KR100324396B1 - Nitride semiconductor light-emitting device and manufacturing method of the same - Google Patents

Abstract

Using an indium-containing third-group nitride semiconductor layer with a multi-phase structure consisting of a main phase and sub-phases having different indium contents (In-contents) as a light emitting layer Wherein the sub-faces are formed mainly of a crystal surrounded by a strained layer at a boundary between the sub-faces and the main face.

Description

TECHNICAL FIELD [0001] The present invention relates to a nitride semiconductor light emitting device and a nitride semiconductor light emitting device,

The present invention relates to a nitride semiconductor light emitting device using an indium-containing Group III nitride semiconductor layer having a multi-face structure composed of a mainphase and a sub-phase having different indium contents as a light emitting layer, And a manufacturing method thereof.

The indium-containing Group III nitride semiconductor is represented by the general formula Al _x Ga _y In _z N _a M _1-a (x + y + z = 1, 0 x, y <1, 0 & 1, and M is a Group 5 element other than nitrogen) and is used as a light emitting layer of a nitride semiconductor light emitting device that emits short wavelength light. Particularly, a gallium nitride indium mixed crystal (Ga _b In _1-b N: 0? B <1) is a typical constituent material of a light emitting layer (see Japanese Patent Laid-Open Publication No. 55-3834). In reference to the prior art, a gallium nitride indium mixed crystal (Ga _0.80 In _0.20 N) having an indium content of 20% was used as a light emitting layer of a blue light emitting diode (LED) emitting approximately 450 nm wavelength light. In addition, a gallium nitride indium mixed crystal having an indium content of 45% was used as a light emitting layer of a green light emitting diode which emits light of about 525 nm wavelength.

The gallium nitride indium mixed crystal is also used as a well layer of a single or multiple quantum well structure functioning as a light emitting portion (see Japanese Patent Application Laid-Open No. 9-36430). It has heretofore been thought that a gallium nitride indium mixed crystal widely used as a light emitting layer is preferably uniform in indium content (see Japanese Patent Application Laid-Open No. 9-36430). However, recently, it has been known that a gallium indium nitride layer having a non-uniform indium content is advantageous as a light emitting layer (see Japanese Patent Application Laid-open No. 10-107315). This so-called multiphase structure gallium indium nitride is a layer formed by a set of faces with different indium contents.

As described above, the high intensity emission from the multiphase structure gallium indium layer, which exhibits " variation " of indium content and indium content, is due to quantized light emitters such as quantum dots Concluded. The gallium indium nitride layer having a multi-faced structure generally consists of a main face (matrix phase) and sub-faces, and the main face occupies most of the volume face (see Japanese Patent Application Laid-open No. 10-56202). Subphases usually have an indium content different from the main face. Indium content is always different between subphases. The subphases have roughly spherical or island-shaped microcrystals, which are scattered in the main face.

According to the prior art, a quantization level formed at the boundary between the microphase (sub-faces) and the main face surrounding them in light emission is mentioned (see Japanese Patent Laid-Open No. 10-107315). The microcrystallite size is several nanometers to several tens of nanometers in diameter, and microcrystals are large enough to act as quantum dots. These subphases behave as quantum dots and are known to participate in luminescence from a luminescent layer composed of indium-containing Group III nitride semiconductors.

Although subfaces (quantum dots) participate in light emission from a light emitting layer composed of an indium-containing Group III nitride semiconductor, there is no method for obtaining stable light emission characteristics, that is, stable light emission intensity and stable light emission wavelength from the light emission layer. The luminescent properties obtained so far are unstable.

The main reason why stable luminescence characteristics have not been obtained in the prior art is that the requirements for making subphases function as quantized phosphors are not known. In order to obtain stable luminescence characteristics, especially stable luminescence characteristics at high luminescence intensities, it is necessary to clearly identify the microcrystals, that is, the requirements for the subphases to function effectively with the quantum dots.

The present invention aims to provide a nitride semiconductor light emitting device and a method of manufacturing the same that can provide stable and excellent light emission characteristics from a light emitting layer by describing requirements for allowing subphases to function effectively as quantum dots .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an illustration of an exemplary crystal lattice obtained by photographing a light emitting layer of a nitride light emitting device according to the present invention with a transmission electron microscope (TEM). FIG.

2 is a view illustrating a laminated structure of a light emitting device according to a first embodiment of the present invention.

3 is a view of a crystal lattice obtained by photographing a light emitting layer of the light emitting device of the first embodiment using a transmission electron microscope (TEM).

4 is a cross-sectional view taken along line 4-4 of FIG.

5 is a plan view of the light emitting device of the first embodiment.

