SEMICONDUCTOR DEVICES FOR LASING APPLICATIONS AND METHODS OF MANUFACTURING SUCH DEVICES

Abstract

A structure having first and second layers is disposed on a substrate. The second layer is disposed on the first layer, is compressively strained, and comprises the alloy including germanium and tin. The structure comprises first and second members spaced a distance from each other along a direction, a strip located between the first and second members and extending along an axis intersecting the direction, and arms connecting the first and second members to a first end of the strip. The first and second members, the strip and the arms comprise respective portions of the first and second layers. A portion of the first layer at the strip and arms is removed such that the strip and arms become suspended and the arms remain anchored to the first layer via the first and second members. Tensile strain is induced in the alloy via the arms. The alloy may perform lasing.

Claims

1. A manufacturing method comprising: providing a structure disposed on a substrate, the structure having first and second layers, wherein the first layer is a sacrificial layer, and wherein the second layer is a compressively strained layer disposed on the first layer, the second layer comprising an alloy including germanium and tin, the structure comprising: first and second members spaced a distance from each other along a direction, a strip located between the first and second members and extending along an axis intersecting said direction, and arms connecting the first and second members to a first end of the strip, wherein the first and second members, the strip and the arms comprise respective portions of the first and second layers; and removing at least a portion of the first layer at the strip and arms such that the strip and arms become suspended and the arms remain anchored to the first layer via the first and second members.

2. The method of claim 1, wherein the removal of at least a portion of the first layer causes at least part of the compressive strain in the second layer of the strip and arms to be released, and wherein the release of compressive strain causes the arms to lengthen and to pull at the first end of the strip such that tensile strain is induced in the strip along said axis.

3. The method of any of the preceding claim 1, wherein providing said structure comprises: providing a substrate on which the first and second layers are disposed; and removing material via etching from at least the second layer to form at least the strip, the arms, and the first and second members in at least the second layer.

4. The method of claim 1, wherein the removal of at least a portion of the first layer is performed via selective etching of the first layer.

5. The method of claim 1, wherein the first layer is a germanium layer or an insulator layer.

6. (canceled)

7. The method of claim 1, wherein the structure further comprises additional arms connecting the first and second members to a second end of the strip, wherein the additional arms comprise respective portions of the first and second layers, the method comprising: removing at least a portion of the first layer at the strip, arms, and additional arms such that the strip, arms, and additional arms become suspended and the arms and the additional arms remain anchored to the first layer via the first and second members.

8. (canceled)

9. The method of claim 1, wherein the structure further comprises: third and fourth members spaced a distance from each other along said direction, the strip being located between the third and fourth members; and additional arms connecting the third and fourth members to a second end of the strip, wherein third and fourth members and the additional arms comprise respective portions of the first and second layers, the method comprising: removing at least a portion of the first layer at the strip, arms, and additional arms such that the strip, arms, and additional arms become suspended, the arms remain anchored to the first layer via the first and second members, and the additional arms remain anchored to the first layer via the third and fourth members.

10. (canceled)

11. The method of claim 1, wherein the structure further comprises an anchoring member connected to a second end of the strip, wherein the anchoring member comprises portions of the first and second layers, the method comprising: removing at least a portion of the first layer at the strip and arms such that the strip and arms become suspended, the strip remains anchored to the first layer via the anchoring member, and the arms remain anchored to the first layer via the first and second members.

12. (canceled)

13. A device comprising a substrate and a structure disposed on the substrate, wherein the structure comprises: first and second members spaced a distance from each other along a direction; a strip located between the first and second members and extending along an axis intersecting said direction; and arms connecting the first and second members to a first end of the strip, wherein the first and second members comprise respective portions of a first layer, wherein the first layer is a sacrificial layer, wherein the first and second members, the strip and the arms comprise respective portions of a second layer, wherein the second layer comprises an alloy including germanium and tin, wherein the portions of the second layer located in the first and second members are disposed on the respective portions of the first layer located in the first and second members, wherein the portions of the second layer located in the first and second members are compressively strained, wherein the strip and arms are suspended above the substrate, and wherein the arms are anchored to the first layer via the first and second members.

14. The device of claim 13, wherein the arms pull at the first end of the strip such that tensile strain is induced in the strip along said axis.

15. The device of claim 13, wherein the substrate is arranged along a plane, and wherein said direction and said axis are both parallel to said plane.

