JP6385004B2 - Group 13 element nitride crystal layer and functional device - Google Patents

Description

  The present invention relates to a group 13 element nitride crystal layer and a functional element. INDUSTRIAL APPLICABILITY The present invention is applied to a technical field that is required to have high quality, for example, a high color rendering blue LED called a post fluorescent lamp, a blue-violet laser for high-speed and high-density optical memory, and a power device used for an inverter for a hybrid vehicle. Can be used.

  In recent years, semiconductor devices such as blue LEDs, white LEDs, and blue-violet semiconductor lasers are manufactured using group 13 element nitrides such as gallium nitride, and application of the semiconductor devices to various electronic devices has been actively studied. Yes.

  As the application of white LEDs expands, LED chips are required to have higher performance. High performance means high efficiency and high brightness.

In a structure in which a GaN thin film (light emitting part) is formed on a sapphire substrate, which is generally used at present, by MOCVD, the dislocation density of the light emitting part is very high, 1 × 10 ⁹ to 1 × 10 ¹⁰ / cm ^2. Therefore, non-radiative recombination of carriers occurs at the dislocation part, and it is difficult to improve luminous efficiency.

Attempts have been made to reduce the dislocation density in the light emitting part in gas phase methods such as MOCVD and HVPE. For example, in Patent Document 1, a GaN thin film is formed by forming a SiO ₂ mask on a seed crystal and growing or growing a GaN crystal on the seed crystal by a vapor phase method, thereby blocking or bending dislocations propagating from the seed crystal. Of low dislocation.

  When a gallium nitride crystal is grown by directly reacting metal gallium with nitrogen, high-temperature and high-pressure conditions such as 1500 ° C. and 1 GPa are required. On the other hand, the flux method is one of liquid phase methods. In the case of gallium nitride, the temperature required for crystal growth of gallium nitride is reduced to about 800 ° C. and the pressure is reduced to several MPa by using metallic sodium as the flux. Can do. Specifically, nitrogen gas is dissolved in a mixed melt of metallic sodium and metallic gallium, and gallium nitride becomes supersaturated and grows as crystals. In such a liquid phase method, dislocations are less likely to occur than in a gas phase method, so that high-quality gallium nitride having a low dislocation density can be obtained.

  In the Na flux method, it is known that dislocations spontaneously decrease near the interface between the seed crystal and the growth part. Non-Patent Document 1 describes a dislocation reduction mechanism by the Na flux method. According to this, when the supersaturation degree in the initial stage of the flux method growth is small, the (10-11) plane of the GaN crystal appears on the surface, and as the process proceeds and the supersaturation level increases, the (0001) plane gradually increases. Will develop. Along with this, dislocations propagating from the seed crystal initially grow in the c-axis direction, but gradually tilt, and eventually a plurality of dislocations after the tilting are polymerized to form a dislocation bundle. The (10-11) plane is formed several microns from the interface, and the (0001) plane develops several tens of microns from the interface.

  In Patent Document 2, by intentionally making the surface of the seed crystal used in the flux method uneven, a part of dislocations propagating from the seed crystal is bent and confined inside the uneven structure, and a GaN crystal having a low dislocation density is formed. Aiming to grow.

  In Patent Document 3, in the initial stage of crystal growth by the flux method, nitrogen is intentionally held in an unsaturated state, and the seed crystal surface layer with low crystallinity and many dislocations is removed by melting back the surface of the seed crystal. The aim is to realize GaN crystals with low dislocation density.

JJAP Vol.45, 2006, pp.2528-2530

JP2000-349338 JP2005-281067 JP2009-012986

In the structure described in Patent Document 1, it is necessary to provide a fine SiO ₂ mask on the seed substrate surface, which complicates the manufacturing process. Further, since the lateral overgrowth of the crystal on the SiO ₂ mask is utilized, it is necessary to increase the thickness of the crystal layer in order to reduce the dislocation density on the surface of the grown crystal layer. For example, in order to reduce the dislocation density on the surface of the crystal layer to 10 ⁶ / cm ² , the thickness of the GaN crystal layer needs to be about 200 μm.

  In Non-Patent Document 1, the dislocation density can be reduced at an early stage as compared with the vapor phase method, but a thickness of several tens of microns is required to sufficiently reduce the dislocation on the crystal layer surface. Therefore, for example, in the region where the thickness of the crystal layer grown by the flux method is 50 μm or less, the dislocation density is not sufficiently reduced. For this reason, when the obtained crystal layer is thinly polished, a number of threading dislocations appear on the polished surface of the crystal layer, so that current leakage is likely to occur through the threading dislocation.

