Electroluminescence in thin hexaphenyl-layers

We present results of the generation and detection of electroluminescence in thin ParaHexaPhenyl(PHP)-layers. For the characterization we use a Scanning-Tunneling-Microscope (STM). PHP can be used as a very stable emitting layer in blue LightEmitting-Devices (LEDʹs). The mechanisms of electroluminescence in PHP, which is an organic semiconductor, differ from those in conventional inorganic devices, therefore it is of high interest to investigate the physics of the processes. With an STM it is possible to investigate both the topography and optical properties of semiconducting surfaces in sub-micron dimensions. Hence relations between the generation of electroluminescence and structural properties of the semiconducting layers (highly oriented or disordered) can be found. Electrons were injected by the scanning tip, the holes by the conducting substrate (Indium-Tin-Oxide ITO on glass). The luminescence emission is limited to very small areas (a few nm2), making the results interesting for applications such as nano-lightsources.