Civil Rights
Movements, leaders, victories and the continuing fight for equality.
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Explore the people, places, events, achievements, struggles and stories that shaped our journey.
Movements, leaders, victories and the continuing fight for equality.
Innovation, patents, science, technology and world-changing contributions.
Pioneers, champions, Negro Leagues, records, activism and excellence.
Meet the people whose lives, choices and achievements shaped the journey.
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Moments that changed communities, movements, institutions and the nation.
In 1968 Shirley Chisholm became the first Black woman elected to the United States Congress. In 1972 she launched a campaign for the Democratic presidential nomination, breaking another political barrier.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
Srabanti Chowdhury is an Indian American Electrical Engineer who is a professor of electrical engineering at Stanford University. She is a senior fellow of the Precourt Institute for Energy. At Stanford she works on ultra-wide and wide-bandgap semiconductors and device engineering for energy-efficient electronic devices. She serves as Director for Science Collaborations at the United States Department of Energy Energy Frontier Research Center ULTRA.
Wide-bandgap semiconductors (also known as WBG semiconductors or WBGSs) are semiconductor materials which have a larger band gap than conventional semiconductors. Whereas conventional semiconductors like silicon, germanium (due to a slightly wider bandgap than silicon), and selenium have a bandgap in the range of 0.7 – 1.5 electronvolt (eV), wide-bandgap materials have bandgaps in the range above 2 eV. Generally, wide-bandgap semiconductors have electronic properties which fall in between those of conventional semiconductors and electrical (not thermal) insulators. Wide-bandgap semiconductors allow devices to operate at much higher voltages, frequencies, and temperatures than conventional semiconductor materials like silicon, germanium, and gallium arsenide. They are the key component used to make short-wavelength (green-UV) LEDs or lasers, and are also used in certain radio frequency applications, notably military radars. Their intrinsic qualities make them suitable for a wide range of other applications, and they are one of the leading contenders for next-generation devices for general semiconductor use. The wider bandgap is particularly important for allowing devices that use them to operate at much higher temperatures, on the order of 300 °C. This makes them highly attractive for military applications, where they have seen a fair amount of use. The high temperature tolerance also means that these devices can be operated at much higher power levels under normal conditions. Additionally, most wide-bandgap materials also have a much higher critical electrical field density, on the order of ten times that of conventional semiconductors. Combined, these properties allow them to operate at much higher voltages and currents, which makes them highly valuable in military, radio, and power conversion applications. The US Department of Energy believes they will be a foundational technology in new electrical grid and alternative energy devices, as well as the robust and efficient power components used in high-power vehicles from plug-in electric vehicles to electric trains. Most wide-bandgap materials also have high free-electron velocities, which allows them to work at higher switching speeds, which adds to their value in radio applications. A single WBG device can be used to make a complete radio system, eliminating the need for separate signal and radio-frequency components, while operating at higher frequencies and power levels. Research and development of wide-bandgap materials lags behind that of conventional semiconductors, which have received massive investment since the 1970s. However, their advantages in many applications, combined with some unique properties not found in conventional semiconductors, has led to increasing interest in their use in everyday electronic devices instead of silicon. Their ability to handle higher power density is particularly attractive for attempts to sustain Moore's law – the observed steady rate of increase in the density of transistors on an integrated circuit, which has, over decades, doubled roughly every two years. Conventional technologies, however, appear to be reaching a plateau of transistor density.
Strain engineering refers to a general strategy employed in semiconductor manufacturing to enhance device performance. Performance benefits are achieved by modulating strain, as one example, in the transistor channel, which enhances electron mobility (or hole mobility) and thereby conductivity through the channel. Another example is semiconductor photocatalysts strain-engineered for more effective use of sunlight.
Band-gap engineering is the process of controlling or altering the band gap of a material. This is typically done to semiconductors by controlling the composition of alloys, constructing layered materials with alternating compositions, or by inducing strain either epitaxially or topologically. A band gap is the range in a solid where no electron state can exist. The band gap of insulators is much larger than in semiconductors. Conductors or metals have a much smaller or nonexistent band gap than semiconductors since the valence and conduction bands overlap. Controlling the band gap allows for the creation of desirable electrical properties.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Shirley Chisholm, elected in 1968.