Semiconductor thin film structure, and electronic device including the same

Abstract

To provide a semiconductor thin-film structure, and an electronic element including the same.SOLUTION: In a semiconductor thin-film structure, a unit layer including a first layer with a first bandgap energy and first thickness, a second layer with a second bandgap energy and second thickness, and a third layer with a third bandgap energy and third thickness is repeatedly stacked a plurality of times. In the unit layer, one of the first layer, the second layer, and the third layer with the lowest bandgap energy includes a buffer layer disposed between the other two layers and a semiconductor layer formed on the buffer layer. Thus, by using the buffer layer, a semiconductor layer formed on a heterogeneous substrate has high thin-film quality.SELECTED DRAWING: Figure 1B

Description

Technical Field

[0001] The present invention relates to a semiconductor thin film structure and an electronic device including the same.

Background Art

[0002] Recently, systems using high power have increased, and the development of electronic devices using nitride semiconductors has been actively carried out. A pure nitride semiconductor substrate is small in size and expensive, and it is common to grow a nitride semiconductor on a heterogeneous substrate such as a sapphire, silicon carbide (SiC), or silicon (Si) substrate and fabricate an element on top of it.

[0003] When growing a nitride semiconductor on a heterogeneous substrate, there are problems such as defects due to a mismatch in lattice constant and warping or cracking due to a mismatch in the coefficient of thermal expansion (CTE).

[0004] Therefore, various methods have been explored to grow a nitride semiconductor to a thickness of several μm or more while minimizing defects and cracks due to differences in lattice constant and coefficient of thermal expansion between the heterogeneous substrate and the nitride semiconductor.

Summary of the Invention

Problems to be Solved by the Invention

[0005] The problem to be solved by the present invention is to provide a semiconductor thin film structure having a semiconductor layer of good quality. The problem to be solved by the present invention is also to provide an electronic device including the semiconductor thin film structure.

Means for Solving the Problems

[0006] According to one type, a semiconductor thin film structure is provided, which includes a substrate; a unit layer formed on the substrate, the unit layer including a first layer having a first bandgap energy and a first thickness, a second layer having a second bandgap energy and a second thickness, and a third layer having a third bandgap energy and a third thickness, the unit layer being repeatedly stacked a plurality of times, in the unit layer, a buffer layer in which the layer having the lowest bandgap energy among the first layer, the second layer, and the third layer is disposed between the remaining two layers; and a semiconductor layer formed on the buffer layer.

[0007] The unit layer is also arranged in the order of the first layer, the second layer, and the third layer along a first direction from the substrate toward the semiconductor layer.

[0008] The second thickness is thinner than the first thickness and the third thickness. The first layer is also a layer for adjusting the warp of the substrate.

[0009] The first bandgap energy is larger than the second bandgap energy and smaller than the third bandgap energy.

[0010] The first thickness is thicker than the second thickness and the third thickness. The sum of the first thickness and the second thickness is also in the range of 2 to 15 times the third thickness.

[0011] The sum of the first thickness and the second thickness is also in the range of 4 to 9 times the third thickness. The third layer is also a layer for suppressing the current flow in the first direction within the buffer layer.

[0012] The difference between the second bandgap energy and the third bandgap energy is also at least twice the difference between the second bandgap energy and the first bandgap energy.

[0013] The first layer is Al w Ga (1-w)It consists of N(0 < w ≤ 0.5). The second layer is Al y Ga (1-y) It consists of N(0 ≤ y ≤ 0.1, y < w).

[0014] The third layer is Al x Ga (1-x) It consists of N(w < x ≤ 1). The third layer is Al x Ga (1-x) It consists of N(0.7 ≤ x ≤ 1).

[0015] The unit layer may be disposed on the third layer and further include a fourth layer having a fourth bandgap energy with a distribution that changes from the third bandgap energy to the first bandgap energy.

[0016] The fourth layer is Al z Ga (1-z) It consists of N, and z has different values depending on the position in the first direction, and the average value z(average) of the z values can satisfy the condition of y < w < z(average) < x.

[0017] The unit layer may be disposed between the second layer and the third layer and further include a fifth layer having a fifth bandgap energy with a distribution that changes from the second bandgap energy to the third bandgap energy.

[0018] The fifth layer is Al v Ga (1-v) It consists of N, and v has different values along the first direction, and the average value v(average) of the v values can satisfy the condition of y < w < v(average) < x.

[0019] The second layer consists of In y Ga (1-y) It consists of N(0 ≤ y ≤ 0.2), and the third layer also consists of AlN.

[0020] The first layer is also made of GaN. In this case, the second layer is made of InGaN, and the third layer is also made of AlN.

[0021] The first layer, the second layer, and the third layer each contain Al, In, Ga, and N, and are also made of quaternary nitrides with different composition ratios.

[0022] Going in the direction from the buffer layer towards the semiconductor layer, the average value of the bandgap energy of the layers included in each of the plurality of unit layers also becomes smaller.

[0023] According to one type, there is provided an electronic device including any one of the semiconductor thin film structures described above, a source electrode and a drain electrode that are respectively in contact with both sides of the semiconductor layer and are formed so as to be separated from each other, and a gate electrode formed on the semiconductor layer.

[0024] The electronic device may further include a depletion layer formed between the semiconductor layer and the gate electrode. The depletion layer is also p-GaN.

