JP3097596B2 - Group III nitride semiconductor light emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a group III nitride semiconductor light emitting device having a light emitting layer made of a group III nitride semiconductor, and more particularly to a light emitting device which is excellent in monochromaticity and emits high-luminance short-wavelength visible light. The present invention relates to a structure of a light emitting layer that provides an element.

[0002]

2. Description of the _Related Art Al _x Gay In _1-xy N (0 ≦ x ≦
1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) and other III nitride semiconductors emit light (e.g., LED) or visible laser diode (e.g., LED) that emits short-wavelength visible light such as blue or green light. : LD), which is used as a light emitting layer. In particular, gallium-indium mixed crystals (Ga _x I
It is well known that n _1-x N: 0 <x <1) is commonly used as a light emitting layer (for example, see Japanese Patent Publication No. 55-3834). Like gallium nitride-indium mixed crystal III
In the present invention, a light emitting device having a light emitting layer made of a group III nitride semiconductor is referred to as a group III nitride semiconductor light emitting device for convenience.

The conventional specifications required for the gallium-indium nitride mixed crystal (Ga _x In _1-x N: 0 <x <1) as the light-emitting layer are omitted.
Was the main composition ratio. This is based on the conventional insight that the main factor influencing the emission wavelength from the gallium nitride-indium mixed crystal layer is the indium composition ratio (see Japanese Patent Publication No. 55-3834 described above). For example, about 450 nanometers (nm) with high visibility
In the vicinity of the light-emitting layer intended for blue light emission, the gallium nitride / indium composition ratio is set to about 5% to 20%.
Indium mixed crystals have been preferred.

Here, the problem of the conventional group III nitride semiconductor light emitting device provided with a gallium nitride / indium mixed crystal which is sufficient as the light emitting layer by satisfying the specification of the indium composition ratio is proposed. First, the color of the emitted light changes depending on the voltage (current) applied to the light emitting element. That is, there is an applied voltage (current) value dependency of the emission wavelength. The second problem is that if the voltage value applied to the light emitting element exceeds a certain boundary value, the main emission wavelength will correspond to the indium composition ratio, but the hue is unified (emission monochromaticity). Are still coexisting with the secondary luminescence that is hindered. The third is also related to monochromaticity of light emission. For example, in a light emitting diode (abbreviation: LED), the half width of the light emission spectrum is other than that of another material such as aluminum arsenide / gallium mixed crystal (AlGaAs). This is extremely large as compared with an LED made of a group III compound semiconductor material. When compared with specific numerical values, a red band LED having a pn junction type double hetero junction structure using an aluminum gallium arsenide mixed crystal (AlGaAs) as a light emitting layer.
Is generally less than 100 angstroms (Å), whereas that of a group III nitride semiconductor light emitting device is generally at least about 150 °,
In many cases, the actual size is as large as about 200 ° to about 700 °. As described above, the problems associated with the conventional group III nitride semiconductor light-emitting device, particularly with the conventional LED using a gallium-indium nitride crystal as a light-emitting layer, are mainly due to insufficient monochromaticity of light emission. In other words, this suggests that the monochromaticity of light emission in the LED having the gallium indium nitride light emitting layer is not uniquely determined by the indium composition ratio of the light emitting layer.

A group III nitride semiconductor light-emitting device, whose monochromaticity is expected to be improved by reducing the thickness of the light-emitting layer, has recently been reported (S. Nakamura et al.
J. Appl. Phys. Vol. 34 (199
5), see pages L1332 to L1335). In particular,
In a blue LED having a light emitting wavelength of 450 nm and having a light emitting portion called a quantum well structure having a thin light emitting layer having a layer thickness of less than about 10 nanometers (nm) as a well layer, 20
It is said that a half width of nm was obtained. This suggests that the half width of the emission spectrum depends on the thickness of the light emitting layer. However, even if the thickness of the light emitting layer is made as thin as in the above-mentioned disclosed example and the indium composition ratio is precisely controlled, all of the above problems have not been solved. In fact, the problem of coexistence of secondary spectra in addition to the main spectra has not been overcome. FIG. 1 is an example of a typical spectrum exhibiting a secondary emission which has not been solved yet, and shows a main emission spectrum (10%).
This shows an example in which a secondary spectrum (102) is generated in the immediate vicinity of 1). As presented in this example, thinning the gallium-indium nitride light-emitting layer affects the narrowing of the half-width of the main emission spectrum, but conventional technical means of simply reducing the thickness of the light-emitting layer coexist. However, it is not sufficiently effective to suppress the generation of secondary spectra and to improve the monochromaticity of light emission in general.

Another specification conventionally required for a gallium-indium nitride mixed crystal layer as a light emitting layer is the homogeneity of the mixed crystal. If the gallium-indium nitride mixed crystal layer having a so-called single composition phase having a uniform mixed crystal composition ratio and uniform crystallinity is suitable for improving the emission intensity and monochromaticity, it is vaguely. It is due to what has been speculated. The gallium nitride-indium mixed crystal as the light emitting layer is required to have uniformity and uniformity, while the gallium nitride-indium mixed crystal (Ga _x In _1-x N: 0 <x <
It has already been taught in (1) that mixed crystals having a rather homogeneous composition are accompanied by growth difficulties (Jpn. J. Ap).
pl. Phys. , 46 (8) (1975), 343
2. reference). This is mainly due to the fact that the gallium-indium nitride crystal layer potentially has the property of being separated into phases having different mixed crystal composition ratios (see the above-mentioned document Jpn.
J. Appl. Phys. , 46 (8) (1975)). In the gallium indium nitride indium crystal layer, non-uniformity of the mixed crystal composition ratio in the mixed crystal layer due to immiscibility due to the difference in the covalent radius of both gallium nitride and indium nitride that constitute the mixed crystal does not occur. (The 57th Autumn Meeting of the Japan Society of Applied Physics, Proceedings No. 1, Autumn No. 8p-ZF-14, p. 209, 1996). In other words, contrary to what has conventionally been considered, it is becoming clear that the gallium-indium nitride crystal layer used as the light emitting layer is unlikely to be a crystal layer having a uniform mixed crystal composition and a homogeneous phase. is there.

In the case of a light emitting layer made of gallium / indium nitride as an example, a heterogeneous layer composed of a plurality of phases means that a plurality of phases having different indium composition ratios are mixed. . If more specific examples are shown, they can be collectively referred to as a gallium indium indium light emitting layer,
The layer has an indium composition ratio in which a plurality of phases having different indium composition ratios such as GaN (corresponding to an indium composition ratio = 0), Ga _0.95 In _0.05 N and Ga _0.80 In _0.20 N are mixed. Means a non-uniform layer. From a morphological point of view, it is almost always the case that a phase having a different indium composition ratio is present as a microcrystal (fine crystal grains) inside a main phase having a certain indium composition ratio. is there. Recently, it has been pointed out that there is a relationship between the existence of microcrystals as a result of non-uniformity and the light emitting mechanism of the gallium indium nitride crystal layer (see Japanese Patent Application No. 8-208486). According to the inventor's insight, the light emitted through the microcrystal decreases in energy as the diameter of the microcrystal increases, that is, the energy of light emitted from the microcrystal decreases, i.e., the wavelength of light emission becomes longer. Such as
There is one similar to light emission from a silicon (Si) microcrystal (EUROPEAN MATERIALS RES)
EARCH SOCIETY SIMPOSIA PR
ODEEDINGS 43, "Light Emiss
ion from Silicon ”(NORTH-H
OLLAND (ELSEVIOR SCIENCE
B. V. ) (1994), pp. 1-4). It is also presumed that the inhomogeneity of the crystal structure of the group III nitride semiconductor layer forming the light emitting layer leads to an improvement in the light output of the light emitting device.

Along with the expectation that the emission characteristics can be improved, a conventional homogeneous layer consisting of a single phase is not used as a light emitting layer, but a crystal structure consisting of a mother phase and a plurality of phases such as microcrystals. It is a recent technical trend to form a light emitting layer from a non-uniform layer. This is because it is mainly free from the technical difficulty of trying to achieve irrational homogenization of the light emitting layer for the following reasons. (A) As described above, in the case of a highly immiscible material such as gallium indium or the like, phase separation occurs naturally due to heating at the time of film formation or heat receiving in a subsequent process (for example, mother material). (Separation into phases and microcrystals). (B) Indium (atoms) are easily diffused, and tend to accumulate and aggregate in strains and crystal defects. As a result, a phase having a different indium composition (concentration) from the parent phase is generated inside the parent phase. However, while it is easy to form and the emission output is expected to be improved, what is "heterogeneity" in the crystal structure that leads to an improvement in the monochromaticity of the emission has not yet been clearly explored. . Especially in the gallium indium nitride crystal layer commonly used as a light emitting layer, the degree of monochromaticity and "heterogeneity" on the emission spectrum, for example,
The quantitative relationship with the total amount of microcrystals containing indium in the parent phase is still unclear.

