Modulation doped tunnel junction
View Patent ↗A vertical cavity surface emitting laser (VCSEL) includes a substrate; a first mirror stack over the substrate; an active region having a plurality of quantum wells over the first mirror stack; a tunnel junction over the active region, the tunnel junction including a modulation-doped layer; and a second mirror stack over the tunnel junction. The modulation doped layer can be used for either the n-layer or the p-layer, or the both layers of the tunnel junction. Such tunnel junctions are especially useful for a long wavelength VCSEL.
1. A vertical cavity surface emitting laser comprising:
a substrate;
a first mirror stack over the substrate;
an active region having a plurality of quantum wells over the first mirror stack;
a tunnel junction over the active region, the tunnel junction including:
a p-layer that includes a modulation doped layer comprising an AlInAs layer epitaxially grown as a digital alloy of p-type doped AlAs and InAs; and
an n-layer that includes an n-layer of a compound selected from the group consisting of InP, AlInAs, AlInGaAs, InGaAsP, GaAs, AlAs, AlGaAs, InGaAs, AlGaAsSb, GaAsSb, AlAsSb, AlPSb, GaPSb, AlGaPSb, and combinations thereof; and
a second mirror stack over the tunnel junction.
2. A vertical cavity surface emitting laser according to claim 1 , wherein the modulation layer is doped with a concentration greater than 1×10 19 cm −3 .
3. A vertical cavity surface emitting laser according to claim 1 , wherein the p-type AlAs layer is doped with carbon to a concentration greater than 1×10 19 cm −3 , and wherein an effective doping concentration of the modulation doped layer is greater than 1×10 19 cm −3 .
4. A vertical cavity surface emitting laser according to claim 1 , further including an n-type spacer adjacent the active region, and wherein the first mirror stack is an n-type DBR.
5. A vertical cavity surface emitting laser according to claim 1 , further including a p-type spacer adjacent the tunnel junction, and wherein the second mirror stack is an n-type DBR.
6. A vertical cavity surface emitting laser according to claim 1 , further including:
an n-type bottom spacer adjacent the active region, and wherein the first mirror stack is an n-type DBR; and
a p-type top spacer adjacent the tunnel junction,
wherein the first and second mirror stacks are each an n-type DBR.
7. A vertical cavity surface emitting laser according to claim 1 , wherein the p-layer is doped with carbon with a concentration greater than 1×10 19 cm −3 .
8. A vertical cavity surface emitting laser according to claim 1 , wherein the active region includes one of InGaAsP and AlInGaAs.
9. A vertical cavity surface emitting laser according to claim 1 , wherein the first and second mirror stacks are lower and upper mirror stacks, respectively.
10. A vertical cavity surface emitting laser comprising:
a substrate;
a first mirror stack over the substrate;
an active region having a plurality of quantum wells over the first mirror stack;
a tunnel junction over the active region, the tunnel junction including:
an n-layer that includes a modulation doped layer comprising an SiAs layer and an AlGaInAs layer; and
a p-layer that includes a p-layer of a compound selected from the group consisting of InP, AlInAs, AlInGaAs, InGaAsP, GaAs, AlAs, AlGaAs, InGaAs, AlGaAsSb, GaAsSb, AlAsSb, AlPSb, GaPSb, AlGaPSb, and combinations thereof; and
a second mirror stack over the tunnel junction.
11. A vertical cavity surface emitting laser according to claim 10 , wherein the thickness of the SiAs layer is about 1/1000 of the AlGaInAs layer.
12. A vertical cavity surface emitting laser according to claim 10 , wherein an effective doping concentration of the modulation doped layer is greater than 1×10 19 cm −3 .
13. A tunnel junction including a modulation doped layer that comprises an AlInAs layer epitaxially grown as a digital alloy of p-type doped AlAs and InAs.
14. A tunnel junction according to claim 13 , wherein the modulation-doped layer is doped with an effective carrier concentration greater than 1×10 19 cm −3 .
15. A tunnel junction according to claim 13 , wherein a total thickness of the modulation-doped layer is in a range of about 0.1 nm˜about 2 nm.
16. A tunnel junction according to claim 13 , wherein the p-type AlAs layer is doped with carbon to a concentration greater than 1×10 19 cm −3 , and wherein an effective doping concentration of the modulation doped layer is greater than 1×10 19 cm −3 .
17. A tunnel junction according to claim 13 , wherein the tunnel junction includes an n-type layer.