Photovoltaic device

• US 20080251118A1
• Filed: 03/28/2008
• Published: 10/16/2008
• Est. Priority Date: 07/25/2001
• Status: Active Grant

• Current Assignee: Lumentum Operations, LLC (Lumentum Holdings Inc.)
• Original Assignee: Imperial Innovations Limited (Imperial College London)
• Inventors: Mazzer, Massimo, Rohr, Carsten, Ekins-Daukes, Nicholas, Connolly, James P., Barnham, Keith W.J., Ballard, Iam M.
• Granted Patent: US 7,868,247 B2
• Time in Patent Office: Days
• 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 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 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 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. A photovoltaic device comprising:

an underlying layer; and

a multiple quantum well portion formed of a plurality of quantum wells and a plurality of barriers disposed on the 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, the tensile strained layers and the compressively strained layers having compositions and thicknesses selected taking into account the elastic properties such that each period of one tensile strained layers and one compressively strained layers exerts substantially no shear force on a neighboring structure.

8. The photovoltaic device of claim 7, 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.

9. The photovoltaic device of claim 8, 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.

10. The photovoltaic device of claim 7, wherein the compositions and thicknesses are selected using linear elastic theory.

11. The photovoltaic device of claim 7, wherein the number of quantum wells is from 30 to 60.

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

13. The photovoltaic device of claim 12, 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.

14. The photovoltaic device of claim 12, 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 a Group III/V semiconductor composition with a bandgap higher than if the barrier had a lattice constant equal to the substrate lattice constant.

15. The photovoltaic device of claim 7, 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.

16. The photovoltaic device of claim 13, wherein the substrate is InP and the compressively strained layer is In_xGa_1-xAs, where x>

0.53.

17. The photovoltaic device of claim 14, wherein the substrate is InP and the tensile strained layer is In_xGa_1-xAs_1-yP_y where y>

0.

18. The photovoltaic device of claim 17, wherein y=1 such that the tensile strained layer is GaInP.

19. The photovoltaic device of claim 12, wherein the substrate is InP and the multiple quantum well portion is formed of layers of Al_xGa_1-xAs_ySb_1-y, where 0≦

x≦

1 and 0≦

y≦

1.

20. The photovoltaic device of claim 12, wherein the substrate is GaSb and the multiple quantum well portion is formed of layers of In_xGa_1-xAs_ySb_1-y where 0≦

x≦

1 and 0≦

y≦

1.

21. The photovoltaic device of claim 12, wherein the substrate is GaAs.

22. The photovoltaic device of claim 21, 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 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.

23. The photovoltaic device of claim 22, wherein the substrate is InP and the compressively strained layer is In_xGa_1-xAs, where x is larger than z of In_zGa_1-zAs, which is lattice-matched to the virtual substrate.

24. The photovoltaic device of claim 21, 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 a Group III/V semiconductor composition with a bandgap higher than if the barrier had a lattice constant equal to the substrate lattice constant.

25. The photovoltaic device of claim 21, 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.

26. The photovoltaic device of claim 7, 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.

27. The photovoltaic device of claim 26, wherein the virtual substrate is InP_1-yAs_y, where 0<

y<

1, and the substrate is InP.

28. The photovoltaic device of claim 7, wherein the photovoltaic device is a thermophotovoltaic device.

29. The photovoltaic device of claim 7, wherein the quantum wells have a bandgap substantially equal to or less than 0.73 eV.

30. The photovoltaic device of claim 7, wherein the quantum wells comprise the compressively strained layers.

31. The photovoltaic device of claim 7, wherein the barriers comprises the tensile strained layers.

32-49. -49. (canceled)

50. A photovoltaic device comprising:

a plurality of quantum wells; and

a plurality of barriers, 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 strained layers and the compressively strained layers having compositions such that a period of one tensile strained layer and one compressively strained layer exerts substantially no shear force on a neighboring structure, the number of quantum wells being from 30 to 60.