Similarly, in the structure of Patent Document 2, it is difficult to reduce the dislocation density on the surface of the crystal layer unless the thickness of the crystal layer is increased. For example, according to the example of Patent Document 3, in order to realize a dislocation density of 10 ⁶ / cm ^{2 on} the surface of the crystal layer, the thickness of the GaN crystal layer has to be several hundred μm.

  In Patent Document 3, since meltback can be performed during the crystal growth process, the process itself is simple, but it is difficult to control the amount of meltback in a high-temperature and high-pressure Na flux, and practicality is poor.

  An object of the present invention is a crystal layer made of a group 13 element nitride grown on a seed crystal made of a group 13 element nitride, which can reduce the thickness of the crystal layer and reduce the dislocation density on the surface of the crystal layer. It is to provide a structure that can be reduced.

The present invention is a crystal layer made of a group 13 element nitride grown on a seed crystal made of a group 13 element nitride,
The crystal layer has an interface layer along a smooth interface between the seed crystal and the group 13 element nitride crystal layer, and a growth layer provided on the interface layer;
The interface layer has the initial dislocation extending towards the surface of the Group 13 element nitride crystal layer, and an inclined dislocations extending in a direction crossing the initial dislocation is bent from the initial dislocation, the When the boundary at which 99% of initial dislocations terminates is defined as the boundary between the interface layer and the growth layer, the thickness of the interface layer is 15 μm or less.

  Moreover, this invention has the seed crystal | crystallization which consists of a group 13 element nitride, and the group 13 element nitride crystal layer as described in any one of the said Claims 1-5 provided on this seed crystal. The present invention relates to a composite substrate.

  In addition, the present invention relates to a functional element comprising the group 13 element nitride crystal layer and a functional layer made of a group 13 element nitride formed on a surface of the crystal layer. It is.

  The present inventor examined the microstructure of various Group 13 element nitride crystal layers described in the section of the prior art in detail using a TEM, a fluorescence microscope, etc., and reduced dislocations when the crystal layer was thin. Or I have been studying the microstructure that can be extinguished.

  For example, in the vapor phase method as described in Patent Document 1, many dislocations extend almost straight from the interface toward the surface of the crystal layer. For this reason, in order to reduce a dislocation | rearrangement using a lateral overgrowth, considerable thickness is required. Also, when dislocations extend in the horizontal direction, dislocations extending in the horizontal direction meet to form a dislocation bundle extending in the vertical direction again, and the dislocation bundle tends to appear on the surface of the crystal layer.

  The dislocation reduction mechanism by the flux method as described above will be described with reference to the reference diagram of FIG.

  As shown in FIG. 4, a group 13 element nitride crystal layer 10 is grown on the surface 1 a of the seed crystal 1. Here, at the initial stage of crystal growth, for example, the (10-11) plane of a GaN crystal appears on the surface. Along with this, the initial dislocation 13a extends substantially perpendicular to the interface I. Next, as the process proceeds and the degree of supersaturation of the melt increases, the (0001) plane gradually develops. Along with this, dislocations propagated from the seed crystal 1 initially extend in the c-axis direction, but gradually tilt with respect to the initial dislocations 13a as in 13b to 13c. Then, a plurality of tilted dislocations 13 c are polymerized to form, for example, a dislocation bundle 15 that extends substantially perpendicular to the interface I in the region D. The (10-11) plane is formed with a thickness of several microns from the interface I, and the (0001) plane develops with a thickness of several tens of microns from the interface I. When the crystal growth is further continued, the plurality of dislocation bundles 15 are polymerized in the region E to form new dislocation bundles 16.

  As a result, even if the crystal layer 10 is thickened, the dislocation bundle appearing on the surface 10a is not easily reduced. Even when growth is continued until the dislocation bundle is reduced on the surface 10a, if the crystal layer is polished and thinned, many dislocations appear on the polished surface. Therefore, the crystal layer is thin and has a low surface dislocation density. Can't get.

  Based on the above knowledge, the present inventor tried to control the crystal growth mode by precisely controlling the conditions at the start of crystal growth, and to bend the dislocations in the horizontal direction very close to the interface. This point will be described with reference to the schematic diagram of FIG.

  That is, when growing the crystal layer 2 from the surface 1a of the seed crystal 1, the present inventor suppresses growth on the (10-11) plane as much as possible in the initial stage of growth, and first promotes growth in the vertical direction. By developing the surface and then switching the growth mode early, we succeeded in growing in the lateral direction.

