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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 7 — Mar. 26, 2012
  • pp: 7142–7150
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Free carrier induced spectral shift for GaAs filled metallic hole arrays

Jingyu Zhang, Bin Xiang, Mansoor Sheik-Bahae, and S. R. J. Brueck  »View Author Affiliations


Optics Express, Vol. 20, Issue 7, pp. 7142-7150 (2012)
http://dx.doi.org/10.1364/OE.20.007142


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Abstract

For a GaAs filled metallic hole array on a pre-epi GaAs substrate, the free carriers, generated by three-photon absorption (3PA) assisted by strongly enhanced local fields, reduce the refractive index of GaAs in ~200-nm thick active area through band filling and free carrier absorption. Therefore, the surface plasma wave (SPW) resonance, and the related second harmonic (SH) spectrum blue shifts with increasing fluence; For the plasmonic structure on a substrate with surface defects, free carrier recombination dominates. The band gap emission spectral peak wavelength decreases 10-nm with increasing fluence, showing the transition from nonradiative-, at low excitation, to bimolecular-recombination at high carrier concentrations.

© 2012 OSA

1. Introduction

When the plasmonic sample is thinned by back-side etching, surface defects are introduced. Free carrier recombination dominates at room temperature. The SHG spectrum shifts slightly but the PL spectrum shifts more dramatically, by about 15 nm with increasing fluence, due to the transition from nonradiative carrier recombination at low excitation to bimolecular radiative recombination at high carrier concentration. When the sample is cooled down to 77K, the SHG and BE spectra exhibit constant peak wavelengths with narrowed linewidths.

The sample is fabricated on a double polished pre-epi GaAs substrate with GaAs posts (110-nm height) extending through holes in Au film arrays (540-nm pitch; 220-nm diameter, 100-nm height). The fabrication flow and structure have been described in Ref [10

10. J. Zhang, L. Wang, S. Krishna, M. Sheik-Bahae, and S. R. J. Brueck, “Saturation of the second harmonic generation from GaAs filled metallic hole arrays by nonlinear absorption,” Phys. Rev. B 83(16), 165438 (2011). [CrossRef]

]. The linear spectrum is measured by Fourier transform infrared spectroscopy (FTIR). The first order SPW coupling (observed as a transmission dip) is at 1880-nm and the coupled first order transmission peak is at 2190-nm [13

13. J. Zhang and S. R. J. Brueck, “Multi-photon absorption and second harmonic generation in GaAs-Filled Nanoplasmonic Arrays,” in Asia Communications and Photonics Conference and Exhibition (ACP)(Academic,Shanghai, China, 2009)

, 14

14. J. Zhang, “Metallic photonic crystals: transmission resonance and second harmonic generation,” (Ph. D thesis of University of New Mexico, 2009), Chap. 4. http://repository.unm.edu/handle/1928/10357

]. The unit cell includes one GaAs post. By using a near infrared (~2090-nm) fundamental wavelength at normal incidence, the SPWs are coupled into local modes with strongest enhanced electric fields Ex and Ez, which give the dominant contribution to the SHG, as shown in Ref [10

10. J. Zhang, L. Wang, S. Krishna, M. Sheik-Bahae, and S. R. J. Brueck, “Saturation of the second harmonic generation from GaAs filled metallic hole arrays by nonlinear absorption,” Phys. Rev. B 83(16), 165438 (2011). [CrossRef]

], as a result of the 4¯3mGaAs crystal point group

We exploited the measurement setup described in Ref [10

10. J. Zhang, L. Wang, S. Krishna, M. Sheik-Bahae, and S. R. J. Brueck, “Saturation of the second harmonic generation from GaAs filled metallic hole arrays by nonlinear absorption,” Phys. Rev. B 83(16), 165438 (2011). [CrossRef]

]. A pulsed laser with 200 fs pulse duration and 1 kHz repetition rate with a tunable wavelength is focused to the backside of the test sample at normal incidence. The fundamental laser pulse is 70-nm linewidth at near-infrared (NIR). The sample is located in a Dewar for ambient temperature control. Both the band gap photoluminescence (BE) and the second-harmonic radiation are collected and focused to a monochrometer and InGaAs detector with a scanning wavelength from 800- to 1700-nm.

