Analysing Power Semiconductor Devices Engineering Essay

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Semiconductor is a material that behaves in between a conductor and an insulator. At ambient temperature, it conducts electricity more easily than an insulator, but less readily than a conductor.  At very low temperatures, pure or intrinsic semiconductors behave like insulators. At higher temperatures though or under light, intrinsic semiconductors can become conductive.  The addition of impurities to a pure semiconductor can also increase its conductivity.

Power semiconductor is like a switch or device used to control and convert electrical power into electronic circuits. In general these devices are found in semiconductor elements, like silicon, gallium arsenide and germanium. Power devices usually eliminate more than one watts power during standard operation. They are normally intended as the powerICs when it is used in a integrated circuits. When the single semiconductor is connected together, it contains millions of devices.

There are several types of Power semiconductor, The main Power Semiconductor can be divided into two main categories based on the terminal. Semiconductor has 2-terminal devices and 3-terminal devices. The Majority carrier devices are in 2-terminal devices that will be Power diode, Schottky diode, Metal Oxide Semiconductor Field-Effect Transistor (MOSFET) and Junction Field-Effect Transistor (JFET) and for the 3-terminal devices will be Insulated Gate Bipolar transistor (IGBT), Bipolar Junction transistor (BJT) and a Thyristor.

Power diodes are considered carry electric currents in a forward direction and prevent current from coming in a reverse direction. Power Metal Oxide Semiconductor Field-Effect Transistor (MOSFET) are one of the most extensively used types of low-voltage power semiconductor applications. Particularly, they are less than 200 volts and they usually use for DC to DC convertor, motor controllers and power supplies. Thyristor has three electrodes, it is made of four layers of alternating P type and N type materials. Thyristor is designed to control a numerous volume of power using a small triggering current or voltage. Figure 1 will show 2-terminal devices and 3-terminal devices in detail.

Fig 1

Power Diode

Power Diode is known as the Power Semiconductor Diode. It has larger PN junction area compared to its smaller signal diode. The forward direction current is up to several hundred amps (KA) and the reverse restrictions voltage is up to several thousand volts (KV). Application above 1MHz is not suitable for power diode that has larger PN junction. Because of the high current and voltage features they can also be used in freewheeling diode. Power diodes are designed to have a forward "ON" resistance of fractions of an Ohm while their reverse blocking resistance is in the mega-Ohms range. Some of the larger value power diodes are designed to be "stud mounted" onto heat sinks reducing their thermal resistance to between 0.1 to 1oC/Watt. Power diode only occurs during the positive half cycle and therefore according i.e. Dc as shown.

Power Diode Rectifier

Schottky Diode

Schottky diodes are a semiconductor devices which has a metal-semiconductor transition as their basic structure and whose basic electronic properties are defined by this transition.Schotty diode is a very special type of diode and has a very low forwards voltage drop. The cause of the voltage drop across the diode terminal is when current flow through a diode. Usually diode have between 0.7 to 1.7 of voltage drop, but for schottky diode voltage drop is between 0.15 to 0.45 the cause of the voltage drop is translates into higher system efficiency.

Metal Oxide Semiconductor Field-Effect Transistor (MOSFET)

MOSFET is like an effect transistor which has "Metal Oxide" gate, which can insulate from N-channel or P-channel semiconductor. Course of the isolation make the input resistance of MOSFET go very high in the Mega Ohms and almost and almost limitless. If there no current flow into the gate , the MOSFET acts like a voltage controlled resistor. This semiconductor can easily damaged if it is not handle it carefully.

Basic MOSFET Structure and Symbol

Junction Field-Effect Transistor (JFET)

JFET is a type of field effect transistor; it can be use in two like a electronically controlled switch or a voltage controlled resistance. JFET come whit two channels that is P-channel and N-channel. JFET gate must be in negatively biased to the source. JFET is use as a no or off switch to control the current to the load and the current flow between the drain and source. By using the bias voltage to the "gate" terminal, the channel is "pinched" this make the electric current to switch off.

