Interface energetics make devices

The energy-level alignment at the ubiquitous interfaces of optoelectronic devices is decisive for their performance and almost all pertinent publications include energy-level diagrams (ELDs). However, in most of these ELDs vacuum-level alignment across the complete heterojunction is assumed, which is oversimplified. On the contrary, the functioning of virtually all optoelectronic devices relies on interface phenomena like band bending, interface dipoles or potential drops. Consequently, such oversimplified ELDs do not help to understand the working mechanism of devices and have limited meaning. In this focus article, we give best practice rules for drawing ELDs: (1) give references for all the values of an ELD. (2) Mention the methods which have been used to obtain these values. (3) Add a disclaimer about the limitations of the ELD. (4) Measure as many energy levels as possible.