Patent Description:
Group III nitride semiconductors can cover a wide bandgap by changing the composition of Ga, Al and In being group III elements. Such semiconductors are widely used in optical semiconductor devices such as light-emitting diodes (LEDs) and semiconductor laser diodes (LDs), and electronic devices for high-frequency and high-output applications. In general, such devices are produced by epitaxial growth of a group III nitride semiconductor layer on a sapphire substrate. A sapphire substrate, however, has a lattice mismatch of <NUM>% to GaN as one of group III nitride semiconductors, represented by {(lattice constant of GaN - lattice constant of sapphire)/lattice constant of GaN}. Thus, there may be caused an increase in defect density in a group III nitride semiconductor epitaxially grown and/or the occurrence of cracks in a group III nitride semiconductor. Such phenomena currently cause deterioration in characteristics and reliability of devices.

The group III nitride semiconductor layer having such a lattice mismatch is aimed at reductions in defects and cracks, and a technique is disclosed which allows GaN to be epitaxially grown on a ScAlMgO<NUM> substrate (PTL <NUM>). ScAlMgO<NUM> has a small lattice mismatch of -<NUM>% to GaN, represented by {(lattice constant of GaN - lattice constant of ScAlMgO<NUM>)/lattice constant of GaN}. Accordingly, a group III nitride semiconductor epitaxially grown on a ScAlMgO<NUM> substrate is reduced in the occurrence of defects and/or the occurrence of cracks. Thus, such a semiconductor is expected to be developed to a high-quality and high-performance group III nitride semiconductor device. PTL <NUM> discloses a group III nitride semiconductor light-emitting device having a group III nitride semiconductor layer structure grown on a MgAl<NUM>O<NUM> substrate. The structure includes a light-emitting layer of a quantum well structure containing an indium-containing nitride semiconductor. A first nitride semiconductor layer having a band gap energy larger than that of the active layer is provided in contact with the active layer. A second nitride semiconductor layer having a band gap energy smaller than that of the first layer is provided over the first layer. Further, a third nitride semiconductor layer having a band gap energy larger than that of the second layer is provided over the second layer. PTL <NUM> discloses a group III nitride semiconductor comprising: a RAMO substrate including a single crystal material expressed by the general formula, RAMO (where "R" represents one or more trivalent elements selected from a group consisting of Sc, In, Y and lanthanoids, "A" represents one or more trivalent elements selected from a group consisting of Fe(III), Ga and Al, and "M" represents one or more divalent elements selected from a group consisting of Mg, Mn, Fe(II), Co, Cu, Zn and Cd); a group III nitride crystal grown on the RAMO substrate; and a different material film located between the RAMO substrate and the group III nitride crystal, including a material different from the material of the RAMO substrate and the group III nitride crystal, and having a plurality of openings.

However, epitaxial growth of a group III nitride semiconductor layer on a substrate made of a single crystal body represented by general formula RAMgO<NUM> (wherein R represents one or more trivalent elements selected from the group consisting of Sc, In, Y, and lanthanoids, and A represents one or more trivalent elements selected from the group consisting of Fe (III), Ga, and Al), typified by a ScAlMgO<NUM> substrate, causes Mg as a constituent element of the ScAlMgO<NUM> substrate to be incorporated into the group III nitride semiconductor layer.

Moreover, the ScAlMgO<NUM> substrate has a lattice constant close to the lattice constant of GaN, but has a lower lattice constant than the lattice constant of GaN. Thus, if the difference in lattice constant between the substrate and a group III nitride crystal to be epitaxially grown thereon is reduced, a higher-quality group III nitride semiconductor crystal layer can be obtained.

The present disclosure has been made in order to solve the above problems, and an object thereof is to provide a high-quality group III nitride semiconductor layer structure. Solution to Problem.

The present invention provides a group III semiconductor light-emitting device according to claim <NUM>.

In the present invention, a proper degree of diffusion of Mg in a GaN layer slightly increases the lattice constant of GaN, and thus allows the lattice constant of the GaN layer to be close to the lattice constant of the light-emitting layer. Thus, the functional layer can be hardly distorted, thereby allowing a group III nitride semiconductor light-emitting device having high characteristics to be provided. On the other hand, an InGaN layer can suppress Mg from being diffused into the functional layer, resulting in an enhancement in crystal quality of the functional layer. Accordingly, a high-quality group III nitride semiconductor light-emitting device can be provided.

