Electron spin dynamics in InAs/GaAs heterostructures consisting of a single layer of InAs (1/3$sim$1 monolayer) embeded in (001) and (311)A GaAs matrix was studied by means of time-resolved Kerr rotation spectroscopy. The spin relaxation time of the sub-monolayer InAs samples is significantly enhanced, compared with that of the monolayer InAs sample. We attributed the slowing of the spin relaxation to dimensionally constrained Dtextquoteright{}yakonov-Pereltextquoteright{} mechanism in the motional narrowing regime. The electron spin relaxation time and the effective g-factor in sub-monolayer samples were found to be strongly dependent on the photon-generated carrier density. The contribution from both Dtextquoteright{}yakonov-Pereltextquoteright{} mechanism and Bir-Aronov-Pikus mechanism were discussed to interpret the temperature dependence of spin decoherence at various carrier densities.
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