Development of detectors based on binary semiconductors in ... · Material: LEC SI GaAs (bulk...

Development of detectors Development of detectors based on binary semiconductorsbased on binary semiconductors

inin Ioffe PhysicoIoffe Physico--Technical InstituteTechnical Institute

E. Verbitskaya

Ioffe Physico-Technical Institute of Russian Academy of SciencesSt. Petersburg 194021, Russia

1st RD50 Workshop on radiation hard semiconductor devicesfor very high luminosity colliders

CERN 2-4 October 2002

OutlineOutline

Part 1Part 1: : p-i-n heterostructure detectors based on bulk SI GaAs withepitaxial high-doped contact layers

1.1. Design and processing of SI GaAs heterostructure detectors 1.2. I-V characteristics of detector heterostructures1.3. Electric field distribution and charge collection efficiency in SI GaAs detectors 1.4. Experimental CCE on V dependencies and carrier transport parameters1.5. Current pulse response enhancement controlled by carrier injection and electric field profile transformation

Part 2Part 2: Radiation hardness of SiC detectors with respect to medium and high energy protons

2.1. Material parameters and detector structures based on 6H-SiC epitaxial films 2.2. Experimental results on CCE vs. V dependencies in proton irradiated detectors

ConclusionConclusion: : considerations on radiation hardness of semiconductors alternative from high resistivity Si

E. Verbitskaya, 1st RD50 Workshop, CERN, 2-4 October 2002

Part 1Part 1

pp--ii--n heterostructure n heterostructure detectors based on SIdetectors based on SI GaAs GaAs with with epitaxialepitaxial highhigh--doped layersdoped layers

E. Verbitskaya1, T. J. Bowles2, V. Eremin1, V. Gavrin3, A. Ivanov1, Yu. Kozlova3,A. Markov4, A. Polyakov4, Yu. Sevost’ianova, N. Strokan1, V. Vasil`ev1,

E. Veretenkin3

1Ioffe Physico-Technical Institute of RAS, St. Petersburg, Russia2Los Alamos National Laboratory, Los Alamos, USA

3Institute for Nuclear Research of RAS, Moscow, Russia4Research Institute of Rare Metals, Moscow, Russia

Supported by Russian Ministry of Science and Technology


MotivationMotivationGaAs properties advantageous for detectors: • band gap - wider than Si (1.42 eV)• extremely high µe (>7000 cm2/Vs)• high absorption probability (Z ~ 48)

R&D on GaAs detectors in Ioffe Institute:

Material: LEC SI GaAs (bulk semiconductor), ρ ∼ 107 Ohm⋅cm, µe ≥ 7000 cm2/VsUnique detector performance: p+-i-n+ heterostructure

• i - SI GaAs• p+, n+ - high doped layers of binary and trinary A3B5 semiconductors with

different composition grown by Liquid Phase Epitaxy[1- E. Verbitskaya et al., Nucl. Instr. Meth. A 439 (2000) 634-646]

Our earlier results:• material study [A. Markov et al, Nucl. Instr. Meth.: A439 (2000) 651 and A466 (2001) 14];• investigation of CCE and carrier transport parameters (see [1])


program on solar neutrino detection:experiment SAGE,

Neutrino Lab in Baksan, Russia

experience onGaAs heterostructure performance

and application in Ioffe Institute+

Design Design and performance of and performance of SISI GaAsGaAs detectorsdetectors

Aup+ GaAs

p+ AlGaAs

n+ AlGaAs

n+ GaAs

SISI GaAsGaAs

Au

Ioffe Inst.: p+-i-n+ heterostructure

• p+ AlxGa1-x As - SI GaAs - heterojunction• x≥ 0.3 - layers are transparant for laser wavelength in TCT measurements• p+ and n+ layers have different composition: (AlGaAs, GaInAs, GaAsSb)

pad GR

grid

pitch

SISI GaAsGaAs

Standard:Schottky barrier structure

GR - guard ringPad, GRs and grid – thin metal films


Cristalline structure of epitaxial layersCristalline structure of epitaxial layers

