We fabricated single-, double- and triple-layered beta-FeSi2-particles structure on Si(001) substrates by reactive deposition epitaxy (RDE) for beta-FeSi2 and by molecular beam epitaxy (MBE) for Si, and realized electroluminescerice (EL) at 310K. Photoluminescence (PL) measurements revealed that the 77K PL intensity of beta-FeSi2 increased almost proportionally with the number of beta-FeSi2-particles/Si layers. It was also found that the multilayered structure enhanced the EL intensity of beta-FeSi2 particularly at low temperatures

Hasegawa, F

Li, C

Ozawa, Y

Suemasu, T

Sunohara, T

李成

Japanese Journal of Applied Physics

Xiamen University Institutional Repository

This content has been downloaded from IOPscience. Please scroll down to see the full text.Download details:IP Address: 218.104.71.166This content was downloaded on 03/04/2015 at 02:45Please note that terms and conditions apply.Growth and Characterization of Si-Based Light-Emitting Diode with β-FeSi2-Particles/SiMultilayered Active Region by Molecular Beam EpitaxyView the table of contents for this issue, or go to the journal homepage for more2005 Jpn. J. Appl. Phys. 44 3951(http://iopscience.iop.org/1347-4065/44/6R/3951)Home Search Collections Journals About Contact us My IOPscienceGrowth and Characterization of Si-Based Light-Emitting Diodewith -FeSi2-Particles/Si Multilayered Active Region by Molecular Beam EpitaxyTsuyoshi SUNOHARA, Cheng LI, Yoshinori OZAWA, Takashi SUEMASU and Fumio HASEGAWAInstitute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, Japan(Received September 16, 2004; accepted February 14, 2005; published June 10, 2005)We fabricated single-, double- and triple-layered -FeSi2-particles structure on Si(001) substrates by reactive depositionepitaxy (RDE) for -FeSi2 and by molecular beam epitaxy (MBE) for Si, and realized electroluminescence (EL) at 310K.Photoluminescence (PL) measurements revealed that the 77K PL intensity of -FeSi2 increased almost proportionallywith the number of -FeSi2-particles/Si layers. It was also found that the multilayered structure enhanced the EL intensity of-FeSi2 particularly at low temperatures. [DOI: 10.1143/JJAP.44.3951]KEYWORDS: -FeSi2, LED, electroluminescence, reactive deposition epitaxy1. IntroductionSemiconducting iron disilicide (-FeSi2) has been attract-ing significant interest as a Si-based light emitter with awavelength (1:5 mm) suitable for optical fiber communi-cations.1) In 1997, Leong et al. reported low-temperatureelectroluminescence (EL) from -FeSi2 precipitates embed-ded in a Si p–n junction by ion-beam synthesis (IBS).2)However, room-temperature (RT) EL has been difficult toachieve due to the presence of a large number of induceddefects. We therefore adopted reactive deposition epitaxy(RDE; deposition of Fe on hot Si) instead of IBS to form -FeSi2, and developed a formation technique for single-crystalline -FeSi2 particles embedded in Si by molecularbeam epitaxy (MBE), which enabled us to realize the firstRT 1.6 mm EL.3) There have been several reports thus far onRT EL at approximately 1.6 mm,4–8) and further efforts havebeen made to enhance the luminescence intensity of -FeSi2.9,10) One way to enhance the EL intensity of -FeSi2 isto embed a -FeSi2 continuous film in Si as an active regioninstead of -FeSi2 particles, and to form Si/-FeSi2 film/Sidouble heterostructures (DH). Very recently, a Si/-FeSi2film/Si DH was realized on Si(111) substrates,11–13) but therehas been no report on the formation of Si/-FeSi2 film/SiDH on Si(001). Epitaxial -FeSi2 film on Si(001) is found toeasily aggregate into isolated islands when it is annealed at ahigh temperature for improving the crystalline quality orembedded in Si by MBE at high temperatures.14) It istherefore difficult to embed a continuous -FeSi2 film in Siand to realize Si/-FeSi2 film/Si DH LEDs on Si(001).Another way of enhancing the luminescence intensity of -FeSi2 is by increasing the volume of -FeSi2 particlesembedded in Si. We have been