Development of imaging arrays for solar UV observations based on wide band-gap materials

Development of imaging arrays for solar

UV observations based on wide band-gap

materials

Udo Schühle

*a

, Jean-François Hochedez

b

, José Luis Pau,

Carlos Rivera, Elias Muñoz

c

, José Alvarez, Jean

-

Paul Kleider

d

, Philippe Lemaire

e

,

Thierry Appourchaux, Bernhard Fleck, Anthony Peacock

f

, Mathias Richter, Udo Kroth,

Alexander Gottwald

g

, Marie-Claude Castex

i

, Alain Deneuville, Pierre Muret

k

, Milos

Nesladek

m

, Franck Omnes

n

, Joachim John, Chris Van Hoof

p,

Emanuele Pace

q a

Max-Planck-Institut für Aeronomie;

b

Royal Observatory of Belgium;

c

Universidad

Politécnica de Madrid,

d

Laboratoire de Génie Electrique de Paris,

e

Institut

d’Astrophysique Spatiale Orsay,

f

European Space Agency Noordwijk,

g

Physikalisch-Technische Bundesanstalt Berlin,

i

Université de Paris-Nord,

k

Laboratoire d’Etudes des

Propriétés Electroniques des Solides CNRS Grenoble,

m

IMO Institute for Material

Research Diepenbeek,

n

Centre de Recherche sur l'Hétéro-Epitaxie et ses Applications

(CRHEA-CNRS) Valbonne,

p

Interuniversity Microelectronics Ctr. Leuven,

q

XUVLAB

Outline of the talk

1. Introduction: Why new detectors?

2. Requirements for new detectors

3. Prospects towards new semiconductor devices

4. Prototype wide band-gab sensors: GaN, AlGaN

devices

5. Efficiency measurements with new one-pixel

devices

Conclusions of last years talk:

• SOHO UV instruments have been very stable

due to the successful cleanliness program.

but

• SOHO UV detectors have been remarkably

unstable.

Those were either channel plate

devices, or (intensified) CCDs!

Those were either channel plate

devices, or (intensified) CCDs!

MCP detectors

Anode design options

• Wedge and strip anode

• Cross Delay line anode

• Cross strip anode

• CCD

Example: flatfield of SUMER XDL detector

•

Distortion

•

ADC nonlinearity

•

Multifiber bundles (hexagonal)

•

Moire pattern (from 3 MCPs)

•

Dead pores

Intensified CCDs

„Ultra Compact Design“

Quest for high resolution

0.5 arcsec

Solar Orbiter mission

High-resolution

mission to the Sun and Inner Heliosphere

EIT

TRACE

Payload instrumentation:

o EUV spectrograph

o EUV imagers

o UV coronograph

What are our goals?

Imaging sensors with high sensitivity and resolution,

• large pixel array

• radiation hard

• smallest pixel size

• high count rate

• sensitive in a huge wavelength range

• solar blind

• stable calibration

• low dark noise

Advantages/disadvantages

S i l i c o n D e t e c t o r s

W i d e B a n d g a p D e t e c t o r s

N e e d c o o l i n g t o - 6 0 C o r l e s s

( D a r k c u r r e n t & r a d i a t i o n s )

R o o m t e m p e r a t u r e o p e r a t i o n s

(sim p l e r & c o s t - e f f e c t i v e )

C o n t a m i n a n t s s t i c k a n d p o l y m e r i z e

( c o l d t r a p )

L o w c o n t a m i n a t i o n r i s k , l o n g - t e r m s t a b i l i t y

D e g r a d a t i o n o f t h e c h a r g e t r a n s f e r e f f i c i e n c y

b y i o n i z i n g r a d i a t i o n

R a d - h a r d n e s s

W h o l e m ission lifetim e i n c r e a s e d

C o s m i c r a y h i t s p l a g u e t h e s i g n a l

( p o i n t s & s t r i k e s )

S m a l l e r c r o s s - s e c t i o n = > l e s s a r t i f a c t s

Q E i n s u f f i c i e n t , i n h o m o g e n e o u s , a n d

u n s t a b l e

H i g h e r Q E . S t a b i l i t y a n d f l a t - f i e l d

i m p r o v e d

M C P I n t e n s i f i e r s n e e d e d

V U V s e n s i t i v e

M inim a l p i x e l s i z e ~ 1 0 m i c r o n s

P o t e n t i a l l y m u c h s m a l l e r

M o s t s e n s i t i v e i n v i s i b l e , f i l t e r s n e e d e d

( f r a g i l e , a b s o r b i n g U V )

V i s i b l e - B l i n d

S o m e f i l t e r s c a n b e r e m o v e d

G a i n i n e f f e c t i v e a r e a

Devices fabricated for tests

MSM GaN device

Schottky GaN device

1x 6 linear micro-array of

MSM photodiodes

Single-photodetectors

Metal-semiconductor-metal

§

Active areas: 500 x 500 µm

2

250 x 250 µm

2

50 x 50 µm

2

30 x 30 µm

2

§

Finger widths (Pt/Ti/Au or Ni/Au)

and spacings: 2,4,7 and 10 µm

Schottky photodiodes

§

Extended Ti/Al or Ti/Al/Ti/Au ohmic contact.

§

Active areas: 1 mm, 600 µm, 400 µm and 200

µm diameter disks.

§

Semitransparent 100 Å-thick Au.

§

Ni (300 Å)/ Au (1000 Å) pad.

§

Passivation: SiO

₂

or SiN.

Solar-blindness of present WBGS detectors

200

400

600

800

1000

1E-8

1E-7

1E-6

1E-5

1E-4

1E-3

0,01

0,1

1

10

100

E = 28 KV/cm

electron/photon

Wavelength (nm)

Pace

et al.

2000.

Nitride

Diamond

Pau

et al.

2003.

10-1 101 103 10-10 10-8 10-6 x = 0 x = 0.19 x = 0.26 x = 0.35 λ = 325 nm Photocurrent (A) Irradiance (W/m2 ) 280 320 360 400 440 480 10-3 10-2 10-1 100 Al_xGa_1-xN x = 0 x = 0.19 x = 0.26 x = 0.35

Responsivity (a.u.)

Wavelength (nm)

Micro-arrays

0.1 1 10 100 1000 10000 Pixel 1 Pixel 2 Pixel 3 Pixel 4 Pixel 5 Pixel 6

Current (pA)

0.01 0.1 1 Pixel 1 Pixel 2 Pixel 3 Pixel 4 Pixel 5 Pixel 6

AC Responsivity (a.u.)

• Minimum pixel size: 30 x 30 µm

2

.

• Finger widths: 2, 4 and 7 µm.

• Homogeneity studies.

• Pixel-to-pixel cross-talk analysis.

• Image persistence effects.

VUV efficiency of MSM GaN devices

100 150 200 250 7 µm 4 µm 2 µm

DC Responsivity (a.u.)

Wavelength (nm)

Finger width

EUV efficiency of GaN Schottky device

• Absolute responsivity

measured at the electron

storage ring BESSY II

• Compared to a

calibrated PtSi reference

diode