Light emitting diode precursor and its fabrication method

1 . A method of forming a Light Emitting Diode (LED) precursor comprising:

forming a LED stack comprising a plurality of Group III-nitride layers on a substrate, the LED stack comprising a LED stack surface formed on an opposite side of the LED stack to the substrate;

masking a plurality of first portions of the LED stack surface with a masking layer leaving a plurality of second portions of the LED stack surface exposed;

subjecting the plurality of second portions of the LED stack surface to a poisoning process such that a plurality of second regions of the LED stack below the second portions of the LED stack surface comprising at least one of the Group III-nitride layers of the LED stack has a relatively higher resistivity than a resistivity of the respective Group-III nitride layer in a plurality of first regions of the LED stack below the first portion of the LED stack surface; and

removing the masking layer and forming a contact layer covering the plurality of first and second portions of the LED stack surface.

2 . A method of forming a LED precursor according to claim 1 , wherein forming the LED stack comprises:

forming a first semiconducting layer comprising a Group III-nitride on the substrate;

forming an active layer comprising a Group III-nitride on the first semiconducting layer; and

forming a p-type semiconducting layer comprising a Group III-nitride on the active layer, wherein a major surface of the p-type semiconducting layer on an opposite side of the p-type semiconducting layer to the active layer provides an LED stack surface of the LED stack.

3 . A method according to claim 2 , wherein

the plurality of second regions of the LED stack includes a plurality of second regions of the p-type semiconducting layer, and

the plurality of first regions of the LED stack includes a plurality of first regions of the p-type semiconducting layer.

4 . A method according to claim 2 , wherein

the plurality of second regions of the LED stack includes a plurality of second regions of the active layer; and

the plurality of first regions of the LED stack includes a plurality of first regions of the active layer.

5 . A method according to claim 2 , wherein

the plurality of second regions of the LED stack includes a plurality of second regions of the first semiconducting layer; and

the plurality of first regions of the LED stack includes a plurality of first regions of the first semiconducting layer.

6 . A method according to claim 1 , wherein the second portion of the LED stack surface encircles the first portion of the LED stack surface.

7 . A method according to claim 1 , wherein the plurality of second portions of the LED stack surface are arranged in an annular or chequerboard pattern.

8 . A method according to claim 1 , wherein

the poisoning process comprises exposing the second portion of the LED stack surface to a plasma comprising hydrogen ions.

9 . A method according to claim 1 , wherein

the LED stack formed comprises a column having a regular trapezoidal cross-section in a plane normal to the LED stack surface.

10 . A method according to claim 9 , wherein forming the LED stack comprises:

forming a first semiconducting layer comprising a Group III-nitride on a substrate surface of the substrate,

the first semiconducting layer having a growth surface on an opposite side of the first semiconducting layer to the substrate;

selectively removing a portion of the first semiconducting layer to form a mesa structure such that the growth surface of the first semiconducting layer comprises a mesa surface and a bulk semiconducting surface;

monolithically forming a second semiconducting layer comprising a Group III-nitride on the growth surface of the first semiconducting layer such that the second semiconducting layer covers the mesa surface and the bulk semiconducting surface;

forming an active layer comprising a Group III-nitride on the first semiconducting layer; and

forming a p-type semiconducting layer comprising a Group III-nitride on the active layer, wherein a major surface of the p-type semiconducting layer on an opposite side of the p-type semiconducting layer to the active layer provides an LED stack surface of the LED stack, and

wherein the active layer and the p-type semiconducting layer are formed on the second semiconducting layer.

11 . A method according to claim 10 , wherein

the plurality of second regions of the LED stack includes plurality of a second regions of the second semiconducting layer; and

the plurality of first regions of the LED stack includes a plurality of first regions of the second semiconducting layer.

12 . A method according to claim 11 , wherein

the second semiconducting layer is formed on the growth surface of the first semiconducting layer to provide an inclined sidewall portion extending between a first portion of the second semiconducting layer on the mesa surface of the first semiconducting layer and a second portion of the second semiconducting layer on the bulk semiconducting surface of the first semiconducting layer.

13 . A method according to 11 , wherein

forming the first semiconducting layer on the substrate comprises:

forming a first semiconducting sublayer comprising a Group III-nitride on the substrate surface;

forming a dielectric sublayer on the first semiconducting sublayer, the dielectric sublayer defining an aperture through a thickness of the dielectric sublayer; and

forming a second semiconducting sublayer comprising a Group III-nitride on the dielectric sublayer, and

wherein selectively removing a portion of the first semiconducting layer to form a mesa structure comprises selectively removing a portion of the second semiconducting sublayer to form a mesa structure which is aligned with the aperture of the dielectric sublayer.

14 . A method according to claim 2 , wherein

the active layer of the LED stack comprises a plurality of quantum well layers configured to output visible light.

15 . A method according to claim 1 , wherein

the LED precursor is a micro LED precursor wherein the LED stack has a surface area on the substrate of no greater than 100 μm×100 μm, or no greater than 10 μm×10 μm.