Scanning microscope with variable resolution is used

CrossCross--section of p+ layers section of p+ layers p+ GaAs - p+AGaAs: mesamesa--etched structure of entrance windowetched structure of entrance window

p+-GaAsSurface of p+-GaAlAsafter etching of entrance window in p+-GaAs


Crystalline structure of epitaxial layers vs. epitaxial growth tCrystalline structure of epitaxial layers vs. epitaxial growth temperatureemperature

CrossCross--section and surface of entrance window mesasection and surface of entrance window mesa--etched structureetched structureMicroscope beam is tilted at 30°

top: Au + p+-GaAs

? = 750 ?

p+-GaAlAs surface (entrance window) after etching p+-GaAs

? = 650 ?

crosscross--sectionsection crosscross--sectionsection

p+-GaAlAs: single crystal structure p+-GaAlAs: amorphous structure

Detector characteristics are insensitive to crystal structure of p+-GaAlAs!


ExperimentalExperimental

Detectors: based on bulk SI GaAs

19981998--20002000: p+ GaAs – p+ AlxGa1-xAs - SI GaAs – (n+ AlxGa1-xAs) - n+ GaAs (x ≥ 0.3)

20012001--20022002: new composition of high doped layers, reduced T of epitaxial growth

p+ GaAsxSb1-x - SI GaAs – (n+ GaAsxSb1-x) - n+ GaAs (x ≤ 0.03)

p+ InxGa1-x As - SI GaAs – (n+ InxGa1-x As) - n+ GaAs (x ≤ 0.03)

wafer thickness 400 µm, size: 4x4 mm2, entrance window 7.8 mm2

reduced size: diameter 300 µm, entrance window 0.071 mm2

compared with Schottky barrier structures

Experimental methods: 1. I-V characteristics

1. Current pulse response, Charge collection efficiency:- TCT with pulse laser, λ = 840 nm;- amplitude spectra from α-particles 244Cm, Eα = 5.8 MeV


I-V characteristics of Si GaAs heterostructure detectors

p+ GaAs – p+ AlxGa1-xAs - SI GaAs

0 200 400 600 800 1000 12000

100

200

300

400

Rev

erse

cur

rent

(nA

)

Reverse voltage (V)

513-2-b1 517-2-b3 533-8-b4

0 200 400 600 800 10000.0

0.5

1.0

1.5

2.0

2.5

3.0

p+ InGa As - SI GaAswafer # 554-23 a3

b3 c3 d3 e3

Rev

erse

cur

rent

(nA

)

Reverse voltage (V)

new p+ layers

• Maximum operational bias is as high as 1 kV

•The difference in reverse current values (~100 times) corresponds to the difference in detector dimensions


1 kV

Comparison of reverse current densities for detectorComparison of reverse current densities for detector heterostructuresheterostructureswith different dimensions and pwith different dimensions and p++ layer compositionlayer composition

0 200 400 600 800 1000 12000

2

4

6

8

10

12

100 nA

I = µ A

j (µ A

/cm2 )

V (Volt)

p+ AlGaAs - SI GaAsS = 7.8 mm 2

p+ GaInAs - SI GaAsS = 0.071 mm

2

• Different types ofheterostructures show similar reverse current densities

• Reduction of detector dimensions does not lead to the increased surface generation current: the bulk component is dominating in reverse current


Statistics of reverse current densities in SIStatistics of reverse current densities in SI GaAs heterostructuresGaAs heterostructuresj (µA/cm2) at V = 800 V

p+ GaAs – p+ AlxGa1-xAs- SI GaAs

Entrance window: 7.8 mm2

#/# a b1 1.22 1.41 1.33 1.19 1.14 0.91 1.17

1 1.42 1.793 0.544 0.8

wafer # 533-e35

wafer # 512-4

new heterostructures:new heterostructures: p+ GaInAs (GaSbAs) -- SI GaAsSI GaAsEntrance window: 0.071 mm2

# a b c d e1 1.55 1.12 1.12 1.55 1.72 1.55 1.3 1.55 1.55 1.553 1.3 1.4 1.4 1.4 1.554 1.55 1.55 1.4 1.55 1.55

# a b c d e1 1.7 1.4 1.3 1.55 1.42 2 1.7 1.4 1.4 1.43 2.2 1.8 1.8 1.4 1.44 x 1.7 1.9 1.7 1.75 x 2 2 2 2.2

wafer 554-23 p+ InGa As - SI GaAs

wafer 554-23 p+ GaSbAs - SI GaAs

High reproducibility of the results!


