Loading...
Please wait, while we are loading the content...
Similar Documents
Self-assembled Nanorings and Stressor Quantum Dots
| Content Provider | Semantic Scholar |
|---|---|
| Author | Riikonen, Juha |
| Copyright Year | 2006 |
| Abstract | In this thesis, the main focus is in the fabrication and characterization of self-assembled III-V compound semiconductor nanostructures. The samples were fabricated by metalorganic vapor phase epitaxy (MOVPE). Atomic force microscopy (AFM) and photoluminescence (PL) measurements were used to examine surface morphology and optical characteristics of the samples, respectively. Quantum dot (QD) heterostructures are typically realized by embedding self-assembled islands in a matrix of another semiconductor material with a higher band gap. In this work, however, islands were used as stressors on top of a near-surface quantum well (QW) to induce three-dimensional potential enclosures into the QW. These QD structures are known as strain-induced QDs (SIQDs) or stressor QDs. Firstly, a new material system utilizing InAs stressor islands to create strain-induced InGaAs(P)/InP QDs was demonstrated. Up to four PL peaks from the QD ground and excited states were clearly resolved in the spectra. The island ensemble was optimized using a growth temperature ramp-down during the InAs island deposition. The luminescence wavelength was tuned by varying the QW composition. On the other hand, the QD confinement was modified by altering the height of the stressor islands or by varying the distance of the QW from the surface. Secondly, transformation of self-assembled InAs islands into volcano-like nanorings was investigated. In the method introduced in this thesis, contrary to previous techniques utilizing partial capping of islands, only phosphorus annealing was applied. It is assumed that the material redistribution, i.e., the island-to-ring transformation, is caused by the exchange of As atoms to P atoms along with the strain-driven migration of In atoms outwards from the island. Thirdly, surface passivation of GaAs by an in situ grown epitaxial ultrathin GaN layer was studied. Near-surface InGaAs/GaAs QWs were used as low-dimensional test structures, on which the passivation was applied. PL measurements were used to assess the effect of the passivation. Significant enhancement of the PL intensity shows that the growth of an ultrathin GaN layers is an efficient method in the passivation of GaAs surfaces.%%%%Tassa vaitostyossa valmistettiin ja tutkittiin itsejarjestyvia yhdistepuolijohteiden nanorakenteita. Naytteet valmistettiin metallo-orgaanisella kaasufaasiepitaktisella (engl. metalorganic vapor phase epitaxy, MOVPE) menetelmalla. Atomivoimamikroskopiaa (engl. atomic force microscopy, AFM) kaytettiin pinnan morfologian tutkimiseen. Optisia ominaisuuksia tutkittiin fotoluminesenssimittauksilla (engl. photoluminescence, PL). Kvanttipisteita on tyypillisesti valmistettu peittamalla itsejarjestyneita puolijohdesaarekkeita toisella puolijohteella, jolla on saarekemateriaalia suurempi energia-aukko. Tassa tyossa kvanttipisteita kuitenkin valmistettiin pinnan laheisyydessa olevaan kvanttikaivoon saarekkeiden indusoiman jannityksen avulla (nk. jannityskvanttipisteet). Aluksi toteutettiin jannityskvanttipisteiden valmistamiseen soveltuva… |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://aaltodoc.aalto.fi/bitstream/handle/123456789/2711/isbn9512281821.pdf?isAllowed=y&sequence=1 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