[0009]

SUMMARY OF THE INVENTION A group III nitride semiconductor light-emitting layer having a heterogeneous crystal structure consisting of a plurality of existing forms such as a parent phase (main phase) and a microcrystalline body containing indium is used. In addition to clarifying the relationship between monochromaticity (purity of emission color) in light emission of the light emitting element and the heterogeneous structure of the light emitting layer, the heterogeneity of the light emitting layer, which is effective for improving the monochromaticity, is clarified. Requirements are presented with the total number of microcrystals as a factor.

[0010]

That is, the present invention provides (1)
Including parent phase and indium (In) scattered in the parent phase III
30 nm in diameter or width made of group nitride semiconductor
A light emitting layer composed of the following substantially spherical or island-shaped crystals, wherein the total amount of the crystals contained in the matrix is 2 ×
An object of the present invention is to provide a group III nitride semiconductor light emitting device having a light emitting layer of 10 ¹⁸ / cm ³ or less. The present invention is particularly characterized in a light emitting layer having a thickness of 20 nm or less,
The total amount of the crystals contained in the unit volume (1 cm ³ ) of the light emitting layer is calculated as dmax. (Pieces / cm ³ ) = 5.0 × 10 ^{23 with} respect to the layer thickness (t: cm) of the light emitting layer. × t (pcs / cm
³ ) The above-described group III nitride semiconductor light-emitting device comprising a light-emitting layer having a value equal to or less than dmax.

[0011] II for forming the light emitting layer according to the present invention
The I-V nitride semiconductor, the general formula Al _x Ga _y In _z N
There is an indium-containing material represented by (x + y + z = 1, 0 ≦ x, y <1, 0 <z ≦ 1). Typical luminescent layer application material on the previous gallium indium nitride of as a being denoted by the general formula _{(Ga x In 1-x N} : 0 <x <1)
There is. Moreover, the general formula _{Al x Ga y In z N 1} -a As a
(X + y + z = 1, 0 ≦ x, y <1, 0 <z ≦ 1, 0 ≦
a <1), or the general formula _{Al x Ga y In z N 1-} a P a
(X + y + z = 1, 0 ≦ x, y <1, 0 <z ≦ 1, 0 ≦
A nitride compound semiconductor containing arsenic (element symbol: As) or phosphorus (element symbol: P) which is a Group V element other than nitrogen represented by a <1) as a constituent element is exemplified. As an example of a semiconductor material belonging to this, gallium arsenide nitride (GaN _1-x As _x : 0), which can also take a cubic crystal structure, is used.
<X <1). The crystal system of the semiconductor material forming the light emitting layer is not particularly limited, and may be a hexagonal system (hexagonal system) or a cubic system such as gallium indium nitride. In addition, crystals of these different crystal classes may be mixed.

The parent phase is a phase in the group III nitride semiconductor material constituting the light emitting layer, which occupies a large space in space. Here, for example, even a crystal phase generically referred to as gallium indium nitride is regarded as a different solid phase if the indium concentration is different. As an example, a Ga _0.82 In _0.18 N phase having an indium composition ratio of 0.18 and a volume fraction of about 15% and a volume fraction of about 7%, respectively.
% Ga _0.92 In with an indium composition ratio of 0.08
_It is assumed that a gallium-indium nitride light-emitting layer is composed of a _0.08 N phase and a compositionally indium composition ratio of about 78% and an indium composition ratio of approximately 0, which is close to gallium nitride. The phase that occupies the largest volume of space, that is, the phase with the largest volume fraction, is the mother phase according to the present invention. In the above example, the phase considered gallium nitride in composition due to a sufficiently small indium composition ratio having the largest volume fraction is the parent phase. As can be seen when gallium-indium nitride mixed crystal (Ga _x In _1-x N: 0 <x <1) is selected as the crystal layer forming the light emitting layer, the material forming the light emitting layer contains indium, for example. Do
Even in the case of a group III nitride semiconductor material, the mother phase is not always a phase containing indium.

It is recognized that the other phases containing a relatively large amount of indium other than the parent phase change their morphology due to the heating of the light-emitting layer, and all become indium-containing crystals (crystal grains). In the present invention, this is referred to as a light emitting layer including a mother phase and a crystal made of a group III nitride semiconductor containing indium (In) dispersed in the mother phase. The outer shape of the crystal is mainly a substantially spherical shape, a hemispherical shape, or an island shape having a trapezoidal vertical cross section, as confirmed in an example in which a gallium indium nitride crystal layer is used as a light emitting layer. Here, the shape of a crystal that can take various external shapes will be described as “substantially spherical or island-like”. The size of the crystal varies depending on factors such as the semiconductor material forming the light emitting layer and the conditions for forming the light emitting layer.
In the present invention, the size of the crystal is described as "diameter or width" because the external shape of the crystal is collectively described as "substantially spherical or island-shaped". What affects the monochromaticity is a substantially spherical or island-shaped crystal having a diameter or width of about 30 nm or less. Crystals having a diameter or width exceeding about 30 nm do not particularly give an emission spectrum to the short-wavelength visible light region of blue, blue-green, green, yellow or red, and are particularly remarkable in the monochromaticity of the short-wavelength visible light-emitting device. Has no significant effect. Therefore, the present invention focuses on a substantially spherical or island-shaped crystal having a diameter or a width of 30 nm or less.
The presence of the crystal is confirmed by observing the internal structure of the light emitting layer at a high magnification by a cross-sectional TEM method using a transmission electron microscope (abbreviation: TEM), and the number of crystals can be measured.

If it is known that the crystal exists in the matrix at a constant density (represented by the symbol d (pieces / cm ³ )) in the thickness direction of the light emitting layer, the volume is increased to V (cm ³ ). The total amount of crystals existing in the light emitting layer (indicated by the symbol N) is expressed by the formula d.
Calculated from × V. However, the density of the crystalline body in the matrix is not always constant, for example, in the direction in which the thickness of the light emitting layer increases. In the case of a light emitting layer inserted between semiconductor layers having different thermal properties such as thermal conductivity or thermal expansion coefficient, an n-type gallium nitride layer and a p-type aluminum nitride P in the middle of gallium mixed crystal
In the gallium-indium nitride light-emitting layer arranged to form an n-junction double heterojunction structure, it can be seen that the density of the indium-containing crystal is increased almost at the center of the light-emitting layer in the direction in which the layer thickness increases. . This is because the magnitude of the thermal strain (thermal stress) applied to the light emitting layer or the distribution of the stress due to the difference in the coefficient of thermal expansion between the gallium indium nitride light emitting layer and the semiconductor layers bonded to both sides thereof. It is considered to be caused, but it is not clear. In addition, since the crystals in the gallium / indium nitride light-emitting layer are often present in the region near the interface between the light-emitting layer and the bonding layer that forms the bond between the light-emitting layer, the density of the crystals increases in the thickness direction of the light-emitting layer. In some cases, the data is not uniform. As described above, when the crystals are non-uniformly distributed in the layer thickness direction, the total number of crystals contained in the matrix may be, for example, actually measured from a cross-sectional TEM image or divided into certain layer thicknesses. The average density is determined based on the density of the crystals in each range, and the total number of crystals is calculated from the multiplication of the average density value and the thickness of the light emitting layer. Regardless of the mode of density distribution, the present invention specifies the total number of crystals in the matrix constituting the light emitting layer made of a group III nitride semiconductor.

