JP6115092B2 - Semiconductor light emitting device and method for manufacturing semiconductor light emitting device - Google Patents

Description

  The present invention relates to a semiconductor light emitting device having a structure in which an n-type cladding layer, an active layer, and a p-type cladding layer are stacked, and a method for manufacturing the semiconductor light emitting device.

  A structure in which an n-type cladding layer, an active layer, and a p-type cladding layer are stacked is employed in a semiconductor light emitting device such as an ultraviolet light emitting diode (LED) or a semiconductor laser. In order to improve the luminous efficiency of the light emitting device, various studies have been made on the structure of the cladding layer in contact with the active layer (see, for example, Patent Document 1).

Japanese Patent No. 2735057

  In the semiconductor light emitting device having the above structure, when the flatness of the n-type cladding layer deteriorates, crystal defects are likely to occur during the growth of the active layer formed on the n-type cladding layer. Due to the generation of crystal defects, the luminous efficiency in the active layer is reduced, and the threshold voltage Vf cannot be lowered because the well layer and barrier layer of the active layer cannot be thinned.

  In view of the above problems, an object of the present invention is to provide a semiconductor light emitting device in which the flatness of the surface of an n-type cladding layer in contact with an active layer is improved and a method for manufacturing the semiconductor light emitting device.

According to one aspect of the present invention, (a) the first nitride semiconductor layer made of n-type GaN, AlGaN Tona is, the film thickness is less doped 100nm second nitride semiconductor layer, and n-type GaN And (b) an active layer disposed on the third nitride semiconductor layer of the n-type cladding layer, and (c) an active layer. A semiconductor light emitting device is provided comprising a p-type cladding layer disposed thereon.

According to another aspect of the present invention , (b) forming an n-type layer made of a nitride semiconductor at a first growth temperature, and (b) at a second growth temperature lower than the first growth temperature, forming a first nitride semiconductor layer made of n-type GaN on the n-type layer; and (c) AlGaN on the first nitride semiconductor layer at a third growth temperature not higher than the second growth temperature. And (d) a third nitride layer made of n-type GaN on the second nitride semiconductor layer at a fourth growth temperature lower than or equal to the third growth temperature. (E) forming an active layer on the third nitride semiconductor layer at a fifth growth temperature lower than the fourth growth temperature; and (f) forming an active semiconductor layer on the active layer. forming a p-type cladding layer . A method for manufacturing a semiconductor light emitting device is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the semiconductor light-emitting device with which the planarity of the surface of the n-type clad layer which contact | connects an active layer was improved, and the manufacturing method of a semiconductor light-emitting device can be provided.

It is typical sectional drawing which shows the structure of the semiconductor light-emitting device concerning embodiment of this invention. It is a table | surface which shows the characteristic of the semiconductor light-emitting device which concerns on embodiment of this invention, and the semiconductor light-emitting device of a comparative example. 6 is a graph for explaining a method of manufacturing a semiconductor light emitting device according to an embodiment of the present invention.

  Embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  Further, the embodiments described below exemplify apparatuses and methods for embodying the technical idea of the present invention, and the embodiments of the present invention include the material, shape, structure, arrangement, etc. of components. Is not specified as follows. The embodiment of the present invention can be variously modified within the scope of the claims.

(First embodiment)
As shown in FIG. 1, the semiconductor light emitting device 1 according to the first embodiment of the present invention includes a first nitride semiconductor layer 31 made of n-type GaN, In _X Al _Y Ga _1-XY N (0 ≦ X An n-type cladding layer in which a second nitride semiconductor layer 32 made of <1, 0 ≦ Y <1, 0 <X + Y <1) and a third nitride semiconductor layer 33 made of n-type GaN are laminated in this order. 30, an active layer 40 disposed on the third nitride semiconductor layer 33 of the n-type cladding layer 30, and a p-type cladding layer 50 disposed on the active layer 40.

  Further, in the semiconductor light emitting device 1 shown in FIG. 1, a buffer layer 11 and an n-type layer 20 made of an n-type nitride semiconductor are stacked on a substrate 10, and an n-type cladding layer 30 and an active layer are formed on the n-type layer 20. 40 and p-type cladding layer 50 are stacked in this order. The n-type layer 20, the n-type cladding layer 30, the active layer 40, and the p-type cladding layer 50 are formed by epitaxial growth using, for example, a metal organic chemical vapor deposition (MOCVD) method.

  As the substrate 10, for example, a sapphire substrate, silicon carbide (SiC), silicon (Si) substrate, or the like can be used.

