In order to get the optical constants and the thickness of the porous silicon layer, a reflectance spectrum in the range 200 ... 1100 nm has been measured and fitted by an optical model. To save time, here only the results of this investigation are discussed shortly. The reflectance fit is contained in the SCOUT configuration tu2_ex3_step0.sc2 and should be loaded into SCOUT. This configuration is the start of the following PL discussion.

The fit looks like this:

Above 400 nm the pronounced interference fringes indicate an almost absorption free porous silicon layer, whereas below 400 nm strong interband transitions lead to significant absorption and an opaque porous silicon. Although porous silicon is a multiphase-composite (a silicon skeleton embedded in air in the simplest approach) it is treated here as a homogeneous material for simplicity. The obtained dielectric function (the model is based on OJL interband transitions) is the following:

The thickness of the porous silicon layer is 1125 nm.

It should be noted that the reflectance fit is not perfect, especially above 800 nm. Here the measured reflectivity is higher than the simulated one. A closer inspection showed that the porous silicon layer is not homogeneous in depth but features a density gradient. To keep this tutorial as simple as possible this effect is ignored in the following.