The present work reports Er-doped channel oxidized porous silicon waveguides (OPSWG) formed from n+-type Si by the two-step anodisation process. Er has been introduced into porous silicon before oxidation by a cathodic treatment in 0.1 M Er (NO3)3 aqueous solution. A correlation between Er concentration and refractive index profiles has shown dominant core doping with Er relative to cladding regions. Reported Er concentration of 0.8 at.% in the OPSWG is large enough to attain the amplification effect

A. FERRARI

BALUCANI, Marco

G. LAMEDICA

L. DOLGYI

N. KAZUCHITS

N. VOROZOV

S. VOLCHEK

V. BONDARENKO

V. PETROVICH

V. YAKOVTSEVA

English

Balucani, M.

Bondarenko, V. P.

Lamedica, G.

Ferrari, A.

Yakovtseva, V. A.

Dolgyi, L.

Vorozov, N.

Volchek, S. A.

Petrovich, V. A.

Kazuchits, N.

Belarusian State University of Informatics and Radioelectronics Repository

Er-doped oxidized porous silicon waveguidesBalucani M. «Foreign» 1Bondarenko V. 2Lamedica G. «Foreign» 3Ferrari A. «Foreign» 4Yakovtseva V. 5Dolgyi L. 6Vorozov N. 7Volchek S. 8 Petrovich V. 9Kazuchits N. «Foreign» 105, 6, 7, 8, 9 Belarussian State University of Informatics and RadioelectronicsAbstract. The present work reports Er-doped channel oxidized porous silicon waveguides (OPSWG) formed from n+-type Si by the two-step anodisation process. Er has been introduced into porous silicon before oxidation by a cathodic treatment in 0.1 M Er (NO3)3 aqueous solution. A correlation between Er concentration and refractive index profiles has shown dominant core doping with Er relative to cladding regions. Reported Er concentration of 0.8 at.% in the OPSWG is large enough to attain the amplification effect.Keywords: Erbium; Porous silicon; Optoelectronic devices.http://dx.doi.org/10.1016/S0040-6090(01)01155-5http://www.sciencedirect.com/science/article/pii/S0040609001011555

