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Sunday, May 20, 2018

#387 Solar cells and LEDs

 Some more about light and semiconductor diodes….


In terms of interactions with light, semiconductor diodes represent two distinct, very different classes of devices. Some of them are converting light into electricity and those are obviously solar cells working of the principles of the photovoltaic effect and photodiodes working as light detectors.


The devices in the second group work in the exactly opposite direction and convert electricity into light with light emitting diodes, or LEDs in short, being a prime example of light emitting device. Here, the effect of photoluminescence is a foundation of the device operation.


Posted by Jerzy Ruzyllo at 07:58 AM | Semiconductors | Link

Sunday, April 22, 2018

#386 Photovoltaic, photoelectric

Two well established physical effects occuring in solids are photovoltaic and photoelectric effects. As they are quite often confused here is a quick explanation of what is what.

In the case of photovoltaic effect, free charge carriers generated as a result of absorption of energy from sunlight remain within the solid and contribute to the current flowing across it. The most common way to exploit this effect is by constructing semiconductor diodes which are well known as solar cells. In contrast, in the case of the photoelectric effect electrons generated by absorption of light are emitted to the outside of the solid. The prime use of this effect is in the detection of light.



Posted by Jerzy Ruzyllo at 11:23 AM | Semiconductors | Link

Sunday, March 11, 2018

#385 Diodes

As mentioned in the previous blog presence of the potential barrier makes a piece semiconductor display non-symatrical (rectifying) diode-like current-voltage characteristics and the type of the potential barrier determines type of diode. And again, a p-n junction barrier  forms  p-n junction diode, while metal-semiconductor originating potential barrier forms Schottky diode. New message is that this is it as far as types of semiconductor diodes are concerned.


Posted by Jerzy Ruzyllo at 08:15 PM | Semiconductors | Link

Sunday, February 18, 2018

#384 Potential barrier at M-S contact

In reference to blog #382....


An alternative to p-n junction way of potential barrier formation is by bringing into contact semiconductor and metal featuring different work functions and to form the metal-semiconductor contact also known as Schottky contact (after German physicist Walter Schottky, 1886 -1976). In this case difference in work functions of materials in contact alters potential distribution across the junction which results in formation of a potential barrier. 


Similarly to p-n junction, a reverse bias voltage applied to the Schottky junction increases height of the potential barrier and prevents the flow of majority carriers from semiconductor to metal.  A forward bias, lowers the potential barrier at the contact  and allows large current to flow from semiconductor to metal. Similarly to  p-n junction, the result is a non-symmetrical, rectifying current-voltage characteristic making metal-semiconductor contact a diode known as Schottky diode.

Posted by Jerzy Ruzyllo at 03:38 PM | Semiconductors | Link

Sunday, February 11, 2018

#383 Semiconductor Glossary

In the case you would be interested in my "Semiconductor Glossary" in either hard copy or ebook version check this site.

Posted by Jerzy Ruzyllo at 07:25 PM | Semiconductors | Link

Sunday, January 28, 2018

#382 Potential barrier

Following on the concept of potential barrier mentioned in previous blog.


The most obvious way to create a potential barrier in semiconductors is to bring to contact two semiconductors with different work functions.  Actually, these may be two pieces of the same material such as silicon, providing however, each of them is doped at the different level and/or feature different conductivity type (p-type semiconductor and n-type semiconductor), and thus, feature different work function.  A potential barrier is formed in the piece of semiconductor in the absence of the voltage bias when p-type and n-type semiconductors are brought into contact to form a structure known as a p-n junction.


Posted by Jerzy Ruzyllo at 08:52 PM | Semiconductors | Link

Sunday, January 14, 2018

#381 Constructing semiconductor device

There are two fundamental features that are indispensable elements in the making of the functional semiconductor device. First, it needs to be assured that the electric current can flow in and out of semiconductor comprising a device in the entirely undisturbed fashion. To accomplish this task, ohmic contacts need to be formed at the device input and output.


Assuming ohmic contacts are in place, second feature making active semiconductor device is building into it an ability to vary in the controlled fashion its resistance by applying bias voltage between device terminals. To accomplish this last feature a potential barrier must be built into the device structure. The most common way of accomplishing it is to form a p-n junction within semiconductor material.

Posted by Jerzy Ruzyllo at 05:49 PM | Semiconductors | Link

Sunday, December 17, 2017

#380 What is "semiconductor device"?

The term “semiconductor device” is referring to the piece or a thin-film of semiconductor material, combined as needed with thin layers of insulators and conductors, which is configured in such way that it can perform in the controlled fashion predetermined electronic, photonic, or electro-mechanical functions. Electronic functions are performed by electronic devices which operation is based on the interactions of electric charge carriers and in which electrons are acting as information/energy carriers. Term photonic devices is concerned with devices involving interactions of photons (“packets” of electromagnetic energy carried by light) and in which photons are acting as information/energy carriers.  Finally, electro-mechanical devices are taking advantage of the mechanical characteristics, such as elasticity and fracture toughness of some semiconductor materials, silicon in particular.


In contrast to electronic and photonic functions,  which involve interactions solely within semiconductor material systems, electro-mechanical functions require involvement of solids capable of converting mechanical action into electrical signal such as piezoelectrics which convert mechanical stress into electrical signal and vice versa.


Posted by Jerzy Ruzyllo at 03:15 PM | Semiconductors | Link

Sunday, December 3, 2017

#379 The concept of "equivalent gate length" (EGL) is bound to come

The Equivalent Oxide Thickness (EOT) is a number (in nm) which expresses thickness of the SiO2 gate oxide that is needed to obtain the same capacitance of the MOS gate stack as the one obtained with physically thicker than SiO2, but featuring higher than SiO2 dielectric constant k.


Here, I suggest the term Equivalent Gate Length (EGL) as the represenation of the same as EOT idea, but used in relation to the MOSFETs gate scaling process.


It appears that scaling of the physical gate length in advanced CMOS ciruits below 5 nm  may be practical only under some special circumstances. Yet, the progress beyond 5 nm technology node will continue except that by means of vastly expanding pool of materials used to construct transistor and by drastically modifying its architecture rather than by gate scaling. When those times will come the term Equivalent Gate Length will be very handy. As an example, EGL = 1 nm would mean that the transistor performance equivalent to the performance of the ficticious transistor featuring gate length of 1 nm can be in some situations accomplished using MOSFETs with longer physical gate length such as for instance 7 nm.


Posted by Jerzy Ruzyllo at 02:15 PM | Semiconductors | Link

Sunday, November 26, 2017

#378 IEDM 2017

As usual at this time of the year, a quick update regarding this year IEDM (IEEE International Electron Device Meeting).

Time: Dec. 2-6, 2017

Place: San Frncisco Hilton

Porgram: click here.


Consider checking it out to see current trends in broadly understood semiconductor science and engineering.

Posted by Jerzy Ruzyllo at 04:49 PM | Semiconductors | Link

›› is the personal blog of Jerzy Ruzyllo. With over 35 years of experience in academic research and teaching in the area of semiconductor engineering (currently holding position of a Distinguished Professor of Electrical Engineering and Professor of Materials Science and Engineering at Penn State University), he has a unique perspective on the developments in this progress driving technical domain and enjoys blogging about it.

With over 2000 terms defined and explained, Semiconductor Glossary is the most complete reference in the field of semiconductors on the market today.

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