Photovoltaic device

• US 7,868,247 B2
• Filed: 03/28/2008
• Issued: 01/11/2011
• Est. Priority Date: 07/25/2001
• Status: Expired due to Fees

• Current Assignee: Lumentum Operations, LLC (Lumentum Holdings Inc.)
• Original Assignee: Imperial Innovations Limited (Imperial College London)
• Inventors: Barnham, Keith W. J., Mazzer, Massimo, Ballard, Ian M., Rohr, Carsten, Ekins-Daukes, Nicholas, Connolly, James P.
• Primary Examiner(s): Ward; Jessica L
• Assistant Examiner(s): Yoon; Kevin E
• Application Number:
  US12/078,315
• Publication Number:
  US 20080251118A1
• Time in Patent Office: 1,019 Days
• Field of Search: 136243-265
• US Class Current: 136/255
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: H01L 31/035236 Superlattices; Multiple quantum well structures
• CPC Class Codes: H01L 31/0735 comprising only AIIIBV compound semiconductors, e.g. GaAs/AlGaAs or InP/GaInAs solar cells
• CPC Class Codes: H01L 31/075 the potential barriers being only of the PIN type, e.g. amorphous silicon PIN solar cells
• CPC Class Codes: H02S 10/30 Thermophotovoltaic systems photovoltaic cells specially adapted for conversion or sensing of infrared [IR] radiation H01L31/00; thermoelectric devices H10N10/00
• CPC Class Codes: Y02E 10/544 Solar cells from Group III-V materials
• CPC Class Codes: Y02E 10/548 Amorphous silicon PV cells

Abstract

A method of forming a photovoltaic device includes a plurality of quantum wells and a plurality of barriers. The quantum wells and barriers are disposed on an underlying layer. The barriers alternate with the quantum wells. One of the plurality of quantum wells and the plurality of barriers is comprised of tensile strained layers and the other of the plurality of quantum wells and the plurality of barriers is comprised of compressively strained layers. The tensile and compressively strained layers have elastic properties. The method includes selecting compositions and thicknesses of the barriers and quantum wells taking into account the elastic properties such that each period of one tensile strained layer and one compressively strained layer exerts substantially no shear force on a neighboring structure; providing the underlying layer; and forming the quantum sells and barriers on the underlying layer according to the derived compositions and thicknesses.

Claims

1. A method of forming a photovoltaic device comprising a multiple quantum well portion comprising a plurality of quantum wells and a plurality of barriers, the quantum wells and barriers being disposed on an underlying layer, the barriers alternating with the quantum wells, one of the plurality of quantum wells and the plurality of barriers comprised of tensile strained layers and the other of the plurality of quantum wells and the plurality of barriers comprised of compressively strained layers, the tensile and compressively strained layers having elastic properties, comprising:

selecting compositions and thicknesses of the barriers and quantum wells using an equation taking into account the elastic properties of the tensile strained layers and the compressively strained layers such that each period of one tensile strained layer and one compressively strained layer exerts substantially no shear force on a neighboring structure;

providing the underlying layer; and

forming the quantum wells and barriers on the underlying layer according to the derived compositions and thicknesses.

2. The method of claim 1, wherein the neighboring structure is selected from the group consisting of:

a further period of one tensile strained layer and one compressively strained layer; and

the underlying layer.

3. The method of claim 2, wherein the underlying layer is selected from the group consisting of:

a layer of arbitrary doping having a lattice constant; and

a substrate having a lattice constant.

4. The method of claim 1, wherein the selecting step is carried out using linear elastic theory.

5. The method of claim 1, wherein the number of quantum wells formed is from 30 to 60.

6. The method of claim 1, wherein the underlying layer is a substrate with a substrate lattice constant α

₀, the alternating tensile strained layers have a lattice constant α

₁, a thickness t₁ and elastic stiffness coefficients C₁₁ and C₁₂, and the alternating compressively strained layers have a lattice constant α

₂, a thickness t₂ and elastic stiffness coefficients C₂₁ and C₂₂, the tensile strained layers and the compressively strained layers having compositions and thicknesses selected to substantially meet the conditions;

7. The method of claim 1, wherein the photovoltaic device is a crystalline photovoltaic device grown upon a substrate with a substrate lattice constant.

8. The method of claim 7, wherein at least one of the tensile strained layers or the compressively strained layers is a quantum well having a lattice constant not equal to the substrate lattice constant and having a Group III/V semiconductor composition with a bandgap lower than if the quantum well had a lattice constant equal to the substrate lattice constant.

9. The method of claim 8, wherein the substrate is InP and the compressively strained layer is In_xGa_1-xAs, where x>

0.53.

10. The method of claim 7, wherein at least one of the tensile strained layers or the compressively strained layers is a barrier having a lattice constant not equal to the substrate lattice constant and having a Group III/V semiconductor composition with a bandgap higher than if the barrier had a lattice constant equal to the substrate lattice constant.

11. The method of claim 10, wherein the substrate is InP and the tensile strained layer is In_xGa_1-xAs_1-yP_y, where y>

0.