Hereinafter, Embodiments of the present invention will be described with reference to the drawings.

The substrate for use in the present Embodiment is a RAMgO<NUM> substrate made of a single crystal body represented by RAMgO<NUM> (wherein R represents one or more trivalent elements selected from the group consisting of Sc, In, Y, and lanthanoids, and A represents one or more trivalent elements selected from the group consisting of Fe (III), Ga, and Al). Hereinafter, an example will be described where the RAMgO<NUM> substrate is a ScAlMgO<NUM> substrate, but the substrate for use in the present Embodiment is not limited to the ScAlMgO<NUM> substrate.

A single crystal of ScAlMgO<NUM> constituting the ScAlMgO<NUM> substrate has a structure where a ScO<NUM> layer having a rock salt type structure and an AlMgO<NUM> layer having a hexagonal structure are alternately stacked, and can be cleaved in the (<NUM>) plane as in graphite and hexagonal BN. ScAlMgO<NUM> has a very low degree of lattice mismatch {(lattice constant of GaN - lattice constant of ScAlMgO<NUM>)/lattice constant of GaN} of -<NUM>% to GaN (GaN has a slightly low lattice constant as compared with ScAlMgO<NUM>), as compared with a sapphire substrate and the like. In addition, the difference in coefficients of thermal expansion between ScAlMgO<NUM> and GaN {(coefficient of thermal expansion of GaN - coefficient of thermal expansion of ScAlMgO<NUM>)/coefficient of thermal expansion of GaN} is about -<NUM>%. A low degree of lattice mismatch is effective for a decrease in crystal defects, and it is expected that the ScAlMgO<NUM> substrate is used to form a group III nitride semiconductor layer decreased in defects.

<FIG> (right drawing) illustrates one configuration example of light-emitting diode (LED) <NUM> including group III nitride semiconductor <NUM> according to the present Embodiment. Light-emitting diode <NUM> of the present Embodiment has a configuration where Si-doped n-GaN layer <NUM>, Si-doped n-InGaN layer <NUM>, Si-doped n-AlGaN layer <NUM>, InGaN light-emitting layer <NUM>, and p-AlGaN layer <NUM> are disposed on ScAlMgO<NUM> substrate <NUM>. <FIG> (left drawing) also illustrates the concentration profiles of impurities (Mg and Si) between Si-doped n-GaN layer <NUM> and InGaN light-emitting layer <NUM> in light-emitting diode <NUM>.

Light-emitting diode <NUM> (group III nitride semiconductor <NUM>) of the present Embodiment can be formed by epitaxial growth on a ScAlMgO<NUM> substrate with the MOCVD method (Metal Organic Chemical Vapor Deposition).

Hereinafter, one example of the method for forming light-emitting diode <NUM> of the present Embodiment is shown, but the present Embodiment is not limited thereto. A group III raw material for forming each layer is, for example, trimethyl gallium (TMG), trimethyl indium (TMI), or trimethyl aluminum (TMA), and a V group raw material that can be used for forming each layer is, for example, ammonia (NH<NUM>) gas. A carrier gas that can be used is, for example, hydrogen or nitrogen.

First, before each layer is formed on ScAlMgO<NUM> substrate <NUM>, ScAlMgO<NUM> substrate <NUM> is preferably introduced into a furnace and subjected to thermal cleaning in a hydrogen atmosphere at <NUM>,<NUM> for <NUM> minutes. Such thermal cleaning can remove any carbon-based contamination attached onto the surface of ScAlMgO<NUM> substrate <NUM>.

Thereafter, the surface temperature of ScAlMgO<NUM> substrate <NUM> is dropped to <NUM>, TMG, ammonia, and the like are fed into the furnace, and a buffer layer (not illustrated) is formed on ScAlMgO<NUM> substrate <NUM> at a low temperature. The thickness and the composition of the buffer layer can be adjusted depending on the growth time and the group III raw material to be fed. The buffer layer here formed is a layer made of GaN, having a thickness of <NUM>.

