of a: DLC films were reported [4,5]. There have been previous reports on electronic doping of a:DLC films with various elements [6-11]. Electrical resistivity reduction, which was reported, was achieved by: phosphine or diborate doping [6], incorporation of metals [9,10] and incorporation of nitrogen during the film decomposition [7,8,11 ]. Crystalline materials are being doped by using atoms which may change the local structure of bonding by introducing these atoms interstitially or substitutionally. In amorphous materials these types of coping can be made by addition of large concentrations of doping elements, to compensate the existing traps and dangling bonds. In this paper we examine the possibility of doping of a:DLC films which were grown with incorporation of * Corres ?onding author. 0925-9635/97/$17.00 © 1997 Elsevier Science S.A. All rights reserved. PII S0925-9635 (96) 00736-4
nitrogen and iodine during the deposition process. Tile hardness, optical energy gap and tile electrical conductivity of nitrogen- and iodine-incorporated a:DLC fihns (a:N DLC and a:l DLC, respectively) were measurcd It) determine the element incorporation influence on these properties.
2. Experimental details Thin films of a:DLC films were grown on several substrates, such as: silicon, germanium, several types of glasses and on several metals. The films were deposited by plasma decomposition of methane (CH4) using a r.f. generator (13.56 MHz) at room temperature substrates. The deposition conditions of the a:DLC films were: high vacuum (10-6Torr), generator power of 200W and CH4 pressure of 5 mTorr. The a:DLC films were found to be hard (4700 kg mm -2) with an optical band gap of 1.1 eV and electrical resistance of 10u f~. cm. The deposition apparatus and conditions, together with the mechanical, optical and electrical measurements have been described elsewhere [1-3]. Iodine-doped films were fabricated (a:I-DLC) [12]. Iodine in its crystalline form was stored in a vessel outside the deposition system for incorporation in the
556
.~I. :lth,n-Alahdl ,V ('roitortt Diam,mdw,t Rchm,d Mawr*aL~'(~i iooTi 555 55,~
films during the growing process, A heating element, in the temperature range of 30-60 C, heated the iodine crystal and transformed it in iodine gas that was admitted into the vacuum chamber. The total deposition gas pressure in the chamber was 5 mTorr and the partial pressure of the iodine was varied between 0 and 20% of it. Increasing the iodine partial pressure has increased the iodine incorporation in the films. Nitrogen-doped films (a:N-DLC) were also fabricated [ 13]. Nitrogen gas was added to the methane gas during the decomposition process to create nitrogen-doped films. The amount of the nitrogen during the incorporation process was controlled by the partial pressure in the chamber. Microhardness tests were conducted on doped and undoped films deposited (thickness, t =2000 2500 A) on silicon substrates. The tests x~,et'emade using Vickers method for thin films. Optical measurements were carried out on films deposited (t-,. 2500.&} on optical coming ghtss. The visible light measurements were performed by using a monochromator, at wavelengths of 400--800 nm, and a scanning detector. Electrical measurements were also performed on films that were deposited in a lateral MIM device. For the MIM device, the films were deposited on insulating substrates (coming glass}, and with thickness (t) of of about 3000,~. Top metal contacts were sputtered through a mask to obtam the I-cm wide lateral M IM device with 10-l.tm spacing between the contacts.
