CURRENT INJECTION STRUCTURES FOR LIGHT-EMITTING DIODE CHIPS
Solid-state lighting devices including light-emitting diodes (LEDs) and more particularly current injection structures for LED chips are disclosed. Current injection structures include integrated layers or materials with high work functions as part of contact structures for epitaxial layers of active LED structures. Exemplary structures provide high work function contact layers for p-type epitaxial layers to enhance hole mobility and transport. Further contact structures include combinations of high work function layers with other current spreading layers. Exemplary materials for high work function layers include transition metal oxides.
1 . A light-emitting diode (LED) chip comprising:
an active LED structure comprising an n-type layer, a p-type layer, and an active layer between the n-type layer and the p-type layer;
a current spreading layer on the p-type layer; and
a contact layer between the current spreading layer and the p-type layer, the contact layer comprising a transition metal oxide.
2 . The LED chip of claim 1 , wherein the transition metal oxide comprises molybdenum oxide.
3 . The LED chip of claim 1 , wherein the transition metal oxide comprises at least one of tungsten oxide and vanadium oxide.
4 . The LED chip of claim 1 , wherein the transition metal oxide comprises molybdenum oxide and the current spreading layer comprises indium tin oxide.
5 . The LED chip of claim 1 , wherein the contact layer comprises a work function in a range from 6 electron volts (eV) to 10 eV.
6 . The LED chip of claim 1 , wherein the contact layer comprises a thickness in a range from 1 nanometer (nm) to 100 nm.
7 . The LED chip of claim 1 , further comprising:
a dielectric reflector layer on the p-type layer;
a metal reflector layer on the dielectric reflector layer; and
a plurality of reflective layer interconnects that extend through the dielectric reflector layer to form a plurality of electrically conductive paths between the metal reflector layer and the current spreading layer.
8 . The LED chip of claim 7 , wherein the plurality of electrically conductive paths comprises a portion of the contact layer between the p-type layer and each reflective layer interconnect of the plurality of reflective layer interconnects.
9 . The LED chip of claim 1 , wherein the contact layer comprises a first sublayer and a second sublayer with different work functions.
10 . The LED chip of claim 9 , wherein:
the first sublayer has a higher work function than the second sublayer; and
the first sublayer is closer to the p-type layer than the second sublayer.
11 . A light-emitting diode (LED) chip comprising:
an active LED structure comprising an n-type layer, a p-type layer, and an active layer between the n-type layer and the p-type layer;
a current spreading layer on the p-type layer; and
a contact layer between the current spreading layer and the p-type layer, the contact layer comprising a work function that is in a range from 6 electron volts (eV) to 10 eV.
12 . The LED chip of claim 11 , wherein the contact layer comprises at least one of molybdenum oxide, tungsten oxide, and vanadium oxide.
13 . The LED chip of claim 11 , wherein the contact layer comprises molybdenum oxide and the current spreading layer comprises indium tin oxide.
14 . The LED chip of claim 11 , further comprising:
a dielectric reflector layer on the current spreading layer;
a metal reflector layer on the dielectric reflector layer; and
a plurality of reflective layer interconnects that extend through the dielectric reflector layer to form a plurality of electrically conductive paths between the metal reflector layer and a plurality of discontinuous regions of the current spreading layer.
15 . A light-emitting diode (LED) chip comprising:
an active LED structure comprising an n-type layer, a p-type layer, and an active layer between the n-type layer and the p-type layer;
a current spreading layer forming a plurality of discontinuous current spreading layer regions on the p-type layer; and
a contact layer between the current spreading layer and the p-type layer.
16 . The LED chip of claim 15 , wherein the contact layer forms a plurality of discontinuous contact layer regions.
17 . The LED chip of claim 15 , wherein the contact layer comprises a transition metal oxide.
18 . The LED chip of claim 17 , wherein the transition metal oxide comprises at least one of molybdenum oxide, tungsten oxide and vanadium oxide.
19 . The LED chip of claim 15 , wherein the contact layer comprises a work function in a range from 6 electron volts (eV) to 10 eV.
20 . The LED chip of claim 15 , further comprising:
a dielectric reflector layer on the current spreading layer;
a metal reflector layer on the dielectric reflector layer; and
a plurality of reflective layer interconnects that extend through the dielectric reflector layer to form a plurality of electrically conductive paths between the metal reflector layer and the plurality of discontinuous current spreading layer regions.