References [1] A Puente, M Casas, Comput. Mater Sci. 2 (1994) 441 [2] G Bastard, Wave Mechanics Applied to Semiconductor Heterostructures, Les Editions de Physique, Les Ulis, 1988. [3] L I Serra, E Lipparini, Europhys. Lett. 40 (1997) 667. [4] F Arias de Saaverda, J Boronat, A Polls, A Fabrocini, Phys. Rev. B 50 (1994) 4248. [5] M Barranco, M Pi, S M Gatica, E S Hemandez, J Navarro, Phys. Rev. B 56 (1997) 8997. [6] A Puente, L I Serra, M Casas, Z. Phys. D 31 (1994) 283. [7] A R Plastino, M Casas, A Plastino, Phys. Lett. A281 (2001) 297. [8] A Schmidt, Phys. Lett. A 353 (2006) 459. [9] S H Dong, M Lozada-Cassou, Phys. Lett. A 337 (2005) 313. [10] I O Vakarchuk, J. Phys. A ; Math. Gen. 38 (2005) 4727. [11] C Y Cai, Z Z Ren, G X Ju, Commun. Theor. Phys. 43 (2005) 1019. [12] B Roy, P Roy, Phys. Lett. A 340 (2005) 70. [13] B Gonul, M Kocak, Chin. Phys. Lett. 20 (2005) 2742. [14] A de Souza Dutra, C A S Almeida, Phys Lett. A 275 (2000) 25. [15] T Gora, F Williams, Phys. Rev. 177 (1969) 1179. [16] D J Ben Danial, and C B Duke, Phys. Rev. 152 (1966) 683. [17] Q G Zhu, H Kroemer, Phys. Rev. B 27 (1983) 3519. 10