The crystal is changed from an OK conductor to a good conductor. Since electrons carry a negative charge, this type of crystal with extra electrons is known as an N-type or N-doped semiconductor. Doping the crystal with boron or gallium also turns the crystal into a conductor, but it does so by leaving it with a shortage of electrons. Physicists say that the crystal has holes, which make the crystal positive or P-type. When N-type and P-type crystals come together, something surprising happens.
The junction acts as a barrier to the flow of electricity in one direction but presents almost no resistance in the other direction. This one-way valve can be used in an electronic device called a diode. Around the middle s, engineers discovered that junction diodes made from a material called gallium arsenide emitted light although it was only much later that usable lasers and LEDs were made this way.
Alas, explaining this phenomenon introduces more vocabulary terms. Free electrons traveling through a semiconductor crystal have a fairly high level of energy, so they are said to be in the conduction band. When an electron meets a hole in the crystal, it tends to stay there. When the energy difference or band gap between the high conduction band state and the lower state is small, as it is in silicon, the light is released at the invisible infrared frequencies. When the band gap is large, the emission is visible light.
This happens in all types of diodes, but in an ordinary silicon diode the silicon itself absorbs most of the light. Light emitting diodes are constructed so that most of the light radiates outward. There would be no radios, no TV's, no computers, no video games, and poor medical diagnostic equipment. Although many electronic devices could be made using vacuum tube technology, the developments in semiconductor technology during the past 50 years have made electronic devices smaller, faster, and more reliable.
Think for a minute of all the encounters you have with electronic devices. Chip companies are emerging leaner and more efficient. Chip production now resembles a gourmet restaurant kitchen, where chefs line up to add just the right spice to the mix.
This requires very expensive manufacturing processes. As a result, many semiconductor companies carry out design and marketing but choose to outsource some or all of the manufacturing. Known as fabless chip makers, these companies have high growth potential because they are not burdened by the overhead associated with manufacturing, or "fabrication.
Aside from investing in individual companies , there are several ways to monitor the investment performance of the overall sector. There are also indices that break the sector down to chip makers and chip equipment makers. The latter develops and sells machinery and other products used to design and test semiconductors. In addition, certain markets overseas, such as Taiwan, South Korea, and to a lesser extent Japan, are highly dependent on semiconductors and therefore their indices also provide clues on the health of the global industry.
If semiconductor investors can remember one thing, it should be that the semiconductor industry is highly cyclical. Semiconductor makers often see "boom and bust" cycles based on the underlying demand for chip-based products. When times are good, profit margins can run very high for chipmakers; when demand falls through, however, chip prices can fall dramatically and have a major effect on many industries' supply chains.
Demand typically tracks end-market demand for personal computers, cell phones, and other electronic equipment. When times are good, companies like Intel and Toshiba can't produce microchips quickly enough to meet demand. When times are tough, they can be downright brutal. Slow PC sales, for instance, can send the industry—and its share prices—into a tailspin. At the same time, it doesn't make sense to speak of the "chip cycle" as if it were an event of singular nature. While semiconductors is still a commodity business at heart, its end markets are so numerous—PCs, communications infrastructure, automotive, consumer products, etc.
Surprisingly, the cyclicality of the industry can provide a degree of comfort for investors. In some other technology sectors, like telecom equipment, one can never be entirely sure whether fortunes are cyclical or secular.
By contrast, investors can be almost certain that the market will turn at some point in the not-so-distant future. While cyclicality offers some comfort, it also creates a risk for investors. Chipmakers must routinely take part in high-stakes gambling. The big risk comes from the fact that it can take many months, or even years, after a major development project for companies to find out whether they've hit the jackpot, or blown it all. One cause of the delay is the intertwined but fragmented structure of the industry: Different sectors peak and bottom out at different times.
For instance, the low point for foundries frequently arrives much sooner than it does for chip designers. Another reason is the industry's long lead time : It takes years to develop a chip or build a foundry, and even longer before the products make money. Semiconductor companies are faced with the classic conundrum of whether it's the technology that drives the market or the market that drives the technology. Investors should recognize that both have validity for the semiconductor industry.
Because companies spend a large amount of revenue on research and development that can take several months or even years to pay off—and sometimes not even then if the technology is faulty—investors should be wary of statements made by companies who claim to have the latest and greatest technology in the semiconductor industry. A semiconductor essentially functions as a hybrid of a conductor and an insulator. Whereas conductors are materials with high conductivity that allow the flow of charge when applied with a voltage, and insulators do not allow current flow, semiconductors alternately act as an insulator and conductor where necessary.
An n-type semiconductor is an impurity mixed semiconductor that uses pentavalent impure atoms like phosphorus, arsenic, antimony, bismuth. A p-type semiconductor is a type of extrinsic semiconductor that contains trivalent impurities such as boron and aluminum which increases the level of conductivity of a normal semiconductor made purely of silicon. An intrinsic or pure semiconductor is a semiconductor that does not have any impurities or dopants added to it, as in the case of p-type and n-type semiconductors.
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