Improved turn-on characteristics of 4HSiC asymmetrical thyristor with double epitaxial n-base

Accepted Manuscript Improved turn-on characteristics of 4H SiC asymmetrical thyristor with double epitaxial n-base Qing Liu, Hongbin Pu, Xi Wang, Jiaqi Li PII:

S0749-6036(18)31828-7

DOI:

https://doi.org/10.1016/j.spmi.2018.12.011

Reference:

YSPMI 5973

To appear in:

Superlattices and Microstructures

Received Date: 7 September 2018 Revised Date:

29 October 2018

Accepted Date: 10 December 2018

Please cite this article as: Q. Liu, H. Pu, X. Wang, J. Li, Improved turn-on characteristics of 4H SiC asymmetrical thyristor with double epitaxial n-base, Superlattices and Microstructures (2019), doi: https://doi.org/10.1016/j.spmi.2018.12.011. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT Improved turn-on characteristics of 4H-SiC Asymmetrical Thyristor with double epitaxial n-base Qing Liu, Hongbin Pu, Xi Wang, and Jiaqi Li

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Xi’an University of Technology, Xi’an, 710048, China Abstract

A new 4H-SiC asymmetrical thyristor with double epitaxial n-base is proposed and

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evaluated by the two-dimensional numerical simulations. It features a high-low doping profile to modify the electric field of the thin n-base in vertical direction. The

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built-in electric field enhances the injected minority carriers flow through the n-base as fast as possible and reducing the combination in n-base. As a result, the current gain of the upper p-n-p transistor in 4H-SiC thyristor is promoted. Compared to the conventional thyristor, the turn-on characteristics of the new structure are improved

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significantly. Simulation results indicate that the turn-on time of the new thyristor is reduced from 317ns that in conventional 6500V 4H-SiC thyristor to 96ns, under the

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load current of 180A/cm2 and bus voltage of 800V.

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Keywords: 4H-SiC, Thyristors, Turn-on time

1. Introduction

High-voltage thyristors are widely used in high-power pulsed systems and HVDC voltage-source converters (VSC), which require high-voltage power switches for small size and high power density [1-2]. High-voltage thyristors based on silicon have been a monopoly position, but it merely stands the highest blocking voltage of 10kV

ACCEPTED MANUSCRIPT due to the limitation of silicon material nature [3]. The limitation could be overcome by replacing the Si thyristors with SiC thyristors. Owing to the advantages of 4H-SiC material properties, such as wider bandgap, higher breakdown electric field and

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higher thermal conductivity. Therefore, high-voltage thyristors based on 4H-SiC have a rapid development in recent years [4]. As high power switching devices, 4H-SiC

excellent switching characteristics [5-6].

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asymmetrical thyristors not only withstand super-high blocking voltage, but also show

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The SiC thyristor requires gate current for trigger into on-state. In order to reduce the turn-on power loss, much work has been done. Agarwal et al. first reported that turn-on characteristics of SiC thyristors could be improved by elevating the voltage between the anode and cathode [7]. Owing to increasing the voltage between the

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anode and cathode, the width of depletion layer increased and therefore the turn-on delay is improved. Unfortunately, this method has a drawback that it is limit for improvement turn-on speed and increases the complexity of switching test circuits.

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Subsequently, another way to reduce the turn-on delay by increasing the gate current

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delivered to thyristor was presented [8-9]. At the same time, however, it leads to an increase of the driving loss. Therefore, in addition to the improvement of the external circuit outlined above, Agarwal et al. observed that elevating the temperature also can promote the turn-on speed [10]. Because the impurity atoms, especially the acceptor atoms are not completely ionized at room temperature [11], elevating the temperature, the ionized holes density of p+ emitter can substantially increase and therefore the current gain of the upper p-n-p transistor is improved. However, this method leads to

ACCEPTED MANUSCRIPT substantial increase of the turn-off time in SiC thyristors. Although the methods mentioned above for decreasing the turn-on time are valid to some extent, some disadvantages will be introduced in SiC thyristors. Better solutions

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could be expected to deal with these problems. In 2010, the double base epilayer 4H-SiC n-p-n BJT for improving the current gain was demonstrated [12]. The p-base of this 4H-SiC BJT was a two-layer structure, one p layer was 0.35µm with