[0025] According to one type, there is provided a buffer structure including at least one unit layer including a first layer having a first bandgap energy and a first thickness, a second layer having a second bandgap energy and a second thickness, and a third layer having a third bandgap energy and a third thickness, and in the first layer, the second layer, and the third layer, the layer having the lowest bandgap energy is disposed between the remaining two layers.

Advantages of the Invention

[0026] The semiconductor thin film structure described above includes a buffer layer having a structure capable of reducing the stress between the heterogeneous substrate and the semiconductor layer, and can provide a semiconductor layer of good quality.

[0027] The semiconductor thin film structure described above is also applicable to various electronic devices such as power devices and light-emitting devices.

Brief Description of the Drawings

[0028]

Figure 1A

Figure 1B

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Figure 2B

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Figure 3B

Figure 4A

Figure 4B

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Figure 16

DETAILED DESCRIPTION OF THE INVENTION

[0029] Hereinafter, with reference to the accompanying drawings, this embodiment will be described in detail. The described embodiments are merely exemplary, and various modifications are possible from such embodiments. In the following drawings, the same reference numerals refer to the same components, and on the drawings, the size of each component may be exaggerated for clarity and convenience of explanation.

[0030] In the following, those described as "upper" or "above" may include not only those in direct contact and directly above but also those not in contact and above.

[0031] Terms such as first and second are used in the description of various components, but are used only for the purpose of distinguishing one component from another. Such terms do not limit that the substances or structures of the components are different.

[0032] Singular expressions include plural expressions unless the context clearly indicates otherwise. Also, when a part includes a certain component, it means that, unless there is a special contrary description, it does not exclude other components and may further include other components.

[0033] Also, terms such as “… part” and “module” described in the specification mean a unit that processes at least one function or operation, which may be embodied by hardware or software, or may also be embodied by a combination of hardware and software.

[0034] The use of the term “the foregoing” and similar directive terms applies to both singular and plural.

[0035] If there is no clear mention that the steps constituting the method must be performed in the described order, they may also be performed in an appropriate order. Also, the use of all exemplary terms (e.g., such as) is merely for the purpose of explaining the technical idea in detail, and unless limited by the claims, the scope of rights is not limited by such terms.

[0036] FIG. 1A is a cross-sectional view showing a schematic structure of a semiconductor thin film structure according to the present embodiment, and FIG. 1B is a drawing showing both a detailed structure in which a part of the buffer layer provided in the semiconductor thin film structure of FIG. 1A is enlarged and a change in band gap energy in the thickness direction.

[0037] The semiconductor thin film structure 1000 includes a substrate 100, a buffer layer 200 formed on the substrate 100, and a semiconductor layer 300 formed on the buffer layer 200. A nucleation layer 120 may be disposed between the substrate 100 and the buffer layer 200.

[0038] The semiconductor layer 300 is an active layer used in various electronic devices and may include a III-V compound semiconductor. The semiconductor layer 300 is also a nitride semiconductor. That is, one or more of the group III elements are selected from Al, Ga, and In, and the group V element is N. Although the semiconductor layer 300 is illustrated as a single layer, this is an example for convenience, and it may also be composed of a plurality of layers. The semiconductor layer 300 is also an undoped layer or a layer doped with a predetermined conductive carrier. Some of the plurality of layers constituting the semiconductor layer 300 are doped with an n-type dopant, and some other parts are doped with a p-type dopant. The plurality of layers constituting the semiconductor layer 300 may include layers doped with the same type of conductive carrier at different concentrations.

[0039] The substrate 100 is also a heterogeneous substrate different from the semiconductor layer 300. For example, when the semiconductor layer 300 is a III-V compound semiconductor, the substrate 100 may be a substrate made of sapphire, silicon carbide (SiC), or silicon (Si).

[0040] The buffer layer 200 is introduced to alleviate the occurrence of defects, cracks, stress, etc. due to the lattice constant mismatch and the thermal expansion coefficient mismatch between the substrate 100 and the semiconductor layer 300, and to realize a semiconductor layer 300 of good quality.

[0041] For example, if a GaN thin film is directly grown on a silicon substrate, due to the difference in the thermal expansion coefficients between GaN and Si, during cooling, thermal tensile stress is generated in the GaN layer, resulting in warping of the substrate. Further, if the thermal tensile stress exceeds the critical point, cracks will occur. Also, defects due to the difference in lattice constants may occur.

[0042] To mitigate such a phenomenon, the semiconductor thin film structure 1000 according to the present embodiment includes a buffer layer 200 having a superlattice structure in which a plurality of unit layers UL having different bandgap energies are repeatedly arranged between a substrate 100 and a semiconductor layer 300.

[0043] The nucleation layer 120 is formed between the substrate 100 and the buffer layer 200, and can prevent the melt-back phenomenon caused by the reaction between the nitride semiconductor material contained in the buffer layer 200 and the substrate 100, and enable the buffer layer 200 to be grown later to be well wetting. The nucleation layer 120 is also made of AlN. At the initial stage of the growth stage of the nucleation layer 120, an Al source is first injected, thereby preventing the substrate 100 from being first exposed to ammonia and nitrided. The nucleation layer 120 can have a thickness ranging from several tens of nm to several hundreds of nm. The nucleation layer 120 is formed, for example, to have a thickness in the range of about 50 nm to 300 nm.

