Overcoming II-VI barrier
Traditionally, metals such as palladium are used to contact II-VI semiconductor laser structures with the green light emitter ZnTe. These components have a large contact resistance causing thermal stress and a high rate of degradation, limiting the service life of the semiconductor component. Therefore the durability of II-VI blue-green laser diodes is not adequate for commercial applications.
The BAOBERLIN invention lowers the contact resistance and permits the operation of semiconductor laser diodes with lower operating voltages resulting in longer service life. Patents have been granted for the technology development. The researchers are looking for license agreements with industry partners. Laser diode prototyping and optimisation and investigation of laser durability under working conditions need to be carried out.
The new contact structure is composed of a thin lithium nitride (Li3N) intermediate layer between the ZnTe and the covering metal, usually palladium or gold/palladium.
The invention also includes methods for production of the structure. Thermal vapour deposition, electron beam vapour deposition or vacuum sputtering result in a Li3N layer of 2-20nm thickness. To avoid oxidation of the Li3N from contact with air, the layer is covered with palladium or gold/palladium. Typically the thickness of the covering layer ranges from 5-1000nm. Lateral oxidation is prevented through additional isolation materials such as silicon nitride. A further reduction of the contact resistance can be achieved by tempering/annealing to prolong the service life of the semiconductor component even more. Another possibility to improve the contact properties is to use an extra adhesive layer of metal, for example.
Special applications include the use of the laser diodes for colour laser TVs (without a cathode-ray tube), improvements in laser printing, light emitting diodes (LED) or II-VI-detectors for military applications.
Contact heike.hanspach@berlin.ihk.de
http://www.baoberlin.de
