Quantum Mechanics Meets Semiconductors

In the 1920s, Louis de Broglie in France was studying the new science theories of quantum mechanics.  He knew that physicists now believed light waves--usually thought of as a constantly fluctuating electromagnetic wave--could sometimes behave like particles as hard and precise as billiard balls.  He realized that perhaps the reverse was true too.  Perhaps particles such as electrons could sometimes behave like waves. 

Another scientist, Swiss theorist Erwin Schroedinger incorporated this mathematically into a set of equations. These--known, not surprisingly, as Schroedinger equations--could descibe with utmost precision all the behavior of electrons and other atomic particles. 

In the 1930s, these equations became fully accepted as the scientific community tried to apply them to complicated systems of atoms like those found in crystals and metals.  Physicists--usually professors and students in universities--threw themselves into the task of analyzing these basic structures. Key steps were taken in Germany, Britain, the United States, and the Soviet Union among other places. 

When scientists began to think of the electrons in crystals as waves, they discovered fascinating, and often surprising, new patterns of movement. This was behavior unlike anything that simple particles might do. For instance, if the usually perfectly-ordered atoms in a crystal  had even a single atom out of place, the electron waves' movement as it traveled through would be seriously changed. 

One of the applications for these new rules about electrons was in semiconductors--mysterious crystals that sometimes conducted electricity and sometimes didn't. Eugene Wigner and his student Frederick Seitz worked long and hard on this issue at Princeton University in the 1930s.  They were the first to figure out just how these waves could make different kinds of materials conduct or not conduct electricity.  (Answer: Some atoms are set up so that electron waves can easily move to the right place where they can then move through the material as a current.  In others atoms the waves simply can't make the jump to the necessary location.) 

Work like this laid down the ground work for the research Bell Labs would do a decade later turning a semiconductor crystal into a transistor. 

Resources: 
-- Where Does the Weirdness Go? Why Quantum Mechanics is Strange, But Not as Strange as You Think, David Lindley 
-- What is Quantum Mechanics?  A Physics Adventure, Transnational College of LEX 
-- The Handy Physics Answer Book, P. Erik Gundersen 
-- Albert Einstein exhibit at the American Institute of Physics
-- Heisenberg exhibit at the American Institute of Physics