Combined Optical, Structural and Theoretical Assessment Of Mocvd Grown Multiple GaAs Quantum Wells
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ABSTRACT A combined characterization of theoretical calculation and experimental measurements, including Raman scattering, photoluminescence and cross sectional transmission electron microscopy, has been made on GaAs-AlxGalixAs multiple quantum wells (MQW) structures with different well widths grown by metalorganic chemical vapor epitaxy (MOCVD) with a modified reactor. Various parameters of these MQXks are obtained. The results with and without the alkyl push flow are compared. Related physical phenomena are discussed.
INTRODUCTION In recent years, high quality GaAs-AIGaAs quantum well (QW) and superlattice (SL) structures have been extensively investigated. These heterostructures can be applied in light emitting diodes, semiconductor lasers, infrared detectors and other
electronic devices. Various technologies have been employed to grow these microstructures, among which molecular beam epitaxy (MBE) and metalorganic
chemical vapor deposition (MOCVD) can provide the best quality of epitaxial layers and structures. After various and continual efforts, MOCVD growth technique has improved greatly and challenged the MBE market for the growth and manufacture of electronic materials and devices. One of such efforts is presented here. In this study, a modified horizontal MOCVD reactor was used to grow GaAsAlxGal.xAs multiple quantum wells (MQWs) with a variety of well widths. A combined investigation of cross section electron microscopy (XTEM), photoluminescence (PL) at 2, 77 and 300 K, Raman scattering and theoretical calculation was performed to assess the properties of these GaAs MQWs. Some physical problems on the growth and characterization are discussed. EXPERIMENT Experimental samples were. grown at Westinghouse Science and Technology Center, employing an in-house built MOCVD system with trimethylgallium (TMG) and trimethylaluminum (TMA) as the reactant sources. Originally, epitaxial deposition used two growth rates to reduce structural growth time and increase throughput, and the alkyl lines were provided with a hydrogen "push" line to dilute the alkyl flow out and reduce possible condensation of the alkyls. However, due to the different flow rates in the main alkyl and push lines, this can lead to additional dilution of the alkyl, causing the low Al-composition and the Al-grading in the GaAs-AlxGal~xAs interfaces. To 359 Mat. Res. Soc. Symp. Proc. Vol. 326. @1994 Materials Research Society
remove the interfacial grading during the growth of multilayers, the horizontal reactor was designed with a more accurate vent/run pressure-balancing capability and the "push" flow line can be removed to prevent formation of the dilution and grading. Based upon these tests [1], a new fast-spinning disc reactor in replacing the ordinary horizontal reactor was designed with the gas flow manifold to allow positive shutoff of the push flow to each alkyl line. In addition, individual active pressure control was provided for the reactor, injector tube manifolds, and each alkyl bubbler. This system, coupled with accurate tempera
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