II--V characteristics of SIV characteristics of SI GaAsGaAs detectors withdetectors with SchottkySchottky barriersbarriers

0 100 200 300 400 500 600 7000

200

400

600

800

1000

a3 b3 c3 d3 e3

Rev

erse

cur

rent

(nA

)

Reverse voltage (V)

entrance window:12 mm2

Statistics of maximal operational Statistics of maximal operational reverse biasreverse bias

1 330 180 180 240 270

2 238 278 240 699 699

3 363 242 182 644 644

4 291 278 222 652 302

# / # a b c d e

Wafer # 554-1

• Reverse current and maximum operational reverse bias vary • Maximal operational reverse biases are in the range of 500 to 700 V -

less than Vmax ~ 1 kV for heterostructures


Collected charge vs. reverse voltage dependenceCollected charge vs. reverse voltage dependence

−−=

t

to E

WdE

qQτµ

τµexp1

Bulk SI GaAs: ρ = 106-108 Ohm⋅cm; n = 106-108 cm-3

• Fermi level is pinned at midgap due to DD EL2+ (~0.8 eV; Nt ~1015-1016 cm-3)• For EL2+: σe increases up to 10-13 cm2 at E≥ 10 kV/cm

Specific distribution of electric field E(x) in the depleted regSpecific distribution of electric field E(x) in the depleted region of ion of SISI GaAsGaAs detectorsdetectors:

1. W = W0 + γV [µm] W0 ~ 24 µm; γ – electric field penetration rate

Depleted redion depth depends linearly on reverse voltage Depleted redion depth depends linearly on reverse voltage -- different from irradiated Si[D. S. McGregor et al., J. Appl. Phys. 75 (1994) 7910]

2. Electric field increases within W0 and is constant at x > W0 [experiment: A. Castaldini et al., Nucl. Instr. and Meth. A 410 (1998) 79]

two regions in Q vs. V dependence:• Q increase (µE ↑)• Q saturation

Charge collection and current pulse responseCharge collection and current pulse response


Measurements of CCE and carrier transport parametersMeasurements of CCE and carrier transport parameters

n+

-V

α, hνdrift

depletedregion:high E

p+

τh

Reverse V:Reverse V:drift in drift in high E,high E,

trapping trapping lifetimelifetime

-V

α, hνdrift

depletedregion:high E

p+ n+

τe , γ

Forward V: Forward V: drift in low E, drift in low E,

quasiquasi--equilibriumequilibrium

trapping trapping lifetimelifetime

n+

+V

α, hνdrift

p+

τeo neutral region:low E+V

α, hν drift

p+

n+

τho neutral region:low E


Experimental Q on V dependenciesExperimental Q on V dependenciesHeterostructures p+ AlxGa1-xAs - SI GaAs and Schottky barriers

P1 = µτ/γd; P2 = γ/µEτ; P1⋅P2 = 1/Vfd

Transport parameters: high E / low E

• CCEmax is 30-35% due to τ ~ 1 ns⋅ τe < τe0 – enhanced trapping in high E

# γ (µm/V) τe (ns) τe0 (ns)

512-1-b3 1 1.8512-1-b3 1 1.4 (holes)553-1-a1 1.7 0.97 1.45554-1-c1 1.2 0.6554-1-e3 1.17 0.61 1.1554-34-a1 1.27 0.61554-34-c1 1.1 0.6 1

0 50 100 150 200 250 300 3500.00

0.05

0.10

0.15

0.20

0.25

0.30 SI GaAswafer # 512-1

experiment fit

fit:q = P

1*[1 - exp(-P

2*V)]

P

1 = 0.302

P2 = 0.014 V-1

τeff

= 1.3 ns

Reverse voltage (V)

Q (a

rb. u

nits

)


electron collection

Q Q on on V dependenciesV dependenciesheterostructures p+ GaAsSb - SI GaAs, p+ InGaAs – SI GaAs

Electron collection

Parameters derived from fit:τe = 1.2 ns; γ = 0.48 µm/V

200 400 600 800 10000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

fit:q = P1*[1 - exp(-P2*V)] P1 = 0.632P2 = 0.00405 V-1

p+ GaAsSb - SI GaAswafer # 554-23

experiment fit

Q (a

rb. u

nits

)

Reverse voltage (V)


1. Range of pulse operation up to 1 kV without noise increase2. τe ~ 1 ns - similar to p+ AlGaAs - SI GaAs heterostructures:

CCE is controlled by SI GaAs properties3. Q is not saturated, Qmax is twice larger than Qmax for p+ AlGaAs - SI GaAs

structures - charge gain?

