Formation of Ohmic contacts in III-nitride light emitting devices
View Patent ↗P-type layers of a GaN based light-emitting device are optimized for formation of Ohmic contact with metal. In a first embodiment, a p-type GaN transition layer with a resistivity greater than or equal to about 7 Ω cm is formed between a p-type conductivity layer and a metal contact. In a second embodiment, the p-type transition layer is any III-V semiconductor. In a third embodiment, the p-type transition layer is a superlattice. In a fourth embodiment, a single p-type layer of varying composition and varying concentration of dopant is formed.
1. A light-emitting diode comprising:
a substrate;
an n-type layer of GaN formed over the substrate;
an active region, formed over the n-type layer;
a p-type Al x Ga (1−x) N (0≦×≦1) layer, formed over the active region;
a p-type transition layer, formed over the p-type Al x Ga (1−x) N layer, the p-type transition layer comprising a superlattice, the superlattice further comprising:
a first sublayer of doped p-type material;
a second sublayer of material, wherein a concentration of dopant in the second sublayer is less than a concentration of dopant in the first sublayer; and
a metal n-type contact and a metal p-type contact, the n-type contact being connected to the n-type layer, the p-type contact being directly connected to the p-type transition layer superlattice.
2. The light-emitting diode of claim 1 wherein the dopant is Mg and the dopant concentration of the first sublayer is about 1e20 cm −3 to about 5e21 cm −3 .
3. The light-emitting diode of claim 1 wherein the dopant is Mg and the dopant concentration of the second sublayer is undoped to about 1e20 cm −3 .
4. The light-emitting diode of claim 1 wherein each of the first and second sublayers has a thickness from about 2 to about 20 nm.
5. The light emitting diode of claim 1 wherein a driving voltage of the light emitting diode is less than about 3.5 volts.
6. The light-emitting diode of claim 1 wherein the p-type contact is directly connected to the p-type transition layer.
7. A light emitting diode comprising:
a substrate;
an n-type layer of GaN formed over the substrate;
an active region, formed over the n-type layer;
a p-type Al x Ga (1−x) N (0≦×≦1) layer, formed over the active region;
a p-type transition layer, formed over the p-type Al x Ga (1−x) N layer, the p-type transition layer comprising a sublayer of a p-type doped material and a sublayer consisting essentially of a single element; and
an n-type contact and a p-type contact, the n-type contact being connected to the n-type layer, the p-type contact being connected to the p-type transition layer.
8. The light emitting diode of claim 7 wherein the element is Mg.
9. The light emitting diode of claim 7 further comprising a p-type conductive layer of GaN, formed over the p-type Al x Ga (1−x) N layer.
10. The light emitting diode of claim 7 wherein a driving voltage of the light emitting diode is less than about 3.5 volts.
11. The light-emitting diode of claim 7 wherein the p-type contact is directly connected to the p-type transition layer.