  We study experimentally the electron transport properties of gated quantum
dots formed in InGaAs/InP and InAsP/InP quantum well structures grown by
chemical-beam epitaxy. For the case of the InGaAs quantum well, quantum dots
form directly underneath narrow gate electrodes due to potential fluctuations.
We measure the Coulomb-blockade diamonds in the few-electron regime of a single
quantum dot and observe photon-assisted tunneling peaks under microwave
irradiation. A singlet-triplet transition at high magnetic field and
Coulomb-blockade effects in the quantum Hall regime are also observed. For the
InAsP quantum well, an incidental triple quantum dot forms also due to
potential fluctuations within a single dot layout. Tunable quadruple points are
observed via transport measurements.
