On the application of capacitance-time and charge-time measurements to determine the generation lifetime and surface generation velocity in silicon-on-insulator (SOI) substrates

Abstract

To predict accurately the leakage currents in silicon-on-insulator transistors (SOI), the minority carrier generation lifetime in the body region and the surface generation velocity at the body/buried interface must be known. It is demonstrated in this paper that both these quantities can be found from the application of charge-time and capacitance-time measurements. The measurements are applied to a SOI capacitor and consequently the standard theory for both techniques is modified for this structure. By taking account of the effective generation width, the charge-time technique yields an accurate measurement of the minority carrier generation lifetime in the body. The value obtained was 270 ns and is shown to agree well with that obtained from gated diode measurements. By careful choice of step voltage amplitude the capacitance-time technique yields both the surface generation velocity at the body/buried oxide interface and the generation lifetime in the bulk body. Since the latter is known from the charge-time measurement the surface generation velocity can now be found. It is shown that to maintain current continuity a charge storage effect occurs at the body/buried interface whose magnitude is exacerbated in large-area test structures introducing a significant error. This effect is treated in some detail.