After formation of the buffer layer, the temperature of ScAlMgO<NUM> substrate <NUM> is raised to <NUM>,<NUM>, resulting in formation of Si-doped n-GaN layer <NUM> (thickness: <NUM>). During formation of Si-doped n-GaN layer <NUM>, not only TMG and ammonia, but also monosilane gas (SiH<NUM>) as a raw material gas for doping with Si is fed with the molar ratio thereof being adjusted. The concentration of Si in n-GaN layer <NUM> obtained here is about <NUM> × <NUM><NUM> cm-<NUM>. The "concentration" in the present disclosure means the concentration of any atom, unless particularly noted. The speed of growth is about <NUM>/h. Herein, an n-AlGaN layer may also be prepared by feeding of TMA in growth of n-GaN layer <NUM>. That is, n-GaN layer <NUM> is composed of AlxGa<NUM>-xN (<NUM> ≤ x < <NUM>).

Next, feeding of TMG and SiH<NUM> is stopped, and the substrate temperature is dropped from <NUM>,<NUM> to <NUM> in a mixed atmosphere of ammonia, hydrogen and nitrogen. Feeding of a hydrogen carrier gas is then stopped, and thereafter additional feeding of TMG, TMI and SiH<NUM> is made to form n-InGaN layer <NUM> (thickness: <NUM>). The amount of In can be controlled by adjustment of the molar ratio of TMG and TMI to be fed. While n-InGaN layer <NUM> is a layer doped with Si in the present Embodiment, the layer may also be doped with no Si. In the case of doping with Si, the concentration of Si in n-InGaN layer <NUM> can be about <NUM> × <NUM><NUM> cm-<NUM> as in n-GaN layer <NUM>. The composition of In in n-InGaN layer <NUM> is preferably adjusted to <NUM> atom% to <NUM> atom%, more preferably adjusted to about <NUM> atom%. A concentration of In of more than <NUM> atom% may cause the lattice mismatch between GaN and InGaN to be too high, resulting in deterioration in crystallinity, and a concentration of less than <NUM> atom% may cause no effect of suppressing diffusion of Mg to be obtained.

Next, the substrate temperature is raised to <NUM>, <NUM> while growing a GaN layer (not illustrated) with feeding of only TMI being stopped. Such an operation is to prevent In in n-InGaN layer <NUM> from being evaporated in temperature rise. After the substrate temperature reaches <NUM>, <NUM>, a hydrogen carrier gas and TMA are further fed to form n-AlGaN layer <NUM> (thickness: <NUM>). The concentration of Si in n-AlGaN layer <NUM> can be about <NUM> × <NUM><NUM> cm-<NUM> as in n-GaN layer <NUM>. Herein, n-AlGaN layer <NUM> may not contain Al depending on the design of LED. That is, n-AlGaN layer <NUM> is composed of AlyGa<NUM>-yN (<NUM> ≤ y < <NUM>) including an n-type dopant (which is here Si).

Next, feeding of TMG, TMA, and SiH<NUM> is stopped, and the substrate temperature is dropped from <NUM>,<NUM> to <NUM> in a mixed atmosphere of ammonia, hydrogen and nitrogen. Feeding of a hydrogen carrier gas is then stopped, and additional feeding of TMG and TMI is made to form InGaN light-emitting layer <NUM> (thickness: <NUM>). When the composition of In in InGaN light-emitting layer <NUM> is about <NUM> atom%, blue light at about <NUM> is emitted in LED operation. InGaN light-emitting layer <NUM> may be a single InGaN layer, or may be a multiple quantum well where an InGaN layer and a GaN layer are periodically stacked repeatedly. While InGaN light-emitting layer <NUM> is not doped, the layer may also be doped with Si, provided that the concentration of Si is about <NUM> × <NUM><NUM> cm-<NUM> or less.

Next, the substrate temperature is raised to <NUM>,<NUM> while growing a GaN layer (not illustrated) with feeding of only TMI being stopped. After the substrate temperature reaches <NUM>,<NUM>, a hydrogen carrier gas, TMA and cyclopentadienyl magnesium (Cp<NUM>Mg) are added to form Mg-doped p-AlGaN layer <NUM> (thickness: about <NUM>). The concentration of Mg can be about <NUM> × <NUM><NUM> cm-<NUM>.

Herein, an n-electrode (not illustrated) is formed on a part of any of Si-doped n-GaN layer <NUM>, n-InGaN layer <NUM>, and n-AlGaN layer <NUM> in production of a device such as an LED, and such an n-electrode is preferably formed in a region (first region described below) where the concentration of Si is higher than the concentration of Mg in the case of formation of such an electrode on a part of n-GaN layer <NUM>.

