of Semiconductor Detectors

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1 Νοε 2013 (πριν από 3 χρόνια και 9 μήνες)

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New Materials and Designs

of Semiconductor Detectors

New developments are driven by particle physics

and applications in:



Medical & Synchrotron X
-
ray Imaging



Nuclear Medicine
-

g
-
Ray Detection



Astronomy
-

X
-
ray Detection



Non
-
destructive testing

Risto Orava


June 2002


Need to improve performance & reduce the dose.

1



Rad hard Si
-
detectors,


Oxygenated Si



Crystalline Compound


Semiconductors: CdTe,


CdZnTe,...



High Purity Epitaxial


Materials: SiC, GaAs,...



Polycrystalline CVD


Materials: Diamond,...



Large Area


Polycrystalline


Materials: a
-
Si, a
-
Se,


CdTe, HgI,...

For high performance detectors material

technologies are combined with device

engineering and instrument design.



Slicing, dicing



Chemical etching



Polishing



Metallization



Electrode deposition



Metal sputtering



Surface passivation



Contact technologies:


Ohmic vs. blocking


contacts



Uni
-
polar devices



Flip
-
chip bonding



3D
-
structures



Modality



g
-
energies



Packaging



Operating environment:


Temperature


Radiation


Electronic noise


Mechanical stresses



Resolution



DQE



MTF



Frame rate



Fill factor

Material Technology

Device Engineering

Instrument Design

1


I Material Technology


Need high purity, homogenous, defect
-
free material

High Z



-

small radiation length X
o
for high QE
(X
o

= 716.4gcm
-
2
A/[Z(Z+1)ln(287/Z)])


Large enough band gap


-

high resistivity (
> 10
9



cm)
and low leakage current for low noise





operation
(high resistivity is achieved in high band gap materials with small intrinsic charge carrier


concentrations and by controlling
the extrinsic and intrinsic defects to pin Fermi
-
level near mid
-
gap)


Small enough band gap


-

small electron
-
hole ionization energy (< 5eV)
(in general, need a minimum band gap




of

1.5eV to control thermally generated currents and losses in energy resolution & noise. With




sufficiently high
-

and stable
-

number of e
-
h pairs the S/N
-
ratio is high.


High intrinsic
mt
product


-

the carrier drift length,
mt
E
(
m
=carrier mobility,
t
=carrier lifetime, E the applied electric




field. Charge collection is determined by the fraction of detector thickness traversed by the photo
-


generated electrons and holes dur
ing the collection time. In the ideal case the carrier drift length




would be much longer than the detector thickness for complete charge collection. This is possible for




electrons but, most often, not for the holes. This broadens the photopeak and worsens the resolution.)


High purity, homogenous, no defects

-

good charge transport properties
(low leakage currents, no conductive short circuits




between the detector contacts
-

single crystals for avoiding grain boundaries and other extended




defects)


High surface resistivity


-

low noise due to surface conductivity
(the surfaces should be stable to prevent




increased surface leakage currents with time, the electric field lines should not terminate at the non
-




contacted surfaces for complete charge collection and for preventing build
-
up of surface charges)


Material manufacturing


-

growth method vs. yield
(stochiometry, ingot
-
to
-
ingot variations, doping, compensation,




elimination of large defects, crystal size, quality control, cost)





1

Why compound semiconductors?


Uniqueness of compound semiconductors


Band gap engineering


Heterostructure devices


Hg
1
-
x
Cd
x
Te :
-
0.25 ~ 1.6 eV


Al
x
Ga
1
-
x
As :


AlAs : 2.16 eV, indirect


GaAs : 1.43 eV, direct


Larger electron and/or hole mobility


Good for high speed (high frequency) devices


Direct band gap materials


Optoelectronic devices (lasers, LED’s)


Compound semiconductor processing


Cost


Compound material growth is not cheap.


Difficulty of fabrication (example: GaAs,...)


Doping


Some dopants are amphoteric. (Donor in the Ga site and acceptor in the As site).


Oxidation


Ge
2
O
3

and As
2
O
3

: oxidation rates are different.

