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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 17, Iss. 21 — Oct. 12, 2009
  • pp: 18571–18580
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Optical modulation in silicon waveguides via charge state control of deep levels

D F Logan, P E Jessop, A P Knights, G Wojcik, and A Goebel  »View Author Affiliations


Optics Express, Vol. 17, Issue 21, pp. 18571-18580 (2009)
http://dx.doi.org/10.1364/OE.17.018571


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Abstract

The control of defect mediated optical absorption at a wavelength of 1550nm via charge state manipulation is demonstrated using optical absorption measurements of indium doped Silicon-On-Insulator (SOI) rib waveguides. These measurements introduce the potential for modulation of waveguide transmission by using the local depletion and injection of free-carriers to change deep-level occupancy. The extinction ratio and modulating speed are simulated for a proposed device structure. A ‘normally-off’ depletion modulator is described with an extinction coefficient limited to 5 dB/cm and switching speeds in excess of 1 GHz. For a carrier injection modulator a fourfold enhancement in extinction ratio is provided relative to free carrier absorption alone. This significant improvement in performance is achieved with negligible increase in driving power but slightly degraded switching speed.

© 2009 OSA

1. Introduction

Optical detection via defect-enhanced carrier generation in SOI ridge waveguides is now established as a viable method for sub-bandgap optical to electrical conversion [1

1. A. P. Knights, J. D. B. Bradley, S. H. Gou, and P. E. Jessop, “Silicon-on-insulator waveguide photodetector with self-ion-implantation engineered-enhanced infrared response,” J. Vac. Sci. Technol. A 24(3), 783–786 (2006). [CrossRef]

3

3. Y. Liu, C. W. Chow, W. Y. Cheung, and H. K. Tsang, “In-line channel power monitor based on Helium ion implantation in silicon-on-insulator waveguides,” IEEE Photon. Technol. Lett. 18(17), 1882–1884 (2006). [CrossRef]

]. In the previously reported work defects are introduced into the waveguide through ion implantation (with or without a post-implantation thermal anneal), which increases the optical absorption for wavelengths around 1550 nm through the (essentially) mid-gap divacancy or interstitial cluster level [4

4. H. Y. Fan and A. K. Ramdas, “Infrared absorption and photoconductivity in irradiated silicon,” J. Appl. Phys. 30(8), 1127–1134 (1959). [CrossRef]

]. Integrated p-i-n diode structures are used to extract the optically generated carriers from the device volume supporting the optical mode, thus allowing for signal detection directly from the waveguide. The degree of absorption may be changed by varying the concentration of defects, and thus the amount of signal that is sampled may be varied from a few per cent to virtually the entire signal. As a result, defect-enhanced photodetectors may be implemented as both in-line power monitors and as end-of-line signal detectors. Their potential advantages over competing technologies rely on the fact that they are fabricated entirely using standard silicon processing methods and do not involve hybrid integration or the hetero-growth of germanium.

The photodetectors reported to date are fabricated in the intrinsic (or low-doped) silicon overlayer of a silicon-on-insulator (SOI) structure, and therefore the influence of background dopant concentration on device performance has not been studied. In the case of carrier generation via the divacancy defect, the background dopant concentration will affect the charge state of the divacancies, which in turn will influence the defect mediated absorption. Evidence consistent with this postulate has been reported previously [5

5. C. S. Chen and J. C. Corelli, “Infrared spectroscopy of divacancy-associated radiation-induced absorption bands in silicon,” Phys. Rev. B 5(4), 1505–1517 (1972). [CrossRef]

], and has recently been demonstrated using a waveguide geometry [6

6. D. Logan, P. E. Jessop, A. P. Knights, R. M. Gwilliam, and M. P. Halsall, “The effect of doping type and concentration on optical absorption via implantation induced defects in silicon-on-insulator waveguides.” in COMMAD 2008 IEEE Proc. Conf. on Optoelectronic and Microelectronic Materials and Devices. (Sydney, Australia, 2008). pp. 152–5.

].