The left drawing (graph) of <FIG> illustrates the concentration profiles of impurities (the concentration of Mg and the concentration of Si) in light-emitting diode <NUM> (LED) actually produced, the diode including group III nitride semiconductor <NUM> of the present Embodiment. The concentration of Mg was analyzed by a SIMS method (Secondary ION Mass Spectrometry). The concentration of Mg in n-GaN layer <NUM> located closest to ScAlMgO<NUM> substrate <NUM> had a highest value in a region in contact with ScAlMgO<NUM> substrate <NUM>, and is about <NUM> × <NUM><NUM> cm-<NUM> to <NUM> × <NUM><NUM> cm-<NUM>.

A comparative light-emitting diode having the same structure except that no n-InGaN layer <NUM> is included was also produced, and was subjected to profiling of the concentrations of impurities. The concentration of Mg in the light-emitting diode is monotonically decreased as the measurement position is farther from the ScAlMgO<NUM> substrate towards the surface of the diode, as illustrated in a dotted line in the left drawing (graph) of <FIG>. The reason is because a Mg atom constituting ScAlMgO<NUM> substrate <NUM> is diffused in the group III nitride semiconductor formed thereon. As illustrated in <FIG>, a Mg atom is diffused into InGaN light-emitting layer <NUM> in the comparative light-emitting diode including no n-InGaN layer <NUM>. Such a Mg atom diffused forms point defects such as an interstitial atom in InGaN light-emitting layer <NUM>, and thus serves as a non-light-emission center to thereby reduce the luminous efficiency of an LED. The reduced luminous efficiency causes a carrier subjected to electricity injection in device operation to be converted to heat, resulting in degradation of such a light-emitting layer itself and/or an electrode and thus deterioration in reliability.

On the contrary, the light-emitting diode of the present Embodiment, including n-InGaN layer <NUM>, allows diffusion of a Mg atom from ScAlMgO<NUM> substrate <NUM> to be suppressed in n-InGaN layer <NUM> as illustrated by a solid line in the left drawing (graph) of <FIG>, resulting in a significant decrease in the concentration of Mg in n-AlGaN layer <NUM> as compared with the concentration of Mg in n-GaN layer <NUM>. Thus, the concentration of Mg in InGaN light-emitting layer <NUM> is decreased to about <NUM> to <NUM> × <NUM><NUM> cm-<NUM> or less which corresponds to the detection limit of the SIMS method. In other words, n-InGaN layer <NUM> suppresses diffusion of Mg, thereby allowing the concentration of Mg in n-GaN layer <NUM> to be higher than the concentration of Mg in n-AlGaN layer <NUM>, in the present Embodiment.

Here, n-AlGaN layer <NUM> has the function of efficient injection of an electronic carrier into InGaN light-emitting layer <NUM>. A large amount of Mg present in n-AlGaN layer <NUM> naturally results in a large amount of Mg diffused to InGaN light-emitting layer <NUM>. On the contrary, diffusion of Mg is suppressed by the ability to prevent diffusion of n-InGaN layer <NUM>, thereby resulting in a low concentration of Mg in n-AlGaN layer <NUM>, and a higher concentration of the n-type dopant in n-AlGaN layer <NUM> than the concentration of Mg in n-AlGaN layer <NUM>.

In the present Embodiment, all the concentrations of Si in Si-doped n-GaN layer <NUM>, n-InGaN layer <NUM>, and n-AlGaN layer <NUM> are about <NUM> × <NUM><NUM> cm-<NUM>. In addition, the concentration of Si diffused in a stacked structure is higher than the concentration of Mg diffused therein except for a region of n-GaN layer <NUM>, in contact with ScAlMgO<NUM> substrate <NUM>. In the following description, a region of n-GaN layer <NUM>, being located closer to ScAlMgO<NUM> substrate <NUM> and having the concentration of Si lower than the concentration of Mg is also referred to as "second region", and a region of n-GaN layer <NUM>, being located closer to n-InGaN layer <NUM> and having the concentration of Si higher than the concentration of Mg is also referred to as "first region".

