Nanocrystals electroluminesce bright white light
Eugene D. Jungbluth
Quantum confinement effects occurring in nanocrystals can effectively increase the bandga¥in silicon materials from about one electron volt, which corresponds to the infrared range, to several electron volts, which corresponds to the visible or ultraviolet range. Scientists at Structured Materials Industries (Piscataway, NJ) are using these effects to control electron-transport mechanisms and generate bright UV (<350-nm), visible white, and IR (greater than 850-nm) light from electrically stimulated silicon.
A silicon-rich silicon dioxide layer nominally 1 µm thick was formed on a silicon substrate by low-pressure chemical-vapor deposition and then annealed to precipitate out excess silicon. This process is used to create a nanocrystal surface with crystal sizes ranging from 1 to 5 nm. Electrical contact is made via probes to deposited indium tin oxide contacts (3-9-mm diameter) from which intense visible white-light emission is evident even in ambient light.
President Gary Tompa said that his company is working on ac-type electroluminescent devices (about 100 V), but dim emission is observed at only 10 V. Tompa said, "We are working on methods to tailor the emission wavelength in a controllable way." He explained that the emission wavelength depends on the crystal size--the emission wavelength shifts to the red as the size increases--but surface chemistry may also have an effect on wavelength. Because silicon is used, the well-known advantages of silicon integrated-circuit (IC) processing technology can be exploited. Tompa envisions various product applications including lamps, displays, and photonic ICs.