  As a result, in the interface layer 2b in the initial stage of growth, short initial dislocations 3a extending in the vertical direction are generated, the initial dislocations 3a are bent at an early stage, and inclined dislocations 3c and 3b that are inclined with respect to the initial dislocations 3a are generated. I understood it. Moreover, at this time, it has been found that the dislocations 3b extending substantially parallel to the interface I terminate before polymerizing with other dislocations to form terminal dislocations.

  As a result, a growth layer 2c having a dislocation density lower than that of the interface layer 2b is generated on the interface layer 2b. At this time, the bending of dislocations starts as 3c and 3b while the thickness t of the interface layer 2b is small. In addition, the inclined dislocations 3b terminate in the middle, hardly associate with other inclined dislocations, and do not easily form dislocation bundles, so that the threading dislocations hardly appear on the surface 2a of the crystal layer 2 even if the total thickness of the crystal layer 2 is small. The dislocation density on the surface can be reduced. That is, as described in Non-Patent Document 1, a thickness of several tens of μm is not required.

(A) is a schematic diagram which shows the group 13 element nitride crystal layer 2 formed on the seed crystal 1, (b) is a schematic diagram which shows the composite substrate 4, (c) is a composite substrate 4 is a schematic diagram showing a functional element 15 formed by forming a functional element structure 5 on 4. (A) is a schematic diagram showing a nucleus 6 generated on the seed crystal 1, and (b) is a schematic diagram showing a growth direction from the nucleus 6. It is a schematic diagram for demonstrating the structure of the crystal layer of this invention. It is a schematic diagram for demonstrating the structure of the crystal layer of a reference example. It is a TEM photograph of the crystal layer obtained in the example of the present invention. It is a fluorescence micrograph of the crystal layer obtained by the Example of this invention.

The present invention will be further described below with reference to the drawings as appropriate.
In a preferred embodiment, as shown in FIG. 1A, a group 13 element nitride crystal layer 2 is formed on the surface 1a of the seed crystal 1 made of gallium nitride. Next, preferably, the surface 2a of the crystal layer 2 is polished to make the crystal layer 3 thinner as shown in FIG. 3a is the surface after polishing.

  A functional layer 5 is formed on the surface 3a of the composite substrate 4 obtained in this way by a vapor phase method to obtain a functional element 15 (FIG. 1C). However, 5a, 5b, 5c, 5d, and 5e are epitaxial layers designed according to the use grown on the surface 3a.

  It is not essential to polish the surface 2a of the group 13 element nitride crystal layer 2 before forming the functional layer 5, and the growth surface can be used as it is. In addition, after the composite substrate 4 of FIG. 1B is manufactured, the seed crystal 1 can be removed by grinding or the like, and then the functional layer 5 can be formed on the surface of the crystal layer 3.

(Seed crystal)
In the present invention, the seed crystal is not particularly limited as long as the group 13 element nitride crystal layer can be grown. Here, the group 13 element is a group 13 element according to the periodic table established by IUPAC. The group 13 element is specifically gallium, aluminum, indium, thallium, or the like. This group 13 element nitride is particularly preferably GaN, AlN, or GaAlN.

  The seed crystal may form a self-supporting substrate (support substrate) by itself, or may be a seed crystal film formed on another support substrate. This seed crystal film may be a single layer, or may include a buffer layer on the support substrate side.

  As a method for forming the seed crystal film, a vapor deposition method is preferable, but a metal organic chemical vapor deposition (MOCVD) method, a hydride vapor deposition (HVPE) method, a pulsed excitation deposition (PXD) method, MBE Method and sublimation method. Metalorganic chemical vapor deposition is particularly preferred. The growth temperature is preferably 950 to 1200 ° C.

When the seed crystal film is formed on the support substrate, the material of the single crystal constituting the support substrate is not limited, but sapphire, AlN template, GaN template, GaN free-standing substrate, silicon single crystal, SiC single crystal, MgO single Examples thereof include crystals, spinel (MgAl ₂ O ₄ ), LiAlO ₂ , LiGaO ₂ , LaAlO ₃ , LaGaO ₃ , NdGaO _{3 and} other perovskite complex oxides, SCAM (ScAlMgO ₄ ). The composition formula _{[A 1-y (Sr 1-} x Ba x) y ] _{[(Al 1-z Ga z)} 1-u · D u ] _O 3 (A is a rare earth element; D is niobium and One or more elements selected from the group consisting of tantalum; y = 0.3-0.98; x = 0-1; z = 0-1; u = 0.15-0.49; x + z = 0 .1 to 2) cubic perovskite structure composite oxides can also be used.

