CN106784181B - Method and structure for improving luminous efficiency of green light or longer wavelength InGaN quantum well - Google Patents

Abstract

The invention discloses a method and a structure for improving the luminous efficiency of a green light or longer wavelength InGaN quantum well. The method comprises the following steps: adopting a substrate with atomic steps, wherein the chamfer angle formed by adjacent atomic steps on the substrate is more than 0.2 degrees; forming a buffer layer on the atomic step surface; forming a high-temperature n-type GaN layer on the buffer layer; an InGaN quantum well is formed on the high temperature n-type GaN layer. The method for improving the light emitting efficiency of the InGaN quantum well by adopting the substrate with the large chamfer angle adopts the substrate with the chamfer angle larger than 0.2 degrees to grow the active region of the green light or longer wavelength InGaN quantum well, can realize the atomic step flow growth of the green light or longer wavelength InGaN quantum well, improve the appearance of the atomic step flow growth, and improve the internal quantum efficiency of the InGaN quantum well. In addition, the InGaN quantum well prepared by the method can be widely applied to GaN-based green light or longer-wavelength LEDs and GaN-based green light or longer-wavelength lasers, and can also be widely applied to multi-quantum well solar cells.

Description

Method and structure for improving luminous efficiency of green light or longer wavelength InGaN quantum wells

technical field

The invention belongs to the technical field of semiconductors, and in particular relates to a method and a structure for improving the luminous efficiency of a green light or longer wavelength InGaN quantum well.

Background technique

GaN-based green or longer wavelength lasers and LEDs are widely used in semiconductor displays and lighting. The InGaN quantum well active region is the core structure of GaN-based lasers and LEDs, and its growth behavior and morphology have a very important impact on the optical properties of InGaN quantum wells and device performance.

Since the equilibrium vapor pressure of InN is very high and the In-N bond energy is weak, the decomposition temperature of InN is low. Therefore, InGaN with high In composition must be grown at low temperature to ensure sufficient In incorporation into the epitaxial layer. Generally, the temperature for growing InGaN by MOCVD is between 650°C and 750°C. But usually at lower growth temperatures, the mobility of surface atoms is low and the migration distance is short. For green light or longer wavelength InGaN quantum wells, since the InGaN quantum well layer has a higher In composition to obtain long-wavelength luminescence, a lower temperature and a higher In/Ga ratio are required when growing by MOCVD. . When epitaxial growth is carried out on a substrate with a small chamfer angle, due to the large width of the atomic step, when the atoms fall on the surface of the sample, they cannot migrate to the position where the edge of the atomic step is suitable for incorporation, but directly on the surface of the atomic step. Nucleation, the AFM morphology of InGaN in this case is generally some two-dimensional island-like morphology distributed along the atomic steps. Regrowing the quantum barrier layer on top of this 2D island morphology will cause the surface roughness between the InGaN quantum well and the quantum barrier layer, which in turn affects the optical properties of the InGaN quantum well active region.

SUMMARY OF THE INVENTION

In order to solve the above-mentioned problems in the prior art, the purpose of the present invention is to provide a method for improving the luminous efficiency of green light or longer wavelength InGaN quantum wells, so as to obtain InGaN quantum wells grown in atomic step flow and with high internal quantum efficiency .

The present invention provides a method for improving the luminous efficiency of green light or longer wavelength InGaN quantum wells, comprising:

Using a substrate with atomic steps, wherein the chamfer angle formed by adjacent atomic steps on the substrate is greater than 0.2°;

forming a buffer layer on the atomic step surface;

forming a high temperature n-type GaN layer on the buffer layer;

InGaN quantum wells are formed on the high temperature n-type GaN layer.

Further, the chamfer angle formed by every two adjacent atomic steps is equal; and/or the chamfer angle formed by adjacent atomic steps on the substrate is 0.2°˜15°.

Further, the buffer layer is a low temperature undoped GaN layer, and the thickness of the low temperature undoped GaN layer is 10 nm˜30 nm.

Further, the thickness of the high temperature n-type GaN layer is less than 5000 nm.

Further, the electron concentration of the high temperature n-type GaN layer is between 10 ¹⁷ cm ^-3 and 10 ¹⁹ cm ^-3 .

Further, the green light or longer wavelength InGaN quantum well is an undoped InxGa1 _{- xN} quantum well.

Further, the thickness of the InxGa1 _{- xN} quantum well is 1 nm˜5 nm, and the In composition of the InxGa1 _{- xN} quantum well increases with the increase of the emission wavelength of the InGaN quantum well.

Further, the InGaN quantum wells formed on each level of atomic steps have an atomic step flow morphology.

Further, the height of the atomic step of the InGaN quantum well is equal to the height of the adjacent one-step higher atomic step.

