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Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 15 — Jul. 16, 2012
  • pp: 16504–16509

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THz generation using extrinsic photoconductivity at 1550 nm

J. R. Middendorf and E. R. Brown  »View Author Affiliations


Optics Express, Vol. 20, Issue 15, pp. 16504-16509 (2012)
http://dx.doi.org/10.1364/OE.20.016504


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Abstract

1550-nm pulses from a fiber-mode-locked laser are used to drive an ErAs:GaAs photoconductive switch, resulting in easily measured THz radiation with average broadband (~0.1 to 1.0 THz) power of ≈0.1 mW. The new THz switching mechanism is attributed to fast extrinsic photoconductivity that generates photocarriers (probably electrons) from the ErAs nanoparticles embedded in the material with a lifetime of ~0.45 ps (354 GHz bandwidth). This is the first known demonstration of useful THz power generation by extrinsic photoconductivity.

© 2012 OSA

1. Introduction and background

The quest continues to develop ultrafast phototoconductive (PC) THz sources that can be driven by fiber-optic lasers and components preferably at the 1550-nm (EDFA) or 1030-nm (YDFA) wavelengths. Progress has been steady on PC switches and photomixers for time- and frequency-domain applications, respectively, the most common approach being devices fabricated on InGaAs- or InGaAsP epitaxial layers on InP substrates to reduce the band-gap energy (UG) below the 1550-nm photon (~0.75 eV) and utilize cross-gap (intrinsic) photoconductivity. THz performance has been achieved using a variety of ultrafast recombination mechanisms mostly based on homogeneous or inhomogeneous distributions of metallic nanoparticles or deep defect levels. This includes As precipitates from low-temperature (LT) MBE growth and anneal [1

S. Gupta, J. F. Whitaker, and G. A. Mourou, “Ultrafast carrier dynamics in III-V-semiconductors grown by molecular beam epitaxy at very low substrate temperatures,” IEEE J. Quantum Electron. 28(10), 2464–2472 (1992). [CrossRef]

,2

A. Takazato, M. Kamakura, T. Matsui, J. Kitagawa, and Y. Kadoya, “Detection of terahertz waves using low-temperature-grown InGaAs with 1.56 μm pulse excitation,” Appl. Phys. Lett. 90(10), 101119 (2007). [CrossRef]

], ErAs nanoparticles from normal-temperature MBE [3

D. C. Driscoll, M. P. Hanson, A. C. Gossard, and E. R. Brown, “Ultrafast photoresponse at 1.55μm in InGaAs with embedded semimetallic ErAs nanoparticles,” Appl. Phys. Lett. 86(5), 051908 (2005). [CrossRef]

,4

F. Ospald, D. Maryenko, K. von Klitzing, D. C. Driscoll, M. P. Hanson, H. Lu, A. C. Gossard, and J. H. Smet, “1.55 μm ultrafast photoconductive switches based on ErAs:InGaAs,” Appl. Phys. Lett. 92, 131117 (2008).

], Br-irradiated defects [5

N. Chimot, J. Mangeney, L. Joulaud, P. Crozat, H. Bernas, K. Blary, and J. F. Lampin, “Terahertz radiation from heavy-ion-irradiated InGaAs photoconductive antenna excited at 1.55μm,” Appl. Phys. Lett. 87(19), 193510 (2005). [CrossRef]

], Fe-ion-implanted deep levels [6

M. Suzuki and M. Tonouchi, “Fe-implanted InGaAs terahertz emitters for 1.56μm wavelength excitation,” Appl. Phys. Lett. 86(5), 051104 (2005). [CrossRef]

,7

A. Fekecs, M. Bernier, D. Morris, M. Chicoine, F. Schiettekatte, P. Charette, and R. Arès, “Fabrication of high resistivity cold-implanted InGaAsP photoconductors for efficient pulsed terahertz devices,” Opt. Mater. Express 1(7), 1165–1177 (2011). [CrossRef]

], and standard InGaAs layers with the defects located in intervening InAlAs barriers [8

R. J. B. Dietz, M. Gerhard, D. Stanze, M. Koch, B. Sartorius, and M. Schell, “THz generation at 1.55 µm excitation: six-fold increase in THz conversion efficiency by separated photoconductive and trapping regions,” Opt. Express 19(27), 25911–25917 (2011). [CrossRef] [PubMed]

