Transport measurements are presented on a class of electrostatically defined lateral dots within a high mobility two dimensional electron gas (2DEG). The new design allows Coulomb Blockade(CB) measurements to be performed on a single lateral dot containing 0, 1 to over 50 electrons. The CB measurements are enhanced by the spin polarized injection from and into 2DEG magnetic edge states. This combines the measurement of charge with the measurement of spin through spin blockade spectroscopy. The results of Coulomb and spin blockade spectroscopy for first 45 electrons enable us to construct the addition spectrum of a lateral device. We also demonstrate that a lateral dot containing a single electron is an effective local probe of a 2DEG edge.

Conductance fluctuations have been studied in a soft wall stadium and a Sinai billiard defined by electrostatic gates on a high mobility semiconductor heterojunction. These reproducible magnetoconductance fluctuations are found to be fractal confirming recent theoretical predictions of quantum signatures in classically mixed (regular and chaotic) systems. The fractal character of the fluctuations provides direct evidence for a hierarchical phase space structure at the boundary between regular and chaotic motion.

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Visible-stimulated emission in a semiconductor quantum dot (QD) laser structure has been demonstrated. Red-emitting, self-assembled QDs of highly strained InAlAs have been grown by molecular beam epitaxy on a GaAs substrate. Carriers injected electrically from the doped regions of a separate confinement heterostructure thermalized efficiently into the zero-dimensional QD states, and stimulated emission at approximately 707 nanometers was observed at 77 kelvin with a threshold current of 175 milliamperes for a 60-micrometer by 400-micrometer broad area laser. An external efficiency of approximately 8.5 percent at low temperature and a peak power greater than 200 milliwatts demonstrate the good size distribution and high gain in these high-quality QDs.

Electron-phonon coupling of a two-dimensional electron gas in a Si metal-oxide-semiconductor field-effect transistor in the temperature range 0.3 KϽTϽ4 K has been investigated using phonon-drag thermopower S g and electron energy loss rate F(T). At low temperatures ͑the Bloch limit͒ we find S g ϰT 6 , as expected for electron-phonon scattering mediated by a screened deformation potential, and the magnitude is in excellent agreement with a calculation using no adjustable parameters; the calculation continues to give good agreement at higher temperatures. F(T) has been calculated using the same input parameters as for S g . Reasonably good agreement is found with the observed values for TϾ1.5 K, but at lower temperatures the measured F(T) is much larger than predicted and also exhibits a much weaker temperature dependence. Possible reasons are suggested. ͓S0163-1829͑97͒05143-6͔