Semiconductor Materials Types Groups & Classifications
There are many different types of semiconductor materials which are often classified by their groups and other , but all have slightly different properties.
What is a semiconductor Holes & electrons Semiconductor materials Compound semiconductors Silicon carbide, SiC Gallium nitride, GaN
There are many different types of semiconductor material and each type of semiconductor material has its own properties.
As these different types of semiconductor have slightly different properties they lend themselves to different applications in various forms of semiconductor devices and electronic components.
Some may be applicable for standard signal applications, others for high frequency amplifiers, while other types may be applicable for power applications and harsh environments or others for light emitting applications - in fact there is a whole host of electronic components and devices that sue semiconductors. All these different applications tend to utilise different types of semiconductor materials.
The basic semiconductor materials like silicon and even germanium have been used for many years and silicon in particular has provided the mainstay for the semiconductor industry. Silicon is not only easy to work, but also has many excellent properties that lend it to being used for many semiconductor devices.
However many materials, often compound semiconductors are also being used. These tend to excel in terms of performance in some more niche areas.
As the technology for the fabrication for these new semiconductor types is developed and they start to be used more in their different areas, so the variety of materials or compounds used in semiconductors increases.
Semiconductors types / classifications
There are two basic groups or classifications that can be used to define the different semiconductor types:
Intrinsic material: An intrinsic type of semiconductor material made to be very pure chemically. As a result it possesses a very low conductivity level having very few number of charge carriers, namely holes and electrons, which it possesses in equal quantities.
Extrinsic material: Extrinisc types of semiconductor are those where a small amount of impurity has been added to the basic intrinsic material. This 'doping' uses an element from a different periodic table group and in this way it will either have more or less electrons in the valence band than the semiconductor itself. This creates either an excess or shortage of electrons. In this way two types of semiconductor are available: Electrons are negatively charged carriers.
N-type: An N-type semiconductor material has an excess of electrons. In this way, free electrons are available within the lattices and their overall movement in one direction under the influence of a potential difference results in an electric current flow. This in an N-type semiconductor, the charge carriers are electrons.
P-type: In a P-type semiconductor material there is a shortage of electrons, i.e. there are 'holes' in the crystal lattice. Electrons may move from one empty position to another and in this case it can be considered that the holes are moving. This can happen under the influence of a potential difference and the holes can be seen to flow in one direction resulting in an electric current flow.
It is actually harder for holes to move than for free electrons to move and therefore the mobility of holes is less than that of free electrons. Holes are positively charged carriers.
Semiconductor material groups
Most commonly used semiconductor materials are crystalline inorganic solids. These materials are often classified according to their position or group within the periodic table. These groups are determined by the electrons in the outer orbit the particular elements.
While most semiconductor materials used are inorganic, a growing number of organic materials are also being investigated and used.
The section of the periodic table of elements that includes the semiconductor materials is given in the image below.
Semiconductor materials are present in a number of different groups of the chemical periodic table. It is found that the properties of the different materials change from one group to the next and also as a result of their different atomic numbers.
It can be seen that silicon which is the most widely used materials for creating semiconductor based electronic components is on group IV as is germanium which was the first material that was widely used for transistors and diodes.
However semiconductor materials can also be made from compound semiconductors like gallium arsenide GaAs, Cadmium sulphide CdS, silicon carbide SiC, and many more.
Semiconductor materials list
There are many different types of semiconductor materials that can be used within electronic devices. Each has its own advantages, disadvantages and areas where it can be used to offer the optimum performance.
|Summary of Common Materials used within Semiconductors
|Germanium||Ge||IV||This type of semiconductor material was used in many early devices from radar detection diodes to the first transistors. Diodes show a higher reverse conductivity and temperature coefficient meant that early transistors could suffer from thermal runaway. Offers a better charge carrier mobility than silicon and is therefore used for some RF devices. Not as widely used these days as better semiconductor materials are available.|
|Silicon||S||IV||Silicon is the most widely used type of semiconductor material. Its major advantage is that it is easy to fabricate and provides good general electrical and mechanical properties. Another advantage is that when it is used for integrated circuits it forms high quality silicon oxide that is used for insulation layers between different active elements of the IC.|
|Gallium arsenide||GaAs||III-V||Gallium arsenide is the second most widely used type of semiconductor after silicon. It is widely used in high performance RF devices where its high electron mobility is utilised. It is also used as substrate for other III-V semiconductors, e.g. InGaAs and GaInNAs. However it is a brittle material and has a lower hole mobility than Silicon which makes applications such as P-type CMOS transistors not feasible. It is also relatively difficult to fabricate and this increases the costs of GaAs devices.|
|Silicon carbide||SiC||IV||Silicon carbide finds uses in a number of applications. It is often used in power devices where its losses are significantly lower and operating temperatures can be higher than those of silicon based devices. Silicon carbide has a breakdown capability which is about ten times that of silicon itself. Forms of silicon carbide were types of semiconductor material that were used with some early forms of yellow and blue LEDs. Read more . . .|
|Gallium Nitride||GaN||III-V||This type of semiconductor material is starting to be more widely in microwave transistors where high temperatures and powers are needed. It is also being used in some microwave ICs. GaN is difficult to dope to give p-type regions and it is also sensitive to ESD, but relatively insensitive to ionising radiation. Has been used in some blue LEDs. Read more . . .|
|Gallium phosphide||GaP||III-V||This semiconductor material has found many uses within LED technology. It was used in many early low to medium brightness LEDs producing a variety of colours dependent upon the addition of other dopants. Pure Gallium phosphide produces a green light, nitrogen-doped, it emits yellow-green, ZnO-doped it emits red.|
|Cadmium sulphide||CdS||II-VI||Used in photoresistors and also solar cells.|
|Lead sulphide||PbS||IV-VI||Used as the mineral galena, this semiconductor material was used in the very early radio detectors known as 'Cat's Whiskers' where a point contact was made with the tin wire onto the galena to provide rectification of the signals.|
Ease of processing and cost
When selecting a material for use in a semiconductor device or electronic component, there are a number of considerations. One is the ease with which the material can be processed.
Silicon has the advantage that not only is it widely available, but it is also easy to process. It is easy to grow the silicon crystals in a form where they can be cut or sliced into wafers and then processed into whatever electronic components are required.
As a result of this, the processes for silicon are relatively cheap (when compared to processing other materials) and silicon is also applicable to many devices - it is the ideal semiconductor for many devices. This all means that the processes have been finely honed and there is plenty of capacity available for them.
Other materials may not be as easy to handle even it is may perform well in one area and be ideal for many areas of electronic circuit design, etc.
One such material is Gallium Arsenide. This obviously has issues with the handling of the raw materials as arsenic is highly toxic. However the gallium arsenide material is also not ease to handle.
The overall result is that the processing costs will be much higher for gallium arsenide devices like GaAs FETs, and the like. However the performance advantages may mean that the additional costs are justified.
This means that there will be a balance between performance and cost. In some instances there may be no other way to obtain the required performance and so the additional costs will need to be carried, but in others there may be a cost/ performance balance to be made when considering devices for an electronic circuit design.
There are many different materials that can be used within semiconductor devices. The range of electronic components that use semiconductors these days is enormous, and although silicon is by far the most widely used, many other semiconductor materisla re being used. These are used because their performance excels in one area or another, enabling the performance of various electronic components to be improved in one area or another over that of silicon.
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