]. The problem with all such approaches is critical breakdown field (EC) and the associated dark current. PC switches and photomixers alike display nearly quadratic dependence of THz power on DC bias, so that high EC is crucial. From semiconductor physics, EC tends to vary with band-gap energy superlinearly and studies have yielded universal empirical relationships such as EC = 1.73x105 (UG)2.5 [V/cm, UG in eV] for low-doped direct-band-gap materials [9

J. L. Hudgins, G. S. Simin, E. Santi, and M. S. Khan, “An Assesment of Wide Bandgap Semiconductors for Power Devices,” IEEE Trans. Power Electron. 18(3), 907–914 (2003). [CrossRef]

]. Hence, the difference between the GaAs EC (UG = 1.42 eV) and InGaAs EC is 4.9x, which is rather close to observed difference in maximum bias voltage between homogeneous GaAs and InGaAs ultrafast PC devices. The addition of epitaxial InAlAs barriers enhances the bias standoff of InGaAs devices, but does not prevent breakdown in the lateral direction [8

R. J. B. Dietz, M. Gerhard, D. Stanze, M. Koch, B. Sartorius, and M. Schell, “THz generation at 1.55 µm excitation: six-fold increase in THz conversion efficiency by separated photoconductive and trapping regions,” Opt. Express 19(27), 25911–25917 (2011). [CrossRef] [PubMed]

].

A tempting alternative is to use GaAs with 1030 or 1550-nm drive lasers and utilize sub-band-gap photon absorption mechanisms via the high concentration of defect- or impurity-levels that ultrafast materials generally have. In pulsed-mode, for example, attempts have been made to utilize two-photon absorption and sup-ps recombination via the mid-gap states associated with As-precipitates in low-temperature (LT) GaAs [10

P. Grenier and J. F. Whitaker, “Subband gap carrier dynamics in low-temperature-grown GaAs,” Appl. Phys. Lett. 70(15), 1998–2000 (1997). [CrossRef]

,11

H. Erlig, S. Wang, T. Azfar, A. Udupa, H. R. Fetterman, and D. C. Streit, “LT-GaAs detector with 451 fs response at 1.55-µm via two-photon absorption,” Electron. Lett. 35(2), 173–174 (1999). [CrossRef]

]. This was then used to demonstrate a PC switch, but the resulting photoconductivity was found to be impractically weak compared to the intrinsic cross-gap effect. In cw mode attempts have been made to overcome the weak 1550-nm absorption by embedding the LT GaAs in a dielectric-waveguide, distributed pin photodiode [12

Y.-J. Chiu, S. Z. Zhang, S. B. Fleischer, J. E. Bowers, and U. K. Mishra, “GaAs-based 1.55- μm high speed, high saturation power, low-temperature grown GaAs pin photodetector,” Electron. Lett. 34(12), 1253–1255 (1998). [CrossRef]

]. But the waveguide length required for strong absorption reduces the electrical bandwidth because of difficulties in velocity matching the photonic and RF waves.

2. Basic characteristics

In this work we demonstrate a much stronger mechanism for driving an ultrafast GaAs PC switch with 1550-nm pulses. The ultrafast material is ErAs:GaAs [13

C. Kadow, S. B. Fleischer, J. P. Ibbetson, J. E. Bowers, J. W. Dong, and C. J. Palmstrom, “Self assembled ErAs islands in GaAs: Growth and subpicosecond carrier dynamics,” Appl. Phys. Lett. 75(22), 3548–3550 (1999). [CrossRef]

], an ultrafast photoconductor newer than LT GaAs and one that has shown excellent performance both as a photomixer [14

J. E. Bjarnason, T. L. J. Chan, A. W. M. Lee, E. R. Brown, D. C. Driscoll, M. Hanson, A. C. Gossard, and R. E. Muller, “ErAs:GaAs photomixer with two-decade tunability and 12 µW peak output power,” Appl. Phys. Lett. 85(18), 3983 (2004). [CrossRef]

] and as a PC switch [15

Z. D. Taylor, E. R. Brown, J. E. Bjarnason, M. P. Hanson, and A. C. Gossard, “Resonant-optical-cavity photoconductive switch with 0.5% conversion efficiency and 1.0 W peak power,” Opt. Lett. 31(11), 1729–1731 (2006). [CrossRef] [PubMed]