  The growth direction of the group 13 element nitride crystal layer may be the normal direction of the c-plane of the wurtzite structure, or may be the normal direction of the a-plane and the m-plane.

The dislocation density on the surface of the seed crystal is desirably low from the viewpoint of reducing the dislocation density of the group 13 element nitride crystal layer provided on the seed crystal. From this viewpoint, the dislocation density of the seed crystal is preferably 7 × 10 ⁸ / cm ² or less, and more preferably 5 × 10 ⁸ / cm ² or less. Further, the lower the dislocation density of the seed crystal, the better from the viewpoint of quality, so there is no particular lower limit, but generally it is often 5 × 10 ⁷ / cm ² or more.

(Group 13 element nitride crystal layer)
The manufacturing method of the gallium nitride crystal layer is not particularly limited, but metal organic chemical vapor deposition (MOCVD) method, hydride vapor deposition (HVPE) method, pulse excitation deposition (PXD) method, MBE method, sublimation Examples thereof include gas phase methods such as the method, and liquid phase methods such as the flux method.

  In the group 13 element nitride constituting the crystal layer, the group 13 element is a group 13 element according to a periodic table established by IUPAC. The group 13 element is specifically gallium, aluminum, indium, thallium, or the like. This group 13 element nitride is particularly preferably GaN, AlN, or GaAlN. Examples of the additive include carbon, low melting point metals (tin, bismuth, silver, gold) and high melting point metals (transition metals such as iron, manganese, titanium, and chromium). The low melting point metal may be added for the purpose of preventing oxidation of sodium, and the high melting point metal may be mixed from a container in which a crucible is put or a heater of a growth furnace.

  For example, as shown in the schematic diagram of FIG. 3, the group 13 element nitride crystal layer 2 of the present invention includes an interface layer 2b along the interface between the seed crystal and the group 13 element nitride crystal layer, and on the interface layer. And a provided growth layer 2c.

  Here, the interface layer 2b extends along the interface I. The seed crystal 1 in contact with the interface layer 2b may include a so-called underlayer or buffer layer.

  The interface layer 2b is a layer that includes initial dislocations extending from the interface I and inclined dislocations continuous thereto. From the viewpoint of the present invention, the thickness t of the interface layer 2b is set to 15 μm or less, more preferably 5 μm or less. The thickness t of the interface layer 2b is preferably 1 μm or more. In the interface layer 2b, most of the dislocations continuing from the initial dislocations are terminated and the dislocation density is reduced.

  In the present invention, the boundary where 99% of the initial dislocations are terminated is defined as the boundary between the interface layer and the growth layer. For this reason, 100 initial dislocations are traced from the boundary between the seed crystal and the interface layer toward the growth layer, and the location where 99 of them are terminated is confirmed as the boundary between the interface layer and the growth layer. The distance from the boundary between the seed crystal and the interface layer to the boundary between the interface layer and the growth layer is defined as the thickness of the interface layer.

  Further, from the viewpoint of the present invention, the thickness T of the crystal layers 2 and 3 is preferably 20 μm or less, and more preferably 15 μm or less. The thickness t of the crystal layer is preferably 5 μm or more.

The growth layer 2c on the interface layer is a layer in which most of the dislocations continuing from the initial dislocation existing in the interface layer 2b are terminated and the dislocation density is low. Specifically, after taking a TEM photograph to be described later, the dislocation density is preferably 5 × 10 ⁵ cm ⁻² or less in a visual field of 5 μm × 5 μm.

  In the present invention, the interface layer has initial dislocations extending toward the surface of the group 13 element nitride, and inclined dislocations that are bent from the initial dislocations and extend in a direction intersecting the initial dislocations. Yes.

  The inclination angle of the inclined dislocation relative to the initial dislocation is 30 to 90 °, preferably 60 to 90 ° in the TEM photograph.

  In a particularly preferred embodiment, the inclined dislocations extend substantially parallel to the interface I. As a result, the inclined dislocations are easily terminated at the end, and are difficult to extend to the surface of the crystal layer.

  In a particularly preferred embodiment, the group 13 element nitride crystal layer is grown by a flux method. At this time, the type of the flux is not particularly limited as long as the group 13 element nitride can be generated. In a preferred embodiment, a flux containing at least one of an alkali metal and an alkaline earth metal is used, and a flux containing sodium metal is particularly preferred.

  For the flux, a raw material of a group 13 element is mixed and used. As the raw material, a single metal, an alloy, or a compound can be applied, but a single metal of a group 13 element is preferable from the viewpoint of handling.

