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March, 2002 EEEL Study Accelerates Understanding of Oxidation Mechanisms Important to Laser Manufacturers |
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Researchers in EEEL have shown that the oxidation kinetics of AlGaAs are independent of semiconductor growth method and edge preparation conditions. Native semiconductor oxide layers are critical components of optoelectronic devices, such as vertical-cavity surface-emitting lasers (VCSELs) used in high-speed data communication, in which they provide optical and electrical confinement. VCSEL manufacturers have reported difficulties with the repeatability of their oxidation process.
Alexana Roshko, Mike Chen, and Kris Bertness of the Optoelectronics Division conducted a study of oxidation rate as a function of relevant semiconductor growth and processing variables for initial AlGaAs layers having Al mole fraction from 0.9 to 1.0. They found that, contrary to the expectations of some device manufacturers, the oxidation rate did not depend on whether the initial layers were grown by molecular beam epitaxy (MBE) or metal-organic chemical vapor deposition (MOCVD), the two methods most commonly used by the industry. The oxidation was independent of the V/III ratio of the growth, impurity level in the initial epilayer, and specimen edge preparation, whether wet etched, ion milled, chemically assisted ion-beam etched, or cleaved. As expected, the oxidation reaction kinetics were a sensitive function of semiconductor composition, oxidation temperature, and time. The study did reveal, in one sample set grown by MOCVD by an outside laboratory, unintentional fluctuations in the epilayer composition during growth (as confirmed by SIMS analysis), which decreased the oxidation rate.
The results of the NIST study are providing VCSEL manufacturers valuable insight into the tolerances of their native oxide fabrication process. They are also important input to a broader investigation of the impact of strain on device reliability.
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