]. In comparative PC-switch studies, it has also been shown unequivocally to be superior to LT GaAs when driven with ~780-nm cross-gap lasers [16

F. O’Hara, J. M. O. Zide, A. C. Gossard, A. J. Taylor, and R. D. Averitt, “Enhanced terahertz detection via ErAs:GaAs nanoisland superlattices,” Appl. Phys. Lett. 88(25), 251119 (2006). [CrossRef]

]. For the present experiments we tested switches consisting of a 1.0-micron thick, homogeneous 1%-Er-bearing GaAs films grown by molecular-beam epitaxy on semi-insulating GaAs substrates. The PC switch shown in Fig. 1 consisted of a 9x9 micron gap at the center gap of a 3-turn square-spiral antenna. Laser light from a standard 1550-nm EDFA mode-locked laser was focused onto the gap using a fiber-to-free-space coupler and microscope objective. The laser has a pulse width of ~300 fs, a repetition rate of 36.7 MHz, and a maximum average power of 140 mW. THz radiation emanating from the spiral antenna was coupled into free space using a high-resistivity silicon hyperhemispherical lens.

Fig. 1 ErAs:GaAs PC switch with 9x9 micron center gap.

We first measured the DC photocurrent as a function of bias voltage VB with a fixed 1550-nm power of 140 mW. As shown in Fig. 2(a) , photocurrent approaches zero as VB →0, as expected for any photoconductive effect. We then measured the DC photocurrent versus drive power P0 with the bias voltage fixed at 77 V. As shown in Fig. 2(b), this is concave-down at low P0 but quasi-linear behavior at higher power. This is in contrast to the quadratic-up behavior displayed by LTG-GaAs switches with 1550-nm drive [11

H. Erlig, S. Wang, T. Azfar, A. Udupa, H. R. Fetterman, and D. C. Streit, “LT-GaAs detector with 451 fs response at 1.55-µm via two-photon absorption,” Electron. Lett. 35(2), 173–174 (1999). [CrossRef]

]. The associated current responsivity in Fig. 2(b) at the lowest P0 is ℜ ≈5 μA/mW, but at the highest P0 drops to ≈1.0 μA/mW. This latter is only about 4-times less than the ℜ from an identical type of PC switch (same ErAs:GaAs material) measured at the same VB with a sub-ps pulsed laser source emitting around 780 nm. It suggests that the 1550-nm drive should produce measurable THz power, assuming of course that the bandwidth associated with the new photoconductive mechanism is comparable to that of the traditional intrinsic, cross-gap effect.

Fig. 2 (a) Photocurrent vs bias voltage with 1550-nm laser at maximum power (140 mW). (b) DC photocurrent vs average 1550-nm laser power at a fixed bias voltage of 77 V.

3. THz measurements

We proceeded with the THz power measurements starting with a broadband, calibrated LiTaO3 pyroelectric detector with a 0.01-in black polyethylene window to block 1550-nm leakage and thermal IR radiation. The experimental results for broadband THz power vs VB and P0 are plotted in Figs. 3(a) and 3(b), respectively. The vertical scale in both plots is rms (lock-in amplifier readings). Correcting for the rms reading, we obtain an equivalent peak-to-peak reading of 520 mV (confirmed on an oscilloscope). The pyroelectric detector has a calibrated, broadband external responsivity of ≈5000 V/W between 0.1 and 1.0 THz. So the maximum power measured from the switch is ≈105 μW. This is comparable to the broadband THz power measured from an identical type of switch (same ErAs:GaAs material) at the same VB, but driven with 25 mW of average power from the 780-nm sub-ps pulsed laser source. Hence, the new 1550-nm-driven photoconductive mechanism is about 5-times less efficient in terms of THz-to-laser power ratio. The dependence of THz power on VB and P0 is also somewhat different than the 780-nm-driven switch. The bias-dependence in Fig. 3(a) is close to quadratic (see fit curve) and power-dependence is weaker, PTHz ≈(P0)1.6. The 780-nm performance is usually the opposite with PTHz varying close to quadratic with P0 and slower with VB.

Fig. 3 (a) AC signal (rms) from THz pyroelectric detector vs bias voltage with a constant 1550-nm laser power of 140 mW. (b) AC signal (rms) from same detector vs 1550-nm average laser power at a constant bias of 77 V.