2. Free carrier refraction from plasmon-coupled hole arrays on a pre-epi GaAs substrate at 297K

The SHG signal is monitored as the incident wavelength is tuned from 1900- to 2200 nm across the fundamental SPW resonance at different fluences. The SH signal around 1045-nm wavelength and BE signal at 890-nm wavelength are monitored as a function of the fundamental fluence. As shown in Fig. 1
Fig. 1 At 297K, for the plasmonic structure on a 500µm double polished pre-epi GaAs substrate, (a) BE (PL) spectral peak only slightly shifts (~890 nm); (b) SH spectral peak blueshifts from 1045 to 1023-nm with increasing fluencies from 7- to 127-GW/cm2.
, with the increase of fundamental intensity, no dramatic shift is observed in the BE spectrum, while the SHG spectrum blueshifts from 1045 to 1020-nm as the fluence is increase from 7- to 127-GW/cm2.

The output response of SHG and BE is spectrally integrated and plotted versus the 2090-nm fundamental intensity (input pulse peak power) as shown in the Fig. 5 in Ref [10

10. J. Zhang, L. Wang, S. Krishna, M. Sheik-Bahae, and S. R. J. Brueck, “Saturation of the second harmonic generation from GaAs filled metallic hole arrays by nonlinear absorption,” Phys. Rev. B 83(16), 165438 (2011). [CrossRef]

]. At 297K, for the GaAs substrate at low input peak power <10 GW/cm2, no SH signal was observed. A weak SH signal was observed at higher input peak powers with a slope of 1.1 due to weak focusing. The BE signal increases as the third power of the fundamental fluence. At 297K, for the plasmon coupled hole arrays, the SHG exhibits the expected quadratic power law dependence I ∝ Iω2 at low input power (< 10 GW/cm2), then saturates, with two orders enhancement compared with that of bulk GaAs. The BE signal appears at incident intensities coincident with the saturation of the SHG with a slope of 2.8. The free carrier generation across the GaAs bandgap is excited by 3PA at the fundamental frequency [10

10. J. Zhang, L. Wang, S. Krishna, M. Sheik-Bahae, and S. R. J. Brueck, “Saturation of the second harmonic generation from GaAs filled metallic hole arrays by nonlinear absorption,” Phys. Rev. B 83(16), 165438 (2011). [CrossRef]

].

At room temperature, for the plasmonic structure on a pre-epi GaAs substrate, the spectral peak wavelength and the full width half maximum (FWHM, linewidth) of SHG and BE with fundamental intensity in linear-log coordination have been plotted in Fig. 2
Fig. 2 At 297K, for the plasmon-coupled structure on a double polished 500 µm thick double polished pre-epi GaAs substrate, the spectral peak and linewidth (measured in squares and simulated in solid line) variation with increasing fluences: (a) SHG spectral peaks blueshift from 1045- to 1023-nm shows strong refractive index changes due to bandfilling (in red) and free carrier absorption (FCA) (in blue) and the combined effects (bandfilling and FCA in green); (b) BE spectral peak wavelength (PL) shows 3PA generated carriers recombination without obvious spectral shifting; (c) Linewidth of SHG spectra are broadened from 30- to 58-nm, evidencing the negative Δn with increasing fluences; (d) the linewidth of BE spectrum does not show obvious linewidth broadening.
. The SHG peak wavelength is constant at 1045-nm with input peak power from 1 to 10-GW/cm2, and then blue shifts from 1045- to 1023-nm with the input peak power from 10 to 100-GW/cm2 as shown in Fig. 2(a). The BE spectral peak is relatively constant with increasing fluences, as shown in Fig. 2(b). The linewidth of SHG spectrum is broadened from 30 nm to 58 nm with increasing fluence, as shown in Fig. 2(c). The linewidth of BE spectrum is relatively constant with increasing fluence, as shown in Fig. 2(d). The trend of wavelength shift of SHG peak with increasing input peak power is consistent with that of the intensity of SHG with increasing input peak power as the Fig. 5
Fig. 5 At 77K, for the plasmon-coupled structure on a 20 µm thick GaAs substrate with surface defects by acid etching, the spectral variation of SHG and BE vs fundamental intensity in linear-log plots: (a) SHG spectrum keeps constant at 1030-nm with 2060-nm fundamental wavelength and (b) BE spectrum wavelength shows constant at ~827-nm with increasing fluences. Linewidth of SHG spectra (c) and BE spectra (d) are constant at 20- and 10-nm with increasing input peak power respectively.
in Ref [10