In the blue band, a wavelength having a high visibility of about 450
The relationship between the total amount of crystals and the photoluminescence (English abbreviation: PL) emission intensity will be described using a gallium indium nitride emission layer that emits blue light in the vicinity of nm as an example. FIG.
Is a half-width of an emission spectrum (tentatively referred to as a main spectrum) having a wavelength of about 450 nm from a light-emitting layer having a relatively large thickness of about 50 nm for gallium indium nitride and the total amount of indium-containing crystals. Is shown. The crystal to be measured has a diameter or a width of not less than about 5 angstroms (Å) and not more than 300 (Å) due to the relationship between the observation magnification and the resolution at the time of TEM observation. In the light emitting layer having a relatively large layer thickness as described above, zinc (Zn) of Group II of the periodic table is used as an acceptor impurity as an acceptor impurity in order to increase the light emission intensity from the light emitting layer. Group IV silicon (Si) is co-doped as a donor impurity (see JP-A-6-260860). Both impurities are quantitatively adjusted and doped so as to obtain strong light emission from the light emitting layer. Crystal density is about 2 × 10 ¹⁸
In the case of cm ⁻³ or less, the presence of a secondary spectrum having an intensity so as to reach 1/10 of the intensity of the main spectrum other than the main spectrum having a desired wavelength of 450 nm is not recognized. Further, the half-width of the main spectrum from the light-emitting layer hardly depends on the total amount of crystals, and is good as less than 15 nm. In the present invention, a light-emitting layer that provides good monochromaticity based on the fact that the generation of a light emission spectrum at the room temperature is not observed at the room temperature and the half-width of the main PL spectrum is less than 15 nm. On the other hand, the total amount of crystals is 2 × 10 ¹⁸
If the value exceeds cm ^-3 , a secondary emission spectrum clearly separated from the main spectrum with this value as a critical value appears in the near ultraviolet and blue bands of about 380 to about 430 nm. The spectrum with the secondary emission is very similar to that of FIG. In addition, the secondary spectrum that appears is not always unique. For example, in addition to the near-ultraviolet band spectrum having a wavelength of about 380 to about 400 nm, a wavelength of about 50
A greenish band from 0 to about 550 nm or a reddish spectrum exceeding a wavelength of about 600 nm may also appear. In addition, light emission resulting from the band edge of gallium nitride appears at a wavelength of about 363 nm. For this reason, the emission color of the light-emitting layer is clearly deteriorated in monochromaticity, and the PL emission color becomes white at first glance. The plurality of sub-spectrums show that the indium composition ratio (concentration) is increased by increasing the total amount of crystals.
It is considered that this is caused by an increase in the probability of generation of various crystals having different values. It is appropriate that the wavelength of the secondary spectrum corresponds to the difference in the indium composition ratio (concentration) of the crystal. As described above, the PL spectrum from the gallium indium indium light emitting layer is helium (He)-
Using a cadmium (Cd) laser beam as a light source, and using a very common PL photometer that performs photometry via a photomultiplier tube (photomultiplier) that exhibits sufficient sensitivity in the near ultraviolet or blue band. It was done. The half width of the PL spectrum measured in a state where the surface of the light emitting layer is exposed and the half width of the spectrum of light emitted from an actual LED incorporating the light emitting layer correspond well. Therefore, P
From a simple measuring method such as L photometry, it can be inferred that the half width of the light emitting element is superior or inferior.

From the viewpoint of the emission intensity of the emission spectrum, if the total amount of the crystals exceeds 2 × 10 ¹⁸ cm ^-3 , the wavelength emitted by the light emitting layer is set to about 450 n with this value as a critical value.
The emission intensity of the main spectrum at m sharply drops. When the total amount of crystals in the light emitting layer further increases, the wavelength becomes 450 nm.
The intensity of the nearby main spectrum is attenuated, and conversely, the intensity of the secondary spectrum that appears in the above wavelength region increases. In particular, the intensity of the secondary spectrum in the near-ultraviolet region may exhibit an intensity exceeding the main emission spectrum, rather than 1/10 of the intensity of the main emission spectrum.
Therefore, in the present invention, the density of the indium-containing group III nitride semiconductor crystal in the mother phase is specified to be 2 × 10 ¹⁸ cm ⁻³ or less in order to maintain emission intensity and maintain emission monochromaticity.

The total amount of crystals in the matrix is 2 × 10 ¹⁸ cm ^-3
The following rule specifies that the layer thickness be several tens of nm, especially about 20 n
This is particularly effective for a relatively thick light emitting layer exceeding m. In such a light emitting layer having a relatively large layer thickness, silicon (S
i) and zinc (Zn) are simultaneously doped (see JP-A-8-260681), or the doping ratio of Si and Zn is limited (JP-A-6-1066).
4, 6-10665) was typical of the prior art. However, according to the present invention, by defining the total amount of the crystals inside the light emitting layer, it is not necessary to perform the doping operation of the impurity in the light emitting layer and the precise control of the ratio of the doping concentration of the donor impurity and the acceptor impurity. There is the convenience that the emission intensity is improved in addition to the monochromaticity that is remarkably excellent in the emission color. That is, according to the present invention, in order to obtain monochromaticity of light emission stably and to maintain a high light emission intensity of light of a desired wavelength (expressed as a main spectrum in the above example), it is necessary to use impurities as in the prior art. It is disclosed that if the total amount of the crystals in the mother phase is more strictly defined according to the thickness of the light emitting layer than the means depending on the doping, the effect can be more easily exhibited.

Further, in the present invention, the unit volume (=) is increased as the thickness of the group III nitride semiconductor layer serving as the light emitting layer is reduced.
The total amount of crystals in the same layer per 1 cm ³ ) is reduced. The definition of the total amount of this crystal depends on the thickness of the light emitting layer of the half width of the PL emission spectrum from the light emitting layer and the main P
This is based on the dependence of the intensity of the L emission spectrum on the thickness of the light emitting layer. FIG. 3 shows an indium solid phase composition ratio of about 0.08 (8%). The gallium-indium nitride light-emitting layer grown by the atmospheric pressure (atmospheric pressure) MOCVD method has good monochromaticity and excellent strength. The maximum total amount of crystals allowed per unit volume of the light-emitting layer that results in the PL emission spectrum is stated in relation to the thickness of the light-emitting layer. Nitrogen gallium
The layer referred to as the indium light-emitting layer is solid, gallium nitride or a composition in which the indium solid phase composition ratio is almost 0, and has gallium / indium nitride which is extremely close to nitrogen gallium as a mother phase, and an average diameter containing indium in the mother phase. And has a configuration in which a substantially spherical crystal of about 8 nm is inherent. Good monochromaticity is determined from the half-width of the PL spectrum that is an index of monochromaticity, and is based on the fact that the half-width of the main PL spectrum having the maximum emission intensity at room temperature is less than 15 nm. ing. In addition, a PL spectrum excellent in intensity is used as an index when the emission intensity of the main spectrum is 10 times or more the intensity of a secondary spectrum other than the main spectrum. FIG.
In the case of a light emitting layer made of gallium indium nitride based on the results shown in the above, the maximum total amount allowed per unit volume of the crystal light emitting layer that satisfies the above optical characteristics of the light emitting layer is defined. It is as follows. (A) In a light emitting layer composed of a matrix and a crystal having a layer thickness of 20 nanometers (nm), the maximum amount of crystals in the matrix is 1.0 × 10 ¹⁸ cm ⁻³ . (B) In a light emitting layer composed of a matrix and a crystal having a layer thickness of 10 nanometers (nm), the maximum amount of crystals in the matrix is 5.0 × 10 ¹⁷ cm ⁻³ . (C) In a light emitting layer composed of a matrix and a crystal having a layer thickness of 5 nanometers (nm), the maximum amount of crystals in the matrix is 2.5 × 10 ¹⁷ cm ⁻³ . The maximum amount of crystals per unit volume of the light emitting layer (symbol dmax. (Unit: pieces / piece) allowed to achieve the object of the present invention.
cm ³ ). ) In relation to the thickness of the light emitting layer (symbol t (unit: cm)), dmax. Is a value given by the following relational expression (1) for a light emitting layer having a layer thickness of 20 nm or less. dmax. (pieces / cm ³ ) = 5.0 × 10 ²³ × t (Formula 1) In the present invention, the light emitting layer having a layer thickness of 20 nm or less and a layer thickness of t is used. And the total amount of crystals (pieces / cm ³ )
Stipulates that the value is equal to or less than the numerical value dmax. Given by the above (Equation 1). If a preferable range of dmax. Related to the layer thickness t of the light emitting layer is described, dmax.
This is a range of the following numerical values, that is, a range shown by oblique lines in FIG. According to the above (Equation 1), dmax. Can theoretically take 0 as a numerical value. For example, when a cross-sectional TEM image is taken in a situation where the resolution is insufficient due to improper setting conditions, the presence of an object that clearly exhibits a crystalline state due to the unclear contour may not be visually recognized. However, under the circumstances where the resolution ability can be fully exhibited by precise technical measures such as precise adjustment (alignment) of the irradiation angle of the incident electron beam to improve the resolution or precise adjustment of the thickness of the specimen. According to the observation, dots (d) were formed in the gallium-indium nitride layer with a contrast that makes the outline clear.
The presence of an ot) -shaped crystal can be confirmed. Gallium nitride
The total number of crystals in the indium layer varies depending on the method of forming the same layer and the concentration of indium. However, in TEM observation under high resolution, for example, the indium composition ratio formed by the atmospheric pressure MOCVD method is approximately In a gallium indium nitride layer having a layer thickness of 4 nm (0.04) and a thickness of 10 nm, a crystal of at least about 5 × 10 ¹³ per unit volume of the layer is in the background due to the spacing between the crystals. Exist as. Therefore, it is rare that the number of crystals is 0, that is, the crystals do not actually exist, and the crystals exist with a background concentration corresponding to the thickness of the light emitting layer. This background concentration tends to decrease with a decrease in the thickness of the light emitting layer, but at least about 10 ¹²
/ Cm ³ , the present invention tentatively sets the minimum of the preferable number of crystals to 10 ¹² / cm ³ .

