Temperature Dependent Barrier Height, Ideality Factor, Series Resistance of the Al/Al2O3/p-Si (MIS) Diodes Using Cheung’s Functions in Temperature Range of 200-320 K

Temperature Dependent Barrier Height, Ideality Factor, Si (MIS) Diodes Using -

/p O 3

Series Resistance of the Al/Al 2

Cheung’s Functions in Temperature Range of 200-320 K

1Elif Marıl, 2Mehmet Kosal, 3Şemsettin Altındal

1Department of Property Protection and Securty, Yenice Vocational School, Karabük University, Karabük, Turkey

2Department of Physic, Faculty of Arts and Sciences, Harran University, Şanlıurfa, Turkey 3Department of Physics, Faculty of Sciences, Gazi University, Ankara, Turkey

Abstract- In this study, the main electrical parameters such as barrier height (BH), ideality factor (n), series resistance (Rs) of the fabricated Al/Al2O3/p-Si (MIS) diodes have been investigated as function of temperature. For this purpose, Cheung’s plots were drawn from the downward concave curvature region in the forward bias semi-logarithmic current-voltage (I-V) plots originated from Rs in temperature range of 200-320 K. It is well known that these electrical parameters may be depended of calculation method as well as bias voltage. Since the LnI-V plot has linear only at narrow bias voltage, the reliability and accuracy of the results may be discussed. Therefore, firstly the value of Rs and n were obtained from the slope and intercept of the first-Cheung function (dV/dL(I)-I plot), respectively. Secondly, the value of Rs and BH were obtained from the slope and intercept of second-Cheung function (H(I)-I plot), respectively. All these parameters were found a function of temperature. While the BH increase with increasing temperature as exponentially, Rs and n decrease. The obtained higher value of n and this positive temperature coefficient of BH were attributed to the existence of barrier in-homogeneities or pinch-off /patches at around mean BH, interface traps at Al2O3/p-Si interface.

Keywords: Al/Al2O3/p-Si (MIS) type diodes; The origin of series resistance and ideality factor; Temperature dependent electrical parameters.

1. Introduction

In recent years, many researchers were interested in metal-semiconductor (MS) structures with high-dielectric interfacial layer such as Al2O3, TiO2, SrTiO3, Bi3Ti4O12, metal/graphene doped some polymers by considering their importance in optic, optoelectronic and electric devices [1-5]. In this respect, the choice interface layer at M/S interface was gained a great importance. Therefore, studies focus on improvement of these devices performance by means of growing interfacial layer because of it plays a key role in the main electrical parameters of the MS type Schotkky barrier diodes (SBDs); such as the origin of series resistance (Rs), surface states (Nss), the nature of barrier height (BH) at M/S interface, and conduction mechanisms (CMs), but it is not fully understood yet [6-11]. However, the thickness and homogeneity of the interfacial layer, Nss, Rs, inhomogeneity of the BH, and ununiformed doped semiconductor can also bring the SBDs to the non-ideal case.

Usually, the LnI-V plot at forward biases shows a good linear behavior at intermediate voltages (V≥3kT/q), but it becomes deviation from the linearity at higher forward biases (≥ 0.6-1V) especially due to the Rs and interfacial layer because of applied bias voltage will be shared by Rs , interfacial layer and diode (V=Vd+Vi+VRs). In general, Rs may be routed the rectifier and ohmic back contacts, the existence of an interfacial layer at M/S interface, the resistance of the bulk semiconductor, an extremely non-uniform doping concentration of donor/acceptor atoms in the semiconductor and the particular density distribution of Nss at M/S interface [11-13]. On the other hand, Nss may be routed from the interruption of the periodic lattice of semiconductor crystal, oxide or trapped charges, mobile ionic charges and interface trapped charges [14-16]. Sample temperature is also more effective on the electrical characteristics and conduction mechanism.

Especially at low temperatures, thermionic-field emission (TFE) and field emission (FE) may be effective an additionally to thermionic emission (TE).The main aim of this study is to investigate the current conduction mechanism, the nature of BH, and obtained the main electrical parameters of the fabricated Al/Al2O3/p-Si (MIS) diode as function temperature by using Cheung’s function. For this aim, both the forward and reverse bias I-V characteristics have been carried out in wide range of temperature (200-320 K).