10. J. Zhang, L. Wang, S. Krishna, M. Sheik-Bahae, and S. R. J. Brueck, “Saturation of the second harmonic generation from GaAs filled metallic hole arrays by nonlinear absorption,” Phys. Rev. B 83(16), 165438 (2011). [CrossRef]

]. However, for a bulk GaAs substrate at the same temperature, the wavelength peak of SHG and PL are constant at 1050/1040nm and 890/900nm. Therefore, the free carriers generated by the nonlinear 3PA, associated with the enhanced localized electric field with an four orders enhanced coefficient of 3PA from each unit cell [4

4. W. Fan, S. Zhang, N.-C. Panoiu, A. Abdenour, S. Krishna, R. M. Osgood Jr, K. J. Malloy, and S. R. J. Brueck, “Second harmonic generation from a nanopatterned isotropic nonlinear material,” Nano Lett. 6(5), 1027–1030 (2006). [CrossRef]

], introduces a refractive index change and a consequent spectral shift.

We assume the input pulse has a Gaussian temporal shape with FWHM τ (200 fs)Iω(t)=I0exp[4ln(2)t2τ2] [15

15. R. Schroeder and B. Ullrich, “Absorption and subsequent emission saturation of two-photon excited materials: theory and experiment,” Opt. Lett. 27(15), 1285–1287 (2002). [CrossRef] [PubMed]

]. The generated carriers, Ne = Nh, are excited from 3PA of ω(1.78 eV), as expressed in Eq. (1), is proportional to Iω3, where Iω is the laser irradiance (W/cm2). The carrier concentration is ~1020 cm−3 resulting from 3PA of 3ω(1.78 eV) with ~100 GW/cm2 input peak power. The coefficient of 3PA ρ3PA is 3.8 × 104 from each unit cell at the concentration [10

10. J. Zhang, L. Wang, S. Krishna, M. Sheik-Bahae, and S. R. J. Brueck, “Saturation of the second harmonic generation from GaAs filled metallic hole arrays by nonlinear absorption,” Phys. Rev. B 83(16), 165438 (2011). [CrossRef]

]. The nonlinear absorption coefficient of 3PA K3PA is 3 × 10−19 cm3/W2 [16

16. J. U. Kang, A. Villeneuve, M. Sheik-Bahae, G. I. Stegeman, K. Al-hemyari, J. S. Aitchison, and C. N. Ironside, “Limitation due to three-photon absorption on the useful spectral range for nonlinear optics in AlGaAs below half band gap,” Appl. Phys. Lett. 65(2), 147 (1994). [CrossRef]

,17

17. W. C. Hurlbut, Y.-S. Lee, K. L. Vodopyanov, P. S. Kuo, and M. M. Fejer, “Multiphoton absorption and nonlinear refraction of GaAs in the mid-infrared,” Opt. Lett. 32(6), 668–670 (2007). [CrossRef] [PubMed]

]. The second term on the right-hand side of Eq. (1) is set to zero for calculating the carrier concentration during the laser pulse, given no recombination during the laser pulse. The rate equation for the depletion of the fundamental intensity caused by 3PA and FCA is given in Eq. (2) [18