The premise for controlling the total number of crystals is to precisely control the thickness of the light emitting layer first. The importance of precise control of the layer thickness will be described by taking the case of a gallium indium nitride light emitting layer as an example. FIG. 4 shows about 6% (0.0%).
6) Atmospheric pressure MOCVD with the intention of indium solid phase composition ratio
5 is an example showing the layer thickness dependence of the total number of indium-containing crystals per unit volume of the gallium-indium nitride crystal layer formed by the method. As a general tendency almost independent of the indium composition ratio of the gallium indium nitride layer, the total number of crystals tends to gradually increase with an increase in the layer thickness when the layer thickness is relatively small. The total number of crystals in FIG. 4 is just the total amount of crystals, and does not take into account each number of crystals for each different indium composition ratio. As the layer thickness increases beyond a certain thickness, the total number of crystals tends to increase sharply. The manner in which the total number of crystal bodies increases with an increase in the layer thickness is as follows: (a) MOCVD, MB
Growth methods such as E (molecular beam epitaxial growth method) and VPE (vapor phase growth method by halogen or hydride method); (b) differences in the structure of the film forming apparatus even with the same growth method; Changes depending on growth conditions such as film formation temperature and gas flow rate, and (d) various conditions such as indium composition ratio. Therefore, it is important to previously determine the layer thickness dependence of the total number of crystals under the conditions for forming the light emitting layer. Once the dependence of the total number of crystals on the layer thickness is known, a layer thickness satisfying the total number of crystals defined in the present invention may be reliably reproduced. The layer thickness of the group III nitride semiconductor layer increases in proportion to the supply amount of the group III element source gas to the growth reaction system and the increase and increase of the film formation (growth) time.
In particular, when the supply amount of the group III element source gas is fixed, the obtained layer thickness is proportional to the film formation time. Therefore, under such circumstances, the layer thickness can be precisely controlled by a simple operation for precisely controlling the film formation time.

Even when a measure for precisely controlling the layer thickness of the light emitting layer is implemented, the total number of crystals within the certain layer thickness range of the light emitting layer proposed by the present invention is defined by the present invention. If the total amount does not fall below, the main reasons are as follows. (1) Trimethylgallium ((CH ₃ ) ₃
Ga) or triethylgallium ((C ₂ H ₅ ) ₃ G
a) or triisobutylaluminum ((i-C ₄ H
₉ ) ₃ ) The film formation time is excessively extended due to the low supply of the group III element material such as Al) (extension of the film formation time). (2) Under a higher temperature environment on the light emitting layer III
As is particularly recognized when it is necessary to form a group III nitride semiconductor layer, the transition speed from the growth temperature of the light emitting layer to the film formation temperature for forming the upper layer is small (slow) ( Prolonging the time that the light-emitting layer is exposed to high temperatures). It is inevitable that an increase in the time for forming the light emitting layer results in an increase in the time for maintaining the light emitting layer at a high temperature. The number of crystals increases as the time during which the light-emitting layer receives heat, that is, the time during which it is maintained at a high temperature, increases. This causes a large amount of crystals in the light emitting layer to exceed the total amount proposed by the present invention. In order to satisfy the condition of the total number of the crystals of the present invention, it is particularly preferable that at least the film formation time required for growing the light emitting layer is accommodated within one hour. In particular, in order to more specifically disclose the case where the light emitting layer is formed from gallium indium having an indium solid phase composition ratio of 20% or less, the film forming temperature is set to 80%.
When the temperature is set between 0 ° C. and 900 ° C., it is a particularly preferable example that the film forming temperature is set within 30 minutes. In other words, a gallium-indium nitride light-emitting layer having a desired thickness can be obtained within 30 minutes in the same temperature range.
It is necessary to regulate the supply of Group I element raw materials to the growth reaction system. In addition, the phenomenon of inadvertently increasing the total number of similar crystals is also caused by an inappropriate condition process of the growth process of the next layer on the light emitting layer. A good example of this is that, after the formation of the gallium indium nitride light emitting layer at an appropriate deposition temperature of about 900 ° C. or about 950 ° C. or less, an aluminum gallium nitride mixed crystal layer (Al _{x Ga 1-x N: 0} < can be seen in inadequacy of the heating conditions for servicing the deposition temperature to deposit the x <1). If the rate of temperature rise is particularly slow, the period during which the light-emitting layer receives heat is extended, so that the total amount of crystals unnecessarily increases. A p-type aluminum nitride-gallium mixed crystal layer at 1100 ° C. as a clad layer on a gallium-indium nitride light-emitting layer having an indium solid phase composition ratio of about 6% formed at 850 ° C. by atmospheric pressure MOCVD. Taking the case of deposition as an example, an example of a suitable temperature increase rate at which the film formation temperature of the next layer (here, aluminum nitride / gallium mixed crystal layer) is reached after completion of the formation of the light emitting layer is 25 ° C. or more per minute. is there. Further, preferably, the temperature is raised at a rate of 50 ° C./min or more. When it is necessary to expose the light emitting layer to a higher temperature, a means for instantaneously changing the temperature so that the time for raising the temperature is as short as possible is effective in suppressing an increase in the total number of crystals.

The necessity of raising the temperature of the light-emitting layer to a temperature higher than the film formation temperature of the light-emitting layer and then maintaining the same at a high temperature for a certain period of time occurs very frequently, for example, when forming a laminated structure for a light-emitting element. For example, when laminating a clad layer made of an aluminum nitride-gallium mixed crystal layer on a gallium nitride-indium light-emitting layer, until the formation of the clad layer is completed, that is, the light-emitting layer is kept until the growth time elapses. A good example is exposure to a high temperature environment. After instantaneously raising the temperature to a temperature higher than the temperature at which the light-emitting layer was formed, the means for continuously maintaining the temperature at a high temperature achieves a non-uniform composition of the mother phase and a uniform size of crystals in the light-emitting layer. effective. However, exposing the light-emitting layer containing indium such as gallium nitride and indium as a constituent element for an excessively long time in a high-temperature environment is advantageous for promoting the nonuniformity of the composition of the mother phase, but in parallel, Diffusion of indium to the outside occurs remarkably. If the indium diffuses remarkably, the generation of the indium-containing crystal inside the crystal generated in the mother phase will hinder itself. Crystals containing indium are required to be present as light emitters, and it is preferable that the difference in indium concentration between the parent phase and the group III nitride semiconductor constituting the crystal be constant. It is. Unusual external diffusion of indium that occurs in a high-temperature environment tends to separate into a phase that can be regarded as almost gallium nitride in composition due to the low concentration of indium due to thermal denaturation and a gallium-indium nitride phase with different indium concentrations. As can be clearly seen from the light emitting layer made of gallium indium with nitrogen, the difference between the indium concentrations in the crystals increases as the indium concentration in the crystals decreases. Since the wavelength of light emitted from the gallium indium nitride crystal layer varies depending on the indium concentration (composition), the difference in the indium concentration in the crystal eventually hinders the improvement of monochromaticity of light emission. Taking the gallium indium nitride layer as an example, the extraordinary outdiffusion of indium increases with the length of time the layer is exposed to high temperatures. The period of being exposed to the high temperature is a temperature higher than the formation temperature of the light emitting layer on the light emitting layer, for example,
In consideration of forming a clad layer and a contact layer, this is a film formation time required to obtain a desired layer thickness.
To about 800 ° C. ~ about 900 ° C. temperature the formed gallium indium nitride light emitting layer between the example, in the case you deposited at a temperature between about 1000 ° C. ~ about 1200 ° C. The total adult The film time is preferably less than about 40-45 minutes. More preferably, if it is within 30 minutes, it is particularly effective in suppressing the loss of indium due to external diffusion from the gallium nitride-indium light emitting layer. In other words, it is necessary to select and adjust the supply amount of the raw material to the growth reaction system so that a desired layer thickness is obtained within such a preferable time.

The presence or absence of impurity doping in the light emitting layer also affects the total number of crystals in the light emitting layer. It has been announced that the formation of quantum dots is promoted by the presence of silicon (Si). (The 57th Autumn Meeting of the Japan Society of Applied Physics Preliminary Proceedings, Volume 1 (published by the Japan Society of Applied Physics, September 7, 1996) ), Lecture No. 8p-ZF-10, p. 208). In general, the total number of crystals tends to increase due to impurity doping. In particular, in a light-emitting layer having a small (thin) layer thickness, it is desirable to use an undoped layer in which an impurity is not intentionally added in order to suppress an extreme increase in the total number of crystals. More preferably, the undoped state is to suppress the contamination of the impurities from the growth reaction system or the raw material system and to reduce the concentration of the impurities (residual impurities) remaining in the light emitting layer as low as possible. The light emitting layer made of gallium indium nitride will be specifically described as an example.
nm or less, the total impurity concentration in the light emitting layer is preferably 5 × 10 ¹⁷ cm ⁻³ or less, more preferably 1 × 10 ¹⁷ cm ⁻³ or less.
It is 10 ¹⁷ cm ^-3 or less. Conversely, when the layer thickness is relatively large (thick), for example, in a light emitting layer having a layer thickness of more than about 20 to about 30 nm, the intensity of light emitted from the light emitting layer tends to increase with an increase in the amount of impurities. In some cases, a certain amount of impurity doping may be required. The certain degree means that the emission intensity of the main emission spectrum is maintained at about 10 times or more that of the secondary spectrum. As described above, the "heterogeneous layer in which crystals are mixed in the matrix" according to the present invention is formed almost uniquely by adjusting factors such as the film formation temperature and the amount of heat to be applied in the process after the film formation. You can do it. In summary, the light-emitting layer as defined in the present invention has a crystallographic structure that can be formed more rationally and routinely as compared to the previously unreasonable "homogeneous layer consisting of a single phase". It is.

