Nghiên cứu ảnh hưởng của diện tích bề mặt dẫn điện và các lỗi xếp chồng đến đặc tính của điốt pin 4H-Sic

 Reverse Voltage(V) Forward Voltage(V)
 (4a) 
 (5a) 
 )
 2
 -6 -5
 )
 10 1.2x10 20 250 2
 -7 -6 225°C
 10 1.2x10 175°C
 15 125°C 188
 -8 -7
 10 1.2x10 75°C
 25°C-initial
 10-9 1.2x10-8 10 25°C-final 125
 10-10 225°C 1.2x10-9
 175°C 5 63
 125°C
 Reverse Current(A)
 10-11 75°C 1.2x10-10 Forward Current(A)
 25°C-initial
 Reverse Current Density(A/cm
 25°C-final 0 0
 10-12 1.3x10-11 Forward Current Density(A/cm
 0 500 1000 1500 2000 2500 3000
 0 1 2 3 4 5
 Reverse Voltage(V)
 Forward Voltage(V) 
 (4b) 
 (5b) 
 70 292
 )
 -6 -6 2
 )
 10 4.2x10 2
 60 250
 225°C
 -7 -7
 10 4.2x10 50 175°C 208
 125°C
 -8 -8 40 75°C 167
 10 4.2x10 25°C-initial
 25°C-final
 30 125
 10-9 4.2x10-9
 225°C 20 83
 10-10 175°C 4.2x10-10
 125°C Forward Current(A) 10 42
 Reverse Current(A) 75°C
 -11 25°C-initial -11
 10 4.2x10 0 0
 25°C-final Forward Current Density(A/cm
 Reverse Current Density(A/cm
 10-12 4.2x10-12 0 1 2 3 4 5 6
 Forward Voltage(V)
 0 500 1000 1500 2000 2500 3000 
 Reverse Voltage(V)
 (5c) 
 (4c) Figure 5. Forward characteristics temperature dependence of 2mm2 (5a), 
 Figure 4. Reverse characteristics temperature dependence of 2mm2 (4a), 8mm2 (5b) and 24mm2 (5c) diode 
 2 2
8mm (4b) and 24mm (4c) diode Diodes forward performance has been characterized up 
 6.5kV diodes design and fabrication have been to a current density of 250A.cm-2 corresponding to 60A for 
validated in term of blocking voltage by reverse the 24mm2. To limit the device auto-heating, these 
characterization in a vacuum chamber. The diodes show characteristics have been obtained in pulse mode with a 
also a low leakage current at temperature as high as 225°C. pulse width of 200µs. At 250A.cm-2, the voltage drop is 4.5V 
The next section presents diodes forward performance. for the 2 and 8mm2 diodes and 5V for the 24mm2 diodes. 
3.2. Forward characteristics These values of voltage drop are high with respect to state 
 of the art [4]. This can be due to the high ohmic contact 
 Forward characterizations have been performed on 
 resistance because the ohmic contact of fabricated diodes 
encapsulated diodes. Typical forward characteristics are 
 as measured on TLM test structures is not very good and a 
presented respectively in Fig. 5 (a, b, c) for 2, 8, and 24mm2 
 high value of contact resistance of about 25mΩ.cm-2 is 
diode. 