18. M. P. Hasselbeck, E. W. Van Stryland, and M. Sheik-Bahae, “Scaling of four-photon absorption in InAs,” J. Opt. Soc. Am. B 14(7), 1616–1624 (1997). [CrossRef]

]. The refractive index nω is 3.34. The irradiance independent hole cross section is σH = 1 × 10−16 cm2 [19

19. R. Braunstein and E. O. Kane, “Valance band structure of III-V compounds,” J. Phys. Chem. Solids 23(10), 1423–1431 (1962). [CrossRef]

].

dNedt=ρ3PAK3PA(ω,ω,ω)3ωIω3NeT1
(1)
nωctIω(t)=ρ3PAK3PA(ω,ω,ω)Iω3σh(ω)NeIω (2)
[13]
Δnbandfilling(Ne,ω)=cPπ0α(Ne,ω)α(0,ω)ω2ω2dω (3)
[9]
Δnfreecarrier(Ne,ω)=(e2λ28π2c2ε0nω)(Neme+Nh(mhh1/2+mlh1/2mhh3/2+mlh3/2)) (4)
[9]
n(Ne,ω)=n0(ω)+Δnbandfilling(Ne,ω)+Δnfreecarrier(Ne,ω)
(5)
λSPW(Ne)=Λm(Ren(Ne,ω)2εmn(Ne,ω)2+εm±sinθ) (6)
[2]
Δω=ϕt=ωLcntωLcΔntp
(7)

The high carrier concentration contributes refractive index change due to bandfilling and free carrier absorption (FCA). With the lowest energy states in the conduction band filled, electrons from the valence band require energies greater than the nominal bandgap to be optically excited into the conduction band through 3PA. Hence, there is a decrease in the absorption coefficient α(ω,Ne) at energies above the band gap [12

12. B. R. Bennett, R. A. Soref, and J. A. D. Alamo, “Carrier-induced change in refractive index of InP, GaAs, and InGaAsP,” IEEE J. Quantum Electron. 26(1), 113–122 (1990). [CrossRef]

]. The refractive index changeΔnbandfilling(Ne,2ω), due to free carrier band filling caused by the decease of the absorption coefficient, is expressed as Eq. (3), where P indicates the principal value of the integral [20

20. L. D. Landau and E. M. Lifshitz, Electrodynamics of Continuous Media (Addison-Wesley, Reading, Mass., 1960), p. 260.

]. For intrinsic GaAs bulk, the absorption coefficientα(0,ω)=Chhωωωg+Clhωωωg, at ωωg; and α(0,ω)=0at ω<ωg. ωg is the bad-gap frequency. Chh and Chh refer to heavy and light holes, respectively. Chh=1.5×1012cm1s1/2, and Clh=7.8×1011cm1s1/2 for GaAs [12

12. B. R. Bennett, R. A. Soref, and J. A. D. Alamo, “Carrier-induced change in refractive index of InP, GaAs, and InGaAsP,” IEEE J. Quantum Electron. 26(1), 113–122 (1990). [CrossRef]

]. When the conduction band is filled with electrons, the absorption coefficient is expressed asα(Ne,ω)=α0(ω)[fv(Ea)fc(Eb)] [12

12. B. R. Bennett, R. A. Soref, and J. A. D. Alamo, “Carrier-induced change in refractive index of InP, GaAs, and InGaAsP,” IEEE J. Quantum Electron. 26(1), 113–122 (1990). [CrossRef]

]. fv(Ea) is the probability of a valence band state of energy Ea being occupied by an electron and fc(Eb) is the probability of a conduction band state of energy Eb being occupied by an electron. The detailed derivation of Eq. (3) is referred in Ref [12

12. B. R. Bennett, R. A. Soref, and J. A. D. Alamo, “Carrier-induced change in refractive index of InP, GaAs, and InGaAsP,” IEEE J. Quantum Electron. 26(1), 113–122 (1990). [CrossRef]

].