3, Results and discussion 3,1, X-ray pl~otoeh, ctron spectroscopic t XPS) am~ Auger e&ctron ,~pectroscopy ( A E S ) amdyses
For these analyses, nitrogen- and iodine-doped films (20% partial pressure), 450 A thickness, were grown on silicon substrates. The XPS analyses were performed using Ka radit~tion ( 1486.6 eV ) from an AI source. This analysis for a:N-DLC showed the existence of nitrogen atoms in the film together with the expected carbon atoms and ira.purities of oxygen atoms, which were adsorbed on the film surface. AES depth profile showed that the concentration of nitrogen in the film is constant along the film thickness. XPS analysis in a:I-DLC films showed the existence of iodine atoms together with nitrogen and oxygen atoms, and with the expected carbon atoms in the doped film, The presence of nitrogen and oxygen atoms in the doped film is not suppressed despite the high vacuum in the chamber before the deposition process. The iodine was admitted into the chamber from the outside vessel containing iodine crystals at low vacuum (10 -~ Torr). Atmospheric gases such as oxygen and nitrogen, which
are present in the vessel at this pressure, may penetrate together with the iodine gas into the vacuum chamber and incorporate in the films during the growth process. AES depth profile showed that the concentration of the iodine remains constant along the lilm thickness, the same result as in a:N-DLC. 3.2. Mh'rohar&wss tests
The microhardness test was conducted using the Vickers method for thin films. The hardness values of the films, grown on silicon substrates, were found by applying a determined load on the sample, by an diamond indenter and diagonally received patterns. The hardnesses of the films were calculated using the ,|onsson and Hogmark model [ 14] and compared to Ford's model [15]. The microhardness of the undoped a:DLC film was found to be high (4700-4900 kg mm z). The n~icrohardnesses of the undoped film and of a:N-DLC and a:I-DLC for dopir~g elements of 10 and 20% partial pressure, are shown in Fig. !. The incorporation of elements affects the fihn hardness, in both cases I nitrogen and iodine), and causes decrease in microhardness with increase of concentration of doping elements. 3.3. Optical properties
The optical properties of tile liims were determined by measuring the transmission iT) and reflection JR} of these films, in visible light. From the transmitted and lhe rellected light the complex refractive index { n - i k ) was determined. The absorption coefficient, ~, was estimated from the absorbence cocflicient, k, using the relation, :~--:4~kt~, where t and ~ are the liim thickness and the light wavelength, respectively. The optical absorption in the fiims was found to be high (:~>104cm ~m) for visible light [3]. Hence, for high absorption, the parabolic relation of Tauc is valid [16].
6000 i,
•
doped Nitrogendoped Undoped
.ILI~T._IIodine
i/.SZTZI
5000
-
'
E
E
4000
v 3000 ........
lo
.......
t--2~00
1000
0
i.........l .........! 1u
20
Partial presure of I and N
Fig. I. The microhardness of undoped and nitrogen- and iodinedoped films
.~t. ..t//on-.4/alu/i N. ('t'oiror,
Dimn,md ,m,t Rclatc¢l Materials 6 i 1997 555 55,~'
Using the Tauc relation: {:X" E ) t'2 = B 12 • ( E - - Eg )
{ ~}
the optical band gap of the films was determined. Fig. 2 presents ~he Tauc pJot ~k~r the undoped film and !i)r :,;N-DLC a~d a:l-DJ C fihns !by inc(,rporadon of N ~:nd I elements of 20% partial pressure), tn conclusion, our study shows that nitrogen and iodine incorporation affects the optical band gap of the a:DLC films. Nitrogen increases the optical band gap from 1.I tv 1.39eV, whereas iodine causes a decrease in the E e to 0.78 eV. However, the refractive index, n, was unchanged by the doping, and was found to be n =2.4 for undoped and doped films.
3.4. Eh,ctrical properties The d.c. conductivity (~r) dependence on temperature (T) were measured using lateral MIM devices in the temperature range of 150-300 K. The experimental semilog plots for a:DLC, a:N-DLC and a:I-DLC fihns arc shown on Fig. 3. The electrical field for these measurements was about 10-' V c m 700
557
The conductivity in a : D L ( tibias, whk.h decreases as a function ot" l / 7 l a - e x p ~ - - f / k T~) only a', high temperature ~F>275 K ~, suggests a thermally activated conduction for these values of T. At Ro~er temperatures the variation of cr as a function of T was different, ~hich suggests that other processes have an influence on the conductivity. However, the conductivity in a:N-DLC and a:[-DLC varied with 1/T for all measured temperatures. The value of o was determined and it was found that nitrogen (20% partial pressure) and iodine (10% partial pressure) caused an increase in the value of conductivity of more than three orders of magnitude for nitrogen-doped films and two orders of magnitude for iodine-doped film. Furthermore, it was also shown that p = t.4. [0 s f2.cm at 300 K with an activation energy of 0.34 eV, whereas for a:N-DLC, p=5.10 s f~.cm with an activation energy of 0.20eV, and p = 5 . 1 0 s f ~ . c m with an activation energy of 0.23 eV for a:I-DLC. a:DLC fihns deposited on glass at higher concentration of iodine (20% and more) cracked after a short period of time Ca few hours), which made electrical measurements difficult to perform.
-
4. Conclusions 600
'/3¢" a:DLC '#-" 500
~/¢! ~" .
