AbstractsPhysics

In this work epitaxial growth and in situ characterisation of dilute nitride quantum well (QW) structures are studied. Dilute nitrides are III-V compound semiconductors with low (typically < 5%) composition of nitrogen in the lattice. Metal organic vapor phase epitaxial (MOVPE) system was used to grow the structures and in situ reflectance monitoring in normal incidence at a wavelength of 635 nm was utilised to study the growth process of the structures. Ex situ characterisation was performed by x-ray diffractometry and photoluminescence measurements. The nitrogen content of (In)GaAsN was found to depend on many MOVPE growth parameters. Increased nitrogen content was obtained with decreasing growth temperature, increasing DMHy/V and TBAs/III ratios and when nitrogen (N2) was used as a carrier gas instead of hydrogen (H2). In situ reflectance data was measured during growth of GaAsN/GaAs, InGaAs/GaAs and InGaAsN/GaAs multi quantum well (MQW) structures. The reflectance curve was observed to be different when MQW structures with different compositions were grown. The reflectance data was analysed by an experimental method utilising the dependence of the reflectance change observed during growth of the QW on the QW composition. Additionally, reflectance curves for multi layer stacks were calculated and the measured curves were compared to the calculated ones. With both methods the sample composition can be determined in situ if the growth rates of the layers are known. In the process of comparing calculated and measured reflectance curves, the high temperature complex refractive indices of the various QW materials were obtained. The imaginary part of the complex refractive index of (In)GaAsN was found to be linearly dependent on the nitrogen content, as well as both real and imaginary parts of the complex refractive index of InGaAs depended linearly on the indium content. However, changing the nitrogen content did not change the real part of the complex refractive index of (In)GaAsN. The in situ analysis methods of MQW structures developed in this work can be used to obtain information about the growth process as well as about the materials themselves. Tässä väitöstyössä tutkittiin typpeä sisältävien kvanttikaivorakenteiden epitaktista valmistusta ja karakterisointia in situ. Rakenteet valmistettiin käyttäen metallo-orgaanista kaasufaasiepitaksiaa (engl. metal organic vapor phase epitaxy, MOVPE) ja valmistuksenaikainen tarkkailu toteutettiin MOVPE-laitteeseen kytketyllä kohtisuoran heijastuksen mittauslaitteistolla käyttäen 635 nm aallonpituutta. Valmistuksen jälkeisessä rakenteiden karakterisoinnissa käytettiin röntgendiffraktio- ja fotoluminesenssimittauksia. Monien valmistusparametrien havaittiin vaikuttavan näytteiden typpipitoisuuteen MOVPE-prosessin aikana. Matalassa lämpötilassa valmistettujen näytteiden typpipitoisuus havaittiin suuremmaksi kuin korkeassa lämpötilassa valmistettujen näytteiden. Samaten DMHy/V-suhteen suurentaminen ja TBAs/III-suhteen suurentaminen kasvattivat typpipitoisuutta.…