Escape from Film (Part B): Changing the Surface Structure

In Part A you set up the Escape from film ray-tracing example, visualised the embedded light sources, and inspected the detector output and rendered image.

In this part we focus on the geometry. By changing the shape of the semiconductor surface we can see, in a very direct way, how morphology controls light extraction. Instead of an AFM-derived profile, we will use a simple triangular saw_wave pattern from the Shape Database, re-run the simulation, and compare the resulting ray patterns.

Step 1 – Editing the semiconductor object

Start from the finished state of Part A, where the semiconductor surface is described by an AFM image and the detector is positioned above the structure. The first task is to tell OghmaNano that we want to change the mesh used for the semiconductor object.

1. Right-click the red Semiconductor object in the 3D view.
2. Choose Edit object from the context menu (see ??).

This opens the Object editor, shown in ??. The editor gathers together all properties of the object: its position, replication pattern, colour, and – most importantly for this tutorial – the Object shape that defines the underlying mesh.

In the Object shape section near the bottom of the editor you will see a path pointing to afm_image in the Shape Database. Click the … button next to the Edit field to open the Mesh editor, where the geometry is actually defined.

Step 2 – Choose a new structure from the Shape Database

When the Mesh editor opens, the Shape Database icon at the top should already be selected and the current entry will be afm_image, as shown in ??. The Shape Database is simply a local library of reusable meshes – AFM surfaces, photonic crystal templates, test structures, and so on – stored in OghmaNano’s own format.

To swap in a different surface:

1. Click the … button next to file in the Mesh editor.
2. In the Shape Database browser, double-click saw_wave (??).

After selecting saw_wave, close the Mesh editor and Object editor. Back in the main 3D view, the semiconductor surface now has a triangular profile instead of the original AFM morphology. This kind of simple test structure is handy for building intuition before you move on to realistic measured surfaces.

To learn more about creating your own shapes, importing AFM images, and building libraries of useful geometries, see the dedicated Shape Database tutorial (Part A).

Step 3 – Running the simulation with the new mesh

With the new surface selected, press Run simulation again to re-launch the ray tracer. The exact appearance of the rays will depend on the wavelength you choose. In the example shown in ??, the wavelength is set to 437.5 nm to highlight how the triangular structure redirects and traps light within the film.

You can now repeat exactly the same analysis as in Part A: inspect the detector0 output, plot detector_efficiency0.csv, and view the rendered image. Comparing the results with and without the saw-wave structure is a good way to see how much additional outcoupling (or trapping) a given morphology provides.

By cycling through different shapes from the Shape Database – or importing your own AFM and CAD meshes – you can build up a set of “before and after” comparisons and start to design surfaces that push more light into the escape cone while keeping fabrication realistic.