The dislocation measurement method using a transmission electron microscope (TEM) is as follows.
For the production of TEM observation slices, the FIB (Focused Ion Beam) method was used in order to accurately slice the heterogeneous interfaces with different etching rates.
Specifically, a cross-sectional TEM observation sample was prepared in the order of (1) resin filling, (2) cutting, (3) mechanical polishing, and (4) FIB processing.
(1)
An epoxy resin was used to reinforce the sample.
(2)
It cut out to the magnitude | size of 2.5 * 1.5 * 2mm with the micro cutter.
(3)
Machine polishing was performed with a composite surface plate (slurry: 3 μm) and ceramic surface plate (slurry: 1.5 μm), and the FIB processed surface was mirror finished. Thereafter, the sample was thinned to about 60 to 70 μm by hand polishing, and the sample piece was attached to a Cu single-hole mesh for TEM observation.
(4)
In order to suppress charging during ion beam processing, carbon coating was first performed before moving to the FIB system. Thereafter, Pt vapor deposition was performed in the FIB apparatus in order to protect the thin sample preparation site from damage caused by ion beam processing. Then, the thickness was reduced to about 200 nm or less, centering on the location.
Observation was performed at an acceleration voltage of 200 kV using a transmission electron microscope (JEM-2010). The electron beam incident direction was [11-20] GaN. The state of dislocation was observed by a bright field image and a dark field image (g = -1100, g = 000-2).

(Control example of growth of group 13 element nitride crystal layer)
The suitable control method for growing the group 13 element nitride crystal layer of this invention is illustrated.

  Preferably, in the initial stage, when the growth in the vertical direction is promoted, the crystal growth is performed using only the concentration gradient as much as possible as the driving force by setting the degree of supersaturation as low as possible and suppressing the convection of the melt.

Specifically, in the initial stage, it is preferable to grow by the following method.
(1A) By increasing the average growth temperature of the melt in the crucible, the degree of supersaturation is increased to suppress the formation of nuclei 6 (FIG. 2).
(2A) By holding the upper part of the crucible at a higher temperature than the bottom part of the crucible, the convection of the melt in the crucible is suppressed.
(3A) Do not stir the melt or reduce the stirring speed.
(4A) Lower the partial pressure of the nitrogen-containing gas.

  Thereby, in the initial stage, the formation of the nucleus 6 is suppressed, and the crystal grows upward from the nucleus 6 (arrow C). At this time, the initial dislocations 3a also grow upward and become edge dislocations.

  In a preferred embodiment, after stopping the initial stage conditions, the growth conditions are changed to increase the crystal growth rate (late stage). As a result, the crystal growth 7 is mainly in the lateral direction (arrows A and B), and the dislocation is mainly tilted dislocations 3b and 3c. Further, in the tilted dislocations 3b and 3c, the screw dislocation is mainly used, and changes to the screw dislocation or the mixed dislocation.

At this stage, the following is preferable.
(1B) The degree of supersaturation is reduced by lowering the average growth temperature of the melt in the crucible.
(2B) The natural convection of the melt in the crucible is promoted by keeping the upper part of the crucible at a lower temperature than the bottom part of the crucible, or by keeping the upper part and the lower part at the same temperature.
(3B) Stir the melt to increase the stirring speed or periodically reverse the stirring direction.
(4B) Increase the partial pressure of the nitrogen-containing gas.

For example, the following conditions can be applied.
(Early stage)
(1A) The average growth temperature of the melt in the crucible is set to 860 to 870 ° C.
(2A) Maintain the temperature at the top of the crucible 10-30 ° C. higher than the temperature at the bottom of the crucible.
(3A) The melt is not stirred or the stirring speed is 6 rpm or less. The stirring direction is one direction.
(4A) The partial pressure of the nitrogen-containing gas is set to 3.0 to 3.5 MPa.

(Second stage)
(1B) The average growth temperature of the melt in the crucible is set to 840 to 860 ° C. Moreover, the difference of the average growth temperature with an initial stage shall be 10-20 degreeC.
(2B) Keep the temperature at the bottom of the crucible 0-20 ° C. higher than the temperature above the crucible.
(3B) Stir the melt and periodically change the stirring direction. Furthermore, it is preferable to stop the rotation of the crucible when changing the rotation direction. In this case, the rotation stop time is preferably 100 seconds to 6000 seconds, and more preferably 600 seconds to 3600 seconds. The rotation time before and after the rotation stop time is preferably 10 seconds to 600 seconds, and the rotation speed is preferably 10 to 30 rpm.
(4B) The partial pressure of the nitrogen-containing gas is 4 to 4.5 MPa. Moreover, it is 0.5-1 MPa higher than the partial pressure of the nitrogen-containing gas in the initial stage.

