Dynamics of hot carrier cooling in photo-excited GaAs

Carrier relaxation following excitation with subpicosecond optical pulses, determined from time resolved nearband gap transmission spectrum changes, is described for GaAs. For n < 5×10¹⁷cm^-3 the observed relaxation can be related to carrier-phonon interaction, but at higher densities the rate of relaxation is significantly slowed, possibly due to carrier screening.     

Picosecond time resolved reflectivity of direct gap semiconductors

The relaxation of optically excited hot carrier distributions in GaAs and CdSe has been measured by time resolved reflectivity measurements with sub-picosecond optical pulses from a mode-locked cw dye laser. A characteristic transient in the reflectivity has been interpreted by an analysis of the perturbed optical dielectric function. Estimated energy loss rates are 0.4 eV/ps for electrons and holes having mean energies in the range of 1 to 2 eV for GaAs at room temperature.     

Ultrashort Light Pulses

Ultrashort Light Pulses     

Bases for rings of coinvariants

We study the multiplicative structure of rings of coinvariants for finite groups. We develop methods that give rise to natural monomial bases for such rings over their ground fields and explicitly determine precisely which monomials are zero in the ring of coinvariants. We apply our methods to the Dickson, upper triangular and symmetric coinvariants. Along the way, we recover theorems of Steinberg [17] and E. Artin [1]. Using these monomial bases we prove that the image of the transfer for a general linear group over a finite field is a principal ideal in the ring of invariants. This research is supported in part by the Natural Sciences and Engineering Research Council of Canada