The refractive index change associated with the free carriers, Δnfreecarrier(Ne,ω), is directly proportional to the concentration of electrons and holes and inversely proportional to the square of the photon energy (ω), as expressed in Eq. (4). me, mlh, mhh are the mass of electrons, heavy holes and light holes. me=0.066m0, mhh=0.45m0, mlh=0.084m0, m0=9.11×1031kg, is the free electron rest mass. The parameters for GaAs were listed in Ref [12

12. B. R. Bennett, R. A. Soref, and J. A. D. Alamo, “Carrier-induced change in refractive index of InP, GaAs, and InGaAsP,” IEEE J. Quantum Electron. 26(1), 113–122 (1990). [CrossRef]

,21

21. C. H. Henry, R. A. Logan, and K. A. Bertness, “Spectral dependence of the change in refractive index due to carrier injection in GaAs lasers,” J. Appl. Phys. 52(7), 4457–4461 (1981). [CrossRef]

].

The total index change (Eq. (5)) will introduce the wavelength shift of SPWs. The kinetic model is expressed in the Eq. (6). The shift of linear transmission peak due to the index change is approximately that of the SPW resonance [2

2. W. Fan, S. Zhang, B. Minhas, K. J. Malloy, and S. R. J. Brueck, “Enhanced infrared transmission through subwavelength coaxial metallic arrays,” Phys. Rev. Lett. 94(3), 033902 (2005). [CrossRef] [PubMed]

,3

3. J. Zhang, S. Zhang, D. Li, A. Neumann, C. Hains, A. Frauenglass, and S. R. J. Brueck, “Infrared transmission resonances in double layered, complementary-structure metallic Gratings,” Opt. Express 15, 8737–8744 (2007).

]. The linewidth of linear transmission spectrum (ranging from 1.9 to 2.7-µm) coupled by the first order SPWs is ~500 nm [10

10. J. Zhang, L. Wang, S. Krishna, M. Sheik-Bahae, and S. R. J. Brueck, “Saturation of the second harmonic generation from GaAs filled metallic hole arrays by nonlinear absorption,” Phys. Rev. B 83(16), 165438 (2011). [CrossRef]

]. The input Gaussian shaped laser pulse at the fundamental wavelength (2.09 µm) with ~70 nm linewidth is within the linear transmission spectrum of the plasmonic structure [14

14. J. Zhang, “Metallic photonic crystals: transmission resonance and second harmonic generation,” (Ph. D thesis of University of New Mexico, 2009), Chap. 4. http://repository.unm.edu/handle/1928/10357

]. The shift of the linear spectrum will reshape the input laser pulse. The wavelength of pulse peak will shift with the linear transmission spectrum. The spectral peak of λSHG=λfundamental/2is plotted in Fig. 4(a)
Fig. 4 At 297K, for the plasmon-coupled structure on a 20 µm thick GaAs substrate with surface defects by wet etching, the spectral variation of SHG and BE vs the increasing fluences in linear-log plots: (a) SHG spectrum is constant at 1045-nm with 2090-nm fundamental wavelength at low irradiance (1- to 10-GW/cm2) and shows minor refractive index changes (5-nm) at high irradiance (10- to 100-GW/cm2) and (b) BE (PL) spectrum wavelength shows optical frequency switch from 900- to 887-nm with increase of fluence from 25 to 50 GW/cm2. (c) Linewidths of the SHG spectra are unchanged from 1- to 100-GW/cm2; (d) the BE spectrum shows an averaged 45nm linewidth.
with index changed by band filling (in red) and FCA (in blue). The SHG shift due to the index change resulting from FCA is significant compared with that resulting from band filling. The fundamental intensity is magnified to the order of 10x in simulation for comparing experiment data. The difference of fundamental intensity between experiment and simulation may be due to the inaccuracy of nonlinear coefficiencies and scattering loss in instrument during measurement [10

10. J. Zhang, L. Wang, S. Krishna, M. Sheik-Bahae, and S. R. J. Brueck, “Saturation of the second harmonic generation from GaAs filled metallic hole arrays by nonlinear absorption,” Phys. Rev. B 83(16), 165438 (2011). [CrossRef]

].