[0044] Also, between the nucleation layer 120 and the buffer layer 200, an additional Al x Ga (1-x) N (0 <x <1) layer (not shown) may be further formed.

[0045] The unit layer UL constituting the buffer layer 200 includes a first layer 201, a second layer 202, and a third layer 203. The first layer 201 has a first thickness t1 and a first bandgap energy E1, the second layer 202 has a second thickness t2 and a second bandgap energy E2, and the third layer 203 has a third thickness t3 and a third bandgap energy E3.

[0046] The thicknesses t1, t2, t3 and the band gap energies E1, E2, E3 are set to control the stress applied to the semiconductor layer 300 formed on top of the buffer layer 200 and also to suppress current.

[0047] In the first layer 201, the second layer 202, and the third layer 203 that constitute the unit layer UL, the layer with the lowest band gap energy is disposed between the remaining two layers. For example, when arranged in the order of the first layer 201, the second layer 202, and the third layer 203 in the direction from the substrate 100 toward the semiconductor layer 300, the band gap energy E2 of the second layer 202 is the lowest. Also, the thickness t2 of the second layer 202 with the lowest band gap energy is thinner than the thickness t1 of the first layer 201 and the thickness t3 of the third layer 203.

[0048] If the significance of each layer constituting the unit layer UL is described in detail, it is as follows. The third layer 203 is a layer for suppressing the current flow in the thickness direction of the buffer layer 200 due to the band gap energy difference with the adjacent layer. The band gap energy E3 of the third layer 203 is greater than the first band gap energy E1 and the second band gap energy E2.

[0049] The first layer 201 is a layer for adjusting the warp of the substrate 100. The band gap energy E1 of the first layer 201 is smaller than the band gap energy E3 of the third layer 203. Also, the thickness t1 of the first layer 201 is thicker than the thickness t2 of the second layer 202 and the thickness t3 of the third layer 203.

[0050] The second layer 202 can have the lowest band gap energy E2 in order to maximize the role of the third layer 203, that is, the effect of suppressing the current flow. Also, its thickness t2 is thinner than the thickness of the first layer 201 and the thickness of the third layer 203 in order to minimize the influence on the warp of the substrate 100.

[0051] The sum of the thickness t1 of the first layer 201 and the thickness t2 of the second layer 202 is also in the range of 2 to 15 times the thickness t3 of the third layer 203. The range of the thickness sum (t1 + t2) is, for example, also in the range of 4 to 9 times the thickness t3 of the third layer 203.

[0052] The difference between the band gap energy E3 of the third layer 203 and the band gap energy E2 of the second layer 202 is greater than the band gap energy E1 of the first layer 201. The difference between the band gap energy E3 of the third layer 203 and the band gap energy E2 of the second layer 202 is greater than the difference between the band gap energy E2 of the second layer 202 and the band gap energy E1 of the first layer 201. The difference between the band gap energy E3 of the third layer 203 and the band gap energy E2 of the second layer 202 is also more than twice the difference between the band gap energy E2 of the second layer 202 and the band gap energy E1 of the first layer 201.

[0053] The band gap energies and thicknesses of the first layer 201, the second layer 202, and the third layer 203 are also expressed by the following relative relationships.

[0054] [Table 1]

[0055] That is, the band gap energies E1, E2, E3 and the thicknesses t1, t2, t3 of the first layer 201, the second layer 202, and the third layer 203 can have the relationship of E3 > E1 > E2, t1 > t3 > t2.

[0056] The above relationship is derived from the requirement that when forming unit layers of three or more layers, the layer with the lowest band gap energy is the thinnest and the layer with the intermediate band gap energy is the thickest, but it is not limited thereto. Most of the embodiments described below satisfy it, but some embodiments do not satisfy all the presented requirements simultaneously.

[0057] As described above, the structure of the repeated unit layer UL is named as the first layer 201, the second layer 202, and the third layer 203 in the direction order from the substrate 100 side to the semiconductor layer 300 side. However, the stacking order on the substrate 100 does not necessarily start from the first layer 201.

[0058] To satisfy the above relationships, the unit layer UL can be composed of various layer combinations.

[0059] The first layer 201 can also be AlGaN, and its thickness is also in the range of 10 - 70 nm. The composition range of Al can also be 0 - 50%.

[0060] The second layer 202 can also be GaN, and its thickness is also in the range of 1 - 20 nm. The second layer 202 can also be AlGaN, in which case the composition ratio of Al is also 0 - 10%. The second layer 202 can also be InGaN, in which case the composition ratio of In is also 0 - 20%.

[0061] The third layer 203 can also be AlN, and its thickness is also in the range of 2 - 15 nm. The third layer 203 can also be AlGaN, in which case the composition ratio of Al is also 70 - 100%.

[0062] FIG. 2A is a cross-sectional view showing a schematic structure of a semiconductor thin film structure according to the present embodiment, and FIG. 2B is a drawing showing both the detailed structure of a part of the buffer layer provided in the semiconductor thin film structure of FIG. 2A and the change in bandgap energy in the thickness direction.

[0063] The semiconductor thin film structure 1001 includes a substrate 100, a buffer layer 210, and a semiconductor layer 300. A nucleation layer 120 may be disposed between the substrate 100 and the buffer layer 210. The buffer layer 210 includes unit layers UL1 stacked repeatedly a plurality of times.

