Nitride semiconductor structures with interlayer structures
View Patent ↗A semiconductor structure includes a first layer of a nitride semiconductor material, a substantially unstrained nitride interlayer on the first layer of nitride semiconductor material, and a second layer of a nitride semiconductor material on the nitride interlayer. The nitride interlayer has a first lattice constant and may include aluminum and gallium and may be conductively doped with an n-type dopant. The first layer and the second layer together have a thickness of at least about 0.5 μm. The nitride semiconductor material may have a second lattice constant, such that the first layer may be more tensile strained on one side of the nitride interlayer than the second layer may be on the other side of the nitride interlayer.
1. A semiconductor structure, comprising:
a nucleation layer comprising aluminum nitride;
a graded layer on the nucleation layer, wherein the graded layer is graded from a composition including Al x Ga 1-x N adjacent the nucleation layer, wherein x decreases with distance from the nucleation layer;
a first layer of a nitride semiconductor material on the graded layer;
a substantially relaxed nitride interlayer on the first layer of nitride semiconductor material, the substantially relaxed nitride interlayer having a first lattice constant, wherein the nitride interlayer comprises aluminum and gallium and is conductively doped with an n-type dopant; and
a second layer of the nitride semiconductor material on the nitride interlayer;
wherein the nitride interlayer comprises a plurality of discrete portions therein, wherein the discrete portions have a material composition that is different than a material composition of the nitride interlayer and wherein the nitride interlayer has a first bandgap and the discrete portions have a second bandgap that is lower than the first bandgap.
2. The semiconductor structure of claim 1 , wherein the second layer of the nitride semiconductor material is compressively strained on one side of the substantially relaxed nitride interlayer and the first layer of the nitride semiconductor material is tensile strained on the other side of the substantially relaxed nitride interlayer.
3. The semiconductor structure of claim 1 , further comprising:
a discontinuous mask layer directly on the substantially relaxed nitride interlayer.
4. The semiconductor structure of claim 3 , wherein the discontinuous mask layer comprises SiN and/or MgN.
5. The semiconductor structure of claim 4 , wherein the first layer of the nitride semiconductor material has a first dislocation density below the interlayer and the second layer of the nitride semiconductor material has a second dislocation density lower than the first dislocation density above the interlayer.
6. The semiconductor structure of claim 3 , wherein the discontinuous mask layer comprises BN.
7. The semiconductor structure of claim 3 , further comprising a second discontinuous mask layer directly on the first layer of the nitride semiconductor material, wherein the nitride interlayer is on the second discontinuous mask layer.
8. The semiconductor structure of claim 1 , wherein the nitride interlayer is doped with silicon at a concentration of about 1×10 19 cm −3 to about 1×10 21 cm −3 .
9. The semiconductor structure of claim 1 , wherein the nitride interlayer comprises a graded layer.
10. The semiconductor structure of claim 1 , wherein the nitride interlayer comprises a plurality of sub-layers.
11. The semiconductor structure of claim 1 , wherein the interlayer comprises a plurality of InAlN/GaN pairs, doped with Si.
12. The semiconductor structure of claim 1 , wherein the interlayer comprises a plurality of InAlGaN/GaN pairs, doped with Si.
13. The semiconductor structure of claim 1 , wherein the average strain of the first and second layers of the nitride semiconductor material is less tensile strained than a corresponding semiconductor structure not including the interlayer.
14. The semiconductor structure of claim 1 , further comprising a substrate, wherein the first layer of the nitride semiconductor material is on the substrate and wherein the nitride semiconductor material has a first coefficient of thermal expansion and the substrate has a second coefficient of thermal expansion that is less than the first coefficient of thermal expansion such that the second layer of the nitride semiconductor material tends to be more tensile strained at room temperature than at an elevated growth temperature.
15. The semiconductor structure of claim 1 , wherein the second layer is more relaxed at room temperature than at a growth temperature of the second layer.
16. The semiconductor structure of claim 15 , wherein the second layer is substantially relaxed at room temperature.
17. The semiconductor structure of claim 1 , wherein the first layer and the second layer have less bow at a temperature of about 700 to 800° C. than at a growth temperature of the nitride interlayer.
