Wide Bandgap Semiconductor Research at Mississippi State ... · Bharat Krishnan, Hrishikesh Das, Huang-De Lin, Galyna Melnychuk, Yaroslav Koshka. 1 Mississippi State University, Box

Wide Bandgap Semiconductor Research

at Mississippi State University

Dr. Yaroslav Koshka

Associate Professor

Department of Electrical and Computer EngineeringMississippi State University

Presentation Outline

1. Why SiC

2. History of SiC program at MSU

3. Advancements in SiC epitaxial growth

4. Recombination Induced Defect Reactions involving hydrogen in SiC.

1. Why SiC?




SiC Material Properties(comparing to other semiconductors)

(peak) (peak)2

(pick)12.5(pick)22Saturation drift velocity [105m/s]

8”12”n/a3”4”Commercially available substrates

DIDIIDirect/Indirect Bandgap0.40.3~ 3> 2.4~ 3Critical electric field [MV/cm]12.811.89.0109.7Dielectric constant

65551224~ 90081 (Π)

405 (⊥)980 (Π)865 (⊥ )

Low field electron mobility (300ºK, 1e16cm-3) [cm2/V*s]

1.41.13.393.03.26Bandgap [eV]

0.551.31.34.94.9Thermal conductivity [W/cm*K]

GaAsSiGaN6H-SiC4H-SiCProperty\Material

Drift region resistance

Heavily doped n-type substrate

Drift region

Schottky contact

Cathode contact

Tdrift

Drift region

Heavily doped p-type substrate

DrainSource

P-type epitaxial layer

Sourcecontact

Gatecontact Drain

contact

Body contact

Tdriftdrift

drift spn drift

TR

q Nµ=

P-type anode

Heavily doped n-type substrate

Drift region

Anode contact

Cathode contact

Tdrift ( )drift

drift spn p F a

n driftdrift

TR J

q NT

µ µ τµ

=+

+

Drift region blocking capability(1-D approach)

1 1D

dE x q N xdxϕ ρ

ε ε= = − =

1crit Drift DriftE q N T

ε=

01DriftT 2DriftT

1DriftN 2DriftNdriftT

assuming free carrier concentration to be negligible (no leakage current)for non-”punch-through” layer:

0

( )DriftT

BlockingU E x dx= ∫Voltage drop on drift region is given by:

( ) ,div ε ϕ ρ∇ = −solve the Poisson equationTo find ( ),E x

Drift region blocking capability(1-D approach)

1 1D

dE x q N xdxϕ ρ

ε ε= = − =

01DriftT

driftT

assuming free carrier concentration to be negligible (no leakage current)for non-”punch-through” layer:

0

( )DriftT

BlockingU E x dx= ∫Voltage drop on drift region is given by:

( ) ,div ε ϕ ρ∇ = −solve the Poisson equationTo find ( ),E x

Ecrit 2

Ecrit 1

Ndrift 2 << Ndrift 1

Tdrift 2 >> Tdrift 1

1crit Drift DriftE q N T

ε=

Specific on-resistance of SiC

400x

Advantages of wide bandgap

100

101

102

103

102 103 104

Spe

cific

On-

Res

ista

nce

(mž

cm2 )

Blocking Voltage (V)

Silicon

4H-SiC

(mΩ

cm2

) VB2/ RON = constantVB

2/ RON = constant

• Resistance-Area productof 4H-SiC is 400x lowerthan silicon at any givenblocking voltage

Advantages of wide bandgapIntrinsic carrier concentration

Example:n-type, ND = 1015 cm-3

Advantages in Switching Characteristics

Si pin diode – 1.32 µs SiC Schottky diode – 72 ns

600 V diode recovery comparison


1. Why SiC




1. Why SiC?




History of Wide Band Gap Semiconductors at Mississippi State University

Materials - Devices- Circuits - Systems

MESFET Fab at GE

0 5 10 15 200

200

400

600

800SiC161, Wafer A1x100 µmVg=0V, Vg step=-5V

I DS (m

A/m

m)

VDS (V)