16. The device of claim 13, wherein the structure further comprises: additional arms connecting the first and second members to a second end of the strip, wherein the additional arms comprise respective portions of the second layer, and wherein the additional arms are suspended above the substrate and are anchored to the first layer via the first and second members.

17. The device of claim 13, wherein the structure further comprises: third and fourth members spaced a distance from each other along said direction, wherein the strip is located between the third and fourth members, the third and fourth members comprising respective portions of the first and second layers, wherein the portions of the second layer located in the third and fourth members are disposed on the respective portions of the first layer located in the third and fourth members, and wherein the portions of the second layer located in the third and fourth members are compressively strained; and additional arms connecting the third and fourth members to a second end of the wire, wherein the additional arms comprise respective portions of the second layer, and wherein the additional arms are suspended above the substrate and are anchored to the first layer via the third and fourth members.

18. (canceled)

19. The device of claim 13, wherein the structure further comprises an anchoring member connected to a second end of the strip, wherein the anchoring member comprises portions of the first and second layers, wherein the portion of the second layer located in the anchoring member is disposed on the portion of the first layer located in the anchoring member, wherein the portion of the second layer located in the anchoring member is compressively strained, and wherein the second end of the strip is anchored to the first layer via the anchoring portion.

20. The device of claim 13, wherein: the second layer is at most 400 nm thick; or the second layer comprises a sublayer which is at most 400 nm thick, said sublayer comprising an alloy including germanium and tin.

21. The device of claim 1, wherein the structure occupies an area of less than 50 μm times 50 μm; wherein a distance between the first member and the second member is less than 2 times a length of the strip; or wherein the strip is between 0.1 μm and 10 μm wide.

22. (canceled)

23. (canceled)

24. The device of claim 13, wherein: the second layer has at least 5 atomic percent tin; or the second layer comprises a sublayer which has at least 5 atomic percent tin, said sublayer comprising an alloy including germanium and tin.

25. The device of claim 13, wherein the second layer includes a plurality of sublayers arranged as a stack of sublayers of a first type and sublayers of a second type disposed sequentially on top of each other, wherein the first type of sublayers are germanium sublayers, and wherein the second type of sublayers comprise an alloy including germanium and tin.

26. An infrared laser device comprising the device of claim 13, wherein the strip is arranged to be employed as an infrared light source.

27. A photodetector comprising the device of claim 13, wherein the strip is arranged to be employed as an infrared absorber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In what follows, example embodiments will be described in greater detail with reference to the accompanying drawings, on which:

[0055] FIG. 1 is a perspective view of a structure for inducing tensile strain in a layer comprising an alloy including germanium and tin (Sn), according to an embodiment;

[0056] FIG. 2 is a cross sectional view of the structure in FIG. 1 along the line L;

[0057] FIG. 3 is a perspective view of the structure from FIG. 1, but after removing at least a portion of a first layer, according to an embodiment

[0058] FIG. 4 is a cross sectional view of the structure in FIG. 3 along the line L;

[0059] FIG. 5 is a top view of the structure 100 from FIG. 1 (solid lines) and from FIG. 2 (dashed lines);

[0060] FIGS. 6-8 illustrate a process for obtaining the structure shown in FIGS. 1 and 2, according to an embodiment;

[0061] FIG. 9 is a cross sectional view of an alternative version of the structure from FIG. 1 including a multiple quantum well (MQW), according to an embodiment;

[0062] FIGS. 10-11 illustrate how wafer bonding and etch back may be employed to provide a stack like the one shown in FIG. 6; and

[0063] FIGS. 12-15 are top views of differently shaped structures for inducing tensile strain in a GeSn layer, according to some embodiments.

[0064] All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the respective embodiments, whereas other parts may be omitted or merely suggested.

DETAILED DESCRIPTION

[0065] FIG. 1 is a perspective view of a structure 100 for inducing tensile strain in a layer comprising an alloy including germanium (Ge) and tin (Sn), according to an embodiment. FIG. 2 is a cross sectional view of the structure 100 in FIG. 1 along the line L. The structure 100 is disposed on a substrate 101. The structure 100 comprises a first member 110 and a second member 120 spaced a distance from each other along a direction 102, and a strip 130 located between the first member 110 and the second member 120. The strip 130 extends along an axis 103 intersecting the direction 102. The structure 100 comprises arms 140 and 150 connecting the first member 110 and the second member 120 to a first end 131 of the strip 130, and additional arms 160 and 170 connecting the first member 110 and the second member 120 to a second end 132 of the strip 130. The first and second members 110 and 120, the strip 130, and the arms 140, 150, 160, and 170 comprise respective portions of a first layer 104 and a second layer 105. The first layer 104 is a sacrificial layer disposed on the substrate 101. The second layer 105 is a compressively strained layer disposed on the first layer 104. The second layer 105 comprises an alloy including Ge and Sn.