In the flux method, a single crystal is grown in an atmosphere containing a gas containing nitrogen atoms. This gas is preferably nitrogen gas, but may be ammonia.
The gas other than the gas containing nitrogen atoms in the atmosphere is not limited, but an inert gas is preferable, and argon, helium, and neon are particularly preferable.

  In the initial stage of the growth, it is preferably held for 1 hour or more, more preferably 2 hours or more under the conditions (1A) to (4A) described above. The holding time in the initial stage is preferably 5 hours or less.

  From the viewpoint of the present invention, the ratio (mol ratio) of group 13 element nitride / flux (for example, sodium) in the melt is preferably increased, preferably 15 mol% or more, and more preferably 25 mol% or more. However, if this ratio becomes too large, the crystal quality tends to deteriorate, so 40 mol% or less is preferable.

(Processing and morphology of crystal layer)
In the preferred embodiment, the group 13 element nitride crystal layer is disk-shaped, but other forms such as a square plate may be used. In a preferred embodiment, the crystal layer has a diameter of 25 mm or more. Thereby, an easy-to-handle crystal layer suitable for mass production of functional elements can be provided.

The case where the surface of the group 13 element nitride crystal layer is ground and polished will be described.
Grinding refers to scraping off the surface of an object by bringing fixed abrasive grains, which are fixed by abrasive bonds, into contact with the object while rotating at high speed. A rough surface is formed by this grinding. When grinding the bottom surface of a gallium nitride substrate, it is formed of high hardness SiC, Al ₂ O ₃ , diamond, CBN (cubic boron nitride, the same shall apply hereinafter), etc., and contains abrasive grains having a particle size of about 10 μm to 100 μm Fixed abrasives are preferably used.

In addition, polishing (lapping) refers to contact between a surface plate and an object while rotating each other through loose abrasive grains (referred to as non-fixed abrasive grains hereinafter), or fixed abrasive grains and an object. The surface of the object is polished by rotating and rotating each other. By this polishing, a surface having a surface roughness smaller than that in the case of grinding and a surface rougher than that in the case of fine polishing (polishing) is formed. Abrasive grains formed of SiC, Al ₂ O ₃ , diamond, CBN, or the like having high hardness and having a particle size of about 0.5 μm to 15 μm are preferably used.

  Fine polishing (polishing) means that the polishing pad and the object are brought into contact with each other through rotating abrasive grains, or the fixed abrasive grains and the object are brought into contact with each other while being rotated, and the surface of the object is brought into contact. This means smoothing by smoothing. By such fine polishing, a crystal growth surface having a smaller surface roughness than that in the case of polishing is formed.

(Functional layer and functional element)
The functional layer described above may be a single layer or a plurality of layers. As functions, it can be used for white LEDs with high luminance and high color rendering, blue-violet laser disks for high-speed and high-density optical memory, power devices for inverters for hybrid vehicles, and the like.

  When a semiconductor light emitting diode (LED) is fabricated on a group 13 element nitride crystal layer by a vapor phase method, preferably by a metal organic chemical vapor deposition (MOCVD) method, the dislocation density inside the LED becomes equal to that of the crystal layer.

  The film forming temperature of the functional layer is preferably 950 ° C. or higher, more preferably 1000 ° C. or higher, from the viewpoint of the film forming speed. Further, from the viewpoint of suppressing defects, the film formation temperature of the functional layer is preferably 1200 ° C. or lower, and more preferably 1150 ° C. or lower.

  The material of the functional layer is preferably a group 13 element nitride. Group 13 elements are Group 13 elements according to the periodic table established by IUPAC. The group 13 element is specifically gallium, aluminum, indium, thallium, or the like.

  The light-emitting element structure includes, for example, an n-type semiconductor layer, a light-emitting region provided on the n-type semiconductor layer, and a p-type semiconductor layer provided on the light-emitting region. In the light emitting element 15 of FIG. 1C, an n-type contact layer 5a, an n-type cladding layer 5b, an active layer 5c, a p-type cladding layer 5d, and a p-type contact layer 5e are formed on the composite substrate 4. A light emitting element structure 5 is formed.

  The light emitting structure may further include an n-type semiconductor layer electrode, a p-type semiconductor layer electrode, a conductive adhesive layer, a buffer layer, a conductive support, and the like (not shown).