The present invention also provides a structure for improving the luminous efficiency of green light or longer wavelength InGaN quantum wells by using the above method, comprising: a substrate with atomic steps, and the chamfer angle formed by adjacent atomic steps is greater than 0.2 °; a buffer layer is formed on the atomic step surface; a high temperature n-type GaN layer is formed on the buffer layer; an InGaN quantum well is formed on the high temperature n-type GaN layer.

Beneficial effects of the present invention: the method for improving the luminous efficiency of green light or longer wavelength InGaN quantum wells of the present invention uses a substrate with a chamfer angle greater than 0.2° to grow green light or longer wavelength InGaN quantum well active regions, which can realize green light Atomic step flow growth of optical or longer wavelength InGaN quantum wells, improving their morphology and increasing the internal quantum efficiency of InGaN quantum wells. In addition, the InGaN quantum well prepared by the above method can be widely used not only in GaN-based green light or longer wavelength LEDs, GaN-based green light or longer wavelength lasers, but also in multi-quantum well solar cells.

Description of drawings

The above and other aspects, features and advantages of embodiments of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings, in which:

1 is a flow chart of the steps of a method for improving the luminous efficiency of a green light or longer wavelength InGaN quantum well according to an embodiment of the present invention;

2 is a schematic diagram of the material structure of a green light or longer wavelength InGaN quantum well structure prepared by the method of an embodiment of the present invention;

3 is a perspective view of a green light or longer wavelength InGaN quantum well structure prepared by the method of an embodiment of the present invention;

4 is a schematic diagram of the relationship between the chamfer angle and the atomic step width of a substrate according to an embodiment of the present invention;

Figure 5(a) is an AFM topography of a green light InGaN quantum well formed on a GaN substrate with a chamfer angle of 0.2°;

Figure 5(b) is an AFM topography of a green light InGaN quantum well formed on a GaN substrate with a chamfer angle of 0.54°;

Figure 5(c) is an AFM topography of a green light InGaN quantum well formed on a GaN substrate with a chamfer angle of 0.6°;

Fig. 6(a) is a graph showing the result of a variable temperature PL test of a green light InGaN quantum well formed on a GaN substrate with a chamfer angle of 0.2°;

Fig. 6(b) is a graph showing the result of a variable temperature PL test of a green light InGaN quantum well formed on a GaN substrate with a chamfer angle of 0.56°.

Detailed ways

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the specific embodiments set forth herein. Rather, these embodiments are provided to explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular intended use. The same reference numbers may be used throughout the specification and drawings to refer to the same elements.

In the drawings, the thicknesses of layers and regions are exaggerated for clarity of illustration of components. Furthermore, the same reference numbers may be used throughout the specification and drawings to refer to the same elements.

FIG. 1 is a flow chart of steps of a method for improving the luminous efficiency of a green light or longer wavelength InGaN quantum well according to an embodiment of the present invention.

Referring to FIG. 1, an embodiment of the present invention provides a method for improving the luminous efficiency of a green light or longer wavelength InGaN quantum well, which includes the following steps:

Step S1: using a substrate with atomic steps, wherein the chamfer angle formed by adjacent atomic steps on the substrate is greater than 0.2°;

Step S2: forming a buffer layer on the atomic step surface;

Step S3: forming a high temperature n-type GaN layer on the buffer layer;

Step S4: forming InGaN quantum wells on the high temperature n-type GaN layer.

FIG. 2 is a schematic diagram of the material structure of the InGaN quantum well structure prepared by the method of the embodiment of the present invention. FIG. 3 is a perspective view of an InGaN quantum well structure prepared by the method of an embodiment of the present invention.

Referring to FIGS. 2 and 3 , using the above method, a structure for improving the luminous efficiency of green light or longer wavelength InGaN quantum wells as shown in FIGS. 2 and 3 is prepared, which is referred to as an InGaN quantum well structure here. The InGaN quantum well structure includes a substrate 1 , a buffer layer 2 , a high temperature n-type GaN layer 3 , and an InGaN quantum well 4 . The substrate 1 has atomic steps, and the chamfer angle formed by adjacent atomic steps is greater than 0.2°. The buffer layer 2 is formed on the atomic step surface. The high temperature n-type GaN layer 3 is formed on the buffer layer 2 . InGaN quantum wells 4 are formed on the high temperature n-type GaN layer 3 .

Combined with step S1, the substrate 1 may be a GaN substrate, or a sapphire substrate, a SiC substrate, or a Si substrate. The present invention is not limited to this.

FIG. 4 is a schematic diagram of the relationship between the chamfer angle and the atomic step width of the substrate according to an embodiment of the present invention.