As a rough estimate of the bandwidth of the 1550-nm-driven PC switch, we carried out power measurements using a set of Schottky-diode zero-bias rectifiers mounted in rectangular waveguide and operating in three distinct bands centered around 92 (W-band), 415, and 675 GHz. These rectifiers act as band-limited filters with very sharp low-frequency turn-on (waveguide cutoff) and more gradual high-frequency rolloff. This enables a discrete estimate of the THz switch power spectrum knowing the external responsivity of the rectifiers and their noise equivalent bandwidth. The data is plotted in Fig. 4 , normalized to the signal from the lowest-frequency rectifier.

Fig. 4 AC Signal from THz pyroelectric detector vs frequency at a constant bias of 77 V and constant 1550-nm laser power of 140mW.

The bandwidth is obtained by fitting the discrete spectrum to a single-pole Lorentzian function, S(f) = A/[1 + (2πfτ)2]−1, where A is a constant and τ is the photocarrier lifetime. This has been found to be a good fit to the THz power spectrum of PC switches whose photocarrier lifetime is significantly longer than the RC electrical time constant – a likely condition in our case since the gap capacitance of the switch is << 1 fF. For the experimental data in Fig. 4, the best fit to the data occurs when A = 1.08 and τ = 0.45 ps, This corresponds to a −3-dB frequency-domain bandwidth of B = (2πτ)−1 = 354 GHz, which is comparable to the bandwidth deduced from 780-nm time-domain measurements for the identical type of switch (same ErAs:GaAs material and antenna) with a 780-nm femtosecond laser [17

T. Tongue, Zomega Terahertz Corp., 15 Tech Valley Dr., Suite 102, East Greenbush, NY 12061, private correspondence.

]. However the laser pulse in our experiments (300 fs) is considerably longer than that used at 780 nm, so that the fundamental bandwidth of our switch could be even higher than 354 GHz.

4. Physical interpretation

All of the results presented here are consistent with the new 1550-nm-driven PC switch mechanism being extrinsic photoconductivity rather than the traditional intrinsic (cross-gap) photoconductivity. Extrinsic photoconductivity is distinguished by a transition from a localized-impurity or defect energy level to the closest energy band (conduction or valence), and then subsequent unipolar photocarrier transport (electron or hole) within that band [18

P. Kruse, “Optical and Infrared Detectors” in Optical and Infrared Detectors, 19, 5–69 (Springer, 1980).

]. It is well known in doped GaAs and has long been utilized to make high-power PC switches operating at the ~10-ps time scale [19

J. Yuan, W. Xie, H. Liu, J. Liu, H. Li, X. Wang, and W. Jiang, “High-Power Semi-Insulating GaAs Photoconductive Semiconductor Switch Employing Extrinsic Photoconductivity,” IEEE Trans. Plasma Sci. 37(10), 1959–1963 (2009). [CrossRef]

]. Through growth conditions discovered in Ref [20

K. E. Singer, P. Rutter, A. R. Peaker, and A. C. Wright, “Self-organizing growth of erbium arsenide quantum does and wires in gallium arsenide by molecular beam epitaxy,” Appl. Phys. Lett. 64(6), 707–709 (1994). [CrossRef]

], the present PC switch material contains ErAs in the form of crystalline nanoparticles, and these nanoparticles are associated with a very large density of energy levels near the middle of the GaAs bandgap. This explains the sub-ps electron-hole photocarrier lifetime in intrinsic operation, and should explain the fast extrinsic operation through a large capture cross section for electrons or holes, as the case may be. The ErAs nanoparticules have also been found to display sub-band-gap absorption that reaches a peak strength around λ = 2.5 μm, either through a particle-plasmon [21

E. R. Brown, A. Bacher, D. Driscoll, M. Hanson, C. Kadow, and A. C. Gossard, “Evidence for a strong surface-plasmon resonance on ErAs nanoparticles in GaAs,” Phys. Rev. Lett. 90(7), 077403 (2003). [CrossRef] [PubMed]

], or quantum-dot resonance.

