Light Emitting Diodes Leds And Measuring Plancks Constant By Chan Kee-Lin Steven.pdf

Light Emitting Diodes (LEDs) and measuring
Planck’s constant.
Chan Kee-Lin Steven, pundit@
June 9, 2001
1
1 Introduction
What are diodes? They are electronic devices which allow current to pass
through in only one direction. Diodes can be made using many different
technologies but by far the mon diode today is made with semi-
conductor technology.
2 Semi-conductors
A semi-conductor is a special type of material whose conduction charac-
teristics fall between that of conductors and insulators. What does that
mean? Well it means they conduct a little bit. However their ability to
conduct increases dramatically as the temperature increases. It’mon
knowledge that materials conduct due to the presence of charge carriers.
The more charge carriers, the better the conductor. That’s why metals with
their abundance of free electrons are such good conductors while insulators,
having almost no free electrons, are such poor ones.
Let’s focus on silicon, the most widely used semi-conductor material
today. The intrinsic charge carrier concentration in silicon at room tem-
perature is × 1010 carriers/cm3. That seems like a lot until one realizes
that the density of silicon atoms in 1 cm3 is about × 1022. This im-
plies that there is 1 charge carrier for about every 3000 billion atoms. On
the other hand, in a metal, the number of free electrons probably excee