2. Background to charge state mediated absorption

A 4 µm optical absorption resonance exists in indium doped silicon [9

9. G. J. Parker, S. D. Brotherton, I. Gale, and A. Gill, “Measurement of concentration and photoionization cross section of indium in silicon,” J. Appl. Phys. 54(7), 3926–3929 (1983). [CrossRef]

]. This absorption results from the excitation of an electron from the valence band onto a neutral indium center where it occupies the single negatively charged state lying 157 meV above the valence band. The cross-section for this optically excited transition is approximately 1.7x10−17 cm2 for photons with an energy equivalent 1550 nm wavelengths [8

8. M. J. Keevers and M. A. Green, “Efficiency improvements of silicon solar cells by the Impurity photovoltaic effect,” J. Appl. Phys. 75(8), 4022–4031 (1994). [CrossRef]

]. The excitation of an electron from the indium into the conduction band requires a photon energy of 0.94 eV, and therefore has a negligible optical cross-section for 1550 nm photons. The absorption strength for this wavelength is then proportional to the concentration of neutral (unoccupied) indium, which is dependent on the position of the Fermi level. The absorption coefficient of the 4 µm resonant band for 1550nm can be described as follows:
αd=σpoptx,yΦ(x,y)(Nt(x,y)nt(x,y))dxdy
(1)
where σpopt is the cross-section for optical absorption at 1.55 µm wavelength; Φ(x,y) is the normalized (unit power) optical mode profile of the waveguide; Nt(x,y) is the profile of the indium concentration; nt(x,y) is the profile of the ionized (negatively charged) indium.

For indium doping alone, the device is p-type and the indium acceptors are partially occupied (nt is a fraction of Nt) and the optical absorption for 1550 nm is maximized, as depicted in the left of Fig. 1
Fig. 1 The band diagram of silicon containing a constant concentration of deep acceptors Nt and varying concentrations of shallow donor levels Nd. Without the presence of shallow donors (left), many deep acceptors are unoccupied (nt takes its minimum value ntmin) and therefore electrons are capable of being optically excited from the valence band. Moving to the right, shallow donors are added in increasing concentrations. These donors supply free electrons that are trapped by the vacant deep level acceptors, thus decreasing the number of sites available for electrons to be optically excited into. On the far right, the shallow donor concentration is large enough to completely compensate the deep levels, making the optical excitation process impossible.
. Whereas, for background doping which is n-type the indium acceptors are compensated and thus have an occupation nt which approaches Nt, which reduces the absorption coefficient.

3. Experimental and modelled absorption

Rib waveguides of 4 µm width were fabricated on eleven samples cleaved from 2.5 µm thick silicon overlayer SOI, using a KOH wet etching technique described elsewhere [10

10. P. J. Foster, J. K. Doylend, P. Mascher, A. P. Knights, and P. G. Coleman, “Optical attenuation in defect-engineered silicon rib waveguides,” J. Appl. Phys. 99(7), 073101 (2006). [CrossRef]

]. The etch depth was chosen to ensure the resulting waveguide supported single-mode propagation for 1550 nm light. Windows of varying length L (up to a maximum length of 4 mm), centered on each rib, were defined using 4 µm thick photoresist, and used as a mask during ion implantation of indium at 500 keV for doses varying from 1013 to 6x1014cm−2. The samples were then cleaned of the resist mask and annealed at 1000 C in dry O2 for 50 minutes. Eight of the unmasked samples were subsequently ion implanted with phosphorus at an energy of 175 keV at doses ranging from 6x1012 to 2x1014cm−2, and annealed at 1000 C in dry O2 for a further 150 minutes. These implantation and thermal processes were designed to position the resulting indium and phosphorus concentration profiles coincidently, with a peak concentration at ~1 µm. The concentration of the indium and phosphorus doping at their peak of the profiles are provided in Table 1

Table 1. Summary of Measured and Simulated Loss for Fabricated Waveguide Chips

table-icon
View This Table
.

The unmasked phosphorus implantation contributes to free-carrier absorption over the entire waveguide length W, while the masked indium implant contributes to absorption over the window length L, only. Therefore, the total loss measured for each waveguide has the following form:
TotalLoss(dB)=αdL+αiW+c
(2)
where αd is the absorption coefficient of the indium center from Eq. (1); L is the length of the indium implantation window; αi is the intrinsic absorption coefficient, which includes the effects of enhanced free carrier absorption consequent from phosphorus doping; W is the entire length of the waveguide; and c is the coupling loss.