While the region in n-GaN layer <NUM>, in contact with ScAlMgO<NUM> substrate <NUM>, namely, a region (second region) having the concentration of Mg higher than the concentration of Si, has a thickness of about <NUM> in the present Embodiment, as described below, such a thickness cannot be increased.

As described above, the rate of decrease in the concentration of Mg in the thickness direction in n-InGaN layer <NUM> is higher than the rate of decrease in concentration of Mg in the thickness direction in n-GaN layer <NUM>. Thus, in the case where n-InGaN layer <NUM> is disposed, Mg is inhibited from being diffused towards n-InGaN layer <NUM> and thus easily collected in a region closer to ScAlMgO<NUM> substrate <NUM> rather than n-InGaN layer <NUM>. On the other hand, in the case where n-InGaN layer <NUM> is not disposed, Mg is easily diffused towards InGaN light-emitting layer <NUM>, resulting in a decrease in the concentration of Mg in a region of n-GaN layer <NUM>, in contact with ScAlMgO<NUM> substrate <NUM>, and a decrease in the thickness of the second region.

The concentration profile of Mg is described in more detail with reference to <FIG> illustrates comparison of the concentration profile of Mg according to the SIMS method, between a case where n-InGaN layer <NUM> is included as a diffusion prevention layer as in the present Embodiment (solid line) and a case where no n-InGaN layer <NUM> is included (dashed line). The comparison was performed between a stacked product (stacked product of the present Embodiment) produced by stacking ScAlMgO<NUM> substrate <NUM>/n-GaN layer <NUM>/n-InGaN layer <NUM>/n-AlGaN layer <NUM> in the order presented, and a stacked product (Reference Example) produced by stacking ScAlMgO<NUM> substrate <NUM>/n-GaN layer <NUM>/n-AlGaN layer <NUM> in the order presented.

The concentration of Mg in Reference Example is monotonically decreased as the measurement position is farther from ScAlMgO<NUM> substrate <NUM> towards n-AlGaN layer <NUM>, as illustrated by a dashed line in <FIG>. The concentration of Mg is decreased to the same level (about <NUM> × <NUM><NUM> cm-<NUM>) as that of Si for doping, at a position of about <NUM> away from the interface between ScAlMgO<NUM> substrate <NUM> and n-GaN layer <NUM>. On the other hand, the concentration of Mg in a structure including n-InGaN layer <NUM>, of the present Embodiment, is decreased as the measurement position is farther from ScAlMgO<NUM> substrate <NUM> towards n-AlGaN layer <NUM>, but is significantly changed in n-InGaN layer <NUM>, as illustrated by a solid line in <FIG>. The concentration of Mg at the interface between n-InGaN layer <NUM> and n-AlGaN layer <NUM> is about <NUM> × <NUM><NUM> cm-<NUM>, and decreases by one order of magnitude as compared with the concentration of Mg at the interface between n-GaN layer <NUM> and n-InGaN layer <NUM>. While the effect of suppressing diffusion of Mg by n-InGaN layer <NUM> is not sufficiently figured out, it is presumed that replacement with an In atom having a larger atomic radius than that of Ga allows diffusion of Mg via an interstitial position or a Ga atom position to be suppressed.

<FIG> illustrates the results of measurement of the depth profile of the concentration of Mg with respect to diffusion of a Mg atom into a group III nitride semiconductor, by the SIMS method. Evaluation was made for four stacked products prepared by stacking only n-GaN layer <NUM> as a single layer (about <NUM>) on ScAlMgO<NUM> substrate <NUM> with a low-temperature GaN buffer layer being interposed therebetween. No InGaN layer is formed. As illustrated in <FIG>, the concentration of Mg is likely slightly increased in part in a region of n-GaN layer <NUM>, near ScAlMgO<NUM> substrate <NUM>, but is decreased as the measurement position is farther from ScAlMgO<NUM> substrate <NUM>, and is decreased to the same concentration (<NUM> to <NUM> × <NUM><NUM> cm-<NUM>) as the concentration of Si as an n-type dopant in the present Embodiment, around a region away from the interface between ScAlMgO<NUM> substrate <NUM> and n-GaN layer <NUM> by a thickness of <NUM>. In general, it is known that a Mg atom in GaN has electric characteristics of acceptor impurities, and the acceptor level is deep and the electrical activation efficiency is about <NUM>%. Accordingly, it is preferable for no decrease in the concentration of an n-type carrier based on Si due to compensation of Mg that the concentration of Mg be about <NUM>/<NUM> of the concentration of Si. In the case where the concentration of Mg is <NUM>/<NUM> of the concentration of Si, the amount of Mg electrically activated is <NUM>/<NUM> (<NUM>%).

