Nitride-based light-emitting device
A nitride-based light-emitting device includes, on a GaN substrate: a first-conductivity-side first semiconductor layer; an active layer; and a second-conductivity-side first semiconductor layer, in the stated order, and further includes an electron barrier layer of a second conductivity type between the active layer and the second-conductivity-side first semiconductor layer, the electron barrier layer including a nitride-based semiconductor containing at least Al. The electron barrier layer has a first region in which an Al composition changes. The Al composition in the first region monotonically increases in a direction from the active layer to the second-conductivity-side first semiconductor layer. An impurity concentration in the second-conductivity-side first semiconductor layer is lower in a region nearer the electron barrier layer than in a region farther from the electron barrier layer.
1. A nitride-based light-emitting device comprising, on a GaN substrate:
a first-conductivity-side first semiconductor layer including a nitride-based semiconductor of a first conductivity type;
an active layer including a nitride-based semiconductor containing Ga or In;
a second-conductivity-side first semiconductor layer including a nitride-based semiconductor of a second conductivity type, in the stated order;
a first-conductivity-side second semiconductor layer located between the first-conductivity-side first semiconductor layer and the active layer; and
an electron barrier layer of the second conductivity type between the active layer and the second-conductivity-side first semiconductor layer, the electron barrier layer including a nitride-based semiconductor containing at least Al, wherein:
the electron barrier layer has a first region in which an Al composition changes,
the Al composition in the first region monotonically increases in a direction from the active layer to the second-conductivity-side first semiconductor layer,
an impurity concentration in the second-conductivity-side first semiconductor layer is lower in a region nearer the electron barrier layer than in a region farther from the electron barrier layer,
E1>E2 is satisfied, where E1 is a bandgap energy of the first-conductivity-side first semiconductor layer, and E2 is a bandgap energy of the first-conductivity-side second semiconductor layer, and
at least one of a second region in the first-conductivity-side first semiconductor layer adjacent to an interface between the first-conductivity-side first semiconductor layer and the first-conductivity-side second semiconductor layer and a third region in the first-conductivity-side second semiconductor layer adjacent to an interface between the first-conductivity-side second semiconductor layer and the first-conductivity-side first semiconductor layer forms at least one of a high-concentration impurity region and a composition change region, the high-concentration impurity region being a region doped with an impurity of a concentration higher than an impurity concentration in a fourth region in the first-conductivity-side first semiconductor layer adjacent to the second region and a fifth region in the first-conductivity-side second semiconductor layer adjacent to the third region, and the composition change region being a region in which a composition changes to interpolate an atomic composition from the fourth region to the fifth region.
2. The nitride-based light-emitting device according to claim 1 , further comprising:
a first-conductivity-side third semiconductor layer located between the first-conductivity-side second semiconductor layer and the active layer,
wherein E2>E3, where E3 is a bandgap energy of the first-conductivity-side third semiconductor layer.
3. The nitride-based light-emitting device according to claim 2 ,
wherein at least one of a sixth region in the first-conductivity-side second semiconductor layer adjacent to an interface between the first-conductivity-side second semiconductor layer and the first-conductivity-side third semiconductor layer and a seventh region in the first-conductivity-side third semiconductor layer adjacent to an interface between the first-conductivity-side third semiconductor layer and the first-conductivity-side second semiconductor layer forms at least one of a high-concentration impurity region and a composition change region, the high-concentration impurity region being a region doped with an impurity of a concentration higher than an impurity concentration in an eighth region in the first-conductivity-side second semiconductor layer adjacent to the sixth region and a ninth region in the first-conductivity-side third semiconductor layer adjacent to the seventh region, and the composition change region being a region in which a composition changes to interpolate an atomic composition from the eighth region to the ninth region.
4. The nitride-based light-emitting device according to claim 2 ,
wherein a film thickness of the first-conductivity-side third semiconductor layer is thicker than a film thickness of the first-conductivity-side second semiconductor layer.
5. The nitride-based light-emitting device according to claim 1 ,
wherein an impurity concentration in the high-concentration impurity region is 1×10 18 cm −3 or more and 1.5×10 18 cm −3 or less, and
the high-concentration impurity region is formed in a region from an interface adjacent to the high-concentration impurity region to a distance of 10 nm or more and 20 nm or less from the interface.
6. The nitride-based light-emitting device according to claim 1 ,
wherein an impurity concentration in the high-concentration impurity region is 2×10 18 cm −3 or more and 2.5×10 18 cm −3 or less, and
the high-concentration impurity region is formed in a region from an interface adjacent to the high-concentration impurity region to a distance of 5 nm or more and 10 nm or less from the interface.
7. The nitride-based light-emitting device according to claim 1 ,
wherein an impurity concentration in the composition change region is 5×10 17 cm 3 or more, and
the composition change region is formed in a region from an interface adjacent to the composition change region to a distance of 10 nm or more from the interface.
8. The nitride-based light-emitting device according to claim 1 ,
wherein the electron barrier layer has a tenth region in which an Al composition is constant, and
the tenth region is located between the first region and the second-conductivity-side first semiconductor layer.