From the total number (N) of the crystals, an average size that the crystals can take is calculated. Total volume of light emitting layer V (c
It is assumed that the space corresponding to m ³ ) is spatially occupied by the crystal. Since the total number of crystals present in the light emitting layer is N, the volume occupied by one crystal is V / N (cm ³ ) if the sizes of the crystals are the same. Conveniently V
Is 1 cm ³ , the total number of crystals according to the present invention is 1
When it is × 10 ¹⁸ cm ^-3 , the volume occupied by one crystal is 1 × 10 ^-18 cm ³ . Suppose that the diameter is R
Assuming that the volume occupied by one crystal having a sphere of (nm) as an outer shape, R is about 6.2 from the formula for calculating the volume of a sphere.
It is calculated as nm. If the total number of crystals is 5 × 10 ¹⁷ cm ⁻³ , R is about 7.8 nm. Similarly, when the total number of crystals is 1 × 10 ¹⁷ cm ⁻³ , R is about 13.4 nm. This diameter is, to the last, the total amount of the crystals is at the upper limit in the definition of the present invention, and when the entire light emitting layer is occupied by the crystals, it is assumed that the sizes of the crystals are the same. This is the calculated value when the calculation is performed. However, actually, the entire light emitting layer is not occupied by the crystal, and the crystal occupies a volume corresponding to some percentage of the total volume (V) of the light emitting layer. Even in the future, the volume occupied by each crystal is smaller than the above calculated value even if the size of the crystal is the same. On the other hand, the size of the crystal is not always the same, and the diameter of the crystal has a certain distribution width, and the average crystal diameter is the thickness of the light emitting layer, that is, the thickness of the matrix. It tends to be smaller as a whole. Therefore, the volume occupied by the crystal tends to decrease as the thickness of the light emitting layer decreases. That is, the present invention proposes that in order to improve the monochromaticity and emission intensity of light emission, the total number of crystals and the volume occupied by the crystals in the matrix should be reduced with a decrease in the thickness of the light emitting layer. It is. The content presented by the present invention is not limited to the gallium-indium nitride light-emitting layer as shown in FIG. 3, but is common to the light-emitting layer in which a crystal containing indium is used as a light-emitting body. It is valid.

A total number of indium satisfying the requirements of the present invention.
A group III nitride semiconductor layer containing a crystal containing
In order to obtain a light emitting element provided with
There are no special restrictions on the situation. mis (metal
insulatorsemiconducer) type
Light-emitting layer, single hetero (SH) junction structure
Light emitting layer, pn junction type double hetero (D
H) The light emitting layer, single or
Multiple quantum wells (QantumWcell: QW)
Of various light-emitting layers, such as a light-emitting layer
The arrangement situation is conceived. The light emitting layer including the light emitting layer of the present invention is described below.
An example of a light emitting element having a light portion will be described. (A) N-type group III nitride such as n-type gallium nitride (GaN)
Semiconductor layer / gallium / indium nitride light emitting layer / p-type II
It has a pn junction type DH structure composed of a group I nitride semiconductor layer.
Light-emitting device provided with a light-emitting unit. (A) Group III nitrides of either upper or lower cladding layer
Contains indium-containing crystals whose main phase is a semiconductor material
Undoped or impurity-doped light emitting layer
A light emitting device having a DH structure. (C) Gallium nitride based cladding layers
Indium-containing binder with group III nitride semiconductor material as matrix
Undoped or doped with impurities
A light-emitting element having a DH structure including a light-emitting layer. (D) The solid phase composition ratio of indium is approximately 50% (0.5%).
0) or less and the thickness of the layer is approximately 20 nm or less.
The indium / indium light emitting layer is simply a well layer.
Light emitting devices with one or multiple quantum well structures
In addition, the indium-containing crystal is placed in a barrier layer.
With a light-emitting layer in the region near the interface with
Well structure light emitting device. (E) The solid phase composition ratio of indium is approximately 50% (0.5%).
0) or less, and the thickness of the layer is approximately 10 nm or less.
Pn junction type DH structure using um / indium as the light emitting layer
A light-emitting element provided with gallium nitride as a mother phase.
Injection occurs at almost the center of the parent phase
Includes a light-emitting layer that increases the number (density) of indium-containing crystals
Light emitting device.

[0025]

It has the function of improving the monochromaticity of the emission spectrum from the light emitting layer and increasing the intensity of the emission spectrum of a desired wavelength.

[0026]

【Example】

(Example 1) The present invention will be described by taking as an example a light emitting diode using a laminated structure composed of III-V nitride compound semiconductor layers as a base material. Each layer constituting the laminated structure was formed by the following procedure using a general atmospheric pressure (atmospheric pressure) type MOCVD growth apparatus. Substrate (1
Sapphire (α-Al) having a diameter of about 1 inch (diameter of about 25 mm) and a plane orientation of (0001) (c-plane) set to (03).
₂ O ₃ single crystal) was placed horizontally on a support (susceptor) in a high-purity quartz tube for a semiconductor industry having a particularly low content of alkali metals, which was used as a reaction furnace for forming a film. The thickness of the substrate (103) is about 100 μm. The support base is a wedge shape made of high-purity graphite material. The vertical cross section of the reactor is rectangular and its cross-sectional area is about 1
0.5 cm ² . The inside of the reactor was evacuated to a vacuum via a vacuum evacuation path equipped with a common oil rotary vacuum pump.
A vacuum of about 10 ^-3 Torr is reached and about 10 ^-3
After maintaining the same degree of vacuum for minutes, purified argon gas (Ar) at a flow rate of about 3 liters / minute was passed through the reaction furnace to restore the pressure in the furnace to almost atmospheric pressure.

After purging the inside of the reaction furnace with purified high-purity argon gas for about 5 minutes, the supply of the argon gas to the reaction furnace was stopped. Substitute dew point about minus (-) 9
Supply of purified hydrogen gas (H ₂ ) at 0 ° C. into the reactor was started. The flow rate of hydrogen gas is about 5 liters / minute with an electronic mass controller (so-called mass flow controller (MF)
C)). Thereafter, a high frequency heating coil wound in a circular shape provided on the outer periphery of the reactor having a circular vertical cross section has a frequency of 400 kilohertz (kHz) from a general high frequency power supply.
The high frequency power supply of z) was turned on. Thereby, the substrate (10
The temperature of 3) was increased from room temperature (about 25 ° C.) to 500 ° C. The temperature of the substrate (103) was determined by molybdenum (M) inserted into a through hole having a diameter of about 5 mm pierced in the middle of the support.
o) The temperature was measured with a sheath-type platinum-platinum-rhodium alloy thermocouple (a thermocouple based on Japanese Industrial Standard JIS-R standard). The substrate temperature was precisely controlled to within ± 1 ° C. by a commercially available PID type temperature controller that inputs a thermoelectromotive force signal generated from a thermocouple. The temperature of the substrate (103) is 500 ° C.
Approximately 20 minutes have passed since the ammonia gas (N
At the same time when the supply of H ₃ ) to the reactor was started at a rate of 1 liter per minute, the flow rate of hydrogen gas flowing through the reactor was reduced from 5 liters per minute to 2 liters per minute. Thus, the composition of the gas flowing to the reactor was 1 liter / min of ammonia gas and 3 liters of hydrogen gas per minute.
Next, a low-temperature buffer layer (104) made of undoped aluminum nitride (AlN) was grown on the substrate (103) using trimethyl aluminum ((CH ₃ ) ₃ Al) as an aluminum (Al) source. The layer thickness of the low-temperature buffer layer (104) was about 7 nm.

