Structural Design And Epitaxial Growth Of852nm Laser Diode

For the advantages of the semiconductor laser, including low threshold current,long lifespan, smaller size, high reliability, high-efficiency and so on, thus, it iswidely used in military, optical fiber communication, industrial materials processing,laser medicine and many other fields. In this paper, we demonstrate the design andepitaxial growth of852nm laser diode for Caesium atomic clocks. In order toenhance the wavelength shift with temperature stability of852nm laser diode,weresearch on the design, epitaxial growth and fabrication of852nm laser diode. Themain contents and results of this paper are as follows:1. A semiconductor laser diode was structurally designed for emitting at852nm.Based on the strain theory, the gain of InAlGaAs, InGaAsP, InGaAs and GaAsquantum-wells were calculated by a comprehensive model theory and PICS3Dsoftware, the peak gain and wavelength versus operation temperature of the sixdifferent quantum-wells are compared and discussed. The emission wavelength ofInAlGaAs quantum-well as a function of well width was study. The results indicatethat In_0.15Al_0.11Ga_0.74As/Al_0.3Ga_0.7As quantum well with width of8nm is the mostappropriate candidate for852nm laser diode when the higher gain and bettertemperature stability demanded simultaneously. In order to reduce the seriesresistance, thermal resistance and optical loss of the852nm laser diode, the graded AlGaAs layers and Al_0.55Ga_0.3As layers with multilayer gradual changing dopingwere used in waveguide layers and the cladding layers, respectively.2. The852nm laser diode was grown by metal-organic chemical vapordeposition (MOCVD). The influence of the growth temperature and interruptiontime on the crystal quality of AlGaInAs/AlGaAs quantum well was investigated byreflectance anisotropy spectroscopy (RAS). High growth temperature lead to indiumsegregation from AlGaInAs quantum well to AlGaAs barrier was found by RAS. Bylowering the growth temperature and using interruption time between AlGaInAsquantum well and AlGaAs barriers, the indium segregation effect could beeffectively suppressed. The results of RAS and PL showed the sharp boundariesbetween the AlGaInAs/AlGaAs layer. With optimized growth conditions, thecomplete852nm laser structures have been grown, all the epilayer and growthprocess could be distinguished in situ by RAS transient spectra, RAS prove itself tobe a powerful tool for monitoring growth process of semiconductor lasers.3. Based on the growth conditions and the reactor structure of the MOCVD inlab, the gas flow distribution and temperature distribution of GaAs growth wassimulated by Procom software. During the growth, a significant dependence of theRAS and normalized reflectance signals on the AlGaAs epilayers have been found,The experimental results indicate that the period of normalized reflectanceoscillation could be used to determine the composition and growth rate of theAlGaAs layers. The compositions and growth rate of AlGaAs are calculated bynormalized reflectance transient spectra, the value is in excellent agreement with theexperimental data obtained by scanning electron microscope and high resolutionX-ray diffraction.4. The852nm laser diode with the cavity length of1000μm and the width of100μm was fabricated based on the technological conditions in lab. The full widthhalf maximum (FWHM) is1.1nm, the threshold current is50mA, the slopeefficiency is0.64W/A, the maximum electro-optical efficiency is31.6%and theoutput power is290mW under the injection current of500mA. The wavelength shift with temperature for852nm laser diode is0.256nm/K, the experimental results are ingood agreement with theoretical calculations results.