Er-doped oxidized porous silicon waveguides

Archivio della ricerca- Università di Roma La Sapienza

Ž .Thin Solid Films 396 2001 201203Er-doped oxidised porous silicon waveguidesM. Balucania,, V. Bondarenkoa, G. Lamedicaa, A. Ferraria, L. Dolgyib, N. Vorozovb,V. Yakovtsevab, S. Volchekb, V. Petrovichb, N. KazuchitscaElectronic Department, INFM Unit E6, Uniersity of Rome ‘La Sapienza’, Via Eudossiana 18, 00184 Roma, ItalybBelarussian State Uniersity of Informatics and Radioelectronics, P. Broka 6, 20027 Minsk, BelaruscBelarussian State Uniersity, Skorina Ae. 4, 220050 Minsk, BelarusReceived 9 October 2000; received in revised form 29 March 2001; accepted 15 May 2001AbstractŽ . The present work reports Er-doped channel oxidized porous silicon waveguides OPSWG formed from n -type Si by thetwo-step anodisation process. Er has been introduced into porous silicon before oxidation by a cathodic treatment in 0.1 M ErŽ .NO aqueous solution. A correlation between Er concentration and refractive index profiles has shown dominant core doping3 3with Er relative to cladding regions. Reported Er concentration of 0.8 at.% in the OPSWG is large enough to attain theamplification effect.  2001 Elsevier Science B.V. All rights reserved.Keywords: Erbium; Porous silicon; Optoelectronic devices1. IntroductionŽ .Recently, integrated optical waveguide WG ampli- fiers are growing in interest 1 . If these amplifiers areto be fabricated, WG should be doped with a specificdopant, typical of which is Er. It is essential that theŽ .amplifier is: i transparent to the both Er excitingwavelength and to the wavelength of the travellingŽ .signal; ii contains a large amount of optically activeŽ .Er; and iii can be made into a channel WG using a technology compatible with standard Si processing 1 .Ž .Integrated WGs based on oxidised porous silicon OPS are capable of meeting these criteria 24 . First, broadrange of light transmission has been found to occur inOPSWGs. Second, porous structure promotes Er intro-Ž .duction into porous silicon PS in abundance. A subse-quent oxidation of PS makes Er to be optically active.Third, technology of Er-doped channel OPSWGs iscompatible with standard silicon microelectronic tech- Corresponding author. Fax: 44-06-44-585-409.Ž .E-mail address: balucani@die.ing.uniroma.it M. Balucani .nology. Previously, we reported Er-doped OPSWGsformed from p-type Si by one-step anodisation withelectrochemical Er introduction and Er-related pho- toluminescence from the waveguide formed 5 . In thepresent work, n-type Si and two-step anodisation wereemployed to produce Er-doped OPSWGs with ad-vanced optical parameters suitable for optical ampli-fiers.2. ExperimentalThe process sequence to produce a channel Er-dopedŽ . OPSWG is shown in Fig. 1. The starting 100 n -typeSi wafers of 0.01-Ohmcm resistivity were oxidised toform a 0.7-m thick masking SiO layer. Using pho-2tolithography, the SiO layer was patterned to define2layout of waveguides, which were designed as straightŽ .lines of width 10 m and of length 3 cm Fig. 1a .Selective anodization of Si within openings in the maskwas performed in the electrolyte consisted of 48% HFand ethylene glycol in the ratio of 2:3. To provide WGwith core and cladding regions of controlled porosities0040-609001$ - see front matter  2001 Elsevier Science B.V. All rights reserved.Ž .PII: S 0 0 4 0 - 6 0 9 0 0 1 0 1 1 5 5 - 5( )M. Balucani et al.  Thin Solid Films 396 2001 201203202Fig. 1. The process sequence to produce an Er-doped channel OP-SWG.and thicknesses, two-step anodisation process waselaborated. The first anodization step was performed atthe current density of 40 mAcm2 for 4 min providingŽ .a 7-m thick PS 1 layer Fig. 1b . On further oxidation,this layer is expected to form compact OPS for the coreregion. Then the current density was raised to 80mAcm2 and the samples were anodized for 45 sproviding a waveguide periphery with a 3-m thick PSŽ .2 layer Fig. 1c . On the following oxidation step, thislayer is expected to form a cladding layer. After thesecond anodisation step, the remainder of the SiO2mask was of 0.15 m in thickness. Next, the samplesŽ .were immediately placed into a 0.1 M Er NO solu-3 3tion and a cathodic treatment was performed for 8 minat the cathodic current density of 50 mAcm2. AnŽ .Er-containing layer of Er OH composition was elec-3Ž .trochemically deposited into PS Fig. 1d . A subsequentetching in 20% HCl removed the Er-containing layerfrom the surface while the layer within the PS layerŽ .remained intact Fig. 1e . Next, three-step thermal oxi-Ž .dation was performed: i at 300C for 60 min in dryŽ . Ž .O ; ii at 1000C for 25 min in wet O ; and iii at2 2Ž .1150C for 60 min in dry O Fig. 1f .2X-Ray microanalysis using an EDX-SpectrometerAN-10000 was performed to study Er distribution withinŽ .the OPSWG. Photoluminescence PL spectroscopy wasperformed by direct end-fire pumping the waveguideswith focused light from an Xe lamp. The PL signal wascoupled out by a prism and the transmitted spectrumwas analyzed with a grating spectrometer MDR-23equipped with a liquid nitrogen-cooled Ge detector.The attenuation spectrum was determined from a setof WG transmission spectra recorded at various prismpositions. Refractive index of OPS was determined at0.63 m by refractive near field measurement.3. Results and discussionFig. 