12. The method of claim 7, wherein the substrate is GaAs.

13. The method of claim 12, wherein the multiple quantum well portion is formed of layers of In_xGa_1-xAs_yP_1-y, where 0≦

x≦

1 and 0≦

y≦

1.

14. The method of claim 1, wherein the multiple quantum well portion is formed of alternating quantum well layers and barrier layers having a Group III/V semiconductor composition, wherein a period of one quantum well layer and one quantum barrier layer contains at least four different elements and has an average lattice constant substantially matching a neighboring structure lattice constant.

15. The method of claim 1, wherein the multiple quantum well portion is formed upon a virtual substrate composed of a strain relaxed buffer layer having a virtual substrate lattice constant different from a substrate lattice constant of an underlying substrate.

16. The method of claim 1, wherein the photovoltaic device is a thermophotovoltaic device.

17. The method of claim 1, wherein the quantum wells comprise the compressively strained layers.

18. The method of claim 1, wherein the barriers comprises the tensile strained layers.

19. A method of forming a photovoltaic device comprising:

forming a plurality of alternating tensile strained layers and compressively strained layers on an underlying layer of material, the alternating layers comprising barriers and quantum wells having compositions and thicknesses selected based on their elastic properties;

wherein each period of one tensile strained layer and one compressively strained layer exerts substantially no shear force on a neighboring structure.

20. The method of claim 19, wherein the step of forming a plurality of alternating tensile strained layers and compressively strained layers comprises forming between 30 and 60 quantum wells.

21. The method of claim 19, wherein the neighboring structure is the underlying layer.

22. The method of claim 19, wherein the neighboring structure is another period of one tensile strained layer and one compressively strained layer.

23. The method of claim 19, wherein the underlying layer of material is selected from the group consisting of a layer of arbitrary doping having a lattice constant and a substrate having a lattice constant.

24. The method of claim 19, further comprising the step of selecting the compositions and thicknesses of the barriers and quantum wells using linear elastic theory.

25. The method of claim 19, wherein the underlying layer of material is a substrate with a substrate lattice constant α

₀, the alternating tensile strained layers have a lattice constant α

₁, a thickness t₁ and elastic stiffness coefficients C₁₁ and C₁₂, and the alternating compressively strained layers have a lattice constant α

₂, a thickness t₂ and elastic stiffness coefficients C₂₁ and C₂₂, the tensile strained layers and the compressively strained layers having compositions and thicknesses selected to substantially meet the conditions;

26. The method of claim 19, wherein the photovoltaic device is a crystalline photovoltaic device grown upon a substrate with a substrate lattice constant.

27. The method of claim 26, wherein the substrate is InP and the compressively strained layer is selected from the group consisting of In_xGa_1-xAs where x>

0.53.

28. The method of claim 26, wherein the substrate comprises GaAs.

29. The method of claim 28, wherein the alternating tensile strained layers and the compressively strained layers comprise In_xGa_1-xAs_yP_1-y, where 0≦

x≦

1 and 0≦

y≦

1.

30. The method of claim 19, wherein a period of one quantum well layer and one quantum barrier layer within the plurality of alternating tensile strained layers and compressively strained layers contains at least four different elements and has an average lattice constant substantially matching a lattice constant of a neighboring structure.

31. The method of claim 19, wherein the compressively strained layers are quantum wells.

32. A method of forming a photovoltaic device comprising:

forming a plurality of alternating layers of quantum wells and barriers, wherein the alternating layers alternate between tensile strained layers and compressively strained layers, the tensile strained layers and the compressively strained layers having compositions selected based on the elastic properties thereof such that a period of one tensile strained layer and one compressively strained layer exerts substantially no shear force on a neighboring structure, and wherein the number of quantum wells is between 30 and 60.

33. The method of claim 32, wherein the neighboring structure is an underlying layer or another period of one tensile strained layer and one compressively strained layer.

34. The method of claim 32, further comprising the step of selecting the compositions of the quantum wells and barriers using linear elastic theory.

35. The method of claim 32, wherein the step of forming a plurality of alternating layers forms the plurality of alternating layers on a substrate having a substrate lattice constant α

₀, and wherein the alternating tensile strained layers have a lattice constant α

₁, a thickness t₁ and elastic stiffness coefficients C₁₁ and C₁₂, and the alternating compressively strained layers have a lattice constant α

₂, a thickness t₂ and elastic stiffness coefficients C₂₁ and C₂₂, the tensile strained layers and the compressively strained layers having compositions and thicknesses selected to substantially meet the conditions;

36. The method of claim 35, wherein the substrate is InP.

37. The method of claim 35, wherein the substrate comprises GaAs.

38. The method of claim 37, wherein the quantum wells and barriers comprise In_xGa_1-xAs_yP_1-y, where 0≦

x≦

1 and 0≦

y≦

1.

39. The method of claim 32, wherein a period of one quantum well layer and one quantum barrier layer within the plurality of alternating tensile strained layers and compressively strained layers contains at least four different elements and has an average lattice constant substantially matching a lattice constant of a neighboring structure.

40. The method of claim 32, wherein the compressively strained layers are quantum wells.