Semiconductors are materials that have electrical conductivity properties somewhere between those of conductors (such as copper) and insulators (such as rubber). One of the most common and widely used semiconductors is silicon. However, germanium was also widely used in the past, and still has some niche applications today. In this blog post, we will explore the reasons why silicon is used so much more than germanium in the semiconductor industry, as well as the specific niche applications where germanium is still used.
First, it's important to understand some basic properties of semiconductors. The conductivity of a semiconductor can be controlled by introducing impurities into the material, a process called doping. Doping a semiconductor with impurities that donate electrons (such as phosphorus) creates an n-type semiconductor, while doping it with impurities that accept electrons (such as boron) creates a p-type semiconductor.
One of the key factors that makes silicon so widely used is its abundance. Silicon is the second most abundant element on Earth (after oxygen), and is found in many common materials, including sand, quartz, and rocks. This means that it is relatively cheap and easy to obtain large quantities of high-purity silicon for use in the semiconductor industry.
Another important factor is silicon's energy bandgap. This is a measure of the energy required to move an electron from the valence band (where it is bound to an atom) to the conduction band (where it is free to move and conduct electricity). Silicon has a relatively wide bandgap of 1.1 electron volts (eV), which means that it requires a relatively high amount of energy to excite an electron into the conduction band. This makes silicon a good choice for applications where high voltages are involved, such as power electronics.
Germanium, on the other hand, has a much narrower bandgap of only 0.67 eV. This makes it more sensitive to temperature changes and other environmental factors, which can cause its conductivity to vary significantly. This makes it less suitable for many mainstream applications in the semiconductor industry, where stability and predictability are key factors.
However, germanium still has some important niche applications where its unique properties are advantageous. One such application is in the field of infrared (IR) detectors. Germanium has a higher refractive index than silicon, which means that it is more efficient at absorbing IR radiation. This makes it a good choice for IR detectors, which are used in a variety of applications such as night vision devices and temperature sensors.
Another application of germanium is in the field of high-speed electronics. Germanium has a higher electron mobility than silicon, which means that it can conduct electricity faster. This property makes germanium a good choice for high-speed transistors and other electronic components where speed is important.
Germanium is also used in some niche applications in the field of quantum computing. Germanium has a narrower bandgap than silicon, which makes it a good candidate for certain types of quantum computing devices that rely on the properties of quantum dots.
Finally, germanium is sometimes used as a substrate material for growing other semiconductors such as gallium arsenide (GaAs). Germanium has a lattice structure that is a good match for GaAs, which makes it a good choice for growing high-quality GaAs crystals for use in electronic and optoelectronic devices.
In conclusion, while germanium is less widely used than silicon in the semiconductor industry, it still has some important niche applications where its unique properties are advantageous. However, silicon's abundance, energy bandgap, oxide layer stability, and early adoption have made it the most widely used semiconductor material today.