Did you know that metalloids are useful as semiconductors in modern electronics? While many elements commonly recognized as metalloids, their place in the periodic table and their chemical and electrical properties are well documented, there is still a lack of a widely accepted definition within the scientific community. Let’s find out what metalloids are and how they conduct electricity. You’ll also learn why metalloids and their compounds are used throughout the semiconductor industry.
What Are Metalloids?
Metalloids are among the most strange of all the elements in the periodic table. They exhibit both metallic properties as well as other characteristics found in non-metals. Because of this, there is no definitive way of grouping them into either category of elements, and are sometimes referred to as semi-metals. They are not, however, what is meant by transition metals which are clearly metals.
A metalloid should not be confused with a semiconductor either, since not all of them display an aptitude for very good electrical conductivity. However, many metalloids are semiconductor materials while others can form compounds that have semiconductor properties which are used to manufacture electronic components found in many of the modern devices we use every day.
Metalloids In Our Periodic Table
If you look at a periodic table of elements, the metalloids (in grey) are located in a zigzag pattern separating the metals and the non-metals as shown in the diagram below. This is very different from other families of elements like noble gases (in purple) which are grouped in a line or block on the table.
Let’s look at what gives metalloid elements their unique properties compared to metals and non-metals.
Metalloids are brittle solids because of their elasticity which is characteristic of non-metallic elements. On the other hand, they look shiny with a metallic appearance to them.
Intermediate Ionization Energies And Chemical Behavior
Their ionization energies and electronegativity values contribute to their chemical properties. Metalloids behave largely like non-metals and the oxides they form are weakly acidic. Another strange aspect is the way metalloids interact with other elements. For example, boron will behave like a non-metal in the presence of sodium, but act as a metal when interacting with fluorine. They can be used to form alloys with metals which make them stronger and push them towards more metallic characteristics.
How Metalloids Conduct Electricity
The electronic band structure of a metalloid is what gives many of them relatively good electrical conductivity. Some metalloids in their standard state have valence electrons that can be excited and jump the band gap, creating charge carriers, effectively making them conductors of electricity. This is why many of them like silicon and germanium are used in the semiconductor industry to manufacture computer chips.
Even the elements like antimony and arsenic which are not semiconductors in their standard can be combined with other elements to be used in semiconductor components. The band theory is what explains why some elements like insulators are poor conductors, while others end up being metallic conductors and semiconductors.
Metalloids With Semiconducting Properties At Their Most Thermodynamically Stable Forms
Silicon is a metalloid that is the second-most abundant element found in the Earth’s crust and is also widely used for the manufacture of semiconductor components. Let’s look at a few of these metalloids that also behave as semiconductors.
Silicon (Si) as mentioned before is a semiconductor material that is used in the manufacture of microprocessors found in many of our consumer electronics devices as well as solar cells and liquid crystal displays. Its conductivity can be increased by combining it with elements like gallium and boron. Silicon can also be alloyed with aluminum to make engine components in automotive applications.
Boron (B) when ignited burns with a bright green flame which makes it useful in pyrotechnics and fireworks displays. It can be used to produce borosilicate glass which is highly resistant to thermal shock and a popular material for glass bakeware. Boron has also been used for the control rods that are found in nuclear reactors. It is also found in cleaning products like detergents and used for pest control.
Germanium (Ge) is another semiconductor that is used for making transistors. Due to its high refractive index, it is also used in making camera and microscope lenses. Germanium is also used in fiber optic technology and infrared spectroscopy.
Arsenic (As) is one of the most toxic substances around and has a notorious reputation for being used in many assassinations throughout history. However, this toxicity does have its uses, and arsenic was widely used as a pesticide. It was also used as a wood preservative against bacteria, insects, and fungi, although many are now moving away from arsenic in favor of less toxic substances.
Arsenic can be useful when alloyed with gallium which makes it viable for the manufacture of infrared light-emitting diodes (LEDs).
Antimony (Se) is very important to the aircraft and automobile industries where it is used as an ingredient in the making of flame retardants. Its various alloys are used for making cable sheathing, and bullets as well as being used as a catalyst in the manufacture of polymers.
The ductility of stainless steel and copper can be improved using tellurium (Te). Its semiconducting properties can be used in the manufacture of solar cells and when combined with zinc, the element can be used to make gamma-ray detectors while combining it with mercury can be used to produce an infrared detector. Finally, tellurium is also used in blastic caps and in the production of ceramics.
Polonium (Po) was discovered by the famous scientist Marie Curie and the element is named after her homeland of Poland. It can be used to prevent static electricity in spinning synthetic fibers and paper rolling machines. Artificial satellites have their thermoelectric cells made from polonium and the element was also used in many lunar rovers to maintain a stable operating temperature for their internal components.
While we’ve covered all the main elements from silicon to arsenic that are commonly recognized as metalloids, others exhibit similar properties. Selenium (Se) is one such example. While it has semiconducting properties, its chemical characteristics are like a non-metal. There is also astatine (At) which is normally classified as a non-metal and aluminum (Al) which most people consider to be a metal, although both exhibit unusual qualities that make it difficult to categorize neatly.
While aluminum clearly behaves as a metal in terms of electrical conductivity, it is used heavily in the semiconductor manufacturing industry for various applications. Aluminum phosphide or AlP semiconductor materials are used all the time in the making of light-emitting diodes, diode lasers, solar cells, and even high-frequency military radar applications.
Metalloids Are Useful As Semiconductors
As you can see, some metalloids like silicon and germanium are semiconductors while others like arsenic can be useful in their manufacture. Many of the modern consumer electronics we rely on daily, industrial applications, and even space travel are possible because of metalloids and their usefulness in making semiconductors.
Metalloids are elements that display physical, chemical, and electrical properties that are a mixture of both metals and non-metals.
The elements most commonly recognized as metalloids are silicon, germanium, boron, arsenic, antimony, tellurium, and polonium.