After the growth of the low-temperature buffer layer (104) is completed, the supply of hydrogen gas to the reaction furnace is stopped in parallel with the purpose of suppressing the loss due to sublimation and the like of the low-temperature buffer layer in the heating process described later. The supply of argon gas to the reactor was started at a flow rate of 4 L / min. Similarly, the supply amount of ammonia gas to the reaction furnace was kept unchanged for the purpose of suppressing volatilization at the time of raising the temperature of nitrogen, which is a constituent element of the low-temperature buffer layer,
While maintaining the rate at 1 liter / min, the amount of power applied to the high-frequency coil was increased, and the temperature of the substrate (103) was increased from 500 ° C. to 1130 ° C. As soon as the substrate temperature measured by the thermocouple reached 1130 ° C., the supply amount of ammonia to the reactor was increased from 1 liter per minute to 3.5 liters per minute using an electronic mass flow meter. At the same time, the supply rate of argon gas was reduced from 4 liters / minute to 1.3 liters / minute, and the supply rate of hydrogen gas to the reactor was 1.3 minutes / minute.
It was restarted with a liter flow rate. As a result, a total of 6.1 liters / minute of hydrogen, argon, and ammonia flowed into the reactor constituted by the high-purity quartz tube. After the temperature of the substrate (103) reaches 1130 ° C. and waits for 5 minutes, an n-type gallium nitride layer (105) doped with silicon (Si) serving as a lower cladding layer is grown on the low-temperature buffer layer (104). I let it. Gallium (Ga)
The source used was trimethylgallium ((CH ₃ ) ₃ Ga) whose purity for the semiconductor industry was guaranteed to be 5N (99.999%). Trimethylgallium was stored in a stainless steel bubbler (foamed) container whose inner surface was polished to a mirror surface, and the temperature of the container was maintained at 0 ° C. using an electronic thermostat. During the growth of the n-type gallium nitride layer (105), the liquefied trimethylgallium is subjected to a bubbling operation with a hydrogen gas at a flow rate of 30 cc / min, and a hydrogen bubbling gas accompanied by the trimethylgallium is supplied into the reactor. A gallium source was provided. Silicon is disilane (Si ₂ H) diluted to about 1 ppm by volume with high-purity hydrogen.
₆ ) was added as a doping source. The flow rate of the disilane doping gas was set to 20 cc / min by an electronic mass flow meter. The carrier concentration on the surface of the same layer (105) measured by a general electrolytic CV method is about 1 × 10 ¹⁸ cm ^−3.
Met. The layer thickness was about 3.2 μm.

The flow of the gallium source into the reactor was stopped to stop the formation of the n-type gallium nitride layer (105). At the same time, the supply of hydrogen gas into the reactor was stopped. The flow rate of ammonia gas was maintained at 3.5 liters per minute.
Thus, the gas species flowing in the reactor were argon gas and ammonia. While the atmosphere in the reaction furnace is composed of argon and ammonia gas, the amount of high frequency power applied to the high frequency coil is reduced to reduce the temperature of the substrate (103) to 113.
The temperature was reduced from 0 ° C. to 870 ° C. in about 4 minutes. On the way, when the temperature of the substrate reached around 900 ° C., the flow rate of argon flowing through the reactor was increased from 1.3 liters per minute to 2.6 liters per minute. Therefore, the flow rate of the gas flowing through the reaction furnace was 6.1 liters per minute in total as in the case of forming the n-type gallium nitride layer (105). Substrate temperature is 87
After waiting for 3 minutes until the temperature is stabilized at 0 ° C., supply of both the gallium source and the indium source into the growth atmosphere composed of argon and ammonia gas is resumed, and the silicon doped n
An undoped gallium indium nitride (GaInN) light emitting layer (106) was grown on the shaped gallium nitride layer (105). The above-mentioned trimethylgallium was used as the gallium (Ga) source, and the temperature of the bubbler container of the gallium source was set to 0 ° C. The flow rate of hydrogen gas for bubbling for entraining the vapor of trimethylgallium was controlled at 5 cc / min by an electronic mass flow meter. Trimethyl indium ((CH ₃ ) ₃ In) was used as a source of indium (In). Trimethylindium has an internal volume of about 100cc
And stored in a stainless steel cylinder container, which is precisely 35 ° C using an electronic thermostat.
Held. Hydrogen gas at a flow rate of 13.3 cc / min was passed through the cylinder vessel containing the indium source to entrain the sublimated trimethylindium vapor into the reactor. From these holding temperature and flow rate conditions related to Group III element raw materials, the solid phase composition ratio of indium was about 6%.
(About 0.06) gallium indium nitride light emitting layer (1
For the purpose of film formation 06), the ratio of the supply amount of the indium source to the total amount of the gallium source and the indium source supplied into the reaction furnace, that is, the so-called gas phase composition ratio of indium was set to 0.10. The vapor phase composition ratio of indium is such that the vapor pressure of trimethylgallium at 0 ° C. is about 64.4 Torr.
And the vapor pressure of trimethylindium at 35 ° C. was determined as 3.0 Torr. Precisely for 15 minutes, the group III and V element raw materials are maintained for 15 minutes while maintaining the flow rate of ammonia gas as a nitrogen (N) source at 3.5 liters per minute and the flow rate of argon gas at 2.6 liters / minute. And an undoped gallium-indium nitride light emitting layer (1) having a layer thickness of about 6 nm by continuously supplying hydrogen and an argon carrier gas.
06) was formed. Gallium nitride with similar layer thickness
It took about 40 minutes to obtain the indium light emitting layer (Ga _0.94 In _0.06 N) when the flow rate of the hydrogen gas for bubbling trimethylgallium was 3.0 cc / min.
Therefore, in this embodiment, the flow rate of the hydrogen gas for bubbling trimethylgallium is set to 5 cc / min so that the growth can be sufficiently completed within 30 minutes, and the total number of indium-containing crystals in forming the light emitting layer is unnecessary. We have taken measures to prevent any significant increase.

The supply of the gallium source and the indium source to the reaction furnace was interrupted to terminate the formation of the light emitting layer (106). While adjusting the amount of power from the high-frequency power source applied to the high-frequency coil based on the thermo-electromotive force signal from the thermocouple inserted into the middle of the support while maintaining the flow rates of both the argon and ammonia gases at the above values, the substrate is Set the temperature of (103) to 8
The temperature was raised from 70 ° C to 1130 ° C again. In order to suppress the generation of indium-containing crystals in excess of the total number specified in the present invention due to an inadvertently gradual setting of the heating rate in the heating process, the temperature is raised from 870 ° C. to 1130 ° C. in 3 minutes. did. That is, the heating rate was set to about 86.7 ° C. per minute. Substrate (1
Immediately after the temperature of 03) reached 1130 ° C., the flow rate of argon was reduced to 1.3 liters per minute, and at the same time hydrogen gas was supplied at a flow rate of 1.3 liters per minute. From this, the total flow rate of hydrogen to 6.1 liter / min.
A growth atmosphere consisting of an argon-ammonia mixed gas was created. After instantaneously adjusting the flow rates of hydrogen and argon, the carrier gases aluminum and gallium
A group III element source and a magnesium source are supplied into a reactor to form a first layer which is a lower layer of an upper cladding layer (107) made of an aluminum-gallium nitride mixed crystal (Al _0.07 Ga _0.93 N) doped with magnesium (Mg). The upper clad layer (107-1) was overlaid on the light emitting layer. As the aluminum source, trimethylaluminum was used as in the growth of the low-temperature buffer layer (104). Trimethylaluminum was stored in a stainless steel cylinder container similar to that of trimethylgallium, and the temperature of the container was maintained at 20 ° C. by an electronic thermostat. Trimethylaluminum liquefied while being maintained at a temperature not lower than the melting point (about 15 ° C.) of trimethylaluminum is used as a bubbling gas at 10.0 min / min.
cc of hydrogen gas was passed. The gallium source used was the above-mentioned trimethylgallium. Trimethylgallium was maintained at exactly 0 ° C. in an electronic thermostat, and the flow rate of hydrogen gas for bubbling and entrainment of trimethylgallium vapor was 30 cc / min. The doping source of magnesium is bis-methylcyclopentadienyl magnesium (bi
Using _{s- (CH 3 C 5 H 4} ) 2 Mg). The magnesium doping source contained in the stainless steel cylinder container was kept at a constant temperature of 60 ° C. by an electronic constant temperature bath.
In the bis-methylcyclopentadienyl magnesium liquefied while being kept at the same temperature, a hydrogen gas whose flow rate was precisely controlled to 20 cc / min by an electronic mass flowmeter and controlled was circulated for the purpose of bubbling. The first upper clad, which is a constituent layer of the upper clad layer (107) having a thickness of about 0.5 μm by continuously supplying the group III element source and the magnesium source to the reactor for 12 minutes. The layer (107-1) was formed.

