Photodetector on Silicon
Heng Yang
Outline
• Introduction
• Si Photodetector in 770 ~ 850 nm
Range
• IR Schottky barrier photodetector
Introduction
• Essentially - p-n diode
under the reverse bias
• Operate in the
photoconductive mode
• Main usage - for the
conversion of the optical
signal
• works at 0.3 - 1.1 µm
(peak responsivity at 0.8
µm).
Si Photodetector in 770 ~ 850 nm
Range
•
•
•
•
Optical communication range.
Absorption length for Si: 10 ~ 15 mm.
Requirements: High responsivity and Fast?
pn, pin and msm.
n
Depletion region
p
J = Jdrfit + Jdiff
Interdigitated Electrode
Interdigitated electrodes
are often used to increase
the active region area while
optimizing the electric fields
in the carrier collection
region.
Electrode can either be
P+/N+ or just metal.
Silicon Lateral Trench Photodetector
Finger space = 3.3 mm
Trench depth = 8 mm
Finger size = 0.35 mm
For l=845 nm,
BW=1.5 GHz,
Responsivity = 0.47 A/W
at 5V
Min Yang, Kern Rim, Dennis L. Rogers, et al., IEEE ELECTRON DEVICE LETTERS,
VOL. 23, NO. 7, JULY 2002
MSM Photodetector by Trench
Formation
For l = 790 nm, BW = 2.2 GHz, Responsivity = 0.14 A/W @ 5V
Jacob Y. L. Ho and K. S. Wong, IEEE Photonics Technology Letters, 8(8), 1996
Resonant-Cavity-Enhanced HighSpeed Si Photodetector
Three pair of quarter wavelength
SiO2 and polysilicon at bottom
(LPCVD).
Etched seed window.
SiO2 Side-wall to prevent defects
at the edge of poly.
RPCVD Si.
Two pairs of ZnSe-MgF on top
(evaporated).
J. D. Schaub, R. Li, C. L. Schow, J. C. Campbell, G. W. Neudeck, and J. Denton
,IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 11, NO. 12, DECEMBER 1999
Photodetector on SOI
• Thin active layer, and
small finger space
result in high speed.
• Device with 100nm
active layer and
100nm finger space
was made. l=780 nm
BW=140 GHz,
responsivity=5.7
mA/W @ 5V.
Silicon dioxide
Silicon
M. Y. Liu, E. Chen, and S. Y. Chou, Appl. Phys. Lett. 65 (7), 15 August 1994
IR Schottky Barrier (SB)
Photodetector
300,000 PtSi/p-Si
Schottky barrier IR
detector focal plane
arrays have been
developed and used
on Air Force B-52
IR Schottky Barrier Photodetector
Internal Photoemission
1.24
lC 
q B
Intrinsic Mechanism
Issues
• High dark current, has to operate at low
temperature (40 ~ 80 K).
• Low quantum efficiency (QE).
h  qB 
2
QE  C1
h
1 1 
 1.24C1l   
 l lC 
2
High lC gives high QE. In order to expand the spectrum,
efforts were made to decrease the barrier height.
Fowler Plot
• The dark current is
thermionic limited. It
is given by:
J 0  A * *T 2 exp( qB / kT )
• A** is Richardson
constant
• By plotting J0/T2 vs
1/T, qB can be
obtained from the
slope.
PtSi/p-Si Schottky Barrier
• Second lowest barrier height (0.22eV).
More than IrSi (0.16eV).
• Low expense.
• Compatible with standard IC process.
• Stable.
• Good uniformity over large area.
• Good growth and etching selectivity.
PtSi Schottky-Barrier Infrared Focal
Plane Arrays
Masafumi Kimata, Tatsuo Ozaki, Natsuro Tsubouchi and Sho Ito,
Proceeding of SPIE, 1998
SBD with a shallow P+ layer
• PtSi/p-Si, qFB = 0.22 eV, lc =
5.6 mm. (M. Kimata, M. Denda et. al, Inter.
J. of Infrared and millimeter waves, 6(10),
1985)
• PtSi/p+ (100 ~ 300 nm)/p-Si,
qFB < 0.22 eV, with hole
tunneling, lc = 7 mm. (CY Wei, W.
Trantraporn, W. Katz and G. Smith, 93,
1981)
• PtSi/p+ (1nm)/p-Si,
qFB =
0.057 eV, lc = 22 mm. (TL Lin, JS
Park et. al, Appl. Phys. Lett. 62(25), 1993)
TL Lin, JS Park et al.
Appl. Phys. Lett. 62(25), 1993
Porous Silicon (PS) Schottky
Barrier Detector
• The modification was
made just to make the PtSi
on top of the PS in stead
of Si. Pt was deposited by
electrodeposition
• The cut-off wavelength of
7 mm was reported.
• QE ~ 10% @ 7 mm
• Random orientation of the
junctions increase the
number of holes that can
be injected into Si.
Farshid Raissi and Mansoor Mohtashami Far, IEEE Sensors Journal, 2 (5) 2002