Three-terminal vertical cavity surface emitting laser (VCSEL) and a method for operating a three-terminal VCSEL
A three-terminal VCSEL is provided that has a reduced fall time that allows the VCSEL to be operated at higher speeds. Methods of operating the three-terminal VCSEL are also provided. The VCSEL can be operated at higher speeds without decreasing the optical output of the VCSEL when its in the logical HIGH state.
1. A three-terminal vertical cavity surface emitting laser (VCSEL) comprising:
a substrate having at least a top surface and a bottom surface;
an emitter contact corresponding to a first terminal;
a first plurality of n-type layers disposed on top of the top surface of the substrate, wherein the first plurality of n-type layers comprise pairs of layers of alternating high and low refractive index that operate as a first distributed Bragg reflector (DBR);
at least one n-type cavity confining layer disposed on top of the first plurality of n-type layers;
a plurality of active layers containing one or more quantum wells disposed on top of the n-type cavity confining layer, the active layers comprising a light-emitting material and being either lightly p-doped or intrinsic;
at least one p-type cavity confining layer disposed on top of the plurality of active layers;
a base contact disposed on or in a portion of the p-type cavity confining layer such that the base contact is in contact with at least one of the active layers, the base contact corresponding to a second terminal of the VCSEL;
a second plurality of n-type layers disposed on top of a portion of the p-type cavity confining layer, wherein the second plurality of layers comprise pairs of layers of alternating high and low refractive index that operate as a reflector;
an n-type collector contact layer disposed on top of the second plurality of n-type layers;
a collector contact disposed on or in a portion of the n-type collector contact layer, the collector contact corresponding to a third terminal of the VCSEL; and
a third plurality of layers disposed on top of the collector contact layer, wherein the third plurality of layers comprise pairs of layers of alternating high and low refractive index that operate as a DBR, the third plurality of layers being one of non-conducting intrinsic semiconductor layers and dielectric material layers.
2. The VCSEL of claim 1 , wherein the substrate is an n-type substrate.
3. The VCSEL of claim 1 , wherein the substrate is a semi-insulating substrate.
4. The VCSEL of claim 1 , wherein the pairs of layers of the second plurality of n-type layers comprise a second DBR.
5. The VCSEL of claim 4 , wherein at least some of the layers of the second DBR that have high indexes of refraction include quantum wells.
6. The VCSEL of claim 1 , wherein at least some of the layers of the third plurality of layers that have high indexes of refraction include quantum wells.
7. The VCSEL of claim 1 , further comprising an interconnect that connects the base contact to the collector contact.
8. A three-terminal vertical cavity surface emitting laser (VCSEL) comprising:
a p-type substrate having at least a top surface and a bottom surface;
an emitter contact corresponding to a first terminal;
a first plurality of p-type layers disposed on top of the top surface of the substrate, wherein the first plurality of p-type layers comprise pairs of layers of alternating high and low refractive index that operate as a first distributed Bragg reflector (DBR);
at least one p-type cavity confining layer disposed on top of the first plurality of p-type layers;
a plurality of active layers containing one or more quantum wells disposed on top of the p-type cavity confining layer, the active layers comprising a light-emitting material and being either lightly n-doped or intrinsic;
at least one n-type cavity confining layer disposed on top of the plurality of active layers;
a base contact disposed on or in a portion of the n-type cavity confining layer such that the base contact is in contact with at least one of the active layers, the base contact corresponding to a second terminal of the VCSEL;
a second plurality of p-type layers disposed on top of a portion of the n-type cavity confining layer, wherein the second plurality of layers comprises pairs of layers of alternating high and low refractive index that operate as a reflector;
a p-type collector contact layer disposed on top of the second plurality of p-type layers;
a collector contact disposed on or in a portion of the p-type collector contact layer, the collector contact corresponding to a third terminal of the VCSEL; and
a third plurality of layers disposed on top of the collector contact layer, wherein the third plurality of layers comprise pairs of layers of alternating high and low refractive index that operate as a DBR, the third plurality of layers being one of non-conducting intrinsic semiconductor layers and dielectric material layers.
9. The VCSEL of claim 8 , wherein the pairs of layers of the second plurality of p-type layers comprise a second DBR.
10. The VCSEL of claim 9 , wherein at least some of the layers of the second DBR that have high indexes of refraction include quantum wells.
11. The VCSEL of claim 8 , wherein at least some of the layers of the third plurality of layers that have high indexes of refraction include quantum wells.
12. The VCSEL of claim 8 , further comprising an interconnect that connects the base contact to the collector contact.
13. A method for operating a three-terminal VCSEL, the method comprising:
providing a three-terminal VCSEL having an emitter, a base, a collector, an emitter contact disposed on the emitter, a base contact disposed on the base and a collector contact disposed on the collector, the emitter contact corresponding to a first terminal of the VCSEL, the base contact corresponding to a second terminal of the VCSEL, and the collector contact corresponding to a third terminal of the VCSEL, wherein a base-emitter junction exists at an intersection of the base and the emitter and a base-collector junction exists at an intersection of the base and the collector;
applying an electrical potential across the base and emitter contacts to place the base-emitter junction in a forward-biased condition, wherein placing the base-emitter junction in the forward-biased condition causes an optical signal to be output from the base with an optical intensity level that is above a lasing threshold level of the VCSEL, wherein the lasing threshold level is in between a logical HIGH level and a logical LOW level of the VCSEL;
applying an electrical potential across the base and collector contacts to place the base-collector junction in a forward-biased condition, wherein placing the base-collector junction in the forward-biased condition while the base-emitter junction is in the forward-biased condition causes the optical output signal output from the base to transition to a logical HIGH level; and
applying an electrical potential across the base and collector contacts to place the base-collector junction in a reverse-biased condition, wherein placing the base-collector junction in the reverse-biased condition causes the intensity level of the optical signal being output from the base to decrease with time such that the optical signal has a falling edge, and wherein the base-collector junction is maintained in the reverse-biased condition on the falling edge of the optical signal to increases a rate at which the intensity level of the optical signal being output from the base transitions from the logical HIGH level to the logical LOW level.