  InAs self-assembled quantum dots were grown on strained layers of GaxIn1-xP
(0 < x < 0.3) on InP substrates. We show that the quantum dots have narrow
vertical dimensions, ranging between 2 to 10 monolayers only. The dot layer
photoluminescence spectrum is composed of distinct spectral peaks, resulting
from the discrete distribution of the dot heights. The dot height distribution
depends on the total amount of InAs deposited and on the Ga content of the
strained GaxIn1-xP layer underneath. Our experimental results are corroborated
by an 8 band k(dot)P model calculations. In particular, we identify and
quantify the diffusion of Ga from the GaxIn1-xP layer into the quantum dots.
