KR20090051333A - Nitride semiconductor device - Google Patents

Abstract

The nitride semiconductor device includes a p-type and n-type nitride semiconductor layer and an active layer having a multi-quantum well structure formed by alternately stacking a plurality of quantum well layers and a plurality of quantum barrier layers therebetween, wherein the plurality of quantum barrier layers At least one has a region doped with a p-type impurity. The quantum barrier layer doped with the at least one p-type impurity may include a diffusion barrier layer having a p-type impurity concentration lower than that of another internal region doped with the quantum barrier layer at an interface contacting the quantum well layer.

Nitride semiconductor devices, muti quantum wells, p-type dopants

Description

Nitride Semiconductor Devices {NITRIDE SEMICONDUCTOR DEVICE}

The present invention relates to a nitride semiconductor device, and more particularly, to a nitride semiconductor device having improved hole injection efficiency to improve recombination efficiency in the entire quantum well structure.

In general, nitride semiconductors are widely used in green or blue light emitting diodes (LEDs) or laser diodes (LDs), which are provided as light sources in full color displays, image scanners, various signal systems, and optical communication devices. The nitride semiconductor device generates and emits light in an active layer using a recombination principle of electrons and holes.

The active layer has a single quantum well (SQW) structure having one quantum well layer and a muti quantum well (MQW) structure having a plurality of quantum well layers smaller than about 100 ms. In particular, the active layer of the multi-quantum well structure is actively used because of its superior light efficiency and high luminous output compared to a single quantum well structure.

The optical efficiency of the nitride semiconductor device is determined by the probability of recombination of electrons and holes in the active layer, that is, internal quantum efficiency. In order to improve the internal quantum efficiency, research has been conducted mainly to improve the structure of the active layer itself or to increase the effective mass of the carrier.

However, since the hole mobility and injection length are much smaller than the electron mobility and injection length, most recombination occurs only in the quantum well adjacent to the p-type nitride semiconductor layer. This problem is more serious in light emitting devices having a multicolor active layer (blue-green active layer) that has been actively studied in recent years. That is, in the case of a light emitting device having a multi-color active layer, it is important to generate a desired blue spectrum and a green spectrum with similar outputs, but limited light emission occurs only in the region adjacent to the p-type nitride semiconductor layer, resulting in output of only light in a specific region. There is a problem that it becomes difficult to obtain a desired mixed effect.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and an object thereof is to provide a nitride semiconductor device having a multi-quantum well structure in which holes injected from a p-type nitride semiconductor layer can be smoothly injected into the entire quantum well region. It is.

In order to achieve the above technical problem, the present invention,

a p-type and n-type nitride semiconductor layer and a plurality of quantum well layers and an active layer having a plurality of quantum barrier layers alternately stacked therebetween, wherein at least one of the plurality of quantum barrier layers is p A nitride semiconductor element having a region doped with a type impurity is provided.

Specifically, the p-type impurity may be at least one element selected from the group consisting of Mg, Zn, Cd, Be, Ca, and Ba.

Preferably, the quantum barrier layer doped with the at least one p-type impurity includes a diffusion barrier layer having a p-type impurity concentration lower than that of another doped internal region of the quantum barrier layer at an interface in contact with the quantum well layer. .

In this case, the p-type impurity concentration of the internal doped region of the quantum barrier layer may be 5 × 10 ¹⁵ to 1 × 10 ¹⁷ / cm 3.

Preferably, the p-type impurity concentration of the diffusion barrier layer may be 0.1 times or less than the p-type impurity concentration of the other inner doped region of the quantum barrier layer at an interface in contact with the quantum well layer. More preferably, the diffusion barrier layer may be a region intentionally undoped.

The thickness of the n-type impurity diffusion barrier of the at least one quantum barrier layer is preferably 1/10 to 3/10 of the thickness of the quantum barrier layer.

In detail, the thickness of the at least one quantum barrier layer may be about 10 nm to about 30 nm, and the thickness of the n-type impurity diffusion barrier may be about 1 nm to about 10 nm.

