Studies on Strained (Indium,Gallium)Arsenide/Gallium-Arsenide Semiconductors and Optical Devices.

Abstract

The work described here embodies a detailed study of strained single and multilayered In-containing III-V compounds grown by molecular beam epitaxy, their characterization and determination of some important properties of guided wave devices and photodiodes in the 1-1.55 $\\mu$m wavelength range using these materials. The refractive index step of In$\\sb x$Ga$\\sb{1-x}$As/GaAs heterojunctions, necessary for optical confinement and guided wave applications, is calculated from the shifts in the b and gaps due to alloying and strain effects. Defects in GaAs isoelectronically doped with In has been studied. Deep-level densities and the densities of defects observed in the photoluminescence spectra are found to decrease with the incorporation of small amounts of In. GaAs doped with 1% is found to be very suitable for the fabrication of optical waveguides. This conclusion is corroborated by losses as low as 0.6dB/cm measured in ion-milled In$\\sb{0.01}$Ga$\\sb{0.99}$As single-mode ridge waveguides at a wavelength of 1.15$\\mu$m. Coupling coefficients of $\\sim$16/cm are measured in coplanar couplers. InGaAs/GaAs strained layer superlattices (SLS) and multiple quantum wells (MQW) were studied for their use in optical and opto-electronic devices. Deep level traps in as-grown and Si-implanted and lamp annealed InGaAs/GaAs SLS have been characterized. Measured trap densities of are $\\sim$10$\\sp{14}$ cm$\\sp{-3}$. Ridge waveguides made by wet chemical etching of In$\\sb{0.2}$Ga$\\sb{0.8}$As (100 A)/GaAs (25 A) SLS show losses $\\sim$3dB/cm at 1.15$\\mu$m. Intensity-dependent measurements on single mode In$\\sb{0.3}$Ga$\\sb{0.7}$As (100 A)/GaAs (150 A) SLS ridge waveguides yield a nonlinear refractive index coefficient of 2.2 $\imes$ 10$\\sp{-7}$ cm$\\sp2$/W at a wavelength of 1.15$\\mu$m which is comparable to the value measured in GaAs/AlGaAs MQW. Non-linear coupling is also observed in couplers fabricated with the same material. The performance of photodetectors made with the strained materials have been studied. In In$\\sb{0.2}$Ga$\\sb{0.8}$As (235 A)/GaAs (125 A) SLS diodes, an impact ionization coefficient ratio, $\\alpha/\\beta\\sim5$ are measured. 20 $\imes$ 25 $\\mu$m$\\sp2$ photodiodes made with SLS absorption regions exibit responsivities $\\sim$0.4 A/W. The impulse response of these devices are characterized with convoluted risetimes of $\\sim$60-100 ps. Finally p-i-n electroabsorption modulators using SLS i-regions have been integrated with low-loss GaAs:In waveguides. The integrated structures are realized by molecular-beam epitaxial regrowth. A 20% modulation depth at 1.15 $\\mu$m is measured with an integrated In$\\sb{0.34}$Ga$\\sb{0.66}$As (100 A)/GaAs (150 A) modulator at room temperature.