Narrow Results

The essential steps required to create thick GaN films and seed crystals for bulk crystal growth are described. These include the growth of low dislocation density GaN films by hydride vapor phase epitaxy and the separation of films from their growth substrates. Also addressed are issues of processing thin and thick films to create compliant layer substrates for thick film HVPE growth and chemical mechanical polishing methods to enhance surface morphology and remove material damage free. Growth of both gallium and nitrogen polar films is discussed with key issues identified regarding polarity inversion during growth and impurity incorporation along the -c growth direction. These are illustrated with examples that emphasize the growth of material with low threading dislocation density.

The expansion of the U.S. corn seed trade is not well understood. This article econometrically investigates world demand for U.S. corn seeds, focusing on trade costs impeding exports, including transportation, tariffs, and sanitary and phytosanitary (SPS) regulations. The analysis estimates a derived demand for seed by foreign corn producers using data from 48 countries for the years 1989 to 2004. An SPS count variable captures shifts in the cost of seeds faced by foreign users. A sample selection framework accounts for the large presence of zero trade flows. All trade costs have a significantly negative impact on U.S. com seed exports.