In a preferred embodiment, the quantum barrier layer doped with the p-type impurity may be a quantum barrier layer close to the p-type nitride semiconductor layer.

In addition, when there are a plurality of quantum barrier layers doped with the p-type impurity, at least one of the quantum barrier layers doped with the p-type impurity may have a different p-type impurity concentration than other quantum barrier layers. In this case, preferably, the plurality of quantum barrier layers doped with the p-type impurity have the highest p-type impurity concentration of the quantum barrier layer in contact with the p-type nitride semiconductor layer, and are close to the n-type nitride semiconductor layer side. The higher the impurity concentration can be arranged.

In a particular application of the present invention, there is an additional active layer having a plurality of quantum well layers and a plurality of quantum barrier layers for emitting wavelengths different from the emission wavelength of the active layer, wherein the additional active layer is adjacent to the n-type nitride semiconductor layer. Can be deployed.

According to the present invention, the present invention can improve relatively poor hole injection efficiency by selectively or totally doping the quantum barrier layer with an appropriate amount of p-type impurities. Uniform light emission is possible in the entire quantum well layer, thereby greatly increasing the recombination efficiency, that is, the light emission efficiency.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a side cross-sectional view showing a nitride semiconductor device according to one embodiment of the present invention.

As shown in FIG. 1, the nitride semiconductor element 20 is formed of an n-type nitride semiconductor layer 23, an active layer 25 having a multi-quantum well structure, and a p-type nitride semiconductor layer 27 sequentially on the substrate 21. It includes. The active layer 25 is provided in a multi-quantum well structure having a plurality of quantum barrier layers 25a and a plurality of quantum well layers 25b.

The n-side electrode 29a is formed in the upper region of the n-type nitride semiconductor layer 27 exposed by mesa etching, and the transparent electrode layer 28 and the p-side electrode 29b are formed on the upper surface of the p-type nitride semiconductor layer 23. It is formed in turn.

The quantum barrier layer (25a) can be appropriately selected from _{Al x1 In y1 Ga 1-x1} -y1 N (x 1 + y 1 = 1, 0≤x 1 ≤1, 0≤y 1 ≤1), The quantum well layer 25b is smaller than the quantum barrier layer 25a and has an energy bandgap corresponding to a desired emission wavelength.Al _x2 In _y2 Ga _1-x2-y2 N (x ₂ + y ₂ = 1, 0 ≤ x ₂ ≤ 1, 0 ≤ y ₂ ≤ 1) can be used as appropriate.

In particular, in the active layer 25 of the multi-quantum well structure employed in this embodiment, the quantum well layer 25b is made of an undoped nitride layer such as InGaN, whereas the quantum barrier layer 25a is formed of p such as GaN. It consists of a nitride layer doped with type impurities.

As such, the quantum barrier layer 25a doped with the p-type impurity may increase the hole injection efficiency in the active layer 25. That is, as described above, since the hole is about 10 to several hundred times smaller than the injection path or mobility, the amount of holes is drastically reduced in the specific region, thereby lowering the recombination efficiency. The quantum barrier layer 25a employed in the present invention can mitigate such abrupt decrease of holes through activated p-type impurities, and consequently, improve recombination efficiency.

In order to improve the recombination efficiency through the activated p-type impurity of the quantum barrier layer 25, it is preferable that the p-type impurity concentration of the quantum barrier layer is in the range of 5 × 10 ¹⁵ to 1 × 10 ¹⁷ / cm 3. .

As the p-type impurity, at least one element selected from the group consisting of Mg, Zn, Cd, Be, Ca, and Ba may be used. For example, when the Mg element is selected as an impurity in the MOCVD process, the Cp ₂ Mg gas can be easily injected to form the quantum barrier layer.

2 is a schematic energy band diagram showing the structure of an improved active layer in accordance with an embodiment of the present invention. It can be understood as the active layer of Fig. 1 and its surroundings.

