AIST, 2 CREST/AIST, 3 Univ. Of Tsukuba

Transcription

1 A. Traoré 1, A. Nakajima 1, T. Makino 1,2, D. Kuwabara 1,2,3, H. Kato 1,2, M. Ogura 1,2, D. Takeuchi 1,2, and S. Yamasaki 1,2,3 1 AIST, 2 CREST/AIST, 3 Univ. Of Tsukuba aboulaye.traore@aist.go.jp

2 Diamond Device Team: Permanent: D. Takeuchi, H. Kato, H. Okushi, M. Ogura, S. Yamasaki, T. Makino, Y. Kato Student: D. Kuwabara, H. Kawashima, K. Driche, T. Honbu Technical staff: H. Sakuma, M. Mikami, N. Senda, Y. Umeno NIMS S. Koizumi Toshiba M. Suzuki Tsukuba Univ. T. Matsumoto, D. Kuwabara, K. Shirota Tokyo Institute of Technology M. Hatano, T. Iwasaki, Y. Hoshino, K. Tsuzuki Kanazawa University N. Tokuda 2

3 This talk General and unique properties of diamond Diamond unique properties & devices Diamond pin diode switching characteristics (first test results)

4 Outline Diamond properties o General properties o Impurities levels in diamond o Diamond unique properties Diamond unique properties & devices o Examples of diamond devices SBD Bipolar transistor JFET PIN diode Diamond mosfet o Diamond Schottky-pn diode (new concept) o Semiconductor vacuum switch (NEA) o Diamond p + in + diode (hopping conduction) Diamond pin diode turn-off characteristics o o o o motivation Turn-off characteristic Dynamic breakdown Summary Conclusion

5 Diamond: Breakdown field higher than 10 MV (30 times higher than the Si limit ) Thermal conductivity of 22 W/cmK (5 times higher than the copper) 5

6 Diamond: Breakdown field higher than 10 MV (30 times higher than the Si limit ) Thermal conductivity of 22 W/cmK (5 times higher than the copper) Higher Figures Of Merit (FOM) than its main challengers (SiC, GaN) Diamond is one the best semiconductors for high power devices 6

7 Main issue Deep impurities levels Dopant energy level (mev, n, p) Si SiC GaN Diamond 45 (P) 70 (N) 25 (Si) 570 (P) 45 (B) 200 (Al) 150 (Mg) 380 (B) Growth: Microwave plasma enhanced chemical vapor deposition Pressure: Torr Temperature: C Microwave power: W Gas mixture in growth chamber: methane (CH 4 ) + hydrogen (H 2 ) In-situ doping: Microwave plasma Diamond substrate Substrate holder n-type diamond: Gas mixture + phosphine PH 3 p-type diamond: Gas mixture + diborane B 2 H 6 7

8 5.5 ev Band diagram Conduction band Phosphorous (P) Nitrogen (N) 0.57 ev 1.7 ev n-type diamond Ionization energy Vs. doping density 0.57 ev Phosphorus donor Hopping conduction N D cm -3 5x10 20 cm -3 Boron (B) 0.38 ev Valence band p-type diamond Boron is the shallowest dopant, and preferentially used for unipolar devices Hopping conduction (dopants band) plays an important role in carrier transport at impurities level 0.38 ev Boron acceptor Metal transition Klein et al. PRB 75, 1-7 (2007) cm -3 5x10 20 cm -3 N A 8

9 5.5 ev Band diagram Conduction band Phosphorous (P) Nitrogen (N) 0.57 ev 1.7 ev At high impurities density (N A, N D > cm 3 ), a minimum resistivity is obtained due to the hopping conduction T. Makino et al, Jpn. Appl. Phys. 53 (2014) 05FA12 n-type: phosphorus doped diamond p-type diamond: boron doped diamond Boron (B) 0.38 ev Valence band Boron is the shallowest dopant, and preferentially used for unipolar devices Hopping conduction 9

10 Outstanding electrical and thermal properties than its challengers (Si, SiC, GaN) Deep dopants levels General properties Main issues: Hopping conduction Key mechanism to reduce diamond devices serial resistance Electronic grade diamond wafers High Pressure High Temperature (HPHT) diamond substrates Max. size ~10 x 10 mm 2 Chemical Vapor Deposition (CVD) diamond substrates Homo epitaxial growth (Max. size ~10 x 10 mm 2 ) Mosaic technology (Japan, AIST-Kansai) size up to 50 x 40 mm 2 10

