Growth of III-V Compound Semiconductor Quantum Structures and Devices by Gas-Source Molecular Beam Epitaxy
Date Issued
2009
Date
2009
Author(s)
Lin, You-Ru
Abstract
The dissertation contains subjects: namely, GaAsSb/GaAs type-II quantum well (QW) with an adjacent InAs quantum-dot (QD) stressor layer and GaAs grown on Si nano-trench. The growths in both subjects are carried out by gas-source molecular-beam epitaxy (GSMBE). irst, we study the structural and optical properties of a composite structure consisting of GaAsSb type-II QW well with an adjacent InAs QD stressor layer. From 19-K photoluminescence (PL) spectra, we observed a 44-meV red-shift in emission energy in the composite structure with 5-nm thick spacer layer in between the QW and QD as compared with a type-II GaAsSb/GaAs single QW structure, which indicates that the strain induced by the adjacent QDs produces local potential minimums in the interface of the type-II QW. From the temperature-dependent PL results, the sample with composite structure shows stronger intensity and broader line-width than the GaAsSb/GaAs single QW structure. With increasing temperature, a part of carriers localized in the QDs are thermalized. Their escape leaves the QDs charged, which modulates the electric field between the QDs and the QW and enhances the potential fluctuation in the interface of QW. As a result, the probability of carrier recombination increases due to the additional confinement provided by the modified potential fluctuation. We use the composite structure as the active region of edge-emission laser diodes. Lasers with composite structure show lower threshold current density and internal optical loss than the GaAsSb/GaAs QW lasers. Better internal quantum efficiency, modal gain and characteristic temperature are also demonstrated. We ascribe these advantages in laser characteristics to the larger optical transition element in the composition structure, resulting from the additional potential fluctuation provided by the charged QDs. n the second part of this work, we studied the growth of GaAs in patterned Si nano-trenches provided by TSMC. In order to avoid the shadowing effect, the major molecular beams were aligned with the longitudinal direction of the nano-trenches. We found that when the growth temperature is higher than 580C, no GaAs is left on the surface of SiO2, and the selective epitaxial growth of GaAs in Si trenches is achieved successfully. Cross-sectional transmission electron microscopic images show that no threading dislocations but micro-twins exist in the GaAs deposited in the Si nano-trenches. Raman spectroscopy and cathodoluminescence (CL) were used to analyze the GaAs grown in the Si nano-trenches. Beside the LO and TO modes of GaAs, we indentified three additional modes, a surface mode in between the TO and LO modes, the Si-2TA mode, and a mode with its peak wave-number smaller than that of the TO mode. Room temperature CL bands from GaAs grown on Si nano-trenches show broaden linewidths and peak energies deviated from that of bulk GaAs, which is attributed to the cross-doping during the growth, strain in the GaAs resulting from lattice mismatch, and Stark shift resulting from the surface and interface depletion regions. In addition, emission bands from SiO2 were also observed. As far as we know, it is the first GaAs epitaxial film grown in Si nano-trench with a width less than 100 nm by GSMBE.
Subjects
InAs/GaAs quantum dot
GaAsSb/GaAs quantum well
nano-Si-trench
Type
thesis
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