Here, the vertical axis refers to the absolute size (eV) of the energy band gap, and the horizontal axis refers to the distance in the vertical direction from the n-type nitride semiconductor layer to the p-type nitride semiconductor layer.

Referring to FIG. 2, four quantum well layers 25b between the n-type nitride semiconductor layer 23 and the p-type nitride semiconductor layer 27 and three quantums having a larger band gap than the quantum well layer 25b are shown. An energy bandgap diagram for the active layer 25 composed of the barrier layer 25a is shown.

In this diagram, more specifically, the n-type nitride semiconductor layer 23 is n-type GaN, and the p-type nitride semiconductor layer 27 includes an undoped GaN spacer layer 27a, a p-type AlGaN electron barrier layer 27b, and the like. and p-type GaN layer 27c.

As such, the quantum barrier layer 25a may mitigate a sharp decrease in holes through activated p-type impurities. Therefore, the amount of holes that can reach the quantum well layer close to the n-type nitride semiconductor layer can be increased, thereby improving the luminous efficiency.

In this embodiment, all the quantum barrier layers 25a are illustrated as doped with p-type impurities, but the present invention is not limited thereto. That is, p-type impurity doping for the quantum barrier layer may be selectively performed on a specific quantum barrier layer, and may be implemented to have different impurity concentrations.

Preferably, doping the impurities by doping the p-type impurities with a limited increase in the relative amount of holes due to the p-type impurities activated by selecting and doping around the quantum barrier layer adjacent to the p-type nitride semiconductor layer 27 side This can reduce the influence on the crystallinity. This type of active layer can be described with reference to the energy band diagram shown in FIG.

Referring to FIG. 3, four quantum well layers 35b between the n-type GaN semiconductor layer 33 and the p-type nitride semiconductor layer 37 and three quantums having a band gap larger than that of the quantum well layer 35b are shown. An active layer 35 composed of barrier layer 35a is shown.

Of the three quantum barrier layers 35a, only two quantum barrier layers 35a 'closer to the p-type nitride semiconductor layer 37 are doped with p-type impurities. In particular, the two quantum barrier layers 35a 'doped with the p-type impurity are arranged to have a higher impurity concentration as they are closer to the p-type nitride semiconductor layer. This is because, as described above, the hole injection efficiency improvement effect due to the p-type impurities activated in the quantum barrier layer adjacent to the p-type AlGaN semiconductor layer 37 is large.

As such, by selectively doping only a portion of the quantum barrier layer 35 'with p-type impurities, a negative effect on crystallinity due to the doping of impurities may be alleviated. In the illustrated form, only the two quantum barrier layers 35 'are doped with p-type impurities, but only one quantum barrier layer is doped with p-type impurities, and the position thereof is also p-type nitride. It would be desirable to arrange adjacent to the semiconductor layer.

4 is a side sectional view showing a nitride semiconductor device according to another embodiment of the present invention.

Referring to FIG. 4, the nitride semiconductor device 110 is sequentially formed on the substrate 111 similarly to the device shown in FIG. 1, the n-type nitride semiconductor layer 113, the active layer 115 having a multi-quantum well structure, and p. The type nitride semiconductor layer 117 is included. The active layer 115 is provided in a multi-quantum well structure having a plurality of quantum barrier layers 115a and a plurality of quantum well layers 115b.

The n-side electrode 119a is formed in the upper region of the n-type nitride semiconductor layer 117 exposed by mesa etching, and the transparent electrode layer 118 and the p-side electrode 119b are formed on the upper surface of the p-type nitride semiconductor layer 113. It is formed in turn.

In the active layer 115 of the multi-quantum well structure, the quantum barrier layer 115a is p-doped only in the inner region 115a ', unlike the shape shown in FIG. 1, and at the interface with the quantum well layer 115b. It has a structure including a diffusion barrier film (115a ") of the undoped region.