[0064] The unit layer UL1 constituting the buffer layer 210 includes a first layer 201, a second layer 202, and a third layer 203. The first layer 201 has a first thickness t1 and a first bandgap energy E1, the second layer 202 has a second thickness t2 and a second bandgap energy E2, and the third layer 203 has a third thickness t3 and a third bandgap energy E3.

[0065] The unit layer UL1 of the present embodiment further includes a fourth layer 204 disposed on the third layer 203 and having a fourth thickness t4 and a fourth bandgap energy E4.

[0066] The fourth bandgap energy E4 has a distribution that changes from the third bandgap energy E3 to the first bandgap energy E1 along the thickness direction within the fourth layer 204. In the drawing, it is illustrated as a linear and continuous distribution, but that is exemplary. For example, the fourth bandgap energy E4 can have a non-linear changing distribution from the third bandgap energy E3 to the first bandgap energy E1. Or, the fourth bandgap energy E4 can have a discontinuous changing distribution from the third bandgap energy E3 to the first bandgap energy E1. For example, it can have a stepped changing distribution. Or, the fourth bandgap energy E4 can also have a distribution in which a continuous distribution (linear or non-linear) and a discontinuous distribution such as a stepped shape are mixed as the distribution changing from the third bandgap energy E3 to the first bandgap energy E1.

[0067] The thickness t4 of the fourth layer 204 is also in the range of 2 nm to 25 nm. The fourth layer 204 is, for example, Al z Ga (1-z) N and z can have different values depending on the position in the thickness direction.

[0068] FIG. 3A is a cross-sectional view showing a schematic structure of a semiconductor thin film structure according to the present embodiment, and FIG. 3B is a drawing showing both a detailed structure of a part of the buffer layer provided in the semiconductor thin film structure of FIG. 3A and a change in bandgap energy in the thickness direction.

[0069] The semiconductor thin film structure 1002 includes a substrate 100, a buffer layer 220, and a semiconductor layer 300. A nucleation layer 120 may be disposed between the substrate 100 and the buffer layer 220. The buffer layer 220 includes unit layers UL2 stacked repeatedly a plurality of times.

[0070] The unit layer UL2 constituting the buffer layer 220 includes a first layer 201, a second layer 202, and a third layer 203. The first layer 201 has a first thickness t1 and a first bandgap energy E1, the second layer 202 has a second thickness t2 and a second bandgap energy E2, and the third layer 203 has a third thickness t3 and a third bandgap energy E3.

[0071] The unit layer UL2 of the present embodiment further includes a fifth layer 205 disposed between the second layer 202 and the third layer 203 and having a fifth thickness t5 and a fifth bandgap energy E5.

[0072] The fifth bandgap energy E5 has a distribution within the fifth layer 205 along the thickness direction, changing from the second bandgap energy E2 to the third bandgap energy E3. In the drawings, it is illustrated as a linear and continuous distribution, but that is exemplary. For example, the fifth bandgap energy E5 can have a non-linear distribution changing from the second bandgap energy E2 to the third bandgap energy E3. Or, the fifth bandgap energy E5 can have a discontinuous distribution changing from the second bandgap energy E2 to the third bandgap energy E3. For example, it can have a stepped distribution. Or, the fifth bandgap energy E5 can also have a distribution in which a continuous distribution (linear or non-linear) and a discontinuous distribution such as a stepped shape are mixed as the distribution changing from the second bandgap energy E2 to the third bandgap energy E3.

[0073] The range of the thickness t5 of the fifth layer 205 is also in the range of 2 nm to 25 nm. The fifth layer 205 can be composed of Al v Ga (1-v) N, but v can have different values depending on the position in the thickness direction.

[0074] FIG. 4A is a cross-sectional view showing a schematic structure of the semiconductor thin film structure according to the present embodiment, and FIG. 4B is a drawing showing both the detailed structure of a part of the buffer layer provided in the semiconductor thin film structure of FIG. 4A and the change in the bandgap energy in the thickness direction.

[0075] The semiconductor thin film structure 1003 includes a substrate 100, a buffer layer 230, and a semiconductor layer 300. A nucleation layer 120 may be disposed between the substrate 100 and the buffer layer 230. The buffer layer 230 includes unit layers UL3 laminated repeatedly a plurality of times.

[0076] The unit layer UL3 that constitutes the buffer layer 230 includes a first layer 201, a second layer 202, and a third layer 203. The first layer 201 has a first thickness t1 and a first bandgap energy E1, the second layer 202 has a second thickness t2 and a second bandgap energy E2, and the third layer 203 has a third thickness t3 and a third bandgap energy E3.

[0077] The unit layer UL3 of the present embodiment further includes a fifth layer 205 that is disposed between the second layer 202 and the third layer 203 and has a fifth thickness t5 and a fifth bandgap energy E5, and a fourth layer 204 that is disposed on the third layer 203 and has a fourth thickness t4 and a fourth bandgap energy E4.

[0078] The bandgap energies and thicknesses of the fourth layer 204 and the fifth layer 205 can have energy distributions and thickness ranges as described in FIGS. 2B and 3B, respectively.