[0066] FIG. 3 is a perspective view of the structure 100 from FIG. 1, but after removing at least a portion of the first layer 104 at the strip 130 and arms 140, 150, 160, and 170, according to an embodiment. FIG. 4 is a cross sectional view of the structure 100 in FIG. 3 along the line L. The removal of the first layer 104 at the strip 130, and the arms 140, 150, 160, and 170 causes the strip 130, and the arms 140, 150, 160, and 170 to become suspended above the substrate 101, but the arms 140, 150, 160, and 170 remain anchored to the first layer 104 via the first and second members 110 and 120.

[0067] FIG. 5 is a top view of the structure 100. The solid lines show the shape of the structure 100 before the removal of the first layer 104 at the strip 130, and the arms 140, 150, 160, and 170, which corresponds to the shape of the structure 100 in FIG. 1. The dashed lines 500 show how the structure 100 looks after the removal of the first layer 104 at the strip 130, and the arms 140, 150, 160, and 170, and this corresponds to the shape of the structure 100 in FIG. 2. When the first layer 104 is removed below the strip 130 and the arms 140, 150, 160 and 170, the compressive strain in the second layer 105 is released. The release of compressive strain causes the strip 130 and arms 140, 150, 160 and 170 to lengthen. In the present embodiment, the arms 140, 150, 160 and 170 form a circle (or loop) around the strip 130. The release of compressive strain causes the ring to expand. Since the arms 140, 150, 160, 170 are anchored to the first layer via the first and second members 110 and 120, the circle cannot grow in the direction 102, and therefore grows only along the axis 103 so that it becomes oval. The deformation of the circle causes the circle to grow more in the axial direction 103 than the strip 130 would grow by itself when the first layer 104 is removed. Hence, the arms 140, 150, 160 and 170 pull at the ends 131 and 132 of the strip 130 such that tensile strain is induced in the strip 130 along the axis 103.

[0068] The tensile strain induced in the GeSn layer 105 of the strip 130 causes the GeSn to become direct bandgap material, which may for example emit and detect light in the infrared (IR) range. Hence, the direct bandgap tensile strained GeSn may for example be used as infrared IR lasers or sensors in many different applications, from IR cameras for bio and military applications to on-chip light sources for optical data transfer between processor cores. The direct bandgap tensile strained GeSn may for example be a promising candidate for fabrication of IR camera sensors which are expensive and limited today. The structure 100 described above with reference to FIGS. 1-5 may for example be employed to produce tensile strained GeSn which is able to perform lasing at higher temperatures (for example as high as regular room temperature) than the earlier solution described in the background section.

[0069] Previously proposed bandgap group IV semiconductors (such as those mentioned in the background section) are just at the border of the transition between direct bandgap and indirect bandgap, which may be one reason for the low efficiency of light emissions. The structure 100 described above with reference to FIGS. 1-5 may be employed to provide tensile strained GeSn having an energy band gap structure deep in the direct bandgap region. More specifically, the tensile strained GeSn may have more than 0.1 eV difference between direct and indirect bandgap.

[0070] The removal of the first layer 104 at the strip 130 and the arms 140, 150, 160 and 170 may for example be performed by selective etching, which does not, or at least very little in comparison to the first layer, remove the second layer 105, but removes those parts of the first layer 104 that are exposed. Since the first and second portions 110 and 120 are larger (or wider), portions of the first layer 104 remain after the selective etching, while the first layer 104 has been removed completely (or at least sufficiently) at the strip 130, and the arms 140, 150, 160, 170. This is illustrated in FIG. 4 where open space 106 separates the second layer 105 in the strip 130 from the substrate 101, while part of the first layer 104 remains at the first member 110.

[0071] FIGS. 6-8 illustrate a process for obtaining the structure 100 shown in FIGS. 1 and 2, according to an embodiment. FIGS. 6-8 show the layers of the structure 100 from the side (cross-sectional views).

