The Estimation and revision of barrier heights in 4H- SiC and 6H-sic Schottky Diodes
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Mat. Res. Soc. Symp. Proc. Vol. 512 ©1998 Materials Research Society
THE MODELING OF THE SCHOTTKY BARRIER HEIGHT OF SiC A. EXPERIMENTAL DATA FOR BARRIER HEIGHTS Among the various SiC polytypes such as 2H-, 4H-, 6H-, 15R-, 3C-SiC, the 4H-SiC and 6HSiC are the most widely used SiC polytypes because of the high-quality crystals in vapor phase epitaxy [3,4]. The SiC has the face-polarity so that electrical properties are different for Si-face vs. C-face. Therefore, four different cases for barrier heights exist. These data are arranged in Tablel.The data of 4H-SiC was obtained from Itoh-group and the data of 6H-SiC was obtained from Waldrop-group. Table 1. The barrier height of various metals in (a) n-type 4H- SiC[5] and (b) 6H-SiC [1,2,7,8] according to the face polarities.
(a)
Ti Au Ni
0.,
Si-face
C-face
4.33 5.10 5.15
1.10 1.71 1.60
1.20 1.85 1.58
(b) 0,, Mg Mn Ag Al Ti W Au Pd Ni
3.65 4.12 4.26 4.28 4.33 4.55 5.10 5.12 5.15
6H-SiC Si-face 0.30 0.85 0.90 0.30 0.74 0.79 1.42 1.16 1.27
C-face 0.33 1.14 0.90 1.04 1.21 1.60 1.68
Both 4H-SiC [5] and 6H-SiC [1,2,7,8] employed n-type SiC wafers, since native oxides grown on n-type SiC wafers have lower interface state densities and much lower effective oxide charge densities than those grown on p-type SiC wafers [6]. The 6H-SiC data took the mean of the values of XPS, C-V method and I-V method at 300 K.
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B. EMPIRICAL RELATIONSHIP BETWEEN 0, AND qB In order to estimate the electron barrier height, qB of the linear function of metal work function, ,,.the LSM is employed. The relationship between oB and 0,,, by LSM is extracted as (1).
(1)
0 = aq,,, + b
a
where
2
. -EXgY_. mB
In
b
l=.)/ E02
aaZB.
-
From the above data, the linear functions of four different cases are estimated as follows. Table2. The data of LSM in 4H-SiC and 6H-SiC
•'¢=: Z••b
1B 01,, a b
n-type 4H-SiC Si-face C-face 14.58 14.58 71.28 71.28 4.63 4.41 22.77 21.72 0.63 0.69 -1.89 -1.52
n-type 6H-SiC C-face Si-face 31.89 40.56 147.28 184.96 7.89 7.74 36.87 36.26 072 0.64 -2.00 -2.15
The linear estimation of electron barrier height in 4H-SiC and 6H-SiC and the experimented data [1,2,5,7,8] are shown in Fig. 1 and Fig.2, respectively.
2.0 '-1 1.8
2.
4H-SiC @.3001K
6H-SiC @300 0K C-face
0)o•1.6
:2 1.4
"ES1.2 , 1.0 0.8 0.6 0.4 0.2
C-face
/K2.0-
Si-face
•.1.4
nSi-face~1~1
1.2 10 0
o *
w]
C-face Si-face
'.0" 3.5"4'.0"4.5" 5.0" 5'.5"6.00.35"40
0.4 0.2
C-face •*Si-face 0
•
AJ
45"50"55"60
Metal Work Function [eVJ (b) (a) Fig.1 The barrier height of 4H-SiC (a) and 6H-SiC (b).
Metal Wobrk Function [eVi
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It is shown that the barrier heights on C-faces are higher than those on Si-faces. There is the case such as AI(6H-SiC Si-face) that the estimation is not reasonable. However, the estimation is reasonable in most metals, especially in Ti (4H-SiC,6H-SiC), Pd (6H-SiC Si-face), Al (6HSiC C-face) and Mg (6H-SiC Si-face).
C. THE REVISED EQUATION IN SiC The barrier height of Si was shown in reference [9]. However this equation is not valid in SiC. So, we ha
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