SEMICONDUCTOR DEVICE AND METHOD FOR FORMING THE SAME

1 . A semiconductor device, comprising:

a substrate, comprising an upper surface;

a buffer layer, formed on the upper surface; and

an element structure, formed on the buffer layer;

wherein the substrate comprises a plurality of holes extending from the upper surface of the substrate to an inside of the substrate and forming a plurality of openings at the upper surface of the substrate; and

wherein in a cross-sectional view of the semiconductor device, at least two of the holes have different depths.

2 . The semiconductor device of claim 1 , wherein the plurality of openings is irregularly distributed on the upper surface of the substrate.

3 . The semiconductor device of claim 1 , wherein a distribution density of the plurality of openings on the upper surface of the substrate is in a range of 1E7 cm −2 to 1E10 cm −2 .

4 . The semiconductor device of claim 1 , wherein at least two of the openings have different maximum widths on the upper surface of the substrate.

5 . The semiconductor device of claim 1 , wherein the element structure comprises a semiconductor light-emitting stack formed on the buffer layer, wherein the semiconductor light-emitting stack comprises a first-type semiconductor layer, a second-type semiconductor layer and an active region formed between the first-type semiconductor layer and the second-type semiconductor layer.

6 . The semiconductor device of claim 5 , wherein the plurality of openings each comprises a maximum width on the upper surface of the substrate, and the maximum width is less than or equal to a maximum wavelength of the light emitted by the active region.

7 . The semiconductor device of claim 5 , wherein in the cross-sectional view the plurality of holes each comprises a depth that is less than a maximum wavelength of the light emitted by the active region.

8 . The semiconductor device of claim 7 , wherein the depth does not exceed twice a minimum wavelength of light emitted by the active region.

9 . The semiconductor device of claim 1 , wherein each of the plurality of openings on the upper surface of the substrate comprises a maximum width between 1 nm and 100 nm.

10 . The semiconductor device of claim 1 , wherein in the cross-sectional view the plurality of holes each comprises a depth between 10 nm and 200 nm.

11 . The semiconductor device of claim 1 , wherein a depth difference of at least two of the holes and/or a maximum width difference of at least two of the openings is between 5 nm and 100 nm.

12 . The semiconductor device of claim 1 , wherein the buffer layer comprises a full width at half maximum (FWHM) between 100 arcsec and 300 arcsec in an X-ray diffraction pattern of <002> crystal phase, or between 250 arcsec and 500 arcsec in the X-ray diffraction pattern of <002> crystal phase.

13 . The semiconductor device of claim 1 , wherein the buffer layer comprises a root mean square roughness between 0.5 nm and 5.0 nm.

14 . A method for forming a semiconductor device, comprising steps of:

providing a substrate comprising an upper surface;

epitaxially forming a buffer layer on the upper surface, and after forming the buffer layer, the substrate comprises a plurality of holes, and a plurality of openings is formed by the plurality of holes at the upper surface of the substrate; and

forming an element structure on the buffer layer.

15 . The method of claim 14 , further comprising a step of heat treatment before, after or when forming the buffer layer, and the temperature of the heat treatment step is not less than 1200° C. and the duration thereof is not less than 40 minutes.

16 . The method of claim 14 , wherein the step of epitaxially forming the buffer layer comprises:

supplying a nitrogen-containing gas and an aluminum-containing gas by a first mode to epitaxially grow a first buffer portion on the upper surface of the substrate; and

supplying the nitrogen-containing gas and the aluminum-containing gas by a second mode to epitaxially grow a second buffer portion on the first buffer portion;

wherein the first mode comprises supplying the nitrogen-containing gas and/or the aluminum-containing gas by a pulse mode, and the second mode comprises supplying the nitrogen-containing gas and the aluminum-containing gas simultaneously and continuously.

17 . The method of claim 16 , wherein the step of epitaxially growing the first buffer portion comprises:

supplying the nitrogen-containing gas and the aluminum-containing gas by a first pulse mode to form a buffer base layer on the upper surface of the substrate; and

supplying the nitrogen-containing gas and the aluminum-containing gas by a second pulse mode to form a buffer middle stack on the buffer base layer;

wherein in the first pulse mode and/or the second pulse mode, an introducing duration and a closing duration of the nitrogen-containing gas are different, and an introducing duration and a closing duration of the aluminum-containing gas are different; and

wherein the introducing duration and/or the closing duration of the nitrogen-containing gas in the first pulse mode are different from those in the second pulse mode, and the introducing duration and/or the closing duration of the aluminum-containing gas in the first pulse mode are different from those in the second pulse mode.

18 . The method of claim 17 , wherein the step for epitaxially growing the first buffer portion further comprises:

supplying the nitrogen-containing gas and the aluminum-containing gas by a third pulse mode to form a buffer upper layer on the buffer middle stack;

wherein the third pulse mode is different the first pulse mode and/or the second pulse mode.

19 . The method of claim 18 , wherein an introducing duration of the nitrogen-containing gas in the third pulse mode is different from those in the first pulse mode and/or the second pulse mode.

20 . The method of claim 16 , wherein during epitaxially growing the first buffer portion, the upper surface of the substrate is randomly etched to form the holes extended toward an inside of the substrate.