For an abrupt heterojunction between two otherwise homogeneous semicon
ductors in one dimension, the effective-mass Hamiltonian H=-<(h)over b
ar (2)>/2 m(z)(alpha) alpha(z)(v) d/dz m(z)(beta) alpha(z)(-2v) d/dz m
(z)(alpha) alpha(z)(v)+E(c)(z) is examined with 2 alpha+beta=-1, where
m(z), a(z), and E(c)(z), are the position dependent effective mass. t
he local lattice parameter, and tile local conduction band edge, respe
ctively. Tile exact Schrodinger equation is compared with that for the
effective-mass equation in the case of an analytically solvable model
. In the asymptotic limit of the energy close to the hand edge, the co
nclusions obtained are shown to be dependent on tile parity of the ban
ds.