An AlN thin film with improved luminescence efficiency and its preparation method

Abstract

This invention discloses an AlN thin film with improved luminous efficiency and its preparation method. The preparation method includes the following steps: taking a non-polar or semi-polar sapphire substrate, growing a first AlN template layer on the sapphire substrate; subjecting the first AlN template layer to positive pressure annealing to recrystallize the first AlN template layer and form an AlN recrystallized layer; growing a second AlN template layer on the AlN recrystallized layer to obtain an AlN thin film with improved luminous efficiency. This invention, by appropriately controlling the positive pressure annealing treatment between the two AlN template layers to achieve AlN recrystallization, combined with a non-polar or semi-polar sapphire substrate, improves the Al mobility during AlN thin film growth and reduces dislocations and stacking faults, thereby improving the quality of the AlN thin film and simultaneously enhancing the photoelectric conversion efficiency of the corresponding deep ultraviolet LED epitaxial wafer.

Description

Technical Field

[0001] This invention relates to the field of semiconductors, and in particular to an AlN thin film with improved luminescence efficiency and its preparation method. Background Technology

[0002] Most current ultraviolet LEDs use sapphire with a polarized C-plane (i.e., (0001) plane) as the substrate. AlGaN materials exhibit strong spontaneous polarization in the c-direction and piezoelectric polarization from the underlying AlN, resulting in a strong built-in electric field within the thin film (specifically at the active layer quantum well). This generates the quantum confined Stark effect, and the polarization field significantly alters the band structure of the heterojunction. The polarization field in the quantum well causes electrons and holes to be spatially separated within the injected well, hindering their injection into the quantum well. This leads to an increase in the operating voltage of the ultraviolet LED, a decrease in luminous efficiency, and a redshift—a drawback of existing ultraviolet LEDs.

[0003] AlGaN films grown on some non-C-plane sapphire substrates (such as R-plane or M-plane) are nonpolar or semi-polar, which can mitigate the negative effects caused by polarization fields in light-emitting devices. While nonpolar or semi-polar materials have certain advantages, they also exhibit high dislocation densities after growth on nonpolar or semi-polar sapphire substrates. Furthermore, nonpolar and semi-polar materials are prone to stacking faults, a condition rarely observed when using polar surfaces. Consequently, AlGaN films prepared on non-C-plane sapphire substrates do not possess the same film quality as those prepared on C-plane sapphire substrates. This limits the growth of high-quality AlGaN films on nonpolar or semi-polar sapphire substrates. Therefore, a new preparation method is needed to address the shortcomings of existing technologies. Summary of the Invention

[0004] The purpose of this invention is to provide an AlN thin film with improved luminescence efficiency and its preparation method, thereby solving the problem that it is difficult to grow high-quality AlGaN thin films on non-polar or semi-polar sapphire substrates in the prior art.

[0005] To solve the above-mentioned technical problems, the first solution provided by the present invention is: a method for preparing an AlN thin film with improved luminous efficiency, comprising the following steps: taking a non-polar or semi-polar sapphire substrate, growing a first AlN template layer on the sapphire substrate; subjecting the first AlN template layer to positive pressure annealing to recrystallize the first AlN template layer and form an AlN recrystallized layer; growing a second AlN template layer on the AlN recrystallized layer to obtain an AlN thin film with improved luminous efficiency.

[0006] Preferably, the first AlN template layer and the second AlN template layer are grown using metal-organic chemical vapor deposition or hydride vapor phase epitaxy.

[0007] The specific process of positive pressure annealing is as follows: the first AlN template layer is placed in a high-temperature furnace and evacuated to a pressure below 0.1 mbar; argon and ammonia are introduced, with a volume ratio of argon to ammonia of 100:1 to 1000:1, and the total gas flow pressure is gradually increased to the annealing pressure; the annealing pressure is maintained, the temperature is raised to 1500℃ to 1900℃, and annealing is performed for a duration of 600 to 1800 seconds. After annealing, the temperature is allowed to cool naturally to room temperature.

[0008] Preferably, in the positive pressure annealing step, the ammonia gas introduction rate is 0.5 to 5 L / min.

[0009] Preferably, in the positive pressure annealing step, the annealing pressure is 1000–5000 mbar.

[0010] Preferably, in the positive pressure annealing step, the heating rate is 1 to 2 °C / s.

[0011] Preferably, the growth surface of the sapphire substrate is any one of the a-plane, r-plane, or m-plane.

[0012] Preferably, the thickness of the first AlN template layer is 10–500 nm; the thickness of the second AlN template layer is 500–5000 nm; and the growth temperature of the second AlN template layer is 1200–1400 °C.