Emerging Materials Research Laboratory

EMRL

Emerging Materials Research Laboratory

EMRL

0.3 µm n channel

Semi-insulating substrate

0.55 µm p- buffer

ONR N00014-01-C-0167

C. Wood

ONR N00014-01-C-0167

C. Wood

SiC Epi at MSU

Testing at GE & MSU ADPC

SMDC DASG60-00-C-0074

L. Riley

SMDC DASG60-00-C-0074

L. Riley

Power Electronics Prototyping / Power

Component Test BedPEP/PCT

Power Electronics Prototyping / Power

Component Test BedPEP/PCT

Prototype Power

Electronics at MSU

Modify HMMWV at

MSU

Sentinel Demo by

MSU/Guard/SMDC

Commercial Packaging

Miss. Center for Advanced Semiconductor Prototyping

MCASP

Miss. Center for Advanced Semiconductor Prototyping

MCASP

AFRL/MDA F33615-01-D-2103

J. Scofield

AFRL/MDA F33615-01-D-2103

J. Scofield

SiC SBD Design

SBD Fab at MSU

Leveraging Basic Research into Production -Rapid, economical transfer of government sponsored technology development into systems

LAM 9400 EtcherAIXTRON SiC Reactor

• Multi Wafer SiC Epi• Sub-micron lithography• Multi Wafer Plasma Etching• Multi Wafer PECVD• Multi Wafer Metal Deposition

MCASPMississippi Center for Advanced

Semiconductor Prototyping

EMRL• SiC CVD Epi Research

• Defect Engineering

• Materials Characterization

• Device Design

Component Production• Mississippi Small Business

• SBIR’s

www.ece.msstate.edu/mcasp

Epitaxial Process Simulation

SiH4

Si(g)

Material Science Program at MSU

Novel epitaxial growth techniques

Defects and Impurities. Defect Engineering in WBG Semiconductors

SiC for Nanotechnologies

PL DLTS

SEM FTIR

…

Traditional Material Characterization

ONR, AFRL, SBIR/STTR…

Novel Non-ContactMaterial Characterization

Techniques


1. Why SiC




1. Why SiC?




Lower-temperature epitaxial growth of 4H-SiC

using CH3Cl carbon gas precursor.

Huang-De Lin, Galyna Melnychuk, Yaroslav Koshka

1 Mississippi State University, Box 9571, Mississippi State, MS 39762, USA

The hot-wall CVD reactors.

Traditional Precursors:SiH4 and C3H8

• Growth temperatures >15000C• Lower temperatures => morphology degradation => polycrystalline

Silane decomposition

SiH4

SiH2

Si<g>

CH3Cl

CH4

C2H4

Cl

Chloromethane decomposition

Simulated kinetics of chemical reactions of SiC epitaxial growth

in the cross-section of the CVD reactor

Our new model – vapor-phase formation of Si droplets (clusters)

Dense silicon-droplet

cloud

Growth at Lower Temperatures

13000C

View of the susceptor from the rear-port window

• Si vapor condensation (cloud) is detrimental for epiquality and growth rate.

High Si/C ratioLow Si/C ratio

50 µm

Optimized

Surface morphology of the 13000C growth

2 µm

>2 µm/hr

J. of Crystal Growth Patent Pending

0

0.5

1

1.5

2

2.5

0 10 20 30

Gro

wth

rate

, 1/h

rCH3Cl flow

TGrowth = 1300 0C

SiH4 flow, sccm

Exponentialfitting

Degraded morphology

Growth rate dependence on silane flow @13000C

The saturation of the growth rate at higher SiH4 flows is due to

silicon vapor condensation in clustersreducing the amount of Si available for epitaxial

growth

⎟⎟⎠

⎞⎜⎜⎝

⎛ ><−−∝><

4

44 exp1)(

SiH

SiHSiHRττ SiH4

J. of Crystal Growth

Arhenius temperature dependences: (a) exponential rate coefficient of the SiH4 flow dependence

compared to (b) the growth rate temperature dependence.

⎟⎟⎠

⎞⎜⎜⎝

⎛ ><−−∝><

4

44 exp1)(

SiH

SiHSiHRττ SiH4 (T)

The value of EA is the same for R and τ SiH4 => the growth rate is determined by silicon vapor condensation.

1

10

0.57 0.59 0.61 0.63

1000/T, K-1G

row

th ra

te, u

m/h

r

EA = 0.573 eV

(a)

Gro

wth

rate

R (µ

m/h

r)1000/T, K-1

1

10

100

0.57 0.59 0.61 0.63

1000/T, K-1

Exp

onen

tial r

ate

coef

ficie

nt

(scc

m) EA = 0.576 eV

(b)

τ SiH

4(s

ccm

)

1000/T, K-1

Dense cloud of Si clusters Strongly reduced cloud

(a) No HCl (b) With HCl added

HCl experiment:Rear view of the glowing susceptor

during 13000C epitaxial growth

Selective epitaxial growth of 4H-SiC with SiO2 mask.

