Abstract

A method of manufacturing optical coatings for germanium optics used at terahertz frequencies has been developed. The various optical coatings used at terahertz frequencies are difficult to manufacture conventionally because these coatings must be as thick as several tens of micrometers, which is far thicker than those used in the optical region. One way to overcome this problem is to form a silicon oxide layer through plasma-enhanced chemical-vapor deposition, with silane (SiH4) as a source gas. Using this method, I formed 21-μm-thick silicon oxide films as antireflection (AR) layers for germanium optics and obtained low reflection at 1.7 THz (wavelength, λ = 175 μm). This method is easily applied to large-aperture optics and micro-optics as well as to optics with a complex surface form. The AR coatings can also be formed for photoconductive detectors made from germanium doped with gallium at a low temperature (160 °C); this low temperature ensures that the doped impurities in the germanium do not diffuse. Fabrication of optical coatings upon substrates that have refractive indices of 3.84–11.7 may also be possible by control of the refractive indices of the deposited layers.

© 2003 Optical Society of America

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References

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    [CrossRef]
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    [CrossRef]
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    [CrossRef]
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    [CrossRef]
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    [CrossRef]
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    [CrossRef]

2000 (2)

A. J. Gatesman, J. Waldman, M. Ji, C. Musante, S. Yngvesson, “An anti-reflection coating for silicon optics at terahertz frequencies,” IEEE Microwave Guided Wave Lett. 10, 264–266 (2000).
[CrossRef]

Q. Chen, Z. P. Jiang, M. Tani, X.-C. Zhang, “Electro-optic terahertz transceiver,” Electron. Lett. 36, 1298–1299 (2000).
[CrossRef]

1998 (1)

1996 (3)

N. Hiromoto, M. Fijiwara, H. Shibai, H. Okuda, “Ge:Ga far-infrared photoconductors for space applications,” Jpn. J. Appl. Phys. 35, 1676–1680 (1996).
[CrossRef]

D. A. DeCrosta, J. J. Hackenberg, J. H. Linn, “Characterization of high oxygen: tetraethylorthosilicate ratio plasma-enhanced chemical vapor deposition films,” J. Electrochem. Soc. 143, 1079–1084 (1996).
[CrossRef]

K. Kawase, M. Sato, T. Taniuchi, H. Ito, “Coherent tunable THz-wave generation from LiNbO3 with monolithic grating coupler,” Appl. Phys. Lett. 68, 2483–2485 (1996).
[CrossRef]

1993 (1)

1991 (1)

E. Gornik, ed., special issue on far-infrared semiconductor lasers, Opt. Quantum Electron. 23, S111–S349 (1991).

1974 (1)

1967 (1)

Armstrong, K. R.

Chen, Q.

Q. Chen, Z. P. Jiang, M. Tani, X.-C. Zhang, “Electro-optic terahertz transceiver,” Electron. Lett. 36, 1298–1299 (2000).
[CrossRef]

DeCrosta, D. A.

D. A. DeCrosta, J. J. Hackenberg, J. H. Linn, “Characterization of high oxygen: tetraethylorthosilicate ratio plasma-enhanced chemical vapor deposition films,” J. Electrochem. Soc. 143, 1079–1084 (1996).
[CrossRef]

Dobrowolski, J. A.

Fijiwara, M.

N. Hiromoto, M. Fijiwara, H. Shibai, H. Okuda, “Ge:Ga far-infrared photoconductors for space applications,” Jpn. J. Appl. Phys. 35, 1676–1680 (1996).
[CrossRef]

Gatesman, A. J.

A. J. Gatesman, J. Waldman, M. Ji, C. Musante, S. Yngvesson, “An anti-reflection coating for silicon optics at terahertz frequencies,” IEEE Microwave Guided Wave Lett. 10, 264–266 (2000).
[CrossRef]

Hackenberg, J. J.

D. A. DeCrosta, J. J. Hackenberg, J. H. Linn, “Characterization of high oxygen: tetraethylorthosilicate ratio plasma-enhanced chemical vapor deposition films,” J. Electrochem. Soc. 143, 1079–1084 (1996).
[CrossRef]

Hiromoto, N.