Charge gain in detector heterostructures Charge gain in detector heterostructures pp++ GaAsGaAsSbSb -- SISI GaAsGaAs, p, p++ InGaAsInGaAs –– SISI GaAsGaAs

Gain effect was observed earlier in SI GaAs detectors (X-ray 241Am)[A. Cola et al, IEEE Trans. Nucl. Sci. 46 (1999) 171-175]

244244Cm: Cm: •• increase of increase of Q and Q and “tail” of pulses “tail” of pulses with high E with V increase;with high E with V increase;•• no noise increaseno noise increase

Possible reason: : carrier multiplication due to high electric field enhancement at the end of α-particle track

Effect observed earlier forSi detectors:[E. Verbitskaya et al., Sov. Phys. Semicond. 21 (1987) 1388]

2 3 4 5 6 7 80

20

40

60

-500 V

-750 V

p+ GaAsSb - SI GaAswafer # 554-23

-1000 V

coun

ts p

er c

hann

el

E (MeV)


Current pulse response enhancement controlled by carrier injectiCurrent pulse response enhancement controlled by carrier injectiononand electric field profile redistributionand electric field profile redistribution

n+

hνlas

-V

drift

high E

p+

injection:hνDC

Current pulse response:laser illumination of n+ (back) side - hole collection

Carrier injection:performed by DC light on p+ side, e and h generation

ResultResult:

enhanced current pulse response originated from hole collection


p+ n+

W

E

0

hνDC

EL2+

trapping

hνp+ n+

W

E

0

hν

EL2+

hνDC

Electric field transformationcontrolled by DC carrier injection

Electron trapping to EL2+:• ↓ [EL2+];• W ↑ and becomes = d, Vfd ↓• pulse response amplitude A ↑

Experiment for heterostructure GaInAs – SI GaAs

1. Pulse response amplitude on V

E(x) transformation and CCE increase due to carrier injection:• similar to E(x) manipulation observed earlier in heavily irradiated Si detectors;• specific for semiconductors enriched with deep levels

[B. Dezillie et al, IEEE Trans. NS-46 (1999) 221, E. Verbitskaya et al, IEEE Trans. NS-49 (2002) 258]

E. Verbitskaya, 1st RD50 Workshop,CERN, 2-4 October 2002

no hνDCHole collection

0

1

2

3

4

0 200 400 600 800 1000

reverse voltage (V)

pu

lse

amp

litu

de

(arb

.un

t.)

injection currentJ = 10 µ A/mm2

Vfdwithout hνDC

Vfdwith hνDC

0

1

2

3

4

100 1000 10000 100000

laser frequency (Hz)

pu

lse

amp

l. (a

rb.u

nt.) V = 800 V

J =10 µA/mm2

2. Current pulse responseenhancement with laser frequency increase

3. Hysterethis in current pulseresponse amplitude changes caused by carrier injection

EL2+: 0.8 eV, large de-trapping constant

Hole collection

plas ≈ [Nh-trap][Nh-trap] ↓, τh ↑


n, plas-inj ~ flaslaser generated holes are trappedby hole traps during drift - leads to τh increase

0

1

2

3

0 5 10 15 20

Inject. current (µ A/mm2)P

uls

e am

pl.

(arb

. un

t.) down

up

V = 700 Vθ = 50 µs

Summary on Summary on GaAs GaAs detectorsdetectors

1. Performance of SI GaAs detectors as heterostructures with high dopedepi-layers and mesa-etched design results in the achievement of Vmaxup to 1 kV in steady-state and pulse operational mode

2. Carrier injection in SI GaAs detectors results in the Vfd reduction andCCE increase that is caused by electric field redistribution controlled by carrier trapping. This effect is similar to electric field manipulation inheavily irradiated Si detectors

3. The combined effect of high operational voltage along with Vfd reduction using carrier injection is promising for development of SI GaAs detectors with increased depleted region depth

