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Improvement of Recovery Time of Bipolar Power Devices by Si1-xGex Misfit Dislocations
Published online by Cambridge University Press: 25 February 2011
Abstract
A new technique for improving the recovery time of bipolar power devices by misfit dislocations to fast switching speed levels is described. Misfit dislocations formed in situ at abrupt SiGe/Si heteroepitaxial interfaces are used as recombination centers in the space charge regions of devices. The density of misfit dislocations was varied over a wide range by controlling the Ge concentration and the number of Ge-containing layers in both <111> and <100> orientations. The structural properties of misfit dislocations were studied by optical microscopy, TEM, and X-ray topography. Power rectifier recovery and electrical parameters, DLTS, and minority carrier lifetime were employed to evaluate the electrical behavior of dislocations with and without gold diffusion. Fast recovery times with low leakage current and forward voltage drop were achieved by the introduction of misfit dislocations. Monotonically decreasing recovery times were obtained with increasing dislocation density. For the same recovery time, introduction of misfit dislocations produced about 50% reduction in high-temperature leakage current and similar forward voltage drop compared to devices subjected to Au diffusion. The combination of dislocations and metal impurities is also investigated and found to provide an excellent mechanism for further tailoring of the recovery characteristics of power devices. In this application the metals were preferentially accumulated in the depletion region at the misfit dislocations from small background metal concentrations leading to additional reduction of recovery time, while maintaining small leakage current and forward voltage drop.
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- Copyright © Materials Research Society 1991