In the quantum barrier layer 115a employed in the present embodiment, the internal region 115a 'doped with p-type impurities for replenishing holes is used to maintain the crystallinity of higher quality. It is preferable to have a concentration smaller than the impurity concentration of). Specifically, the inner region 115a ″ of the quantum barrier layer may have an impurity concentration of 5 × 10 ¹⁵ to 1 × 10 ¹⁷ / cm 3.

In this embodiment, as shown, the quantum barrier layer 115a is provided with an intentionally undoped diffusion barrier film 115a "at an interface in contact with the quantum well layer 115b. Such a diffusion barrier film 115a". Is a structure for preventing the diffusion of unwanted impurities from the inner region 115a 'to the quantum well layer 115b.

The diffusion barrier film 115a ″ employed in this embodiment is exemplified as an undoped region, but an impurity concentration lower than the concentration of the internal region 115a 'of the doped quantum barrier layer 115a is preferable. Even if doped to have a p-type impurity concentration of 0.1 times or less, the amount of impurities that can diffuse into the quantum well layer 115b can be significantly reduced.

Further, in the case where the diffusion barrier film 115a ″ is formed as an undoped region as in the present embodiment, or configured to have a constant impurity concentration at 10% or less of the concentration of other internal regions, the diffusion barrier film 115a ″ is formed on the quantum barrier layer 115a. An additional advantage can be obtained that the process conditions and surface morphology can be prevented from growing when the quantum well layer 115b is grown.

The thickness t _a of the diffusion barrier film 115a ″ is preferably formed to be 1/10 to 3/10 of the total thickness t of the quantum barrier layer. The thickness t of the diffusion barrier film 115a ″. _{If a} ) is less than 0.1 times the total thickness t of the quantum barrier layer, the function of preventing the diffusion of impurities into the quantum well layer 115b is weak. If greater than 0.3 times, the quantum barrier layer doped with impurities ( The internal region 115a "of 115a is too small to effectively play a role of lowering the forward voltage. In a more specific example, when the thickness t of the quantum barrier layer 115a is about 10 nm to about 30 nm. The thickness t _a of the diffusion barrier 115a ″ may be about 1 nm to about 10 nm.

As such, the quantum barrier layer 115a having the internal region 115a "doped with the p-type impurity can increase the hole injection efficiency in the active layer 115. As a result, the recombination efficiency can be improved. In addition, the diffusion barrier film 115a ″ may prevent the p-type impurities from diffusing into the quantum well layer 115b to ensure reliability of the quantum well layer.

FIG. 5 is a schematic energy band diagram of an active layer employed in the nitride semiconductor device shown in FIG.

Referring to FIG. 5, three quantum well layers 115b between the n-type GaN semiconductor layer 113 and the p-type nitride semiconductor layer 117 and three quantums having a larger band gap than the quantum well layer 115b are provided. An energy band diagram for the active layer 115 composed of the barrier layer 115a is shown. Similarly to the foregoing embodiment, more specifically, the n-type nitride semiconductor layer 113 is n-type GaN, and the p-type nitride semiconductor layer 117 includes an undoped GaN spacer layer 117a and a p-type AlGaN electron barrier layer 117b. ) And a p-type GaN layer 117c.

The quantum barrier layer 115a may be a diffusion barrier layer formed on both surfaces in contact with the quantum well layer and the internal region 115a 'doped with p-type impurities to increase the probability of recombination of electrons and holes in the quantum well layer 115b. 115a ". The diffusion barrier film 115a" has a lower p-type impurity concentration than other regions, that is, an internal region 115a ', and preferably has an impurity concentration that is 0.1 times or less of the impurity concentration, and more. Preferably it may be formed into an undoped region.

Therefore, the hole-increasing effect can be expected through the p-type impurity activated in the inner region 115a 'of the quantum barrier layer, and the quantum well layer 115b is formed by a lightly doped or undoped diffusion preventing film 115a ". Diffusion can be reduced or prevented.

