Carbon doped GaAsSb suitable for use in tunnel junctions of long-wavelength VCSELs
View Patent ↗GaAs (1−x) Sb x layers are grown by MOCVD. For lattice matching with InP, x is set to 0.5, while beneficial alternatives include setting x to 0.23, 0.3, and 0.4. During MOVCD, TMGa (or TEGa), TMSb, and AsH 3 (or TBAs) are used to fabricate the GaAs (1−x ) Sb x layer. Beneficially, the GaAs (1−x) Sbx layer's composition is controlled by the ratio of As to Sb. The MOCVD growth temperature is between 500° C. and 650° C. The GaAs (1−x) Sb x layer is beneficially doped using CCl 4 or CBr 4 . A heavily doped GaAs (1−x) Sb x layer can be used to form a tunnel junction with n-doped layers of InP, AlInAs, or with lower bandgap materials such as AlInGaAs or InGaAsP. Such tunnel junctions are useful for producing long wavelength VCSELs.
1. A method of fabricating a vertical cavity surface emitting laser (VCSEL) with a tunnel junction, the method comprising:
locating a substrate in an MOCVD chamber;
forming an active region over the substrate, the active region having a plurality of quantum wells;
setting a temperature of the MOCVD chamber between 500° C. and 650° C.; and
growing a tunnel junction including GaAs (1−X) Sb x over the active region using an MOCVD process in which a source of Ga, a source of Sb, and a source of As are present.
2. The method according to claim 1 , wherein x has a value corresponding to a ratio of As to Sb.
3. The method according to claim 2 , wherein the value of x is 0.5.
4. The method according to claim 2 , wherein the value of x is less than 0.5.
5. The method according to claim 1 , wherein the source of Ga is TMGa or TEGa, and the source of Sb is TMSb.
6. The method according to claim 1 , wherein the source of As is AsH 3 or TBAs.
7. The method according to claim 1 , further including carbon doping the GaAs (1−x) Sbx x using CCl 4 or CBr 4 .
8. A tunnel junction comprising:
a p-doped GaAs (1−x) Sb x layer, wherein x is set at a value such that the p-doped GaAs (1−x) Sb x layer is substantially lattice matched with an InP based active region and has a strain less than 1.95%; and
an n-doped layer of InP, AlInAs, AlInGaAs, or InGaAsP, wherein the n-doped layer is doped with a concentration greater than 5×10 19 cm −3 .
9. The tunnel junction according to claim 8 , wherein the p-doped GaAs (1−x) Sb x layer is doped with carbon with a concentration greater than 1×1 19 cm −3 .
10. The tunnel junction according to claim 8 , wherein the GaAs (1−x) Sb x layer is doped with a concentration greater than 5×10 19 cm −3 , and wherein the tunnel junction is less than about 10 nanometers thick.
11. The tunnel junction according to claim 8 , wherein the n-doped layer is InP, and wherein x has a value of 0.5.
12. A vertical cavity surface emitting laser, comprising:
an active region having a plurality of quantum wells, and
a tunnel junction over said active region, wherein said tunnel junction includes a GaAs (1−x) Sb x layer.
13. The vertical cavity surface emitting laser according to claim 12 , further including an n-type bottom spacer adjacent the active region, and an n-type bottom DBR adjacent the n-type bottom spacer.
14. The vertical cavity surface emitting laser according to claim 12 , further including an n-type top spacer adjacent the tunnel junction and an n-type top DBR adjacent the n-type top spacer.
15. The vertical cavity surface emitting laser according to claim 12 , wherein the GaAs (1−x) Sb x layer is grown by MOCVD.
16. The vertical cavity surface emitting laser according to claim 12 , wherein the GaAs (1−x) Sb x layer is doped with carbon with a concentration greater than 5×10 19 cm −3 .
17. The vertical cavity surface emitting laser according to claim 12 , wherein said active region includes InGaAsP or AlInGaAs.
18. The vertical cavity surface emitting laser according to claim 17 , wherein said tunnel junction includes an n-type InP layer.
19. The vertical cavity surface emitting laser according to claim 12 , wherein x is 0.5.
20. The vertical cavity surface emitting laser according to claim 12 , wherein the tunnel junction has a thickness of less than about 10 nm.