  In this light emitting structure, when light is generated in the light emitting region due to recombination of holes and electrons injected from the semiconductor layer, the light is transmitted to the translucent electrode or the group 13 element nitride single crystal film side on the p-type semiconductor layer. Take out from. The translucent electrode is a translucent electrode made of a metal thin film or a transparent conductive film formed on almost the entire surface of the p-type semiconductor layer.

The material of the semiconductor constituting the n-type semiconductor layer and the p-type semiconductor layer is made of a III-V group compound semiconductor, and the following can be exemplified.
Al _y In _x Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1)
Examples of the doping material for imparting n-type conductivity include silicon, germanium, and oxygen. Moreover, magnesium and zinc can be illustrated as a dope material for providing p-type conductivity.

  Examples of the growth method of each semiconductor layer constituting the light emitting structure include various vapor phase growth methods. For example, an organic metal compound vapor phase growth method (MOCVD (MOVPE) method), a molecular beam epitaxy method (MBE method), a hydride vapor phase growth method (HVPE method), or the like can be used. Among them, the MOCVD method can obtain a semiconductor layer with good crystallinity and flatness. In the MOCVD method, alkyl metal compounds such as TMG (trimethyl gallium) and TEG (triethyl gallium) are often used as the Ga source, and gases such as ammonia and hydrazine are used as the nitrogen source.

  The light emitting region includes a quantum well active layer. The material of the quantum well active layer is designed so that the band gap is smaller than the materials of the n-type semiconductor layer and the p-type semiconductor layer. The quantum well active layer may have a single quantum well (SQW) structure or a multiple quantum well (MQW) structure. The material of a quantum well active layer can illustrate the following.

  As a preferred example of the quantum well active layer, an AlxGa1-xN / AlyGa1-yN-based quantum well active layer (x = 0.15, y = 0.20) having a thickness of 3 nm / 8 nm, respectively, 3 An MQW structure formed for 10 to 10 periods is mentioned.

Example 1
(Preparation of seed crystal substrate)
Using a MOCVD method, a low-temperature GaN buffer layer of 40 nm was deposited on a c-plane sapphire substrate having a diameter of 2 inches and a thickness of 500 μm at 530 ° C. Next, a seed crystal film made of GaN having a thickness of 3 μm was deposited at 1050 ° C. The defect density by TEM observation was 1 × 10 ⁹ / cm ² . The substrate was subjected to ultrasonic cleaning with an organic solvent and ultrapure water for 10 minutes and then dried to obtain a seed crystal substrate.

(Liquid phase GaN crystal growth)
In a glove box filled with an inert gas, metal Ga and metal Na were weighed at a molar ratio of 20:80, and placed together with the seed crystal substrate at the bottom of an alumina crucible. The crucible was housed in a stainless steel holding container, and this holding container was placed on a turntable provided in a pressure-baked container that had been baked in advance, and then the pressure-resistant container was covered and sealed. Next, the inside of the pressure vessel was evacuated to 0.1 Pa or less with a vacuum pump.

  Subsequently, by heating the heater installed inside the pressure vessel, the raw material in the crucible was melted to produce a Ga—Na mixed melt. While heating so that the melt surface vicinity was 870 ° C. and the crucible bottom was 850 ° C., nitrogen gas was introduced from the nitrogen gas cylinder until the pressure became 3.5 MPa (initial stage).

  After 5 hours, while maintaining the temperature at the bottom of the crucible at 850 ° C., the temperature near the melt surface was changed to 850 ° C., the pressure was changed to 4.0 MPa, and stirring by continuous inversion of the rotary table was started. The crystal growth mode was changed. The rotation conditions were a clockwise rotation and a counterclockwise rotation at a constant cycle at a speed of 20 rpm around the central axis. Acceleration time = 12 seconds, holding time = 600 seconds, deceleration time = 12 seconds, stop time = 0.5 seconds (late stage). After maintaining in this state for 20 hours, it was naturally cooled to room temperature, and the grown gallium nitride crystal plate was recovered.

When the surface of the obtained gallium nitride crystal plate was polished and the dislocation density was evaluated by the cathodoluminescence method, it was 2 × 10 ⁵ / cm ² . Next, when the cross section was polished and subjected to TEM observation, a microstructure as shown in FIGS. 3 and 5 was observed.

Further, when the crystal growth history was examined by observing the cross section with a fluorescence microscope, it was observed that the crystal grown in a columnar shape changed in the middle and was growing smoothly (see FIG. 6). However, the fluorescence microscope image was obtained as follows.
Equipment: Olympus BX61, etc. Measurement conditions: Excitation filter BP340-390nm
Absorption filter BA420IF
Dichroic mirror DM410
Field of view: 5x and 20x objective lens Software: Commercial image capture software (Adobe Photoshop, ImageJ, etc.)

