High-field Electrical Transport in Single Crystal CVD Diamond Diodes, - - PDF document

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High-field Electrical Transport in Single Crystal CVD Diamond Diodes, - - PDF document

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See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/275350879 High-field Electrical Transport in Single Crystal CVD Diamond Diodes, Presentation Conference Paper June 2006 CITATIONS

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SLIDE 1

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/275350879

High-field Electrical Transport in Single Crystal CVD Diamond Diodes, Presentation

Conference Paper · June 2006

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High-field Electrical Transport in Single Crystal CVD Diamond Diodes

Jan Isberg, Markus Gabrysch Uppsala University Antonella Tajani, Daniel Twitchen Element Six Ltd

Uppsala University: Jan Isberg Markus Gabrysch Element Six Ltd: Antonella Tajani Daniel Twitchen

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SLIDE 3

Contents

  • Impact Ionization at high electric fields
  • High voltage diamond diodes
  • Attempts to measure impact ionization

coefficients in SC-CVD diamond

  • Summary
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SLIDE 4

Impact Ionization

  • R. Raghunathan, B. Baliga,

Solid-State Electronics 43 (1999) 199-211

Silicon Carbide

E

Holes and electrons accelerated in high electric field attain enough energy to create new electron hole pairs by impact ionization

Impact Ionisation Diodes Experiment Summary

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SLIDE 5

Modelling Impact Ionization

t E j j j N N n p q E j j r j t p q j j r j t n q p qD E qp j n qD E qn j

p n d a p p n n SRH p p p n n SRH n p p p n n n

∂ ∂ + + = − + − = ⋅ ∇ + + − ⋅ ∇ = ∂ ∂ + + − ⋅ ∇ = ∂ ∂ ∇ − = ∇ + =

− +

ε ε α α α α µ µ ) ( | | | | | | | |

Drift-diffusion currents Continuity eq. including avalanche generation Poisson eq. Total current

E p b E n b

e a e a

p p n n − −

= = α α

Cynoweth relation

Impact Ionisation Diodes Experiment Summary

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SLIDE 6

Avalanche Simulation

α

t=0 2kV over 50µm 7.2kV over 50µm

Hole conc.

Impact Ionisation Diodes Experiment Summary

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SLIDE 7

Avalanche simulation movies

Impact Ionisation Diodes Experiment Summary

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SLIDE 8

Charge multiplication

Low voltage: no carrier multiplication, electrons extracted quickly, holes extracted after transit High voltage: generation of electron-hole pairs by impact ionization

Impact Ionisation Diodes Experiment Summary

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SLIDE 9

p+ (~ 1020 [B]/cm3)

50-500 µm

HV p-i-metal Diamond Diode

anode Ti/Al/Au or Ti/Al/Pt/Au p++ boron ion-implanted intrinsic (< 1013 [B]/cm3, very low [N]) few µm Al or Au cathode

Impact Ionisation Diodes Experiment Summary

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SLIDE 10

Boron Doping

  • In-growth B doping in the range 1015 to 1021 cm-3

for thick layers

  • No contamination between doped and undoped

layers

  • Sharp interfaces (<1 µm)

i p

Optical micrograph

p i

SIMS analysis

Impact Ionisation Diodes Experiment Summary

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SLIDE 11

HV p-i-metal diamond diodes

p+

Au cathode anode p++ intrinsic Space charge limited hole current in intrinsic layer Similar to vacuum diode

Edge field enhancement Impact Ionisation Diodes Experiment Summary

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SLIDE 12

Forward Conduction

Similar to vacuum diode

e-

Forward conduction: space charge limited hole current in intrinsic layer p+ i

+

  • L

Ideally: Mott – Gurney behaviour

3 2

8 9 L V j

h

εµ =

2 2 / 3

9 8 L V m q j

e

ε =

c.f. Child’s law for vacuum tubes (ballistic transport)

Impact Ionisation Diodes Experiment Summary

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SLIDE 13

Layer thickness

C-V measurement

  • n 1.2 mm2 diode.

Note almost constant capacitance in this type of diode Diode illuminated from side, 10 μm i-layer

Impact Ionisation Diodes Experiment Summary

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SLIDE 14

EBIC in diamond

no secondary impact ionization at attainable bias voltage…

Ti/Al/Au Au p+ i

Impact Ionisation Diodes Experiment Summary

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SLIDE 15

Impact ionization experiment

Two α-emitting spherical gold tips made at The Svedberg Lab (3 & 5 kBq) Advantages:

  • Small contact area
  • Experiment can be done in insulating oil

→ higher bias possible

Impact Ionisation Diodes Experiment Summary

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SLIDE 16

Alpha particle penetration

Isotropic distribution

0° incidence

Impact Ionisation Diodes Experiment Summary

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SLIDE 17

Impact ionization setup

Impact Ionisation Diodes Experiment Summary

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SLIDE 18

Preliminary results

Noise (shot noise) due to excessive leakage current

Solid line: ap= 4.0·106 cm-1, bp=1.1·107 V/cm Dashed line: ap= 6.0·105 cm-1 and bp=0.8·107 V/cm Impact Ionisation Diodes Experiment Summary

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SLIDE 19

Summary

  • Measurements of impact ionization

coefficients in diamond difficult due to th very high electric fields necessary

  • Carrier multiplication from impact

ionization at high electric fields has been observed

  • Reduced leakage currents necessary to
  • btain reliable data on avalanche

ionization coefficients

Impact Ionisation Diodes Experiment Summary

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