The atomic step width on the surface of the substrate 1 is reduced, and when the high In composition green light or the longer wavelength InGaN quantum well 4 is grown at a low temperature, the atoms can migrate to the edge of the atomic step and be incorporated, and grow in the atomic step flow growth mode to obtain Good surface morphology and crystal quality. As shown in FIG. 4 , FIG. 4 is a schematic diagram showing the relationship between the chamfer angle and the width of the atomic step. Assuming that the slope between two adjacent atomic steps of the substrate 1 is the chamfer angle α, the height of the atomic steps is h, and Lt is the width of the atomic steps, then tanα=h/Lt, that is, Lt=h/tanα. Then, when the atomic step height h is constant, the atomic step width Lt decreases with the increase of the chamfer angle α of the substrate 1 . In this embodiment, the slope between two adjacent atomic steps is greater than 0.2°, that is, the substrate 1 with the chamfer angle α greater than 0.2° is used to grow high In composition green light or longer wavelength InGaN quantum wells 4 . When the chamfer angle α of the substrate 1 is larger, the width of the atomic steps on the surface is smaller, and the atoms can migrate to the edge of the atomic steps and merge into the atomic steps during growth at low temperature, forming the growth mode of atomic step flow. Further, the chamfer angle α formed by the adjacent atomic steps can be greater than 0.2° and less than 15°. For green light InGaN quantum wells, it is preferably 0.4° to 0.7°, and for longer wavelength InGaN quantum wells, the optimal chamfer angle is larger, the present invention is not limited thereto.

Preferably, in this embodiment, the atomic steps are regularly increasing steps. The chamfer angle α formed by every two adjacent atomic steps is equal.

Combining steps S2, S3 and S4, the growth method of the buffer layer 2, the high temperature n-type GaN layer 3 and the InGaN quantum well 4 can be MOCVD or MBE. MOCVD refers to a new type of vapor phase epitaxy growth technology developed on the basis of vapor phase epitaxy (VPE). MBE refers to a crystal growth technique of molecular beam epitaxy. However, the present invention is not limited to this.

Specifically, in combination with step S2, the buffer layer 2 is formed on the atomic step surface of the substrate 1, and the buffer layer 2 is specifically a low-temperature undoped GaN layer. Specifically, the thickness of the low-temperature undoped GaN layer is 10 nm˜30 nm.

Combined with step S3, a high temperature n-type GaN layer 3 is formed on the buffer layer 2, the thickness of which is less than 5000 nm, and the electron concentration is between 10 ¹⁷ cm ^-3 and 10 ¹⁹ cm ^-3 .

In this embodiment, the low-temperature undoped GaN layer (buffer layer 2 ) and the high-temperature n-type GaN layer 3 are sequentially formed on the upper surface of the atomic step, that is, the surface with the atomic step width Lt (as shown in FIG. 4 ) superior.

Combined with step S4, the InGaN quantum well 4 is an undoped InxGa1 _{- xN} quantum well. The thickness of the In _x Ga _1-x N quantum well is between 1 nm and 5 nm, and its In composition increases with the increase of the emission wavelength of the InGaN quantum well. For example, the In composition in the InGaN quantum well with the emission wavelength of 520 nm is approximately 25%, and the In composition in the InGaN quantum wells with longer emission wavelengths is also higher.

It can be seen from FIG. 3 that the InGaN quantum wells 4 on each atomic step have an atomic step flow shape, and the InGaN quantum wells 4 on each atomic step are exactly filled with the atomic steps. In other words, the InGaN quantum wells 4 are distributed on the outer edge of the horizontal step plane of the atomic step. More specifically, the InGaN quantum well 4 is flush with the upper surface of its adjacent high-level atomic steps, or they are located at the same height (same level).

According to the method for improving the luminous efficiency of an InGaN quantum well by using a substrate with a large chamfer angle according to an embodiment of the present invention, a substrate 1 with a large chamfer angle is used to sequentially grow the buffer layer 2, the high-temperature n-type GaN layer 3, and the InGaN quantum well 4, Since the width of the atomic steps of the substrate 1 is narrow, when the green light or longer wavelength InGaN quantum wells 4 are grown at a specific temperature and a specific growth rate, the migration distance of the atoms is certain. When the width of the atomic steps is narrow, the atoms have a larger The probability migrates to the edge of the atomic step and merges into the atomic step, thus forming the atomic step flow growth mode. It is found that the InGaN quantum well 4 in the atomic step flow growth mode of the embodiment of the present invention has a higher internal quantum efficiency by measuring the internal quantum efficiency of the variable temperature PL.

FIG. 5( a ) is an AFM topography diagram of an InGaN quantum well 4 formed on a GaN substrate with a chamfer angle of 0.2°. Figure 5(b) is an AFM topography of an InGaN quantum well formed on a GaN substrate with a chamfer angle of 0.54°. Figure 5(c) is an AFM topography of an InGaN quantum well formed on a GaN substrate with a chamfer angle of 0.6°.

