Japanese University Develops Si-based LED Using Ge Quantum Dots

May 25, 2010
Tetsuo Nozawa, Nikkei Electronics

Tokyo City University developed a silicon-based light emitting device by using germanium (Ge) quantum dots and confirmed that it emits light by current excitation at room temperature.

The university claims that the light emitting device will help realize a silicon (Si) photonics because it can be produced by using a manufacturing process compatible with a CMOS process and possibly is capable of laser oscillation.

The light emitting device was developed by the Research Center for Silicon Nano-Science (SNS) of the Advanced Research Laboratories (ARL) at Tokyo City University. It is made by embedding Ge microparticles (quantum dots) with a diameter of several tens of nanometers to 100nm in the i-layer of a Si-based device with a pin structure.

The Ge microparticles enhance the recombination rate of electrons and holes, said Takuya Maruizumi, director of the SNS and professor of the faculty of Engineering at the university.

"The quantum dots are made by using the MBE (molecular beam epitaxy) method at a temperature of about 400°C," Maruizumi said. "That's why the manufacturing process for the device is compatible with a CMOS process."

The diameter of the device's active layer is about 3μm.

The university has already confirmed that the device emits light with a wavelength of about 1.2μm by current injection at room temperature (300K). The internal quantum efficiency of the light emission is 10-2.

"In addition to the high quantum efficiency, the device is both thermally and chemically stable," Maruizumi said. "So, it is superior to existing silicon-based light emitting devices."

Furthermore, the emission intensity of the device tends to drastically increase as the injected current increases.

"If a resonator structure is formed by using a photonic crystal, it will be capable of laser oscillation," Maruizumi said. "We will change the emission wavelength to the 1.5μm band, which can be used for communications. And, in two or three years, we would like to develop a device that works as an optical switch and commercialize it."