[0079] A buffer layer (e.g., buffer layers 200, 210, 220, 230 and buffer layer 250 (FIG. 13)) according to any exemplary embodiment described herein can exist independently of the semiconductor layer 300 and / or the substrate 100 and / or the nucleation layer 120. In such an exemplary embodiment, a buffer layer according to any exemplary embodiment is also referred to as a "buffer layer structure" and is also a thin film structure that does not include a semiconductor layer and / or a substrate and / or a nucleation layer. A buffer layer (e.g., buffer layers 200, 210, 220, 230 and buffer layer 250 (FIG. 13)) according to any exemplary embodiment described herein may include a plurality of unit layers, or a single individual unit layer, where the single individual unit layer includes any exemplary embodiment of the unit layer described in the present application.

[0080] FIGS. 5 to 12 are cross-sectional views showing specific examples related to unit layers applicable to the buffer layer provided in the semiconductor thin film structure according to the present embodiment.

[0081] In the following description, a nitride semiconductor material is exemplified to explain the composition of each layer, but it is not limited thereto, and various III-V compound semiconductor materials satisfying the above-described bandgap energy relationship may be employed between adjacent layers.

[0082] Referring to FIG. 5, the first layer 201 is made of AlGaN, the second layer 202 is made of GaN, and the third layer 203 is also made of AlN.

[0083] Referring to FIG. 6, the first layer 201 is made of Al w Ga (1-w) N (0 < w ≦ 0.5), the second layer 202 is made of Al y Ga (1-y) N (0 ≦ y ≦ 0.1, y < w), and the third layer is made of Al x Ga (1-x) N (w < x ≦ 1). Alternatively, the third layer is made of Al x Ga (1-x) N (0.7 ≦ x ≦ 1).

[0084] The first layer 201, the second layer 202, and the third layer 203 are made of a ternary system including Al, Ga, and N, and each composition ratio is set based on the relationship between the above-described bandgap energies. In each layer, the composition ratios w, y, and x of Al have a relationship of x > w > y.

[0085] Referring to FIG. 7, the first layer 201 is made of AlGaN, the second layer 202 is made of In y Ga (1-y) N (0 ≦ y ≦ 0.2), and the third layer 203 is also made of AlN. The Al composition ratio of the first layer 201 is also 0.5 or less.

[0086] Referring to FIG. 8, the first layer 201 is made of GaN, the second layer 202 is made of InGaN, and the third layer 203 is also made of AlN. The In composition ratio of the second layer 202 is also 0.2 or less.

[0087] Referring to FIG. 9, the first layer 201, the second layer 202, and the third layer 203 may also be formed of a quaternary system including Al, In, Ga, and N.

[0088] The first layer 201 consists of Al w In c Ga (1-w-c) and N, the second layer 202 consists of Al y In b Ga (1-y-b) and N, and the third layer 203 may consist of Al x In a Ga (1-x-a) and N. In the range of 0 ≦ x, y, w, a, b, c ≦ 1, the numerical values indicating the composition ratios may also be determined according to the band gap energy requirements of each layer.

[0089] Referring to FIG. 10, the unit layer is composed of four layers, including three layers with band gap energies E1, E2, E3 respectively, and a layer with a distribution where the band gap energy changes from E3 to E1. The first layer 201 consists of Al w Ga (1-w) and N (0 < w ≦ 0.5), the second layer 202 consists of Al y Ga (1-y) and N (0 < y ≦ 0.1, y < w), and the third layer may consist of Al x Ga (1-x) and N (w < x ≦ 1). The third layer may consist of Al x Ga (1-x) and N (0.7 ≦ x ≦ 1). The fourth layer 204, with a distribution where the band gap energy changes from E3 to E1, may consist of Al z Ga (1-z) and N, and is disposed on the third layer 203.

[0090] The first layer 201, the second layer 202, the third layer 203, and the fourth layer 204 are composed of a ternary system including Al, Ga, and N, and each composition ratio is set according to the relationship between the aforementioned band gap energies. That is, the relationship of E3 > E1 > E2, and the composition ratio is determined so that the band gap energy of the fourth layer 204 satisfies the distribution changing from E3 to E1.

[0091] In the first layer 201, the second layer 202, and the third layer 203, the composition ratios w, y, x of Al have the relationship of y < w < x. The Al composition ratio z of the fourth layer 204 can have different values depending on the position in the thickness direction. The average value z(average) of the z values can satisfy the condition of y < w < z(average) < x.

[0092] Referring to FIG. 11, the unit layer is composed of four layers including three layers with band gap energies E1, E2, E3 respectively, and a layer with a distribution where the band gap energy changes from E2 to E3. The first layer 201 is composed of Al w Ga (1-w) N (0 < w ≤ 0.5), the second layer 202 is composed of Al y Ga (1-y) N (0 < y ≤ 0.1, y < w), the third layer is composed of Al x Ga (1-x) N (w < x ≤ 1). The third layer is also composed of Al x Ga (1-x) N (0.7 ≤ x ≤ 1). The fifth layer 205, which has a distribution where the band gap energy changes from E2 to E3, is also composed of Al v Ga (1-v) N and is disposed between the second layer 202 and the third layer 203.

[0093] In the first layer 201, the second layer 202, and the third layer 203, the composition ratios w, y, x of Al have the relationship of y < w < x. The Al composition ratio v of the fourth layer 204 can have different values depending on the position in the thickness direction. The average value v(average) of the v values can satisfy the condition of y < w < v(average) < x.