From the work presented here, we can only speculate on the exact absorption mechanism. However, we know with certainty that it creates photocarriers, which in turn exhibit good electrical transport (i.e., good mobility) and the sub-picosecond lifetime necessary to generate useful levels of THz radiation in photoconductive switches. In GaAs this would favor electrons over holes because of their superior band transport. In any case, the absorption coefficient is likely much weaker than the cross-gap value around 780 nm, which is typically ~104 cm−1. And this would partially explain the 4-times lower external current responsivity and 5-times lower laser-to-THz conversion efficiency of the 1550-nm-driven switch. But lower absorption has a beneficial aspect which is more gradual photocarrier and thermal generation with depth than normally occurs in GaAs photoconductive devices. This should help improve the reliability and maximum drive power, which are often limited by electric and/or thermal stress at the surface of planar photoconductive devices. And the fact remains that 1550-nm photons are much more affordable than 780-nm photons, and much easier to route and control via the wide variety of active and passive components available from the fiber-optic telecomm industry.

5. Conclusion

We have shown that an ErAs:GaAs photoconductive switch can demonstrate useful levels of THz power when driven by an ultrafast 1550-nm fiber-mode-locked laser. The external responsivity and THz generation efficiency are lower than those in the same switch driven by 780 nm sub-ps pulses, but the absolute THz power level is comparable. The likely mechanism for the 1550-nm excitation is extrinsic n-type (electron) photoconductivity from the ErAs-nanoparticles to the conduction band, although more research is necessary to prove this unequivocally.

Acknowledgments

This work was sponsored by Wright State University through a Grant from the Ohio Board of Regents, and the Center for Surveillance Research at the Ohio State University – a consortium of U.S. Air Force, NSF, and Industrial partners.

References and links

1.

S. Gupta, J. F. Whitaker, and G. A. Mourou, “Ultrafast carrier dynamics in III-V-semiconductors grown by molecular beam epitaxy at very low substrate temperatures,” IEEE J. Quantum Electron. 28(10), 2464–2472 (1992). [CrossRef]

2.

A. Takazato, M. Kamakura, T. Matsui, J. Kitagawa, and Y. Kadoya, “Detection of terahertz waves using low-temperature-grown InGaAs with 1.56 μm pulse excitation,” Appl. Phys. Lett. 90(10), 101119 (2007). [CrossRef]

3.

D. C. Driscoll, M. P. Hanson, A. C. Gossard, and E. R. Brown, “Ultrafast photoresponse at 1.55μm in InGaAs with embedded semimetallic ErAs nanoparticles,” Appl. Phys. Lett. 86(5), 051908 (2005). [CrossRef]

4.

F. Ospald, D. Maryenko, K. von Klitzing, D. C. Driscoll, M. P. Hanson, H. Lu, A. C. Gossard, and J. H. Smet, “1.55 μm ultrafast photoconductive switches based on ErAs:InGaAs,” Appl. Phys. Lett. 92, 131117 (2008).

5.

N. Chimot, J. Mangeney, L. Joulaud, P. Crozat, H. Bernas, K. Blary, and J. F. Lampin, “Terahertz radiation from heavy-ion-irradiated InGaAs photoconductive antenna excited at 1.55μm,” Appl. Phys. Lett. 87(19), 193510 (2005). [CrossRef]

6.

M. Suzuki and M. Tonouchi, “Fe-implanted InGaAs terahertz emitters for 1.56μm wavelength excitation,” Appl. Phys. Lett. 86(5), 051104 (2005). [CrossRef]

7.

A. Fekecs, M. Bernier, D. Morris, M. Chicoine, F. Schiettekatte, P. Charette, and R. Arès, “Fabrication of high resistivity cold-implanted InGaAsP photoconductors for efficient pulsed terahertz devices,” Opt. Mater. Express 1(7), 1165–1177 (2011). [CrossRef]

8.

R. J. B. Dietz, M. Gerhard, D. Stanze, M. Koch, B. Sartorius, and M. Schell, “THz generation at 1.55 µm excitation: six-fold increase in THz conversion efficiency by separated photoconductive and trapping regions,” Opt. Express 19(27), 25911–25917 (2011). [CrossRef] [PubMed]

9.

J. L. Hudgins, G. S. Simin, E. Santi, and M. S. Khan, “An Assesment of Wide Bandgap Semiconductors for Power Devices,” IEEE Trans. Power Electron. 18(3), 907–914 (2003). [CrossRef]

10.

