Introduction

In recent years, especially during the COVID-19 pandemic when supplies of semiconductor parts were in short supply, it was rare to hear the word "semiconductor" in the news on television or radio. However, since the pandemic began, it feels like I've started hearing the word "semiconductor" almost every day.

As someone working in the semiconductor industry, I am pleased to see this kind of attention being paid to semiconductors, and I hope that this global trend of interest in semiconductors is not a passing fad, but will continue into the future.

By the way, how much do you understand about semiconductors?
Many people probably think of things like diodes, transistors, and CPUs used in computers as "semiconductors."

What I have just mentioned is not strictly speaking a "semiconductor" but rather a "semiconductor element" or "semiconductor device".

What is a "semiconductor"?

I'm sure many of you have seen or heard this type of explanation often on video streaming sites and in various media.

・ A semiconductor is a material whose electrical conductivity is between that of a conductor and that of an insulator.
・Materials that become insulators at extremely low temperatures

Similar content can be found in dictionaries that have been on the market for a long time and major online dictionaries.
However, this explanation is now incorrect.

For example, diamond was previously considered an insulator, but research into its semiconductor properties has been ongoing for over half a century. 5.5eV It is a semiconductor with a band gap of .*[1]

Aluminum nitride (Aluminum Nitride, AlN) In the case of a single crystal, 6.2eV This is also a semiconductor with a band gap of 100 nm, which is expected to be used in next-generation power semiconductor devices and deep ultraviolet LED A wide range of research is being conducted with a view to applying it to the following areas:*[2]

Regarding "materials that become insulators at extremely low temperatures," for example, indium nitride (InN) is a semiconductor with a band gap of 0.65 eV, but is also known to exhibit superconducting properties, with electrical resistance reaching almost zero at extremely low temperatures (helium temperatures).* [3]

In this way, there are cases where "materials that are somewhere between conductors and insulators" or "materials that become insulators at extremely low temperatures" cannot explain the phenomenon.

So what exactly is a "semiconductor"?

So what exactly is a "semiconductor"?
I think there are some words that have come up several times in the explanation so far.

It's called "band gap".

A band gap refers to the difference in energy levels between the valence band and the conduction band in a certain material. A detailed explanation would take up an entire university course, so I won't go into it here, but it always exists in semiconductors.

A semiconductor is a material that has a band gap

It is more correct to explain it as follows. However,
It is only in recent years that advances in nanotechnology have given rise to what are known as "one-dimensional semiconductor devices," and I believe that there will come a time when this will no longer be explained solely by the presence or absence of a "band gap."

When the time comes, we can just come up with a new definition, so I will leave that to future generations.

Citation

[1]Characterization of conducting diamond films (https://doi.org/10.1016/0042-207X(86)90279-4)
[2] [Synthesis and properties of nitrides] Synthesis and properties of AlN (https://doi.org/10.11470/oubutsu1932.42.1222)
[3]Electronic structure of superconducting InN (https://doi.org/10.1016/j.stam.2006.06.004)

Inquiry

If you are interested in the content introduced in this article, please feel free to contact us.