2. Experimental Results

The Al/Al2O2/p-Si (MIS) type structures/diodes were grown on the B-doped (p-Si) wafer with (100) float zone, 300 µm thickness, 5.08 cm radius, and 1.4x10¹⁶ cm^-3 doping concentration (NA). Firstly, p-Si wafer was cleaned in the ultrasonic bath in the H2SO4

and H2O2, 20% HF, a solution of 6 HNO3: 1 HF: 35 H2O, 20% HF and then it was also rinsed in high-pure deionized water with for 5min and then it was dried by dry nitrogen (N2) gas. Immediately, pure Al (99.999%) with 1200Å was evaporated on the whole back of the wafer at 10^-6 Torr and was annealed at 450 ^oC in N2 ambient to get low resistivity ohmic contact. After ohmic contact, Al2O3 was grown on the wafer by ALD technique and then high-pure Al dots with 1200 Å and 7.85x10^-3cm² area was evaporated on the Al2O3 layer.

Current-voltage-temperature (I-V-T) measurements were performed using Keithley 2400 I-V source-meter.

3. Results and Discussions

Fig. 1 shows the forward bias LnI-V plots of the Al/Al2O3/p-Si (MIS) diode in the temperature range of 200-320 K and these plots show a linear behavior in the intermediate forward bias region, but deviates from the linearity due to the Rs and interfacial layer [16-17]. When MS or MIS type SBDs have an interfacial layer, Rs, and the value of n higher than unity, the forward bias I-V characteristics in terms of TE theory can be expressed as [12-14]:

 

 



  



 



 





 ( ) 1

exp )

2

exp(

*

nkT IR V q kT

T q AA

I

_Bo ^{s =Io}





 



  



 



 1

exp nkT qV

_D

(1)

Here, the quantities of Io, VD (=V-IRs), n, and T are the saturation current, voltage drop across the diode, ideality factor and temperature in Kelvin, respectively. Thus, the values of Io and n can obtain from the intercept and slope of Ln(I)-V plot for each temperature, respectively.

Ln(I) = Ln(Io) + (q/nkT)V (2)

The value of n is a measure of conformity of the diode to pure TE theory. Thus, both the value of n and zero-bias BH ( BO) can be calculated through the relations:

(ln )

q dV

n kT d I

 

  

 

(3)

2 Bo

ln

o

kT AA T

q I







   

 

⁽⁴⁾

Fig 1. The semi-logarithmic I-V-T plots of the Al/Al2O3/p-Si (MIS) diode.

As can be seen in Fig.1, the forward bias lnI-V plots have not a distinct linear region in the wide range of voltage and hence the reliability and accuracy of the evaluation of the main electrical parameters from these narrow linear regions become discussed. In this case, Norde method [18] and Cheung’s function can be used an alternative to standard TE theory and compared. In this study, the main diode parameters (n, Rs and B) were obtained as function of temperature by using the Cheung’s functions from the part of concave curvature of the lnI-V plot as the following:

(ln )

^s

dV kT

n R I

d I q

 

   

 

⁽⁵⁾

* 2

( ) n k ln n

AA

^{B s}

T I

H I V R I

q T

   

            

⁽⁶⁾

-25 -23 -21 -19 -17 -15 -13 -11 -9 -7

-3 -2 -1 0 1 2 3

V (V)

Ln (I)

200 K 220 K 240 K 260 K 280 K 300 K 320 K

Where B is the barrier height (BH) obtained from data of downward curvature region in the forward bias I-V characteristics. Fig. 2(a,b,c) shows the experimental dV/dln(I)-I and H(I)-I plots of the Al/Al2O3/p-Si (MIS) diode for 200, 240 and 320 K, respectively. It is clear that both dV/dln(I)-I and H(I)-I plot show a good linear region in the wide range of current. Thus, firstly, the values of n and Rs were obtained from the intercept and slope of the dV/dln(I)-I plot by fitting Eq. 6 as 7.246 and 13.67 k at 200 K and 2.253 and 15.94 k at 320 K. respectively. Secondly, by the using these values of ideality factor in Eq.6, the slope and intercept of the H(I)-I plot is also providing a second determination of Rs and B as 15.62 k , 0.498 eV at 200 K and 21.62 k , 0. 958 eV at 320 K, respectively. The obtained experimental values of n, Rs and B

are tabulated in Table 1.

