MBE growth and characterization of TlInGaAsN double quantum well structures

In the pursuit of reducing the temperature dependence of the emission wavelengths of devices, TlInGaAsN double quantum well (DQW) structures with different barriers grown on GaAs substrates by molecular beam epitaxy (MBE) were investigated. Higher Tl incorporation, a key parameter to reduce temperature dependence, could be obtained in the TlGaAsN barrier samples. However, the presence of many dislocations and very rough interfaces together with phase separation reduced the photoluminescence (PL) characteristics. DQW structures with combined barriers of TlGaAsN+TlGaAs+TlGaAsN and those consisting of TlGaAsN with reduced N composition showed improved crystalline characteristics. The (2 2 4) reciprocal space maps of these two samples did not show any diffraction corresponding to phase segregation. However, cross-sectional transmission electron microscopy (X-TEM) images revealed the presence of inhomogeneity (i.e., the presence of nearly perfect regions with good interfaces as well as regions with rough interfaces) in these samples.