K. Kawase, N. Hiromoto, “Terahertz-wave antireflection coating on Ge and GaAs with fused quartz,” Appl. Opt. 37, 1862–1866 (1998).
[CrossRef]

N. Hiromoto, M. Fijiwara, H. Shibai, H. Okuda, “Ge:Ga far-infrared photoconductors for space applications,” Jpn. J. Appl. Phys. 35, 1676–1680 (1996).
[CrossRef]

Ito, H.

K. Kawase, M. Sato, T. Taniuchi, H. Ito, “Coherent tunable THz-wave generation from LiNbO3 with monolithic grating coupler,” Appl. Phys. Lett. 68, 2483–2485 (1996).
[CrossRef]

Ji, M.

A. J. Gatesman, J. Waldman, M. Ji, C. Musante, S. Yngvesson, “An anti-reflection coating for silicon optics at terahertz frequencies,” IEEE Microwave Guided Wave Lett. 10, 264–266 (2000).
[CrossRef]

Jiang, Z. P.

Q. Chen, Z. P. Jiang, M. Tani, X.-C. Zhang, “Electro-optic terahertz transceiver,” Electron. Lett. 36, 1298–1299 (2000).
[CrossRef]

Kawase, K.

K. Kawase, N. Hiromoto, “Terahertz-wave antireflection coating on Ge and GaAs with fused quartz,” Appl. Opt. 37, 1862–1866 (1998).
[CrossRef]

K. Kawase, M. Sato, T. Taniuchi, H. Ito, “Coherent tunable THz-wave generation from LiNbO3 with monolithic grating coupler,” Appl. Phys. Lett. 68, 2483–2485 (1996).
[CrossRef]

Linn, J. H.

D. A. DeCrosta, J. J. Hackenberg, J. H. Linn, “Characterization of high oxygen: tetraethylorthosilicate ratio plasma-enhanced chemical vapor deposition films,” J. Electrochem. Soc. 143, 1079–1084 (1996).
[CrossRef]

Low, F. J.

Macleod, H. A.

H. A. Macleod, “Thin-film optical coating design,” in Thin Films for Optical Systems, F. R. Flory, ed., (Marcel Dekker, New York, 1995), pp. 1–39.

Musante, C.

A. J. Gatesman, J. Waldman, M. Ji, C. Musante, S. Yngvesson, “An anti-reflection coating for silicon optics at terahertz frequencies,” IEEE Microwave Guided Wave Lett. 10, 264–266 (2000).
[CrossRef]

Okuda, H.

N. Hiromoto, M. Fijiwara, H. Shibai, H. Okuda, “Ge:Ga far-infrared photoconductors for space applications,” Jpn. J. Appl. Phys. 35, 1676–1680 (1996).
[CrossRef]

Randall, C. M.

Rawcliffe, R. D.

Sato, M.

K. Kawase, M. Sato, T. Taniuchi, H. Ito, “Coherent tunable THz-wave generation from LiNbO3 with monolithic grating coupler,” Appl. Phys. Lett. 68, 2483–2485 (1996).
[CrossRef]

Shao, J.

Shibai, H.

N. Hiromoto, M. Fijiwara, H. Shibai, H. Okuda, “Ge:Ga far-infrared photoconductors for space applications,” Jpn. J. Appl. Phys. 35, 1676–1680 (1996).
[CrossRef]

Tani, M.

Q. Chen, Z. P. Jiang, M. Tani, X.-C. Zhang, “Electro-optic terahertz transceiver,” Electron. Lett. 36, 1298–1299 (2000).
[CrossRef]

Taniuchi, T.

K. Kawase, M. Sato, T. Taniuchi, H. Ito, “Coherent tunable THz-wave generation from LiNbO3 with monolithic grating coupler,” Appl. Phys. Lett. 68, 2483–2485 (1996).
[CrossRef]

Waldman, J.

A. J. Gatesman, J. Waldman, M. Ji, C. Musante, S. Yngvesson, “An anti-reflection coating for silicon optics at terahertz frequencies,” IEEE Microwave Guided Wave Lett. 10, 264–266 (2000).
[CrossRef]

Yngvesson, S.