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1x1017cm-3 and another p+ layer was 0.15µm with 4.6x1018cm-3 on the top. As a result,

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the common emitter current gain could be improved to over 70. Basing on this idea, an injection modulation of p+-n emitter junction in 4H-SiC light-triggered thyristor by double-deck thin n-base was put forward to decrease the turn-on delay time in our previous work [13]. However, this structure mainly obtains a low turn-on delay time

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by increasing the hole injection efficiency of top p+-n emitter junction. In this work, a new 4H-SiC asymmetrical thyristor with double epitaxial n-base is proposed and investigated by using of commercial device simulation software. The

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turn-on characteristic and turn-on mechanism of the new SiC thyristor are

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investigated by comparing with conventional SiC thyristor. 2. Device structure and simulation setup

To avoid using p-type high-resistance substrate, SiC thyristors choose a p-type region for blocking layer. The structure schematic of a conventional 6500V 4H-SiC asymmetrical

thyristor

is

shown

in

Fig.

1(a).

To

improve

the

hole

transmission-enhanced in n-base, the novel 4H-SiC thyristor is proposed, as shown in

ACCEPTED MANUSCRIPT Fig. 1(b). Compared with the conventional SiC thyristor, the new structure is divided the single epitaxial n-base into double epitaxial n-base, which features a highly-doped and a lightly-doped n-type region. The diagram of doping profiles of the n-base in

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both proposed and conventional thyristors is shown in Fig. 1(c). Parameters ND and ND0 represent the highly-doped n base region and lightly-doped n- region, respectively. The ND0 of lightly-doped n- region is set as 2x1015cm-3 and the ND is the same doping

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concentration of the thin n-base in conventional 4H-SiC thyristor and equals to

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2x1017cm-3. Parameter d indicates the thickness of lightly-doped n- region. Whether the conventional or the proposed structure, the total thickness WB of the n-base layer is fixed as 2.0µm. It is noted that all the epilayers are fabricated by the modified epitaxial process [14], due to the diffusion coefficients of dopants in SiC are very

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small. As shown in Fig. 1(b), the whole n-base is grown as a two-layer structure with a lightly doped n- base, followed by a highly doped n base on top. And it is formed by

+

p-

n-base

p

19

Doping Concentration /(cm-3)

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continuous growth to reduce interface defects. 10 18 10 17 10 16 10 15 10 14 10

ND

(a)

19

10 18 10 17 10 16 10 15 10 14 10

ND 2.0- d

(b)

ND0 d

0

1

2

3

4

5

6

Distance /µm

(a)

(b)

(c)

Fig. 1 Structure schematics of 4H-SiC asymmetrical thyristors. (a) the conventional structure, (b) the new structure, (c) the diagram of doping profiles of the thin n-base in the two structures.

In the new structure shown Fig. 1(b), a built-in electrical field is induced in the

ACCEPTED MANUSCRIPT n-base and its direction is from the highly-doped region to the lightly-doped region. Therefore the transmission of the holes in n-base is changed from diffusion action to diffusion and drift action. As a result, the transport factor of the holes in n-base is

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enhanced, so the common-base current gain of top p-n-p transistor in 4H-SiC thyristor has been improved.

Fig. 2 shows the simulated I-V characteristics of upper p-n-p transistor in the new

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structure and conventional 4H-SiC thyristors. It is clearly demonstrated that the

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current gains of top p-n-p transistor in the new structure is increased significantly under the same driving current conditions (Base current IB=-5e-8A). What’s more, from the Fig. 2(a), with increasing of the thickness d of the slightly-doped n- region in n-base, the current gain of the top p-n-p transistor in thyristors has been promoted.

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The current gain also can be improved by decreasing the doping concentration ND0 of the lightly-doped n- region in n-base, as shown in Fig. 2(b). This is due to the new structure improves the transport factor of the holes and decreases the holes

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recombination in narrow n-base. -7

1.4x10

-7

1.2x10

-7

1.0x10

-7

8.0x10

-8

6.0x10

-8

4.0x10

-8

4.0x10

2.0x10

-8

2.0x10

New structure

d=70%WB

-7

1.2x10

-7

d=50%WB

1.0x10

IAK /A

Conventional structure d=0

New structure

-7

1.4x10

d=60%WB

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IAK /A

-7

1.6x10

1.6x10

-8

Conventional structure

8.0x10

ND0=2e14cm-3 ND0=2e15cm-3 ND0=2e16cm-3 ND0=4e16cm-3 ND0=6e16cm-3

-8

6.0x10

-8

-8

0.0

0.0 0

10

20

30 VAK /V

40

50

0

10

20

30

40

50

VAK /V

Fig. 2 I-V characteristics of top p-n-p transistor in the new and conventional 4H-SiC thyristors. (a) at different thickness d of n- region, (b) at different doping concentration ND0 of n- region.