After the growth time for forming the first upper cladding layer (107-1) has elapsed, the substrate (103)
While maintaining the temperature of 1130 ° C. without changing the gas flow conditions other than the hydrogen gas for bubbling trimethylaluminum, aluminum nitride / gallium mixed crystal (Al _x Ga ₁ -xN: 0 <x <1 ) Layer formation was continued. The flow rate of hydrogen gas for bubbling trimethylaluminum was uniformly reduced over time from 6 cc / min to 10.0 cc / min, which is the flow rate at the time of forming the first cladding layer (107-1), over 6 minutes. Trimethylaluminum was bubbled to reduce the flow rate of the hydrogen gas accompanying the above substance to 0 cc / min, at which point the supply of the hydrogen gas accompanying the trimethylaluminum to the reactor was stopped. An aluminum composition gradient obtained by changing the hydrogen gas related to trimethylaluminum with the lapse of time to a layer thickness of about 0.25 μm. A layer was formed. X near the interface between the first upper cladding layer (107-1) and the aluminum composition gradient layer is set to about 7% (0.07), and x is almost 0 near the surface of the aluminum composition gradient layer, ie, gallium nitride and Considered to be. Even after stopping the flow of hydrogen gas accompanying trimethylaluminum to the reactor, supply of gallium source and nitrogen source to the reactor is continued for 6 minutes, and magnesium-doped nitriding to a layer thickness of about 0.23 μm. A gallium layer was formed. As a result, a second upper cladding layer (107-2) having a multilayer structure of an aluminum gallium nitride mixed crystal layer having a gradient of aluminum composition and a gallium nitride layer was formed. As described above, the total film forming time consumed for forming the first and second cladding layers ((107-1) and (107-2)) constituting the upper cladding layer (107) is 24 minutes. Was.

The second upper cladding layer (107) including a gallium nitride layer also serving as a contact layer of the electrode.
The film formation in -2) was stopped by supplying the group III element raw material to the reaction furnace. At the same time, the supply of the group III element material to the reactor was stopped, and the supply of the magnesium doping source to the growth system was also stopped. After exactly 30 seconds have elapsed since the supply of the group III element raw material to the reactor was stopped, hydrogen was supplied while maintaining the supply of argon and ammonia gas the same as when forming the upper cladding layer (107-2). The supply of the carrier gas was stopped to lower the temperature of the substrate (103). The temperature value displayed on the PID type temperature controller is monitored, and the substrate (1) is monitored.
When the temperature of 03) dropped from 1130 ° C. to 1000 ° C., the supply of the ammonia gas to the reactor was stopped, and only argon was supplied into the reactor. 1000 ° C by program control using PID type temperature controller
The temperature was lowered from 10 to 800 ° C. over exactly 10 minutes. That is, the temperature of the laminated structure composed of the group III nitride semiconductor layers formed on the substrate (103) was lowered at a rate of 20.0 ° C. per minute. The temperature of the substrate (103) is 800 ° C.
Then, the supply of high-frequency power to the high-frequency coil was stopped, and the laminated structure was naturally cooled to room temperature. FIG. 5 shows a cross-sectional structure of the laminated structure of this embodiment.

A portion of the above laminated structure was cut to prepare a strip-shaped sample for observing the structure of the crystal structure inside the light emitting layer using a transmission electron microscope (abbreviation: TEM). In the case of a strip-shaped sample, the hexagonal sapphire (0
A sample with the (100) plane exposed and two kinds with the (1000) plane exposed were produced. That is, a sample in which crystal planes orthogonal to each other were exposed on the long side was used. Prior to TEM observation, the sample was thinned by sputtering with argon ions (Ar ⁺ ) so as to be suitable for cross-sectional TEM observation. Cross-sectional TEM of a typical transmission electron microscope utilizing gallium nitride indium (Ga _0.94 In _{0. 06} N) light-emitting layer (106)
Images were taken at an acceleration voltage of 200 kilovolts (KV). At the interface between the light emitting layer (106) and the lower cladding layer (105) made of n-type gallium nitride, a large island-shaped crystal having a trapezoidal cross section having a width of about 10 nm was rarely observed. Most of the crystals were found to be approximately spherical.
The diameter of the substantially spherical crystal was at most about 3 nm from the captured circular contrast. Further, the tendency of the crystal to segregate in a specific region inside the light emitting layer was not clearly recognized, and the crystal was almost uniformly distributed. The total number of crystals in the light emitting layer (106) was counted from the photographed cross-sectional TEM image. (0
100) The number of crystals taken in the cross-sectional TEM image on the crystal plane side is 50 nm in width and about 6 in height (corresponding to layer thickness).
There were approximately two in the imaging area of nm. Also, (100
0) The total number of crystals counted on the crystal face side was also about 1 to 2 in the same imaging area as above. By changing the region to be imaged, the number of crystals contained on average in a certain volume of spatial region was determined. As a result, the horizontal length is 50
The average number of crystals contained in a space (volume = 1.5 × 10 ⁻¹⁷ cm ⁻³ ) with a height (layer thickness) of 6 nm on the bottom surface with a vertical length of 50 nm and a vertical length of 50 nm is 1 on average. .5.
In terms of the total number of crystals per unit volume (1 cm ³ ), it was 1.0 × 10 ¹⁷ cm ⁻³ . On the other hand, the average distance between the centers of the crystals was about 22 nm. A space whose one side is 22 nm which is the average distance between the crystals (volume = 1.1)
Assuming that one crystal exists within × 10 ⁻¹⁷ cm ⁻³ ), the total number of crystals in a unit volume (1 cm ³ ) is 9.1 ×
The calculated value was 10 ¹⁶ cm ^-3 , which was in good agreement with the above converted value.

The cross section of the thinned sample was observed with a general analytical electron microscope to analyze the crystal structure inside the light emitting layer (106). EPMA was performed to analyze the concentration of indium (e lectron- p robe m i
cro- a nalysis) analysis results of observed that other regions in the crystal, more indium compared to the inside of the so-called matrix is contained. From the mother phase, the signal (si
gnal) was detected, but the S / N ratio was low and the signal was not clearly recognized as a characteristic X-ray signal of indium. That is, it was determined that the constituent of the parent phase was very close to the composition of gallium nitride entirely because of the low indium concentration. Judging from the intensities of the detected indium kα characteristic X-rays, it was found that there was a difference in the indium concentration between the crystals in units of%, but the difference in the concentration was accurately quantified. However, this was not achieved due to the detection performance of the EPMA analyzer. However, the concentration of indium contained in the crystal was at most several percent, and a crystal containing indium exceeding 10% was rare. Also,
At the boundary between the crystal and the surrounding parent phase, there was a region in which the arrangement of the crystal lattice was disturbed, which is considered to be caused by distortion or the like.

(1) Selection of the undoping means in consideration of the layer thickness, (2) adjustment of the rate of temperature rise to the growth temperature of the next layer after film formation, and (3) adjustment of the film formation time at high temperature A light-emitting diode was manufactured using the above-described laminated structure provided with a light-emitting layer obtained by taking measures to suppress an increase in the total number of the base materials as a base material. Titanium (Ti) is formed on the second upper clad constituting layer (107-2) which is the outermost layer of the upper clad layer (107).
Electrode (108-1) and pad electrode (108-1) each having a structure in which aluminum is an underlayer and aluminum is layered
A positive electrode (108) composed of a thin-layer electrode (108-2) having a structure in which gold (Au) electrically bonded to the substrate was formed as a base and titanium nitride (TiN) was layered thereon was disposed thereon. One negative electrode (109) has an upper clad layer (107) and a light emitting layer (10) in a region where the same electrode is to be arranged.
6) and further formed after etching the very surface of the lower cladding layer (105) made of n-type gallium nitride. Each layer on the n-type gallium nitride lower cladding layer (105) in the region where the negative electrode (109) is to be formed is argon-
Methane (CH ₄₎ - it was etched by microwave plasma etching technique using hydrogen mixed gas. The negative electrode (109) was composed of a multilayer of titanium and aluminum similarly to the pad electrode (108-1) forming a part of the positive electrode (108). n-type gallium nitride lower cladding layer (10
What was in direct contact with 5) was a titanium layer.

A DC voltage was applied between the band-like positive and negative electrodes ((108) and (109)) arranged at positions facing each other along the edge line of the end of the device. 1 volt (V)
Blue light emission was already obtained by applying a DC voltage of less than 0.5 V, for example. The intensity of blue light emission increased as the applied voltage increased. In the measurement using a general integrating sphere, a DC voltage of 4.0 V was applied, and the light emission output when a forward current of 23 milliamperes (mA) was passed was 2.2 milliwatts (mW). On the other hand, in the measurement of the emission spectrum using a spectroscope attached to a normal photoluminescence photometer, the emission wavelength of the main emission spectrum is 452.
nm. In addition to the main emission spectrum, a band of gallium nitride (ba
nd) No appearance of spectra other than those attributed to edge emission was observed. In other words, the emission intensity of the secondary spectrum was very weak, less than 1/100 as compared with that of the main spectrum. The wavelengths of the main emission spectrum and the secondary emission spectrum did not change significantly depending on the DC voltage (DC current) applied between the electrodes. Also, the half-width of the main emission spectrum was narrowed to 110 millielectron volts (meV) at room temperature. For this reason, blue light emission was excellent in both intensity and monochromaticity.