Buffer layer 11 is, for _{example, Al x M y Ga 1-} xy N (M is indium (In) or boron (B), 0 <x ≦ 1,0 ≦ y ≦ 1, x + y = 1) from the composed first A multilayer in which sublayers and second sublayers of AlaMbGa1-a-bN (M is In or B, 0 ≦ a <1, 0 ≦ b ≦ 1, a + b = 1, a <x) are alternately stacked. A structure can be adopted. For example, the first sublayer is an aluminum nitride (AlN) film having a thickness of about 0.5 to 5 nm, and the second sublayer is a gallium nitride (GaN) film having a thickness of about 0.5 to 200 nm. In addition, you may handle the laminated body of the board | substrate 10 and the buffer layer 11 as a board | substrate.

The n-type layer 20 is represented by In _α Al _β Ga _1-α-β N (0 ≦ α ≦ 1, 0 ≦ β ≦ 1, 0 ≦ α + β ≦ 1) and doped with an n-type dopant such as Si. It consists of a nitride semiconductor. The n-type layer 20 is made of GaN or AlGaN and has a thickness of about 4 μm, for example.

  The third nitride semiconductor layer 33 made of n-type GaN is a GaN film doped with an n-type dopant such as Si. It is known that the InAlGaN film has a lower flatness than the GaN film. Therefore, for example, the active layer 40 can be grown on a flat film in the semiconductor light emitting device 1 as compared with a case where a nitride semiconductor layer made of InAlGaN is in contact with the active layer 40 as the n-type cladding layer 30.

  The flatness of the third nitride semiconductor layer 33 improves as the film thickness increases. However, if the thickness of the third nitride semiconductor layer 33 is too large, the difference in lattice constant between the average of the entire n-type cladding layer 30 and the active layer 40 is increased, so that the luminance is lowered. For this reason, the film thickness of the third nitride semiconductor layer 33 is 5 nm to 200 nm, more preferably 5 to 50 nm.

Under the third nitride semiconductor layer 33 made of n-type GaN, a second nitride made of In _X Al _Y Ga _1-XY N (0 ≦ X <1, 0 ≦ Y <1, 0 <X + Y <1). By disposing the physical semiconductor layer 32, the second nitride semiconductor layer 32 functions as a buffer layer that absorbs a lattice constant difference between the active layer 40 and the n-type layer 20. Specifically, by setting the average lattice constant and thermal expansion coefficient of the entire n-type cladding layer 30 to an intermediate value between the active layer 40 and the n-type layer 20, the second nitride semiconductor layer 32 becomes a buffer layer. Function as. In order to function as a buffer layer, the thickness of the second nitride semiconductor layer 32 is 10 nm to 500 nm.

  However, the flatness of the second nitride semiconductor layer 32 decreases. In order to suppress a decrease in flatness in the second nitride semiconductor layer 32, it is effective to reduce the doping amount of the n-type impurity in the second nitride semiconductor layer 32 or to make it non-doped. Here, non-doped means that no impurity is intentionally added. If the thickness of the second nitride semiconductor layer 32 is 100 nm or less, no significant increase in the threshold voltage Vf is observed even with non-doping. Furthermore, even when the film thickness is 50 nm or less and non-doping, the threshold voltage Vf is hardly increased.

  In addition, the composition of the InAlGaN layer greatly affects the flatness. In order to obtain good flatness, the In composition ratio is preferably 0.1 or less, and more preferably 0.05 or less. Similarly, the Al composition ratio is preferably 0.1 or less.

  By disposing the first nitride semiconductor layer 31 made of n-type GaN under the second nitride semiconductor layer 32, the flatness of the surface of the n-type cladding layer 30 is further improved. As the first nitride semiconductor layer 31 is thicker, the flatness tends to be improved. However, as in the case of the third nitride semiconductor layer 33, if the thickness of the first nitride semiconductor layer 31 is too large, the difference in lattice constant between the average of the entire n-type cladding layer 30 and the active layer 40 is large. As a result, the luminance decreases. However, since the distance from the active layer 40 is longer than that of the third nitride semiconductor layer 33, there is little decrease in luminance even if the first nitride semiconductor layer 31 is made relatively thick. For this reason, the film thickness of the third nitride semiconductor layer 33 is 5 nm to 200 nm, more preferably 20 to 100 nm.

  Although not shown, an n-side electrode is connected to the n-type cladding layer 30, and electrons are supplied to the n-side electrode from a negative power source outside the semiconductor light emitting device 1. As a result, electrons are supplied from the n-type cladding layer 30 to the active layer 40.