18. The semiconductor structure of claim 1 , wherein the interlayer has a thickness and resistivity such that a voltage drop across the interlayer is less than 0.1V.
19. The semiconductor structure of claim 18 , wherein the interlayer has a thickness of about 0.015 μm and a resistivity less than about 2000 ohm-cm at a current density of about 32 A/cm 2 .
20. The semiconductor structure of claim 1 , wherein the nitride interlayer comprises a first nitride interlayer having a material composition and a doping concentration, the structure further comprising:
a second nitride interlayer on the second layer of nitride semiconductor material, wherein the second nitride interlayer comprises aluminum and gallium and is conductively doped with an n-type dopant, and wherein the second nitride interlayer has a material composition and/or doping concentration that is different from the material composition and/or doping concentration of the first nitride interlayer; and
a third layer of the nitride semiconductor material on the second nitride interlayer.
21. The semiconductor structure of claim 20 , wherein the first nitride interlayer has a first gallium concentration and the second nitride interlayer has a second gallium concentration that is greater than the first gallium concentration.
22. The semiconductor structure of claim 20 , wherein the first nitride interlayer has a first doping concentration and the second nitride interlayer has a second doping concentration that is greater than the first doping concentration.
23. The semiconductor structure of claim 1 , wherein the discrete portions are present in the nitride interlayer in an amount of between about 0.1/μm 2 and about 100/μm 2 .
24. The semiconductor structure of claim 1 , wherein the discrete portions are between 0.01 μm and 0.1 μm in diameter.
25. A semiconductor structure, comprising:
a nucleation layer comprising aluminum nitride;
a graded layer on the nucleation layer, wherein the graded layer is graded from a composition including Al x Ga 1-x N adjacent the nucleation layer, wherein x decreases with distance from the nucleation layer;
a first epitaxial layer of a nitride semiconductor material on the graded layer;
a second epitaxial layer of the nitride semiconductor material; and
a substantially relaxed nitride interlayer between the first epitaxial layer and the second epitaxial layer, wherein the nitride interlayer comprises aluminum and gallium and is conductively doped with an n-type dopant;
wherein the first epitaxial layer, the nitride interlayer, and the second epitaxial layer together have a thickness of at least about 0.5 μm;
wherein the substantially relaxed nitride interlayer having a first lattice constant and the nitride semiconductor material has a second lattice constant different from the first lattice constant;
wherein the first epitaxial layer is more tensile strained than the second epitaxial layer; and
wherein the nitride interlayer comprises a plurality of discrete portions therein, wherein the discrete portions have a material composition that is different than a material composition of the nitride interlayer and wherein the nitride interlayer has a first bandgap and the discrete portions have a second bandgap that is lower than the first bandgap.
26. The semiconductor structure of claim 25 , wherein the nitride interlayer comprises a first nitride interlayer having a material composition and a doping concentration, the structure further comprising:
a second nitride interlayer on the second layer of nitride semiconductor material, wherein the second nitride interlayer comprises aluminum and gallium and is conductively doped with an n-type dopant, and wherein the second nitride interlayer has a material composition and/or doping concentration that is different from the material composition and/or doping concentration of the first nitride interlayer; and
a third epitaxial layer of the nitride semiconductor material on the second nitride interlayer.
27. The semiconductor structure of claim 26 , wherein the first nitride interlayer has a first gallium concentration and the second nitride interlayer has a second gallium concentration that is greater than the first gallium concentration.
28. The semiconductor structure of claim 26 , wherein the first nitride interlayer has a first doping concentration and the second nitride interlayer has a second doping concentration that is greater than the first doping concentration.
29. The nitride semiconductor structure of claim 1 , wherein the graded layer has an aluminum concentration less than 100% at an interface with the nucleation layer.
30. The nitride semiconductor structure of claim 29 , wherein the graded layer has an aluminum concentration of about 70% at an interface with the nucleation layer.
31. The nitride semiconductor structure of claim 25 , wherein the graded layer has an aluminum concentration less than 100% at an interface with the nucleation layer.
32. The nitride semiconductor structure of claim 31 , wherein the graded layer has an aluminum concentration of about 70% at an interface with the nucleation layer.