Mixed alloy defect redirection region and devices including same
View Patent ↗An optical semiconductor device such as a light emitting diode is formed on a transparent substrate having formed thereon a template layer, such as AlN, which is transparent to the wavelength of emission of the optical device. A mixed alloy defect redirection region is provided over the template layer such that the composition of the defect redirection region approaches or matches the composition of the regions contiguous thereto. For example, the Al content of the defect redirection region may be tailored to provide a stepped or gradual Aluminum content from template to active layer. Strain-induced cracking and defect density are reduced or eliminated.
1. A semiconductor light emitting device, comprising:
an Al 2 O 3 substrate;
a planar In k Al x Ga 1-x-k N template layer formed over said substrate, said template layer having threading dislocations originating at said substrate and propagating substantially in a direction perpendicular to the plane of said template layer;
a defect redirection region formed over said template layer, said template layer having threading dislocations transmitted from said template layer which are bent by said defect redirection region so as to propagate within said defect redirection region substantially in a direction other than perpendicular to the plane of said template layer;
an active region having a composition In z Al y Ga 1-y-z N, formed over said defect redirection region said active region having threading dislocations transmitted from said defect redirection region, said threading dislocations propagating both in a direction perpendicular to the plane of said template layer and in a direction other than perpendicular to the plane of said template layer, the number of said threading dislocations propagating in a direction perpendicular to the plane of said template layer in said active region being substantially less than the number of threading dislocations propagating in a direction perpendicular to the plane of said template layer in said template layer; and
wherein said defect redirection region comprises a plurality of groups of layer pairs, a first of said layer pairs comprising In r Al s Ga 1-s-r N, and a second of said layer pairs comprising In q Al t Ga 1-t-q N, and wherein each group has an average aluminum concentration, the average aluminum concentration of the group proximate the template layer approaching or equal to x, and the average aluminum concentration of the group proximate the active region approaching or equal to y.
2. The semiconductor light emitting device of claim 1 , wherein for each group the different layers comprising that group periodically repeat in order a plurality of times.
3. The semiconductor light emitting device of claim 2 , wherein for each group the concentration of the first element in each of the at least one layers in that group is the same.
4. The semiconductor light emitting device of claim 2 , wherein the average concentration of the first element varies periodically from group to group along a height of the defect redirection region.
5. A semiconductor light emitting device, comprising:
an Al 2 O 3 substrate;
a planar In k Al x Ga 1-x-k N template layer formed over said substrate, said template layer having threading dislocations originating at said substrate and propagating substantially in a direction perpendicular to the plane of said template layer;
a defect redirection region formed over said template layer, said template layer having threading dislocations transmitted from said template layer which are bent by said defect redirection region so as to propagate in said defect redirection region substantially in a direction other than perpendicular to the plane of said template layer;
a structural region formed over said defect redirection region and comprising at least in part a first element;
an active region having a composition In z Al y Ga 1-y-z N, formed over said structural region said active region having threading dislocations transmitted from said defect redirection region, said threading dislocations propagating both in a direction perpendicular to the plane of said template layer and in a direction other than perpendicular to the plane of said template layer, the number of said threading dislocations propagating in a direction perpendicular to the plane of said template layer in said active region being substantially less than the number of threading dislocations propagating in a direction perpendicular to the plane of said template layer in said template layer; and
said defect redirection region further comprising a plurality of groups of layers, at least one layer within each said group comprised at least in part of the first element, an average concentration of the first element being higher in the group closest to the template layer relative to all groups in the defect redirection region, and the average concentration of the first element being lower in the group closest to the structural region relative to all groups in the defect redirection region.
6. The semiconductor light emitting device of claim 5 , wherein the defect redirection region is comprised of a plurality of groups of layers, each group comprising at least one layer sub-group, a first layer of each layer sub-group comprised at least in part of the first element and a second layer of the layer sub-group not including the first element.
7. The semiconductor light emitting device of claim 6 , wherein for each group the concentration of the first element is the same for all said first layers with said group.
8. The semiconductor light emitting device of claim 7 , wherein each group has an average concentration of the first element, the average concentration of the first element being higher in the group closest to the template layer relative to all groups in the defect redirection region, and the average concentration of the first element being lower in the group closest to the active region relative to all groups in the defect redirection region.
9. The semiconductor light emitting device of claim 6 , wherein the number of groups is two.
10. The semiconductor light emitting device of claim 9 , wherein the number of layers in each sub-group is two.
11. The semiconductor light emitting device of claim 6 , wherein the average concentration of the first element in the group closest to the template layer is in the range of 70-85%, and the average concentration of the first element in the group closest to the active region is in the range of 50-65%.
12. The semiconductor light emitting device of claim 5 , wherein the first element is aluminum.
13. The semiconductor light emitting device of claim 5 , wherein the average concentration of the first element varies periodically from group to group along the elevation of the defect redirection region.
14. The semiconductor light emitting device of claim 6 , wherein the structural region is composed of AlN, the active region has an aluminum concentration between 30% and 40%, the average aluminum concentration in the group closest to the template layer is in the range of 70-85%, and the average aluminum concentration in the group closest to the active region is in the range of 50-65%.
15. The semiconductor light emitting device of claim 1 , wherein said defect reduction region comprises a periodically varying mixed alloy comprising a plurality of modulated sections.
16. The semiconductor light emitting device of claim 15 , wherein each modulated section in the periodic mixed alloy has a thickness of substantially one atomic monolayer.
17. The semiconductor light emitting device of claim 15 , wherein the alloy composition of the modulated sections varies such that there is no well-defined thickness in any one of said modulated sections over which the alloy composition is constant.
18. A semiconductor light emitting device, comprising:
an Al 2 O 3 substrate;
a planar In k Al x Ga 1-x-k N template layer formed over said substrate, said template layer having threading dislocations originating at said substrate and propagating substantially in a direction perpendicular to the plane of said template layer;
a defect redirection region formed over said template layer, said template layer having threading dislocations transmitted from said template layer which are bend by said defect redirection region so as to propagate within said defect reduction region substantially in a direction other than perpendicular to the plane of said template layer, said defect redirection region comprising:
at least two groups of layer pairs, each layer pair comprising a first layer of composition
In z Al x Ga 1-x-z N where 0< x≦ 1, 0≦ z< 1
and a second of composition
In p Al y Ga 1-y-p N where 0< y≦ 1, 0≦ p≦ 1
a first of said groups proximate said template layer having an average aluminum content equal to or approaching the aluminum content of said template layer; and
a second of said groups proximate said template layer having an average aluminum content equal to or approaching the aluminum content of said template layer; and
an active region having a composition In z Al y Ga 1-y-z N, formed over said defect redirection region said template layer having threading dislocations transmitted from said defect redirection region, said threading dislocations propagating both in a direction perpendicular to the plane of said template layer and in a direction other than perpendicular to the plane of said template layer, the number of said threading dislocations propagating in a direction perpendicular to the plane of said template layer in said active region being substantially less than the number of threading dislocations propagating in a direction perpendicular to the plane of said template layer in said template layer.
19. The semiconductor light emitting device of claim 18 , wherein the light emitting device produces light in the wavelength range of between 250 nm and 360 nm.