But, the researchers didn’t stop there. By internally connecting the base and collector of a light-emitting transistor, they created a new form of light-emitting diode, which modulates at up to 7 gigahertz, breaking the speed record once again.
In a pair of papers published in the June 15 issue of Applied Physics Letters, researchers at the University of Illinois and at U. of I. licensee Quantum Electro Opto Systems in Melaka, Malaysia, report the fabrication and testing of the new high-speed light-emitting transistor and the new “tilted-charge” light-emitting diode.
“Simple in design and construction, the tilted-charge light-emitting diode offers an attractive alternative for use in high-speed signal processing, optical communication systems and integrated optoelectronics,” said Nick Holonyak Jr., a John Bardeen Chair Professor of Electrical and Computer Engineering and Physics at Illinois, and a co-author of both papers.
The modulation speed of either a light-emitting diode or a light-emitting transistor is limited by the rate at which electrons and holes (the minus and plus charges – the carriers of current) recombine. The recombination lifetime is important in determining device speed.
With a usual “slow” recombination process, the speed of a light-emitting diode is limited to approximately 1.7 gigahertz, which corresponds to a carrier lifetime of 100 picoseconds. For more than 40 years, scientists thought breaking the 100-picosecond barrier was impossible.
Recombination speeds of less than 100 picoseconds are not readily achieved in light-emitting diodes because equal number densities of electrons and holes are injected into the active region to preserve charge neutrality, said Holonyak, who invented the first practical visible light-emitting diode more than 40 years ago.
These charges become stuck, stacked-up waiting to recombine, Holonyak said. To achieve high recombination speeds, an extremely high injection level and a very high charge population are required in light-emitting diodes. These conditions are not necessary in transistors, however.
“Unlike a diode, a transistor does not store charge,” said Milton Feng, the Holonyak Chair Professor of Electrical and Computer Engineering, and a co-author of the two papers. “Charges are delivered to the transistor’s quantum well active region, where they either recombine almost instantly, or they are kept moving on out of the device. The charges do not become stacked-up, waiting to recombine with their oppositely charged twins.”
To increase the modulation speed of their light-emitting transistor, the researchers reduced the emitter size, increased the so-called collector thickness (the third terminal region), and utilized a special internal common collector design. These changes resulted in a faster signal at a very low current level, and at low heat dissipation.
Having a “fast” recombination process, the modulation speed of the light-emitting transistor was measured at 4.3 gigahertz, which corresponds to a recombination lifetime of 37 picoseconds, well under the “100-picosecond barrier.”
“In the light-emitting transistor, the third terminal – the collector – effectively ‘tilts’ the charge and removes carriers with slower recombination lifetimes,” said Holonyak, who also is a professor in the university’s Center for Advanced Study, one of the highest forms of campus recognition.
“As opposed to the charge ‘pile-up’ condition found in a normal diode, the dynamic ‘tilted’ charge flow condition in the transistor base is maintained with the collector in competition with the base recombination process,” Holonyak said. “If the charge doesn’t recombine and generate a photon fast enough, it is swept away by the current in the collector.”
By preventing the build-up of “slow” charges in the base, the “fast” picosecond recombination dynamics also provided the basis for the researchers’ light-emitting transistor rewired internally as a new type of light-emitting diode.
The tilted-charge light-emitting diode achieved a record-breaking modulation speed of 7 gigahertz, corresponding to a recombination lifetime of 23 picoseconds.
“The tilted-charge light-emitting diode is simple to make, low cost, and easy to package and use,” Holonyak said.
Because of the tilted base population in the device, current flow, which is a function of the slope of the charge distribution, makes possible high current densities without requiring extreme carrier densities.
“That’s the trick of the transistor,” Holonyak said. “And now we’ve incorporated it into a diode. The physics has been there all along. It just wasn’t recognized.”
With Feng and Holonyak, co-authors of the paper are lead author Gabriel Walter (chief executive officer at Quantum Electro Opto Systems), and graduate students Chao-Hsin Wu and Han Wui Then.
Funding was provided by the U.S. Army Research Office and the Brain Gain Malaysia Diaspora Program. Device fabrication and testing was performed at the university’s Micro and Nanotechnology Laboratory.
Quantum Electro Opto Systems is a company formed by Walter, Feng and Holonyak to commercialize the light-emitting transistor and tilted-charge light-emitting diode technology.
James E. Kloeppel | University of Illinois
Further reports about: > 100-picosecond barrier > Electro > Ferchau Engineering > Illinois River Watershed > LIGHT > Malaysia > Modulation > Physic > Quantum > high-speed signal processing > integrated optoelectronics > light-emitting diode > light-emitting transistor > optical communication systems
Basque researchers turn light upside down
23.02.2018 | Elhuyar Fundazioa
Attoseconds break into atomic interior
23.02.2018 | Max-Planck-Institut für Quantenoptik
A newly developed laser technology has enabled physicists in the Laboratory for Attosecond Physics (jointly run by LMU Munich and the Max Planck Institute of Quantum Optics) to generate attosecond bursts of high-energy photons of unprecedented intensity. This has made it possible to observe the interaction of multiple photons in a single such pulse with electrons in the inner orbital shell of an atom.
In order to observe the ultrafast electron motion in the inner shells of atoms with short light pulses, the pulses must not only be ultrashort, but very...
A group of researchers led by Andrea Cavalleri at the Max Planck Institute for Structure and Dynamics of Matter (MPSD) in Hamburg has demonstrated a new method enabling precise measurements of the interatomic forces that hold crystalline solids together. The paper Probing the Interatomic Potential of Solids by Strong-Field Nonlinear Phononics, published online in Nature, explains how a terahertz-frequency laser pulse can drive very large deformations of the crystal.
By measuring the highly unusual atomic trajectories under extreme electromagnetic transients, the MPSD group could reconstruct how rigid the atomic bonds are...
Quantum computers may one day solve algorithmic problems which even the biggest supercomputers today can’t manage. But how do you test a quantum computer to...
For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.
In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...
Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale
Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...
15.02.2018 | Event News
13.02.2018 | Event News
12.02.2018 | Event News
23.02.2018 | Physics and Astronomy
23.02.2018 | Health and Medicine
23.02.2018 | Physics and Astronomy