1

semiconductors

electronic

semiconductors

mixed

conductors

ionic

conductors

intrinsic

semiconductors

extrinsic

semiconductors

n
-
type

extrinsic

p
-
type

extrinsic

Requirements for sensors:



band gap 1
-
6 eV



n
-

or p
-
type conduction



no ionic conduction



chemical and thermal stability



solubility of dopants in host


lattice

covalent

bonding

Semiconductors
-
classification

1

Elemental and compound semiconductors are

in everyday use.

Elementary semiconductors

Si, Ge

IV Compounds


SiC, SiGe

Binary III
-
V Compounds

AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, InSb

Binary II
-
VI Compounds

ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe

Si



rectifiers, transistors, IC’s

Ge



early transistors and diodes

Compounds


high
-
speed devices, light absorption applications

GaAs, GaP



LED’s

ZnS



fluorescent
-

TV screens

InSb, CdSe, PbTe, HgCdTe

light detectors

Si, Ge



IR and ionizing radiation detectors

GaAs, InP



microwaves (the Gunn diode)

GaAs, AlGaAs,...


semiconductor lasers

II

III

IV

V

VI

VII

Be

B

C

N

O

F

Mg

Al

Si

P

S

Cl

Ca Zn

Ga

Ge

As

Se

Br

Sr Cd

In

Sn

Sb

Te

I

p
-
type

n
-
type

dopants for
Si

and
Ge

1

Elemental

Compound semiconductors


no. of electrons

IV
-
IV bonding III
-
V bonding

II
-
VI bonding

per unit



C







6


SiC







10


Si


AlP





14


GeSi


AlAs, GaP

ZnS



23


Ge


AlSb,GaAs,InP

ZnSe,CdS


32



GaSb, InAs

ZnTe, CdSe,HgS


41


Sn


InSb


CdTe,HgSe


50





HgTe



66

atomic bonding forces become more ionic

Elemental & Compound Semiconductors

1

Elemental and compound semiconductors have

crystalline, polycrystalline or amorphous
structure.

Crystalline Solids:

Atoms are arranged in a periodic fashion

Amorphous solids:

No periodic structure at all

Polycrystalline:


Many small regions of single
-
crystal material

Lattice:



The periodic arrangement of atoms in a crystal

Basic Lattice:


simple cubic, body
-
centered cubic, face
-
centered




cubic

Miller Indices:


The smallest set of integers (h,l,m) proportional




to (1/a, 1/b,1/c)



Crystal Growth:


Czochralski Si, Floating
-
Zone Si, High Pressure


Bridgman (HPB), Travelling Heater Method (THM),


Modified Markov Techique (MMT)...

Epitaxy:

1

Gallium Arsenide (GaAs) has a zinc
-
blend
structure, which is a superstructure of
the diamond structures.


Silicon

is

the

most

widespread

semi
-

conductor

used

for

digital

electronics
.


Si

is

cheap,

abundant,

structurally

robust

and

environmentally

harmless
.


Crystalline Solids

Polycrystalline

Amorphous: No periodic structure

1

Se

1



Lattice symmetry is essential: atomic shells


electron energy bands


Energy gap between valence and conduction bands.




Dope material with nearby valence atoms:



donor atoms



n
-
type



acceptor atoms



p
-
type




Dopants provide shallow doping levels (normally ionized at room temperature)


conduction band occupied at room temperature


NB strong T dependence




Two basic devices: p
-
n diode, MOS capacitor


Detector Structure

conduction

band

Band

gap

+

-

electron

valence

band

Si: E
g

= 1.1 eV
,

c
= 1130 nm

hole

h


Electron
-
hole

generation

E

Simple detector: conductivity

increase of semiconductor

when illuminated.

P
-
I
-
N photo
-
detector
: low dark


current, quick response.

Reverse biased!

