| Summary: | 碩士 === 國立臺灣大學 === 光電工程學研究所 === 88 === In order to obtain broadband characteristics in optical communication wavelength, InGaAsP/InP ridge waveguide lasers and superluminescent diodes with nonidentical multiple quantum wells (MQW) are designed and fabricated. According to the photoluminescence experiment of GaAs/AlGaAs and InGaAsP/InP nonidentical MQW, nonuniform carrier distribution inside MQW is discovered at low temperature, especially below 150K. Theoretical study confirms the experimental result.
The ridge waveguide InGaAsP/InP laser diodes and superluminescent diodes are fabricated with standard processing techniques. Then their electrical and optical properties are measured. The measured results show that electron is the dominant carrier controlling the 2D carrier distribution inside our MQW structures, in contrast to the common concept that hole is the dominant one. The reason is the separate confinement heterostructure of MQW structure is so long that it takes much more time for hole than electron to diffuse through. Analysis also suggests that a shorter quantum-mechanical capture time of carriers into QW (0.04ps for hole and 0.1ps for electron) than common concept (0.2ps for hole and 1ps for electron) is required to explain the experimental results. The sequence of the nonidentical MQW is experimentally shown to have significant influence on the L-I properties, emission spectra, and temperature characteristics, showing very different carrier distribution scheme in each sequence. Significant drift of lasing wavelength under same current level of the same laser diode, and abrupt switch of lasing wavelength within small temperature variation (5℃), are observed. Also, spectral width of superluminescent diode covering from 1.3μm to 1.55μm (near 300nm) is obtained from one particular sequence of the MQW structures. Simple calculations are performed to analyze these phenomena.
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