Measurements of photoluminescence (PL) are important in study of electronic states and recombination processes in a-Si:H. The results of PL measurements also yield considerable information of defects, since the lifetime and intensity of the PL are strongly affected by defects. Non-exponential PL decay in Si:H is understood by considering lifetime distribution which is obtained directly from the measurements of the PL by means of frequency resolved spectroscopy (FRS). However, the lifetime distribution of electron-hole pairs in a-Si:H is broad and featureless. In such cases, interpretation of the FRS results is difficult. In order to overcome the problem, we need to develop various analysis of the experimental results of FRS.
In the FRS measurements, the excitation intensity is modulated with various frequency and PL is measured by using a lock-in amplifier. The PL signals are obtained as two components, i.e., in-phase and out-of-phase signals. In most of the FRS studies in a-Si:H, reported in 1990s, only the out-of-phase signals are presented since the in-phase signal is not necessary to show the lifetime distribution. However, information of the lifetime distribution is also available from the in-phase signal. In more detailed analysis of the lifetime distribution, the in-phase signal is useful [1].
The a-Si:H film used in this study was prepared from a mixture of silane and hydrogen in a capacitively coupled glow discharge reactor. The FRS measurements were done at the temperature of 10 - 200 K under excitation of 3.06 eV.
The results have been compared with those expected for Gaussian lifetime distributions. The width of the Gaussian distribution was optimized by using least squares method. The in-phase and out-of-phase components expected for the Gaussian distribution are well fitted to the experimental results. In this presentation, temperature variation of the lifetime distribution is discussed together with the width of the distribution.
[1] C. Ogihara, J Mater Sci: Mater Electron, vol.28 (2017) 7121.