Optoelectronic devices

Abstract

This invention relates to optoelectronic devices of improved efficiency. In particular it relates to light emitting diodes, photodiodes and photovoltaics. By careful design of periodic microstructures, e.g. gratings, associated with such devices more efficient light generation or detection is achieved.

1 . An optoelectronic device comprising: 
 a dielectric layer or a semiconductor layer sandwiched between electrode structures,    wherein at least one of the electrodes is substantially metal comprising and at least semi-transparent,    a periodic microstructure in contact with at least one surface of the substantially metal comprising and at least semi-transparent electrode,    characterised in that the structure and positioning of the periodic microstructure is such that:    surface plasmon (SP) polariton modes supported mainly at the interface between the dielectric layer or semiconductor layer and the metal comprising, semi-transparent electrode    are substantially scattered into propagating light, said propagation being out of the plane of the dielectric layer or semiconductor layer and the metal comprising, semi-transparent electrode interface.    
     
     
         2 . A device according to  claim 1  wherein the periodic microstructure is selected from the following structures 
 the metal comprising electrode comprises a grating type structure on each of its surfaces, wherein the relationship between the microstructure of the two metal comprising surfaces is such that they are out of phase by π radians or substantially π radians;    a grating type structure present only at the interface between the metal comprising electrode and the semiconductor or dielectric layer;    a grating type structure present at the metal comprising electrode/air interface only;    a further dielectric layer present at the surface of the metal comprising electrode remote from the dielectric/semiconductor layer, on which is present a grating type structure.    
     
     
         3 . A device according to  claim 2  wherein the periodic microstructure is selected from a grating type structure present at the metal comprising electrode/air interface only wherein there is present an encapsulating layer on the electrode.  
     
     
         4 . A device according to  claim 1  wherein the periodic microstructures are a periodic sequence of valleys and hills, or a periodic sequence of grooves.  
     
     
         5 . A device according to  claim 1  wherein the periodic microstructures are a grating type structure which is a series of holes in the metal comprising electrode.  
     
     
         6 . A device according to  claim 1  wherein the periodic microstructures are periodic in more than one direction on the surface.  
     
     
         7 . A device according to  claim 1  wherein the periodic microstructures are sub-wavelength.  
     
     
         8 . A device according to  claim 1  wherein the metal comprising electrode is an aluminium cathode.  
     
     
         9 . A device according to  claim 1  wherein the device is chosen from a light emitting diode, a photovoltaic cell or a photodiode.  
     
     
         10 . A device according to  claim 9  wherein the light emitting diode is an organic light emitting diode.