ACCEPTED MANUSCRIPT 3. Results and discussions To explore the static and dynamic characteristics of the proposed 4H-SiC thyristor, the device-level simulation was performed by the Sentaurus-TCAD software. The models used in the simulation contain the incomplete ionization [15], Auger

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recombination, electron-hole scattering, band-gap narrowing, Mobility model with doping and high field dependence, impact ionization and, Shockley-Read-Hall

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recombination with the Scharfetter [16]. And all the simulation were performed at room temperature (300K) and the relationship between lifetimes and doping

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concentration are shown in [16] and the minority carrier lifetime is set at τp0=0.1µs in n-base and τn0=2.0µs [17] in wide p- blocking base.

3.1. Turn-on characteristics of 4H-SiC thyristor

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The dynamic turn-on characteristics of the new and conventional 4H-SiC thyristor shown in Fig. 1 are simulated. The bias of anode-cathode is set as 800V and the load resistance is 4.4Ω·cm2, therefore the on-state current density is about 180A/cm2. A

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negative gate current pulse is applied to turn-on the thyristor. As shown in Fig. 3, the

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turn-on cathode voltage and current waveforms of the two structures are performed. From the turn-on characteristics shown in Fig. 3, we can conclude that the turn-on time of the conventional 4H-SiC thyristor is approximately 317ns and the rise time is about 200ns, which is in accordance with the turn-on time reported at present [18-19]. Similarly, the turn-on time in the new structure is reduced to 153ns, in case where the ratio of the lightly-doped n- region is 50%WB (WB is the whole thickness of n-base) and the doping concentration is 2e15cm-3. The turn-on characteristics in the proposed

ACCEPTED MANUSCRIPT structure have been improved significantly. Therefore, the turn-on mechanism with double epitaxial n-base in thyristor is worth researching deeply. 0

-Ig

Turn-on 0

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Solid: conventional thyristor Hollow: new thyristor -3 (d=50%WB, ND0=2e15cm ) -120

-400

-600

-800

-180

1.0x10

-7

2.0x10

-7

3.0x10

-7

4.0x10

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-7

0.0

2

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Cathode voltage /V

Cathode current density /(A/cm )

-200

-7

5.0x10

Time /s

Fig. 3 Cathode voltage and current waveforms of the two structures during turn-on process.

After comprehensively studying the turn-on characteristics of the two structures, we go deeply into the turn-on process of the new 4H-SiC thyristor. Investigation of the

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effects of proportion of lightly-doped n- region in whole n-base and its doping concentration on the turn-on time has been made. It is noted that the selection of the

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parameters d and ND0 are without sacrificing the forward blocking characteristics. Fig. 4 represents the turn-on time as a function of the proportion and doping concentration

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of lightly-doped n- region in n-base layer for the new structure, respectively. Apparently, the turn-on time is reduced significantly with the increasing in the lightly doped thickness d and the decreasing in the doping concentration ND0. Fig. 5 summarizes the impact of the ratio and doping level of n- region on the turn-on time. When the ratio of lightly-doped n- region varies from 50%WB to 70%WB (WB is the whole thickness of n-base), the turn-on time of the new thyristor is reduced to 96ns, which is approximate a third of that in conventional 4H-SiC thyristors’ (317ns). And

ACCEPTED MANUSCRIPT at a fixed ratio of 50%WB, in the case where the doping concentration ND0 decreases to 2e14cm-3 or 2e15cm-3, the turn-on time is about 152ns. The reason for the result can be illustrated that the transmission of the holes in the n-base is enhanced. Because the

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thin n-base is separated into two regions with high-low doping concentration, thus an additional built-in electrical field is induced in n-base and the width of the carriers transit the n-base by diffusion mode is shortened. As a result, in the lightly-doped n-

