Research Experience

Electrical Transport in Coupled Quantum Dots

For my Ph.D., I measured electrical transport through a pair of quantum dots with adjustable interdot coupling. The dots were lithographically defined in a two-dimensional electron gas by means of surface gates on a GaAs/AlGaAs heterostructure. With my colleague Carol Livermore, we measured both the I-V characteristics and the zero-bias current when varying the interdot coupling, to observe the effect of changing interdot coupling on the Coulomb blockade in this system. This work was done in Bob Westervelt’s laboratory at Harvard University.

Our work was published in Applied Physics Letters (Crouch et al, Appl. Phys. Lett. 71, 817 (1997)) and in Science (Livermore et al, Science 274, 1332 (1996)), and presented at several conferences.

Fabrication and Optoelectronic Properties of Silicon Microstructures

Irradiating a crystalline silicon surface with a train of high-power femtosecond laser pulses (fluence above the damage threshold) in a sulfur hexafluoride environment produces a quasiordered array of microspikes on the surface. The size and aspect ratio of the
spikes depends on the laser fluence, but the spikes can be 10 micrometers or more deep and extremely sharp, with tips less than 1 micrometer across. The irradiated surface looks black to the eye and absorbs more than 95% of incident visible light. More remarkably, it absorbs over 90% of incident light in the infrared, at energies below the band gap of ordinary silicon. This below-band gap absorption most likely occurs because sulfur is incorporated into the silicon in high concentrations on the surface of the spikes. I studied the dependence of the optical properties on chemical composition and fabrication conditions, and studied the process by which these spikes form. This work was done in Eric Mazur’s laboratory at Harvard University, in collaboration with James Carey, Claudia Wu, Mengyan Shen, Rebecca Younkin, and many others.

Our work was published in Applied Physics Letters and Applied Physics A, and presented at several conferences. For the current status of this project, see Eric Mazur’s group web site.

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