[0013] To solve the above-mentioned technical problems, the second solution provided by the present invention is: an AlN thin film with the function of improving luminous efficiency, which is prepared by the preparation method of the AlN thin film with the function of improving luminous efficiency in the first solution.

[0014] To solve the above-mentioned technical problems, the third solution provided by the present invention is: a deep ultraviolet LED epitaxial wafer, comprising an AlN thin film with the function of improving luminous efficiency as described in the second solution above, an n-type AlGaN layer, a quantum well active layer, an electron blocking layer, and a p-type AlGaN layer; the n-type AlGaN layer, the quantum well active layer, the electron blocking layer, and the p-type AlGaN layer are sequentially stacked on a second AlN template layer.

[0015] The beneficial effects of this invention are as follows: Unlike the prior art, this invention provides an AlN thin film with improved luminous efficiency and its preparation method. By performing appropriate positive pressure annealing between two AlN template layers, AlN is recrystallized. Combined with a non-polar or semi-polar sapphire substrate, the mobility of Al during the growth of the AlN thin film is improved, and dislocations and stacking faults are reduced, thereby improving the quality of the AlN thin film. At the same time, the photoelectric conversion efficiency of the corresponding deep ultraviolet LED epitaxial wafer is also improved. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of an embodiment of the AlN thin film with the function of improving luminous efficiency in this invention;

[0017] Figure 2 This is a schematic diagram of the structure of one embodiment of the deep ultraviolet LED epitaxial wafer in this invention;

[0018] Figure 3 These are optical microscope images of the AlN thin films prepared in Example 1 and Comparative Example 7 of the present invention: a is Example 1, and b is Comparative Example 7. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] The preparation effect of the AlN thin film with the function of improving luminescence efficiency in this invention is characterized and analyzed below through specific embodiments and comparative examples.

[0021] Example 1

[0022] The specific preparation steps of the AlN thin film with improved luminescence efficiency in this embodiment are as follows:

[0023] (1) Take a sapphire substrate with the M side and grow a first AlN template layer with a thickness of 200nm on the sapphire substrate;

[0024] (2) The first AlN template layer is subjected to positive pressure annealing. The first AlN template layer is placed in a high-temperature furnace and evacuated to a pressure below 0.1 mbar. Argon and ammonia are introduced with a volume ratio of 500:1. The total gas pressure is gradually increased to the annealing pressure of 3000 mbar. The annealing pressure is maintained and the temperature is increased to 1800℃ at a heating rate of 2℃ / s. Annealing is carried out for 1200s to allow the first AlN template layer to recrystallize and form an AlN recrystallized layer. After annealing, the temperature is naturally cooled to room temperature.

[0025] (3) A second AlN template layer with a thickness of 2000 nm is grown on the AlN recrystallized layer. During the growth of the second AlN template layer, the ammonia flow rate is 1 L / min and the growth temperature is 1350℃, so as to obtain an AlN film with the function of improving luminescence efficiency.

[0026] Based on the prepared AlN thin film with improved luminous efficiency, epitaxial growth was continued to prepare a deep ultraviolet LED epitaxial wafer. The specific steps are as follows:

[0027] (4) An n-type AlGaN layer with an Al composition percentage of 70% and a thickness of 1000 nm is grown on the second AlN template layer at 1100℃.

[0028] (5) Cool down to 1050℃ and grow a quantum well active layer on the n-type AlGaN layer. The barrier has an Al composition percentage of 60% and a thickness of 10nm; the well has an Al composition percentage of 45% and a thickness of 2nm.

[0029] (6) Cool down to 1000℃ and grow an electron blocking layer on the active layer of the quantum well with an Al composition percentage of 75% and a thickness of 30nm.

[0030] (7) Cool down to 900℃ and grow a p-type AlGaN layer on the electron blocking layer. The Al composition is 40% and the thickness is 30nm. The dopant is Mg with a doping concentration of 1E18~5E20cm. -3 Deep ultraviolet LED epitaxial wafers were prepared.

[0031] Example 2

[0032] This embodiment is based on the preparation steps of Example 1, except that the annealing temperature in step (2) is adjusted to 1600℃, and other preparation conditions are kept the same as in Example 1, so as to obtain the corresponding AlN film and deep ultraviolet LED epitaxial wafer.

[0033] Example 3

[0034] This embodiment is based on the preparation steps of Example 1, except that the annealing duration in step (2) is adjusted to 900s, and the other preparation conditions are kept the same as in Example 1, so as to obtain the corresponding AlN film and deep ultraviolet LED epitaxial wafer.

