physics mini project

LED
WHAT IS LED?
A light-emitting diode (LED) is a semiconductor device that emits light when current flows
through it. Electrons in the semiconductor recombine with electron holes, releasing energy in
the form of photons. The color of the light (corresponding to the energy of the photons) is
determined by the energy required for electrons to cross the band gap of the semiconductor.
White light is obtained by using multiple semiconductors or a layer of light-emitting phosphor
on the semiconductor device.
Appearing as practical electronic components in 1962, the earliest LEDs emitted low-intensity
infrared (IR) light. Infrared LEDs are used in remote-control circuits, such as those used with a
wide variety of consumer electronics. The first visible-light LEDs were of low intensity and
limited to red.
Construction of LED
The recombination of the charge carrier occurs in the P-type material, and hence P-
material is the surface of the LED. For the maximum emission of light, the anode is
deposited at the edge of the P-type material. The cathode is made of gold film, and it is
usually placed at the bottom of the N-region. This gold layer of cathode helps in
reflecting the light to the surface.
The gallium arsenide phosphide is used for the manufacturing of LED which emits red
or yellow light for emission. The LED lights are also available in green, yellow amber
and red in color.
The simple transistor can be used for off/ on of a LED as shown in the figure above.
The base current IB conducts the transistor, and the transistor conducts heavily. The
resistance RC limits the current of the LED
Working of LED
The working of the LED depends on quantum theory. The quantum theory states that
when the energy of electrons decreases from the higher level to lower level, it emits
energy in the form of photons. The energy of the photons is equal to the gap between
the higher and lower level.
The LED is connected in the forward biased, which allows the current to flow in the
forward direction. The flow of current is because of the movement of electrons in the
opposite direction. The recombination shows that the electrons move from the
conduction band to valence band, and they emit electromagnetic energy in the form of
photons. The energy of photons is equal to the gap between the valence and the
conduction band
Advantages of LED
1. The LED are smaller in sizes, and they can be stacked together to form numeric
and alphanumeric display in the high-density matrix.
2. The intensity of the light output of the LED depends on the current flowing
through it. The intensity of their light can be controlled smoothly.
Disadvantages of LED
• An expensive option: LED lights are far more expensive compared to traditional
light bulbs.
• Require special controllers: Most LED lights need to be fixed with traditional
lighting dimmers. Thus, a small investment in LED-compatible dimmers is
quintessential and will be a wise decision in the long term.
OLD
The organic light-emitting diode (OLED), also known as organic electroluminescent (organic EL)
diode, is a light-emitting diode (LED) in which the emissive electroluminescent layer is a film of
organic compound that emits light in response to an electric current. This organic layer is
situated between two electrodes; typically, at least one of these electrodes is transparent.
OLEDs are used to create digital displays in devices such as television screens, computer
monitors, and portable systems such as smartphones and handheld game consoles. A major
area of research is the development of white OLED devices for use in solid-state lighting
applications.
There are two main families of OLED: those based on small molecules and those employing
polymers. Adding mobile ions to an OLED creates a light-emitting electrochemical cell (LEC)
which has a slightly different mode of operation.
How does an OLED work?
OLEDs work in a similar way to conventional diodes and LEDs, but instead of using
layers of n-type and p-type semiconductors, they use organic molecules to produce their
electrons and holes. A simple OLED is made up of six different layers. On the top and
bottom there are layers of protective glass or plastic. The top layer is called the seal and
the bottom layer the substrate. In between those layers, there's a negative terminal
(sometimes called the cathode) and a positive terminal (called the anode). Finally, in
between the anode and cathode are two layers made from organic molecules called the
emissive layer (where the light is produced, which is next to the cathode) and the
conductive layer (next to the anode).
Advantages of OLED
OLEDs use less power than LCDs since they generate light directly. OLEDs are very thin and
lightweight, making them ideal for portable devices. OLEDs use fewer layers than LCDs, making
them thinner and lighter without sacrificing performance or battery life.
Disadvantages of OLED
• Lifetime - While red and green OLED films have longer lifetimes (46,000 to 230,000
hours), blue organics currently have much shorter lifetimes (up to around 14,000 hours
(about 1 and a half years).
• Manufacturing - Manufacturing processes are expensive right now.
• Water - Water can easily damage OLEDs.

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LED

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