ctu prague rd50 group · michael solar rd50 workshop cern 3.- 5.11.2003 ctu prague rd50 group...

Michael Solar RD50 Workshop CERN 3.- 5.11.2003

CTU Prague RD50 Group

Detector structures on GaAs(Mesa with Guard Rings)

T. Horazdovský, D. Chren, Z. Kohout, M. Solar, B. Sopko ME CTUV. Jurka, E. Hulicius IP ASCR

S. Pospisil IEAP CTU


2

ContentsMotivation

Structure of detectors

Technology for GaAs detectors

Results

Conclusion

References


3

MotivationThe structure of detector on SI GaAs substrate was created using Schottky contact.

The properties of the Schottky contact depend on metallization technology.

The diffusion technology eliminate the influence of a substrate material on detector performance.

For more stable properties we made the structure with PN – junction (diffused or epi layer).


4

Motivation

Diffusion solid-to-solid of Zn or MOCVD epi layer give us possibility to make ohmic contact on P+ side and give further possibility for research of detection structure.


5

Structure of the detectorsSI GaAs substrate , thick. 500 um

1. P+ (Zn) junction depth (2 – 4 ) umMetallization of P+ (front) side : TiAu (10 nm + 200 nm)Metallization of back side: AuGeNi (200+100+100)nm (Fig.1)

or

2. MOCVD epi layer P+ (C) thickn. 0,5 umMOCVD epi layer N+ (Si) – back sideMetallization of P+ and back side : TiAu (10 nm + 200 nm)

(Fig. 2, 3)


6

Technology for GaAs detectorsDiffused type

deposition of SiO2 + ZnO layersdiffusion of Zn (solid – to – solid)- bellow 800 °C, in FG

removing of SiO2 + ZnO layers

making a ohmic contact on P+ and N+ side of structure(standard metallization : TiAu, AuGeNi, annealing 400 °C in FG)

separation of detector chips (cutting) - after cutting of the wafer to detector chips (5 x 5 mm) the sides of the chips was prepared

by a special protectiv layer(Protection technology similar as for HV diodes)


7

Structure of the detectors

AuGeNi

SI GaAs

TiAu

P+ (Zn)

Fig.1:Vertical structure of detectors - diffusion type of structure


8

Technology for GaAs detectorsMOCVD type without guard ring

deposition of MOCVD epi layer (P+ , dot. C)back side deposition of MOCVD epi layer (N+, dot. Si)

making a ohmic contact on P+ and N+ side of structure(standard metallization : TiAu, AuGeNi, annealing 400 °C in FG)

separation of detector chips (cutting) - after cutting of the wafer to detector chips (5 x 5 mm) the sides of the chips was prepared

by a special protectiv layer


9


Fig.2: Vertical structure of detectors - MOCVD epi type of structure

TiAu

SI GaAs

TiAu

MOCVD P+ (C)

N+ epi (Si)


10

Technology for GaAs detectorsMOCVD type with guard ring

deposition of MOCVD epi layer (P+ , dot. C)back side deposition of MOCVD epi layer (N+, dot. Si)

making a ohmic contact on P+ and N+ side of structure- standard metallization : TiAu

etching of the metallization to designed pattern

following etching of GaAs (patterned metallization serves as etching mask) to form MESA structure

This structure had not passivated surface


11


TiAu

SI GaAs

TiAu

MOCVD P+ (C)

N+ epi (Si)

Fig.3: Vertical structure of detector with guard ring - MOCVD epi type of structure


12

ResultsI-V characteristic - diffused type

0,00

200,00

400,00

600,00

800,00

1000,00

1200,00

0,00 10,00 20,00 30,00 40,00 50,00 60,00 70,00 80,00 90,00 100,00

U [V]

I [nA

]


13

Resultscip1 45V

0

10

20

30

40

50

60

0 200 400 600 800 1000 1200 1400 1600 1800 2000

channel

coun

ts

cip1 90V

0

10

20

30

40

50

60

0 200 400 600 800 1000 1200 1400 1600 1800 2000

channel

coun

ts

cip1 132V

0

5

10

15

20

25

30

35

0 200 400 600 800 1000 1200 1400 1600 1800 2000

channel

coun

ts All presented spectra were measured using alpha-particle source

Am241Pu239


14

Results I-V characteristic - MOCVD type

0,00

100,00

200,00

300,00

400,00

500,00

600,00

700,00

800,00

0,00 20,00 40,00 60,00 80,00 100,00 120,00

U [V]

I [nA

]


15

Results

cip2 133V

0

10

20

30

40

50

60

0 200 400 600 800 1000 1200 1400 1600 1800 2000

channel

coun

ts

cip2 47V

0

10

20

30

40

50

60

0 200 400 600 800 1000 1200 1400 1600 1800 2000

channel

coun

ts

cip2 91V

0

10

20

30

40

50

60

0 200 400 600 800 1000 1200 1400 1600 1800 2000

channel

coun

ts


16

Results

Fig.4: The photo of MESA type detectors with guard rings


17

Results I-V characteristic - MESA type (MOCVD)

0,00

2,00

4,00

6,00

8,00

10,00

12,00

14,00

16,00

0,00 50,00 100,00 150,00 200,00 250,00 300,00 350,00 400,00

U [V]

I [nA

]


18

Results50V

0

10

20

30

40

50

60

0 200 400 600 800 1000 1200 1400 1600 1800 2000

channel

coun

ts

150V

0

10

20

30

40

50

60

0 200 400 600 800 1000 1200 1400 1600 1800 2000

channel

coun

ts

250V

0

10

20

30

40

50

60

0 200 400 600 800 1000 1200 1400 1600 1800 2000

channel

coun

ts

350V

0

10

20

30

40

50

60

0 200 400 600 800 1000 1200 1400 1600 1800 2000

channel

coun

ts


19

Conclusions

•Experiments show the ability of described technology to prepare functional detectors on GaAs

•The results show the MESA type has better leaking current in comparison with “surface preserved” type even the guard rings were not biased

•In near future we will study:- the influence of guard ring bias on the detector properties,- the spectra using gamma and rtg sources,- the influence of protective materials on I-V characterics


20

References1. C.R.M.Grovenor: Structure of the Au/Ga As interface, EMIS Datareview RN=11126, September 1989

2. B.Tuck, T. Harrison: Diffusion of Zn in Ga As, EMIS Datareview RN=15150, February 1990

3. J.Ivančo at all: Semi-insulating Ga As – based Schottky contacts for the detector of Ionising radiation: An effect of the interface treatment,6th International Workshop on GaAs and related compounds, Praha – Průhonice, June 22-26,1998

4. P.J.Selin at all : Characterisation of X-ray detectors fabricated from thick epitaxial Ga As NIM A 460 (2001) 159-164


CTU Prague RD50 Group

Thank you for your attention

ctu prague rd50 group · michael solar rd50 workshop cern 3.- 5.11.2003 ctu prague rd50 group...

Documents