Description of the Related Art [0002]

2, 102: light emitting layer 21, 201: main face

22, 202: Subface 23, 203: Strain layer

In order for the microcrystals constituting the subphases to function as quantized emitters, the invention defines the structure of each subphase and the region near the border between the main faces surrounding the subphase. Specifically, the nitride semiconductor light-emitting device of the present invention using the indium-containing Group III nitride semiconductor layer having a multiphasic structure composed of main faces and sub-faces having different indium contents as the light-emitting layer is characterized in that the sub- Is formed by a crystal surrounded by a strained layer.

The method of manufacturing a nitride semiconductor light emitting device of the present invention using an indium-containing Group III nitride semiconductor layer having a multi-face structure composed of main faces and sub-faces having different indium contents as the light emitting layer, Annealing the light emitting layer at a heat treatment temperature, cooling the light emitting layer at a rate of 20 ° C or more per minute to 950 ° C at the heat treatment temperature, cooling the light emitting layer at a rate of 20 ° C or less per minute from 950 ° C to 650 ° C, And forming strained layers at boundaries between the faces.

As described above, in the present invention, since each subphase is mainly formed of a crystal having a strained layer at the boundary with the surrounding main face, the strained layer existing around the subphases is a carrier . Therefore, crystals constituting the subphases act effectively as a quantized light emitting medium, and short wavelength visible light emitted from the nitride semiconductor light emitting device including the light emitting layer can exhibit high light emission intensity and excellent monochromaticity.

These and other objects and features of the present invention will become more apparent from the following detailed description in conjunction with the accompanying drawings.

A crystal phase having a substantially constant indium content (concentration) and spatially occupying a certain region is hereinafter referred to simply as a phase. A face occupying a large area is called a main phase, and a face occupying a smaller area than a main face is called a sub-phase. The subfaces may be distributed substantially uniformly at the main face or may be non-uniformly positioned in the region near the junction boundary with other layers. The main faces and subphases are not distinguished by the indium content, but by the space occupied by the volume.

The main face is mainly formed of a layer structure single crystal obtained by laminating monocrystalline layers. In some cases, the main face may include locally polycrystalline regions or amorphous regions. Regardless of the crystal form, occupying a large area is the main face. Almost all subphases are small crystals (microcrystals). Microcrystals are made of single crystal, polycrystalline or amorphous. Alternatively, microcrystals may be a mixture of these materials. Generally, the microcrystalline shape is an island-like shape or a polygonal shape. The diameter of the subphases is about several nm to several tens nm, and in the island shape, the width is about several nm to several tens nm. A relatively large indium deposition sometimes occurs from indium nuclei deposited at the junction boundary with other layers to several μm to several tens of μm. In the present invention, however, crystals having a size of about several nm to several tens nm are treated as sub-faces.

In the present invention, the light emitting layer is formed of an indium-containing Group III nitride semiconductor having a multi-face structure composed of a main face and sub-faces. The average layer thickness of the layer-like medium constituting the main face is the layer thickness of the light emitting layer. When the light emitting layer has an extremely thin thickness of less than about 1 nm, continuity as a layer is obtained. The light emitting layer formed of the discontinuous layer has a disadvantage of reducing the forward voltage of the light emitting device. On the contrary, when the light emitting element is a thick layer having a thickness of about 300 nm, the surface structure is deteriorated and can not be used as a light emitting layer for increasing the light emitting intensity. Therefore, the thickness of the light emitting layer should be about 1 to 300 nm.

The light emitting layer may be formed of an indium-containing Group III nitride semiconductor intentionally doped with an impurity. The light emitting layer may also be formed of an indium-containing Group III nitride semiconductor doped with a non-intentionally impurity. In addition, the light emitting layer may also be formed in a laminated structure of non-doped and doped layers. In terms of light emission intensity, the doped luminescent layer must be made somewhat thick. The thickness thereof should be approximately 10 to 300 nm. The non-doped luminescent layer must be made thinner. The thickness of the non-doped luminescent layer should be within the range of approximately 1 to 10 nm.

The conduction type of the light emitting layer should be n-type. This is because the transfer of carriers, especially electrons, between the main face and the subphases mainly determines the emission intensity. Therefore, it is preferable that electrons are used as majority carriers in the light emitting layer, and therefore, the light emitting layer is preferably n-type. It is preferable that the carrier concentration of the light emitting layer is not less than 1 x 10 ¹⁶ cm ^{-3 and not} more than 1 x 10 ¹⁹ cm ^-3 . It is absolutely necessary that the carrier concentration of the main face and subphases be approximately equal. For example, the carrier concentration of the main face may be 1 x 10 ¹⁸ cm ^-3 and the carrier concentration of the subphases may be 1 x 10 ¹⁷ cm ^-3 . Regardless of the difference between the carrier concentration of the main face and the subphases, the carrier concentration must be within the aforementioned concentration range throughout the light emitting layer.

