Growth and characterization of Ge 1-x Sn x alloys grown on Ge(001) and GaAs(001)

Transcription

1 Superficie y Vacío 17(4), diciembre de 2004 Sociedad Mexicana de Ciencia de Superficie y de Vacío Growth and characterization of aoy grown on Ge(001) and GaA(001) H. Pérez Ladrón de Guevara Intituto Tecnoógico de San Lui Potoí Avenida Tecnoógico S/N Km. 1 carretera a Rio Verde, C. P , San Lui Potoí, S.L.P.,Mex. A. G. Rodríguez, H. Navarro-Contrera, M. A. Vida Intituto de Invetigación en Comunicación Óptica (IICO), Univeridad Autónoma de San Lui Potoí Avenida Karakorum 1470, Loma 4ta ección, C.P , San Lui Potoí, S.L.P.,Mex. Singe cryta aoy were grown on Ge(001) and GaA(001) ubtrate uing a RF magnetron Sputtering. HRXRD and Raman pectrocopy were ued to determine the Sn concentration of the aoy, HRXRD ao how that aoy with Sn<0.04 are peudomorphic. Optica propertie of the aoy were anayed in order to determinate the band gap tranition. Keyword: 1. Introduction One of the mot facinating idea in modern emiconductor phyic repreent the reaization of direct energy-gap materia baed fuy on group IV eement Singe cryta aoy have intereting optica and eectrica propertie. Thee aoy have been reported to tranform from indirect to direct fundamenta band gap for x arger than 0.12.[1] Becaue of thi property they open the poibiity to deveop totay baed group IV opteectronic infrared materia ytem. The Ge 1- x aoy exhibit the firt direct band gap tunabe from > E DG > ev for x = 0.06 to 0.15, [1,2] but it i expected that at higher Sn ( 0.4) concentration the E DG decreae to 0 ev [3]. In addition, woud be expected to exhibit high carrier mobiity becaue of a ower effective ma than that of the Ge and the ack of poar optica cattering [3,4] inherent to III-V materia. Thu thi reativey new emiconductor aoy i the ony known exampe of a direct band gap emiconductor among the compound which can be formed from coumn IV eement. In thi work we report the tructura, Raman, and optica characterization of aoy obtained by RF magnetron puttering grown on two different ubtrate Ge(100) and GaA(100) with Sn concentration up to 14%. 2. Experimenta Procedure and anayi. In the HRXRD anayi we ued the Expreion of Macrander[5] defined for aymmetrica diffraction pane (figure 1) where ω + = θ+ τ and ω - = θ- τ are defined for thee pane. Then we obtain the reation + ω + ω θ = 2 + ω ω τ = 2 co τ enθ coτ enθ a = a = a coτ enθ co( τ + τ ) en( θ + θ ) enτ enθ enτ enθ a = a = a enτ enθ en( τ + τ ) en( θ + θ ) Thee reation are obtained from Bragg aw and trigonometric expreion. In thee expreion the eatic contant of the fim are not neceary. The vaue of ω + and ω - are obtained from HRXRD meaurement. They are defined a the eparation between the maximum of the diffraction peek in the Rocking Curve (figure 2) in the aimetric pane (in thi cae ω + and ω - are the eparation in the pane (-1-15) and (115) repectivey). The attice parameter of the aoy, the Sn concentration and the reaxation of the fim were found uing the Macrander reation and auming the Vegard aw. It found that the aoy with ow Sn concentration x<0.04 have peudomorphic characteritic, ince the in-pane attice parameter in both grown on Ge and GaA have the ame vaue of the ubtrate attice parameter (figure 3). The thickne of the aoy that preent peudomorphica characteritic were compared with evera critica thickne mode [6-9] (figure 10

