For 10 points, identify these circuit elements which only allow current to pass in one direction.
One type of these exhibit a peculiar behavior which can be described by the Ridley-Watkins-Hilsum two-valley model; that type shows a negative differential resistance profile for fields higher than 3 KV per centimeter. Another type, which make use of quantum tunnelling, are named for Esaki, and they can be employed to rectify AC current into DC current. The ideal behaviour of these is governed by the Shockley equation, and another type employs the avalanche breakdown effect named for Zener. Yet another one of these is formed by the contact of the semiconductor, and they are symbolized by a forward triangle touching a vertical bar. For 10 points, identify these circuit elements which only allow current to pass in one direction.
One type of these exhibit a peculiar behavior which can be described by the Ridley-Watkins-Hilsum two-valley model; that type shows a negative differential resistance profile for fields higher than 3 KV per centimeter.
{diode}