LIGHT-INDUCED CAPACITANCE SPECTROSCOPY AND METHOD FOR OBTAINING CARRIER LIFETIME WITH MICRON/NANOMETER SCALE

摘要

Measurement of capacitance and derivative capacitance (dC/dV) on a semiconductor structure under light-pumped condition is documented to measure carrier lifetime with a spatial resolution limited by physical law, depending on material properties (10 nm 100µm). An atomic force microscope or probe-station is used to position a nanometer scale tip over the surface of a semiconductor material to be probed, which is also illuminated with a controlled light source for carrier generation. The capacitance-voltage (C-V) curves or dC/dV versus voltage curves between the tip and the semiconductor are measured under these illuminating conditions with a sensitive capacitance sensor. The unique method for transient spectroscopy incorporates a unique control system and procedure in which capacitance or dC/dV signal are measured as a function of time synchronized to changing the illuminating condition. The capacitance transient can be measured at any dc voltage, but particularly useful information such as carrier density is obtained if the probe is biased at the semiconductor flatband voltage. A simple, one-dimensional model is used to determine, from the measurement of C-V or dC/dV curves, capacitance transients, and frequency-dependent capacitance variance, the carrier recombination rate, and carrier generation and recombination lifetimes in the semiconductor with a microscopic spatial resolution: The limitation of spatial resolution of this measurement is by physical law not by instrumentation. The invention encompasses several methods of acquiring the carrier lifetime on time scales of microseconds and longer with a highly localized probe which are unique with respect to previous practices. The method can easily be incorporated into various commercial instruments such as atomic force microscope, surface profiler, and probe station.