Website: https://tapchikhcn.haui.edu.vn Vol. 56 - No. 1 (Feb 2020) ● Journal of SCIENCE & TECHNOLOGY 5
 KHOA H ỌC CÔNG NGHỆ P - ISSN 1859 - 3585 E - ISSN 2615 - 961 9 
 extracted. The increase in voltage drop for the largest 
 )
 diodes is probably due to an insufficient number of bonded 20 250 2
 wires (6 wires of 125µm diameter for 24mm2 diodes) 0h
 1h30
 leading to a bad current spreading. We can also see that 15 3h 188
 the on-state voltage drop decreases with increasing 23h
 43h
 temperature. The decrease of voltage drop is explained by 10 125
 the increase of carrier lifetime with temperature. This 
 decrease of on-state voltage could be seen as a handicap 5 63
 because thermal excess can occur. However the change in Forward Current(A)
 voltage drop remains low, less than 0.5V in the tested 0 0
 temperature range. It is noted that SiC bipolar devices have Forward CurrentDensity(A/cm 
 a threshold voltage of about 3V thus these devices require 0 1 2 3 4 5 6 7 8
 a case with good thermal conductivity. Targeting a current Forward Voltage(V) 
 -2
 density of 80A.cm , a case with a thermal conductivity of (6b) 
 300W.cm-2 and a high voltage capability must be used. 
 70 292
 The forward and reverse electrical characteristics 
 )
 measured at 25°C after thermal stress do not show any 60 250 2
 performance degradation so these diodes are stable with 0h
 50 1h30 208
 temperature. The next section presents and discusses the 3h
 influence of electrical stress on the diodes performance. 40 23h 167
 43h
 4. ELECTRICAL STRESS 30 125
 4.1. Evolutions of diode characteristics 
 20 83
 The electrical stress has been performed on the all three 
 diode types. Stress condition is defined by a continued bias Forward Current(A) 10 42
 forward voltage to maintain a constant current density of 0 0
 100A.cm-2. For a thermal equilibrium, the diodes are Forward Current Density(A/cm
 mounted on a radiator with cooling fan. Diodes forward 0 2 4 6 8 10
 and reverse measurements have been taken at 25°C after Forward Voltage(V) 
 1h30, 3h, 23h and 43h stress time. It is noted that no sub (6c) 
 threshold forward nor reverse characteristic change are Figure 6. Forward characteristics evolutions of 2mm2 (6a), 8mm2 (6b) and 
 observed. By contrast, high current forward characteristics 24mm2 (6c) diode 
 are damaged. Typical forward characteristics evolutions are 
 4.2. Diodes forward degradation interpretation 
 shown respectively in Fig. 6 (a, b, c) for 2, 8, and 24mm2 
 diode. An important forward voltage drift has been It is known that the presence of basal plane dislocation 
 observed for the three diodes. The most important (BPDs) can generate stacking faults (SFs). These SFs act as 
 degradation occurs in the first 1h30 stress time. After 23h recombination centers which reduce the carrier lifetime. 
 stress time, the voltage drift stabilizes and then reaches the Electron-hole pair recombination at the BPDs in forward 
 saturation. We can also see that the larger diode active area mode conduction leads to the propagation of SFs thus 
 is, the more important degradation is. These observations increases the voltage drop of bipolar devices [5, 6]. So our 
 are interpreted in the next section. diodes forward performance degradation can be explained 
 by the presence of BPDs and the expansion of SFs within 
 )
 5 250 2 the diodes active area. As the quantity of BPDs within a 
 device active area is finite, a finite quantity of SFs can thus 
 0h
 4 1h30 200 generate. Furthermore, there is a finite space for the SFs to 
 3h expand through (drift layer thickness), the total possible 
 23h
 3 43h 150 affected area is also finite. Thus, the voltage drift saturation 
 observed above is interpreted by the expansion of every 
 2 100 SFs through the drift layer and the possibility of a larger 
 BPDs density within the large active area diode explains the 
 1 50
 Forward Current(A)Forward more important degradation for these diodes. In the next 
 section of the paper, the electronic energy level of these 
 0 0 Forward Current Density(A/cm
 SFs determined by admittance spectroscopy technique is 
 0 1 2 3 4 5 6 7 presented and we also measure the reduction of carrier 
 Forward Voltage(V) lifetime induced by these SFs using open-circuit voltage 
 (6a) decay technique (OCVD). 