  The p-type cladding layer 50 is, for example, a stacked body of a GaN film with a thickness of about 200 nm doped with a p-type dopant and an AlGaN film with a thickness of about 20 nm. The p-type dopant is magnesium (Mg), zinc (Zn), cadmium (Cd), calcium (Ca), beryllium (Be), carbon (C), or the like.

  Although not shown, a p-side electrode is connected to the p-type cladding layer 50, and holes are supplied to the p-side electrode from a positive power source outside the semiconductor light emitting device 1. As a result, holes are supplied from the p-type cladding layer 50 to the active layer 40.

  The active layer 40 has, for example, a multiple quantum well (MQW) structure in which AlInGaN films and AlInGaN films having different composition ratios are alternately stacked. The thickness of the AlInGaN film constituting the active layer 40 is about several μm to several tens of μm. The electrons supplied from the n-type cladding layer 30 and the holes supplied from the p-type cladding layer 50 are recombined in the active layer 40 to generate light.

As described above, in the semiconductor light emitting device 1 according to the first embodiment, the first nitride semiconductor layer 31 made of n-type GaN, In _X Al _Y Ga _1-XY N (0 ≦ X <1, By laminating the second nitride semiconductor layer 32 made of 0 ≦ Y <1, 0 <X + Y <1) and the third nitride semiconductor layer 33 made of n-type GaN, the n-type cladding layer 30 is flattened. Can be improved. As a result, according to the semiconductor light emitting device 1 shown in FIG. 1, the generation of crystal defects during the growth of the active layer 40 is reduced, and therefore the reduction in the light emission efficiency in the active layer 40 is suppressed. Furthermore, since the thickness of the well layer and the barrier layer of the active layer 40 can be reduced, the threshold voltage Vf decreases.

  Further, when the flatness of the n-type cladding layer 30 is poor, there arises a problem that the in-plane of the active layer 40 does not emit light uniformly, and a problem that reliability is lowered due to local concentration of current. In the semiconductor light emitting device 1 shown in FIG. 1, since the active layer 40 is grown on the n-type clad layer 30 with good flatness, uniform light emission can be obtained in the plane and a decrease in reliability is suppressed. .

  Comparative example in which the n-type cladding layer 30 is a semiconductor light emitting device of comparative example 1 in which the n-type cladding layer 30 is made of GaN, and the n-type cladding layer 30 is a structure in which a nitride semiconductor layer made of GaN and a nitride semiconductor layer made of AlGaN are stacked in this order. FIG. 2A shows the result of comparing the characteristics of the semiconductor light emitting device 2 and the semiconductor light emitting device 1 according to the embodiment. In the embodiment of the semiconductor light emitting device 1 shown in FIG. 2A, the first nitride semiconductor layer 31 and the third nitride semiconductor layer 33 are n-type GaN, and the second nitride semiconductor layer 32 is AlGaN. FIG. 2A shows the brightness and threshold voltage Vf when a current of 20 mA is passed. Here, “brightness” is a value indicating the light output (arbitrary unit: a.u.) of the semiconductor light emitting device. As shown in FIG. 2A, the brightness of the semiconductor light emitting device 1 shown in FIG. 1 is improved without increasing the threshold voltage Vf as compared with Comparative Examples 1 and 2. This is because, in the semiconductor light emitting device 1, since the flatness of the n-type cladding layer 30 is improved, generation of crystal defects during the growth of the active layer 40 is suppressed, so that the well layer and the barrier layer of the active layer 40 need to be thickened. This is because the emission efficiency is improved.

  Note that a silicon substrate has a larger lattice constant difference from a nitride semiconductor film and a different thermal expansion coefficient than a sapphire substrate or a SiC substrate. For this reason, when a silicon substrate is used, the flatness of the lower layer of the n-type cladding layer 30 is worse than when a sapphire substrate is used. Therefore, when a silicon substrate is used as the substrate 10, the effect of the semiconductor light emitting device 1 that improves the flatness of the n-type cladding layer 30 is greater.

  With reference to FIG. 3, the example of the manufacturing method of the semiconductor light-emitting device 1 shown in FIG. 1 is demonstrated. In addition, the manufacturing method of the semiconductor light-emitting device 1 described below is an example, and it is needless to say that it can be realized by various other manufacturing methods including this modification.

