Abstract
In this dissertation, we have described the growth and characteristics for the 1.3 µm InAsP/InP strained multiple quantum well (SMQW) and InAsP/InGaP strain-compensated multiple quantum well (SCMQW) laser diodes (LDs) grown by metalorganic chemical vapor deposition (MOCVD). The influence of growth temperature on the luminescent and structural properties of InAsyP1-y/InP SMQWs and strained single quantum wells (SSQWs) was first studied toward achieving a high-quality crystalline InAsP/InP SMQW structure. A AsH3/(AsH3+PH3) gas flow ratio of 0.50 and 1.48 % at 580 and 650 °C growth temperatures, respectively, will result in an InAsP layer with y = 0.3 solid composition. The experimental photoluminescence (PL) emission energies at 10 K with different well thicknesses for the InAsyP1-y/InP SSQWs grown at 580 and 650 °C are in well agreement with the trend of the calculated curves. The transmission electron microscope (TEM) lattice image of an InAsP/InP SSQW grown at 580 °C on the order of two monolayers has been demonstrated for the first time. The InAsP/InP SSQW structure grown at 580 °C appears to be extremely abrupt, uniform, free of misfit dislocations, and narrow PL linewidth. Besides, the growth of InAsP/InP SMQWs at 580 °C maintains its structural integrity throughout the deposition sequence with smooth interface and well-defined periodicity. However, the InAsP/InP SSQWs or SMQWs exhibit an adverse property at 650 °C growth temperature. Thus, the lower growth temperature is necessary for the InAsP/InP SMQW growth by MOCVD. We next explored the temperature dependence of PL from InAsP/InP SSQW, SSQW stack and SMQW structures for understanding their optical properties. The high-quality crystalline InAsyP1-y(72Å)/InP SSQW structure with y £ 0.36 exhibits a 9.9 meV full width at half maximum (FWHM) of 10 K PL spectra. The peaks in the PL spectra for SSQW stack structure with a well thickness of 8, 14, and 35 Å vanish above 100, 150, and 296 K, respectively, presumably due to the decrease of photons yielded by electron-hole recombination in thinner quantum well regions when increasing temperature. In addition, the variations of the PL peak energy and FWHM in all the InAsP/InP SSQW, SSQW stack, and SMQW structures are described in detail. Based on the above results, 1.3 µm InAsP/InP SMQW LDs with separate confinement heterostructure grown at 580 °C by MOCVD were fabricated. Although the InAsP/InP SMQWs grown at 580 °C maintain its structural integrity throughout the deposition sequence, the slightly broader PL half width for InAsP/InP SMQW structure is attributed to the dislocations resulted from a large net strain. Laser emission can be achieved by using the InAsP/InP SMQWs and the lasing wavelength is in a good agreement with our designed structure. The experimental data of broad-area and ridge-waveguide LDs are described in detail. In order to improve the characteristics of InAsP/InP SMQW LDs, the effect of rapid thermal annealing (RTA) on the performance of LDs grown by MOCVD was studied. From the PL measurements, the optimal RTA temperature for the InAsP/InP SSQW stack is 700 °C. The 700-°C annealed SSQW stack has a stronger PL peak intensity, no spectrum broadening and little peak shift, indicating that the interdiffusion of group-V elements can be much alleviated. The threshold current and slope efficiency of the 700-°C RTA LDs can be reduced significantly as compared to the as-grown LDs. 1.3 µm InAsP/InP/InGaP strain-compensated multiquantum well (SCMQW) LDs were fabricated by introducing InGaP tensile strained layer as barriers to counteract the compressive strain induced by the InAsP layer. Sharp satellite peaks with narrow width in double-crystal x-ray diffraction (DC-XRD) for the InAsP/InP/InGaP SCMQW structure are observed, indicating that good epitaxial-layer quality can be obtained through the use of strain-compensation coupled by InGaP barrier layers. A redshift of the PL peak position with increasing InGaP barrier thickness above 6 nm is observed for the first time in (100) oriented strained layers, is probably attributed to redistribution across the samples of the huge built-in electric field induced by the piezoelectric effect. The threshold current density of InAsP/InP/InGaP SCMQW LDs decreases by a factor of 3 through the employ of tensile-strained InGaP barrier layer and lasing wavelength is in a good agreement with our design structure. Additionally, we report the effects of InGaP barrier thickness on the performance of 1.3 µm InAsP/InP/InGaP SCMQW-RWG LDs. The threshold current decreased from 78.8 to 33.8 mA through the employ of tensile-strained InGaP barrier layer of 20 Å and lasing emission wavelength is 1.307 µm under 44 mA. These results indicate that adequate thickness of tensile-strained InGaP barrier is must be employed to compensate the compressive strain of InAsP system for optoelectronic devices.