Photodetector on SiliconHeng Yang
OutlineIntroductionSi Photodetector in 770 ~ 850 nm RangeIR Schottky barrier photodetector
IntroductionEssentially - p-n diode under the reverse biasOperate in the photoconductive modeMain usage - for the conversion of the optical signalworks at 0.3 - 1.1 m (peak responsivity at 0.8 m).
Si Photodetector in 770 ~ 850 nm RangeOptical communication range.Absorption length for Si: 10 ~ 15 mm. Requirements: High responsivity and Fast?pn, pin and msm.
pnDepletion regionJ = Jdrfit + Jdiff
Interdigitated ElectrodeInterdigitated 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
Min Yang, Kern Rim, Dennis L. Rogers, et al., IEEE ELECTRON DEVICE LETTERS, VOL. 23, NO. 7, JULY 2002
Finger space = 3.3 mmTrench depth = 8 mmFinger size = 0.35 mm For l=845 nm, BW=1.5 GHz, Responsivity = 0.47 A/W at 5V
MSM Photodetector by Trench FormationJacob Y. L. Ho and K. S. Wong, IEEE Photonics Technology Letters, 8(8), 1996For l = 790 nm, BW = 2.2 GHz, Responsivity = 0.14 A/W @ 5V
Resonant-Cavity-Enhanced High-Speed Si PhotodetectorJ. 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 1999Three 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).
Photodetector on SOIThin 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.M. Y. Liu, E. Chen, and S. Y. Chou, Appl. Phys. Lett. 65 (7), 15 August 1994SiliconSilicon dioxide
IR Schottky Barrier (SB) Photodetector300,000 PtSi/p-Si Schottky barrier IR detector focal plane arrays have been developed and used on Air Force B-52
IR Schottky Barrier PhotodetectorInternal PhotoemissionIntrinsic Mechanism
IssuesHigh 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.
Fowler PlotThe dark current is thermionic limited. It is given by:A** is Richardson constantBy plotting J0/T2 vs 1/T, qfB can be obtained from the slope.
PtSi/p-Si Schottky BarrierSecond 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+ layerPtSi/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 DetectorThe modification was made just to make the PtSi on top of the PS in stead of Si. Pt was deposited by electrodepositionThe 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
Si Peak R = 0.5 A/WWhy 770 ~ 850 nm?BSGSEG, processAqua regia. Ir Iridium How it works? 1040 by 1040, 20 by 20 mmWhy?