Electron affinity engineered VCSELs

• US 7,065,124 B2
• Filed: 01/29/2004
• Issued: 06/20/2006
• Est. Priority Date: 11/28/2000
• Status: Expired due to Term

• Current Assignee: II-VI Delaware, Inc. (Coherent Corp.)
• Original Assignee: Finlsar Corporation
• Inventors: Johnson, Ralph H., Johnson, Klein L., Biard, James R.
• Primary Examiner(s): Menefee, James
• Application Number:
  US10/767,920
• Publication Number:
  US 20050031011A1
• Time in Patent Office: 873 Days
• Field of Search: 372/99, 372/50.1
• US Class Current: 372/99
• CPC Class Codes: H01S 2301/166 Single transverse or lateral mode
• CPC Class Codes: H01S 5/0421 characterised by the semiconducting contacting layers electrodes H01S5/0425
• CPC Class Codes: H01S 5/18308 having a special structure for lateral current or light confinement
• CPC Class Codes: H01S 5/18358 containing spacer layers to adjust the phase of the light wave in the cavity
• CPC Class Codes: H01S 5/2009 by using electron barrier layers
• CPC Class Codes: H01S 5/205 Antiguided structures
• CPC Class Codes: H01S 5/3211 characterised by special cladding layers, e.g. details on band-discontinuities
• CPC Class Codes: H01S 5/423 having a vertical cavity

Abstract

A VCSEL having an N-type Bragg mirror with alternating layers of high bandgap (low index) and low bandgap (high index) layers of AlGaAs. The layers may be separated by a step change of Al composition followed by a graded region, and vice versa for the next layer, in the N-type mirror to result in a lower and more linear series resistance. Also, an N-type spacer layer may be adjacent to an active region of quantum wells. There may be a similar step in a change of Al composition from the nearest layer of the N-type mirror to the N-type spacer formed from a lower bandgap direct AlGaAs layer to provide lower free carrier absorption. With electron affinity engineering, a minority carrier hole barrier may be inserted adjacent to the quantum wells to improve hole confinement at high current density and high temperature.

Claims

1. A VCSEL system comprising:

a substrate;

a first mirror stack situated on the substrate;

an active region situated on the first mirror stack;

a second mirror stack situated on the active region;

wherein;

the first mirror stack comprises a plurality of pairs of AlAs and GaAs layers;

at least one interface of first and second interfaces, is situated between each AlAs layer and GaAs layer;

the first interface comprises;

a ramp increase of Al from GaAs to Al_xGa<sub>1−

x</sub>As; and

a step increase of Al from Al_xGa<sub>1−

x</sub>As to Al_yGa<sub>1−

y</sub>As; and

the second interface comprises;

a step decrease of Al from Al_yGa<sub>1−

y</sub>A to Al_xGa<sub>1−

x</sub>As; and

a ramp decrease of Al from Al_xGa<sub>1−

x</sub>As to GaAs; and

wherein x ramps to a final value that is ≦

0.4 for the first and second interfaces.

2. The system of claim 1, wherein 0.3≦

x≦

0.4; and

0.9≦

y≦

1.0.

3. The system of claim 2, wherein:

we first mirror stack is a distributed Bragg reflector;

and the first mirror stack has an N-type doping.

4. The system of claim 3, further comprising a first spacer layer situated between the first mirror stack and the active region.

5. The system of claim 4, wherein:

the spacer layer comprises Al_zGa<sub>1−

x</sub> As;

0.3≦

z≦

0.4;

and the spacer has an N-type doping.

6. The system of claim 5, further comprising a first hole confinement layer situated between the first spacer layer and the active region.

7. The system of claim 6, wherein the first hole confinement barrier comprises AlAs.

8. The system of claim 7, further comprising a transition barrier situated between the hole confinement barrier and the active region.

9. The system of claim 8, wherein the transition barrier comprises:

a composition of Al that has a ramp variation from Al_wGa<sub>1−

w</sub>As to Al_vGa<sub>1−

v</sub>As;

wherein;

the Al_vGa<sub>1−

v</sub>As is adjacent to the active region;

0.3≦

w≦

0.4; and

0.2≦

v≦

0.3.

10. The system of claim 9, wherein;

the active region comprises;

at least one well; and

at least one well barrier proximate to the well;

and the well barrier comprises;

Al_uGa<sub>1−

u</sub>As; and

0.2≦

u≦

0.3.

11. The system of claim 1, wherein:

x≈

0.33

y≈

1.0.

12. The system of claim 11, further comprising:

a first spacer layer situated between the first mirror stack and the active region;

and wherein the spacer layer comprises;

Al_zGa<sub>1−

z</sub>As; and

z≈

0.38.

13. The system of claim 12, further comprising:

a first hole confinement layer situated between the first spacer layer and the active region; and

wherein the first hole confinement layer comprises AlAs.

14. The system of claim 13, further comprising:

a transition barrier situated between the first hole confinement layer and the active region; and

wherein;

the transition barrier comprises a composition of Al that has a ramp variation from Al_wGa<sub>1−

w</sub>AS to Al_vGa<sub>1−

v</sub>As;

the Al_vGa<sub>1−

v</sub>As is adjacent to the active region;

w≈

0.38; and

v≈

0.25.