Thus, formation of n-InGaN layer <NUM> on n-GaN layer <NUM> having a thickness of <NUM> (corresponding to a thickness allowing the concentration of Si and the concentration of Mg to be the same or less) enables the amount of Mg electrically activated to be decreased to about <NUM>%, as described above.

As described above, the lattice constant of GaN is extremely close to, but is slightly lower than that of the ScAlMgO<NUM> substrate (rate of lattice mismatch: -<NUM>%). In the case of formation of n-GaN layer <NUM> on ScAlMgO<NUM> substrate <NUM> as in the present Embodiment, diffusion of <NUM> × <NUM><NUM> cm-<NUM> or more of Mg into n-GaN layer <NUM> results in a slight increase in the lattice constant, thereby allowing the lattice constant of ScAlMgO<NUM> substrate <NUM> to be closer to that of n-GaN layer <NUM>, resulting in suppression of the occurrence of defects at the same interface. In the present Embodiment, n-InGaN layer <NUM> is included, and thus diffusion of Mg is limited in the layer as illustrated in <FIG>. Accordingly, the concentration of Mg in n-GaN layer <NUM> is likely to be higher than that in Reference Example including no n-InGaN layer <NUM>, resulting in a further improvement in lattice matching. As described above, the thickness in a region where the concentration of Mg in n-GaN layer <NUM> is <NUM> × <NUM><NUM> cm-<NUM> or more is likely to be increased is <NUM> to <NUM> (a typical value is about <NUM>), in the light-emitting device according to the present invention. The thickness is significantly thicker than the thickness (about <NUM>) in n-GaN layer <NUM> in Reference Example. In order to provide a sufficiently high lattice constant in the second region of n-GaN layer <NUM>, the thickness in a region where the concentration of Mg in n-GaN layer <NUM> is <NUM> × <NUM><NUM> cm-<NUM> or more is preferably <NUM> or more, more preferably <NUM> or more.

A further increase in the lattice constant of n-GaN layer <NUM> or the like due to diffusion of Mg easily allows the lattice constant of InGaN light-emitting layer <NUM> and the lattice constant of n-AlGaN layer <NUM> or the like, which are higher than the lattice constant of GaN, to be close to each other. In other words, any distortion remaining in InGaN light-emitting layer <NUM> is decreased to improve light-emitting characteristics, according to the present Embodiment.

A concentration of Mg of more than <NUM> × <NUM><NUM> cm-<NUM> in the second region of n-GaN layer <NUM> is not preferable because the crystal quality of GaN is deteriorated. Accordingly, the concentration of Mg in the second region of n-GaN layer <NUM> is desirably <NUM> × <NUM><NUM> cm-<NUM> or more and <NUM> × <NUM><NUM> cm-<NUM> or less.

Thus, in the present Embodiment, n-InGaN layer <NUM> can be used as a diffusion prevention layer of Mg, resulting in suppression of defects at the interface between the ScAlMgO<NUM> substrate and n-GaN layer <NUM> and suppression of diffusion of a Mg atom serving as a non-light-emission center into InGaN light-emitting layer <NUM> at the same time. In particular, n-InGaN layer <NUM> can be disposed at a position of <NUM> or more away from the interface between ScAlMgO<NUM> substrate <NUM> and n-GaN layer <NUM>, thereby providing an LED structure where the concentration of an n-type carrier is kept.