Laser light close to 1550 nm in wavelength was coupled into each waveguide through a tapered optical fibre, and the transmitted light collected by an objective lens and focused onto a free-space InGaAs photodetector.

The measured variation in the total loss between waveguides on a single sample is due to the variation in L (the waveguides have constant length W). The value of αd can be extracted from a fit to the total loss vs. L, examples of which are shown in Fig. 2
Fig. 2 Example plots of total loss measured for each waveguide for the chip with indium implanted at a dose of 6x1014cm−2, while the various phosphorus doses are also indicated. A fit to the data using Eq. (2) provides the excess loss due to the indium doping, αd (the slope of the line, which is observed to decrease with increasing phosphorus dose).
. The summary of variation in indium and phosphorus doping for each sample and the measured αd is provided in Table 1 and plotted as Fig. 3
Fig. 3 Extracted values of αd vs. peak phosphorus concentration for all samples with indium implanted to a dose of 6x1013 cm−2 (black squares) and 6x1014 cm−2 (white triangles), illustrating the significant decrease of αd resulting from co-doping with phosphorus. The solid lines are fits to the data derived from Eqs. (1) and (3).
.

The modelled excess optical loss due to the presence of indium doping is shown in the far right column of Table 1. Using the implantation conditions given above the dopant concentration profiles were simulated using the software code ATHENA [11

11. Silvaco Data Systems Inc, © 1984–2008. [online]. Available: www.silvaco.com.

]. The optical cross-section for excitation of an electron from the valence band to the unoccupied indium level, σpopt, was assumed to be 1.7x10−17 cm2 [8

8. M. J. Keevers and M. A. Green, “Efficiency improvements of silicon solar cells by the Impurity photovoltaic effect,” J. Appl. Phys. 75(8), 4022–4031 (1994). [CrossRef]

]. The optical mode profile Φ(x,y) was obtained from commercial Beam Propagation software [12

12. RSoft Design Group, Inc., © 2002. [online]. Available: www.rsoftdesign.com.

].

For example, the calculated nt/Nt is plotted in Fig. 4
Fig. 4 Occupation fraction of indium vs. donor concentration Nd for Nt = 1017 cm−3 and 1018 cm−3.
for Nt = 1017 cm−3 and 1018 cm−3 for varying values of Nd.

The results in Table 1 indicate that the variation in occupation of the indium dopant caused by the presence of shallow donor atoms manifests as a variation in optical absorption. We note that while the largest indium implantation dose would be expected to produce a peak indium concentration of 6x1018 cm−3, and therefore an absorption in the region of 130 dB/cm, the activated indium concentration is limited by the solid solubility of indium in silicon. This solid solubility has been determined previously to be 1.4 – 1.5x1018 cm−3, for an activation temperature of 1000 C which limits the accessible absorption [14

14. A. Sato, K. Suzuki, H. Horie, and T. Sugii, “Determination of Solid Solubility Limit of In and Sb in Si using Bonded Silicon-On-Insulator (SOI) Substrate.” in Proc. IEEE 1995 Int. Conf. on Microelectronic Test Structures. (Nara, Japan, vol. 8, 1995) pp. 259–263.

,15

15. J. Liu, U. Jeong, S. Mehta, J. Sherbondy, A. Lo, K. Ha Shim, and J. Eun Lim, “Investigation of Indium Activation by C-V Measurement.” in Proc. IEEE Int. Conf. on Ion Implantation Technology, H. Ryssel et al., ed. (Alpbach, Austria, 2000) pp. 66–69.

]. This effect has been taken into account also in the modelling. Implicit is that indium which is not activated does not support electronic excitation.

