Effects of Electron Radiation on the Optical Constants of P-Type Silicon
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EFFECTS OF ELECTRON RADIATION ON THE OPTICAL CONSTANTS OF P-TYPE SILICON
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ONOFRIO L. RUSSO*and KATHERINE A. DUMAS ** New Jersey Institute of Technology, Department of Physics, Newark, NJ 07102 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 93555
ABSTRACT The optical constants n and k are determined for p-type silicon at the E 0 and El and critical point energies for oj MeV el•9tron iradiated samples. The value for fluences of 10 and The 10 e-/cm are compared to samples before irradiation. real,', and imaginary,e 2 components of the dielectric function, e, usea to find n and k, were obtained by measurement of tanV and 8 using spectroscopic ellipsometry (SE). The data show that changes in 8, in particular, are greater in the region about Eo with electrolyte This is consistent than of E1 . electroreflectance (EER) results in which the Lorentz line shape is narrower for Eo than for E1 . The value of n is found to increase and k to decrease with e- radiation at the critical The change in n points, although, neither does so monotonically. at the Eo critical point is greater than at the higher energy main structure E1 whereas,k is a slower varying function in this region.
INTRODUCTION The optical constants n and k, where n is the real part of the complex refractive index 6, and k the imaginary part, called the extinction coefficient is related by n%= n -ik. The region of interest for silicon where the first direct optical transitions occur is in the near-visible region around the 3.40 eV complex. Numerous investigators have measured the optical constants which includes this region. The values of n and k in the visible-ultraviolet region from reflectivity measurements were determined using the Kramers-Kronig relation [1-4]. The effect of a native oxide on the reflectivity measurements [4] and of films on silicon by ellipsometry have been considered [5]. Spectroscopic ellipsometric analysis and measurements on the effects of the interface between silicon and thermally grown oxides [6] are in reasonable agreement with fixed-wavelength null ellipsometry [7]. The results for (100), (110) and (111) sample orientations show an interfacI consisting of atomically mixed Si and 0 with a width of 7 ± 21 and an average stoichiometry for SiOx of x = 0.4 ± 0.2 with a gradual transition range [6]. The refractive index for this transition region of n = 3.2 ± 0.5 at a
Mat. Res. Soc. Symp. Proc. Vol. 302. ©1993 Materials Research Society
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wavelength of 5461A clearly causes a change in the measured quantities V and 8 which are used to calculate n and k. The quantity 8 is the phase difference between the reflected wave amplitude parallel, Rp, and that perpendicular, Rs, to the plane of incidence for plane polarized incident light, whereas,V is given as the ratio of the amplitudes, tanV = Rp/Rs. The critical point energies consisting of a weak transition at E and the main structure, E1 have been resolved for irradiated ana non irradiated p-type silicon [8]. The values of Eo and E1 were obtained by
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