11 Outstanding electrical and thermal properties than its challengers (Si, SiC, GaN) Deep dopants levels General properties Main issues: Hopping conduction Key mechanism to reduce diamond devices serial resistance Electronic grade diamond wafers High Pressure High Temperature (HPHT) diamond substrates Max. size ~10 x 10 mm 2 Chemical Vapor Deposition (CVD) diamond substrates Homo epitaxial growth (Max. size ~10 x 10 mm 2 ) Mosaic technology (Japan, AIST-Kansai) size up to 50 x 40 mm 2 10 mm Hetero epitaxial growth on silicon (Japan, AIST-Tsukuba) Low cost and should accelerate the achievement of large size diamond wafer 11

12 Diamond unique properties: Hopping conduction Key mechanism to reduce the diamond devices serial resistance Surface conductive layer (2D-hole channel, Hydrogen terminated diamond) Diamond metal-insulator-semiconductor FET Stable exciton state even at room temperature Exciton Ultraviolet LED Negative Electron Affinity (NEA) Semiconductor vacuum switch Extremely long spin-lattice relaxation time Quantum devices operating at room temperature AIST diamond device team: Diamond investigation, Diamond power devices, New devices concept taking advantage of the diamond unique properties 12

13 Outline Diamond properties o General properties o Impurities levels in diamond o Diamond unique properties Diamond unique properties & devices o Examples of diamond devices SBD Bipolar transistor JFET PIN diode Diamond mosfet o Diamond Schottky-pn diode (new concept) o Semiconductor vacuum switch (NEA) o Diamond p + in + diode (hopping conduction) Diamond pin diode turn-off characteristics o o o o motivation Turn-off characteristic Dynamic breakdown Summary Conclusion

14 SBD Bipolar Transistor JFET PIN diode Diamond mosfet SCHOTTKY BARRIER DIODE H. UMEZAWA et al. DRM 24 (2012) BIPOLAR TRANSISTOR H. Kato et al. DRM (2012) JUNCTION FIELD EFFECT TRANSISTOR T. Iwasaki et al. APEX 5 (2012) M. Suzuki et al, PSS (a) 210 (2013) 2035 PIN DIODE 14

15 SBD Bipolar Transistor JFET PIN diode Diamond mosfet Inversion channel diamond MOSFET p-channel mosfet on n-type diamond MOS structure: Metal/Al 2 O 3 /diamond Matsumoto et al. Scientific Report 6, (2016) Diamond metal-insulator-semiconductor FET Surface conductive layer (2D-hole channel) Hydrogen-terminated diamond Structure: Metal/Al 2 O 3 / diamond Liu et al. JAP 118, (2015) 15

16 Merged Schottky junction and pn junction T. Makino et al, JJAP. 53 (2014) 05FA12 Conduction state: The on-current level depends on the highly conductive p+ layer The majority carrier is hole Equilibrium Blocking state: The n-type diamond is the active layer The maximum blocking voltage depends on the n layer 16

17 Merged Schottky junction and pn junction T. Makino et al, JJAP. 53 (2014) 05FA12 Promising concept for high current and high blocking voltage diamond devices High conduction current density A/cm 6 V Rectification ratio of 12 order of ± 6 V Breakdown field over 3 MV/cm 17

18 Hydrogen terminated diamond surface Hydrogen termination (H-diamond) Electron Affinity E.A: difference Conduction Band (CB) Vacuum level (V.L) Oxygen terminated diamond Appl. Phys. Lett., 86, , (2005). Physica Status Solidi A202, 2098 (2005) Oxygen terminated diamond 18

19 Diamond pin diode Cathode n layer Drift region Hole H-diamond surface: Negative electron affinity Electron emission from diamond surface Electron H-termination D. Takeuchi et al. JJAP 56 (2012) Electron emission I A I pin p layer Anode Emission Efficiency α = I A /I pin : 10 % (NIMS) 19

20 10 kv vacuum switch Diamond pin diode: α about V device A 10 V diamond pin diode can control 10 kv, even more higher voltage 20

21 Cathode n-type diamond Intrinsic diamond Drift region p-type diamond Anode Diamond pin diode Exciton ultraviolet LED Semiconductor vacuum switch High power pin diode High Breakdown field is achieved using a basic design Breakdown field about 5.1 MV/cm (submitted) M. Suzuki et al, pssa 210, 2035 (2013) Main issues: Resistive n-type diamond resistive ohmic resistance on the n-type diamond From 10 6 to 10-3 cm 2 depending on the donor concentration 21