The modelling also takes into account the decrease of free-carrier absorption within the implantation window as a consequence of electron trapping by indium centers. This is manifest as an added component to Eq. (1) that in certain cases causes αd to take on apparent negative values, as shown in the far-right column of Table 1. A revision to Eq. (1) accounting for this effect yields:
αd=σpoptx,yΦ(x,y)(Nt(x,y)nt(x,y))dxdyσeoptx,yΦ(x,y)e(x,y)dxdy
(4)
where e' is the electron density supplied by phosphorus atoms which has been trapped by indium (i.e. the difference in indium occupation nt between a phosphorus doped sample and a sample without phosphorus doping); σeopt is the cross-section for free electron absorption in silicon at 1550 nm, 6 x 10−18 cm−3 .

4. Potential designs for a modulator structure

It is of interest to consider how the phenomenon described in sections II and III (specifically for the case of indium doping) might be used to produce a modulation effect in a silicon waveguide. It is envisaged that a modulator may function by varying nt (the number of occupied indium acceptors) over a large range to vary αd as described in Eq. (1). For example, if a concentration of indium centres, Nt, is introduced into a waveguide with negligible background doping, nt will be a small fraction of Nt (controlled by the electrical activation of indium) and αd will be a maximum. Subsequent application of an electric field to the waveguide would then cause a depletion effect with the result that holes would be emitted from the indium centres, increasing nt and decreasing the absorption to a minimum level. Alternatively, if Nt indium centers are introduced into a waveguide which is co-doped with shallow donors (such as phosphorus atoms) to a concentration of Nd, such that NdNt, the indium dopant will be fully compensated with the result that nt = Nt (as in Fig. 3) so that minimum absorption occurs. An application of a forward bias causes nt to decrease and thereby enhance absorption. Investigation of these two alternative device designs is the focus of the remainder of this paper. Each design is subsequently referred to as the depletion or injection methods.

Simulations were performed using the commercial software ATLAS [11

11. Silvaco Data Systems Inc, © 1984–2008. [online]. Available: www.silvaco.com.

]. A silicon waveguide structure shown schematically in Fig. 5
Fig. 5 Cross-sectional view of the device modelled in this study, described previously by Geis et al. The p + and n + regions correspond to doping levels of 1018 cm−3, and the p + + and n + + correspond to doping levels of 1019 cm−3 [2].
was described in the Deckbuild environment and electronic levels, having the characteristics of the indium center, were added into the entire overlayer region of the SOI. The structure was subsequently modelled for electrical performance using ATLAS. For each bias condition, the two-dimensional profile of the ionized acceptor trap density, nt(x, y), was determined. The normalized optical mode profile Φ(x,y), obtained from the waveguide propagation simulator BeamPROP, was used to calculate the overlap integral of Eq. (1). As a result, it was possible to acquire αd as a function of electrical bias applied to the device. In addition, free carrier concentration distributions were simulated and used to calculate their absorption contribution. This was also incorporated into a transient simulation, whereby the total absorption was computed at various time intervals following bias application in order to determine the bandwidth of the device.

The device used for this study, shown in Fig. 5, utilises a sub-micron sized structure used previously, for example, to form waveguide photodetectors as described by Geis et al. [2

2. M. W. Geis, S. J. Spector, M. E. Grein, R. T. Schulein, J. U. Yoon, D. M. Lennon, S. Deneault, F. Gan, F. X. Kaertner, and T. M. Lyszczarz, “CMOS-compatible all-Si high-speed waveguide photodiodes with high responsivity in near-infrared communication band,” IEEE Photon. Technol. Lett. 19(3), 152–154 (2007). [CrossRef]

]. Both contact regions are in close proximity to the optical mode, which is beneficial in that any carrier depleted volume or injected hole distribution overlaps strongly with the optical mode.

Depletion Method: A limitation of the depletion method when applied to the device structure shown in Fig. 5 is that it is restricted to relatively small values of indium concentration, Nt. The use of high concentrations of indium severely limits the volume of the waveguide that could be depleted. For instance, αd increases with Nt at a rate given by Eq. (1), but the bias required to achieve nt = Nt increases also. To demonstrate this effect Fig. 6
Fig. 6 Absorption coefficient αd plotted as a function of applied reverse bias, for two uniform indium concentrations, Nt .
plots simulated optical absorption as a function of reverse bias for two values of Nt. The achievable modulation depth is limited to ~5 dB/cm for a relatively large bias of −20 V, while it is difficult to achieve zero loss using the depletion method, even for Nt = 2x1017cm−3. Although the large insertion loss and limited modulation depth limits its applicability, this ‘normally off’ device can provide substantially reduced power consumption over traditional optical modulators, particularly in the case of multiple channel devices where the majority of the channels are required to be in the ‘off’ state for a given time interval.

