Light emitting device with improved internal out-coupling and method of providing the same
The present invention relates to a method of manufacturing a light emitting device with improved internal out-coupling by providing an intermediate layer ( 11 ) with a modulated surface. This is achieved by exposure of a flat glass surface ( 100 ) to a saturated etching fluid or by providing local changes in the chemical surface composition of the glass substrate or by depositing locally separated sub-μm particles. By removal of the etching fluid, either ultrafine particles ( 12 ) are deposited or defects are generated consisting of glass component areas of sub^m-size extension with a high sticking coefficient with respect to the species deposited later on from the gas phase. These ultrafine particles or defects induce locally different growth by different sticking coefficients, with preferential columnar cone shaped growth, leading to small bumps ( 14 ) on the top surface of the intermediate layer ( 11 ), which are then over-coated with the layers ( 200 ) of the light emitting element and induce sufficient scattering by subsequent reflections.
1. A light emitting device comprising:
glass substrate with a flat surface;
a high refractive index layer deposited on said flat surface, the high refractive index layer having a refractive index that is higher than that of the glass substrate; and
a light emitting layer structure with a transparent electrode layer which is deposited on said high refractive index layer;
wherein the flat surface comprises seed points for columnar cone shaped growth of the high refractive index layer, the seed points being formed by sub-μm particles, and
wherein bumps are provided on the top surface of the high refractive index layer, said bumps being caused by columnar cone shaped growth of the high refractive index layer.
2. The device according to claim 1 , wherein said high refractive index layer comprises SiNx, SiOx, SiOxNy, AlOx, or Al2O3:N.
3. The device according to claim 1 , wherein said transparent electrode layer comprises indium tin oxide or tin-doped indium oxide.
4. The device according to claim 1 , wherein said bumps have a cross-sectional dimension in the range of 0.5 to 4 μm.
5. A method of manufacturing a light emitting device, said method comprising:
a) pre-treating a glass substrate by depositing sub-μm particles on a flat surface of the glass substrate to form seed points for columnar shaped layer growth on the flat surface;
b) depositing a high refractive index layer on said flat surface so that columnar cone shaped growth of said high refractive index layer generates bumps on a top surface of said high refractive index layer, the high refractive index layer having a refractive index that is higher than that of the glass substrate; and
c) depositing a light emitting layer structure with a transparent electrode layer on said top surface of said high refractive index layer.
6. The method according to claim 2 , further comprising exposing said flat surface to an etching fluid that is saturated with sub-μm particles and removing said etching fluid to deposit said sub-μm particles.
7. The method according to claim 3 , further comprising saturating the etching fluid with sub-μm particles by etching a sacrificial substrate.