Part 2Part 2

SiCSiC detectors: detectors: radiation hardness with respect to 8 MeV and relativistic protonradiation hardness with respect to 8 MeV and relativistic protonss

A. Ivanov, A. Lebedev, N. Savkina, N. Strokan


SiC SiC films grown in films grown in Ioffe Ioffe InstituteInstitute

6H-SiC Eg = 3 eVgrown by vacuum sublimation epitaxythickness ~ 10 µm

Parameters:n-type, n: 8 ⋅ 1015 cm-3 at the interface and 5 ⋅ 1014cm-3 at the surfaceµe = 350-400 cm2/V⋅s; µh = 80 cm2/V⋅sLDh = 1.7 µm

[A.M. Ivanov, N.B. Strokan, D.V. Davidov et al. Appl. Surf. Sci.,184, 431 (2001)]

Main application: high voltage transistors and thyristors

SiCSiC detector structuresdetector structures

Schottky diodes, 600 µm diameter fabricated by magnetron sputtering of Ni

IrradiationIrradiation• 8 MeV protons, Fp up to 2 ⋅1016 cm-2

• 1 GeV protons, Fp up to 1.3⋅1015 cm-2


Irradiation by 1Irradiation by 1 GeVGeV protonsprotonsDeep levels induced by 1Deep levels induced by 1 GeVGeV protons protons

Fp = 2.7 ⋅ 1014 cm-2

Irradiation by 8 MeV protonsIrradiation by 8 MeV protons• n decreases severely: introduction of electron traps • up to Fp = 8 ⋅ 1015 cm-2 CCE doesn’t degrade [A.A. Lebedev, N.B. Strokan,

A.M. Ivanov et al, Mater.Science Forum 353-35 (2001) 763]

Nt - measured by DLTS: underunder--estimation?estimation?

R - vacancy related defects[A.A. Lebedev, A.I. Veinger, D.V. Davidov et al,

J. Appl. Phys. 88, 1 (2000)].


5×1013< 5×10121.1-1.2R

1.5×10131.5×10130.35-0.4E1/E2

Afterirradiation

Beforeirradiation

Concentration, cm-3

Ec – Et, eVType of center

Charge collection efficiencyCharge collection efficiency1 GeV proton, Fp ≤ 1.3⋅1015 cm-2

0 50 100 150 200 250

500

1000

1500

Ene

rgy

, keV

Voltage, V

1 2

CCE (in energy units) versus voltageα-particles 244Cm, Eα = 5.8 MeV

1 - 3×1014 ; 2 - 1.3×1015

1) For non-irradiated and irradiated by Fp = 3⋅1014 cm-2 :

CCEm ~ 30%

2) Fp = 1.3 ⋅ 1015 cm-2

• compensation by DLs(R and others) →

• neutral base with high resistivity• CCE ~ 30% at voltage three times higher• FWHM still remains high (at V>150 Volt) - characteristic of semiconductor transport properties uniformity

CCE degradation


What is the introduction rate of compensating defects?What is the introduction rate of compensating defects?

Weff = W + LD - effective width of the sensitive region

Weff vs. V1/2 - becomes linear at Fp = 1.3 ⋅ 1015 cm-2

Initially: H6-SiC film of n-type, n ~ 1015 cm-3

Hence, R deep levels are acceptors and NR ≥ 1015 cm-3

Introduction rate (β) for R-defects is ≥ 1cm-1

Conclusion on Conclusion on SiCSiC• Deep level concentrations derived from DLTS measurements are under-estimated• Under-estimations of β and Nt : similarity to Si• At Fp ~1015 cm-2 SiC detectors maintain properties sufficient for effective charge collection


Conclusion: considerations on radiation hardnessConclusion: considerations on radiation hardness

Si CGaAs, …, Cd Te, CdZnTe, SiC…..

β of DLs responsible for degradation is ≥ 1cm-1

Crystal quality(N)

F

1012

1013

1015-1016

Si

epi-GaAs

bulk Si GaAs,CdTe

• Degradation effectis a compromise between initial propertiesand operational fluence range• Whether intrinsic defects in compound semiconductors can act as getters of radiation induced defects?


Development of detectors based on binary semiconductors in ... · Material: LEC SI GaAs (bulk...

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