Cross-sectional view of single wafer capacitive microphone.
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2 Ga + 2 AsCl3 → 2 GaAs + 3 Cl2
Ga(CH3)3 + AsH3 → GaAs + 3 CH4
4 Ga + As4 → 4 GaAs
2 Ga + As2 → 2 GaAs
LEDs used on a train
Red and green traffic signals
LED digital display
LED destination signs on buses
I-V diagram for a diode
The inner workings of an LED
An LED will begin to emit light when the on-voltage is exceeded. Typical on voltages are 2–3 volts.
a packaged laser diode shown with a penny for scale.
the laser diode chip is removed from the above package and placed on the eye of a needle for scale
A laser diode with the case cut away
The actual laser diode chip is the small black chip at the front; a photodiode at the back is used to control output power
Diagram of front view of a double heterostructure laser diode
Diagram of front view of a simple quantum well laser diode
Diagram of front view of a separate confinement heterostructure quantum well laser diode
environmental monitoring of gases for health, safety and air-pollution control.
Detection of important gases of smokes, such as CO2, CO,NO2, NO, O3, SO2, SO3, CH4 for air pollution control.
1- optical techniques
2- chemical techniques
Infrared (IR) technology
Long recognized for accurate identification of gases and reliable concentration measurements.
Infrared radiation has wavelengths ranging from 0.8 to 100 microns.
Different gas molecules have characteristic absorption wavelength bands in the infrared spectrum because of rotational and vibrational excitation modes. Fore example:
CO2 (4.26 µm)
CO (4.65 µm)
CH4 (3.3 µm)
When exposed to a beam of infrared radiation, most gas molecules will absorb IR-radiation at their vibration/rotation frequencies.
An infrared light beam of an IR-source passes a gas cell. Depending on the gases present, a part of the spectrum is absorbed.
An optical tunable filter then analyzes the beam. It passes just one wavelength and blocks other wavelengths, while an IR-detector detects the transmitted intensity.
The wavelength of the filter can be tuned to absorption bands of different gasses.
The laser diode converts electrical energy into energy in form of light.
Figure 1. Terrestrial and space solar spectrum .
جریان الکتریکی از سورس به درین در یک جیفت با کانال پی هنگام اعمال ولتاژ به گیت محدود میشود.
نماد مداری یک جیفت با کانال ان
نماد مداری یک جیفت با کانال پی
نمودار I-V خصوصیات و طرحهای خروجی از JFETنوع n.
ماسفت شامل پایه های گیت(G)،درین(D)،سورس(S) و بدنه(B)