Also in this embodiment, a structure in which a plurality of quantum barrier layers doped with the p-type impurity have different p-type impurity concentrations, or doped with n-type impurities only in a part of the quantum barrier layers, similarly to the form described in FIG. 3 may be implemented in combination with the present embodiment employing the diffusion barrier.

In particular, the structure according to the present invention, which improves the hole injection efficiency problem in the active layer, may be very usefully applied to a light emitting device having a multicolor active layer having different wavelengths. Since an increase in the number of layers is inevitable to implement a multicolor active layer, the problem of hole injection efficiency may be more serious. Also in this case, a desired effect can be obtained by p-type doping the quantum barrier layer of some or all of the active layers to have the above-described structure. Even in this case, it is preferable that the active layer having a specific wavelength having a quantum barrier layer doped with p-type impurities be disposed adjacent to the p-type nitride semiconductor layer.

The present invention is not limited by the above-described embodiment and the accompanying drawings, but by the appended claims. Therefore, it will be apparent to those skilled in the art that various forms of substitution, modification, and alteration are possible without departing from the technical spirit of the present invention as set forth in the claims. Will belong to the technical spirit described in.

1 is a side cross-sectional view showing a nitride semiconductor device according to one embodiment of the present invention.

FIG. 2 is a schematic energy band diagram of an active layer employed in the nitride semiconductor device shown in FIG.

3 is an energy band diagram of another example of an active layer employable in a nitride semiconductor light emitting device according to the present invention.

4 is a side sectional view showing a nitride semiconductor device according to another embodiment of the present invention.

FIG. 5 is a schematic energy band diagram of an active layer employed in the nitride semiconductor device shown in FIG.

Claims (12)

a p-type and n-type nitride semiconductor layer and an active layer of a multi-quantum well structure formed by alternately stacking a plurality of quantum well layers and a plurality of quantum barrier layers therebetween, At least one of the plurality of quantum barrier layers has a region doped with a p-type impurity. The method of claim 1, The quantum barrier layer doped with at least one p-type impurity has a diffusion barrier layer having a p-type impurity concentration at an interface in contact with the quantum well layer that is lower than a concentration of another internal region doped with the quantum barrier layer. . The method according to claim 1 or 2, The p-type impurity is at least one element selected from the group consisting of Mg, Zn, Cd, Be, Ca and Ba. The method of claim 2, The p-type impurity concentration of the internal doped region of the quantum barrier layer is 5 x 10 ¹⁵ to 1 x 10 ¹⁷ / cm 3. The method of claim 2, And a p-type impurity concentration of the diffusion barrier layer is 0.1 times or less than a p-type impurity concentration of another internal doped region of the quantum barrier layer at an interface in contact with the quantum well layer. The method of claim 2, The diffusion barrier is a nitride semiconductor device, characterized in that not intentionally doped. The method of claim 2, The diffusion barrier is a nitride semiconductor device, characterized in that 1/10 to 3/10 of the thickness of the quantum barrier layer. The method of claim 7, wherein The thickness of the at least one quantum barrier layer is 10nm to 30nm, The n-type impurity diffusion barrier layer has a thickness of 1 nm to 10 nm. The method of claim 1, And the quantum barrier layer doped with the p-type impurity is a quantum barrier layer close to the p-type nitride semiconductor layer. The method of claim 1, A plurality of quantum barrier layer doped with the p-type impurity, At least one quantum barrier layer of the quantum barrier layer doped with the p-type impurity has a p-type impurity concentration different from that of the other quantum barrier layer. The method of claim 10, The quantum barrier layer doped with the p-type impurity has the highest p-type impurity concentration of the quantum barrier layer in contact with the p-type nitride semiconductor layer, and is disposed such that the impurity concentration is lower as it is closer to the n-type nitride semiconductor layer side. Nitride semiconductor device characterized in that. The method of claim 1, It has an additional active layer having a plurality of quantum well layer and a plurality of quantum barrier layer for emitting a wavelength different from the emission wavelength of the active layer, And the additional active layer is disposed adjacent to the n-type nitride semiconductor layer.

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