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region, the carriers transit by drift action. Consequently, the holes recombination in

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n-base has reduced, which leading to the turn-on speed has been improved largely. 0

Cathode voltage /V

-200

-3

d=0, ND=2e17cm (conventional) -3

d=50% WB, ND0=2e15cm

-3

-400

d=60% WB, ND0=2e15cm

-3

d=70% WB, ND0=2e15cm

-3

d=50% WB, ND0=2e14cm

-600

-3

d=50% WB, ND0=2e16cm

-3

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d=50% WB, ND0=4e16cm

-3

d=50% WB, ND0=6e16cm

-800

0.0

-7

1.0x10

-7

2.0x10

-7

3.0x10

-7

4.0x10

-7

5.0x10

Time /s

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Fig. 4 The effects of the thickness d and the doping concentration ND0 in the lightly-doped nregion on the turn-on time in new 4H-SiC thyristors.

1E14

Turn-on time /ns

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-3

Doping concentration ND0 /cm 1E15

1E16

1E17

240 220

d=1.0µm(50%WB)

200 180 160 140 120

-3

ND0=2e15cm

100 80

WB=2.0µm 50%WB

60%WB Thickness d /µm

70%WB

Fig. 5 Influence of thickness d and doping concentration ND0 of lightly-doped n- region on turn-on time for new structure.

ACCEPTED MANUSCRIPT 3.2. The turn-on mechanism analyses of the new 4H-SiC thyristor To the best of our knowledge, to turn-on the SiC thyristor, the following condition [20] must be satisfied: (1)

ߙଵ + ߙଶ = ߛଵ ߙ ்ଵ + ߛଶ ߙ ்ଶ ≥ 1

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where the ߙଵ and ߙଶ are the current gain coefficients of top narrow base p-n-p and bottom wide base n-p-n transistors in the common-base circuit, respectively. ߛଵ and

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ߛଶ are the injection efficiency coefficients of top p+-n and bottom n+-p junctions, respectively. The ߙ ்ଵ refers to the transport factor of a narrow base p-n-p transistor

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and ߙ ்ଶ is related to the transport factor of a thick (blocking) base n-p-n transistor. As shown in Fig. 4 and Fig. 5, with the increase in the proportion of n- region in n-base and decrease in the doping concentration of n- region, the transport factor ߙ ்ଵ of the top p-n-p transistor in the thyristor has been enhanced and therefore the turn-on

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time has decreased significantly. To better understand the turn-on mechanism of the new structure, the further illustrations are as follows.

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The impacts of the thickness d and doping concentration ND0 of lightly-doped nregion on electrical field distribution in n-base and partial p- drift layer at initial time

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of turn-on is shown in Fig. 6. With the increase of the proportion and decrease of the doping concentration of the lightly doped n- region, the region with the built-in electrical field becomes wider and higher, which leads to the holes transit the n-base by drift and diffusion action and the drift action is more intensive. As a result, the transport factor ߙ ்ଵ of narrow base p-n-p transistor has been promoted greatly.

ACCEPTED MANUSCRIPT -

n-base

p drift layer

5

5x10

-3

d=0, ND0=2e17cm (conventional) -3

d=50% WB, ND0=2e15cm

5

3x10

-3

d=60% WB, ND0=2e15cm

-3

5

d=70% WB, ND0=2e15cm

2x10

-3

d=50% WB, ND0=2e14cm 5

-3

1x10

d=50% WB, ND0=2e16cm

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Electrical field /(V/cm)

5

4x10

-3

d=50% WB, ND0=4e16cm

0 0.0

-3

d=50%WB , ND0=6e16cm

0.5

1.0

1.5

Distance /µm

2.0

2.5

3.0

different thickness d and doping concentration ND0.

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Fig. 6 Electrical field distribution of n-base and p- drift layer in the initial time of turn-on at

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The holes density distribution in the two structures at different times during turn-on process is shown in Fig. 7. For the conventional 4H-SiC thyristor, the holes cross over the thin n-base by diffusion action completely. However, for the new structure, an electric field is induced due to the existence of an abrupt junction in n-base region.