A. J. Gatesman, J. Waldman, M. Ji, C. Musante, S. Yngvesson, “An anti-reflection coating for silicon optics at terahertz frequencies,” IEEE Microwave Guided Wave Lett. 10, 264–266 (2000).
[CrossRef]

Zhang, X.-C.

Q. Chen, Z. P. Jiang, M. Tani, X.-C. Zhang, “Electro-optic terahertz transceiver,” Electron. Lett. 36, 1298–1299 (2000).
[CrossRef]

Appl. Opt. (4)

Appl. Phys. Lett. (1)

K. Kawase, M. Sato, T. Taniuchi, H. Ito, “Coherent tunable THz-wave generation from LiNbO3 with monolithic grating coupler,” Appl. Phys. Lett. 68, 2483–2485 (1996).
[CrossRef]

Electron. Lett. (1)

Q. Chen, Z. P. Jiang, M. Tani, X.-C. Zhang, “Electro-optic terahertz transceiver,” Electron. Lett. 36, 1298–1299 (2000).
[CrossRef]

IEEE Microwave Guided Wave Lett. (1)

A. J. Gatesman, J. Waldman, M. Ji, C. Musante, S. Yngvesson, “An anti-reflection coating for silicon optics at terahertz frequencies,” IEEE Microwave Guided Wave Lett. 10, 264–266 (2000).
[CrossRef]

J. Electrochem. Soc. (1)

D. A. DeCrosta, J. J. Hackenberg, J. H. Linn, “Characterization of high oxygen: tetraethylorthosilicate ratio plasma-enhanced chemical vapor deposition films,” J. Electrochem. Soc. 143, 1079–1084 (1996).
[CrossRef]

Jpn. J. Appl. Phys. (1)

N. Hiromoto, M. Fijiwara, H. Shibai, H. Okuda, “Ge:Ga far-infrared photoconductors for space applications,” Jpn. J. Appl. Phys. 35, 1676–1680 (1996).
[CrossRef]

Opt. Quantum Electron. (1)

E. Gornik, ed., special issue on far-infrared semiconductor lasers, Opt. Quantum Electron. 23, S111–S349 (1991).

Other (2)

H. A. Macleod, “Thin-film optical coating design,” in Thin Films for Optical Systems, F. R. Flory, ed., (Marcel Dekker, New York, 1995), pp. 1–39.

E. D. Palik, ed., Handbook of Optical Constants of Solids (Academic, Orlando, Fla., 1985), pp. 465–478, 547–569, 749–763.

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Figures (4)

Fig. 1
Fig. 1

Calculated transmittance spectrum of the Ge wafer (1989.5 μm thick) with an AR coating (a 20.9-μm-thick SiO2 layer) on one surface.

Fig. 2
Fig. 2

Measured transmittance of the Ge wafer with an AR coating on one side.

Fig. 3
Fig. 3

Solid line shows the theoretically calculated dependence of the interference amplitude (IAar) at an AR wave number (k ar) on x (the stoichiometric composition of oxygen in SiOx). The k ar corresponding to x is shown on the upper x axis. Filled circles show the measured interference amplitude [IA(meas.)] obtained from the data shown in Fig. 2. For IA(meas.), k ar of the upper x axis is readdressed as k, as in Fig. 2. The point where IAar and IA(meas.) cross indicates the k ar and x values of the AR coating.

Fig. 4
Fig. 4

Solid curves shows the theoretically calculated dependence of the reflectance [R ar(x)] at an AR wave number (k ar) on x (the stoichiometric composition of oxygen in SiOx). Dashed line shows the calculated dependence of the refractive index of the mixture [n m(x)] on x. The k ar corresponding to x is shown on the upper x axis. The R ar and n m values of the AR coating were obtained from the value of x at the crossing point of IAar and IA(meas.) in Fig. 3.

Equations (1)

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karx=14dnm,Rarx=1-4/n2mns+nsn2m+2,IAarx=4RFRarT21-RF1-Rar1-RFRarT22 .

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