Subfaces are generated from inside the main face. For example, subfaces originate from indium as nuclei contained within the main face, where indium is agglomerated in dense regions or dense regions in the main face. When the density of subphases in the main face becomes extremely large, the emitted light from the main face (light emitting layer) loses monochromaticity. When the density of the subphases exceeds 2 × 10 ¹⁸ cm ^-3 , the monochromaticity of the emitted light drastically deteriorates. Therefore, the density of the subphases should be less than 2 × 10 ¹⁸ cm ^-3 . In particular, in the case of a non-doped luminescent layer having a layer thickness of 20 nm or less, it is preferable that the density of the sub-faces is 5.0 x 10 ²³ x t (t is the layer thickness (cm)) or less. When the density of the subphases is within the above-mentioned range, emitted light excellent in monochromaticity having a half width of 15 nm or less can be obtained.

In some cases, a light-emitting layer formed of a vapor-grown indium-containing Group III nitride semiconductor by MOCVD growth at a temperature in the range of 650 ° C to 950 ° C is separated into a plurality of paces in the grown state . However, in the as-grown multiphase, the size of the subphases is extremely non-uniform. When the grown indium-containing Group III nitride semiconductor layer is heat-treated, the main face functions as a parent phase, so that sub-faces can be stably generated, and a multiphase structure can be generated. In the heat treatment method for stably forming a multiphase indium-containing Group III nitride semiconductor functioning as a light emitting layer, the subphases have the following characteristics: (a) a rate of temperature rise from the growth temperature of the light emitting layer to the heat treatment temperature; (b) , And (c) optimizing the cooling rate when the temperature is lowered from the heat treatment temperature. Uniform formation of the indium content (arrangement) in the sub-face as well as the uniformization of the sizes of the sub-faces brings about the effect of increasing the uniformity of the monochromaticity of the emission wavelength and emitted light in particular.

In the present invention, the structure of the boundary region between the main face and the sub-faces in the light emitting layer is additionally defined. Specifically, the feature of the subphases in the present invention is that the subphases have a deformed region (strained layer) at the boundary between the subphases and the surrounding main face. And, the number of subphases with this deformation layer is set to account for more than 50% of the total subphases.

In the heat treatment of the light emitting layer for stably forming the multiphasic structure, the subphases having the peripheral strained layer can be formed by appropriately adjusting the cooling rate from the heat treatment temperature. The most preferred cooling method is to lower the heat treatment temperature between 950 캜 and 1200 캜 by varying the cooling rate. The preferred heat treatment temperature range is 950 ° C to 1200 ° C. In particular, the cooling method includes lowering the temperature from the heat treatment temperature to 950 占 폚 at a rate of 20 占 폚 or more per minute and lowering the temperature at 950 占 폚 to 650 占 폚 at a rate of 20 占 폚 per minute or less, It allows stable formation of subphases. With this cooling method, the proportion of subphases with strained layers can be stably formed to be at least 50% of the total subphases. The ratio of subphases having a strained layer can be determined by counting the number of subphases having a strained layer on a grating photographed by a transmission electron microscope (TEM). If the temperature is lowered at a temperature of 950 占 폚 from the heat treatment temperature at a rate of 20 占 폚 per minute or less, the surface texture of the light emitting layer can not be maintained excellent, resulting in an uneven light emitting layer. Performing rapid cooling at a rate exceeding 20 占 폚 per minute from 950 占 폚 to 650 占 폚 is undesirable because it produces a strained layer exceeding the proper number around the sub-faces.

It is not necessary to independently perform the above-described heat treatment method for forming the multi-face structure. Formation of a multiphase structure can be obtained, for example, when a gallium nitride layer or an aluminum gallium nitride layer is grown on a light-emitting layer formed of an indium-containing Group III nitride semiconductor layer. This is because the growth temperature when these layers are grown on the light emitting layer is within the range of the preferable heat treatment temperature.

Whether the indium-containing Group III nitride semiconductor has a multiphase structure can be confirmed by a typical transverse sectional transmission electron microscopy (TEM) method using a transmission electron microscope (TEM). The cross-section transmission electron microscope (TEM image) of the gallium nitride indium mixed crystals formed in a multiphase structure shows the subphase portion in a substantially spherical, trapezoidal or polygonal black contrast. In some cases, the black contrast may be due to crystal defects such as dislocation. The contrast due to dislocation is generally linear. From the shape of the contrast, it is possible to know whether or not the subphase is present, and the shape of the subphase can be known. The density of subphases in the main face can be measured from the contrast density due to subphases. Using an analytical electron microscope with a component analyzer, such as an electron probe microanalyzer (EPMA), indium content in each of the main face and sub-faces can be analyzed. The difference (change) in indium content between the main face and the sub-faces can also be analyzed by a precision X-ray diffraction method known as the four-crystal method.