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Consequently, the transit mode of the holes in the n-base is drift and diffusion actions, and the larger the ratio of the lightly-doped n- region, the stronger the drift action in

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n-base, which promoting the transit of holes in n-base and therefore the turn-on delay time is shortened. Apparently, as shown in Fig. 7, at a fixed thickness of whole thin

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n-base, with the increasing in the ratio of the lightly-doped n- region, the proportion of drift action also increase, thus the holes recombination rate in n-base is reduced, resulting in the holes density of new structure is higher than the conventional structure’s. Similarly, at a 50%WB fixed thickness of n- region, with the decreasing in the doping concentration of lightly-doped n- region, the built-in electrical field is much higher, which accelerates the transit of holes in n-base by drift action, and also reduces the hole recombination. Hence, the holes density in the new thyristor is much

ACCEPTED MANUSCRIPT higher than that in conventional thyristor. t=0.10µs

16

10

t=0.05µs p drift layer

-3

-3

d=60% WB, ND0=2e15cm

-3

14

d=70% WB, ND0=2e15cm

10

-3

d=50% WB, ND0=2e14cm

-3

d=50% WB, ND0=2e16cm

13

10

-3

d=50% WB, ND0=4e16cm

-3

d=50% WB, ND0=2e15cm

Hole density /cm

-3

Hole density /cm

15

10

-3

d=0, ND=2e17cm (conventional)

15

10

-

p drift layer

n-base

-

n-base

14

10

13

10

-3

d=50% WB, ND0=6e16cm

12

12

10

10

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.0

4.0

0.5

1.0

1.5

t=8.00µs

-

p drift layer

n-base

15

-3

Hole density /cm

14

10

13

10

16

10

n-base

3.0

3.5

4.0

-

p drift layer

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Hole density /cm

-3

10

15

12

10

10

0.0

2.5

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t=0.15µs 16

2.0

Distance /µm

Distance /µm

10

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16

10

0.5

1.0

1.5

2.0

2.5

3.0

Distance /µm

3.5

4.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Distance /µm

Fig. 7 Holes density distribution at different time during turn-on process.

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In order to further illustrate it in detail, the recombination rate in thin n-base of the two structures at different time points is represented in Fig. 8. It can be observed that

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the recombination rate in n-base of the new 4H-SiC thyristor with 50%WB of lightly-doped n- region has reduced evidently. As a result, the injected holes density in

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p- wide base is increased slightly and therefore the subsequent lateral propagation is improved. Because the lateral spreading velocity is proportional to ln(J) over a range of the plasma spread [6] and current density J is proportional to the carriers concentration gradient. As shown in Fig. 9, the lateral current density J at cutline BB’ in two SiC thyristors is presented. Obviously, the current density of the new structure is higher than that in conventional SiC thyristors. As a result, the lateral propagation has been promoted and therefore the rise time is reduced.

ACCEPTED MANUSCRIPT In a word, the new structure with double epitaxial n-base has not only raised the transport factor αT1, but also improved the lateral propagation, which results in two reductions of delay time and rise time. Therefore, the turn-on time of the proposed

24

t=0.05µs

10

23

20

10

19

10

18

10

17

10

21

10

20

10

19

10

18

10

17

16

10

0.5

1.0

1.5

0.0

2.0

24

t=0.15µs

24

10

23

Conventional structure

22

10

21

10

20

10

19

18

10

17

10

16

10

0.0

0.5

1.5

2.0

1.0

1.5

t=8.00µs

Conventional structure

23

10

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New structure

10

1.0

Distance /µm

Distance /µm

10

0.5

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0.0

New structure

10

New structure

16

Conventional structure

22

10

-3

21

10

10

Recombination rate /(cm-3/s)

Recombination rate /(cm /s)

Conventional structure

22

10

10

t=0.10µs

23

10

Recombination rate /(cm-3/s)

Recombination rate /(cm-3/s)

10

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24

10

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new 4H-SiC thyristor is reduced significantly.