Further, the thickness of the interface layer was 5 μm. The dislocation density in the growth layer was 5 × 10 ⁵ / cm ² .

  A blue LED structure was formed on the obtained substrate, and the light emission characteristics were measured. The in-plane distribution of the emission intensity of the 1 mm square LED chip was highly uniform, and no difference was observed between the outer periphery and the center. In addition, the ratio of chips having an optical output of 200 mW or more in the light emission characteristics during current drive at 350 mA was as high as 75%.

(Example 2)
A GaN crystal was grown in the same manner as in Example 1. However, the following points were changed in Example 1.

  After holding for 10 hours in the initial stage, crystal growth in the late stage was performed. That is, crystal growth was started by introducing nitrogen gas from a nitrogen gas cylinder until the pressure reached 3.5 MPa while heating so that the melt surface vicinity was 870 ° C. and the crucible bottom was 850 ° C. (initial stage). After 10 hours, while maintaining the crucible bottom temperature at 850 ° C., the temperature near the melt surface was changed to 850 ° C., the pressure was changed to 4.0 MPa, and stirring by continuous inversion of the turntable was started. The crystal growth mode was changed (late stage).

As a result, a microstructure as shown in FIGS. 3 and 5 was observed. The thickness of the interface layer was 15 μm. The dislocation density in the growth layer was 1 × 10 ⁵ / cm ² .

  A blue LED structure was formed on the obtained substrate, and the light emission characteristics were measured. The in-plane distribution of the emission intensity of the 1 mm square LED chip was highly uniform, and no difference was observed between the outer periphery and the center. In addition, the ratio of chips with an optical output of 200 mW or more in the light emission characteristics at the time of current drive at 350 mA was as high as 80%.

(Comparative Example 1)
In Example 1, the above-mentioned “initial stage” was not grown in the initial stage of crystal growth, and the crystal was grown under the “late stage” manufacturing conditions throughout. Except for this, the experiment was performed in the same manner as in Example 1.

When the surface of the recovered gallium nitride crystal plate was polished and the dislocation density was evaluated by the cathodoluminescence method, it was 2 × 10 ⁷ / cm ² . Next, the crystal cross section was polished and subjected to TEM observation. As a result, dislocations extended from the interface I in an oblique direction and polymerized with growth to form dislocation bundles.

A blue LED structure was formed on this substrate, and the light emission characteristics were measured. The in-plane distribution of the emission intensity of the LED chip of 1 mm square was not uniform and sparsely observed areas where the emission intensity was low. In addition, the ratio of chips having a light output of 200 mW or more in the light emission characteristics at the time of current drive at 350 mA was 50%, which was significantly lower than that of the example. When the leakage current characteristics of the chip with low light output were examined, it was confirmed that leakage current was generated from a low voltage region, and it was found that the cause of the low light output was leakage current.
In this comparative example, the thickness when 99% of the initial dislocations terminated was 60 μm.

Claims (8)

A crystal layer made of a group 13 element nitride grown on a seed crystal made of a group 13 element nitride,
The crystal layer has an interface layer along a smooth interface between the seed crystal and the crystal layer, and a growth layer provided on the interface layer, and the interface layer is formed of the crystal layer. An initial dislocation extending toward the surface, and an inclined dislocation that is bent from the initial dislocation and extends in a direction intersecting the initial dislocation, and a boundary at which 99% of the initial dislocation terminates is the interface. A group 13 element nitride crystal layer , wherein the interface layer has a thickness of 15 μm or less when a boundary between the layer and the growth layer is formed.
  The group 13 element nitride crystal layer according to claim 1, wherein the inclined dislocations extend substantially parallel to the interface. Wherein the thickness of the interfacial layer is 5μm or less, according to claim 1 or 2 Group 13 element nitride crystal layer according. The group 13 element nitride crystal layer according to any one of claims 1 to 3 , wherein a surface of the crystal layer is a polished surface. A composite crystal comprising: a seed crystal composed of a group 13 element nitride; and a group 13 element nitride crystal layer according to any one of claims 1 to 4 provided on the seed crystal. substrate. A group 13 element nitride crystal layer according to any one of claims 1 to 4 , and a functional layer made of a group 13 element nitride formed on the surface of the crystal layer. A functional element. The functional element according to claim 6 , wherein the functional layer has a light emitting function. The functional element according to claim 6 or 7 , further comprising a seed crystal made of a group 13 element nitride, wherein the group 13 element nitride crystal layer is provided on the seed crystal.

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