  FIG. 3 is a graph showing growth temperatures of the buffer layer 11, the n-type layer 20, the n-type cladding layer 30, the active layer 40, and the p-type cladding layer 50. In FIG. 3, periods A, B, C, D, and E indicate growth periods of the buffer layer 11, the n-type layer 20, the n-type cladding layer 30, the active layer 40, and the p-type cladding layer 50, respectively. Periods C1, C2, and C3 indicate growth periods of the first nitride semiconductor layer 31, the second nitride semiconductor layer 32, and the third nitride semiconductor layer 33, respectively. Periods D1 and D2 indicate growth periods of the barrier layer and the well layer of the active layer 40.

  First, the buffer layer 11 is formed on the substrate 10 which is a silicon substrate. The growth temperature T11 of the buffer layer 11 is, for example, 1050 ° C. Then, the n-type layer 20 is formed on the buffer layer 11 at the growth temperature T20 shown in FIG. The growth temperature T20 is 1000 ° C., for example.

  Thereafter, the first nitride semiconductor layer 31 having a thickness of about 20 nm to 100 nm is formed on the n-type layer 20 at the growth temperature T31. The growth temperature T31 is, for example, 850 ° C. Next, a non-doped AlGaN layer having a thickness of about 25 nm is formed on the first nitride semiconductor layer 31 as the second nitride semiconductor layer 32 at the growth temperature T32. The growth temperature T32 is 850 ° C., for example.

  The growth temperature T31 of the first nitride semiconductor layer 31 is set lower than the growth temperature T20 of the n-type layer 20 and equal to or higher than the growth temperature T32 of the second nitride semiconductor layer 32. By reducing the temperature difference between the growth temperature T31 of the first nitride semiconductor layer 31 and the growth temperature T32 of the second nitride semiconductor layer 32, the step of forming the first nitride semiconductor layer 31 and the second step The growth stop time between the nitride semiconductor layer 32 and the film forming process is shortened. Thereby, it can suppress that flatness deteriorates during a growth stop. Therefore, it is most preferable that the growth temperature T31 and the growth temperature T32 are the same temperature. However, since the growth temperature of the InAlGaN film is generally lower than that of the GaN film, the crystallinity of the first nitride semiconductor layer 31 is considered. Therefore, the growth temperature T32 <growth temperature T31 <growth temperature T20 may be satisfied. It is also effective to continuously change the growth temperature T20 of the n-type layer 20 to the growth temperature T32 of the second nitride semiconductor layer 32 when the first nitride semiconductor layer 31 is grown. That is, the first nitride semiconductor layer 31 may be grown while changing the growth temperature as indicated by the broken line L1 in FIG.

  The third nitride semiconductor layer 33 having a thickness of about 5 nm to 50 nm is formed on the second nitride semiconductor layer 32 at the growth temperature T33. The growth temperature T33 is, for example, 850 ° C. Then, the active layer 40 is formed on the third nitride semiconductor layer 33. For example, the growth temperature T41 of the barrier layer of the active layer 40 is set to about 820 ° C., and the growth temperature T42 of the well layer is set to about 720 ° C.

  The higher the growth temperature T33 of the third nitride semiconductor layer 33 is, the better the flatness of the third nitride semiconductor layer 33 is. However, if the difference from the growth temperature of the active layer 40 or the second nitride semiconductor layer 32 is large, the time until the growth temperature is adjusted during the manufacturing process becomes long, and the growth stop time increases. Since there is a phenomenon that the flatness deteriorates when the growth is stopped, the growth temperature T33 of the third nitride semiconductor layer 33 should be as close as possible to the growth temperature of the active layer 40 and the growth temperature of the second nitride semiconductor layer 32. Preferably, they are the same temperature. However, although it is possible to make the growth temperature T41 of the barrier layer and the growth temperature T33 of the third nitride semiconductor layer 33 the same, it is generally the same that the growth temperature T42 of the well layer and the growth temperature T33 are made the same. It is difficult.

  Note that when the third nitride semiconductor layer 33 is grown, the temperature may be continuously changed from the growth temperature T32 of the second nitride semiconductor layer 32 to the growth temperature T41. That is, the third nitride semiconductor layer 33 may be grown while changing the growth temperature as indicated by a broken line L2 in FIG.

  The p-type cladding layer 50 is formed on the active layer 40 at the growth temperature T50. For example, a p-type cladding layer 50 composed of a p-type GaN layer having a thickness of 200 nm and a p-type AlGaN layer having a thickness of 20 nm is formed at 1000 ° C. Thereby, the semiconductor light emitting device 1 shown in FIG. 1 is completed.

The semiconductor light emitting device 1 can use a general source gas, such as ammonia (NH ₃ ) gas, TMG gas, TMA gas, TMI gas, or the like.