As can be seen in Table 1, and Fig.3, while the value of n decrease with increasing temperature, the value of B increase as almost exponentially. On the other hand, the observed discrepancies in Rs can be attributed the voltage dependent of them and freezing-out of the electrons at low temperature.

Fig. 2. The dV/dLn(I) and H(I) versus I plots for 200, 240 and 320 K, respectively.

Table 1. The obtained experimental values of n, Rs and B from Cheung’s function.

dV/dLn(I) - I H(I)-I dV/dLn(I) = 13665x + 0,1251

H(I)= 15622x + 3,6156

0 1 2 3 4

1.0E-06 6.0E-06 1.1E-05

dV/dLnI , H(I) (V)

Current (A) a) 200 K

dV/dLn(I) = 13095x + 0,0833 H(I) = 17513x + 2,6897

0 0.5 1 1.5 2 2.5 3 3.5

1.0E-06 6.0E-06 1.1E-05

dV/dLn(I) (V)

Current (A) b) 240 K ^{#… #…}

y = 15944x + 0,0622 y = 21615x + 2,1651

0 1 2 3

0.0E+00 5.0E-06 1.0E-05 1.5E-05

dV/dLn(I) (V)

Current (A) c) 320 K

dV/dLn(I) H(I)

T (K)

n Rs (k ) (dV/dLnI-

I)

Bo

(eV)

Rs (k ) (H(I)-I)

200 7.246 13.67 15.62

220 6.034 10.34 14.57

240 4.024 13.10 17.46

260 3.835 11.93 17.10

280 3.354 8.14 14.68

300 2.249 11.96 19.95

320 2.253 15.944 21.615

Fig 3. The changes in the ΦBo and n with temperature obtained from Cheung’s function.

The increases of ΦB with increasing temperature is disagreement with the negative temperature coefficient of forbidden bandgap (Eg) of the Si and BH for ideal diodes.

Additionally, the higher values of n especially at low temperatures can be attributed to the existence of interlayer, surface states and barrier in-homogeneities [19-22].

4. Conclusion

In this study, Al/Al2O3/p-Si (MIS) structures were fabricated on the n-Si wafer.

The main electrical parameters of them were obtained from the forward bias I-V characteristics between 200 K and 320 K by 20 K steps. The semi-logarithmic forward bias I-V plots have not a distinct linear region for each temperature. Therefore, the main electrical parameters such n, Rs and B were obtained by using Cheung’s function. All these parameters were found a strong function of temperature especially at low temperatures. Both dV/dln(I)-I and H(I)-I plot show a good linear region in the wide range of current. The values of n and Rs were obtained from the intercept and slope of the dV/dln(I)-I plot by fitting and then the value of Rs and B were found from the slope and intercept of the H(I)-I plot for each temperature. While the value of ΦBo increase with increasing temperature, n decreases and such behavior of them was attributed the existence of many lower values of barriers or patches at around mean BH, surface states, and Al2O3 interfacial layer. In conclusion, the main electrical parameters of the

2 3 4 5 6 7 8

0.45 0.55 0.65 0.75 0.85 0.95

190 240 290

Id e ali ty fa cto r, n



B

(e V )

T (K)

fabricated MS or MIS type structure can successfully obtain from the Cheung’s functions instead of standard TE theory when LnI-V plots have not enough linear range.

REFERENCES

[1] S. Alialy, Ş. Altındal, E. E. Tanrıkulu, D. E. Yıldız, Analysis of temperature dependent current-conduction mechanisms in Au/TiO2/n-4H-SiC (metal/insulator/semiconductor) type Schottky barrier diodes, J. Appl. Phys. 116, 083709 (2014).

[2] Ç. Ş. Güçlü, A. F. Özdemir, Ş. Altındal, Double exponential I–V characteristics and double Gaussian distribution of barrier heights in (Au/Ti)/Al2O3/n-GaAs (MIS)-type Schottky barrier diodes in wide temperature range, Appl. Phys. A 122, 1032 (2016).

[3] S. A. Yerişkin, M. Balbaşı, S. Demirezen, Temperature and voltage dependence of barrier height and ideality factor in Au/0.07 graphene-doped PVA/n-Si structures, Indian J Phys 91:421–30 (2017).