2 shows the Er concentration and refractiveindex as functions of a distance from the surface deepinto the OPSWG. The Er concentration increases ini-tially with depth from 0.4 at.% at the WG surface to0.8 at.% at the depth of 35 m, decreases to 0.2at.% at the depth of 79 m and then decreases tounder 0.1 at.% at the depth of over 10 m. Refractiveindex increases with a depth from 1.41 at the surface to1.458 at a depth of 3 m. On further moving into thePS layer, it decreases to 1.428 at a depth of 7 m. Thenthe refractive index increases sharply to values higherthan 1.5. Referring to Fig. 2, refractive index profiledisplays boundaries of core and cladding regions. Withthe whole WG thickness of 10 m, the core is in therange of 1.57.5 m. The cladding region has an esti-mated thickness of 1.5 m at the surface and 2.5 m atthe WG bottom. The refractive index step between thecore and the cladding at the WG bottom approximates0.03, twice as much as for OPSWGs formed from  p -type Si by one-step anodisation 6 . These resultsare due to the two-step anodisation process in whichthe controlled variation of the current density was usedto form PS layers of varying porosity, with appropriaterefractive index and thickness.Fig. 3 gives Er concentration and refractive indexagainst the WG width on scanning over the WG cross-section at the depth of 3 m. Referring to Fig. 3, Erconcentration profile correlates with refractive indexprofile. A correlation between Er concentration andrefractive index profiles discloses that Er is introducedgenerally into the WG core. Cladding regions weredoped with Er to a lesser extent. Dominant core dopingwith Er relative to cladding regions is of great signifi-cance for WG amplifiers wherein pumping and signalmodes propagate only through the core.Ž .Fig. 2. The Er concentration solid line and the refractive indexŽ .dashed line as functions of the WG depth.( )M. Balucani et al.  Thin Solid Films 396 2001 201203 203Ž .Fig. 3. The Er concentration solid line and the refractive indexŽ .dashed line as functions of the WG width.Fig. 4. The attenuation spectrum of the Er-doped OPSWG.The attenuation spectrum of the Er-doped OPSWGis shown in Fig. 4. Absorption bands at 650, 720, 810,940, 980, 1240 and 1530 nm may be observed from thespectrum, among which 650, 810, 980 and 1530 nmbands are caused by optically active Er, while the restof them seem to be from OH hydroxyl groups. Thetotal losses involving Er-related absorption at 1530 nmand background loss are 7 dBcm. After the high-temperature annealing, the optical loss at 1300 nm wasapproximately 1 dBcm. The losses obtained are lowerthan the losses measured for the OPSWG in p-type SiŽ .  substrates 515 dBcm 24 . This improvement isŽ .due to: i the use of two-step anodization process forn-type Si provides a refractive index jump between thecore and the cladding at the WG bottom of approxi-mately 0.03, that is three times higher than the oneobtained in p-type Si WG, realized by one-step  Ž .anodization process 2,6 ; and ii core of WG made ofoxidized porous silicon material in n-type Si has amuch more dense structure than the p-type Si asshown by the high resolution TEM study.4. ConclusionEr-doped channel OPSWGs formed from n-type Siby the two-step anodization process and electrochemi-Ž .cal cathodic treatment in 0.1 M Er NO solution3 3have been demonstrated. The two-step anodizationprocess allows a formation of PS layers with controlledrefractive index and thickness to form waveguide coreand cladding layers, correspondingly. A correlationbetween Er concentration and refractive index profileshas shown dominant core doping with Er relative tocladding regions. Reported Er concentration in theOPSWG is large enough to attain the amplificationeffect. A more detailed study of the Er-doped OP-SWGs will be conducted in the future.AcknowledgementsThe research described in this publication was madepossible in parts by the European Project OLSI No.28.934 and by Award No. BE2-108 of the CRDF.References  Ž .1 P.G. Kik, A. Polman, MRS Bull. 23 1998 48. 2 G. Maiello, S. La Monica, A. Ferrari, G. Masini, V.P. Bon-darenko, A.M. Dorofeev, N.M. Kazuchits, Thin Solid Films 297Ž .1997 311. 3 H.F. Arrand, T.M. Benson, A. Loni, M.G. Krueger, M.Ž .Thoenissen, H. Lueth, Electron. Lett. 33 1997 1724. 4 V. Yakovtseva, L. Dolgyi, N. Vorozov, N. Kazuchits, V. Bon-darenko, M. Balucani, G. Lamedica, L. Franchina, A. Ferrari,Ž .J. Porous Mater. 7 2000 215. 5 V. Bondarenko, N. Vorozov, L. Dolgyi, V. Yakovtseva, V.Petrovich, S. Volchek, N. Kazuchits, G. Grom, H.A. Lopez, L.Tsybeskov, P.M. Fauchet, In: M.J. Sailor, C.C. Tsai, L.T. Can-Ž . Ž .ham, K. Kanaka Eds. Mater. Res. Soc. Symp. Proc. 536 199969. 6 A. Tomov, V. Filippov, V. Bondarenko, Tech. Phys. Lett. 23Ž .1997 86.

Er-doped Oxidized Porous Silicon Waveguides

https://libeldoc.bsuir.by/bitstream/123456789/11383/2/Er-doped.docx

Er-doped Oxidized Porous Silicon Waveguides

Abstract

Similar works

Full text

Available Versions

Belarusian State University of Informatics and Radioelectronics Repository

Archivio della ricerca- Università di Roma La Sapienza