22

10

21

10

New structure

20

10

19

10

18

10

17

10

16

10

2.0

0.0

0.5

Distance /µm

1.0

1.5

2.0

EP

Distance /µm

Fig. 8 Recombination rate in n-base at different time during turn-on process.

t=0.05µs

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300

300

new structure conventional structure

t=0.10µs

new structure conventional structure

250 2

Current density /(A/cm )

Current density /(A/cm2)

250 200 150 100 50 0

200 150 100 50 0

10

20

Distance /µm

30

10

20

Distance /µm

30

ACCEPTED MANUSCRIPT new structure conventional structure

500

600 2

400 300 200 100

t=8.00µs

new structure conventional structure

500 400 300 200 100 0

0 10

20

10

30

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t=0.15µs

Current density /(A/cm )

2

Current density /(A/cm )

600

20

30

Distance /µm

Distance /µm

Fig. 9 The distribution of lateral current density in p- drift layer at BB’ during turn-on process.

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It is worth mentioning that the structure parameters simulated above are satisfied for the forward blocking characteristics. The optimization of the new 6500V 4H-SiC

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thyristor is implemented without sacrificing the forward blocking voltage. As shown in Fig. 10, the forward blocking characteristics of the new structure with 70%WB nregion and conventional 4H-SiC thyristor are simulated. Results indicate that a slight decrease in forward blocking voltage of the new structure, but the two structures can

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still withstand over the blocking voltage of 6500V. -5

1.0x10

conventional thyristor new thyristor

-6

-6

6.0x10

EP

2

JAK /(A/cm )

8.0x10

-6

4.0x10

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-6

2.0x10

0

2000

4000

6000

8000

VAK /V

Fig. 10 Forward blocking characteristics of new and conventional 4H-SiC thyristors.

4. Conclusion and perspectives

A new 4H-SiC asymmetrical thyristor with double epitaxial n-base is introduced and investigated by numerical simulation. In the first place, the turn-on characteristics of

ACCEPTED MANUSCRIPT the proposed and conventional 4H-SiC thyristor is simulated and analysed. Simulation results indicate that the turn-on characteristic of the new structure has been improved significantly. Subsequently, the optimization of the turn-on characteristics and turn-on

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mechanism of new 4H-SiC thyristor is analyzed. For the new 4H-SiC thyristor, a built-in electric field formed by n-n- junction will enhance the holes transport in n-base by drift action, thus the transport factor of top p-n-p transistor in 4H-SiC

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thyristor has been greatly improved. Furthermore, the lateral propagation has also

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been promoted. Consequently, the turn-on time is reduced to 96ns in case where the lightly-doped n- region is 70%WB and the doping concentration is 2e15cm-3. In conclude, the turn-on speed of proposed 4H-SiC thyristors can be improved evidently,

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Acknowledgment

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and it is a solution for fast switching-on of high-voltage 4H-SiC thyristors.

The work is supported by the National Nature Science Foundation of China grant

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No.51677149.

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ACCEPTED MANUSCRIPT [2] A. K. Agarwal, C. Capell, Q. Zhang, and J. Richmond, “9 kV, 1 cm×1 cm SiC super gto

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for pulse power,” Pulsed

Power

Conference(PPC), Washington, DC, USA, 2009, pp.264-269.

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760-768, Mar. 2017.

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[4] X. Song, A. Q. Huang, M. Lee, C. Peng, L. Cheng, H. O’Brien, A. Ogunniyi, C. Scozzie, and J. Palmour, “22kV SiC Emitter turn-off (ETO) thyristor and its dynamic performance including SOA,” Power Semiconductor Devices & IC's (ISPSD), Hong Kong, China, 2015, pp.277-280.

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[5] Q. Zhang, A. K. Agarwal, C. Capell, and L. Cheng, “SiC super GTO thyristor technology development: Present status and future perspective,” Pulsed Power Conference (PPC), Chicago, IL, USA, 2011, pp.1530-1535.

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[6] H. K. O’Brien, A. A. Ogunniyi, W. Shaheen, and S. H. Ryu, “Turn-ON of

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High-Voltage SiC Thyristors for Fast-Switching Applications,” IEEE Journal of Emerging and Selected Topics in Power Electronics, vol.4, no.3, pp.772-779, Sept. 2016.

[7] A. K. Agarwal, S. H. Ryu, R. Singh, O. Kordina, J. W. Palmour, “2600 V, 12 A, 4H-SiC, Asymmetrical Gate Turn Off (GTO) Thyristor Development,” Materials Science Forum, vols. 338-342, pp.1387-1390, May. 2000.