~
f,
,
~.'-
,4> ~
400,
,,.W~... /
,,~?,,f' g~ a.N-DLC
://., /
Eo i 2" :,0o
~,-o,.c/;,/ / ; # = ,re
2
..¢
,
100
^/
I 1
2
21
Photon energy (eV) Fig. 2. Tauc plot tbr the undoped and doped lihns. 10-~
\
10.~
\,)'\
'E I0~ L)
\
I~ 10 "8
10~
a:N-DLC \\
NN~
a:I-DLC i
a:DLC 10 lo
-* . . . .
2
r
,
. . . . . . . . . . . . . . .
3
4
Amorphous diamond-like carbon lilms were deposited using r.f. plasma decomposition of metl,a;:e gas. Incorporation of nitrogen or iodine into a:DLC fihns, during the film deposition, produced doped a:DLC lilms. XPS analysis of a:N-DLC showed the presence of nitrogen in tile film, and analysis of a:I-DLC showed tile presence of iodine atoms together with carbon, n i l r o g e n ;.ind oxygen atoms. Microhardness tests showed a decrease m microhardhess after nitrogen and iodine doping. Optical measure° ments in visible light showed a reduction of optical energy band in a:I-DLC films, from !.i eV in a:DLC films to 0.78 eV, and an increase of the optical energy band gap in a:N-DLC fihns~ to 1.39 eV. Iodine doping also affects the electrical conductivity. The conductivity increased by more than two orders of magnitude in a:I-DLC films (10% partial pressure) as compared to a:DLC films, and three orders of magnitude in a:N-DLC films (20% martial pressure). Iodine and nitrogen reduce the electrical activation energy of the fihns from 0.34eV for a:DLC to 0.23 and 0.20eV. respectively.
"
T . . . . . .
r
5
6
"
r
,
Acknowledgemen~
,
7
1000/T (K "1)
Fig. 3. The conductivity versus temperature in doped and undoped films.
The author would like to thank Mr. L. Kiibanov (Tei-Aviv University, Israel) for some of the conductivity measurements
558
M, ,qllon~:lhah~?i N, ()~oito~'l~ / DiamotM amt Rebated Matersals 6 t 1997) 5 5 : 5 5 8
Referenees
tSl A. Grill, V. Paid and S. Coheu, Dhmaond R¢,A~I, Mater., 3 ( 19941 281,
[ 1] M. Alaluf, D. Aizenman and N. Croitoru, lst~,el Ah~terhd Engineering Col!ference, IMEC 6, 1993. [2] M. Alalul\ J. Appelbaum, L. Klibanov, D. Brinker, D. Scheimar, and N. Croitoru, Thin Solid Films. 256 (1995) I. [3] M. Allon-Alaluf, L. Kiibanov, A. Seidman and N. Croitoru, Dhamond Relat, Mater,, 5(IO06) 1275, [4] G. Amaratunga, D, Segal and D, Mcknezie, Appl. Phys. Lett,, 59 ( 1991 )69. [5] V. Polyakov, P.I. Perov, M.G, Ermakov and O.N. Ermakova, Thin Solid Fibns, 212 (1992) 226. [6] B. Meyerson and F, Smith, Solid State Commun., 34 (1980) 531. [7] O. Amir and R, Kalish, J, Appl. Phys,, 7() ( 1991 ) 4958.
[91 H, Dimigen, H. Hubsch and R. Memmmg, AppL Phys. Lctt., 50 { 1987~ 1056,
li01 P. Kiages and R, Memmim, Mater, St'i. Forum, 52- 53 11989) 609. [!11 S. Silva and G. Aramatunga, Thin Solid Fibns, 2"PO{ 1995) 194, 1~21 M. Allon-Alaluf, L. Klibanov and N. Croitoru, Diamond Rehlt. Mater., { 1996) in press.
[131 L. Klibanov, M, Alaluf, A. Seidman and N. Croitoru, ,~ttt IEEE Cony. Tel-Aviv, Israel, 1995.
[14] B. Jonsson and S. Hogmark, Thhi Solid Fihns, 114 (1984) 257. [15] l.J. Ford, Thh, Solid Films, 245 (1994) 122. [16] N.F. Mort and E.A. Davis, Eh, ctronic Processes in Non-cr.vstallhze Materials, 2nd edn., Clarendon Press, 1979.