The frequency linewidth due to index change, as expressed as Eq. (7), is converted to wavelength linewidth of index change ΔλλLcΔntpΔn withLctp, where tpis the time for a pulse passing through the active layer of GaAs (~100nm) [10

10. J. Zhang, L. Wang, S. Krishna, M. Sheik-Bahae, and S. R. J. Brueck, “Saturation of the second harmonic generation from GaAs filled metallic hole arrays by nonlinear absorption,” Phys. Rev. B 83(16), 165438 (2011). [CrossRef]

]. Therefore, the linewidth of the SHG spectrum is broaden with the Δn(<0) decrease under increasing fluences. The index decrease is resulted from high free carrier concentration pumped by increased input peak power. The broaden linewidth of SHG from Eq. (7) fits the experimental data trend as shown in Fig. 4(c).

3. Carrier recombination from plasmon-coupled hole arrays on a 20 µm wet etched GaAs substrate at 297K

A ~2 mm diameter hole was etched from back side of the sample by using a solution of H2SO4: H2O2: H2O (1:8:1). The remaining GaAs substrate under the plasmonic structure was ~20 µm thick with a mirror like etched surface full of submicron scale porous and particles. The serious surface defects are likely to be damage to the GaAs giving rise to a decrease in nonradiative recombination time τNR compared to bulk material [10

10. J. Zhang, L. Wang, S. Krishna, M. Sheik-Bahae, and S. R. J. Brueck, “Saturation of the second harmonic generation from GaAs filled metallic hole arrays by nonlinear absorption,” Phys. Rev. B 83(16), 165438 (2011). [CrossRef]

].

The line-width integrated BE and SH intensities versus fundamental intensity are plotted in Fig. 3
Fig. 3 (a) At 297K, for the plasmon-coupled structure on a 20 µm wet etched GaAs substrate with surface defects, SHG intensity (solid square) I ∝ Iω2 at input peak power < 10 GW/cm2, and then I ∝ Iω0.7 at input peak power > 10 GW/cm2; The BE intensity (unfilled square) showed IBE ∝ Iω2.5at input peak power from 10- to 25 GW/cm2, IBE ∝ Iω9 at input peak powers from 25- to 40 GW/cm2, and IBE ∝ Iω2.6at fundamental power > 40 GW/cm2. (b) The simulated radiative recombination carrier density vs. input peak power with τNR = 0.1 ns in log-log plot.
in a log-log coordination. At 297 K, the SHG saturates at the same threshold input peak power, ~10 GW/cm2, as that for the plasmon-coupled structure on pre-epi GaAs substrate. However, the PL intensity shows a trend from 3rd, to 9th, and back to 3rd order dependence on the incident fluence. The BE intensity shows IBE ∝ Iω2.5at fundamental power from 10 to 25-GW/cm2. It is then strongly enhanced at fundamental power from 25 to 40-GW/cm2 with 9th order fundamental intensity dependence, compared with the signal from the plasmon-coupled structure on the pre-epi GaAs substrate with 3rd order fundamental intensity dependence, even under 3PA excitation [10

10. J. Zhang, L. Wang, S. Krishna, M. Sheik-Bahae, and S. R. J. Brueck, “Saturation of the second harmonic generation from GaAs filled metallic hole arrays by nonlinear absorption,” Phys. Rev. B 83(16), 165438 (2011). [CrossRef]

]. The BE power scales back as IBE ∝ Iω2.6at the input peak power higher than 40 GW/cm2. The trend of BE intensity vs. input peak power, as been done in Ref [10