<FIG> illustrates the concentration profiles of impurities in a light-emitting diode including n-GaN layer <NUM>, n-InGaN layer <NUM>, InGaN light-emitting layer <NUM>, and p-AlGaN layer <NUM> stacked. In the light-emitting diode, n-InGaN layer <NUM> is used as a diffusion prevention layer of Mg. <FIG> illustrates the concentrations of impurities (Mg and Si) (solid lines) around InGaN light-emitting layer <NUM> of an LED produced on a ScAlMgO<NUM> substrate (not illustrated), and also illustrates the depth profile (in proportion to the concentration of In: dashed line) of the secondary ion intensity of an In atom. As illustrated in <FIG>, it has been confirmed that a Mg atom (to a concentration of <NUM> to <NUM> × <NUM><NUM> cm-<NUM>) diffused from the ScAlMgO<NUM> substrate (not illustrated) into n-GaN layer <NUM> is suppressed in diffusion in n-InGaN layer <NUM> and the concentration of Mg in InGaN light-emitting layer <NUM> is decreased to the order of <NUM><NUM>. On the other hand, p-AlGaN layer <NUM> located closer to the surface of the LED is doped with Mg, and thus has a concentration of Mg of about <NUM> to <NUM> × <NUM><NUM> cm-<NUM>. The concentration of Si in n-GaN layer <NUM> is about <NUM> × <NUM><NUM> cm-<NUM>, and is higher than the concentration of Mg (<NUM> to <NUM> × <NUM><NUM> cm-<NUM>) diffused from the ScAlMgO<NUM> substrate. While <FIG> does not illustrate any AlGaN layer disposed between InGaN light-emitting layer <NUM> and n-InGaN layer <NUM> for convenience, the same effect is obtained even in the case of formation of any AlGaN layer therebetween. <FIG> illustrates an enlarged view of the vicinity of InGaN light-emitting layer <NUM> in a semiconductor apparatus, and does not illustrate the ScAlMgO<NUM> substrate and the second region (a region located closer to the ScAlMgO<NUM> substrate, where the concentration of an n-type dopant is lower than the concentration of Mg) in n-GaN layer <NUM>. Herein, while the concentration of Si and the concentration of Mg are apparently substantially the same in InGaN light-emitting layer <NUM>, both the concentrations are traces equal to or less the measurement limit, and thus it can also be interrupted that neither Mg nor Si is contained in InGaN light-emitting layer <NUM>.

Although suppression of diffusion of Mg from the ScAlMgO<NUM> substrate has been disclosed in the present Embodiment, the effect of the present Embodiment is not limited to such suppression, and any effect is exerted also in the case of no use of any ScAlMgO<NUM> substrate and the case of intentional or unintentional doping with Mg.

A too thick n-InGaN layer <NUM> can cause absorption of light from a light-emitting layer in LED device operation to be lost. Accordingly, the thickness of n-InGaN layer <NUM> is less than the thickness of n-GaN layer <NUM> or n-AlGaN layer <NUM>. On the other hand, not a too thin n-InGaN layer <NUM> is preferable from the viewpoint that n-GaN layer <NUM> includes a relatively large amount of Mg and the thickness in a region (second region) having a high lattice constant is increased (increased to <NUM> or more). Specifically, the thickness is preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>.

Light-emitting diode <NUM> (group III nitride semiconductor <NUM>) of the present Embodiment has a configuration where Si-doped n-GaN layer <NUM>, Si-doped n-InGaN layer <NUM>, Si-doped n-AlGaN layer <NUM>, InGaN light-emitting layer <NUM>, and p-AlGaN layer <NUM> are disposed on ScAlMgO<NUM> substrate <NUM>, as illustrated in <FIG> also illustrates the concentration profiles of impurities (Mg and Si) between Si-doped n-GaN layer <NUM> and InGaN light-emitting layer <NUM> in light-emitting diode <NUM> (left drawing). Si-doped n-GaN layer <NUM>, Si-doped n-InGaN layer <NUM>, Si-doped n-AlGaN layer <NUM>, InGaN light-emitting layer <NUM>, and p-AlGaN layer <NUM> are the same as in Embodiment <NUM>, and thus the detail description thereof is omitted.

In the present Embodiment, protrusions and recesses are formed in a stripe pattern on the ScAlMgO<NUM> substrate. First, a dielectric mask layer such as SiO<NUM> is deposited on the ScAlMgO<NUM> substrate, and the upper surface of the mask layer is coated with a resist film. Thereafter, the resist film coated is patterned in a stripe pattern according to a photolithography method. Thus, a resist pattern is formed. Next, a part of the mask layer is removed by etching, thereby resulting in not only formation of a stripe-shaped protrusion portion, but also formation of a plurality of openings. For example, dry etching is performed to thereby form a plurality of periodic structures on the mask layer, the structures each having an opening portion having a cross-sectional width of about <NUM> and a protrusion portion having a cross-sectional width of about <NUM> as one cycle.