A transient study was also performed using the depletion method. For the case of Nt = 2x1017 cm−3 the results are shown in Fig. 7
Fig. 7 Simulated absorption coefficient following the application of a −20 V bias, and following the removal of the bias after 10 ns.
. The turn-on time is 0.6 ns, and becomes larger as Nt is increased. The turn-off time is 0.3 ns, and was found to be independent of the value of Nt (for the two values in Fig. 6). There is no significant impact of the magnitude of the reverse bias on the turn-on and turn-off times.

In the simulation results that follow the value of the n-type background doping Nd of the waveguide were fixed such that Nd = Nt. The extinction ratio of the modulator will increase with increasing Nt. Figure 8
Fig. 8 Simulated αd following application of 1 V forward bias as a function of Nt = Nd (dotted line: performance of free-carrier absorption alone).
plots this increase as a function of Nt, showing the seemingly unbounded improvement over a modulator without indium and with a background doping concentration of 1015cm−3 (this is equivalent to a device using free-carrier injection alone to achieve modulation). The limit on modulation improvement will in fact be determined by the solid solubility of indium in the silicon waveguide. For larger devices (on the order of 10 μm2 cross-section), the large donor concentrations will limit the penetration of holes into the device cross-section.

In practice, Nd is unlikely to be matched to Nt, which may lead to an excess insertion loss. If Nd > Nt, the insertion loss will increase due to free carrier absorption; while if Nt > Nd, the insertion loss will increase due to absorption from uncompensated indium. Since the optical cross-section for indium absorption is approximately double that for absorption of free electrons, it is preferred to overcompensate the background doping such that Nd > Nt, as is the case in the passive loss data described in section III. For example, overcompensating such that Nd = 1.1 x 1018 cm−3 while Nt = 1018 cm−3, an insertion loss of 2.6 dB/cm will be present.

The Extinction Ratio vs. Dissipated Power for two indium doping concentrations, one having Nt = Nd = 1018 cm−3 and a second having Nt = Nd = 1017 cm−3, is plotted as Fig. 10
Fig. 10 Extinction ratio vs. Power (both normalized to length) for the enhanced VOA for two levels of indium doping, plotted with the performance of an undoped device operating solely by free-carrier absorption.
, together with that for a device without enhancement from indium absorption.

At Nt = Nd = 1017 cm−3, the enhancement in modulation relative to the undoped device is such that the addition of indium barely compensates for the degradation in absorption from free holes. For Nt = Nd = 1018 cm−3, the increase in absorption is however significant. For example, a device of 1 mm in length would require 40 mW of power to achieve an extinction ratio of 10 dB. Alternatively, a 1 mm VOA using only free-carrier absorption would require approximately 400 mW to achieve a 10 dB extinction ratio.

Assuming the device is sufficiently small, the limiting factor on both extinction ratio and speed is the deep level characteristics, specifically the optical cross-section for excitation of electrons from the valence band to the defect level, σpopt, and the relative capture cross-sections of electrons and holes at the defect level. For instance, the larger the difference in hole and electron cross-sections, the more effective the current injection for changing the occupancy. The speed of the device could be increased by selecting a defect level with larger capture cross-sections of both electrons and holes, while maintaining a significant superiority of holes over electrons for the reasons outlined above.

5. Conclusion

We have investigated the effects of doping type and concentration on the absorption of deep level defects in silicon waveguides using the indium center as an example. The dependence has been shown to be correlated with the defect occupancy, which in turn depends on the location of the Fermi level, and can be changed by depleting or injecting a device with charge carriers. This presents a novel means for fabricating a “normally off” VOA device or enhancing more traditional forms of carrier injection VOA operation. We have shown that both the speed and modulation depth of a sub-micron cross-sectional device depends primarily on the defect characteristics.

References and links

1.