[0094] Referring to FIG. 12, the unit layer is composed of five layers including three layers with band gap energies E1, E2, E3 respectively, a layer with a distribution where the band gap energy changes from E2 to E3, and a layer with a distribution where the band gap energy changes from E3 to E1.

[0095] They are arranged in the order of the first layer 201, the second layer 202, the fifth layer 205, the third layer 203, and the fourth layer 204. The composition ratio of each layer is determined from the relationship between the band gap energies as described above, as shown in FIGS. 10 and 11.

[0096] FIG. 13 is a cross-sectional view showing a schematic structure of the semiconductor thin film structure according to the present embodiment. The semiconductor thin film structure 1005 includes a substrate 100, a buffer layer 250, and a semiconductor layer 300. A nucleation layer 120 may be disposed between the substrate 100 and the buffer layer 250. The buffer layer 250 includes unit layers U 1 ,…,U k ,…U N .

[0097] The unit layer U k (1 ≦ k ≦ N) is also any one of the unit layers UL, UL1, UL2, UL3 of the above-mentioned layer. The average band gap energy Ea_U k included in the unit layer U k (1 ≦ k ≦ N) can satisfy the following conditions. Ea_U 1 ≧ Ea_U 2 ≧…Ea_U k …≧ Ea_U N-1 ≧ Ea_U N

[0098] That is, the average band gap energy decreases as it goes in the direction from the substrate 100 to the semiconductor layer 300. Such a transition can be gradual or have a stepped form by section.

[0099] In order to have such an average band gap energy distribution, the average Al composition ratio included in each unit layer U k (1 ≦ k ≦ N) also becomes lower as it goes in the direction from the substrate 100 to the semiconductor layer 300.

[0100] The unit layer U k (1 ≦ k ≦ N) are all of the same type. The unit layer U k(1 ≦ k ≦ N) can also be in the form of, for example, the unit layer UL illustrated in FIG. 1B, or can have the same type as any one of the unit layer UL1 illustrated in FIG. 2B, the unit layer UL2 illustrated in FIG. 3B, and the unit layer UL3 illustrated in FIG. 4B. However, it is not limited thereto, and as long as the above-described average bandgap energy condition is satisfied, the unit layer U at one position in the buffer layer 250 i and the unit layer U at a different position j can also have different unit layer forms from each other.

[0101] The semiconductor thin film structure according to the above-described embodiment can also be manufactured by using a metal-organic chemical vapor deposition (MOCVD) process, a physical vapor deposition (PVD) process, an atomic layer deposition (ALD) process, or the like.

[0102] For example, when using the MOCVD process, trimethylgallium (TMG) can be used as the raw material for Ga, trimethylaluminum (TMA) can be used as the raw material for Al, trimethylindium (TMI) can be used as the raw material for In, and ammonia (NH 3 ) can be used as the raw material for nitrogen, and N 2 gas and H 2 gas can be used as the carrier gas. By adjusting the amount of each raw material, each layer can be manufactured with a desired composition ratio.

[0103] The above-described semiconductor thin film structure can have a semiconductor layer of good quality by utilizing the buffer layer, and by utilizing it, various electronic elements can be realized. For example, the above-described electronic elements may include a MOS field effect transistor (MOSFET), a high electron mobility transistor (HEMT), or a diode. Moreover, the above-described electronic elements may include a light emitting element.

[0104] FIG. 14 is a cross-sectional view showing a schematic structure of an electronic device according to the present embodiment. The electronic device 2000 includes a substrate 2100, a buffer layer 2200, and a semiconductor layer 2300. A gate electrode G is disposed on the semiconductor layer 2300, and a source electrode S and a drain electrode D are disposed so as to be in contact with both sides of the semiconductor layer 2300 and separated from each other. A nucleation layer 2150 may be disposed between the substrate 2100 and the buffer layer 2200.

[0105] The substrate 2100 is also a sapphire, silicon (Si), or silicon carbide (SiC) substrate. The substrate 2100 is also any other substrate different from the semiconductor layer 2300.

[0106] The buffer layer 2200 relieves deficiencies due to differences in lattice constant and thermal expansion coefficient between the semiconductor layer 2300 and the substrate 2100, and is also a buffer layer according to the various embodiments described above.

[0107] A nucleation layer 2150 may be disposed between the substrate 2100 and the buffer layer 2200. The nucleation layer 2150 is also made of AlN. Further, an Al x Ga (1-x) N (0 <x <1) layer (not shown) may be further formed between the nucleation layer 2150 and the buffer layer 2200.

[0108] The semiconductor layer 2300 may include a first semiconductor layer 2310 and a second semiconductor layer 2320. The first semiconductor layer 2310 may include a III-V semiconductor. For example, the first semiconductor layer 2310 may include GaN, InN, GaAs, or the like. The first semiconductor layer 2310 is also an undoped layer or a layer doped with a predetermined impurity.

