Discerning Intraband Absorption Spectra Techniques for QDIPs and QWIPs

There is vast bibliography on FTIR spectroscopy focused on its use in chemistry, like detecting the presence and concentration of substances in samples such as solutions or crystals, but very little when it comes to the characterization of infrared optoelectronic semiconductor devices.

This is probably why there is a somewhat generalized belief that one can satisfactorily use a well-known single-beam FTIR method for obtaining absorption spectra of QWIPs also for characterizing QDIPs. Apparently, it is a very convenient method because there is no need to manipulate the sample between s and p scans, only the polarizer must be adjusted. But the difference in the selection rules that characterize the intraband absorption of radiation by QWs on one side, and by QDs on the other, advises the use of a special, more complex method for obtaining absorption spectra of QDIPs from the FTIR data.

We present a special single-beam FTIR method for obtaining intraband absorption spectra of detector structures based on QDs. The main difference in the proposed technique is that, instead of using the s-polarized absorption spectrum as a background for the p-polarized spectrum, it uses the scan of the substrate alone, without the active region, as background for the scan of the sample. The theory behind this method is described and the spectral processing needed to overcome possible laboratorial hindrances that the technique implies is suggested.

As an extension of this development, we show how this technique can produce spectra that reveal whether on the electronic transition involved in each intraband absorption peak there is a change in angular momentum. Finally, a case study is presented.