Bharat Krishnan, Hrishikesh Das, Huang-De Lin, Galyna Melnychuk, Yaroslav Koshka.

1 Mississippi State University, Box 9571, Mississippi State, MS 39762, USA

Patent Pending

Plasma Plasma

Semiconductor

Mask

Semiconductor

Pattern formation by Etching

CVD CVD

Semiconductor

Mask

Semiconductor

Pattern formation by Selective Epitaxial Growth

SiO2 mask for low-temperature selective epitaxial growth of 4H-SiC (LTSEG)

SiO2mask

• SiO2 Severely degrade at regular growth temperatures (15000C)• Survives at 13000C of our novel low-temperature growth method

SiCsubstrate

SiO2 mask4H-SiC mesas

2 µm

(a) with SiO2 mask

Low-temperature SEG at 13000C:

4H-SiC mesas4H-SiC substrate

2 µm

(b) SiO2 mask removed

>3 µm / hr

Patent Pending

5 µm

[ 0211 ] (off-axis direction)

Edge defects

SEM image of the mesa-lines selectively grown in SiO2window at 13000C.

Lines oriented in different directions reveal the orientation-dependent defect generation.

Patent Pending

Cross-sectional SEM of 30-µm-wide mesa line selectively grown in SiO2 window at 13000C.

3 µm

SiO2defective region

[ ]0211

1 µmEdge facet

SiO2

Patent Pending


1. Why SiC?




1. Why SiC?




Plasma hydrogenation.

• Processing in new Inductively Coupled Plasma (ICP) system enabled further improvement of hydrogen

incorporation in comparison to RIE hydrogenation.

• Experimental Reactive Ion Etching (RIE) system → Hydrogen Plasma.

Hydrogen plasma

SiC subjected to Plasma Hydrogenation.Incorporated hydrogen forms stable complexes with defects and impurities. Hydrogen concentration profiles repeat profiles of acceptor concentration.

[1] S. Janson, A. Hallén, M. K. Linnarsson, and B. G. Svensson, Phys. Rev. B 64, 195202 (2001)

→ Stable hydrogen-defect complex in SiC→ Mobile hydrogen atom→ Defect or impurity

Effect of plasma hydrogenation on the concentration of active acceptors (Al).

• Passivation of Al acceptors down to 1015cm-3 and to the depth in access of 2 µm was achieved after 2 hrs of hydrogenation.

1E+15

1E+16

1E+17

1E+18

1E+19

0 0.5 1 1.5 2 2.5

depth, µm

Con

cent

ratio

n, c

m-3

Al (SIMS)

Acceptors before hydrogenation (CV)

Acceptors after hydrogenation (CV)

1019

1018

1017

1016

1015

Ec

Ev Al

H

Al-H

Simple Diffusion

⎟⎠⎞

⎜⎝⎛

∂∂

∂∂

=∂

∂xHD

xtH

x][][

H – hydrogen concentration

tHT

xHD

xtH

x ∂∂

−⎟⎠⎞

⎜⎝⎛

∂∂

∂∂

=∂

∂ ][][][][]][[][ HTTHK

tHT ν−=∂

∂

T – concentration of empty traps.HT – concentration of traps filled with hydrogen.

K – trapping constant.ν – dissociation frequency

Trap-Limited Diffusion

H at interstitial sites H trapped by defect or impurity

-13

-8

-3

2

7

4100 4120 4140 4160 4180 4200 4220

PL in

tens

ity, a

rb.u

n.

S0 R0

H3

Wavelength, Å

4Al 15 K

Hydrogenated

Initial

PL spectra before and after plasma hydrogenation of epilayer moderately doped with Al.

Y. Koshka, M. S. Mazzola, Appl. Phys. Lett, 79(6), 752 (2001)

• Efficient trapping of hydrogen by Al acceptors is confirmed by reduction of Al-BE PL;• Al acceptors are not the only trapping centers for hydrogen. H-related PL lines indicate

simultaneous formation of H complex with Si vacancy (VSi-H ).

• A 4B0 peak previously associated with a bound exciton at the neutral boron is in fat related to a hydrogen-defect complex (possibly, B-H).