The presence of the strained layer around the sub-faces can be largely observed on a magnified cross-sectional transmission electron microscope (TEM image). It is best observed when magnified by millions of times.

1 shows an example of a crystal lattice pattern when a light emitting layer of the nitride semiconductor light emitting device of the present invention is photographed using a transmission electron microscope (TEM). This crystal lattice image was obtained by photographing with a bright field section TEM method at 2 × 10 ⁶ magnification. This figure will be described.

The light emitting layer 2 is a multiphase structure composed of subphases 22 having an indium content different from that of the main face 21 and the main face 21. The strained layer 23 is present in the periphery of each sub-face 22 in the main face 21 which functions as a matrix of the light-emitting layer 2. Specifically, the sub-face 22 is a crystal having a strained layer 23 formed at the boundary with the main face 21. Although the thickness of the strained layer 23 is shown generally uniformly around the sub-faces 22, this is not always the case. In some cases, the strained layer 23 is distorted, for example, only grown thick in one direction.

Comparing the spacing of the crystal lattice planes reveals that the spacing of the gratings in the main face 21, sub-faces 22 and strained layers 23 is different. Specifically, it can be seen that the strained layer 23 has a lattice plane (lattice) spacing and a lattice direction different from the main face 21 and the sub-face 22. The spacing on the lattice of the strained layer 23 is intermediate between that of the main face 21 and that of the sub-face 22, and the lattice (phase) thereof is occasionally disordered.

The thickness of the strained layer 23 surrounding the sub-face 22 affects the intensity of the emitted light from the light-emitting layer 2 of the multiphase structure. If the strained layer 23 is thickened, it can not have a large light emission intensity increasing effect. Let d be the thickness of a suitable strained layer 23 for obtaining high intensity luminescence. The thickness (region width) d of the strained layer 23 suitable for high-intensity light emission is equal to or less than 0.5 x D, where D is the size of the sub-face 22. When the sub face 22 is substantially spherical, D can be expressed by the diameter. When the sub face 22 is a ciliary body, D can be expressed as a width. For example, the thickness of the strained layer 23 for a spherical subphase with a diameter of 20 nm is set to 10 (= 0.5 x 20) nm or less.

Although the thickness d of the strained layer 23 is not always uniform, the effect is not reduced even when the average thickness of the strained layer 23 is 0.5 x D or less. However, when the thickness of the strained layer 23 is extremely thin, a large light emission intensity increasing effect is not exhibited. This is because if there is no strained layer 23 between the main face 21 and the sub-face 22, the band structure for generating the quantized carrier that contributes to high-intensity light emission is not completely formed. The thickness of the strained layer 23 should be at least 5 Angstroms, and preferably 10 Angstroms (1 nm) or greater.

On the other hand, the maximum value of the thickness d of the strained layer 23 should be 10 nm or less. This is preferable as the thickness of the strained layer in consideration of the indium content of the indium-containing Group III nitride semiconductor layer mainly used as the light emitting layer 2, which is about 5% to about 50%. Therefore, the thickness d of the strained layer 23 should be set in a range from about 5 angstroms or more to about 10 nm or less.

As described above, after the growth of the indium-containing Group III nitride semiconductor layer serving as the light-emitting layer 2 is completed, the temperature lowering rate is adjusted in the step of heat-treating the light-emitting layer 2 to produce a multi- The thickness d of the strained layer 23 can be controlled. The temperature lowering (cooling) rate in the temperature range between 950 ° C and 650 ° C is the dominant factor for determining the thickness d of the strained layer 23. The temperature lowering rate within this temperature range shall be 20 ℃ or less per minute. By setting the temperature decreasing rate in the range of 5 占 폚 / min to 20 占 폚 / min, more preferably in the range of 7 占 폚 / min to 15 占 폚 / min, the strained layers 23 may be formed. At the same time, under this cooling rate, the proportion of subphases having a strained layer can be stably more than 50%. When the temperature is lowered at a rate exceeding 20 占 폚 / min, the thickness of the strained layer 23 is increased and it is difficult to keep the thickness below 0.5 占.. On the other hand, if the temperature lowering rate is less than 5 占 폚 / min, the thickness d of the strained layer 23 decreases, and even if the temperature lowering rate is less than 3 占 폚 / min, the minimum strained layer thickness of about 5 占 can not be guaranteed.