(Comparative Example 1) In order to clearly show the influence of the total number of crystals contained in the light emitting layer composed of gallium indium nitride on the intensity and monochromaticity of light emission, the total number of crystals was determined in the present invention. The emission characteristics of an LED having a gallium-indium nitride light-emitting layer, which is out of the range, are described as comparative examples.

Except for the light emitting layer, a laminated structure having the same structure as that of the first embodiment was formed. The light-emitting layer was grown using the raw material system described in Example 1, but was formed under the following conditions to make the total number of crystals out of the range specified in the present invention. (A) Gallium indium nitride (Ga _0.94 Al _0.06 N) grown with the intention of indium solid phase composition ratio of 6%
Is grown at 870 ° C. and then heated to 1130 ° C., which is the growth temperature of the upper cladding layer, in which the rate of temperature reduction is reduced from 86.7 ° C./min in Example 1 to 26.0 ° C./min. Changed. That is, the temperature was raised from 870 ° C. to 1130 ° C., which is the growth temperature of the next layer, over 10 minutes. (B) In the process of growing the upper cladding layer at 1130 ° C. on the gallium indium nitride light emitting layer, the light emitting layer is heated at a high temperature until the layer thickness of the upper cladding layer reaches a predetermined layer thickness (0.98 μm in total). (Total 24 minutes) and at the same temperature for exactly 40 minutes. That is, the period during which the light-emitting layer is maintained at a high temperature is set to 1 hour or more, which is more than twice as large as that in Example 1. As described above, the conditions relating to the growth of the light emitting layer were changed so as to increase the total number of crystals.

After forming the laminated structure having the light emitting layer of this comparative example, a cross section TEM image was taken by observing a cross section of the light emitting layer centered on the TEM technique. Although the shapes of the observed crystals are substantially spherical and island-like, it is apparently confirmed that unlike the case of the light emitting layer described in Example 1, the probability of existence of the island-like crystals increases. Was. On the other hand, the diameter of a crystal having a substantially circular cross-section for predicting a substantially spherical outer shape and the width of an island-shaped crystal having a trapezoidal or elliptical or polygonal cross-section are substantially the same between crystals. I was Example 1 has an average width of about 3 nm.
In comparison with the case of the above, the crystal tended to increase in size.
It has been considered that one of the causes of the irregular shape of the crystal and the enlargement of the crystal are the prolongation of the period in which the light emitting layer is exposed to high temperature. On the other hand, the total number of crystals was clearly increased as compared with Example 1, and was calculated to be about 8 × 10 ¹⁷ cm ⁻³ from the average distance between the crystals. With respect to the light emitting layer having a thickness of 6 nm, the total number of the crystals exceeded the value specified by the present invention. It was analyzed that inhomogeneity was promoted with respect to the indium concentration inside the crystals, and it was determined that the difference in indium content between the crystals was promoted. The composition of the parent phase surrounding the crystal was as low as that of Example 1 and the indium concentration was so low that it could be regarded as gallium nitride.

An LED (see FIG. 5) was formed with the same material and arrangement as in Example 1 to form an LED. A DC voltage was applied between both electrodes in the forward direction, and the dependence of the emission spectrum on the applied voltage (current flow) was investigated. The spectrum emitted from the LED in the low current range of less than 100 microamps (μA) was reddish with wavelengths greater than 600 nm and greenish with wavelengths in the range of about 500 nm to about 560 nm. . The intensity of the desired emission spectrum in the blue band is determined by a general photoluminescence (P
L) As measured by a photometric device, it is extremely weak and does not reach even a few microvolts (μV). Compared with the above-mentioned red and green PL spectrum intensities, 1 /
It did not reach 10. When a low current was passed, a phenomenon was observed in which the wavelength of the emission spectrum shifted to the longer wavelength side as the forward current flowing from the red band to the green band increased. That is, a phenomenon in which the emission color (emission wavelength) changes depending on the increase or decrease of the operating current was confirmed. However, on the low current side, the desired emission spectrum in the blue band was not recognized as a main spectrum from the viewpoint of emission intensity. On the other hand, when driven by an extremely general and practical forward current of several tens mA, for example, 20 mA, an emission spectrum of a blue band having a center wavelength of about 446 nm appeared. In terms of intensity, this blue band spectrum was recognized as the main emission spectrum, but other wavelengths of about 38
The appearance of a secondary spectrum was observed in the near ultraviolet band near 0 nm. The intensity of the secondary spectrum reached about 30% of the intensity of the main spectrum resulting in blue emission. Due to the mixture of the secondary spectrum having a relatively large intensity with respect to the main spectrum, the emission color was visually recognized as a whitish blue (blue-white). The half-width of the main emission spectrum was about 320 millielectron volts (meV) at a forward current of 20 mA.
Although the half-width value is smaller than that of the conventional blue LED having the light-emitting layer made of gallium / indium nitride doped with a donor impurity and an acceptor impurity at the same time, it is about 110 meV in Example 1.
Was interpreted to be about three times worse. That is, the half-value width was inferior in color purity due to the enlargement. Further, the light emission output of the LED measured using a general integrating sphere as in the above-described example was 1.2 mW corresponding to about half of the LED described in the example. Therefore, the LED of this comparative example was inferior to the LED of the present invention described in the examples in both characteristics of light emission intensity and light emission monochromaticity (color purity).

[0041]

According to the present invention, in obtaining a light emitting device having a group III nitride semiconductor light emitting layer, by defining the total number of crystals in the light emitting layer, the half width of the main emission spectrum which results in a desired emission color is reduced. In addition, an increase in emission intensity can be achieved. Therefore, there is an effect that a light-emitting element which is excellent in both light emission intensity and color purity and has improved main characteristics of the light-emitting element is provided. In addition, the total number of crystals in accordance with the thickness of the light emitting layer is within the specification of the present invention and the means is to shorten the time required for the process of raising the temperature to a high temperature and the film formation at a high temperature, and to shorten the holding time. In addition, there is also an economical effect that labor can be saved in manufacturing a laminated structure for light emitting element use.

[Brief description of the drawings]

FIG. 1 is a diagram showing a photoluminescence spectrum of a gallium indium nitride crystal layer in which a secondary emission spectrum appears in addition to a desired main emission spectrum.

FIG. 2 is a graph showing the half-width of the emission spectrum of a gallium indium nitride crystal layer having a layer thickness of about 50 nm and a wavelength near 450 nm and the dependence on the total amount of indium-containing crystals.

FIG. 3 shows a PL emission spectrum of a gallium indium indium light emitting layer grown by a normal pressure (atmospheric pressure) MOCVD method, which has good monochromaticity and excellent strength, with an indium solid phase composition ratio of about 0.08. FIG. 5 is a diagram showing an upper limit value of the total amount of crystals that causes the above, in relation to the layer thickness of the light emitting layer.

FIG. 4 is an example showing the layer thickness dependence of the total number of indium-containing crystals in a gallium indium nitride crystal layer formed by a normal pressure MOCVD method with an indium solid phase composition ratio of about 0.06. is there.

FIG. 5 is a schematic diagram illustrating a cross-sectional structure of a laminated structure according to the present embodiment.

[Explanation of symbols]

(101) Main emission spectrum (102) Secondary emission spectrum (103) Substrate (104) Low-temperature buffer layer (105) n-type gallium nitride layer (lower cladding layer) (106) Emission layer (107-1) First (107-2) Second upper cladding constituent layer (108) Positive (+) electrode composed of pad electrode and thin film electrode (108-1) Titanium (T) constituting a part of positive electrode
i) / Aluminum (Al) multilayer pad electrode (108-2) Gold (Au) constituting a part of positive electrode /
Titanium nitride (TiN) thin layer electrode (109) Negative (-) electrode

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-10-215029 (JP, A) JP-A-10-107320 (JP, A) JP-A-4-112584 (JP, A) JP-A-5-105 62896 (JP, A) JP 8-88345 (JP, A) JP 5-82912 (JP, A) JP 4-354323 (JP, A) JP 10-56202 (JP, A) JP-A-10-107315 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 33/00

Claims (2)

(57) [Claims] 1. A mother phase and indium (I) scattered in the mother phase.
n) comprising a substantially spherical or island-shaped crystal having a diameter or a lateral width of 30 nm or less made of a Group III nitride semiconductor containing n), wherein the total amount of the crystal contained in the matrix is A group III nitride semiconductor light emitting device having a light emitting layer of 2 × 10 ¹⁸ / cm ³ or less. 2. A light-emitting layer having a layer thickness of 20 nm or less, wherein the total amount of the crystals contained in the light-emitting layer having a unit volume (1 cm ³ ) is determined by the total thickness of the light-emitting layer (t: cm). Dmax. (Pieces / cm ³ ) = 5.0 × 10 ²³ × t (pieces / cm ³ )
^{3. The} group III nitride semiconductor light emitting device according to claim 1, further comprising a light emitting layer having a value of dmax.