| The quaternary GaInNAs alloy is a very promising material system for optical sources in the 1.2--1.6 mum range with application in telecommunication fiber-optic networks. Unfortunately, this is not a thermodynamically stable alloy and considerable growth challenges need to be overcome to improve the optical emission efficiency of the material. Considerable progress in dealing with these difficulties has been made for alloys containing around 30% indium and 2% nitrogen which emit light around 1.3 mum. The effort to push emission out to 1.5 mum, the wavelength for long-haul networks, by adding more indium (up to 40%) has proven considerably more difficult. Recently, the addition of small amounts of antimony has put this alloy back on track for the 1.5 mum challenge by dramatically improving the luminescence efficiency of the material.; In this work, several different Transmission Electron Microscopy (TEM) techniques are used for the first time as powerful tools in the structural characterization of GaInNAs(Sb) quantum well structures at the atomic level. High Resolution TEM (HRTEM) is used to map out the local strain and compositional fluctuations in the quantum wells and barriers. This is correlated with Energy-Filtered TEM (EFTEM) imaging, Dark-Field (DF) imaging with the (002) and (220) reflections, and Energy Dispersive X-ray Spectroscopy (EDX) profiles across the quantum well regions. Both GaInNAs and GaInNAsSb samples were characterized with these techniques. We found that indium tends to segregate in GaInNAs samples while the antimony is responsible for more uniform distribution of indium in the GaInNAsSb samples.; The results of this work bring further understanding of the performance of real devices. GaInNAs lasers are known to have broad emission spectra and high threshold currents. Researchers have speculated that this could be due to local compositional fluctuations. Our results confirm that these indeed occur and give considerable insight into the role of antimony in improving the material quality and luminescence efficiency. |