It should be noted that the green light InGaN quantum well was used in this test. From the AFM topography test results in Figures 5(a) to 5(c), it can be seen that the surface topography of the green light InGaN quantum well 4 grown on the substrate 1 with a small chamfer angle is a two-dimensional distribution along the atomic steps. Viy island morphology, and the atomic step width is large. The surface morphology of the green light InGaN quantum well 4 grown on the substrate 1 with a larger chamfer angle is an atomic step flow morphology, and the atomic step width is small.

FIG. 6( a ) is a graph showing the result of a variable temperature PL test of an InGaN quantum well formed on a GaN substrate with a chamfer angle of 0.2°. Fig. 6(b) is a graph showing the result of a variable temperature PL test of a green light InGaN quantum well formed on a GaN substrate with a chamfer angle of 0.56°. Among them, the abscissa represents the value of 1000 divided by the temperature, and the ordinate represents the PL integral intensity.

6(a) and 6(b), it can be seen that when the chamfer angle increases from 0.2° to 0.56°, the internal quantum efficiency (IQE) of the green InGaN quantum well 4 increases from 0.67% to 3.5%. Therefore, using the substrate 1 with the chamfer angle greater than 0.2° to grow the green light InGaN quantum well 4 can effectively improve the internal quantum efficiency of the green light InGaN quantum well 4 .

To sum up, according to the embodiments of the present invention, using a substrate with a chamfer angle greater than 0.2° to grow green light or longer wavelength InGaN quantum well active regions can realize the atomic steps of green light or longer wavelength InGaN quantum wells flow growth, improve its morphology, and increase the internal quantum efficiency of InGaN quantum wells. In addition, the InGaN quantum well prepared by the above method can be widely used not only in GaN-based green light or longer wavelength LEDs, GaN-based green light or longer wavelength lasers, but also in multi-quantum well solar cells.

While the invention has been shown and described with reference to specific embodiments, those skilled in the art will appreciate that forms and Various changes in details.

Claims (10)

1. a method of improving green light or longer wavelength InGaN quantum well luminous efficiency, is characterized in that, comprises: A substrate with atomic steps is used, and the chamfer angle formed by adjacent atomic steps on the substrate is 0.2-0.7°; forming a buffer layer on the atomic step surface; forming a high temperature n-type GaN layer on the buffer layer; forming an InGaN quantum well on the high temperature n-type GaN layer; Wherein, the emission wavelength of the InGaN quantum well is not less than 520 nm, the In composition of the InGaN quantum well is not less than 25%, and the growth method for forming the InGaN quantum well on the high temperature n-type GaN layer is MOCVD. 2 . The method for improving the luminous efficiency of green light or longer wavelength InGaN quantum wells according to claim 1 , wherein the chamfer angles formed by every two adjacent atomic steps are equal. 3 . 3. The method for improving the luminous efficiency of green light or longer wavelength InGaN quantum wells according to claim 1, wherein the buffer layer is a low temperature undoped GaN layer, and the thickness of the low temperature undoped GaN layer is It is 10nm～30nm. 4 . The method for improving the luminous efficiency of green light or longer wavelength InGaN quantum wells according to claim 1 , wherein the thickness of the high temperature n-type GaN layer is less than 5000 nm. 5 . 5. The method for improving the luminous efficiency of green light or longer wavelength InGaN quantum wells according to claim 1, wherein the electron concentration of the high temperature n-type GaN layer is 10 ¹⁷ cm ^-3 to 10 ¹⁹ cm ^-3 between. 6. The method for improving the luminous efficiency of green light or longer wavelength InGaN quantum wells according to claim 1, wherein the InGaN quantum wells are undoped InxGa1 _{- xN} quantum wells. 7 . The method for improving the luminous efficiency of green light or longer wavelength InGaN quantum wells according to claim 6 , wherein the InxGa1 _{- xN} quantum well has a thickness of 1 nm to 5 nm, and the In The In composition of the xGa1 _{- xN} quantum well increases with the increase of the emission wavelength of the InGaN quantum well. 8. The method for improving the luminous efficiency of green light or longer wavelength InGaN quantum wells according to any one of claims 1 to 7, wherein the InGaN quantum wells formed on each level of atomic steps are in atomic step flow morphology . 9. The method for improving the luminous efficiency of green light or longer wavelength InGaN quantum wells according to any one of claims 1 to 7, wherein the height of the InGaN quantum wells is the same as the height of an adjacent higher atomic step equal. 10. A structure for improving the luminous efficiency of green light or longer wavelength InGaN quantum wells using the method according to any one of claims 1 to 9, characterized in that, comprising: A substrate with atomic steps, and the chamfer angle formed by adjacent atomic steps is greater than 0.2°; a buffer layer, formed on the atomic step surface; a high temperature n-type GaN layer formed on the buffer layer; InGaN quantum wells are formed on the high temperature n-type GaN layer.

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