Generalized-GIXD (Evanescent Scattering) measurements of ...pf3A/2000C011 Generalized-GIXD...
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3A/2000C011 Generalized-GIXD (Evanescent Scattering) measurements of InAs nano-dots Masao KIMURA 1 , Takeshi URAGAMI 2 , Tamaki SUZUKI 1 , Hiroshi FUJIOKA 2 , and Masaharu OSHIMA 2 1 Nippon Steel Co, Futtsu, Chiba 293-8511, Japan 2 The Univ. of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan Introduction Generalized grazing incidence-angle x-ray diffraction (G-GIXD) or evanescent scattering has been developed to investigate near surface structures of films and dots on Si [1-3]. In this study, this technique has been applied to nano-dots of InAs to investigate change of in-plane structures along the depth-direction. Experiments The method was applied to nano-dots of InAs, ~ 20 H x30 φ nm 3 , grown on Si (001) [3]. Evanescent scattering was measured by keeping the angle of incidence (α i ) around the critical angle of InAs (α c ). Bragg spots were measured systematically by mesh scanning with a scintillation counter (SC)in the Q-space : Q-components parallel (Q x-y ) and perpendicular (Q z ) to the surface, where outline of the profile was also measured by an image plate. Two sets of slits, which limit the height and the width of the beam path, are positioned in front of SC. Resolution function was changed by altering the heights (h slit ), the width (w slit ), and the distance of two slits (d slit ). The typical values are : h slit w slit and = 1-2 mm, d slit = 310 mm; the resolution are ∆Q x-y = 1-2×10 -2 and ∆Q z = 2-4×10 -2 [r.l.u.]. Typical time for measuring intensities by SC was about 1-10 sec. Experiments have been carried out at BL-3A. Results Fig.1 shows the α i dependence of 220 (in-plane) scattering profiles of InAs which corresponds to the Q x-y cross-section of Q(k) at Q z = 0.0. It is clearly observed that the peak maximum shifts towards at a larger Q x-y side as increase of α i , showing the existence of the gradient of the strain field. The scattering intensities are maximum at the condition α I = α c , and their change is consistent with the calculated one. This indicated that the measured intensities come from the evanescent scattering and are not caused by bulk scattering at the side sections of dots. The strain field in the Q x-y direction is calculated from measured intensities. Fig.2 shows the penetration depth: l 1/e dependence of the strain of InAs nano-dots, where the l 1/e = 0 and = 35 nm corresponds the top and the bottom (or the interface of InAs/Si ) of the dots. It is worth noting that the measured strain is the sum of the total region of penetration. The strain is saturated around a depth l 1/e = 35 nm, because the region l 1/e > 35 nm corresponds to the substrate of Si. It is revealed the strain is maximum at the interface InAs/Si and the averaged strain ε x-y = -0.5 % and that the strain is relaxed near the top. The intensities of evanescent wave decays as a function of exp(-z/l 1/e ) (z: depth). The deconvolution of measured strain which was averaged over the depth, can be performed using FEM technique based on the results for different α i [4]. Fig.1 α i dependence of 220 (in-plane) scattering profiles of InAs Fig.2 Penetration depth: l 1/e dependence of the strain of InAs nano-dots. References [1] Y.Takagai and M.Kimura, J.Syncrotron Rad. 5,488 (1998) . [2] M.Kimura et al., PF Act. Rep. #17B,86 (1999) . [3] T.Uragami et al., Jpn. J. Appl. Phys. 39, 4483 (2000). [4] M.Kimura et al., Jpn. J. Appl. Phys. (in preparation). * [email protected] 0 10 20 30 40 50 60 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 Strain Strain in the plane [%] Penetration depth l_1/e [nm] 2.88 2.90 2.92 2.94 2.96 2.98 3.00 0 100 200 300 400 500 600 700 800 Intensities (a.u.) Q / A^-1 ai/ac=0.41 ai/ac=1.01 ai/ac=2.21
Transcript of Generalized-GIXD (Evanescent Scattering) measurements of ...pf3A/2000C011 Generalized-GIXD...
3A/2000C011
Generalized-GIXD (Evanescent Scattering) measurements of InAs nano-dots
Masao KIMURA1, Takeshi URAGAMI2, Tamaki SUZUKI1, Hiroshi FUJIOKA2, and Masaharu OSHIMA2
1Nippon Steel Co, Futtsu, Chiba 293-8511, Japan 2The Univ. of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
Introduction
Generalized grazing incidence-angle x-ray diffraction (G-GIXD) or evanescent scattering has been developed to investigate near surface structures of films and dots on Si [1-3]. In this study, this technique has been applied to nano-dots of InAs to investigate change of in-plane structures along the depth-direction.
Experiments
The method was applied to nano-dots of InAs, ~ 20Hx30φnm3, grown on Si (001) [3]. Evanescent scattering was measured by keeping the angle of incidence (αi) around the critical angle of InAs (αc). Bragg spots were measured systematically by mesh scanning with a scintillation counter (SC)in the Q-space : Q-components parallel (Qx-y ) and perpendicular (Qz) to the surface, where outline of the profile was also measured by an image plate. Two sets of slits, which limit the height and the width of the beam path, are positioned in front of SC. Resolution function was changed by altering the heights (hslit), the width (wslit), and the distance of two slits (dslit). The typical values are : hslit wslit and = 1-2 mm, dslit= 310 mm; the resolution are ∆Qx-y = 1-2×10-2 and ∆ Q z = 2-4×10-2 [r.l.u.]. Typical time for measuring intensities by SC was about 1-10 sec. Experiments have been carried out at BL-3A.
Results Fig.1 shows the αi dependence of 220 (in-plane)
scattering profiles of InAs which corresponds to the Qx-y cross-section of Q(k) at Qz = 0.0. It is clearly observed that the peak maximum shifts towards at a larger Qx-y side as increase of αi , showing the existence of the gradient of the strain field. The scattering intensities are maximum at the condition αI = αc , and their change is consistent with the calculated one. This indicated that the measured intensities come from the evanescent scattering and are not caused by bulk scattering at the side sections of dots.
The strain field in the Qx-y direction is calculated from measured intensities. Fig.2 shows the penetration depth: l1/e dependence of the strain of InAs nano-dots, where the l1/e = 0 and = 35 nm corresponds the top and the bottom (or the interface of InAs/Si ) of the dots. It is worth noting that the measured strain is the sum of the total region of penetration. The strain is saturated around a depth l1/e = 35 nm, because the region l1/e > 35 nm corresponds to the substrate of Si. It is revealed the strain is maximum at the interface InAs/Si and the averaged
strain εx-y = -0.5 % and that the strain is relaxed near the top.
The intensities of evanescent wave decays as a function of exp(-z/l1/e) (z: depth). The deconvolution of measured strain which was averaged over the depth, can be performed using FEM technique based on the results for different αi [4].
Fig.1 αi dependence of 220 (in-plane) scattering profiles of InAs
Fig.2 Penetration depth: l1/e dependence of the strain of
InAs nano-dots.
References [1] Y.Takagai and M.Kimura, J.Syncrotron Rad. 5,488 (1998) . [2] M.Kimura et al., PF Act. Rep. #17B,86 (1999) . [3] T.Uragami et al., Jpn. J. Appl. Phys. 39, 4483 (2000). [4] M.Kimura et al., Jpn. J. Appl. Phys. (in preparation). * [email protected]
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