Characterization and quality control of semiconductor wafers using time-correlated single photon counting

Abstract

Depending on the semiconductor material, the luminescence lifetime of semiconductor wafers can vary over a broad range from microseconds for Si-wafers down to sub-nanoseconds for III/V and II/VI based thin film or organic materials. The lifetime of a given wafer sample depends on the free charge carrier dynamics and can therefore be affected by several parameters. An important example is the influence of bulk or surface defects [1], thus the lifetime is a possible indicator for wafer quality. On dye-sensitized solar cells, lifetime measurements are also useful to characterize the energy transfer process from the sensitizer to the conduction band [2]. We have developed a setup for time-resolved photoluminescence measurements (TRPL) based on pulsed diode lasers and time-correlated single photon counting (TCSPC) with highly sensitive single photon detectors. Depending on the detector type, the instrument response function (IRF) can be as short as 100 ps and the laser pulse rate can be adapted to the luminescence lifetime of the material. The resolvable lifetimes extend from approx. 50 ps up to several hundred microseconds. The electronics can also be integrated into a microscope based setup for imaging with a lateral resolution down to the sub-μm range [3] as well as testing the lifetime behaviour at different injection levels. We will show measurement results of the system on an GaAsP-based Quantum Well.