trying to enhance the ELintensity of -FeSi2 by increasing the volume of -FeSi2embedded in Si through the increase of the size of the -FeSi2 particles.15) However, it was found to merely increasethe defect densities in the surrounding Si. We thereforedeveloped a formation technique for double- and triple-layered -FeSi2-particles/Si structures for the purpose ofincreasing the volume of -FeSi2 in Si with -FeSi2 particlesize kept constant.In this paper, we report that a multiple -FeSi2-particles/Si layered structure enhances the PL (photoluminescence)and EL obtained from p-Si/-FeSi2-particles/n-Si LEDscompared with a single-layered structure.2. Experimental-FeSi2-particles/Si multilayered structures for PL andEL measurements were fabricated as follows. First, 10-nm-thick [100]-oriented -FeSi2 epilayers were grown on nþ-Si(001) substrates by RDE at 470C.16,17) The sample wasthen annealed in situ at 850C for 1 h to improve the crystalquality of the -FeSi2 film. The -FeSi2 film agglomeratedinto islands during this process, due probably to the latticemismatch (1–2%) between the two materials. Consequently,a 0.3-mm-thick undoped Si layer was grown by MBE at500C.4) For a double-layered structure, another 10-nm-thick[100]-oriented -FeSi2 epilayer was grown on the undopedSi layer by RDE at 470C, followed by annealing at 850Cand a subsequent overgrowth of a 0.3-mm-thick undoped Silayer at 500C. This process was repeated for a triple-layeredstructure. For EL measurements, a boron-doped pþ-Si caplayer with a doping concentration of approximately 1:01018 cm3 was grown at 700C on top of the undoped Silayer18) for the single- and double-layered structures.Unfortunately, we did not prepare triple-layered LEDs dueto a problem with the growth chamber. All the samples forthe PL and EL measurements were finally annealed at 900Cfor 14 h in Ar atmosphere to further improve their crystalquality, resulting in -FeSi2 particles embedded in the Simatrix.4) A mesa structure of 1:5 1:5mm2 was made bywet chemical etching. An Al finger-type contact was formedon the pþ-Si layer by standard photolithography and sinteredat 450C for 20min. The backside contact was made ofAuSb. The crystallinity of the grown films was measured byX-ray diffraction (XRD). PL was measured using a He–Cdlaser (442 nm). The EL spectra were measured with 200Hzpulsed current biasing with a 50% duty cycle. The devicewas packaged in a metal can and mounted on a copper holderin a closed-cycle He cryostat. Luminescence was dispersedby a 25-cm-focal-length grating monochromator, and de-tected phase-sensitively using a liquid-nitrogen-cooled InP/InGaAs photomultiplier (Hamamatsu Photonics R5509-72).3. Results and DiscussionCross-sectional SEM images of single-, double- andtriple-layered -FeSi2-particles/Si structures without thepþ-Si capping layer are shown in Figs. 1(a)–1(c), respec-tively. The white parts in these figures are -FeSi2 particles.We can see a clear layered structure of -FeSi2 particles inCorresponding author.Japanese Journal of Applied PhysicsVol. 44, No. 6A, 2005, pp. 3951–3953#2005 The Japan Society of Applied Physics3951these samples. In the –2 XRD curves shown in Fig. 2, only[100]-oriented diffraction peaks of -FeSi2 were observed,indicating that the epitaxial relationship between -FeSi2and Si was preserved even after aggregation and MBE-Siovergrowth.Figure 3 shows PL spectra measured at 77K for thesethree samples. The PL measurements revealed that the1.53 mm PL intensity increased almost proportionally withthe number of -FeSi2-particles/Si layered structures. Thethermal processing repeated for the fabrication of double-and triple-layered structures did not induce dislocation-related characteristic D-line emissions.19–21) This resultindicates that the number of electron–hole pairs whichrecombine radiatively in -FeSi2 is increased by increasingthe number of -FeSi2 particles embedded in Si.Next, we compare the EL characteristics of the double-layered LED with those of the