Journal of Electron Devices, Vol. 9, 2011, pp JED [ISSN: ]

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1 Journal of Electron Device, Vol. 9, 011, pp JED [ISSN: ] CURRENT VOLTAGE-TEMPERATURE (I-V-T) CHARACTERISTICS OF CR/4H-SIC SCHOTTKY DIODES * Shaweta Khanna a, S.Neelehwar a, Arti Noor b a USBAS, GGSIP Univerity, Kahmere Gate, New Delhi, India b School of Electronic, Centre for Development of Advanced Computing Noida, Uttar Pradeh, India Correponding Author: hweta.khanna04@gmail.com (Shaweta Khanna) Received 8/03/011, accepted 30/03/011, online 5/04/011 Abtract: Thi paper report temperature dependent currentvoltage (IV) characteritic of Cr/n-type 4H-SiC Schottky diode within the temperature range of K. The main diode parameter like barrier height and ideality factor were found to be trongly dependent on temperature. It ha been found that with the increae in temperature ideality factor decreae and barrier height increae and the conventional activation energy plot deviate from linearity. According to the thermionic emiion theory the lope of the conventional Richardon plot ln(i 0 /T ) veru 1000/T hould give the barrier height. However experimental data don t correlate with the traight line of linearly fitted curve. Thee dicrepancie from ideal thermionic emiion theory are attributed to the in homogeneitie of the Schottky barrier which perit at metal/emiconductor interface. Thi behavior ha been interpreted on the bai of tandard thermionic emiion theory and Gauian ditribution which yield mean barrier height of 1.05eV and tandard deviation of 0.18eV. Furthermore the modified Richardon plot reulted in mean barrier height of 1.5eV and Richardon contant A * of 138Acm - K -. Thu it can been concluded that the temperature dependence of forward I-V characteritic of n-type Cr/4H-SiC contact can be effectively elucidated on the bai of TE theory with Gauian ditribution of the barrier height. dependence, thermionic emiion, Gauian ditribution. I. INTRODUCTION Silicon Carbide i an attractive material for high power and high temperature application becaue of it remarkable electrical propertie. In recent year a lot of advancement ha been accomplihed in SiC power emiconductor device [1-5]. A ignificant work ha been done in the development of SiC electronic device pecially Schottky contact due to their technological importance. Although SiC Schottky diode are now readily available in the market, yet tudie related to their propertie and application i a topic of current reearch [6-15]. Many invetigator have invetigated/ examined the propertie of SiC Schottky diode Keyword: - Schottky barrier diode, Silicon Carbide, barrier inhomogeneitie, temperature 38

2 on both 4H and 6H-SiC. But out of thee two polytype, 4H-SiC i getting more preference due to high electron mobility and more iotropic nature of many of it electrical propertie [15]. Several tudie relating to electrical tranport in SiC Schottky contact have been carried out during the lat decade. Still current tranport and temperature dependence of the SBH in SiC SBD i a topic of interet. The I-V-T analyi of Schottky diode uing ideal TE theory reveal anomalou behavior uch a decreae in barrier height, increae in ideality factor with decreaing temperature. Thee deviation are generally interpreted by the preence of in-homogeneitie at the interface which might be due to everal phyical reaon like inhomogeneity in doping concentration, high interface tate denity due to interface contamination, urface defect etc [16,17-18]. In literature mainly two approache are propoed to explain experimental data and model the I-V-T characteritic of inhomogeneou Schottky barrier diode. Thee are baed on model propoed by Tung [17] and Werner and Gutler [18]. Thee two approache have been uccefully ued for the interpretation of experimental reult on variou practical SiC Schottky diode [6, 11, 1, 19, and 0]. For explaining deviation from ideality, Tung aumed in hi model the preence of locally non-uniform region or patche with relatively lower or higher barrier with repect to average barrier height. Wherea according to Werner model, barrier height i uppoed to be ditributed according to Gauian function which will uually lead to an apparent barrier height that i both temperature and bia dependent. In thi paper forward I-V characteritic of Cr/ 4H- SiC SBD have been analyzed on the bai of thermionic emiion theory with Gauian ditribution of barrier height to yield information pertinent to Schottky diode parameter and their dependence on temperature. II. FABRICATION AND CHARACTERIZATION The tarting material ued for the fabrication of Schottky diode wa n-type 4H-SiC (0001), 8 0 off Si face epiwafer purchaed from Cree Inc. The ubtrate wa n+-type with a donor concentration of cm-3 with lightly doped (N D = cm-3) n-type epi-layer having pecific reitivity of 0.00 cm. Prior to metal depoition for making Schottky and ohmic contact the ample were degreaed in organic olvent like acetone, trichloroethylene and methanol ucceively. Immediately prior to placing the ample in a vacuum chamber, they were immered in 10% HF for 0 at room temperature followed by rining in DI water and blow drying. Then, Nickel back-ide ohmic contact wa depoited and annealed in N 383

