1. Photodetector on Silicon
Heng Yang

2. Outline Introduction Si Photodetector in 770 ~ 850 nm Range
IR Schottky barrier photodetector

3. 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 µm (peak responsivity at 0.8 µm).
Si Peak R = 0.5 A/W

4. 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
Why 770 ~ 850 nm?
J = Jdrfit + Jdiff p
Depletion region

5. 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.

6. 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
BSG
Min Yang, Kern Rim, Dennis L. Rogers, et al., IEEE ELECTRON DEVICE LETTERS, VOL. 23, NO. 7, JULY 2002

7. MSM Photodetector by Trench Formation
For l = 790 nm, BW = 2.2 GHz, Responsivity = V
Jacob Y. L. Ho and K. S. Wong, IEEE Photonics Technology Letters, 8(8), 1996

8. Resonant-Cavity-Enhanced High-Speed 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).
SEG, process
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

9. 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 5V.
Silicon
Silicon dioxide
M. Y. Liu, E. Chen, and S. Y. Chou, Appl. Phys. Lett. 65 (7), 15 August 1994

10. 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

11. IR Schottky Barrier Photodetector
Internal Photoemission
Intrinsic Mechanism

12. Issues
High dark current, has to operate at low temperature (40 ~ 80 K).
Low quantum efficiency (QE).
High lC gives high QE. In order to expand the spectrum, efforts were made to decrease the barrier height.

13. Fowler Plot The dark current is thermionic limited. It is given by:
A** is Richardson constant
By plotting J0/T2 vs 1/T, qfB can be obtained from the slope.

14. 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.
Aqua regia. Ir Iridium

15. PtSi Schottky-Barrier Infrared Focal Plane Arrays
How it works? 1040 by 1040, 20 by 20 mm
Masafumi Kimata, Tatsuo Ozaki, Natsuro Tsubouchi and Sho Ito, Proceeding of SPIE, 1998

16. 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 = 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

17. 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 ~ 7 mm
Random orientation of the junctions increase the number of holes that can be injected into Si.
Why?
Farshid Raissi and Mansoor Mohtashami Far, IEEE Sensors Journal, 2 (5) 2002