15. The system of claim 14, wherein the active region comprises:

at least one well; and

at least two well barriers adjacent to the at least one well;

and wherein;

the well barrier comprises Al_uGa<sub>1−

u</sub>As; and

u≈

0.25.

16. A VCSEL system comprising:

a first mirror; and

wherein;

the first mirror comprises a plurality of pairs of layers;

each pair of layers of the plurality of pairs has a first layer and a second layer;

the first layer comprises A_xB<sub>1−

x</sub>C;

the second layer comprises A_yB<sub>1−

y</sub>C;

x+y=1;

a transition layer is situated between each first layer and each second layer;

the transition layer, in a direction of a first layer to a second layer, has a ramp change in content of A from x=a first value of x to a second value of x=P, wherein P is less than 0.4, and a step change in content of A from x=P to y;

the transition layer in a direction of a second layer to a first layer, has a step change in content of A from y to y=P and a ramp change from P to the first value of x.

17. The system of claim 16, further comprising:

a spacer layer situated proximate to the first mirror;

and wherein;

the spacer layer comprises A_zB<sub>1−

z</sub>C; and

0≦

z≦

1.

18. The system of claim 17, further comprising:

a barrier layer proximate to the spacer layer; and

wherein the barrier layer is a hole confinement barrier.

19. The system of claim 18, further comprising:

a transition layer proximate to the barrier layer;

and wherein;

the transition layer comprises A_vB<sub>1−

v</sub>C;

0≦

v≦

1; and

v is equal to a value relative to a distance from the barrier layer.

20. The system of claim 19, further comprising:

an active region; and

wherein;

the active region comprises at least one quantum well bound by active region barrier layers;

the at least one quantum well comprises A_wB<sub>1−

w</sub>C;

the active region barrier layers comprises A_uB<sub>1−

u</sub>C;

0≦

w≦

1; and

0≦

u≦

1.

21. The system of claim 16, wherein:

A is Al;

B is Ga;

and C is As.

22. The system of claim 21, wherein:

x≈

0;

and y≈

1.

23. The system of claim 22, wherein 0.3≦

P≦

0.4.

24. The system of claim 23, wherein:

the ramp change from x to P is approximately linear over a distance between 15 and 25 nm; and

the ramp change from P to x is approximately linear over a distance between 15 and 25 nm.

25. The system of claim 24, wherein z<

0.45.

26. The system of claim 25, wherein the barrier layer comprises AlAs.

27. The system of claim 26, wherein 0.25≦

v≦

0.4.

28. The system of claim 27, wherein w≈

1.

29. The system of claim 28, wherein 0.2<

u<

0.3.

30. The system of claim 29, wherein u≈

0.25.

31. The system of claim 30, wherein the first mirror is an N-doped distributed Bragg reflector.

32. The system of claim 31, further comprising a second mirror proximate to the active region.

33. A VCSEL system comprising:

a first mirror; and

wherein;

the first mirror comprises a plurality of pairs of layers;

each pair of layers has a first layer and a second layer;

the first layer comprises A_xC;

the second layer comprises A_yC;

x+y=1;

a transition layer is situated between each first layer and a second layer;

the transition layer, in a direction of a first layer to a second layer, has a first change from x to P, and a second change from P to y, wherein P≦

0.4 for the direction of a first layer to a second layer;

the transition layer in a direction of a second layer to a first layer, has a third change from y to P, and fourth change from P to x; and

P≦

1 for the direction of a second layer to the first layer.

34. The system of claim 33, wherein:

the first and fourth changes are ramp changes; and

the second and third changes are step changes.

35. The system of claim 33, wherein:

the second and third changes are ramp changes; and

the first and fourth changes are step changes.

36. The system of claim 34, further comprising:

a spacer layer situated proximate to the first mirror; and

the active region; and

wherein;

the spacer layer comprises A_zE;

the spacer layer is adjacent to the first mirror; and

0≦

z≦

1.

37. A VCSEL system comprising:

a substrate;

a first mirror stack situated on the substrate;

an active region situated on the first mirror stack;

a second mirror stack situated on the active region;

wherein;

the first mirror stack comprises a plurality of pairs of Al_xGa<sub>1−

x</sub>As and Al_yGa<sub>1−

y</sub>As layers;

an interface between each Al_xGa<sub>1−

x</sub>As layer and Al_yGa<sub>1−

y</sub>As layer;

the interface comprises;

at least one linear ramp change of Al composition from x=first value to x≦

a second value, the second value less than 0.4; and

at least one step change of Al composition from the second value to a third value.

38. A VCSEL system comprising:

a substrate;

a first mirror stack formed over the substrate, the first mirror having pairs of layers, each pair having a first layer and a second layer;

an active region including a plurality of quantum wells formed over the first mirror stack;

a second mirror stack formed over the active region, the second mirror stack having pairs of layers, each pair including a third layer and a fourth layer;

a first spacer layer between the active region and the first mirror stack and a second spacer layer between the active region and the second mirror stack; and

an interface formed between the first layer and second layer of each pair in the first mirror stack, the interface comprising;

a first portion where a composition of a first element ramps from a first value to a second value, and a step in the composition from the second value to a third value, the second value selected such that electron affinity on a first side of the step is substantially the same as an electron affinity on a second side of the step.