TYPE-II-]TYPE-I TRANSITION IN (GAX)(N) (INX)(N)(001) SUPERLATTICES (X=P, SB) AS A FUNCTION OF PERIOD-N/

Coherently strained GaX/InX interfaces (X=P, Sb) lattice matched to a (001)-oriented substrate are predicted to have a type-I band-gap align ment, with both the valence-band maximum and the conduction-band minim um (CBM) located on the In-rich material. At the same time, the CBM wa ve function of short-period (GaX)(n)/(InX)(n) superlattices is predict ed to have larger amplitude on the GaX layers, leading to a type-II al ignment. We show that (i) a type-II-->type-I transition occurs around the period n=4; (ii) this transition has a different origin with respe ct to the well-known case of GaAs/AlAs superlattices; (iii) the band s tructure of ultrathin superlattices cannot be explained in terms of a simple effective-mass theory; (iv) the wave-function localization in s hort-period superlattices is determined by the atomic orbital energies .