P. Grenier and J. F. Whitaker, “Subband gap carrier dynamics in low-temperature-grown GaAs,” Appl. Phys. Lett. 70(15), 1998–2000 (1997). [CrossRef]

11.

H. Erlig, S. Wang, T. Azfar, A. Udupa, H. R. Fetterman, and D. C. Streit, “LT-GaAs detector with 451 fs response at 1.55-µm via two-photon absorption,” Electron. Lett. 35(2), 173–174 (1999). [CrossRef]

12.

Y.-J. Chiu, S. Z. Zhang, S. B. Fleischer, J. E. Bowers, and U. K. Mishra, “GaAs-based 1.55- μm high speed, high saturation power, low-temperature grown GaAs pin photodetector,” Electron. Lett. 34(12), 1253–1255 (1998). [CrossRef]

13.

C. Kadow, S. B. Fleischer, J. P. Ibbetson, J. E. Bowers, J. W. Dong, and C. J. Palmstrom, “Self assembled ErAs islands in GaAs: Growth and subpicosecond carrier dynamics,” Appl. Phys. Lett. 75(22), 3548–3550 (1999). [CrossRef]

14.

J. E. Bjarnason, T. L. J. Chan, A. W. M. Lee, E. R. Brown, D. C. Driscoll, M. Hanson, A. C. Gossard, and R. E. Muller, “ErAs:GaAs photomixer with two-decade tunability and 12 µW peak output power,” Appl. Phys. Lett. 85(18), 3983 (2004). [CrossRef]

15.

Z. D. Taylor, E. R. Brown, J. E. Bjarnason, M. P. Hanson, and A. C. Gossard, “Resonant-optical-cavity photoconductive switch with 0.5% conversion efficiency and 1.0 W peak power,” Opt. Lett. 31(11), 1729–1731 (2006). [CrossRef] [PubMed]

16.

F. O’Hara, J. M. O. Zide, A. C. Gossard, A. J. Taylor, and R. D. Averitt, “Enhanced terahertz detection via ErAs:GaAs nanoisland superlattices,” Appl. Phys. Lett. 88(25), 251119 (2006). [CrossRef]

17.

T. Tongue, Zomega Terahertz Corp., 15 Tech Valley Dr., Suite 102, East Greenbush, NY 12061, private correspondence.

18.

P. Kruse, “Optical and Infrared Detectors” in Optical and Infrared Detectors, 19, 5–69 (Springer, 1980).

19.

J. Yuan, W. Xie, H. Liu, J. Liu, H. Li, X. Wang, and W. Jiang, “High-Power Semi-Insulating GaAs Photoconductive Semiconductor Switch Employing Extrinsic Photoconductivity,” IEEE Trans. Plasma Sci. 37(10), 1959–1963 (2009). [CrossRef]

20.

K. E. Singer, P. Rutter, A. R. Peaker, and A. C. Wright, “Self-organizing growth of erbium arsenide quantum does and wires in gallium arsenide by molecular beam epitaxy,” Appl. Phys. Lett. 64(6), 707–709 (1994). [CrossRef]

21.

E. R. Brown, A. Bacher, D. Driscoll, M. Hanson, C. Kadow, and A. C. Gossard, “Evidence for a strong surface-plasmon resonance on ErAs nanoparticles in GaAs,” Phys. Rev. Lett. 90(7), 077403 (2003). [CrossRef] [PubMed]

OCIS Codes
(160.5140) Materials : Photoconductive materials
(230.6080) Optical devices : Sources
(260.5150) Physical optics : Photoconductivity
(320.7080) Ultrafast optics : Ultrafast devices
(350.5610) Other areas of optics : Radiation
(300.6495) Spectroscopy : Spectroscopy, teraherz

ToC Category:
Ultrafast Optics

History
Original Manuscript: February 28, 2012
Revised Manuscript: March 29, 2012
Manuscript Accepted: March 30, 2012
Published: July 6, 2012

Citation
J. R. Middendorf and E. R. Brown, "THz generation using extrinsic photoconductivity at 1550 nm," Opt. Express 20, 16504-16509 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-15-16504