2 Superficie y Vacío 17(4), diciembre de 2004 Sociedad Mexicana de Ciencia de Superficie y de Vacío θ -τ - θ L -τ L as τ d L τ L θ θ L +τ L θ θ +τ Figure 1. Diagram of a X-Ray diffraction on aymmetrica pane.a i the ubtrate attice parameter, a L and a L are the in-growth and in-pane atitice parameter of the ayer repectivay, θ, θ L, τ and τ L are the bragg ange and the tit ange of the pane of the ubtrate and ayer repectivay. Intenity (a. u.) /Ge/Ge(001) T g = C (004) x = 0.02 x = 0.04 x = 0.09 x = 0.14 x = 0.10 /Ge/GaA(001) T g = C (004) x = 0.06 x = 0.08 x = 0.01 x = ω/2θ (degree) Figure 2. HRXRD rocking curve on the (004) pane of aoy grown on Ge(100) and GaA(100) ubtrate. The curve how the precene of epitaxia ayer. The Sn concentration i ao hown for each curve. d τ 4). It wa found that the ony mode in agreement with our reut i the Peope and Bean mode [9], thi mode wa propoed for the Si x aoy. Thi i a group IV aoy ike aoy and we beieve that thi i the reaon for the agreement in the reut. Raman pectrocopy wa ued to confirm the exitence of the aoy and a another way to determinate the Sn concentration according to the inear reation ω GeSn = ω cm -1 [10] for the Raman hift of the peak of Germanium from ω 0 = cm -1 (figure 5). It wa found that the Sn concentration predicted by the Raman hift of the aoy i very near to the Sn concentration determinate by HRXRD a hown in figure 6. Thi reut probe that Raman pectrocopy i another way to determine the Sn concentration of the aoy. The optica propertie of the aoy were anayed uing a FT-IR interferometer for meauring the tranmittance of the aoy. Tranmittance meaurement were performed for thi aoy (figure 7) and hence the aborption coefficient were obtained for each ampe (figure 8). The energy bandgap tranition vaue were obtained by fitting the aborption edge with a mode that incude the direct, indirect tranition and the Urbach tai energy. Ao the critica point of the tranmittance and the aborption coefficient, the paraboic approximation and the differentiate of thi curve were conidered. The determination of the change between indirect to direct band gap i not eay for Sn concentration 0.6 < x < 0.13 due to the proximitie of the gap ometime ony a tranition vaue i oberved. However it poibe to eparate the gap vaue in aoy with higher Sn concentration. The experimenta reut obtained are not in agreement with the Tight-Binding mode [3] or the Peudo- Potentia mode [11] previouy propoed. The data obtained are very neary to the Potentia of Deformation theory [12] reut pubihed recenty and corroborated by FT-IR [1,2] and pectrocopic eipometry [13], thee reut are hown in figure 9. Athough the change from indirect to direct band gap i expected by Potentia of Deformation Theory around Sn = 10%, we ony oberve experimentay thi change to Sn = 14%. Concuion In concuion, we have hown that it i poibe to grow crytaine ayer of on Ge and GaA ubtrate, with Sn concentration up to x = Coherent ayer (x < 0.04) can be grown on Ge ubtrate according to Peope and Bean critica thickne mode and therefore have 11

3 Superficie y Vacío 17(4), diciembre de 2004 Sociedad Mexicana de Ciencia de Superficie y de Vacío GeSn Ge (301 cm -1 ) attice parameter (Å) a buk aoy Ge /Ge/GaA(100) a a a buk aoy GeSn Intenity (A.U.) T=170 o C P=5x10-2 mbar GeSn128 (Sn 2%) GeSn127 (Sn 14%) GeSn126 (Sn 13%) a buk aoy GaA GeSn125 (Sn 10%) Sn concentration x Figure 3. The a (in-growth), a (in-pane) and a 0 (buk) attice parameter of the aoy are hown a function of Sn concentration Phonon Frecuency (cm -1 ) GeSn/Ge/GaA(100) GaA TO(268 cm -1 ) GaA LO(292 cm -1 ) Ge(301 cm -1 ) critica thickne h c (Å) Frank and Van der Merwe [6] Geometrica [7] Matthew and Bakeee [8] Peope and Bean [9] peudomorphic ayer Sn concentration x Intenity (A.U.) GeSn141 (Sn 8%) GeSn142 (Sn 8%) GeSn144 (Sn 7%) GeSn145 (Sn 6%) GeSn146 (Sn 9%) GeSn147 (Sn 7%) Figure 4. The thickne of the peudomorphica ayer i compare with evera critica thickne mode reported everywere. [6-9] GeSn148 (Sn 7%) Phonon Frecuency (cm -1 ) Figure 5. Raman meaurement of the aoy grown on Ge(100) and GaA(100) ubtrate. The doted ine indicate the poition of the LO and TO mode of Ge and GaA. The Sn concentration of the aoy i ao hown. 12