[0109] The second semiconductor layer 2320 is formed on the first semiconductor layer 2310 and is formed of a material capable of inducing a two-dimensional electron gas layer (2DEG) within the first semiconductor layer 2310. The second semiconductor layer 2320 may include a III-V semiconductor. For example, the second semiconductor layer 2320 may include AlGaN, AlInN, AlGaAs, etc. Such AlGaN, AlInN, and AlGaAs, etc., can induce a two-dimensional electron gas layer in the first semiconductor layer 2310 because they have a larger polarization rate than the first semiconductor layer 2310. When the first semiconductor layer 2310 is a GaN layer, the second semiconductor layer 2320 is also an AlGaN layer or an AlInN layer. When the first semiconductor layer 2310 is an InN layer, the second semiconductor layer 2320 is also an AlInN layer. When the first semiconductor layer 2310 is a GaAs layer, the second semiconductor layer 2320 is also an AlGaAs layer. However, the materials of the first semiconductor layer 2310 and the second semiconductor layer 2320 presented here are exemplary and can be varied in various ways. For example, the second semiconductor layer 2320 can also have a multilayer structure including a plurality of different material layers.

[0110] The two-dimensional electron gas layer formed in the first semiconductor layer 2310 by the second semiconductor layer 2320 can have a high electron concentration. Also, by performing a heat treatment process on the first semiconductor layer 2310, the electron concentration of the two-dimensional electron gas layer formed in the first semiconductor layer 2310 can be further increased.

[0111] The electronic device in FIG. 14 illustrates the basic structure of a high electron mobility transistor (HEMT) used as a power device, and this structure can be variously modified. For example, a gate insulating layer (not shown) or a depletion layer (not shown) may be further provided between the gate electrode G and the second semiconductor layer 2320. Also, after recessing the portion of the second semiconductor layer 2320 where the gate electrode G is formed to a predetermined depth to form a recess region (not shown), the gate electrode G can be formed in the recess region. In that case, the characteristics of the two-dimensional electron gas layer corresponding to the recess region can be changed, and the characteristics of the high electron mobility transistor can be adjusted. In addition, within the range where the source electrode S and the drain electrode D are horizontally arranged, various structures can be deformed.

[0112] FIG. 15 is a cross-sectional view showing a schematic structure of an electronic device according to another embodiment. The electronic device 2001 of this embodiment is an enhanced mode high electron mobility transistor utilizing p-GaN, and is different from the electronic device 2000 in FIG. 13 in that it further includes a depletion layer 2330 between the second semiconductor layer 2320 and the gate electrode G.

[0113] The depletion layer 2330 is also a semiconductor layer doped with p-type impurities. The depletion layer 2330 is also p-type GaN. Mg can be used as the p-type impurity.

[0114] Since the above-described electronic device utilizes a buffer layer that can ensure the quality of the semiconductor layer, it can exhibit good electrical performance. FIG. 16 illustrates a schematic diagram of an electronic device 1600 including the above-described semiconductor thin film structure according to a partially exemplary embodiment.

[0115] As shown in the figure, the electronic device 1600 includes one or more electronic device components including a processor (e.g., a processing circuit) 1620 and a memory 1630 that are communicatively connected to each other via a bus 1610.

[0116] The processing circuit 1620 may include hardware including logic circuits, one or more instances of processing circuits such as a hardware / software combination such as a processor that executes software, or a combination thereof. For example, the processing circuit 2320 may include, but is not limited to, a CPU (central processing unit), an AP (application processor), an ALU (arithmetic logic unit), a GPU (graphics processing unit), a digital signal processor, a microcomputer, an FPGA (field programmable gate array), a SoC (system-on-chip) programmable logic unit, a microprocessor, or an ASIC (application-specific integrated circuit). The memory 1630 may include a non-transitory computer-readable storage device, for example, a solid-state drive (SSD) that stores an instruction program, and the instruction processing circuit 1620 is also configured to execute the instruction program and implement the functions of the electronic device 1600.

[0117] In some exemplary embodiments, the electronic device 1600 may include one or more additional elements 1640 coupled to the bus 1610, and may include, for example, a power supply, an optical sensor, a light-emitting device, or any combination thereof. In some exemplary embodiments, one or more of the processing circuit 1620, the memory 1630, or one or more of the additional elements 1640 may include any of the semiconductor thin film structures described above. Therefore, the electronic device 1600 including such a processing circuit 1620, memory 1630, or one or more additional elements 1640 can have semiconductor layers of good quality due to stress reduction between semiconductor layers, with improved electrical characteristics and enhanced performance and / or reliability.

[0118] The foregoing semiconductor thin film structure and the electronic device including the same have been described with reference to the embodiments illustrated in the drawings, but they are merely exemplary, and those skilled in the art will understand that various modifications and other equivalent embodiments are possible therefrom. In the foregoing description, many matters have been specifically described, but they should be construed as examples of specific embodiments rather than limiting the scope of the invention. The scope of the present invention is therefore defined not by the described embodiments but by the technical idea described in the claims.

Explanation of Signs

[0119] 100, 2100 Substrate 120, 2150 Nucleation layer 200, 210, 220, 230, 250, 2200 Buffer layer 201 First layer 202 Second layer 203 Third layer 204 Fourth layer 205 Fifth layer 300, 2300 Semiconductor layer 1000, 1001, 1002, 1003, 1005 Semiconductor thin film structure 2000 Electronic device

Claims

1. A substrate, which is formed on the substrate, includes a first layer having a first bandgap energy and a first thickness, a second layer having a second bandgap energy and a second thickness, and a third layer having a third bandgap energy and a third thickness. A plurality of unit layers are repeatedly stacked. In the unit layer, the layer with the lowest bandgap energy among the first layer, the second layer, and the third layer is a buffer layer disposed between the remaining two layers, a semiconductor layer formed on the buffer layer, wherein the unit layer is arranged in the order of the first layer, the second layer, and the third layer along a first direction from the substrate toward the semiconductor layer, and the second thickness is thinner than the first thickness and the third thickness, a semiconductor thin film structure.