6 Tạp chí KHOA HỌC & CÔNG NGHỆ ● Tập 56 - Số 1 (02/2020) Website: https://tapchikhcn.haui.edu.vn 
P-ISSN 1859-3585 E-ISSN 2615-9619 SCIENCE - TECHNOLOGY 
 Admittance spectroscopy technique allows detecting 
defects and extracting their activation energy. This 
 E = 0 .1 8 e V
technique has been used to characterize 4H-SiC junction a c
barrier Schottky diodes in a previous paper [7]. It consists in 0 .1 4
 )
applying a small sinusoidal voltage to the structure and to -2
 K
measure the subsequent capacitance Cp and conductance -1
 (s
 2 0 .0 5
Gp of the space charge region of the diode. In the presence /T
 n
of a defect centre, the emission and capture kinetic e
processes of free carriers by the defect centre modify the 
capacitance and conductance of the structure. By varying 0 .0 2
frequency and temperature, it is possible to determine the 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
 -1
activation energy and the capture cross section of the 1 0 0 0 /T (K ) 
defect. Indeed, the presence of a defect involves the Figure 8. Arrhenius plot of the defect signature 
presence of a peak of conductance as a function of The OCVD technique has been performed to evaluate 
temperature. The temperature T of this maximum is varying the ambipolar lifetime of diode before and after electrical 
with frequency, and for this maximum, the frequency is stress. This technique consists to integrate the diode into a 
equal to the thermal emission rate of the defect. The chopper circuit with a high speed switching device (Si-
scanned region is situated near the cross of the Fermi level MOSFET) and to measure the voltage transient across the 
with the defect level. Thus, in an ideal n-type Schottky diode following the abrupt switching-off of the current 
diode, it is possible to detect only electron traps. But in the from a high current injection level [8]. The subsequent 
presence of a pn junction, it is possible to detect electron voltage decrease is related to the ambipolar lifetime by the 
trap in the n-type region and hole trap in the p-type region. following equation [9]: 
 In practice, temperature ramps are imposed to the 1
sample, while measuring Cp and Gp for 20 different 2kT dV 
 τ τn τ p (1) 
frequencies. Measurements are performed in a liquid q dt 
nitrogen cryostat, with an impedance analyser HP4194A for where (dV/dt) is the slope of the linear part in the voltage 
frequencies varying between 300Hz and 20kHz. The decay curve, q is the elementary charge, T is absolute 
frequency range is adjusted in order to detect presented temperature, and k is the Boltzmann constant. 
defects in the structure. An Arrhenius plot of ln(ω/T2) vs. 
 Fig. 9 presents the OCVD voltage transient measured on 
1/T allows to determine the energy level of the defect. 
 a diode before and after stress at room temperature using a 
 Fig. 7 shows conductance spectra obtained on a forward current density of 100A.cm-2. As seen in the figure, 
stressed diode. These conductance peaks is induced by the the linear part slope of the stressed diode is two times 
presence of a defect and its signature is plotted in Fig. 8. higher than the virgin diode. It means that the ambipolar 
For the virgin diode, no peak of conductance is detected in lifetime is reduced two times for the stressed diode. The 
this temperature range. So these conductance spectra can ambipolar lifetime is found to be respectively 2470ns and 
be attributed to an electrical signature of SFs. It 1400ns using Eq. 1 for the diode before and after stress. 
corresponds to an electron trap situated at 0.18eV under Simulated results using Sentaurus with ambipolar lifetime 
conduction band. of 2600ns and 1600ns have been also presented in Fig. 9. 
 1x10-10 Electrons and holes lifetimes are supposed to be equal in 
 the simulations. A good agreement between experimental 
 -10 Frequency (Hz) and simulated curves is observed. 