A. P. Knights, J. D. B. Bradley, S. H. Gou, and P. E. Jessop, “Silicon-on-insulator waveguide photodetector with self-ion-implantation engineered-enhanced infrared response,” J. Vac. Sci. Technol. A 24(3), 783–786 (2006). [CrossRef]

2.

M. W. Geis, S. J. Spector, M. E. Grein, R. T. Schulein, J. U. Yoon, D. M. Lennon, S. Deneault, F. Gan, F. X. Kaertner, and T. M. Lyszczarz, “CMOS-compatible all-Si high-speed waveguide photodiodes with high responsivity in near-infrared communication band,” IEEE Photon. Technol. Lett. 19(3), 152–154 (2007). [CrossRef]

3.

Y. Liu, C. W. Chow, W. Y. Cheung, and H. K. Tsang, “In-line channel power monitor based on Helium ion implantation in silicon-on-insulator waveguides,” IEEE Photon. Technol. Lett. 18(17), 1882–1884 (2006). [CrossRef]

4.

H. Y. Fan and A. K. Ramdas, “Infrared absorption and photoconductivity in irradiated silicon,” J. Appl. Phys. 30(8), 1127–1134 (1959). [CrossRef]

5.

C. S. Chen and J. C. Corelli, “Infrared spectroscopy of divacancy-associated radiation-induced absorption bands in silicon,” Phys. Rev. B 5(4), 1505–1517 (1972). [CrossRef]

6.

D. Logan, P. E. Jessop, A. P. Knights, R. M. Gwilliam, and M. P. Halsall, “The effect of doping type and concentration on optical absorption via implantation induced defects in silicon-on-insulator waveguides.” in COMMAD 2008 IEEE Proc. Conf. on Optoelectronic and Microelectronic Materials and Devices. (Sydney, Australia, 2008). pp. 152–5.

7.

E. Simoen, C. Claeys, E. Gaubas, and H. Ohyama, “Impact of the divacancy on the generation-recombination properties of 10 MeV proton irradiated Float-Zone silicon diodes,” Nucl. Instrum. Methods Phys. Res. A 439(2-3), 310–318 (2000). [CrossRef]

8.

M. J. Keevers and M. A. Green, “Efficiency improvements of silicon solar cells by the Impurity photovoltaic effect,” J. Appl. Phys. 75(8), 4022–4031 (1994). [CrossRef]

9.

G. J. Parker, S. D. Brotherton, I. Gale, and A. Gill, “Measurement of concentration and photoionization cross section of indium in silicon,” J. Appl. Phys. 54(7), 3926–3929 (1983). [CrossRef]

10.

P. J. Foster, J. K. Doylend, P. Mascher, A. P. Knights, and P. G. Coleman, “Optical attenuation in defect-engineered silicon rib waveguides,” J. Appl. Phys. 99(7), 073101 (2006). [CrossRef]

11.

Silvaco Data Systems Inc, © 1984–2008. [online]. Available: www.silvaco.com.

12.

RSoft Design Group, Inc., © 2002. [online]. Available: www.rsoftdesign.com.

13.

K. Dieter, Schroder, Semiconductor Material and Device Characterization. (John Wiley & Sons, 2006). p. 255–8.

14.

A. Sato, K. Suzuki, H. Horie, and T. Sugii, “Determination of Solid Solubility Limit of In and Sb in Si using Bonded Silicon-On-Insulator (SOI) Substrate.” in Proc. IEEE 1995 Int. Conf. on Microelectronic Test Structures. (Nara, Japan, vol. 8, 1995) pp. 259–263.

15.

J. Liu, U. Jeong, S. Mehta, J. Sherbondy, A. Lo, K. Ha Shim, and J. Eun Lim, “Investigation of Indium Activation by C-V Measurement.” in Proc. IEEE Int. Conf. on Ion Implantation Technology, H. Ryssel et al., ed. (Alpbach, Austria, 2000) pp. 66–69.