[0035] Example 4

[0036] This embodiment is based on the preparation steps of Example 1, except that the argon-ammonia volume ratio in step (2) is adjusted to 200:1, and other preparation conditions are kept the same as in Example 1, so as to obtain the corresponding AlN film and deep ultraviolet LED epitaxial wafer.

[0037] Example 5

[0038] This embodiment is based on the preparation steps of Example 1, except that the sapphire substrate in step (1) is adjusted to an r-plane sapphire, and the other preparation conditions are kept the same as in Example 1, so as to obtain the corresponding AlN thin film and deep ultraviolet LED epitaxial wafer.

[0039] Comparative Example 1

[0040] This comparative example is based on the preparation steps of Example 1, except that the annealing temperature in step (2) is adjusted to 1400℃, and other preparation conditions are kept the same as in Example 1, so as to obtain the corresponding AlN film and deep ultraviolet LED epitaxial wafer.

[0041] Comparative Example 2

[0042] This comparative example is based on the preparation steps of Example 1, except that the annealing temperature in step (2) is adjusted to 1950℃, and other preparation conditions are kept the same as in Example 1, so as to obtain the corresponding AlN film and deep ultraviolet LED epitaxial wafer.

[0043] Comparative Example 3

[0044] This comparative example is based on the preparation steps of Example 1, except that the annealing duration in step (2) is adjusted to 500s, and other preparation conditions are kept the same as in Example 1, so as to obtain the corresponding AlN film and deep ultraviolet LED epitaxial wafer.

[0045] Comparative Example 4

[0046] This comparative example is based on the preparation steps of Example 1, except that the annealing duration in step (2) is adjusted to 2000s, and other preparation conditions are kept the same as in Example 1, so as to obtain the corresponding AlN film and deep ultraviolet LED epitaxial wafer.

[0047] Comparative Example 5

[0048] This comparative example is based on the preparation steps of Example 1, except that the argon-ammonia volume ratio in step (2) is adjusted to 50:1, and other preparation conditions are kept the same as in Example 1, so as to obtain the corresponding AlN film and deep ultraviolet LED epitaxial wafer.

[0049] Comparative Example 6

[0050] This comparative example is based on the preparation steps of Example 1, except that the argon-ammonia volume ratio in step (2) is adjusted to 2000:1, and other preparation conditions are kept the same as in Example 1, so as to obtain the corresponding AlN film and deep ultraviolet LED epitaxial wafer.

[0051] Comparative Example 7

[0052] This comparative example is based on the preparation steps of Example 1, except that the positive pressure annealing step in step (2) is removed. The second AlN template layer is grown directly after the first AlN template layer is grown. Other preparation conditions are the same as in Example 1, and the corresponding AlN film and deep ultraviolet LED epitaxial wafer are obtained.

[0053] Comparative Example 8

[0054] In this comparative example, the traditional c-plane sapphire substrate growth process is used. Based on the preparation steps of Example 1, the sapphire substrate in step (1) is adjusted to c-plane sapphire, and the positive pressure annealing step in step (2) is removed. The second AlN template layer is grown directly after the first AlN template layer is grown. Other preparation conditions are the same as in Example 1, and the corresponding AlN thin film and deep ultraviolet LED epitaxial wafer are obtained.

[0055] Specifically, the process parameter adjustments of Examples 1-5 and Comparative Examples 1-7 were statistically analyzed, and the results are shown in Table 1.

[0056] Table 1

[0057]

[0058]

[0059] The AlN films prepared in Examples 1-5 and Comparative Examples 1-7 were subjected to XRD tests, and the photoelectric properties of the prepared deep ultraviolet LED epitaxial wafers were tested and statistically analyzed. The results are shown in Table 2.

[0060] Table 2

[0061]

[0062] The comparison of test data in Table 2 shows that:

[0063] 1) Comparing the test results of Examples 1, 2, 3, Comparative Examples 1, 2, 3, and 4 in Table 2, it can be seen that in the positive pressure annealing step, the annealing temperature and annealing time need to be controlled within a suitable range to obtain AlN films of good quality, while also improving the photoelectric conversion efficiency (WPE) of the deep ultraviolet LED epitaxial wafer. Excessive annealing temperature or annealing time leads to AlN decomposition, while insufficient annealing temperature or annealing time results in inadequate recrystallization, thus significantly reducing both the AlN crystal quality and the photoelectric conversion efficiency of the epitaxial wafer. Therefore, it is evident that specific limits need to be placed on the annealing temperature and annealing time during the aforementioned preparation process to obtain better results.