Insulated Gate Bipolar transistor (IGBT)

IGBT is a three terminal power semiconductor device, IBGT is use for high efficiency and fast switching. Most of the modern equipment is using IBGT to switch electric power. Low pass filters and Pulse width modulation is a synthesize complex waveform. This waveform is from amplifiers that rapidly turn on and off. IGBT is used from medium power to the high power like switched mode power supply ,induction heating and traction motor. If the IGBT in a larger type, it is usually consist of many device in parallel and the current is ability of hundreds of amperes with a blocking voltage of 6000 V.

Bipolar Junction Transistor (BJT)

BJT is a combination of three layer device constructed from two semiconductor diode junction joined together in a forward and reverse biased. BJT has two main bipolar junction transistors which is PNP and NPN transistor. The NPN transistor requires the Base to be more positive than the Emitter while the PNP type requires that the Emitter is more positive than the Base.


Bipolar Transistor Construction


Tyristor has four layers of semiconductor , usually tyristor is used for larger amount of power. Tyristor can be switch on or off and also regulate the power using phase angle control. By using it we can control the amount of the output power by adjusting the input current. Thyristor usually used in dimmer switch of light. Thyristor is suitable for low power applications only, because it only can turned off the current by switching the direction. Thyristor only can conduct current in one direction.


Schottky diode can be used in most of power supply ,

Schottky barriers, with their lower junction voltage, find application where a device better approximating an ideal diode is desired. They are also used in conjunction with normal diodes and transistors, where their lower junction voltage is used for circuit protection (among other things).

Because one of the materials in a Schottky diode is a metal, lower resistance devices are often possible. In addition, the fact that only one type of dopant is needed may greatly simplifyfabrication. And because of their majority carrier conduction mechanism, Schottky diodes can achieve greater switching speeds than p-n junction diodes, making them appropriate to rectify high frequency signals.

MOFET has 10 times fasters switching time than Bipolar Transistor and it only use very smaller switching current. MOFET can be easily damaged by the static electricity if never handle it properly , the reason MOFET can damaged is because it has a very high input gate resistance. MOFET is commonly use in electronic switches or amplifiers source where the power consumption is very small. MOSFET is used in Microprocessors, Memories, Calculators and Logic Gates etc.

This can be summarised in the following switching table.


Vgs = +ve

Vgs = 0

Vgs = -ve

N-Channel Depletion




N-Channel Enhancement




P-Channel Depletion




P-Channel Enhancement




JFET tranconductance is higher than MOSFT , JFET is used in high input-impedance op amps which is a low noise. JFET has less noise than Bipolar Transistor. JFET resistance is very high input and has a high degree in isolation between input and output. The JFET has a very low gain bandwidth product from the conventional transistors . when JFET is using voltage controlled device its is like a tube , if not using voltage controlled device it is like a conventional transistor.

IGBT is one of the first generation, because it is the first generation IGBT has a very slow switching. The basic difference of IGBT and MOSFET is the P substrate under N substrate. IBGT has a low duty cycle , can operated in a high junction temperature and in a high voltage application also.IGBT can go uo to 1400V of switching current.

BJT BJT is a device to control a current like controlling the base current amount of the collector current. BJT can be use in a switch, in a oscillator, in a amplifier or in a nonlinear circuit. BJT can or able to handle high voltage and BJT has the lower state conduction in current loss. But the switching speed is not so fast.


Field Effect Transistor (FET)

Bipolar Junction Transistor (BJT)


Low voltage gain

High voltage gain


High current gain

Low current gain


Very input impedance

Low input impedance


High output impedance

Low output impedance


Low noise generation

Medium noise generation


Fast switching time

Medium switching time


Easily damaged by static



Some require an input to turn it "OFF"

Requires zero input to turn it "OFF"


Voltage controlled device

Current controlled device


Exhibits the properties of a Resistor



More expensive than bipolar



Difficult to bias

Easy to bias



Well year by year the power device are growing rapidly, if im not mistaken in few year time all the power device will be in micro size , faster and more specification or specs. Now there are allot of research on making new power devices in the market. Now days industries are manufacturing thousand of power devices like MOSEFT, Diode, Transistor and a lot more in to chips , because it is cheaper to produces thousand chip rather than one. In china power device market is growing expeditious year by year. China is one of the most upcoming country in the power device manufacturing market. According to the world market for power semiconductor device value was 8.1 billion in year 2009.