single-layered one. Bothsamples showed clear rectifying properties of Si p–njunctions in their current–voltage (I–V) characteristics.Figure 4 shows the dependence of integrated EL intensityon the injected current density J for the single- and double-layered LEDs measured at various temperatures. Theintegrated EL intensity of -FeSi2 increased linearly withJ at low temperatures, and the EL intensity was much moreenhanced in the double-layered LED. Figure 5 shows thetemperature dependence of integrated EL intensity for thesingle- and double-layered LEDs under J ¼ 2A/cm2. Forreference, EL spectra obtained for the single-layered LED atvarious temperatures are shown in the inset. The EL of -FeSi2 is dominant and the EL from other sources wasnegligible. Similar EL spectra were also observed for thedouble-layered LED. The EL intensity of the double-layeredLED was much higher than that of the single-layered LED atlow temperatures. This result indicates that the EL intensitywas greatly enhanced by doubling the -FeSi2-particleslayers than the PL intensity. This difference is probablycaused by the difference in the spatial distributions ofcarriers between the cases of light excitation and currentinjection. In the case of current injection, it is important todesign the doping concentrations of p- and n-type Si so thatthe pn product becomes maximum at the -FeSi2 precip-itates. Thus, it is considered that the pn product in the upper-FeSi2 particles is much higher than that in the lower onesdue to the heavy doping of the nþ-type Si(001) substrate. Onthe other hand, there is not significant difference in the pnFig. 1. SEM cross sections of (a) single-, (b) double- and (c) triple-layered-FeSi2-particles/Si structures for PL measurements. The pþ-Si cappinglayers were not grown.20 30 40 50 60 70 80 90Si(004)Si(002)tripledoublesingleβ(800)β(600)XRD Intensity (arb.units)2θ (deg)β(400)Fig. 2. –2 XRD curves for single-, double- and triple-layered -FeSi2-particles/Si structures for PL measurements.0.7 0.8 0.9 1.0 1.1 1.2single-layered structuredouble-layered structuretriple-layered  structurePL Intensity (arb.units)Energy (eV)77K1.7 1.6 1.5 1.4 1.3 1.2 1.1Wavelength (µm)Fig. 3. PL spectra measured at 77K for single-, double- and triple-layered-FeSi2-particles/Si structures.0.0 0.5 1.0 1.5 2.0 15 20 25 30 35single-layeredLEDdouble-layered LED77K50K8K8KInt. EL Intensity (arb.units)Current Density(A/cm2)Fig. 4. Integrated EL intensity as a function of biasing current density forsingle- and double-layered LEDs measured at various temperatures.3952 Jpn. J. Appl. Phys., Vol. 44, No. 6A (2005) T. SUNOHARA et al.product between the upper and lower -FeSi2 precipitates inthe case of the 442-nm-wavelength light excitation due tothe penetration depth being approximately 1 mm in Si.RT EL spectra were obtained for both single- and double-layered LEDs. Figure 6 shows the EL spectra as a functionof injected current density at 310K obtained for the double-layered LED. The asymmetric EL spectra are caused by thedetection limit of the detector for wavelengths beyond1.6 mm. The inset shows the dependence of EL intensity oninjected current density. In both single- and double-layeredLEDs, a 1.6 mm EL was observed only when J was largerthan 60A/cm2, and the EL intensity increased superlinearlywith J, as observed in our previous single-layered LEDs, dueprobably to nonradiative recombination centers in andaround the -FeSi2 precipitates.3,4) This result suggests thatnumerous defect levels acting as nonradiative recombinationcenters still exist in the LEDs even after annealing at 900C.When the current flowing through the defect levels saturates,the bias current begins to contribute to radiative recombi-nation and a reasonable EL output is obtained. Unfortu-nately, the EL intensity of the double-layered LED wascomparable to that of the single-layered LED at around RT.However, the EL enhancement observed at low temperaturesindicated the potential of the multilayered