2. The semiconductor thin film structure according to claim 1, wherein the first layer is a layer for adjusting the warp of the substrate.

3. The semiconductor thin film structure according to claim 1, wherein the first bandgap energy is larger than the second bandgap energy and smaller than the third bandgap energy.

4. The semiconductor thin film structure according to claim 1, wherein the first thickness is thicker than the second thickness and the third thickness.

5. The semiconductor thin film structure according to claim 1, wherein the sum of the first thickness and the second thickness is in the range of 2 to 15 times the third thickness.

6. The semiconductor thin film structure according to claim 5, wherein the sum of the first thickness and the second thickness is in the range of 4 to 9 times the third thickness.

7. The semiconductor thin film structure according to claim 1, wherein the third layer is a layer for suppressing the current flow in the first direction within the buffer layer.

8. The difference between the second bandgap energy and the third bandgap energy is not less than twice the difference between the second bandgap energy and the first bandgap energy, the semiconductor thin film structure according to claim 1.

9. The first layer is Al ｗ G （１－ｗ） 2. The semiconductor thin film structure of claim 1, wherein w is N, 0<w≦0.

5.

10. The second layer is Al ｙ Ga （１－ｙ） N (0 < y ≤ 0.1, y < w), the semiconductor thin film structure according to claim 9.

11. The third layer is Al ｘ Ga （１－ｘ） N (where w < x ≦ 1), the semiconductor thin film structure according to claim 10.

12. The third layer is Al ｘ Ga （１－ｘ） N (0.7 ≤ x ≤ 1), the semiconductor thin film structure according to claim 11.

13. The unit layer further includes a fourth layer disposed on the third layer and having a fourth bandgap energy with a distribution changing from the third bandgap energy to the first bandgap energy, the semiconductor thin film structure according to claim 11.

14. The unit layer The fourth layer is Al ｚ Ga （１－ｚ） composed of N, z has different values depending on the position in the first direction, and the average value z(average) of the z values satisfies the condition of y < w < z(average) < x. The semiconductor thin film structure according to claim 13.

15. The unit layer The semiconductor thin film structure according to claim 11, further comprising a fifth layer disposed between the second layer and the third layer and having a fifth band gap energy with a distribution changing from the second band gap energy to the third band gap energy.

16. The unit layer is The fifth layer is Al ｖ Ga （１－ｖ） composed of N, where v has different values along the first direction, and the average value v (average) of the v values satisfies the condition of y < w < v (average) < x. The semiconductor thin film structure according to claim 15.

17. The second layer is composed of In ｙ Ga （１－ｙ） N (0 ≤ y ≤ 0.2). The semiconductor thin film structure according to claim 9, wherein the third layer is made of AlN.

18. The semiconductor thin film structure according to claim 1, wherein the first layer is made of GaN.

19. The second layer is made of InGaN, The semiconductor thin film structure according to claim 18, wherein the third layer is made of AlN.

20. The unit layer is The semiconductor thin film structure according to claim 1, further comprising a fourth layer disposed on the third layer and having a fourth band gap energy with a distribution changing from the third band gap energy to the first band gap energy.

21. The unit layer is The semiconductor thin film structure according to claim 1, further comprising a fifth layer disposed between the second layer and the third layer and having a fifth band gap energy with a distribution changing from the second band gap energy to the third band gap energy.

22. The semiconductor thin film structure according to claim 1, wherein the first layer, the second layer, and the third layer each comprise Al, In, Ga, and N and are made of quaternary nitrides having different composition ratios.

23. A substrate, A unit layer formed on the substrate and including a first layer having a first band gap energy and a first thickness, a second layer having a second band gap energy and a second thickness, and a third layer having a third band gap energy and a third thickness is repeatedly laminated a plurality of times. In the unit layer, in the first layer, the second layer, and the third layer, the layer having the lowest band gap energy is a buffer layer disposed between the remaining two layers, A semiconductor layer formed on the buffer layer, A semiconductor thin film structure in which the average value of the band gap energies of the layers included in each of the plurality of unit layers decreases in the direction from the buffer layer to the semiconductor layer.

24. The semiconductor thin film structure according to any one of claims 1 to 23, A source electrode and a drain electrode that are respectively in contact with both sides of the semiconductor layer and are formed so as to be separated from each other, A gate electrode formed on the semiconductor layer, and an electronic device.

25. The electronic device according to claim 24, further comprising a depletion layer formed between the semiconductor layer and the gate electrode.

26. The electronic device according to claim 25, wherein the depletion layer is p-GaN.

27. Comprising at least one unit layer including a first layer having a first bandgap energy and a first thickness, a second layer having a second bandgap energy and a second thickness, and a third layer having a third bandgap energy and a third thickness, arranged in the order of the first layer, the second layer, and the third layer, and the layer having the lowest bandgap energy is arranged between the remaining two layers, The buffer structure in which the second thickness is thinner than the first thickness and the third thickness.

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