ELECTROLUMINESCENCE IN THIN HEXAPHENYL-LAYERS

We present results of the generation and detection of electroluminesce nce in thin ParaHexaPhenyl(PHP)-layers. For the characterization we us e a Scanning-Tunneling-Microscope (STM). PHP can be used as a very sta ble emitting layer in blue Light-Emitting-Devices (LED's). The mechani sms of electroluminescence in PHP, which is an organic semiconductor, differ from those in conventional inorganic devices, therefore it is o f high interest to investigate the physics of the processes. With an S TM it is possible to investigate both the topography and optical prope rties of semiconducting surfaces in sub-micron dimensions. Hence relat ions between the generation of electroluminescence and structural prop erties of the semiconducting layers (highly oriented or disordered) ca n be found. Electrons were injected by the scanning tip, the holes by the conducting substrate (Indium-Tin-Oxide ITO on glass). The luminesc ence emission is limited to very small areas (a few nm(2)), making the results interesting for applications such as nano-lightsources.