A layer of semiconductor material, used in a photovoltaic device, whose properties are essentially those of the pure, undoped, material.

The upper layer of the ocean that is reasonably well mixed due to the action of the wind, tides, or winter convective cooling.

This layer is reasonably homogenous in terms of its temperature, salinity, and nutrient concentrations; this is also the layer where most primary production occurs.

1. A semiconductor to which an impurity has been added so the concentration of electrons is much higher than the concentration of holes; the electrical current is carried chiefly by these electrons.
2. Negative semiconductor material in which there are more electrons than holes; current is carried through it by the flow of electrons.

The area that protects all organisms from the harmful ultraviolet rays of the sun, is located within the stratosphere, between 10 to 30 miles (16 to 48 kilometers) in altitude.

The lower part of the earth's atmosphere that is directly influenced by conditions on the surface; such as, evapotranspiration.

Its height is variable and ranges from 100 to 3,000 meters.