OCIS Codes
(230.2090) Optical devices : Electro-optical devices
(250.4110) Optoelectronics : Modulators

ToC Category:
Optical Devices

History
Original Manuscript: July 29, 2009
Revised Manuscript: September 23, 2009
Manuscript Accepted: September 25, 2009
Published: September 30, 2009

Citation
D F Logan, P E Jessop, A P Knights, G Wojcik, and A Goebel, "Optical modulation in silicon waveguides via charge state control of deep levels," Opt. Express 17, 18571-18580 (2009)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-21-18571


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References

  1. A. P. Knights, J. D. B. Bradley, S. H. Gou, and P. E. Jessop, “Silicon-on-insulator waveguide photodetector with self-ion-implantation engineered-enhanced infrared response,” J. Vac. Sci. Technol. A 24(3), 783–786 (2006). [CrossRef]
  2. M. W. Geis, S. J. Spector, M. E. Grein, R. T. Schulein, J. U. Yoon, D. M. Lennon, S. Deneault, F. Gan, F. X. Kaertner, and T. M. Lyszczarz, “CMOS-compatible all-Si high-speed waveguide photodiodes with high responsivity in near-infrared communication band,” IEEE Photon. Technol. Lett. 19(3), 152–154 (2007). [CrossRef]
  3. Y. Liu, C. W. Chow, W. Y. Cheung, and H. K. Tsang, “In-line channel power monitor based on Helium ion implantation in silicon-on-insulator waveguides,” IEEE Photon. Technol. Lett. 18(17), 1882–1884 (2006). [CrossRef]
  4. H. Y. Fan and A. K. Ramdas, “Infrared absorption and photoconductivity in irradiated silicon,” J. Appl. Phys. 30(8), 1127–1134 (1959). [CrossRef]
  5. C. S. Chen and J. C. Corelli, “Infrared spectroscopy of divacancy-associated radiation-induced absorption bands in silicon,” Phys. Rev. B 5(4), 1505–1517 (1972). [CrossRef]
  6. D. Logan, P. E. Jessop, A. P. Knights, R. M. Gwilliam, and M. P. Halsall, “The effect of doping type and concentration on optical absorption via implantation induced defects in silicon-on-insulator waveguides.” in COMMAD 2008 IEEE Proc. Conf. on Optoelectronic and Microelectronic Materials and Devices. (Sydney, Australia, 2008). pp. 152–5.
  7. E. Simoen, C. Claeys, E. Gaubas, and H. Ohyama, “Impact of the divacancy on the generation-recombination properties of 10 MeV proton irradiated Float-Zone silicon diodes,” Nucl. Instrum. Methods Phys. Res. A 439(2-3), 310–318 (2000). [CrossRef]
  8. M. J. Keevers and M. A. Green, “Efficiency improvements of silicon solar cells by the Impurity photovoltaic effect,” J. Appl. Phys. 75(8), 4022–4031 (1994). [CrossRef]
  9. G. J. Parker, S. D. Brotherton, I. Gale, and A. Gill, “Measurement of concentration and photoionization cross section of indium in silicon,” J. Appl. Phys. 54(7), 3926–3929 (1983). [CrossRef]
  10. P. J. Foster, J. K. Doylend, P. Mascher, A. P. Knights, and P. G. Coleman, “Optical attenuation in defect-engineered silicon rib waveguides,” J. Appl. Phys. 99(7), 073101 (2006). [CrossRef]
  11. Silvaco Data Systems Inc, © 1984–2008. [online]. Available: www.silvaco.com .
  12. RSoft Design Group, Inc., © 2002. [online]. Available: www.rsoftdesign.com .
  13. K. Dieter, Schroder, Semiconductor Material and Device Characterization. (John Wiley & Sons, 2006). p. 255–8.
  14. A. Sato, K. Suzuki, H. Horie, and T. Sugii, “Determination of Solid Solubility Limit of In and Sb in Si using Bonded Silicon-On-Insulator (SOI) Substrate.” in Proc. IEEE 1995 Int. Conf. on Microelectronic Test Structures. (Nara, Japan, vol. 8, 1995) pp. 259–263.
  15. J. Liu, U. Jeong, S. Mehta, J. Sherbondy, A. Lo, K. Ha Shim, and J. Eun Lim, “Investigation of Indium Activation by C-V Measurement.” in Proc. IEEE Int. Conf. on Ion Implantation Technology, H. Ryssel et al., ed. (Alpbach, Austria, 2000) pp. 66–69.

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