In the temperature lowering rate in the cooling step, various temperature lowering patterns can be adopted. For example, cooling from 950 DEG C to 650 DEG C may be performed at a constant temperature drop rate, or cooling may be performed while changing the temperature drop rate. For example, good results can be obtained if the temperature falls from 950 ° C to 800 ° C at a rate of 15 ° C per minute and from 800 ° C to 650 ° C at a rate of 10 ° C per minute. Alternatively, the temperature may be kept constant at a certain temperature between 950 ° C and 650 ° C for a predetermined waiting time after the falling at a constant rate at 950 ° C, and then cooled to 650 ° C. The advantage of keeping the temperature almost constant during a given waiting time of the temperature lowering treatment time is that uniformity of the thickness d of the strained layer 23 around the sub-faces 22 is obtained. Thus, if the temperature decreasing rate defined by the present invention is used with a waiting time temperature decreasing method, the thickness d of the straining layer can be controlled and the uniformity of the thickness d of the straining layer 23 can be obtained . The presence of the strained layer 23 having a controlled and uniform thickness contributes to making the quantum level uniform, resulting in an increase in the emission intensity and monochromaticity of the emitted light.

As described above, in this embodiment, in the light emitting layer formed of indium-containing Group III nitride semiconductor having a multi-face structure composed of main faces and sub-faces having different indium contents, the sub- The strained layer existing around the sub-faces stably generates the carriers contributing to the increase in the light emission intensity. Therefore, the lattice constituting the subphases can effectively function as the quantum luminescent medium, and the short wavelength visible light output from the nitride semiconductor light emitting element including this luminescent layer can be stably emitted with high intensity luminescence and excellent monochromaticity.

Furthermore, since the sub-faces are mainly composed of gratings having strained layers with a width of 0.5 x D or less in comparison with the size (D) of the entire sub-face, the thicknesses of the strained layers are maintained at appropriate values to obtain high- .

Furthermore, since the sub-faces having a strained layer are formed to occupy more than 50% of the total sub-faces, the characteristics of the strained layer contributing to improvement of the light emission intensity can be reliably shown.

Furthermore, since the density of the subphases is set to 2 x 10 ¹⁸ cm ^-3 or less, emission light having a half width of, for example, 15 nm or less and excellent monochromaticity can be obtained.

Now, the nitride semiconductor light emitting device of the present invention will be described in detail. The present invention is not limited to these examples.

First Embodiment:

An example in which the present invention is applied to a light emitting diode (LED) will be described. Using a conventional normal pressure (atmospheric pressure) type metal organic chemical vapor deposition (MOCVD) growth reactor, the constituent layers of the laminated structure used for the LED are successively formed on the substrate according to the following procedure.

2 is a schematic view showing a laminated structure of the LED according to the first embodiment. The laminated structure 11 is manufactured by laminating on the substrate 100. The substrate 100 used is a (0001) (c-plane) sapphire (? -Al ₂ O ₃ single crystal) polished on both sides with a diameter of 2 inches (5 mm) and a thickness of about 90 μm. Trimethyl gallium ((CH _{3) 3} Ga) as a raw material, trimethyl aluminum ((CH _{3) 3} Al) and ammonia, aluminum gallium nitride by a normal pressure MOCVD method using a _{(NH 3) (Al 0.8 Ga} 0.2 N) film A low temperature buffer layer 100a is formed on the substrate 100. The film formation is carried out in a hydrogen gas at a temperature of 430 DEG C for 3 minutes. The hydrogen flow rate is 8 liters per minute and the ammonia gas flow rate is 1 liter per minute. The thickness of the low temperature buffer layer 100a is 15 nm.

Next, a hydrogen gas containing disilane (Si ₂ H ₆ ) having a volume concentration of about 3 ppm was added to the MOCVD reaction system, and an n-type gallium nitride (GaN) was grown in hydrogen-argon GaN) layer 101 is formed on the low-temperature buffer layer 100a. The amount of disilane-hydrogen mixed gas added to the system is precisely controlled to 10 cc per minute by an electronic flow controller (MFC). The n-type gallium nitride layer 101 doped with silicon (Si) has a carrier concentration of 3 × 10 ¹⁸ cm ^-3 and a thickness of about 3 μm.