1

Zinc Blende Semiconductors



sphalerite (ZnS) structure: like diamond


only involving two different types of atoms




note no atom of an element is bonded to


another of the same element

Material



Properties at Room Temperature (295K)



X
o
(cm)
r
(g/cm
3
) E
g
(eV)
r
(

cm)
m
e
t
e
(cm
2
/V)
m
h
t
h
(cm
2
/V)



Diamond(IV) 12 3.51 5.5 >10
11
2

10
-
3
<1.6

10
-
3


Ge(IV) 2.3 5.32 0.66 50 0.8 0.8


Se(VI) x.y 4.82 2.3 10
12


1.5

10
-
9

1.4

10
-
7


Si(IV) 9.4 2.33 1.12 <10
4


0.4


0.2

Compound semiconductor properties
-

Elemental

1




Structure e/h
-
mobility
e/h
-
lifetime growth availability/






cm
2
/V
m
s


yield


Diamond diamond 2800/130
-
2010




Ge diamond 3900/190


Se



monoclinic


Si diamond 1600/430





Intrinsic Dielectric W


e
-
h pairs







carrier constant (eV)


per 0.3%X
o




density (cm
-
3
)


Diamond


5.7 13 7200





Ge


16 2.9 16000



Se


Si 6.68

10
9

11.9 3.6 26000


Se

Ge

Si

Compound semiconductor properties
-

Binary II
-
VI

Material



Properties at Room Temperature (295K)



X
o
(cm)
r
(g/cm
3
) E
g
(eV)
r
(

cm)
m
e
t
e
(cm
2
/V)
m
h
t
h
(cm
2
/V)




Cd(II)S(VI) 2.1 4.87 2.5


Cd(II)Se(VI) 5.655 1.751


Cd(II)Te(VI) 1.5 5.86 1.475 10
9
3.3

10
-
3
2.2

10
-
4


Hg(II)I
2
()


1.2 6.40 2.13


Hg(II)S(VI)



7.72


Hg(II)Se(VI) 8.22


Hg(II)Te(VI) 8.12


Zn(II)S(VI) 4.11 3.68
-
3.911


Zn(II)Se(VI) 5.26 2.822


Zn(II)Te(VI) 5.65 2.394

1

Material



Properties at Room Temperature (295K)



Dopant Structure e/h
-
mobility
e/h
-
lifetime growth availability/






cm
2
/V
m
s


yield

Cd(II)S



wurzite


340/340


Cd(II)Se



wurzite 650/10


Cd(II)Te


Cl zincblende 1050/100 2.0/2.0 THM critical


HgI
2



50
-
65/


HgS



zincblende 10
-
30/10
-
30


HgSe



zincblende 1.5/


HgTe zincblende 35/


ZnS* 165/5(?/100
-
800)


ZnSe 500/30


ZnTe 330
-
530/100
-
900


Compound semiconductor properties
-

Binary II
-
VI


Compound semiconductor properties
-

Binary II
-
VI

Material


Yield of e
-
h pairs/0.3%X
o

at Room Temperature (295K)



X
o
(cm) Intrinsic


Dielectric W


e
-
h pairs







carrier constant (eV)


per 0.3%X
o




density (cm
-
3
)


Cd(II)S


Cd(II)Se




10.2


Cd(II)Te


1.5


10.2 4.4


6600





HgI
2


4.2 4.2


HgS


HgSe


HgTe


ZnS 8.9


ZnSe 9.1



ZnTe 7.4

1

Material



Properties at Room Temperature (295K)



X
o
(cm)
r
(g/cm
3
) E
g
(eV)
r
(

cm)
m
e
t
e
(cm
2
/V)
m
h
t
h
(cm
2
/V)




Al(III)As(V)


3.717



2.153


Al
0.5
(III)Ga
0.5
(V)

x.y 5.85 1.44 >10
5
3.3

10
-
3
2.2

10
-
4


Al(III)N(V)* x.y 3.285/3.255 /6.2 10
11

1.0

10
-
3
5

10
-
4


Al(III)P(V) 2.45





Al(III)Sb(V) 4.29 1.615



Ga(III)As(V) 2.3 5.318 1.424 10
7

8

10
-
3

4

10
-
6


Ga(III)N(V)* x.y 6.10/6.095 3.24/3.44 >10
11
2

10
-
3
<1.6

10
-
3


Ga(III)P(V) 3.5 4.129 2.272


Ga(III)Sb(V) 5.63 0.75


In(III)As(V)







In(III)N(V)* 6.93/6.81 /1.89
-
2.00


In(III)P(V)



In(III)Sb(V) 5.80 0.17


Compound semiconductor properties
-

Binary III
-
V

1


Compound semiconductor properties
-

Binary III
-
V

Material



Properties at Room Temperature (295K)



Dopant Structure e/h
-
mobility
e/h
-
lifetime growth availability/






cm
2
/V
m
s


yield

AlAs





75
-
294/


Al
0.5

Ga
0.5


AlN




300/14


AlP 80/







AlSb 200
-
900/200
-
400



CdS 250
-
300/15?


