Semiconductor laser having low stress passivation layer
View Patent ↗A laser diode having a composite passivation layer configured to control parasitic capacitance, especially in high speed laser applications, is disclosed. In one embodiment, a ridge waveguide laser is disclosed and includes: a substrate, an active layer disposed on the substrate, a ridge structure disposed on the active layer, and a contact layer disposed on the ridge structure. A composite passivation layer is disposed substantially laterally to the ridge structure. The composite passivation layer includes a silicon nitride bottom layer, a silicon nitride top layer, and a silicon dioxide middle layer interposed between the bottom and top layers. The passivation layers possess differing stress components that, when combined, cancel out the overall mechanical stress of the passivation layer. This enables relatively thick passivation layers to be employed in high speed laser diodes without increasing the risk of layer stress cracking and laser damage.
1. A laser die, comprising:
a substrate;
an active layer disposed above the substrate; and
a composite passivation layer disposed above at least a portion of the active layer, the composite passivation layer including at least:
a first compressive layer;
at least one tensile layer; and
a second compressive layer.
2. The laser die as defined in claim 1 , wherein the at least one compressive layer and the at least one tensile layer cooperate to cancel out net mechanical stress otherwise present in the composite passivation layer.
3. The laser die as defined in claim 1 , wherein the at least one compressive layer is adjacent the at least one tensile layer.
4. The laser die as defined in claim 1 , wherein the at least one tensile layer is interposed between the compressive layers.
5. The laser die as defined in claim 1 , wherein the at least one compressive layer is composed of silicon nitride.
6. The laser die as defined in claim 1 , wherein the at least one tensile layer is composed of silicon dioxide.
7. The laser die as defined in claim 1 , wherein the laser die is a ridge waveguide laser.
8. The laser die as defined in claim 7 , wherein the composite passivation layer is laterally disposed with respect to a ridge of the ridge waveguide laser.
9. The laser die as defined in claim 1 , wherein the laser die is a distributed feedback laser.
10. A method for manufacturing a laser die, the method comprising:
defining a substrate and an active layer;
applying a first compressive layer of a composite passivation layer above at least a portion of the active layer;
applying a tensile layer of the composite passivation layer above at least a portion of the active layer and on the compressive layer; and
applying a second compressive layer of the composite passivation layer so as to sandwich the tensile layer between the first and second compressive layers.
11. The method for manufacturing as defined in claim 10 , wherein applying the first compressive layer and tensile layer is performed by chemical vapor deposition.
12. The method for manufacturing as defined in claim 10 , wherein applying the first compressive layer further comprises:
combining a 5% pre-mixed dilute SiH4 solution III a SiNx deposition solution.
13. The method for manufacturing as defined in claim 10 , further comprising:
defining a ridge above the active layer; and
applying the composite passivation layer adjacent the ridge.
14. The method for manufacturing as defined in claim 13 , further comprising:
applying a metal layer atop the composite passivation layer; and
applying a contact layer atop the ridge.
15. The method for manufacturing as defined in claim 10 , further comprising:
configuring a thickness of at least one of the layers of the composite passivation layer so as to control parasitic capacitance of the laser die.