After the temperature of the substrate 100 falls from 1100 캜 to 800 캜, the light emitting layer 102 composed of indium gallium nitride (Ga _0.82 In _0.18 N) having an indium content of 18% on the average is formed on the n-type gallium nitride layer 101, &Lt; / RTI &gt; The growth of the light emitting layer 102 is carried out in the gas of argon. The thickness of the light emitting layer 102 is made 5 nm. Trimethyl gallium is used as a gallium source, and trimethyl indium is used as an indium source. The trimethylgallium is stored at a constant temperature of 0 ° C, and the hydrogen flow rate to be foamed is precisely controlled to 1 cc / minute by MFC. The trimethyl indium is stored at a constant temperature of 50 ° C. The flow rate of hydrogen associated with the sublimed trimethyl indium vapor is set at 13 cc per minute by the MFC. The flow rate of the ammonia gas and the nitrogen source is set so that the V / III ratio in the growth time of the light emitting layer 102 is about 3 × 10 ⁴ . Here, the V / III ratio represents the ratio of the concentration of the nitrogen source to the total concentration of the gallium source and the indium source supplied to the growth reaction system. The growth rate of the light emitting layer 102 is lower than the growth rate of the n-type gallium nitride layer 101, and is set at about 2 nm / min.

After completion of the light emitting layer 102, the substrate 100 is rapidly heated from 800 占 폚 to 1100 占 폚 at a rate of temperature increase of 100 占 폚 / min in argon gas. The air in the MOCVD reaction system is changed to a mixture of argon and hydrogen while waiting for 1 minute at 1100 ° C. and a layer 103 of aluminum gallium mixed crystal (Al _0.5 Ga _0.85 N) doped with magnesium (Mg) And is deposited on the light emitting layer 102. The growth rate is set at 3 nm / min, which is 1.5 times faster than the growth rate of the light emitting layer 102. The growth is continued for 10 minutes to obtain a mixed layer about 30 nm thick. Bis-cyclopentadienyl magnesium (bis- (C ₅ H ₅ ) ₂ Mg) is used as a dopant for magnesium. The supply amount of the magnesium doping source to the MOCVD reaction system is set to 8 × 10 ^-6 ㏖ / min. The concentration of magnesium atoms in the magnesium-doped aluminum gallium nitride layer 103 is determined to be about 6 x 10 ¹⁹ atoms / cm ³ by a conventional SIMS analysis.

Next, a magnesium-doped gallium nitride layer 103a is deposited on the magnesium-doped aluminum gallium nitride layer 103 at a temperature of 1100 ° C in an argon-hydrogen mixed gas for about 20 minutes. Trimethylgallium is used as a gallium source, and the same organomagnesium compound used for the growth of the magnesium-doped aluminum gallium nitride layer 103 is used as the magnesium source. Since the doping rate of magnesium is observed to increase with the decrease of the growth rate, the growth rate is set at about 3 nm / min. The thickness of the magnesium-doped gallium nitride layer 103a is about 60 nm.

After the formation of the constituent layers 100a, 101, 102, 103 and 103a of the laminated structure 11, the ammonia gas is added to the mixed gas containing the same amount of argon and hydrogen, Lt; RTI ID = 0.0 &gt; 950 C. &lt; / RTI &gt; From 1100 ° C to 950 ° C, the flow rate of hydrogen gas, which constitutes air and exhibits a large thermal conductivity, is increased from 4 liters / min to 8 liters / min, and the substrate is substantially forced cooled in one minute. After the temperature of the substrate 100 has dropped to 950 DEG C, the gas that can flow in the MOCVD reactor is limited to argon. The temperature decrease from 950 DEG C to 650 DEG C is carried out at a rate of 10 DEG C / min for 30 minutes. The reduction to 650 DEG C room temperature is carried out using argon-hydrogen air in the MOCVD reactor. It takes about 40 minutes to lower the temperature to about 30 ° C.

After cooling, the internal structure of the light emitting layer 102 is observed at an acceleration voltage of 200 kV by a typical cross-sectional transmission electron microscopy (TEM) method using a part of the laminated structure 11 as a sample.

3 is a diagram showing a crystal lattice image obtained by photographing a light emitting layer of the first embodiment using a transmission electron microscope (TEM). The magnification of observation is 2 x 10 ⁶ . FIG. 3 shows that the light emitting layer 102 of the first embodiment is composed of a main face 201 and a multiphase structure including substantially spherical or island-like sub-faces 202. Island shaped sub-faces 202 are more noticeably observed near the boundary between the light emitting layer 102 and the n-type gallium nitride layer 101 than in other regions. The density of subphases 202 calculated from the number of subphases 202 within the photographed area is about 2 x 10 ¹⁷ cm ^-3 . The indium contents of the main faces 201 and the sub paces 202 are different from each other and the indium concentration of the sub paces 202 is observed to be higher than that of the main face 201. [ Subphases with an indium content of about 30% were also observed.