GaAs




9200/400


GaN




1000
-
1350/100
-
350




GaP 300
-
400/


GaSb



4000
-
5000/680
-
1000









InN* 3200/


InP




4000
-
5000/150
-
600


InSb 70000
-
100000/500
-
1700



1


Compound semiconductor properties
-

Binary III
-
V

Material


Yield of e
-
h pairs/0.3%X
o

at Room Temperature (295K)



X
o
(cm) Intrinsic


Dielectric W


e
-
h pairs







carrier constant (eV) per 0.3%X
o




density (cm
-
3
)

AlAs



Al
0.5

Ga
0.5


AlN x.y 3.285/3.255 4.6
-
8.5/9.14






AlP





AlSb



CdS


GaAs


2.3 2.1

10
6

12.5 4.3 11000






GaN




5.35
-
8.9/9.5
-
10.4




GaP 3.5



11



5200



GaSb









InN* 8.4
-
15.3



InP 2.1


13


4.2


8900


InSb


1

Material



Properties at Room Temperature (295K)



X
o
(cm)
r
(g/cm
3
) E
g
(eV)
r
(

cm)
m
e
t
e
(cm
2
/V)
m
h
t
h
(cm
2
/V)



Al
x
Ga
1
-
x
As



1.424+1.247x



Al
x
Ga
1
-
x
Sb



0.76+1.129x+0.368x
2



Al
x
In
1
-
x
As



0.360+2.012+0.698x
2


Al
x
In
1
-
x
P



1.351+2.23x


Al
x
In
1
-
x
Sb



0.172+1.621x+0.43x
2


GaAs
x
Sb
1
-
x



0.726
-
0.502x+1.2x
2


Ga
x
In
1
-
x
As



0.36+1.064x


Ga
x
In
1
-
x
Sb



0.172+0.139x+0.415x
2


Ga
x
In
1
-
x
P




1.351+0.643x+0.786x
2





GaP
x
As
1
-
x




1.42+1.150x+0.176x
2


InAs
x
Sb
1
-
x



0.18
-
0.41x+0.58x
2


In
x
Ga
1
-
x
N


3.44
-
3.0x




InP
x
As
1
-
x




0.360+0.891x+0.101x
2



CdZn
0.1
Te 49.1 5.78 1.57 2

10
10

4

10
-
3
(0.2
-
5.0)

10
-
5


Sl
-
GaAs 5.32 10
-
5

10
-
6


Compound semiconductor properties
-

ternary

1

Compound semiconductor properties
-

ternary

Material



Properties at Room Temperature (295K)



Dopant Structure e/h
-
mobility
e/h
-
lifetime growth availability/






cm
2
/V
m
s


yield


Al
x
Ga
1
-
x
As





Al
x
Ga
1
-
x
Sb





Al
x
In
1
-
x
As





Al
x
In
1
-
x
P





Al
x
In
1
-
x
Sb





GaAs
x
Sb
1
-
x





Ga
x
In
1
-
x
As





Ga
x
In
1
-
x
Sb





Ga
x
In
1
-
x
P









GaP
x
As
1
-
x




InAs
x
Sb
1
-
x





In
x
Ga
1
-
x
N






InP
x
As
1
-
x







CdZn
0.1
Te
-

large poly 1000/50 1.0/1.0


HPB OK?


