Electrical and optical studies of InGaAs/GaAs quantum dots and GaAsN/GaAs quantum well
| Autor: | Jiin-Shung Wang, 王錦雄 |
|---|---|
| Rok vydání: | 2000 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 88 The electrical and optical characteristics of GaAs-based strained quantum well and quantum dots have been investigated in this dissertation. In the case of compressed strain, the GaAs/InAs/GaAs quantum dots with the InAs thickness varying from 1.1, 2.3 to 3.4 monolayer (ML) are studied. From photoluminescence (PL), cross-sectional transmission electron microscopy (XTEM) and reflection high-energy electron diffraction patterns (RHEED), we observe the presence of quantum dots for 2.3 and 3.4 ML-thick InAs samples. The capacitance-voltage (C-V) measurement shows a carrier confinement for 1.1 and 2.3 ML samples. For 2.3 ML sample, XTEM images show the presence of defect-free self-assembled quantum dots. With increasing the InAs thickness to 3.4 ML, significant carrier depletion caused by the relaxation is observed. In contrast to 1.1 and 2.3 ML samples in which no traps are detected, two broad traps and three discrete traps at 0.54, 0.40 and 0.34 eV are observed in 3.4 ML sample. The traps at 0.34 and 0.54 eV are found to be similar to the traps observed in relaxed GaAs/In Ga As/GaAs single quantum well structure with 1000A-thick InGaAs. By comparing with the XTEM images, the trap at 0.54 eV is identified to be the relaxation-induced dislocation trap in the GaAs layer. The trap at 0.33 eV is found to cause carrier depletion and produce a resistive region in relaxed In Ga As/GaAs single quantum well structure. In order to analyze the capacitance-frequency spectra in such high-resistive structure, a new equivalent circuit model is developed. In contrast to the compressed strain in InGaAs/GaAs material, GaAsN/GaAs material posses a tensile strain. The effect of tensile strain is investigated by continuously varying the GaAsN thickness in GaAs/GaAsN/GaAs single quantum well structures. The x-ray spectra show the interference patterns for the sample with GaAsN up to 590 A, indicating a high flatness of interfaces. The PL data show the decrease of the GaAsN emission energy with increasing the GaAsN thickness, suggesting the effect of quantum confinement. Carrier depletion is observed for the sample with 250A-thick GaAsN. From such sample, three traps at 0.35, 0.45 and 0.75 eV are observed. Among them, the traps at 0.35 and 0.45 eV are speculated to be N-related or strain-induced defects. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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