JP4876002B2 - Melt composition for growing gallium nitride single crystal and method for growing gallium nitride single crystal - Google Patents

Description

  The present invention relates to a melt composition for growing a gallium nitride single crystal and a method for growing a gallium nitride single crystal.

  Gallium nitride has attracted attention as an excellent blue light-emitting device, and has been put to practical use as a material for light-emitting diodes and semiconductor laser diodes. Recently, a method of growing a gallium nitride single crystal from a melt by a flux method has attracted attention.

Ga-Na-A (Li, K, Rb,
Patent Document 1 discloses growing a GaN single crystal by a flux method using a melt having a composition of Cs, Fr) -B (Ca, Sr, Ba, Ra). However, here, one or more elements are selected from at least one of the elements of group A and group B.
PCT WO 2004/013385 A1

Furthermore, Ga-Li-A (Na, K, Rb,
Patent Document 2 discloses that a GaN single crystal is grown by a flux method using a melt having a composition of Cs, Fr) -B (Ca, Sr, Ba, Ra). However, here, one or more elements are selected from at least one of the elements of group A and group B.
PCT WO 2004/067814 A1

Further, Patent Document 3 discloses that a GaN crystal is grown by a flux method using a melt having a Ga-Na-A (a small amount of alkaline earth) composition. The amount of alkaline earth added is 0.002 to 0.05 mol per mol of Ga. In Example III of Patent Document 3, an attempt is made to grow a GaN single crystal using a melt containing sodium, gallium and barium.
US Patent 5,868,837

In the growth of GaN crystals by the Na flux method, it is known that when Li is added to the melt, the flatness and transparency of the crystals are improved (Non-Patent Document 1).
Jpn. J. Appl. Phys. 42 (2003) L565.

Further, it is known that when the amount of Li added is large, Li is taken into the GaN crystal (Non-patent Document 2). When Li is taken into the GaN single crystal, impurity band emission with a center wavelength of about 511 nm increases.
Autumn 2005 Proceedings of the 66th Japan Society of Applied Physics, I, 7a-X-7

  The present inventor examined various elements as additive metal elements in place of Li when growing a GaN single crystal by a flux method using a Ga—Na based melt. As a result, when calcium, which is an alkali metal element, was added, the crystal color was gray and transparent, but blue light emission was observed from the crystal, and the alumina crucible was severely corroded. In addition, when strontium was added, yellow-green light emission was also observed from the crystals.

  As in Patent Document 3, an attempt was made to grow a GaN single crystal using a melt containing gallium and barium. As a result, it was found that light emission from the crystal was suppressed. However, it was also found that the flatness of the obtained crystal was lowered. When the flatness of the crystal is deteriorated, the yield is lowered and the characteristics as an element are also lowered.

  The object of the present invention is to reduce the impurity band emission of the crystal and improve the transparency when the GaN single crystal is grown by the flux method using the Ga—Na based melt, and the flatness of the obtained crystal is also improved. It is to improve.

The present invention is a melt composition for growing a gallium nitride single crystal by a flux method,
It contains gallium, sodium, barium and lithium, and the total amount of barium and lithium is 0.02 to 1.0 mol% and the amount of barium is 0.01 to 0.5 mol% when the amount of sodium is 100 mol% The amount of lithium is 0.01 to 0.5 mol%.

  The present invention also relates to a method for growing a gallium nitride single crystal from the melt composition by a flux method.

  According to the present invention, not only a relatively transparent GaN single crystal is obtained, but also unnecessary light emission due to incorporation of impurity elements into the single crystal is remarkably reduced, and the flatness of the crystal is improved.

For example, lithium, calcium, and strontium elements are alkali metal and alkaline earth metal elements. When calcium is added to the Ga—Na melt, blue impurity band emission is observed. Further, when strontium was added to the Ga—Na-based melt, yellow-green impurity band emission was observed. This luminescence was similar to that when lithium was added. Furthermore, even when a single crystal is grown with a Ga—Na melt (no added metal), blue light emission is observed in the obtained single crystal.
In Patent Document 3, an attempt is made to grow a GaN single crystal using a melt containing gallium and barium, but light emission from the crystal is not described and cannot be predicted.

