6 tion of chemical disorder, and the scattering-strength pa- rameter. In addition, we found that the interior layers in comparison with the surface layer, have significant con- tribution in the optical absorption of the system. The obtained results clearly indicate that, studying the dependence of quantum size effects on the optical prop- erties of doped semiconductors is important for better understanding the process of optical absorption in lay- ered structures, and will be helpful for designing opto- electronic nanodevices. band decreases and shifts to the high-energy side, while the spectrum of the B -type band increases and shifts to the low-energy side. Here, we should mention that, under certain conditions, the width of optical absorption spec- trum in disordered quantum wires can be considerably stronger than that of the present system [4]. An inter- esting point in Fig. 5 is that, in spite of the symmetry of g$_{n}$ ( ω ) for x = 0 . 5 with respect to the center of elec- tronic spectrum, the optical spectrum is not symmetric and the lower band shows a higher value of absorption which is due to the fact that only the k$_{‖}$ = 0 component contributes to this process. It is important to mention that the optical absorption spectrum from each layer is not a measurable quantity in experiment and only the bulk (total) optical absorp- tion spectrum, A ( ω ), is possible. In order to obtain this quantity we should sum over the optical absorption of all layers, i.e., A ( ω ) = ∑ N z n $_{=1}$A$_{n}$ ( ω ). The total optical ab- sorption are shown in Fig. 6(a) and 6(b) for E$_{B}$ = − 3 t and E$_{B}$ = − 8 t , respectively. From the figures we see that, in the case of E$_{B}$ = − 3 t , the absorption spectrum has sharp peaks at the bottom of the optical band for all values of x , and shows that the value of total optical ab- sorption at the band minimum of the amalgamation type (Fig. 6(a)) is higher than that of the persistence type (Fig. 6(b)). The numerical results also confirm that, as in the bulk materials, the transition from the amalgama- tion type to the persistence type in multilayers depends on two parameters Δ and x [10, 11]. ∗ Electronic address: a-saffar@tpnu.ac.ir [1] P. Harrison, Quantum Wells, Wires and Dots , Theoreti- cal and Computational Physics (Wiley, New York, 2000). [2] M. Razeghi, Fundamental of Solid State Engineering , 2nd ed. (Springer, New York, 2006). [3] M. Asada, Y. Miyamoto, and Y. Suematsu, IEEE J. Quantum Electron. 22 , 1915 (1986). [4] C. Fuchs and R.V Baltz, Phys. Rev. B 63 , 085318 (2001). [5] Y. Shinozuka, H. Kida, and M. Fujibayashi, Phys. Stat. Sol. (b) 229 , 553 (2002). [6] Y. Shinozuka, Jpn. J. Appl. Phys. 45 , 8733 (2006). [7] A. Gonis, Green Functions for Ordered and Disorderd Systems (North-Holland, Amsterdam) Studies in Math- ematical Physics, Vol. 4, (1992). [8] P. Soven, Phys. Rev. 156 , 809 (1967). [9] B. Velick´ y, S. Kirkpatrick, and H. Ehrenreich, Phys. Rev. 175 , 747 (1968). [10] Y. Onodera and Y. Toyozawa, J. Phys. Soc. Jpn. 24 , 341 (1968). [11] Y. Toyozawa, Optical Processes in Solids (Cambridge University Press, New York, 2003). [12] S. Yoshikawa and M. Aihara, J. Phys. Soc. Jpn. 76 , 044712 (2007). [13] L.D. Bakalis, I. Rubtsov, and J. Knoester, J. Chem. Phys. 117 , 5393 (2002). [14] M. Takahashi, Phys. Rev. B 70 , 035207 (2004). [15] K. Nikoli´ c and A. MacKinnon, Phys. Rev. B 47 , 6555 (1993). [16] A. Saffarzadeh, Phys. Rev. B 76 , 214201 (2007). [17] A. Okiji, H. Nakanishi, K. Sakata, and H. Kasai, Jpn. J. Appl. Phys. 31 , L706 (1992). [18] H. Hasegawa, Phys. Rev. B 47 , 15073 (1993). Using the single-band tight-binding theory and the single-site CPA, we have studied the influence of substi- tutional disorder on the electronic and optical properties of disordered semiconductor multilayers. The results of this theory which is able to predict either the persistent or amalgamated bands, indicate that the optical absorp- tion is governed by the electronic density of states, which is stronger near the bottom of the band. The values of absorption depend on the layer number, the concentra- CONCLUSION