It has also been observed that each subphase 202 has a strained layer 203 at the interface with the main face 201. The diameter of the nearly spherical sub-faces 202 is about 25 to 35 ANGSTROM (2.5 to 3.5 nm). The width of the island shaped sub-faces 202 is about 35 angstroms. In some cases, the angle difference in the direction of the lattice planes in the sub-face 202 and the strained layer 203 is about 60 degrees. Although the strained layer 203 is not always present in uniform thickness around the sub-face 202, its average thickness is about 10 angstroms. The thickness (width) d of the strained layer 203 surrounding the sub-face 202 having a diameter or width of 25 to 35 ANGSTROM is 8 to 13 ANGSTROM. The thickness d of the strained layer 203 surrounding the sub-face 202 of a relatively small diameter or width (about 10 to 15 ANGSTROM) is from slightly less than 5 ANGSTROM to 7 ANGSTROM. In addition, the ratio of the strained layer having such a thickness is about 86%.

An LED is fabricated based on the laminated structure (11).

Fig. 4 schematically shows the cross-sectional structure of the LED of the first embodiment. The cross section is according to line 4-4 in Fig. 5 is a schematic plan view of the LED. An LED 50 is obtained by providing electrodes in the laminate structure 11.

First, a region for forming the n-type pad electrode 109 is formed by plasma etching using a methane / argon / hydrogen mixed gas. On the surface portion of the n-type gallium nitride layer 101 exposed by etching, an n-type pad electrode 109 having a diameter of 100 m as an aluminum element is formed by a conventional vacuum evaporation method. The thickness of the electrode 109 is made about 2 mu m. The p-type pad electrode 105 is formed on the magnesium-doped gallium nitride layer 103a which is the uppermost surface layer of the remaining portion in the form of a mesa structure by a conventional vacuum evaporation method. A surface of the electrode 105 in contact with the magnesium-doped gallium nitride layer 103a is formed of a gold-beryllium (Au · Be) alloy and an upper surface of the electrode 105 is formed of a gold (Au) element. The total thickness of the electrode 105 is made about 2 mu m. The p-type pad electrode 105 is provided on the opposite corner of the side where the n-type pad electrode 109 is provided on the upper surface of the LED. A thin-film electrode 104 made of transparent gold having a thickness of about 20 nm is provided on the surface of the magnesium-doped gallium nitride layer 103a in electrical contact with the p-type pad electrode 105. In addition, a transparent insulating nickel (Ni) oxide thin film 104a having a thickness of about 10 nm is formed only on the surface of the gold thin film electrode 104. [ The thin film 104a substantially acts as a protective film for the entire exposed surface of the gold thin film electrode 104 and the magnesium-doped gallium nitride layer 103a.

The LED 50 configured as described above operates to emit light by applying a DC voltage between the n-type pad electrode 109 and the p-type pad electrode 105. [ The measured luminescent properties are shown in Table I below.

Second Embodiment:

After the lamination structure 11 of the first embodiment is formed, the structure is cooled under cooling conditions that are partly different from the cooling conditions in the first embodiment. Concretely, after cooling from 1100 캜 to 950 캜 is continued under the same conditions as in the first embodiment, the temperature is lowered from 950 캜 to 800 캜 at a rate of 7.5 캜 / min for 20 minutes. Thereafter, the temperature is maintained at 800 DEG C for 15 minutes. Then, the temperature is lowered from 800 DEG C to 650 DEG C at a rate of 10 DEG C / min. After the temperature reaches 650 DEG C, the air gas fed to the MOCVD reactor is limited to hydrogen and the temperature falls to room temperature. It takes about 45 minutes to cool to about 30 ° C.

After cooling, the internal structure of the luminescent layer is determined by the cross-sectional transmission electron microscopy (TEM) method. The light emitting layer in the second embodiment has a multiphase structure composed of a main face and sub faces similar to the light emitting layer 102 in the first embodiment. The subphases were observed to have a strained layer at the interface with the main face. The indium concentration of the subphases is generally higher than that of the main face, and the indium content of the main face is estimated to be about 15%. The subphases are mostly spherical bodies with a uniform diameter of about 30 angstroms. In addition, the thickness of the strained layers around the subfaces is uniformly about 10 angstroms. As described above, in this second embodiment, the temperature is lowered by a method comprising the step of holding at 800 DEG C for 15 minutes, whereby the shape of the sub-faces can be made substantially spherical, and the thickness of the strained layers Can be more uniformly controlled. In addition, the ratio of subphases having a strained layer, which is found from a cross-sectional transmission electron microscope (TEM image), is about 72%.

Control Example:

After forming the lamination structure described in the first embodiment, the temperature is spontaneously lowered to room temperature at 1100 캜. It takes about 90 minutes for the temperature to drop to about 30 ° C. Thus, the average cooling rate is about 12 ° C / min. According to the prior art (Japanese Patent Laid-Open No. 9-40490), the inert gas air at a temperature of less than 1000 占 폚 is argon. Unlike in the first and second embodiments, no process using air-only hydrogen gas is performed in a temperature range below 650 ° C.