[4] W. Wan, A. D. Bannerman, L. Yang, H. Mak, Poly (Vinyl Alcohol) Cryogels for Biomedical Applications, 283–321(2014).

[5] V. R. Reddy, Electrical properties of Au/polyvinylidene fluoride/n-InP Schottky diode with polymer interlayer, Thin Solid Films 2014;556:300–6.

doi:10.1016/j.tsf.2014.01.036.

[6] S. A. Yerişkin, M. Balbaşı, İ. Orak, The effects of (graphene doped-PVA) interlayer on the determinative electrical parameters of the Au/n-Si (MS) structures at room temperature, J Mater Sci Mater Electron, 28:14040–8 (2017).

[7] Card HC, Rhoderick EH. Studies of tunnel MOS diodes I. Interface effects in silicon Schottky diodes. J Phys D Appl Phys 1971;4:319. doi:10.1088/0022-3727/4/10/319.

[8] Demirezen S, Altındal Ş, Uslu İ. Two diodes model and illumination effect on the forward and reverse bias I–V and C–V characteristics of Au/PVA (Bi-doped)/n-Si photodiode at room temperature. Curr Appl Phys 2013;13:53–9. doi:10.1016/j.cap.2012.06.009.

[9] M. Sharma, S. K. Tripathi, Analysis of interface states and series resistance for Al/PVA:n-CdS nanocomposite metal–semiconductor and metal–insulator–semiconductor diode structures, Appl Phys A 113 491 (2013).

[10] S. Alialy, A. Kaya, E. Marıl, Ş. Altındal, İ. Uslu, Electronic transport of Au/(Ca1.9Pr0.1Co4Ox)/n-Si structures analysed over a wide temperature range, Philosophical Magazine, 95 (13) 1448-1461 (2015)

[11] C. Tozlu, A. Mutlu, Poly(melamine-co-formaldehyde) methylated effect on the interface states of metal/polymer/p-Si Schottky barrier diode, Synth Met 211 99–106 (2016).

[12] S. M. Sze, Physics of Semiconductor Devices, John Wiley & Sons, New York, 1981.

[13] B. L. Sharma, Metal-Semiconductor Schottky Barrier Junctions and Their Applications, Plenum Press, New York and London, 1984.

[14] E. H. Rhoderick, Metal-Semiconductor Contacts, Clarendon Press, Oxford, 1978.

[15] E. H. Nicollian and J. R. Brews, MOS (Metal Oxide Semiconductor) Physics and Technology. New York, USA: Wiley, 1982, pp. 117–129.

[16] E. Özavcı, S. Demirezen, U. Aydemir, Ş. Altındal, A detailed study on current–voltage characteristics of Au/n-GaAs in wide temperature range, Sens. Actuators A, 194, 259-268 (2013).

[17] İ. Taşçıoğlu, S. O. Tan, F. Yakuphanoğlu, Ş. Altındal, Effectuality of barrier height inhomogeneity on the current-voltage-temperature characteristics of metal-semiconductor structures with CdZnO interlayer, J. Electron. Mater. 47, 6059-6066 (2018).

[18] S. K. Cheung, N.W. Cheung, Extraction of Schottky diode parametersfrom forward current-voltage characteristics, Appl. Phys. Lett., 49 (1986) 85

[19] R. T. Tung, J. P. Sullivan, F. Schrey, On the inhomogeneity of Schottky barriers, Mater. Sci. Eng. B. 14, 266-280 (1992).

[20] R. F. Schmitsdorf, T. U. Kampen, W. Mönch, Correlation between barrier height and interface structure of Ag/ Si (111) Schottky diodes, Surf. Sci. 324, 249-256 (1995).

[21] E. Marıl, Ş. Altındal, A. Kaya, S. Koçyiğit, İ. Uslu, On Double Exponential Forward Bias Current-Voltage (I-V) Characteristics of Au/Ca3Co4Ga0.001Ox/n-Si/Au (MS) Type Structures in Temperature Range of 80-340 K, Philosophical Magazine, 95 10 1049-1068 (2015).

[22] E. Marıl, S. O. Tan, Ş. Altındal, İ. Uslu, Evaluation of Electric and Dielectric Properties of Metal–Semiconductor Structures With 2% GC-Doped-(Ca3Co4Ga0.001Ox) Interlayer. IEEE Trans. on Elect Devices. 65 9 3901(2018).