PL spectra of B-doped 4H-SiC epilayer:affect of plasma hydrogenation:

p = 8-9 x 1015 cm-3

tepi = 5 µm

Y. Koshka, Appl. Phys. Lett., 82, 3260 (2003).

Optically-stimulated passivation of defects with hydrogen.

Phenomenon of Recombination-Induced Passivation

(RIP)

→ Stable hydrogen-defect complex in SiC

→ Mobile hydrogen atom→ Defect or impurity

Above band-gap light

Al-HB-H4B0

Schematic illustration of Recombination-Induced Passivation.

Certain amount of the incorporated hydrogen does not form stable complexes with defects (so called “free hydrogen”). Recombination-induced defect migration causes formation of various kinds of stable defect complexes.

T = 15 KT < ~ 250 K

VSi-H

Photoluminescence spectra after Regular Hydrogenation and after Recombination Induced Passivation.

• Al-BE PL additionally quenches and disappears under optical excitation at low T in hydrogenated samples.

-2

0

2

4

6

8

10

12

14

16

3800 3825 3850 3875 3900 3925

Al-BE

Q0

4H-SiC15 K

Wavelength, Å

hydrogenated before excitation

after excitation with above band-gap

initial

Contribution from thesubstrate Contribution from

the substratep = 6-8 x 1016 cm-3

tepi = 2 µ m

after excitation with above bandgap light

Changes in 4B0 PL caused by optical excitation at 15K

Recombination-Induced formation of defects responsible for 4B0 PL (possibly Boron-Hydrogen complex).

-0.6

1.4

3.4

5.4

7.4

9.4

3800 3825 3850 3875 3900 3925

PL in

tens

ity, a

rb.u

n. Q0

Al

B-HH1

15K

Wavelength, Å

(2) 10 min of Optical Excitation

(3) 2 hrs of Optical Excitation

(1) Hydrogenated before optical excitation

-20

30

80

130

180

230

3800 3850 3900 3950

PL in

tens

ity (a

rb.u

nits

)

-20

30

80

130

180

230

3800 3850 3900 3950

PL in

tens

ity (a

rb.u

nits

)

-20

30

80

130

180

230

3800 3850 3900 3950

PL in

tens

ity (a

rb.u

nits

)

Wavelength (Å)

as-hydrogenated4 hrs of optical excitation

H1

recovered @ room T

3916 Å

H1

H1

0

50

100

0 5000 10000 15000

Time of excitation (s)H

1 PL

inte

nsity

Optically induced changes of VSi-H (H1 line). The optically induced growth of H1 can not be masked by the concurren

metastable quenching.

Before Optical Excitation

After Optical Excitation

Recombination-induced formation of a strong radiative recombination channel

(VSi-H emission)

1E+16

1E+17

1E+18

1E+19

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

Depth, um

Con

cent

ratio

n, c

m-3

--- No optical excitation

--- After short excitation…

--- After prolonged excitation with above-bandgap light at 15 K

Deuterium concentration in plasma-deuterated B-doped SiC epitaxial layer.

The spot subjected to an optical excitation at 15K shows much deeper deuterium penetration => recombination-induced athermal migration.

~ NB

SIMS profiles

p+

Inversion of the conductivity type under optical excitation in hydrogenated p-type epilayers: strong recombination-induced passivation of acceptors.

0

2E-11

4E-11

6E-11

8E-11

1E-10

1.2E-10

-20 0 20bias, V

Cap

acita

nce,

pF

120

100

80

60

40

20

0

as-hydrogenatedp = 1-2 x 1017 cm -3

n = 3-4 x 1015 cm -3after excitation n

H+

H0

TC TSiHex

Hypothetical paths for H migration via Bourgoin-Corbett athermal migration mechanism.

Capture e- Capture h+

H0

H+

Recombination-induced formation of Hydrogen-Defect Complexes:

Recombination energy => release of hydrogen from the trapping cites near the surface, athermal migration and trapping by more stable sites (e.g., Al and B acceptors, silicon

vacancies, etc.)

Hydrogen trapped at the surface

after plasma

hydrogenation

Al-H B-H4B0

VSi-H

RIP effect (Above-bandgap light at 4 - 250K)

Remaining questions …The exact path for H migration? The energy position of the hydrogen state responsible for the recombination-induced migration?Device applications?

Documents

Wide Bandgap Semiconductor Research at Mississippi State ... · Bharat Krishnan, Hrishikesh Das, Huang-De Lin, Galyna Melnychuk, Yaroslav Koshka. 1 Mississippi State University, Box