10. J. Zhang, L. Wang, S. Krishna, M. Sheik-Bahae, and S. R. J. Brueck, “Saturation of the second harmonic generation from GaAs filled metallic hole arrays by nonlinear absorption,” Phys. Rev. B 83(16), 165438 (2011). [CrossRef]

], is due to the transition from nonradiative to bimolecular radiative-dominated carrier recombination. The radiative recombination carrier density vs. input peak power with τNR = 0.1 ns, simulated and plotted in Fig. 3(b), as done in Ref [10

10. J. Zhang, L. Wang, S. Krishna, M. Sheik-Bahae, and S. R. J. Brueck, “Saturation of the second harmonic generation from GaAs filled metallic hole arrays by nonlinear absorption,” Phys. Rev. B 83(16), 165438 (2011). [CrossRef]

], shows the transition from nonradiative at low excitation to bimolecular recombination at high carrier concentrations. The model explained the experimental data clearly.

The SHG spectrum peaks and BE spectrum peaks wavelength vs input peak power were plotted in linear-log plots in Fig. 4s. As shown in Fig. 4(a), the SHG spectral wavelength is constant at fluences from 1- to 10-GW/cm2, and then blue shifts slightly at fluences from 10- to 100-GW/cm2 due to the band filling induced refractive index change, as simulated in Fig. 2(a). In Fig. 4(b), the wavelength of PL peaks shows switch trend which consists with trend of the BE intensity dependence of fluences as shown in Fig. 3(a). The PL happens at ~900-nm at low fluences (10- to 25- GW/cm2), blueshifts to 887-nm rapidly with input peak power > 50-GW/cm2. The linewidth of SHG, as shown in Fig. 4(c) is constant with increasing peak power due to slightly varied refractive index compared with the plasmonic structure on pre-epi GaAs substrate. The linewidth of PL is as broad as 45-nm in Fig. 4(d) due to the surface state density.

4. Carrier recombination from plasmon-coupled hole arrays on a 20 µm wet etched GaAs substrate at 77K

For the plasmonic structure on 20 µm wet etched GaAs substrate, when the sample is cooled down to 77K, the SHG spectral peak and BE spectral peak are constant with increasing input peak power as shown in Fig. 5(a) and 5(b). The temperature dependent PL wavelength blue shifts to 827 nm (77K), following Eg(T)=1.5195.41T2/(T+204) in eV for GaAs. The FWHM of SHG and BE spectra are constant at 20- and 10-nm with increasing input peak power as shown in Fig. 5(c) and 5(d), respectively. The reduced linewidth of SHG and BE is due to the decrease of the nonradiative radiation and defects scattering at low temperature.

5. Conclusion

GaAs filled subwavelength metallic hole arrays on a pre-epi GaAs substrate, pumped with a fs-duration near-infrared wavelength laser at 297K, produces SHG that saturates as a result of three-photon band-to-band and free carrier intraband absorption. Free carriers, excited by 3PA with the coefficient of 3PA ρ3PA = 3.8 × 104 from each unit cell due to local field enhancement, induce refractive index change at high carrier concentration (1020/cm2) which blue shifts and broadens the SHG resonance linewidth. The subwavelength periodic structure on a wet etched thin GaAs substrate with surface defects shows carrier recombination emission that shifts with excitation from low frequency (902-nm) to high frequency (886-nm) with fluences from 25- to 50-GW/cm2 at 297K, resulting from a transition from nonradiative carrier recombination at the defected GaAs surface at low excitation to bimolecular recombination at high carrier concentrations.

Acknowledgments

This work was supported by the National Science Foundation under Grant 0515684 and by the ARO under a subcontract from Redondo Optics, Inc.

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R. Schroeder and B. Ullrich, “Absorption and subsequent emission saturation of two-photon excited materials: theory and experiment,” Opt. Lett. 27(15), 1285–1287 (2002). [CrossRef] [PubMed]

16.