 1x10 487.133
 620.741
 790.995
 -11 1007.945 Sim u lated
 8x10 3 .0 D io de be fore s tres s
 1284.4 D io de after s tr ess
 1636.678
 -11 2085.578
 6x10 2 .8 dV/dt=21 kV/s
 (F)
 2657.6
  3386.514
 M e a sure d
 G/ -11 4315.35
 4x10 5498.942 2 .6 
 7007.164
 8929.054 Voltage (V)
 -11 11378.07 2 .4
 2x10 dV/dt=36 kV/s
 14498.79
 18475.45 Sim u la ted
 2 .2
 0 M ea su red
 250 300 350 400 450 500 550 600 650
 0.00002 0.00004 0.00006 0.00008
 Temperature (K)
 T im e (s ) 
 Figure 7. Normalized conductance vs. temperature for 16 different Figure 9. Measured and simulated curves OCVD voltage transient 
frequencies obtained on a stressed diode characteristics of a diode before and after electrical stress 
Website: https://tapchikhcn.haui.edu.vn Vol. 56 - No. 1 (Feb 2020) ● Journal of SCIENCE & TECHNOLOGY 7
 KHOA H ỌC CÔNG NGHỆ P - ISSN 1859 - 3585 E - ISSN 2615 - 961 9 
 Two electrical techniques have been performed [9]. S. Bellone, H. C. Neitzert, and G. D. Licciardo, 2004. An Analog Circuit for 
 justifying the presence of SFs and their influence on the Accurate OCVD Measurements. Solid-State Electronic, 48, 1127-1131. 
 carrier lifetime reduction. This reduction results in a forward 
 voltage drift. On the other hand, as the diodes ohmic 
 THÔNG TIN TÁC GIẢ 
 contact is not stabilized, this can also contribute partly to 
 1 2
 the important forward voltage drift of stressed diode. Nguyễn Duy Minh , Nguyễn Mạnh Quân 
 Because, under the high current density stress, the 1Khoa Kỹ thuật điện, Trường Đại học Điện lực 
 temperature can be high then damaging the contact 1Khoa Điện, Trường Đại học Công nghiệp Hà Nội 
 properties. 
 5. CONCLUSION 
 6.5kV 4H-SiC diodes have been designed and fabricated 
 with three different active areas of 2, 8, and 24mm2. 
 Blocking voltage of 6.5kV has been achieved for the three 
 diodes types. These diodes present a low leakage current 
 and stable operation with temperature up to 225°C and 
 3kV. Electrical stress at a current density as high as 
 100A.cm-2 has been also performed on these diodes. An 
 important forward voltage drift has been observed. This is 
 due to the generation and expansion of SFs in the diodes 
 drift layer under forward conduction. The SFs presence and 
 their influence have been demonstrated using two 
 electrical methods: OCVD and admittance spectroscopy. 
 OCVD measurements determined a carrier lifetime 
 reduction of up to two times. Admittance spectroscopy 
 measurements revealed an electronic energy level of 
 0.18eV under conduction band. 
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 Planson, 2011. Wide Band Gap Semiconductors Benefits for High Power, High 
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 46-51. 
 [2]. Sentaurus, TCAD simulation tool by Synopsys Inc. 
 [3]. D-M. Nguyen, C. Raynaud, N. Dheilly, M. Lazar, D. Tournier, P. Brosselard 
 and D. Planson, 2011. Experimental determination of impact ionization coefficients 
 in 4H-SiC. Diamond & Related Materials, 20, 395-397. 
 [4]. D. Peters, W. Bartsch, B. Thomas, and R. Sommer, 2010. 6.5kV SiC 
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 901-904. 
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 [7]. C. Raynaud, D-M. Nguyen, P. Brosselard, A. Perez-Tomas, D. Planson, 
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 Admittance vs Temperature Analyses. Mater. Sci. Forum, 615-617, 671-674. 
 [8]. N. Dheilly, D. Planson, P. Brosselard, J. Hassan, P. Bevilacqua, D. 
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8 Tạp chí KHOA HỌC & CÔNG NGHỆ ● Tập 56 - Số 1 (02/2020) Website: https://tapchikhcn.haui.edu.vn