Advanced transmission electron microscopy studies of III-V semiconductor nanostructures.

摘要

III -V semiconducting materials allow many novel optoelectronic devices,udsuch as light emitting diodes and lasers, to be developed. Furthermore, recentuddevelopment in crystal growth techniques allows the growth of low-dimensionaludsemiconductor heterostructures. To achieve the best performance, the crystallinityudand the growth mechanism of the devices have to be analysed. In this work, a JEOLudJEM-2010F field emission gun transmission electron microscope (TEM) isudemployed to analyse the nanoscale semiconductor structures. Various techniques,udsuch as conventional TEM, scanning TEM, high resolution TEM and energy-filteredudTEM were employed to characterize the structural properties of III-Vudsemiconducting materials.udIn this thesis, advanced TEM analysis on InAs/GaAs quantum dots withudInAIAs capping layer, GaInNAs/GaAs quantum wells and annealed lowudtemperature-grown GaAs are presented. The former investigates the impact ofudvarying the thicknesses of InAIAs in the combined two-level InAIAs-InGaAsudcapping layer on InAs/GaAs quantum dots. Based on the energy-filtered TEMudimages, the concentration of Al near the apex of the dots is significantly reduced. Anudincrease in the height of the quantum dots has been observed when the thickness ofudInAIAs capping layer is increased. This is attributed to the suppression of indiumudatom detachment rate from the InAs dots during the capping process.udEffects of growth temperature on the structural properties of 1.6 umudGaInNAs/GaAs mUltiple quantum wells were also investigated. TEM studies showudthat compositional modulations and dislocations occurred in the sample grown atud400°C and possible point defect formation in the sample grown at 350 °C. Theudphotoluminescence intensities for samples grown at 350 and 400°C are degradeduddramatically, compared with the sample grown at 375 °C.udThe effects of low temperature-growth GaAs annealed at differentudtemperatures were systematically investigated by TEM. Along with otherudcollaborative measurements, the arsenic precipitate parameters obtained from TEMudimages were employed to develop a semi-quantitative model based on Ostwaldudripening to explain the precipitate formation. Furthermore, the "two-trap" modeludsuccessfully explains the anomalous features in the carrier lifetime and resistivityudtrends in annealed low temperature-grown GaAs.