3 atmophere at 900 C for 10 min. Guard ring wa realized by tandard lithography procee. Schottky contact wa formed uing Cr on 4H SiC epilayer wa done by e-beam metallization proce at a preure ranging between to Torr having thickne of 1500A 0. The contact metal had circular geometry with diameter of 1mm. Structure of the diode i hown in fig.1 The barrier height of each of the fabricated contact wa determined by(1) determining aturation current from meaured current-voltage characteritic (I-V method).the I V meaurement of the diode were performed on a probe tation equipped with Keithley 36. qv qv I I0 exp( )[1 exp( )] (1) nkt kt For V>3kT, exp( qv I I ) 0 nkt where T i the temperature in K, q i the electronic charge, k i the Boltzmann contant and I 0 i revere aturation current which can be given a: I q () kt * b 0 AA T exp( ) A i the effective diode area, A * i effective Richardon contant which i 146Acm - K - for 4H-SiC [] and b i zero bia barrier height, n i the ideality factor which meaure deviation of practical diode from ideal thermionic emiion theory. Fig. () how forward I-V characteritic of Cr/4H-SiC SBD meaured in temperature range of K. Fig. 1. Schematic croection of metal/4h-sic Schottky diode. III. RESULTS AND DISCUSSION III.1 I-V-T characteritic of Cr/4H-SiC Schottky diode I-V-T analyi i ued to identify different conduction mechanim in current tranport phenomenon taking place in Schottky diode. If current i aumed to be due to thermionic emiion then relation between applied voltage and current can be given a [0-1] Fig.. Experimental forward I-V characteritic of Cr/4H-SiC SBD meaured at different temperature. Uing thee characteritic ideality factor and barrier height are calculated from equation (3). 384

4 Fig. (3) plot experimental value of ideality factor and barrier height a a function of temperature. Thi figure how that barrier height decreae and ideality factor increae with the decreae in temperature. * kt AA T b ln( ) q I (3) Barrier height can alo be calculated by uing the Arrheniu or Richardon plot of the aturation current. Natural logarithm of equation () will yield: I T q (4) kt 0 * b ln( ) ln( AA ) can be een that curve trongly deviate from linearity. The dicrepancie from claical thermionic emiion theory oberved in our Cr/4H-SiC Schottky diode uch a increae in barrier height with the increae in temperature and non-linearity of activation energy plot can be cured by conidering patial inhomogeneity of SBH. The patial inhomogeneity i generally illutrated by ome ditributed function, among them Gauian ditribution i mot uccefully ued to explain the non-ideal behavior of Schottky diode. Fig. 3. SBH and ideality factor a a function of temperature. Plot of ln(i 0 /T ) veru q/kt hould give a traight line whoe lope and intercept will give barrier height and Richardon contant repectively. Fig. (4) how the conventional activation energy ln(i 0 /T ) veru 1000/T plot. It Fig. 4. Conventional activation energy plot of Cr/4H- SiC diode. III. Gauian ditribution of barrier height To explain the anomalie oberved in our Schottky diode, we have conidered inhomogeneou barrier, which conit of variou patche of relatively higher or lower barrier height with repect to a mean barrier 385

5 height. Now uing thi aumption, temperature dependence of barrier height can be attributed to inhomogeneou barrier height. Since current tranport acro the metal/emiconductor interface i a temperature activated proce, o at low temperature electron will be able to overcome only lower barrier and current tranport mechanim will be dominated by flow of current through the patche of lower barrier height and having large value of ideality factor. In other word with the increae of temperature more electron have ufficient energy to urmount the higher barrier. Therefore dominant barrier height will increae with the increae of temperature. Here, barrier height inhomogeneity have been modeled with a patial ditribution of the band bending b at m/ interface of Schottky contact uing Gauian ditribution P( b ) with a tandard deviation and mean value of barrier height b which i expreed a: 1 ( b b) P( b ) exp[ ] (5) The total current acro a Schottky diode containing barrier inhomogeneitie can be written a: I( V ) I(, V ) P( ) d (6) b b b Where I ( b,v) i the amount of current for a barrier height of b at a voltage V baed on ideal thermionic theory and P( b ) i the normalized ditribution function which give the probability of occurrence of barrier height. Now uing equ. (5) and (6) current of the Schottky diode with modified barrier will be: q q qv qv (7) * ( ) AA T exp[( )( b )] exp( )[1 exp( )] kt kt napkt kt I V Comparion of equation (1) and (7) give expreion for apparent barrier height a a function of temperature and mean barrier height which i given in equ. (8) q ap b (8) kt According to equ. (8) the plot of ap veru q/kt hould be a traight line with intercept giving mean barrier height b and lope determining tandard deviation. Uing barrier height obtained from I-V meaurement, ap veru q/kt plot ha been plotted a hown in fig. (5). It i apparent that 386

