The study of non-linearities in photodiodes using electrical auto-correlation

As we move towards the Tera era it is important to understand how to make measurements in this frequency domain. Over the past 20 years measurement techniques in this area have been developing. The main technique has been electro-optic sampling and probing. When measuring the response of photodiodes a simpler alternative, electrical autocorrelation, is available. In this case the non-linear current response is measured as a function of the overlap of the two trains of optical pulses focused onto a photodiode. As the electrical auto-correlation technique is based on the non-linearities in the device it is possible to study these non-linearities using the technique. In fact complex non-linear behaviour can lead to misinterpretation of the auto-correlation signal making it essential to understand the non-linear behaviour of a device when using the technique. In this work we concentrate on the non-linear behaviour. We observe both sub- and super-linear behaviour corresponding to field screening and impact ionization, respectively.