[0072] In the present embodiment, the substrate 101 is a Silicon (Si) wafer, and the first layer 104 is a Ge layer disposed on the substrate 101. The GeSn layer 105 is epitaxially grown on the Ge layer 104, and therefore becomes compressively strained. The Ge layer 104 and the GeSn layer 105 together form a stack 600 of layers. A protective layer 601 is applied on the second layer 105 in the form of a photosensitive resin. A pattern corresponding to the desired structure may then be defined in the protective layer 601 using photolithography, thereby defining which parts to protect during the subsequent etching steps. Etching 602 is then performed to form the first and second members 110 and 120, the strip 130, and the arms 140, 150, 160 and 170 in the first and second layers. Deep reactive-ion etching (DRIE) may for example be employed, using a plasma of chlorine gas to remove material from the GeSn 105. The etching 602 may for example be stopped when it reaches down to the Ge layer 104, or may continue to also remove material from the Ge layer 104.

[0073] Selective etching 603 may then be applied to remove the Ge layer 104 beneath the GeSn layer 105. The selective etching 603 may be designed to more rapidly etch Ge in comparison to GeSn. Ideally, the selective etching 603 may be designed not to remove material from the GeSn layer 105 but some etching might of course occur. Selective etching may for example be obtained using a CF4 gas in a RIE system. As described above with reference to FIG. 4, the first and second members 110 and 120 are wider (or larger) than the strip and the arms such that the selective etching 603 does not remove all of the Ge layer 104 at the first and second members 110 and 120. The strip 130 and the arms 140, 150, 160 and 170 may for example be a couple of μm wide, while the first and second members 110 and 120 may for example be tens of μm wide. In any case, the selective etching 603 causes the second layer 105 in the strip 130, and the arms 140, 150, 160 and 170 to become suspended above the substrate 101.

[0074] Using a Si wafer 101 with a Ge buffer layer 104 and an epitaxially grown GeSn layer 105, as described above withy reference to FIGS. 6-8, is advantageous in comparison to using a Germanium or Germanium on insulator (GOI) wafer, for example, because Si wafers are less expensive and less difficult to manufacture.

[0075] Thus, it will be appreciated that the substrate 101 may comprise other materials than Ge. The substrate 101 may for example be a Si wafer.

[0076] As will be described below with reference to FIGS. 10-11, the first layer 104 may comprise other materials than Ge. The first layer 104 may for example comprise an insulator material such as Si oxide or Al Oxide.

[0077] It will also be appreciated that the second layer 105 may comprise other elements in addition to Ge and Sn. The second layer 105 may for example comprise an alloy including Ge, Sn and Si. The second layer 105 (or portions thereof) may for example be n-doped or p-doped.

[0078] FIG. 9 is a cross sectional view of an alternative version 900 of the structure 100, according to an embodiment. The cross section showed in FIG. 9 is taken along the line L in FIG. 1. In the present embodiment, the second layer 105 includes a plurality of sublayers arranged as a stack of sublayers of a first type 105a and sublayers of a second type 105b disposed sequentially on top of each other. In other words, every second sublayer is of the first type 105a and every second sublayer is of the second type 105b. In the present embodiment, the first type of sublayers 105a are Ge sublayers 105a, and the second type of sublayers 105b are GeSn sublayers 105b. The stack of layers forms a multiple quantum well (MQW). By keeping the GeSn sublayers 105b thin, defects in the crystal structure may be avoided. The GeSn sublayers 105b may for example be 25 nm thick. The Ge sublayers 105a may for example be 25 nm thick.

[0079] To protect the Ge sublayers 105a during the selective etching of the Ge layer 104, the Ge sublayers 105a may for example be protected by an oxide 105c (not shown in FIG. 9). Before the selective etching, the GeSn sublayers 105b are under compressive stress, which is released when the Ge layer 104 is removed via the selective etching. The arms 140, 150, 160, and 170 then pull at the ends of the strip 130 such that tensile strain is induced in the GeSn sublayers 105b in the strip 130.

[0080] FIGS. 10-11 illustrate how wafer bonding and etch back may be employed to provide a stack 200 like the stack 600 described with reference to FIG. 6, but with layers of other materials. FIG. 10 is a side view of two wafers illustrating wafer bonding. A first Si substrate 201 is provided with a Si oxide layer 202. Another Si substrate 203 is provided with a Ge layer 204, a GeSn layer 205, and a Ge oxide layer 206. The GeSn layer 205 has been epitaxially grown on the Ge layer 204 and is therefore compressively strained. The second substrate 203 and its layers 204-206 have been placed over the first substrate 201 and its oxide layer 202 so that the two oxide layers 202 and 206 are in physical contact and the two stacks can be bonded together. FIG. 11 is a side view of the structure shown in FIG. 10 after the second Si substrate 202, and the Ge layer 204 have been removed via etching. Although the Ge layer 204 has been removed, the compressive strain in the GeSn layer 205 is maintained by the Ge oxide 206 layer.