Sl
-
GaAs

1

Compound semiconductor properties
-

ternary

Material


Yield of e
-
h pairs/0.3%X
o

at Room Temperature (295K)



X
o
(cm) Intrinsic


Dielectric W


e
-
h pairs







carrier constant (eV)


per 0.3%X
o




density (cm
-
3
)

Al
x
Ga
1
-
x
As





Al
x
Ga
1
-
x
Sb





Al
x
In
1
-
x
As





Al
x
In
1
-
x
P





Al
x
In
1
-
x
Sb





GaAs
x
Sb
1
-
x





Ga
x
In
1
-
x
As





Ga
x
In
1
-
x
Sb





Ga
x
In
1
-
x
P









GaP
x
As
1
-
x




InAs
x
Sb
1
-
x





In
x
Ga
1
-
x
N






InP
x
As
1
-
x







CdZn
0.1
Te x.y



11 4.7



Sl
-
GaAs



1

Material



Properties at Room Temperature (295K)



X
o
(cm)
r
(g/cm
3
) E
g
(eV)
r
(

cm)
m
e
t
e
(cm
2
/V)
m
h
t
h
(cm
2
/V)




a
-
Se



4.3 2.3 10
12


5

10
-
9
1.4

10
-
7


a
-
Si



2.3 1.8 10
12
6.8

10
-
8
2

10
-
8

Compound semiconductor properties
-

amorphous

1



Dopant Structure e/h
-
mobility
e/h
-
lifetime growth availability/






cm
2
/V
m
s


yield




a
-
Se




0.13/0.007





a
-
Si



1/0.1



X
o
(cm) Intrinsic


Dielectric W


e
-
h pairs







carrier constant (eV)


per 0.3%X
o




density (cm
-
3
)



a
-
Se



6.6


a
-
Si



11.7


Material



Properties at Room Temperature (295K)



X
o
(cm)
r
(g/cm
3
) E
g
(eV)
r
(

cm)
m
e
t
e
(cm
2
/V)
m
h
t
h
(cm
2
/V)



Pb(II)I
2
()



6.2

2.3 10
12
8

10
-
6


Si(IV)C(IV)** 8.1 3.21 2.36
-
3.23


Tl(I)Br(VII)* 81/35 7.5 2.7 10
11

10
-
4

10
-
5

Compound semiconductor properties
-

other

1



Dopant Structure e/h
-
mobility
e/h
-
lifetime growth availability/


cm
2
/V
m
s


yield



PbI
2



hexag.crystal 8/2



SiC**




200/20(800
-
400/320
-
90)




Tl(I)Br*



cubic 30/7








X
o
(cm) Intrinsic


Dielectric W


e
-
h pairs







carrier constant (eV)


per 0.3%X
o




density (cm
-
3
)


PbI
2





SiC** 8.1 <10
10

9.7 15900








Tl(I)Br*






Compound semiconductor properties

1

Antimonide
-
Based Compound
Semiconductors

(6.1 Angstrom Compounds)

5.4 5.6 5.8 6.0 6.2 6.4 6.6

Lattice Constant (
Å
)

3

2

0

1

Band Gap (eV)

III
-
V Nitrides


1

Ge

Si

GaAs

CdTe

Compound semiconductor properties

1

GaSe

HgI
2

PbI
2

TlBr

Compound semiconductor properties

1


II Device Engineering



Slicing, dicing



Chemical etching



Polishing



Metallization



Electrode deposition



Metal sputtering



Surface passivation



Contact technologies: Ohmic vs. blocking contacts



Uni
-
polar devices



Flip
-
chip bonding



3D
-
structures

Device engineering facilitates efficient, robust and stable sensor
operation.

1

Detector configuration is optimized for optimum

performance for a given application.

Single element planar

structure


Co
-
planar grid structure


Pixel detector structure

-
small pixel effect.


1


III Instrument Design



Modality



g
-
energies



Packaging



Operating environment: Temperature, Radiation,


Electronic noise, Mechanical


stresses



Resolution



DQE



MTF



Frame rate



Fill factor

Instrument design aims at optimal use of the sensor technology in
different applications.

1

Material


Resolution DQE MTF Frame Rate Fill Factor


(line
-
pairs/mm) (%) (5lp/mm) (frames/sec) (%)


a
-
Se


2.5
-
4 10
-
70 0.2
-
15 57
-
86


a
-
Si 2.5
-
4 10
-
70 0.3
-
0.4 0.2
-
15 57
-
80


Cd
0.9
Zn
0.1
Te 11
-
13 >90 0.7 15
-
30 100

Bench Marks in Instrument Design

1

Resolution, Detective Quantum Efficiency (DQE), Modular
Transfer Function (MTF), Frame rate and Fill Factor
constitute the bench marks for instrument design