9. The nitride-based light-emitting device according to claim 8 ,
wherein a film thickness of the tenth region is thinner than a film thickness of the first region.
10. The nitride-based light-emitting device according to claim 8 ,
wherein the electron barrier layer has an Al composition decrease region,
the Al composition decrease region is located between the tenth region and the second-conductivity-side first semiconductor layer,
an Al composition in the Al composition decrease region monotonically decreases in the direction from the active layer to the second-conductivity-side first semiconductor layer,
a film thickness of the tenth region is 2 nm or less, and
a film thickness of the Al composition decrease region is 5 nm or less.
11. The nitride-based light-emitting device according to claim 1 ,
wherein a maximum ratio of an Al composition in the electron barrier layer is 25% or more.
12. The nitride-based light-emitting device according to claim 1 ,
wherein an impurity concentration in the electron barrier layer is 1×10 19 cm −3 or more.
13. The nitride-based light-emitting device according to claim 1 ,
wherein a film thickness of the region nearer the electron barrier layer in the second-conductivity-side first semiconductor layer is 200 nm or more and 300 nm or less, and
an impurity concentration in the region nearer the electron barrier layer in the second-conductivity-side first semiconductor layer is 1×10 18 cm −3 or more and 5×10 18 cm −3 or less.
14. The nitride-based light-emitting device according to claim 1 , further comprising:
a second-conductivity-side second semiconductor layer located between the active layer and the electron barrier layer.
15. The nitride-based light-emitting device according to claim 14 , further comprising:
a second-conductivity-side third semiconductor layer located between the second-conductivity-side second semiconductor layer and the second-conductivity-side first semiconductor layer, and having a bandgap energy that is higher than a bandgap energy of the second-conductivity-side second semiconductor layer and not higher than a bandgap energy of the first region.
16. The nitride-based light-emitting device according to claim 1 ,
wherein a change in a band structure of a valence band of the electron barrier layer caused by a piezoelectric field is canceled out by a change in the valence band structure caused by the Al composition change of the first region.
17. A nitride-based light-emitting device comprising, on a GaN substrate:
a first-conductivity-side first semiconductor layer including a nitride-based semiconductor of a first conductivity type;
an active layer including a nitride-based semiconductor containing Ga or In;
a second-conductivity-side first semiconductor layer including a nitride-based semiconductor of a second conductivity type, in the stated order;
a first-conductivity-side second semiconductor layer located between the first-conductivity-side first semiconductor layer and the active layer;
a first-conductivity-side third semiconductor layer located between the first-conductivity-side second semiconductor layer and the active layer, and
an electron barrier layer of the second conductivity type between the active layer and the second-conductivity-side first semiconductor layer, the electron barrier layer including a nitride-based semiconductor containing at least Al, wherein:
the electron barrier layer has a first region in which an Al composition changes,
the Al composition in the first region monotonically increases in a direction from the active layer to the second-conductivity-side first semiconductor layer,
an impurity concentration in the second-conductivity-side first semiconductor layer is lower in a region nearer the electron barrier layer than in a region farther from the electron barrier layer,
E1>E2 is satisfied, where E1 is a bandgap energy of the first-conductivity-side first semiconductor layer, and E2 is a bandgap energy of the first-conductivity-side second semiconductor layer,
E2>E3 is satisfied, where E3 is a bandgap energy of the first-conductivity-side third semiconductor layer, and
at least one of a second region in the first-conductivity-side second semiconductor layer adjacent to an interface between the first-conductivity-side second semiconductor layer and the first-conductivity-side third semiconductor layer and a third region in the first-conductivity-side third semiconductor layer adjacent to an interface between the first-conductivity-side third semiconductor layer and the first-conductivity-side second semiconductor layer forms at least one of a high-concentration impurity region and a composition change region, the high-concentration impurity region being a region doped with an impurity of a concentration higher than an impurity concentration in a fourth region in the first-conductivity-side second semiconductor layer adjacent to the second region and a fifth region in the first-conductivity-side third semiconductor layer adjacent to the third region, and the composition change region being a region in which a composition changes to interpolate an atomic composition from the fourth region to the fifth region.
18. The nitride-based light-emitting device according to claim 17 ,
wherein an impurity concentration in the high-concentration impurity region is 1×10 18 cm −3 or more and 1.5×10 18 cm −3 or less, and
the high-concentration impurity region is formed in a region from an interface adjacent to the high-concentration impurity region to a distance of 10 nm or more and 20 nm or less from the interface.
19. The nitride-based light-emitting device according to claim 17 ,
wherein an impurity concentration in the high-concentration impurity region is 2×10 18 cm −3 or more and 2.5×10 18 cm −3 or less, and
the high-concentration impurity region is formed in a region from an interface adjacent to the high-concentration impurity region to a distance of 5 nm or more and 10 nm or less from the interface.
20. The nitride-based light-emitting device according to claim 17 ,
wherein an impurity concentration in the composition change region is 5×10 17 cm −3 or more, and
the composition change region is formed in a region from an interface adjacent to the composition change region to a distance of 10 nm or more from the interface.