  Therefore, when barium and lithium are simultaneously added to the Ga—Na-based melt, light emission from the GaN single crystal can be remarkably reduced and the flatness of the crystal can be improved. Is an unexpected effect.

  When producing the melt composition of the present invention, at least a gallium raw material, a sodium raw material, a barium raw material, and a lithium raw material are mixed and melted.

As the gallium source material, a gallium simple metal or a gallium alloy (for example, Ga ₄ Na) can be applied, but a gallium simple metal is also preferable in terms of handling.

As the sodium raw material, a sodium simple metal or a sodium alloy (for example, Ga ₄ Na) can be applied, but a sodium simple metal is also preferable in terms of handling.

As the barium source material, a barium simple metal, a barium alloy (for example, Ba ₈ Ga ₇ , GaGa ₂ , BaGa ₄ , Ba ₁₀ Ga) or a barium compound (for example, Ba ₃ N ₂ ) can be used. Is also preferable.

As the lithium source material, a lithium simple metal, a lithium alloy (Ga ₁₄ Li ₃ , Ga ₂ Li, GaLi), or a lithium compound (Li ₃ GaN ₂ ) can be applied, but a lithium simple metal is preferable.

  The molar ratio of gallium and sodium in the melt is not particularly limited. For example, when the amount of sodium is 100 mol%, the number of moles of gallium is preferably 10 mol% or more, and more preferably 25 mol% or more. The number of moles of gallium is preferably 60 mol% or less, and more preferably 50 mol% or less. If the amount of gallium is less than that of sodium, the gallium raw material due to crystal growth tends to be depleted.

When the amount of sodium in the melt is 100 mol%, the total number of moles of barium and lithium is 0.02 mol% or more, and more preferably 0.1 mol% or more. The total number of moles of barium and lithium is 1.0 mol% or less, and more preferably 0.6 mol% or less.

When the amount of sodium in the melt is 100 mol%, the number of moles of barium is 0.01 mol% or more, and more preferably 0.05 mol% or more. The number of moles of barium is 0.5 mol% or less, and more preferably 0.3 mol% or less. If the amount is too small, it is difficult to obtain the effect, and if the amount is too large, multinuclei are likely to be generated, and it becomes difficult to obtain good quality crystals.

When the amount of sodium in the melt is 100 mol%, the number of moles of lithium is 0.01 mol% or more, and more preferably 0.05 mol% or more. Further, the number of moles of lithium is 0.5 mol% or less, and more preferably 0.3 mol% or less. If the amount is too small, the effect of adding is difficult to appear. If the amount is too large, it is likely to be incorporated into the crystal and the emission of impurity bands increases.

  In addition to gallium, sodium, barium, and lithium, for example, calcium, aluminum, indium, tin, zinc, bismuth, antimony, silicon, magnesium, and the like can be added to the melt.

  The material of the growth vessel for performing the reaction of the melt is not particularly limited as long as the material is durable under the intended heating and pressurizing conditions. Examples of such materials include refractory metals such as tantalum, tungsten, and molybdenum, oxides such as alumina, sapphire, and yttria, nitride ceramics such as aluminum nitride, titanium nitride, zirconium nitride, and boron nitride, tungsten carbide, tantalum carbide, and the like. And pyrolytic products such as p-BN (pyrolytic BN) and p-Gr (pyrolytic graphite). Among these, alumina (sapphire) is most preferable.

  In carrying out the present invention, for example, the raw material mixture is melted in an atmosphere containing at least nitrogen gas and / or ammonia to generate a melt. And it is set as predetermined single crystal growth conditions. Such conditions are not limited, but the total pressure of the atmosphere is preferably 3 to 200 MPa. The growth temperature is preferably 800 to 1200 ° C, and more preferably 850 to 1000 ° C.