The internal structure of the luminescent layer of the laminated structure cooled under the above-mentioned ordinary conditions is observed by the cross-sectional transmission electron microscopy (TEM) method. Although linear black contrasts believed to be mainly due to dislocations are observed, spherical or island-shaped contrasts due to a population of indium, representative of subphases, are not clearly observed. The density of the sub-picture from the face number of substantially spherical or island-like in contrast, located in the shooting range was found to be not more than 1 × 10 ¹² ㎝ ^-3. Essentially, it is not clear that the light emitting layer is composed of a multiphase structure.

The laminated structures cooled under the conditions of the second embodiment and the control embodiment are processed in the manner of the first embodiment for manufacturing LEDs. Each LED operates to emit light by applying a DC voltage between its electrodes. The measured luminescent properties are shown in Table I.

Table I

Characteristics unit First Embodiment Second Embodiment Control Example Emission wavelength Nm 448 450 431 Emission intensity MW 1.8 2.1 0.4 Half Width Nm 9 7 18 Forward voltage V 3.9 3.8 3.9 Reverse voltage V > 40 > 40 > 40

From the comparison of the luminescence characteristics of the LEDs of the first and second embodiments and the control example shown in Table I, it can be seen that the luminescence wavelength is in the range of 430 to 450 nm and there is no large difference between the luminescence wavelengths. In addition, no substantial difference is observed between the forward voltage when the forward current is set to 20 mA or the reverse voltage when the reverse current is set to 5 μA. On the other hand, in the light emission intensity measured by an ordinary method using a conventional integrating sphere, the LED of the second embodiment, which is composed of the light emitting layer including subphases having substantially uniform strain layers, It should be noted that it shows the highest value. The light emission intensity of the LED of the control example is the lowest, i.e., 0.4 mW. The half width (FWHM) of the main emission spectrum is considerably different. The LED of the second embodiment has the smallest half-width value at 7 nm. The LED of the first embodiment has a half-width value of 9 nm, and the half-width value of the LED of the control embodiment is the largest at 18. The LED of the control example shows luminescence lost monochromaticity.

While the above examples describing the present invention have been applied to light emitting diodes (LEDs), the present invention may be similarly applied to other light emitting elements such as laser diodes (LDs).

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art without departing from the spirit and scope of the present invention as defined by the appended claims.

In the present invention, since each subphase is mainly formed of crystals having a strained layer at the boundary with the surrounding main face, the strained layer existing around the subphases stably generates a carrier which increases the light emission intensity. Therefore, crystals constituting the subphases act effectively as a quantized light emitting medium, and short wavelength visible light emitted from the nitride semiconductor light emitting device including the light emitting layer can exhibit high light emission intensity and excellent monochromaticity.

Claims (8)

(Amorphous) indium-containing Group III nitride semiconductor layer having a different indium content and mainly composed of a layered single crystal and a multi-face structure composed of sub-faces dispersed in the main face and composed of microcrystalline, In the nitride semiconductor light emitting device to be used, Wherein the subphases are mainly formed by crystals whose boundary with the main face is surrounded by a strained layer. (Correction) The method according to claim 1, Wherein the sub-faces are formed of the crystal having the strained layer, the width of which is 0.5 x D or less, when the total size of the sub-face is D, respectively. (Correction) The method according to claim 1, Wherein the thickness of the strained layer is in the range of 5 to 10 nm. (Correction) In any one of claims 1 to 3, Wherein the number of subphases having the strained layer is greater than or equal to 50% of the total number of subphases. (Correction) In any one of claims 1 to 3, And the density of the subphases is 2 x 10 ¹⁸ cm ^-3 or less. (Correction) In any one of claims 1 to 3, Wherein the thickness of the light emitting layer is in the range of 1 nm to 300 nm. A method for manufacturing a nitride semiconductor light-emitting device using an indium-containing Group III nitride semiconductor layer having a multi-face structure composed of a main face and sub-faces having different indium contents, as a light emitting layer, (a) heat-treating the light-emitting layer at a heat treatment temperature within a range of 950 ° C to 1200 ° C; (b) cooling the light emitting layer at a rate of 20 ° C or more per minute up to 950 ° C at the heat treatment temperature; And (c) cooling the light emitting layer at a rate of not more than 20 占 폚 per minute from 950 占 폚 to 650 占 폚 to form a strained layer at a boundary between the main face and the sub-faces. Lt; / RTI &gt; (Correction) The method according to claim 7, Wherein the light emitting layer is maintained at a temperature selected arbitrarily between 950 ° C and 650 ° C during the cooling of the light emitting layer from the heat treatment temperature for a predetermined time.