structure. Byoptimizing the diode structure and doping profile, we believethat practical Si-based LEDs will be obtained in the nearfuture.4. ConclusionWe fabricated -FeSi2-particles/Si multilayered LEDstructures on Si(001) substrates by RDE for -FeSi2 andby MBE for Si, and achieved RT 1.6 mm EL from both thesingle- and double-layered LEDs. It was found that the PLintensity increased almost proportionally with the number oflayered structures, and that the EL intensity of the double-layered LED was much more enhanced than the PLintensity, particulary at low temperatures.AcknowledgementsThis work was supported in part by the Ministry ofEducation, Culture, Sports, Science and Technology(MEXT), the TARA project of the University of Tsukubaand the Industrial Technology Research Grant Program in2003 of the New Energy and Industrial Technology Devel-opment Organization (NEDO) of Japan.1) M. C. Bost and J. E. Mahan: J. Appl. Phys. 58 (1985) 2696.2) D. Leong, M. Harry, K. J. Reeson and K. P. Homewood: Nature 387(1997) 686.3) T. Suemasu, Y. Negishi, K. Takakura and F. Hasegawa: Jpn. J. Appl.Phys. 39 (2000) L1013.4) T. Suemasu, Y. Negishi, K. Takakura, F. Hasegawa and T. Chikyow:Appl. Phys. Lett. 79 (2001) 1804.5) M. A. Lourenco. T. M. Butler, A. K. Kewell, R. M. Gwilliam, K. J.Kirkby and K. P. Homewood: Jpn. J. Appl. Phys. 40 (2001) 4041.6) S. Chu, T. Hirohda, K. Nakajima, H. Kan and T. Hiruma: Jpn. J. Appl.Phys. 41 (2002) L1200.7) L. Martinelli, E. Grilli, M. Guzzi and M. G. Grimaldi: Appl. Phys.Lett. 83 (2003) 794.8) C. Li, Y. Ozawa, T. Suemasu and F. Hasegawa: Jpn. J. Appl. Phys. 43(2004) L1492.9) Y. Maeda, Y. Terai, M. Itakura and N. Kuwano: Thin Solid Films 461(2004) 160.10) Y. Terai and Y. Maeda: Appl. Phys. Lett. 84 (2004) 903.11) S. Chu, T. Hirohada, H. Kan and T. Hiruma: Jpn. J. Appl. Phys. 43(2004) L154.12) M. Takauji, N. Seki, T. Suemasu, F. Hasegawa and M. Ichida: J. Appl.Phys. 96 (2004) 2561.13) M. Takauji, C. Li, T. Suemasu and F. Hasegawa: Jpn. J. Appl. Phys. 44(2005) 2483.14) T. Suemasu, M. Tanaka, T. Fujii, S. Hashimoto, Y. Kumagai andF. Hasegawa: Jpn. J. Appl. Phys. 36 (1997) L1225.15) Y. Ozawa, C. Li, T. Suemasu and F. Hasegawa: J. Appl. Phys. 95(2004) 5483.16) J. E. Mahan, K. M. Geib, G. Y. Robinson, R. G. Long, X. Yan, G. Bai,M. A. Nicolet and M. Nathan: Appl. Phys. Lett. 56 (1990) 2126.17) M. Tanaka, Y. Kumagai, T. Suemasu and F. Hasegawa: Jpn. J. Appl.Phys. 36 (1997) 3620.18) C. Li, T. Ohtsuka, T. Ozawa, T. Suemasu and F. Hasegawa: J. Appl.Phys. 94 (2003) 1518.19) D. A. Drozdov, A. A. Patrin and V. D. Tkachev: JETP Lett. 23 (1976)597.20) B. Suezawa, Y. Sasaki and K. Sumio: Phys. Status Solidi A 79 (1983)173.21) R. Sauer, J. Weber, J. Stolz, E. Weber, K. Kusters and H. Alexander:Appl. Phys. A 36 (1985) 1.0 20 40 60 80 100 120 1400.7 0.8 0.9 1.0 1.150K70K90K110KEL Int. (arb.units)Energy (eV)10302040single-layered   LEDdouble-layered LEDInt. EL Intensity (arb.units)Temperature (K)50J=2A/cm2Fig. 5. Temperature dependence of integrated EL intensity for single- anddouble-layered LEDs when injected current density was 2A/cm2. Theinset shows the EL spectra at various temperatures with J ¼ 2A/cm2 forthe single-layered LED.0.7 0.8 0.9 1.0 1.1 1.280A/cm260A/cm284A/cm289A/cm2EL Intensity (arb.units)Energy (eV)1.7 1.6 1.5 1.4 1.3 1.2 1.10 806040EL Int. (arb.units)J (A/cm2)20Wavelength (µm)310KFig. 6. EL spectra under various injected current densities measured at310K for the double-layered LED. The inset shows the dependence ofintegrated EL intensity on injected current density.Jpn. J. Appl. Phys., Vol. 44, No. 6A (2005) T. SUNOHARA et al. 3953

Growth and characterization of Si-based light-emitting diode with beta-FeSi2-particles/Si multilayered active region by molecular beam epitaxy

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Growth and characterization of Si-based light-emitting diode with beta-FeSi2-particles/Si multilayered active region by molecular beam epitaxy

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