Properties of deep level defects in polycrystalline CdS junctions were investigated using transient capacitance spectroscopy. A total of seven electron traps and one hole trap was observed with activation energies of 0.16, 0.31, 0.38, 0.42, 0.53, 0.69, 0.96, and 0.32 eV, respectively. The emission rate, capture cross section and concentration of the traps are presented. The temperature dependence of the capture cross section for the electron traps at 0.53 and 0.69 eV are also given.
We have measured the frequency chirp in gain-guided, weakly index-guided, and strongly index-guided InGaAsP lasers under direct-current modulation. The measured chirp width is largest for gain-guided and smallest for weakly index-guided ridge waveguide lasers. The chirp width for 1.5-μm InGaAsP lasers is about a factor of 2 larger than that for 1.3-μm InGaAsP lasers of the same structure. The frequency chirping results from a modulaton of the carrier density which modulates the effective refractive index of the guided mode. The frequency chirping can introduce a limitation on the performance of single-frequency injection laser sources for high bit-rate digital transmission in fiber communication systems at 1.55 μm.
Deep level defects in epitaxially grown high-conductivity zinc selenide were investigated using transient capacitance spectroscopy. A total of seven electron traps was observed in Au/ZnSe Schottky diodes and ZnSe/GaAs n-p heterojunctions, having activation energies of 0.24, 0.33, 0.35, 0.42, 0.54, 0.71, and 0.86 eV, respectively. The emission rate, capture cross-section prefactor, and concentration of each trap are reported in this paper. Trap concentrations ranged from 1011 to 1014 cm−3 depending upon the epitaxial growth conditions. A defect model involving selenium vacancies and divacancies as well as deep donor impurities satisfactorily describes the variation of electron trap concentration with zinc/selenium ratio in the vapor phase.
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