  Further, the crystal quality of the n-type cladding layer 30 can be improved by making the film-forming pressure when forming the n-type cladding layer 30 larger than the film-forming pressure when forming the active layer 40. Specifically, the film formation pressure of the active layer 40 is about 400 Torr, and the film formation pressure of the n-type cladding layer 30 is about 600 Torr or 760 Torr.

  Furthermore, in the example of the manufacturing method, the example in which the second nitride semiconductor layer 32 is an AlGaN film is shown. However, the same effect as described above can be obtained by using the second nitride semiconductor layer 32 as an InGaN film. Has an effect.

  FIG. 2B shows a semiconductor light emitting device of Comparative Example 1 in which the n-type cladding layer 30 is made of GaN, a nitride semiconductor layer in which the n-type cladding layer 30 is made of GaN, and a nitride semiconductor layer made of InGaN in this order. The result of having compared the characteristic at the time of making the 2nd nitride semiconductor layer 32 into InGaN in the semiconductor light-emitting device of the comparative example 2 which is the structure made, and the semiconductor light-emitting device 1 which concerns on embodiment is shown. In the embodiment of the semiconductor light emitting device 1 shown in FIG. 2B, the first nitride semiconductor layer 31 and the third nitride semiconductor layer 33 are made of n-type GaN, and the second nitride semiconductor layer is formed. 32 is made of InGaN. FIG. 2B also shows the brightness and threshold voltage Vf when a current of 20 mA is passed, as in the case of FIG. As shown in FIG. 2B, the brightness of the semiconductor light emitting device 1 shown in FIG. 1 is improved without increasing the threshold voltage Vf as compared with Comparative Examples 1 and 2.

(Other embodiments)
As mentioned above, although this invention was described by embodiment, it should not be understood that the description and drawing which form a part of this indication limit this invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  In the description of the embodiment already described, the case where the n-type cladding layer 30, the active layer 40, and the p-type cladding layer 50 are stacked in this order on the substrate 10 is exemplarily shown. However, in the completed semiconductor light emitting device 1 The p-type cladding layer 50, the active layer 40, and the n-type cladding layer 30 may be disposed on the substrate in this order.

  As described above, the present invention naturally includes various embodiments not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

DESCRIPTION OF SYMBOLS 1 ... Semiconductor light-emitting device 10 ... Substrate 11 ... Buffer layer 20 ... N-type layer 30 ... N-type clad layer 31 ... 1st nitride semiconductor layer 32 ... 2nd nitride semiconductor layer 33 ... 3rd nitride semiconductor layer 40 ... active layer 50 ... p-type cladding layer

Claims (7)

The first nitride semiconductor layer made of n-type GaN, Ri AlGaN Tona, second nitride semiconductor layer having a film thickness of 100nm or less of the non-doped, and the third nitride semiconductor layer made of n-type GaN is in this order A laminated n-type cladding layer;
An active layer disposed on the third nitride semiconductor layer of the n-type cladding layer;
And a p-type cladding layer disposed on the active layer. The n-type cladding layer on a silicon substrate, said active layer, a semiconductor light emitting device according to claim 1, wherein the p-type cladding layer is disposed. Forming an n-type layer of nitride semiconductor at a first growth temperature;
Forming a first nitride semiconductor layer made of n-type GaN on the n-type layer at a second growth temperature lower than the first growth temperature;
Forming a second nitride semiconductor layer made of AlGaN on the first nitride semiconductor layer at a third growth temperature lower than the second growth temperature;
Forming a third nitride semiconductor layer made of n-type GaN on the second nitride semiconductor layer at a fourth growth temperature equal to or lower than the third growth temperature;
Forming an active layer on the third nitride semiconductor layer at a fifth growth temperature lower than the fourth growth temperature;
Forming a p-type cladding layer on the active layer. A method for manufacturing a semiconductor light emitting device. 4. The method of manufacturing a semiconductor light emitting device according to claim 3 , wherein the second growth temperature and the third growth temperature are equal. The method of manufacturing a semiconductor light emitting device according to claim 3 or 4, wherein the third growth temperature and the fourth growth temperature are equal. 6. The method of manufacturing a semiconductor light emitting device according to claim 3, wherein the second nitride semiconductor layer is a non-doped nitride semiconductor layer having a thickness of 100 nm or less. The first nitride semiconductor layer, the second nitride semiconductor layer, the third nitride semiconductor layer, the active layer, and the p-type cladding layer are formed on a silicon substrate. 7. A method for manufacturing a semiconductor light emitting device according to any one of 3 to 6 .

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