6 the data fit adequately with a traight line and intercept and lope of thi linearly fitted traight line yield mean barrier height of 1.05eV and tandard deviation of 0.18eV. A tated earlier that conventional energy plot of Cr/4H-SiC SBD deviate from linearity. To explain thi dicrepancy equ. (4) can be rewritten and yield equ.(9). intercept of fitted traight line barrier height and Richardon were found to be 1.5eV and 138 Acm - K - repectively and thi value i in cloe agreement with the theoretical value of 146 Acm - K - for 4H-SiC. I q q b (9) T k T kt 0 * ln( ) ( ) ln( AA ) Fig. 6. Modified Richardon ln(i 0 /T )- (q /k T )veru q/kt plot for Cr/4H-SiC Schottky diode. IV. CONCLUSION Fig. 5. ap veru q/kt plot. Baed on the equ. (9) the modified activation energy plot of ln(i 0 /T )-q /kt veru q/kt ha been plotted. Thi plot take into account the deviation of the barrier height and mut give a traight line whoe lope and y-axi intercept yield mean barrier height and Richardon contant repectively. Fig. 6. Show the modified activation plot which i reaonably linear and from the lope and In thi paper the I-V characteritic of n-type Cr/4H-SiC Schottky diode were meaured in the temperature range of K. The electrical parameter of the diode uch a ideality factor and barrier height were found to be trongly temperature dependent. The departure from the claical thermionic emiion theory were illutrated by auming the preence of barrier inhomogeneitie at m/ interface and modeling them with a Gauian ditribution. Uing the ap veru q/kt plot, 388

7 the mean value and tandard deviation of the Gauian ditribution of barrier height were determined to be 1.05eV and 0.18eV repectively. The activation energy plot wa een to deviate from linearity but the modified Richardon plot which conider the Gauian ditribution of the barrier height fitted nicely with a traight line. The mean barrier height and the Richardon contant from the modified Richardon plot were found to be 1.5eV and 138 Acm - K -. The linearity of the modified activation energy plot and the nearne of the calculated Richardon contant to it theoretical value verify the ucce of the Gauian ditribution in explaining temperature dependence of I-V characteritic of Cr/4H-SiC Schottky diode. Acknowledgement The fabrication work wa upported by Central Electronic Engineering Reearch Intitute (CEERI) Pilani, India. The author would like to thank Dr. Chandraekhar, Director CEERI and Dr. Jamil Akhtar and hi group for their help, upport and dicuion. Reference:- [1] J.R. Waldrop, R.W. Grant, Appl. Phy. Lett. 6 (1993) 685. [] V. Saxena, J.N. Su, A.J. Steckl, IEEE Tran. Electron Dev. 46 (1999) 456. [3] C. Raynaud, K. Ioird, M. Lazar, C.M. Johnon, N. Wright, J. Appl. Phy. 91 (00) [4] M.O. Aboelfotoh, C. Fröjdh, C.S. Peteron, Phy. Rev. B 67 (003) [5] F. Roccaforte, F. La Via, A. Baeri, F. Roccaforte, V. Raineri, L. Calcagno, F. Mangano, J. Appl. Phy. 96 (004) [6] S. Duman, S. Dogan, B. Gürbulak, A. Turut, Appl. Phy. A: Mater. Sci. Proce. 91 (008) 337. [7] D. Defive, O. Noblanc, C. Dua, C. Brylinki, M. Bartula, V. Aubry-Fortuna, F. Meyer, IEEE Tran. Electron Dev. 46 (1999) 449. [8] B.J. Skromme, E. Luckowki, K. Moore, M. Bhatnagar, C.E. Weitzel, T. Gehoki, D.Ganer, J. Electron. Mater. 9 (000) 376. [9] R. Wei, L. Frey, H. Ryel, Appl. Surf. Sci. 184 (001) 413. [10] F. Roccaforte, F. La Via, V. Raineri, R. Pierobon, E. Zanoni, J. Appl. Phy. 93 (003) [11] R. Perez, N. Metre, J. Monterrat, D. Tournier, P. Godignon, Phy. Stat. Sol. (a) 0 (005) 69. [1] D.J. Ewing, Q. Wahab, R.R. Ciechonki, M. Syvajarvi, R. Yakimova, L.M. Porter, Semicond. Sci. Technol. (007)

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