  Gases other than nitrogen and ammonia in the atmosphere are not limited, but inert gases are preferable, and argon, helium, and neon are particularly preferable.

The material of the growth substrate for epitaxially growing the gallium nitride crystal is not limited, but sapphire, AlN template, GaN template, silicon single crystal, SiC single crystal, MgO single crystal, spinel (MgAl ₂ O ₄ ), LiAlO ₂ , LiGaO ₂ , perovskite complex oxides such as LaAlO ₃ , LaGaO ₃ , and NdGaO ₃ can be exemplified. 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. SCAM (ScAlMgO ₄ ) can also be used.

  An AlN template refers to an AlN single crystal epitaxial thin film formed on a sapphire single crystal substrate. The GaN template substrate refers to a GaN single crystal epitaxial thin film formed on a sapphire substrate. The film thickness of the template may be appropriate, but it needs to be greater than the film thickness that melts back at the start of growth. The AlN template is less likely to melt back than the GaN template. For example, the AlN template may have a film thickness of 1 micron or more, and the GaN template may have a film thickness of 3 microns or more.

  In the single crystal growth apparatus, an apparatus for heating the raw material mixture to generate a melt is not particularly limited. This apparatus is preferably a hot isostatic pressing apparatus, but other atmospheric pressure heating furnaces may be used.

  In the production of a single crystal, for example, as schematically shown in FIG. 1, a plurality of heating elements 6A, 6B, 6C are installed in the vertical direction, and the heating value is independently controlled for each heating element. That is, multi-zone control is performed in the vertical direction. It is generally difficult to control the temperature gradient in the vertical direction because the inside of the pressure vessel is high temperature and high pressure, but it is difficult to control the temperature gradient in the vertical direction. The temperature difference at can be optimally controlled.

  When each heating element is heated, a nitrogen-containing atmosphere is passed through the gas tank 1, the pressure control device 2, and the pipe 3 to the growth vessel 7 in the atmosphere control vessel 4, and when heated and pressurized, the mixed raw materials are mixed in the growth vessel. All dissolve and form a melt. Here, if the predetermined single crystal growth conditions are maintained, nitrogen is stably supplied into the growth raw material melt, and a single crystal film grows on the seed crystal.

  The material of the heating element is not particularly limited, but alloy heating elements such as iron-chromium-aluminum and nickel-chromium, refractory metal heating elements such as platinum, molybdenum, tantalum and tungsten, silicon carbide, molybdenum silicite, carbon Non-metallic heating elements such as

(Comparative Example 1)
Metal box 0.88 g (0.038 mol), metal gallium 1 g (0.014 mol) (37 mol% with respect to 100 mol% metal sodium), metal lithium (0.5 mol% with respect to 100 mol% Na) glove box Weighed inside. This raw material was filled into an alumina crucible growing container having an inner diameter of φ17 mm. At this time, a seed crystal substrate was placed at the bottom of the crucible growing container. A 10 mm square GaN template substrate was used as a seed crystal substrate. The substrate was placed horizontally on the bottom of the crucible growing container so that the single crystal thin film of the template was facing upward.

  Subsequently, the crucible was set in the growing apparatus and pressurized to 3.5 MPa with nitrogen gas. A GaN single crystal was grown by holding at 870 ° C. for 100 hours. At this time, the oscillation cycle was 10 rpm and the oscillation angle was 15 °. After natural cooling to room temperature, the crucible growing container was taken out from the growing apparatus and treated in ethanol to dissolve Na and Ba. Then, it was put on thin hydrochloric acid, the remaining Ga was removed, and the GaN single crystal was taken out. The obtained GaN single crystal had almost the same shape as the template, and was one size larger. The crystal dimensions were about 11 mm × 11 mm × thickness about 0.6 mm. The crystals had a slight brown color but were transparent. Incorporation of cracks and miscellaneous crystals was not observed. This photograph is shown in FIG.

