Determination of size dependent carrier capture in InGaN/GaN quantum nanowires by femto-second transient absorption spectroscopy: effect of optical phonon, electron-electron scattering and diffusion.

Understanding the ultrafast processes corresponding to carrier capture, thermalization and relaxation is essential to design high speed optoelectronic devices. Here, we have investigated a size dependent carrier capture process in InGaN/GaN 20, 50 nm nanowires and quantum well systems. Femto-second transient absorption spectroscopy reveals that the carrier capture is a two-step process. The carriers are captured in the barrier by polar optical phonon (POP) scattering. They further scatter into the active region by electron-electron and POP scatterings. The capture is found to slow down for quantum confined structures. A significant number of carriers are found to disappear from the barrier during the diffusion process. All the experimental observations are explained in a simulation framework depicting various scattering mechanisms.

Strong Size Dependency on the Carrier and Photon Dynamics in InGaN/GaN Single Nanowalls Determined Using Photoluminescence and Ultrafast Transient Absorption Spectroscopy.

Here, we have demonstrated strong size dependency of quasi-equilibrium and nonequilibrium carrier and photon dynamics in InGaN/GaN single nanowalls using photoluminescence and transient absorption spectroscopy. We demonstrate that two-dimensional carrier confinement, strain relaxation, and modified density of states lead to a reduced Stokes shift, smaller full width at half-maxima, increased exciton binding energy, and reduced nonradiative recombination. The ultrafast transient spectroscopy shows that carrier capture is a two-step process dominated by optical phonons and carrier-carrier scattering in succession. The carrier capture is a strongly size-dependent process and becomes slower due to modulation of the density of available states for progressively decreasing nanowall sizes. The slowest process is the electron-hole recombination, which is also extremely size-dependent and the rate increases by almost an order of magnitude in comparison to that of quantum-well structures. Electron-hole wave function overlap and modified density of states are among the key aspects in determining all the properties of these structures.

Thyroglossal Duct Cyst, Variation in Presentation, Our Experience.

Thyroglossal duct cysts are most common midline congenital swelling in head and neck region. It results from incomplete involution of thyroglossal duct. They present as midline painless swelling in neck. We have studied variation in their presentation. The retrospective study carried out in department of ENT in Gandhi Medical College Bhopal from Jan 2009 to Sept 2013. Objective of this study is, to study incidence of Thyroglossal Duct Cyst in different age and sex group and variation in presentation. Clinical records, medical records and histopathological records were studied. 10 patients diagnosed as Thyroglossal Duct Cyst included in study. 10 patients were found to be diagnosed as Thyroglossal Duct Cyst. Out of 10 pt. 6 were pediatric patients and 4 were adults. 8 patients presented with cyst while 2 presented with fistula. Out of 10 patients 3 presented with suprahyoid, 2 at the level of hyoid and 5 had infrahyoid presentation. 7 patients undergone sistrunk operation procedure while 3 undergone simple excision. Out of 3 patients who undergone simple excision 1 patient develop recurrence. Thyroglossal Duct Cyst are one of the most common asymptomatic midline neck swelling and should be differentiated with other swellings with proper investigations.