J. U. Kang, A. Villeneuve, M. Sheik-Bahae, G. I. Stegeman, K. Al-hemyari, J. S. Aitchison, and C. N. Ironside, “Limitation due to three-photon absorption on the useful spectral range for nonlinear optics in AlGaAs below half band gap,” Appl. Phys. Lett. 65(2), 147 (1994). [CrossRef]

17.

W. C. Hurlbut, Y.-S. Lee, K. L. Vodopyanov, P. S. Kuo, and M. M. Fejer, “Multiphoton absorption and nonlinear refraction of GaAs in the mid-infrared,” Opt. Lett. 32(6), 668–670 (2007). [CrossRef] [PubMed]

18.

M. P. Hasselbeck, E. W. Van Stryland, and M. Sheik-Bahae, “Scaling of four-photon absorption in InAs,” J. Opt. Soc. Am. B 14(7), 1616–1624 (1997). [CrossRef]

19.

R. Braunstein and E. O. Kane, “Valance band structure of III-V compounds,” J. Phys. Chem. Solids 23(10), 1423–1431 (1962). [CrossRef]

20.

L. D. Landau and E. M. Lifshitz, Electrodynamics of Continuous Media (Addison-Wesley, Reading, Mass., 1960), p. 260.

21.

C. H. Henry, R. A. Logan, and K. A. Bertness, “Spectral dependence of the change in refractive index due to carrier injection in GaAs lasers,” J. Appl. Phys. 52(7), 4457–4461 (1981). [CrossRef]

OCIS Codes
(190.4350) Nonlinear optics : Nonlinear optics at surfaces
(310.6628) Thin films : Subwavelength structures, nanostructures

ToC Category:
Nonlinear Optics

History
Original Manuscript: January 23, 2012
Revised Manuscript: February 28, 2012
Manuscript Accepted: March 4, 2012
Published: March 13, 2012

Citation
Jingyu Zhang, Bin Xiang, Mansoor Sheik-Bahae, and S. R. J. Brueck, "Free carrier induced spectral shift for GaAs filled metallic hole arrays," Opt. Express 20, 7142-7150 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-7-7142


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References

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  14. J. Zhang, “Metallic photonic crystals: transmission resonance and second harmonic generation,” (Ph. D thesis of University of New Mexico, 2009), Chap. 4. http://repository.unm.edu/handle/1928/10357
  15. R. Schroeder and B. Ullrich, “Absorption and subsequent emission saturation of two-photon excited materials: theory and experiment,” Opt. Lett.27(15), 1285–1287 (2002). [CrossRef] [PubMed]
  16. J. U. Kang, A. Villeneuve, M. Sheik-Bahae, G. I. Stegeman, K. Al-hemyari, J. S. Aitchison, and C. N. Ironside, “Limitation due to three-photon absorption on the useful spectral range for nonlinear optics in AlGaAs below half band gap,” Appl. Phys. Lett.65(2), 147 (1994). [CrossRef]
  17. W. C. Hurlbut, Y.-S. Lee, K. L. Vodopyanov, P. S. Kuo, and M. M. Fejer, “Multiphoton absorption and nonlinear refraction of GaAs in the mid-infrared,” Opt. Lett.32(6), 668–670 (2007). [CrossRef] [PubMed]
  18. M. P. Hasselbeck, E. W. Van Stryland, and M. Sheik-Bahae, “Scaling of four-photon absorption in InAs,” J. Opt. Soc. Am. B14(7), 1616–1624 (1997). [CrossRef]
  19. R. Braunstein and E. O. Kane, “Valance band structure of III-V compounds,” J. Phys. Chem. Solids23(10), 1423–1431 (1962). [CrossRef]
  20. L. D. Landau and E. M. Lifshitz, Electrodynamics of Continuous Media (Addison-Wesley, Reading, Mass., 1960), p. 260.
  21. C. H. Henry, R. A. Logan, and K. A. Bertness, “Spectral dependence of the change in refractive index due to carrier injection in GaAs lasers,” J. Appl. Phys.52(7), 4457–4461 (1981). [CrossRef]

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