Russo-German spin-out focuses on defect reduction
A wafer-manufacturing company with expertise in quantum-dot lasers and metamorphic structures for microelectronic devices has been spun out of the Ioffe Institute in St Petersburg, Russia, and the Technical University of Berlin in Germany.
Called Nanosemiconductor (NSC), the Dortmund-based start-up recently attracted €7 million in venture capital funding led by Germany-based PolyTechnos Venture Partners.
The company’s technology is based on quantum-dot laser research that NSC’s chief scientific officer Nikolai Ledentsov and his team have been developing for over a decade.
NSC currently has a cleanroom facility featuring one MBE reactor and can grow onto 2-6 inch GaAs and silicon wafers at its facility. It is focusing primarily on InGaAs-based long-wavelength quantum-dot VCSELs. Bernd Meyer, the company’s general manager, says that NSC will begin shipping wafers to ‘several’ optoelectronics customers in January 2004.
“Our scientists are the pioneers of quantum-dot lasers,” Meyer said. The NSC team says that its 1.3 µm quantum-dot VCSEL is developed and tested. Ledentsov and colleagues have also recently fabricated a 1.5 µm edge emitting laser based on GaAs. The pulsed laser had an output power of 7 W and operated at up to 85 deg. C (Elec. Letts. 39 15 1126).
NSC claims that its ‘nanoepitaxy’ growth technology greatly reduces the number of defects in compound semiconductor wafers, thus improving device characteristics and reliability.
The defect reduction technology (DRT) involves a manufacturing step where dislocations in the wafer structure are selectively removed (US patent application 2003 0203531). “We create strain fields around the dislocations by strained-layer growth. Then we deposit a temperature-stable capping layer that undergoes repulsive interaction with the dislocated regions,” explained Ledentsov.
“When the layer is annealed, this selectively creates holes at a certain depth, in regions where the dislocations were present. We can then overgrow a defect-free top layer.” DRT is said to be particularly good at reducing the number of threading dislocations in strain-relaxed metamorphic layers, and local defects (e.g. defect dipoles and dislocation loops) in quantum-dot structures.
Ledentsov says that the 20-minute DRT step, which takes place in situ and does not require removal of the wafer from the MBE or MOCVD chamber, typically reduces the dislocation density by an order of magnitude. He added that the DRT step can be repeated to further reduce dislocation densities.
The team has applied the growth process to GaN on sapphire, reducing the dislocation density to 3x107/cm2 from 109/cm2 with one DRT step. GaN devices are typically very sensitive to dislocation density; the fabrication of most GaN-based lasers requires the wafer to be removed from from an MOCVD chamber for lithography and etching before a time-consuming epitaxial lateral overgrowth (ELOG) step is performed. Ledentsov says that NSC’s manufacturing process will lead to cheaper, more reliable GaN-based lasers, and LEDs that can be driven at higher currents to achieve high brightness and long operating lifetime.
NSC is also targeting microelectronics applications, particularly m-HBTs and m-HEMTs, and Meyer says that devices based on NSC’s metamorphic InGaAs-on-GaAs structures exhibit the same performance as InP-based devices with all the inherent advantages of the more mature technology.
“The challenge in microelectronics is to produce low-noise, high-mobility devices,” said Ledentsov. “Using metamorphic InGaAs-on-GaAs structures gives us the high electron mobility at a much lower cost than devices based on InP.”
Ledentsov says that DRT can also be applied to SiGe and strained-silicon structures for low-noise UHF amplifiers such as high-speed 77 GHz devices mooted for automotive radar systems.