  When this crystal was irradiated with an ultraviolet lamp, only visible light was observed with a microscope through an ultraviolet cut filter, and impurity band emission was observed, and yellow-green emission was observed (FIG. 3).

Example 1
A GaN single crystal was grown in the same manner as in Comparative Example 1. However, metal barium was also added to the melt (0.27 mol% Ba relative to 100 mol% Na). The amount of metallic lithium was 0.25 mol% of Li with respect to 100 mol% of Na. The obtained GaN single crystal had almost the same shape as the template, was larger by one, and was about 11 mm × 11 mm and the thickness was about 0.8 mm. The color was almost colorless and transparent. Incorporation of cracks and miscellaneous crystals was not observed. This photograph is shown in FIG.

  Similarly, when this crystal was observed for impurity band emission with a fluorescence microscope, slight yellow-green emission was observed (FIG. 5). By simultaneously adding Ba and Li, step growth was achieved as shown in FIG. 5, and the flatness of the crystal surface was improved. In addition, since the amount of Li addition can be reduced compared to the case of growing only with Li, it was confirmed that the amount of emission of impurity bands was reduced compared to the case where only Li was added.

(Comparative Example 2)
A GaN single crystal was grown in the same manner as in Comparative Example 1. However, Li was not added, and 0.27 mol% of Sr was added to 100 mol% of Na. The obtained GaN single crystal had almost the same shape as the template, was larger by one, and was about 11 mm × 11 mm and the thickness was about 0.7 mm. The color was mostly gray and the edge was brown. Incorporation of cracks and miscellaneous crystals was not observed. This photograph is shown in FIG.

  Similarly, when this crystal was observed for impurity band emission with a fluorescence microscope, yellow-green emission was observed (FIG. 7). Moreover, the alumina crucible and the sapphire portion of the GaN template used as a seed substrate were slightly corroded.

(Comparative Example 3)
A GaN single crystal was grown in the same manner as in Comparative Example 1. However, Li was not added, and Ca was added at 0.1 mol% with respect to Na 100 mol%. The obtained GaN single crystal had almost the same shape as the template, and was one size larger. The thickness was about 0.6 mm. The color was mostly dark gray but transparent. Incorporation of cracks and miscellaneous crystals was not observed. This photograph is shown in FIG.

  When the impurity band emission of this crystal was observed with a fluorescence microscope in the same manner as in Comparative Example 1, blue emission was observed (FIG. 9). The alumina crucible was severely corroded, and it was confirmed that the sapphire portion of the GaN template used as a seed substrate was thin and melted.

It is a block diagram which shows typically the breeding apparatus which can be used in the case of implementation of this invention. In Comparative example 1 which added lithium, it is a photograph which shows the external appearance of a GaN single crystal. In Comparative example 1 which added lithium, it is a fluorescence micrograph of a GaN single crystal. In Example 1 which added lithium and barium, it is a photograph which shows the external appearance of a GaN single crystal. In Example 1 which added lithium and barium, it is a fluorescence micrograph of a GaN single crystal. It is a photograph which shows the external appearance of a GaN single crystal in the comparative example 2 which added strontium. In Comparative example 2 which added strontium, it is a fluorescence micrograph of a GaN single crystal. It is a photograph which shows the external appearance of a GaN single crystal in the comparative example 3 which added calcium. In the comparative example 3 which added calcium, it is a fluorescence micrograph of a GaN single crystal.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Gas tank 2 Pressure control apparatus 3 Piping 4 Atmosphere control container 6A, 6B, 6C Heating body 7 Growth container

Claims (2)

A melt composition for growing a gallium nitride single crystal by a flux method,
It contains gallium, sodium, barium and lithium, and the total amount of barium and lithium is 0.02 to 1.0 mol% and the amount of barium is 0.01 to 0.5 mol% when the amount of sodium is 100 mol% The melt composition is characterized in that the amount of lithium is 0.01 to 0.5 mol% . A method for growing a gallium nitride single crystal from the melt composition according to claim 1 by a flux method.

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