Introduction to Semiconductors-edited.ppt

Editor's Notes

• #7: This lab, students graphed the next slides data.
• #8: Students’ graph should illustrate that resistance (ohms) decreases in a metal as temperature rises but with a semiconductor (germanium), the exact opposite happens.
• #78: John Bardeen and Walter Brattain, working at Bell Telephone Laboratories, were trying to understand the nature of the electrons at the interface between a metal and a semiconductor (germanium). They realized that by making two point contacts very close to one another, they could make a three terminal device - the first "point contact" transistor were very impressed that it didn't need time to "warm up" (like the heaters in vacuum tube circuits). They immediately realized the power of this new technology.
• #89: No warm-up period for cathode heaters required after power application. Lower power dissipation and generally greater energy efficiency. Some transistorized devices produced more than 30 years ago are still in service. Complementary devices available, facilitating the design of circuits, something not possible with vacuum tubes. Insensitivity to mechanical shock and vibration, thus avoiding the problem of microphonics in audio applications.
• #91: Rectifiers are used in the vast majority of consumer electronics today and are required for most devices to work properly. Because of this,
• #97: For most electrical demands, a bridge rectifier is used. A rectifier bridge is four diodes configured so that the output always has the same polarity regardless of the polarity of the input. Rectifier bridges are most often used to convert alternating current into full-wave direct current for power supplies and throttles.
• #104: Silicon has been the heart of the world's technology boom for nearly half a century, but microprocessor manufacturers have all but squeezed the life out of it. The current technology used to make microprocessors reached its limit around 2005.
• #107: Lithography is akin to photography in that it uses light to transfer images onto a substrate. In the case of a camera, the substrate is film. Silicon is the traditional substrate used in chip making. To create the integrated circuit design that's on a microprocessor, light is directed onto a mask. A mask is like a stencil of the circuit pattern. The light shines through the mask and then through a series of optical lenses that shrink the image down. This small image is then projected onto a silicon, or semiconductor, wafer. The wafer is covered with a light-sensitive, liquid plastic called photoresist. The mask is placed over the wafer, and when light shines through the mask and hits the silicon wafer, it hardens the photoresist that isn't covered by the mask. The photoresist that is not exposed to light remains somewhat gooey and is chemically washed away, leaving only the hardened photoresist and exposed silicon wafer. The key to creating more powerful microprocessors is the size of the light's wavelength. The shorter the wavelength, the more transistors can be etched onto the silicon wafer. More transistors equals a more powerful, faster microprocessor. That's the big reason why an Intel Pentium 4 processor, which has 42 million transistors, is faster than the Pentium 3, which has 28 million transistors.
• #108: An international science team from Penn State University in the United States and the University of Southampton in the United Kingdom has developed a process for growing a single-crystal semiconductor inside the tunnel of a hollow optical fiber.  The device adds new electronic capabilities to optical fibers, whose performance in electronic devices such as computers typically is degraded by the interface between the fiber and the device. 
• #109: Now, chipmakers will have to look to other technologies to cram more transistors onto silicon to create more powerful chips The key to creating more powerful microprocessors is the size of the light's wavelength. The shorter the wavelength, the more transistors can be etched onto the silicon wafer. More transistors equals a more powerful, faster microprocessor.
• #110: In an effort to help create faster, better and cheaper light sources for chips, UC San Diego researchers, in collaboration with Cymer, Inc., are developing laser-produced light sources for next generation Extreme Ultraviolet Lithography (EUVL).
• #111: LEDs are based on the semiconductor diode.
• #112: Instead of using silicon as the semiconductor, we use a different material, notably an alloy of aluminum and gallium arsenide (indium gallium arsenide phosphide is another popular choice). Electrons are injected into the diode, they combine with holes, and some of their excess energy is converted into photons, which interact with more incoming electrons, helping to produce more photons—and so on in a kind of self-perpetuating process called resonance. This repeated conversion of incoming electrons into outgoing photons is analogous to the process of stimulated emission that occurs in a conventional, gas-based laser.
• #113: Claire Gmachl holding a chip containing eight quantum cascade (QC) lasers. QC lasers are the world's first semiconductor lasers that can be tailored to emit light at any specific wavelength within a wide range of the infrared spectrum. The emitted wavelength is not determined by the band gap of the used material but on the thickness of the constituent layers The technology allows for the detection and monitoring of environmental gases in sub parts per Million sensitivity.
• #114: Quantum cascade lasers are small and efficient sources of mid-infrared laser beams, which are leading to new devices for medical diagnostics and environmental sensing. Gmachl's group discovered that a quantum cascade laser they had built generated a second beam with very unusual properties, including the need for less electrical power than the conventional beam. "If we can turn off the conventional beam, we will end up with a better laser, which makes more efficient use of electrical power," said Gmachl.
• #117: Solar powered air conditioner.