Method for manufacturing semiconductor light emitting device

1. A method for manufacturing a semiconductor light emitting device,

the device including:

an n-type semiconductor layer;

a p-type semiconductor layer; and

a light emitting unit provided between the n-type semiconductor layer and the p-type semiconductor layer,

the method comprising:

forming a first buffer layer made of a crystalline AIN on a first substrate, forming a second buffer layer made of a crystalline Al x Ga 1-x N (0.8≦x≦1) on the first buffer layer, and forming a GaN layer on the second buffer layer;

stacking the n-type semiconductor layer, the light emitting unit, and the p-type semiconductor layer on the GaN layer; and

separating the first substrate,

wherein the p-type semiconductor layer includes a first p-type layer provided on the light emitting unit and a p-type contact layer provided on the first p-type layer, and

the first p-type layer is Mg-doped p-type AlGaN formed to have a concentration profile including a higher Mg concentration on a side of the light emitting unit and a lower Mg concentration on a side opposite to the light emitting unit, so that a piezoelectric field in the first p-type layer is canceled by the concentration profile.

2. The method according to claim 1 , wherein the first buffer layer contains carbon and a second buffer layer has a lower carbon concentration than the first buffer layer.

3. The method according to claim 2 , wherein the first buffer layer is a layer having a carbon concentration of not less than 3×10 18 cm −3 and not more than 5×10 20 cm −3 , and a thickness of not less than 3 nanometers and not more than 20 nanometers.

4. The method according to claim 2 , wherein the second buffer layer is a layer having a carbon concentration of not less than 1×10 16 cm −3 and not more than 3×10 18 cm −3 , and a thickness of not less than 0.6 micrometers and not more than 6 micrometers.

5. The method according to claim 2 , wherein:

the first buffer layer is epitaxially grown by low-pressure metalorganic chemical vapor deposition at a first temperature with a first ratio of (a supply rate of group V atoms)/(a supply rate of group III atoms) of 0.7 to 50, and

the second buffer layer is epitaxially grown by metalorganic chemical vapor deposition at a second temperature higher than the first temperature with a second ratio of (a supply rate of group V atoms)/(a supply rate of group III atoms) higher than the first ratio.

6. The method according to claim 1 , wherein a total film thickness of the first buffer layer and the second buffer layer is 1 micrometer to 4 micrometers.

7. The method according to claim 1 , wherein the first buffer layer and the second buffer layer has a higher thermal conductivity than the GaN layer.

8. The method according to claim 1 , wherein the n-type semiconductor layer includes an Si-doped n-type GaN layer provided on the GaN layer, and an Si-doped n-type AlGaN layer provided on the Si-doped n-type GaN layer.

9. The method according to claim 8 , wherein the Si-doped n-type GaN layer has a silicon concentration of not less than 1×10 19 cm −3 and not more than 2×10 19 cm −3 , and the Si-doped n-type AlGaN layer has a silicon concentration lower than the silicon concentration of the Si-doped n-type GaN layer.

10. The method according to claim 1 , wherein the light emitting unit includes a multiple-quantum-well structure having barrier layers and well layers alternately stacked.

11. The method according to claim 10 , wherein the barrier layer is a Si-doped n-type AlGaInN and has a silicon concentration of 1.1×10 19 to 3.0×10 19 cm −3 .

12. The method according to claim 1 , wherein the p-type contact layer is Mg-doped p-type GaN and has a lower Mg concentration on a side of the first substrate than on a side opposite to the first substrate.

13. The method according to claim 1 , wherein the device further includes a spacer layer provided between the light emitting unit and the p-type semiconductor layer, and the spacer layer includes AlGaInN and has an Si concentration of 1×10 16 cm −3 to 3.0×10 18 cm −3 .

14. The method according to claim 1 , wherein a peak wavelength of emitted light of the light emitting unit is longer than 370 nanometers and shorter than 400 nanometers.

15. The method according to claim 1 , wherein a second substrate is bonded on a side of the p-type semiconductor layer opposite to the light emitting unit before the separating the first substrate.

16. The method according to claim 1 , wherein an electrode is formed on the side of the p-type semiconductor layer opposite to the fight emitting unit before bonding the second substrate.

17. The method according to claim 1 , wherein at least one of projections or depressions is formed on a surface on a side of the p-type semiconductor layer opposite to the light emitting unit at a spacing not longer than a wavelength of emitted light of the light emitting unit.

18. The method according to claim 1 , wherein the stacking the n-type semiconductor layer, the light emitting unit, and the p-type semiconductor layer includes growing a crystalline AlGaN served as the first p-type layer included in the p-type semiconductor layer, and a Mg concentration on a side of the light emitting unit is higher than a Mg concentration on a side opposite to the light emitting unit.

19. The method according to claim 1 , wherein the stacking the n-type semiconductor layer, the light emitting unit, and the p-type semiconductor layer includes forming the light emitting unit including a barrier layer made of an AlGaInN quarternary mixed crystal having an In component ratio in group III elements not less than 0.3% and not more than 2%.

20. The method according to claim 19 , wherein the stacking the n-type semiconductor layer, the light emitting unit, and the p-type semiconductor layer includes growing the AlGaInN quarternary mixed crystal having a Si concentration not less than 1.1×10 19 and not more than 3.0×10 19 cm −3 .