ENGINEERED WAFER WITH SELECTIVE POROSIFICATION FOR MULTI-COLOR LIGHT EMISSION

1 . An engineered wafer comprising a plurality of mesa structures, the plurality of mesa structures comprising:

a first mesa structure comprising:

a first porous layer of a first semiconductor material having a first lattice constant, the first porous layer characterized by a first porosity; and

a first layer of a second semiconductor material on the first porous layer, the second semiconductor material characterized by a second lattice constant greater than the first lattice constant; and

a second mesa structure comprising:

a second porous layer of the first semiconductor material, the second porous layer characterized by a second porosity different from the first porosity; and

a second layer of the second semiconductor material on the second porous layer.

2 . The engineered wafer of claim 1 , wherein:

the first semiconductor material includes a first III-nitride semiconductor material; and

the second semiconductor material includes a second III-nitride semiconductor material.

3 . The engineered wafer of claim 1 , wherein the first semiconductor material includes GaN and the second semiconductor material includes InGaN.

4 . The engineered wafer of claim 1 , further comprising:

a substrate; and

an n-type layer of the first semiconductor material on the substrate, wherein the plurality of mesa structures is on the n-type layer of the first semiconductor material.

5 . The engineered wafer of claim 1 , further comprising:

a first active region on the first layer of the second semiconductor material, the first active region configured to emit light of a first color; and

a second active region on the second layer of the second semiconductor material, the second active region configured to emit light of a second color different from the first color.

6 . The engineered wafer of claim 5 , wherein:

the first active region includes an In x Ga 1-x N quantum well layer; and

the second active region includes an In y Ga 1-y N quantum well layer, where y is different from x.

7 . The engineered wafer of claim 6 , wherein x is greater than 0.2.

8 . The engineered wafer of claim 1 , wherein the first layer of the second semiconductor material and the second layer of the second semiconductor material include In x Ga 1-x N, where 0<x≤0.2.

9 . The engineered wafer of claim 1 , wherein:

the first mesa structure comprises a first distributed Bragg reflector (DBR) that includes the first porous layer, the first DBR configured to reflect light in a first wavelength band; and

the second mesa structure comprises a second DBR that includes the second porous layer, the second DBR configured to reflect light in a second wavelength band.

10 . The engineered wafer of claim 1 , wherein the plurality of mesa structures further comprises:

a third mesa structure comprising:

a third porous layer of the first semiconductor material, the third porous layer characterized by a third porosity different from the first porosity and the second porosity; and

a third layer of the second semiconductor material on the third porous layer.

11 . A light source comprising:

a semiconductor substrate; and

a plurality of light emitting pixels on the semiconductor substrate, the plurality of light emitting pixels comprising:

a first set of light emitting pixels, each light emitting pixel of the first set of light emitting pixels comprising:

a first porous layer of a first semiconductor material having a first lattice constant, the first porous layer characterized by a first porosity;

a first layer of a second semiconductor material on the first porous layer, the second semiconductor material characterized by a second lattice constant greater than the first lattice constant; and

a first active region on the first layer of the second semiconductor material, the first active region configured to emit light in a first color; and

a second set of light emitting pixels, each light emitting pixel of the second set of light emitting pixels comprising:

a second porous layer of the first semiconductor material, the second porous layer characterized by a second porosity different from the first porosity;

a second layer of the second semiconductor material on the second porous layer; and

a second active region on the second layer of the second semiconductor material, the second active region configured to emit light in a second color.

12 . The light source of claim 11 , wherein:

the first active region includes an In x Ga 1-x N quantum well layer; and

the second active region includes an In y Ga 1-y N quantum well layer, where y is different from x.

13 . The light source of claim 11 , wherein:

each light emitting pixel of the first set of light emitting pixels further comprises:

a first distributed Bragg reflector (DBR) that includes the first porous layer, the first DBR configured to reflect light in a first wavelength band; and

a first mirror, the first mirror and the first DBR forming a first cavity, wherein the first active region is in the first cavity; and

each light emitting pixel of the second set of light emitting pixels further comprises:

a second DBR that includes the second porous layer, the second DBR configured to reflect light in a second wavelength band; and

a second mirror, the second mirror and the second DBR forming a second cavity, wherein the second active region is in the second cavity.

14 . The light source of claim 11 , wherein the plurality of light emitting pixels comprises a third set of light emitting pixels, each light emitting pixel of the third set of light emitting pixels comprising:

a third porous layer of the first semiconductor material, the third porous layer characterized by a third porosity different from the first porosity and the second porosity;

a third layer of the second semiconductor material on the third porous layer; and

a third active region on the third layer of the second semiconductor material, the third active region configured to emit light in a third color.

15 . A method comprising:

forming a plurality of mesa structures on a layer of a first semiconductor material having a first lattice constant, each mesa structure of the plurality of mesa structures comprising:

an n + -type layer of the first semiconductor material; and

a layer of a second semiconductor material on the n + -type layer, the second semiconductor material having a second lattice constant different from the first lattice constant;

performing a first porosity treatment process on a first set of mesa structures of the plurality of mesa structures to form porous layers in the n + -type layers of the first set of mesa structures;

performing a second porosity treatment process on a second set of mesa structures of the plurality of mesa structures to form porous layers in the n + -type layers of the second set of mesa structures; and

thermally treating the plurality of mesa structures to cause the layer of the second semiconductor material to relax.

16 . The method of claim 15 , further comprising:

growing a first active region on each mesa structure of the first set of mesa structures, the first active region including an In x Ga 1-x N quantum well layer; and

growing a second active region on each mesa structure of the second set of mesa structures, the second active region including an In y Ga 1-y N quantum well layer, where y is different from x.

17 . The method of claim 15 , wherein:

performing the first porosity treatment process comprises electrochemically etching the n + -type layers of the first set of mesa structures for a first time period; and

performing the second porosity treatment process comprises electrochemically etching the n + -type layers of the second set of mesa structures for a second time period.

18 . The method of claim 15 , wherein:

performing the first porosity treatment process comprises electrochemically etching the n + -type layers of the first set of mesa structures using a first voltage signal for a time period; and

performing the second porosity treatment process comprises electrochemically etching the n + -type layers of the second set of mesa structures using a second voltage signal for the time period, wherein the second voltage signal is higher than the first voltage signal.

19 . The method of claim 15 , wherein performing the first porosity treatment process comprises:

implanting ions in the n + -type layers of the first set of mesa structures to change a donor density of the n + -type layers of the first set of mesa structures; and

electrochemically etching the n + -type layers of the first set of mesa structures.

20 . The method of claim 15 , wherein each mesa structure of the plurality of mesa structures comprising a plurality of layers between the layer of the first semiconductor material and the layer of the second semiconductor material, the plurality of layers including:

a first set of unintentionally doped layers of the first semiconductor material; and

a second set of n + -type layers of the first semiconductor material, the second set of n + -type layers including the n + -type layer of the first semiconductor material,

wherein the first set of unintentionally doped layers and the second set of n + -type layers are interleaved; and

wherein, for each mesa structure of the first set of mesa structures, the first porosity treatment process forms a respective porous layer in each of the second set of n + -type layers.