European Conference on Energy Dispersive X-Ray Spectrometry EDXRS 2002 June 16 to 21, 2002 in Berlin, Germany.

From the Book of Abstracts of EDXRS 2002 Conference, Berlin, Germany, p. 16.   Investigation of Si1-a-b Gea Cb / Si Strain-Compensated Heterojunction by the X-rays Backdiffraction Method   Hakob P. Bezirganyan and Siranush E. Bezirganyan, Faculty of Physics, Yerevan State University, #1, A. Manoogian Street, Yerevan 375025, Armenia; Hayk H. Bezirganyan (Jr.), Faculty of Informatics and Applied Mathematics, Yerevan State University, #1, A. Manoogian Street, Yerevan 375025, Armenia; Petros H. Bezirganyan (Jr.), Dep. of Computer Science, State Engineering University of Armenia, #105, Terian Street, Yerevan 375009, Armenia.   Si-based optoelectronic devices need to be monolithically integrated with Si-based microelectronics and operate in the infrared wavelength region, suitable for fiber-optic communications. To achieve an efficient photo-response at the 1,3 mm wavelength region with SiGe/Si photodetectors, the Ge concentration should be in excess of 35%. The lattice constant of Ge is 4,2% larger than that of Si. Therefore if a bulk Ge layer is placed on a bulk Si layer in an attempt to form a single crystal, every 24th Si atom at the interface would not be able to form a bond with a Ge atom. The lattice mismatch between Si and Ge constrains the design of SiGe heterojunction devices because of the limited thickness for pseudomorphic SiGe epilayers on a Si platform, i.e. there exists a maximum thickness called the critical thickness above which is necessary too much energy to strain additional layers of material into coherence with the substrate. As the result a defects, e.g. a misfit dislocations, appear in the system to relieve the strain (see figure 1). strain - compensated Si1-a-b GeaCb layer misfit dislocation relaxed Si1-a Gea layer misfit dislocation bulk silicon substrate Figure 1. Proposed model of the Si1-a-b GeaCb / Si strain-compensated heterojunction.   Incorporation of C into Si1-aGea layer to form ternary Si1-a-b GeaCb alloy makes it possible to reduce the compressive strain between the SiGe epilayer and the Si substrate, and therefore to control the strain about the lattice matching condition for Si substrates [1-4]. If (a / b) ~ 10, then the lattice constant in the growth direction is equal to that of the substrate [1]. The proposed model of the Si1-a-b GeaCb / Si strain-compensated heterojunction is presented in the figure 1. The strain-compensated Si1-a-b GeaCb thin layer and the silicon substrate have the same value of the spacing period along the growth surface - the entrance surface of the x-rays according to this model. However, there exists a shift between their space periods stipulated by a misfit dislocations (see figure 1). The investigations, sensitive to the phase shift, can be performed using the Grazing-Angle Incidence X-ray Backdiffraction (GIXB) technique, i.e. the x-ray diffraction in the conditions, when the Bragg angle is more than one or two critical angles of incidence [5]. It is considered theoretically the GIXB depending on the values of phase shift between the space periods, and of the Bragg angle.     References: B. Dietrich, H. J. Osten, H. Rucker, M. Methfessel, and P. Zaumseil, Phys. Rev. B, 49 (1994), 17185. J. Kolodzey, P. R. Berger, B. A. Orner, D. Hits, F. Chen, A. Khan, X. Shao, M. M. Waite, S. Ismat Shah, C. P. Swann, and K. M. Unruh, J. Cryst. Growth, 157 (1995), 386. X. Shao, S. L. Rommel, B. A. Orner, P. R. Berger, and J. Kolodzey, IEEE Electron Device Lett., 18 (1997), 7. X. Shao, Ralf Jonczyk, M. Dashiell, D. Hits, B. A. Orner, A.-S. Khan, K. Roe, J. Kolodzey, P. R. Berger, M. Kaba, M. A. Barteau, and K. M. Unruh, J. Appl. Phys., 85 1 (1999), 578. A. P. Bezirganyan and P. A. Bezirganyan, Phys. Stat. Sol. (a), 105 (1988), 345.

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