[0064] 2) Comparing the test results of Examples 1, 4, 5 and 6 in Table 2, it can be seen that the volume ratio of argon to ammonia needs to be controlled within a suitable range in the positive pressure annealing step. A certain amount of ammonia is introduced to prevent AlN decomposition at high temperature. If the proportion of ammonia is too low, AlN will decompose, while if the proportion of ammonia is too high, the quality of AlN film will be reduced.

[0065] 3) Compare the test results of Examples 1, 5, 7, and 8 in Table 2, and combine them with... Figure 3 It can be seen that in Comparative Example 7, when a non-polar or semi-polar sapphire substrate was used but no annealing treatment was performed, the morphology of the prepared AlN film was very poor, and the photoelectric conversion efficiency was far lower than that of Example 1. In Comparative Example 8, when a c-plane sapphire substrate was used but no annealing treatment was performed, the growth quality and photoelectric conversion efficiency of the AlN film also did not reach the level of Example 1. This proves that using a non-polar or semi-polar sapphire substrate and performing the aforementioned annealing treatment can significantly improve the quality of the AlN film and the photoelectric conversion efficiency of the epitaxial wafer.

[0066] Unlike existing technologies, this invention provides an AlN thin film with improved luminous efficiency and its preparation method. By appropriately controlling the positive pressure annealing process between two AlN template layers, AlN is recrystallized. Combined with a non-polar or semi-polar sapphire substrate, this improves the mobility of Al during AlN film growth and reduces dislocations and stacking faults, thereby enhancing the quality of the AlN thin film and simultaneously improving the photoelectric conversion efficiency of the corresponding deep-ultraviolet LED epitaxial wafer. Due to the elimination of the quantum confinement Stark effect, the forward voltage is also significantly reduced.

[0067] It should be noted that all the above embodiments belong to the same inventive concept, and the descriptions of each embodiment have different focuses. Where the description in a particular embodiment is not detailed, please refer to the description in other embodiments.

[0068] The embodiments described above are merely illustrative of implementation methods of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing an AlN thin film with improved luminescence efficiency, characterized in that, Includes the following steps: A nonpolar or semipolar sapphire substrate is taken, and a first AlN template layer is grown on the sapphire substrate; the growth surface of the sapphire substrate is any one of the a-plane, r-plane, or m-plane; The first AlN template layer is subjected to positive pressure annealing to recrystallize the first AlN template layer and form an AlN recrystallized layer; A second AlN template layer is grown on the AlN recrystallized layer to obtain an AlN thin film with improved luminescence efficiency. The first AlN template layer and the second AlN template layer are grown using metal-organic chemical vapor deposition or hydride vapor phase epitaxy. The specific process of the positive pressure annealing is as follows: The first AlN template layer was placed in a high-temperature furnace and evacuated to a pressure below 0.1 mbar. Argon and ammonia are introduced, with a volume ratio of argon to ammonia of 100:1 to 1000:1, and the total gas pressure is gradually increased to the annealing pressure. Maintain the annealing pressure, raise the temperature to 1500℃~1900℃, and anneal for 600~1800 s. After annealing, allow the temperature to cool naturally to room temperature.

2. The method for preparing an AlN thin film with improved luminescence efficiency according to claim 1, characterized in that, The thickness of the first AlN template layer is 10~500 nm.

3. The method for preparing the AlN thin film with improved luminescence efficiency according to claim 1, characterized in that, In the positive pressure annealing step, the total gas flow rate of argon and ammonia is 1~20 L / min.

4. The method for preparing an AlN thin film with improved luminescence efficiency according to claim 1, characterized in that, In the positive pressure annealing step, the annealing pressure is 1000~5000 mbar and the heating rate is 1~2 ℃ / s.

5. The method for preparing an AlN thin film with improved luminescence efficiency according to claim 1, characterized in that, In the second AlN template layer growth step, the thickness of the second AlN template layer is 500~5000 nm, the growth temperature of the second AlN template layer is 1200~1400 ℃, and the ammonia gas introduction rate is 0.5~5 L / min.

6. An AlN thin film with the function of improving luminous efficiency, characterized in that, The AlN thin film with improved luminous efficiency is prepared by any of the preparation methods of AlN thin films with improved luminous efficiency as described in claims 1 to 5.

7. A deep ultraviolet LED epitaxial wafer, characterized in that, Includes the AlN thin film with improved luminescence efficiency, n-type AlGaN layer, quantum well active layer, electron blocking layer and p-type AlGaN layer as described in claim 6; The n-type AlGaN layer, the quantum well active layer, the electron blocking layer, and the p-type AlGaN layer are sequentially stacked on the second AlN template layer.

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