33I-V PLOTS OF LIGHT EMITTING DIODES (LEDs)
I. OBJECTIVES
a. Collect current-voltage (I-V) data for one resistor and several light emitting diodes
b. Plot I versus V for the resistor and the diodes
c. Compare the I-V plot of the resistor with those of the diodes
II. EQUIPMENT
Resistor, diodes, 10 volt DC power supply, voltmeter, ammeter, connecting wires
III. INTRODUCTION
An incandescent lamp consists of a metal filament made out of tungsten which is heated to a high temperature by an electric current that passes through it. The filament is enclosed in an evacuated glass envelope to avoid oxidation of the filament by the surrounding air. Most of the light emitted by an incandescent lamp is in the infrared and therefore is not visible. Incandescent lamps are inefficient light sources because only a small part of the electrical power they consume is converted into visible light. Light emitting diodes (LEDs) which are made out of semiconductor materials such as gallium arsenide (GaAs )are much more efficient light sources.
Below we describe briefly the operating principle of these diodes. Pure semiconductors (also called “intrinsic”) do not contact electricity at room temperature and are thus not useful for the fabrication of electric and electronic devices. Semiconductors conduct electricity if we dope them with a small amount of impurity atoms. In the case of Silicon (Si) these would be any atom other than Si. Impurities are divided into two broad categories: Donors and Acceptors. A donor is an impurity atom that has more electrons in its outermost shell that is necessary to form chemical bonds with their neighboring atoms. Each Silicon atom has four electrons in its outermost shell; these electrons are involved in forming the chemical bonds with the neighboring Si atoms. An Arsenic (As) atom on the other hand has 5 electrons in its outermost shell. If we add it as an impurity silicon it will act as a donor because it...