ACCEPTED MANUSCRIPT [8] S. H. Ryu, A. K. Agarwal, R. Singh, and J. W. Palmour, “3100 V, asymmetrical, gate turn-off (GTO) thyristors in 4H-SiC,” Electron Device Letters IEEE, vol. 22, no. 3, pp.127-129, Mar.2001.

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[9] A. K. Agarwal, C. Capell, Q. Zhang, and J. Richmond, “9 kV, 1 cm×1 cm SiC super gto technology development for pulse power,” IEEE Pulsed Power Conference, Washington, DC, USA, 2009, pp.264-269.

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[10] A. K. Agarwal, P. A. Ivanov, M. E. Levinshtein, J. W. Palmour, and S. L.

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Rumyantsev, “Dynamic Performance of 3.1 kV 4H-SiC Asymmetrical GTO Thyristors,” Materials Science Forum, vols. 389-393, pp.1349-1352, Apr. 2002. [11] M. E. Levinshtein, T. T. Mnatsakanov, A. K. Agarwal, and J. W. Palmour, “Analytical and numerical studies of p+-emitters in silicon carbide bipolar

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devices,” Semiconductor Science and Technology, vol. 26, no. 5, 2011. [12] Q. Zhang, Y. Zhang, Y. Zhang, and Y. Wang, “High temperature characterization

11, 2010.

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of double base epilayer 4H-SiC BJTs,” Journal of Semiconductors, vol. 31, no.

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[13] X. Wang, H. B. Pu, Q. Liu, C. L. Chen, and Z. M. Chen, “Injection modulation of p+-n emitter junction in 4H-SiC light triggered thyristor by double-deck thin n-base,” Chinese Physics B, vol. 26, no. 10, 2017.

[14] W. S. Lee, K. W. Chu, C. F. Huang, L. S. Lee, M. J. Tsai, K. Y Lee, and F. Zhao, “Design and Fabrication of 4H-SiC Lateral High-Voltage Devices on a Semi-Insulating Substrate,” IEEE Transactions on Electron Devices, vol. 59, no. 3, pp. 754-760, March 2012.

ACCEPTED MANUSCRIPT [15] L Cheng, A. K. Agarwal, C Capell, M. O’Loughlin, K. Lan, J. Richmond, Edward Van Brunt, A. Burk, J. W. Palmour, H. O’Brien, A. Ogunniyi, and C. Scozzie, “20 kV, 2cm2 4H-SiC gate turn-off thyristors for advanced pulsed

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power applications,” IEEE Pulsed Power Conference (PPC), 2013: pp.1-4. [16] M. E. Levinshtein, S. L. Rumyantsev, M. S. Shur, T. T. Mnatsakanov, S. N. Yurkov, Q. J. Zhang, A. K. Agarwal, L. Cheng, and J. W. Palmour, “Holding

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current and switch-on mechanisms in 12 kV, 100 A 4H-SiC optically triggered

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thyristors,” Semiconductor Science & Technology, vol. 28, no. 1, pp.15008-15012, Jan. 2013.

[17] M. E. Levinshtein, T. T. Mnatsakanov, S. N. Yurkov, A. G. Tundoev, Sei-Hyung, and J. W. Palmour, “High-Voltage Silicon-Carbide Thyristor with an n -type

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Blocking Base,” Semiconductors, vol. 50, no. 3, pp. 404-410, 2016. [18] S. Sundaresan, A. M. Soe, and R. Singh, “Static and Switching characteristics of 6500V silicon carbide anode switched thyristor modules,” in Proc. IEEE ECCE,

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Raleigh, NC, USA, Sep. 2012, pp.1515-1519.

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[19] L. Lin, and J. H. Zhao, “Fabrication and Characterization of 4H-SiC 6kV Gate Turn-Off Thyristor,” Materials Science Forum, vols. 717-720, pp. 1163-1166, May. 2012.

[20] B. J. Baliga, “Fundamentals of power semiconductor devices,” Springer Science & Business Media, 2010.

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Highlights 1. A new 4H-SiC asymmetrical thyristor with double epitaxial n-base is proposed. 2. A built-in electrical field induced in n-base enhances the transmission of the holes and weakens its recombination.

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3. Compare to the conventional 4H-SiC thyristor, the turn-on time of the new 4H-SiC asymmetrical thyristor is approximately reduced to a third (96ns).