4 Superficie y Vacío 17(4), diciembre de 2004 Sociedad Mexicana de Ciencia de Superficie y de Vacío Ge 1-X Sn X Ge 1-X Sn X /Ge/GaA(100) Raman Shift (cm -1 ) Sn Concentration (%) by HRXRD Figure 6. Raman hift of the aoy compare with the Sn concentration determined by HRXRD. The oid ine i the Raman hift ω GeSn = ω cm -1 [10] reported for aoy Aborption Coefficient (α) E Direct Sn=0.14 E Indirect Sn=0.14 GeSn Ge Ge Tranmittance Sn=0.10 Sn=0.13 Sn=0.09 Sn= Figure 7. Tranmittance meaurement of the aoy grown on Ge(100) ubtrate. The Sn concentration of th e aoy i hown for each curve Figure 8. Aborption coefficient obtained from the tranmittance meaurement of the Ge 0.86 Sn 0.14 aoy. The determined direct and indirect band gap tranition of the aoy are hown Γ Thigth-Binding L Thigth-Binding Direct Gap/Ge Indirect Gap/Ge Direct Gap/GaA Indirect Gap/GaA Direct Gap (M. R. Bauer et a.[9]) Direct Gap (Atwater et a.[1,2]) Indirect Gap (Atwater et a.[1,2]) L Pot. of Def. Γ Pot. of Def Sn concentration by HRXRD Figure 9. Experimentay energy Band Gap vaue of the aoy compared with the predicted by the Potentia of Deformation Theory. The Sn concentration vaue in the graph were determined by HRXRD. 13

5 Superficie y Vacío 17(4), diciembre de 2004 Sociedad Mexicana de Ciencia de Superficie y de Vacío epiayer that are totay diocation free. The Ge 1- x aoy preent a tunabe band gap. The vaue of the Direct and Indirect band gap are very imiar to the vaue predicted by the Potentia of Deformation Theory. A direct tranition i experimentay oberved for aoy with Sn concentration up to Reference [1] Gang He and Harry A. Atwater, Phy. Rev. Lett. 79, 1937 (1997). [2] Regina Ragan and Harry A. Atwater, App. Phy. Lett. 77, 3418 (2000). [3] D. W. Jenkin and J. D. Dow, Phyica Rev. B 36, 7994 (1987). [4] S.I. Shah, J.E. Green, L. L. Abe, Qi Yao and P.M. Raccah, J. Cryta Growth 83, 3 (1987). [5] H. Pérez Ladrón de Guevara, A. Gaona Couto, M. A. Vida, J. Luyo Avarado, M. Meéndez Lira and M. López-López, J. Phy. D. 35, 1408 (2002). [6] F. C. Frank and J. H. Van der Merwe, Proc. Roy. Soc. (London) A 198 (1949) 216; J. H. Van der Merwe, J. App. Phy. Lett. 34 (1963) 117; J. H. Van der Merwe, In Singe Crita Fim (Pergamon, New York, 1964) p [7] D. J. Duntan, S. Young and R. H. Dixon, J. App. Phy 70 (6), 15 eptember [8] J. W. Matthew and A. E. Bakeee, J. Of Cryta Growth, 27 (1974) p [9] R. Peope and J. C. Bean, App. Phy. Lett. 47 (3) Augut [10] M. Roja-López, H. Navarro and J. Greene, J. Of App. Phy. 84, 2219 (1998). [11] K. A. Mäder, A. Baderechi, Soid State Communication, 69, 12 (1989). [12] J. Barden, W. Shockey, Phy. Rev. 80,72 (1950). [13] M. Bauer, J. Toe, C. Bungay, Soid Styate Communication, 127, 355 (2003). 14