[0081] The GeSn layer 205 and the Ge oxide layer 206 form a stack 200 which may be employed in the same way as the stack 600 described above with reference to FIG. 6. More specifically, the first and second members 110 and 120, the strip 130, and the arms 140, 150, 160 and 170 may be formed by etching the stack 600. The Ge oxide layer 206 may act as a sacrificial layer (in analogy with the first layer 104 described above with reference to FIGS. 1-8) which is selectively etched away to release the compressive strain in the GeSn layer 205 in the strip 130, and arms 140, 150, 160 and 170. The GeSn layer 205 in the strip 130 is then subjected to tensile strain in the same way as the GeSn layer 105 described above with reference to FIGS. 1-8.

[0082] The ring-shaped structure 100 described above with reference to FIGS. 1-5 is merely one of several possible ways to induce tensile strain in an alloy including Ge and Sn. Differently shaped arms may also be designed to pull at the ends of the strip 130 when the compressive strain of the second layer 105 is released. FIGS. 12-15 are top views of differently shaped structures for inducing tensile strain in a GeSn layer, according to some embodiments.

[0083] In FIG. 12, the structure 1200 has straight arms 1240, 1250, 1260 and 1270 forming a diamond shape around the strip 1230. The solid lines show the shape of the structure 1200 before the removal of the first layer 104 at the strip 1230, and the arms 1240, 1250, 1260, and 1270. The dashed lines 1280 show how the structure 1200 looks after the removal of the first layer 104 at the strip 1230, and the arms 1240, 1250, 1260, and 1270. The arms 1240, 1250, 1260, and 1270 bend somewhat when the tensile strain is released, as shown by the dashed lines 1280.

[0084] In the present embodiment, the arms extend diagonally (at an angle of 45 degrees) from the first and second members 1210 and 1220 to the ends of the strip 1230 before the compressive strain in the second layer 105 is released. However, other angles may also be envisaged. Simulations show that an angle of about 45 degrees may be a suitable tradeoff between different factors influencing the amount of tensile strain induced at the strip 1230 (such as bending of the arms, and the ratio between the length of the arms and the length of the strip).

[0085] In FIG. 13, the structure 1300 has curved arms 1340, 1350, 1360 and 1370 forming a reversed (or inverted) ring shape around the strip 1330.

[0086] In FIG. 14, the arms 1440, 1450, 1460, 1470 of the structure 1400 do not form a closed loop around the strip 1430. Instead, two of the arms 1440 and 1450 connect one end of the strip 1430 to first and second members 1410 and 1420, and the other two arms 1460 and 1470 connect the other end of the strip 1430 to third and fourth members 1480 and 1490. The first, second, third and fourth members 1460, 1470, 1480 and 1490 are separate from one to another.

[0087] The structure 1500 shown in FIG. 15 is similar to one half of the structure 1400 described above with reference to FIG. 10. The other half of the structure 1400 has been replaced by an anchoring member 1590 connected to an end of the strip 1530 for anchoring the strip 1530 to the first layer 104. The arms 1540 and 1550 therefore pull at one end of the strip 1530, while the other end of the strip 1530 is held in place by the anchoring member 1590.

[0088] The structures described above with reference to FIGS. 1-15 provide the benefit of inducing strain to the active GeSn layer 105 using a relatively small area of a chip. For example, a circle (such as the one formed by the arms in FIG. 1) of radius 10 μm may be sufficient to provide a 1 μm wide strip (or wire) with 6 μm length.

[0089] The wire 130 described above with reference to FIG. 1-5 may for example be between 0.1 μm and 10 μm wide. The wire 130 may for example be between 1 μm and 50 μm long. The structure 100 may for example fit within a square shaped area of less than 50 μm times 50 μm, for example 20 pm times 20 μm.

[0090] The first layer 104 may for example be between 10 nm and 5 μm thick. The second layer 105 may for example be between 100 nm and 5 μm thick.

[0091] The person skilled in the art realizes that the present invention is by no means limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, it will be appreciated that arms of different shapes than those shown in FIGS. 1-15 may be employed. Additionally, variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.