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References

  1. S. Gupta, J. F. Whitaker, and G. A. Mourou, “Ultrafast carrier dynamics in III-V-semiconductors grown by molecular beam epitaxy at very low substrate temperatures,” IEEE J. Quantum Electron.28(10), 2464–2472 (1992). [CrossRef]
  2. A. Takazato, M. Kamakura, T. Matsui, J. Kitagawa, and Y. Kadoya, “Detection of terahertz waves using low-temperature-grown InGaAs with 1.56 μm pulse excitation,” Appl. Phys. Lett.90(10), 101119 (2007). [CrossRef]
  3. D. C. Driscoll, M. P. Hanson, A. C. Gossard, and E. R. Brown, “Ultrafast photoresponse at 1.55μm in InGaAs with embedded semimetallic ErAs nanoparticles,” Appl. Phys. Lett.86(5), 051908 (2005). [CrossRef]
  4. F. Ospald, D. Maryenko, K. von Klitzing, D. C. Driscoll, M. P. Hanson, H. Lu, A. C. Gossard, and J. H. Smet, “1.55 μm ultrafast photoconductive switches based on ErAs:InGaAs,” Appl. Phys. Lett.92, 131117 (2008).
  5. N. Chimot, J. Mangeney, L. Joulaud, P. Crozat, H. Bernas, K. Blary, and J. F. Lampin, “Terahertz radiation from heavy-ion-irradiated InGaAs photoconductive antenna excited at 1.55μm,” Appl. Phys. Lett.87(19), 193510 (2005). [CrossRef]
  6. M. Suzuki and M. Tonouchi, “Fe-implanted InGaAs terahertz emitters for 1.56μm wavelength excitation,” Appl. Phys. Lett.86(5), 051104 (2005). [CrossRef]
  7. A. Fekecs, M. Bernier, D. Morris, M. Chicoine, F. Schiettekatte, P. Charette, and R. Arès, “Fabrication of high resistivity cold-implanted InGaAsP photoconductors for efficient pulsed terahertz devices,” Opt. Mater. Express1(7), 1165–1177 (2011). [CrossRef]
  8. R. J. B. Dietz, M. Gerhard, D. Stanze, M. Koch, B. Sartorius, and M. Schell, “THz generation at 1.55 µm excitation: six-fold increase in THz conversion efficiency by separated photoconductive and trapping regions,” Opt. Express19(27), 25911–25917 (2011). [CrossRef] [PubMed]
  9. J. L. Hudgins, G. S. Simin, E. Santi, and M. S. Khan, “An Assesment of Wide Bandgap Semiconductors for Power Devices,” IEEE Trans. Power Electron.18(3), 907–914 (2003). [CrossRef]
  10. P. Grenier and J. F. Whitaker, “Subband gap carrier dynamics in low-temperature-grown GaAs,” Appl. Phys. Lett.70(15), 1998–2000 (1997). [CrossRef]
  11. H. Erlig, S. Wang, T. Azfar, A. Udupa, H. R. Fetterman, and D. C. Streit, “LT-GaAs detector with 451 fs response at 1.55-µm via two-photon absorption,” Electron. Lett.35(2), 173–174 (1999). [CrossRef]
  12. Y.-J. Chiu, S. Z. Zhang, S. B. Fleischer, J. E. Bowers, and U. K. Mishra, “GaAs-based 1.55- μm high speed, high saturation power, low-temperature grown GaAs pin photodetector,” Electron. Lett.34(12), 1253–1255 (1998). [CrossRef]
  13. C. Kadow, S. B. Fleischer, J. P. Ibbetson, J. E. Bowers, J. W. Dong, and C. J. Palmstrom, “Self assembled ErAs islands in GaAs: Growth and subpicosecond carrier dynamics,” Appl. Phys. Lett.75(22), 3548–3550 (1999). [CrossRef]
  14. J. E. Bjarnason, T. L. J. Chan, A. W. M. Lee, E. R. Brown, D. C. Driscoll, M. Hanson, A. C. Gossard, and R. E. Muller, “ErAs:GaAs photomixer with two-decade tunability and 12 µW peak output power,” Appl. Phys. Lett.85(18), 3983 (2004). [CrossRef]
  15. Z. D. Taylor, E. R. Brown, J. E. Bjarnason, M. P. Hanson, and A. C. Gossard, “Resonant-optical-cavity photoconductive switch with 0.5% conversion efficiency and 1.0 W peak power,” Opt. Lett.31(11), 1729–1731 (2006). [CrossRef] [PubMed]
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