22 Cathode n-type diamond Intrinsic diamond Drift region p-type diamond At high impurities density (N A, N D > cm 3 ): Negligible ohmic resistance on doped diamond layers Low resistivity of n-type and p-type diamond layers due to hopping conduction T. Makino et al, Jpn. Appl. Phys. 53 (2014) 05FA12 Anode p-type n-type hopping conduction 22

23 Cathode n + diamond Base region p + diamond Diamond p + in + diode: Band conduction + hopping conduction Lower forward voltage drop Diamond p + in + diode Vs. pin diode T. Makino et al, JJAP 53 (2014) 05FA12 Anode Hopping conduction: Key mechanism to reduce diamond devices serial resistance 23

24 Outline Diamond properties o General properties o Impurities levels in diamond o Diamond unique properties o Diamond surface termination Diamond unique properties & devices o Examples of diamond devices SBD Bipolar transistor JFET PIN diode Diamond mosfet o Diamond Schottky-pn diode (new concept) o Semiconductor vacuum switch (NEA) o Diamond p + in + diode (hopping conduction) Diamond pin diode turn-off characteristics o o o o motivation Turn-off characteristic Dynamic breakdown Summary Conclusion

25 Cathode n layer Electron Base region hole n-type and p-type layer : band conduction + hopping conduction Base region: Three particle model (electron, hole, free exciton) CB I d p layer Binding energy of free exciton: 80 mev Transport mechanisms still known Anode up to date Open questions: Influence of hopping conduction on carrier injection in the base region? Investigation methods: VB Recombination mechanisms taking into account the exciton generation and recombination? Free carrier distribution, existence of a charge - carrier plasma and its dynamic during switching? Static characterization, Photoluminescence Dynamic characterization TCAD simulation 25

26 Standard clamped inductive switching Schematic diagram A diamond pin diode is used as freewheeling diode (DUT) First test: A 200 µm diameter diamond pin diode has been used Cathode n layer: 1 µm thick n layer N D ~ cm 3 Base region Base region (i layer): 8 µm thick N D, N A < cm 3 I F = 0. 1 A (320 A/cm 2 50 V I R = 10 7 A/cm -100 V p layer Anode p layer: 3 µm thick N A ~ cm K 26

27 Turn-off characteristic illustrating the reverse-recovery Conduction current level I F = A (445 A/cm 2 66 V Input voltage: 500 V Reverse-recovery comfirming the bipolar nature of diamond pin diode Reverse-recovery time t rr ~ 150 ns Extracted charge Q rr ~ 9 nc The voltage builds up at the same time as the current turns to negative 27

28 Influence of the on-current level on the turn-off waveforms Input voltage about 400 V The diamond diode can commutated from a conduction state at 850 A/cm 2 to a block state at 400 V Weak modification of the turn-off waveforms for an on-current level higher than 400 A/cm 2 Extracted charge Q rr ~ 6 nc 28

29 Influence of the input voltage on the turn-off waveforms Input voltage: 300 V, 400 V, 500 V The turn-off waveforms are relatively similar Extracted charge Q rr : ~ 7 nc (@300 V) ~ 8 nc (@400 V) ~ 9 nc (@500 V) 29

30 Influence of the input voltage on the turn-off waveforms Input voltage: 600 V Dynamic breakdown Voltage Current 30

31 For an input voltage of 600 V, the dynamic breakdown of diamond pin diode occurs Dynamic breakdown Change on diode static characteristics 31

32 First test of a diamond pin diode as a freewheeling diode Basic diode design (no junction termination) The reverse-recovery occurs during the diamond diode turn-off, thus confirming its bipolar nature The diamond diode can commutated from a conduction state at 850 A/cm 2 to a block state at 400 V Future works: Comparison TCAD simulation and experimental turn-off Charge carrier dynamics Recombination process Influence of Exciton Carrier lifetime investigation in a complete diamond pin diode by Open Circuit Voltage Decay (OCVD) Resistance I d pin diode τ eff 2k BT q dv dt 1 V d V cc Switch 32

33 Diamond has huge potential for high power applications Most of the well-known devices technologies can be fabricated using diamond. Diamond unique properties are needed to take full advantage of its great potential, while confronting its many challenges. Hopping conduction (minimization of devices serial resistance) NEA, vacuum switch device (New concept) for high power application Diamond heteroepitaxial growth on silicon should accelerate the achievement of low cost electronic grade diamond wafer 33

34 Thanks for your attention D. Takeuchi H. Kato H. Okushi M. Ogura S. Yamasaki T. Makino Acknowledgments Diamond Device Team: Permanent: Student: Technical staff Secretary D. Kuwabara H. Kawashima N. Kudo H. Sakuma N. Senda Y. Umeno M. Mikami 34