Next, the mask is removed to allow n-GaN layer <NUM> to be formed on ScAlMgO<NUM> substrate <NUM> having protrusions and recesses with a low-temperature GaN buffer layer (not illustrated) being interposed therebetween. A GaN crystal is grown upward and laterally from each protrusion portion of ScAlMgO<NUM> substrate <NUM> having protrusions and recesses. The GaN crystal formed on each protrusion portion is bound and thus formed into flat n-GaN layer <NUM>. As a result, void portion <NUM> is formed between n-GaN layer <NUM> and ScAlMgO<NUM> substrate <NUM> having protrusions and recesses. GaN on void portion <NUM> corresponds to a crystal laterally grown, and is formed not in contact with the ScAlMgO<NUM> substrate as a different substrate and thus is a high-quality crystal extremely less in dislocation. Thereafter, Si-doped n-InGaN layer <NUM>, Si-doped n-AlGaN layer <NUM>, InGaN light-emitting layer <NUM>, and p-AlGaN layer <NUM> are stacked, thereby providing light-emitting diode <NUM> of the present Embodiment. Herein, the method for forming the layers to be formed after n-InGaN layer <NUM> and the configurations of such layers are the same as in Embodiment <NUM>.

The ScAlMgO<NUM> substrate having protrusions and recesses is used, resulting in not only the effect of reducing dislocation, but also the effect of increasing the extraction efficiency due to light outwardly radiated by light scattering with such protrusions and recesses in LED device operation.

Formation of protrusions and recesses on the ScAlMgO<NUM> substrate is not limited to a stripe manner, and the same effects are exerted even in the case of formation of protrusions and recesses in an island-shaped manner, and the periodicity is also not necessarily required.

Although the above Embodiments have disclosed growth of GaN in the +c plane direction by use of the ScAlMgO<NUM> substrate having the (<NUM>) plane, the same effects are also obtained with respect to growth in the -c plane direction (N plane) with growth conditions of GaN being appropriately adjusted. The same effects are also obtained in the case of use of an off substrate where the c-axis is inclined by about <NUM> to <NUM> degrees in any direction.

Furthermore, while the case where the substrate is ScAlMgO<NUM> is described above as an example, the same effects are obtained as long as any substrate represented by general formula RAMgO<NUM> is adopted. Such a substrate represented by RAMgO<NUM> is constituted by a substantially single crystal material represented by general formula RAMgO<NUM>. In the general formula, R represents one or more trivalent elements selected from the group consisting of Sc, In, Y, and lanthanoids (atomic number: <NUM> to <NUM>), and A represents one or more trivalent elements selected from the group consisting of Fe (III), Ga, and Al. The "substantially single crystal material" refers to a crystalline solid containing <NUM> atom% or more of RAMgO<NUM> constituting a plane epitaxially grown and being the same in the orientation even in any portion of the plane epitaxially grown with respect to any crystal axis. It is noted that not only any solid having a crystal axis locally changed in the orientation, but also any solid locally including lattice defects is treated as such a single crystal. Herein, O represents oxygen and Mg represents magnesium. As described above, R preferably represents Sc and A preferably represents Al.

A main group III elemental metal constituting group III nitride is most preferably gallium (Ga), and such a main group III elemental metal may be, for example, aluminum (Al), indium (In), or thallium (Tl). Such metals may be used singly or in combinations of two or more kinds thereof. For example, the n-InGaN layer may further contain aluminum (Al). In such a case, the composition of the n-InGaN layer is represented by AlsGatIn{<NUM> - (s +t)}N (wherein <NUM> ≤ s < <NUM>, <NUM> ≤ t < <NUM>, and s + t < <NUM>).

The n-type dopant is not particularly limited, and examples include oxygen and Ge, in addition to Si. While the MOCVD method is used in the present Examples, the same effects can also be obtained with a HVPE method, an OVPE (Oxygen Vapor Phase Epitaxy) method, a sputtering method, a MBE method, or the like as the epitaxial growth method.

While an aspect where each layer to be formed between the ScAlMgO<NUM> substrate and the InGaN light-emitting layer is of n-type is described above as a preferable example, an aspect where the dopant in each layer is not activated can also be encompassed within the scope of the present disclosure. Specifically, GaN layer <NUM> illustrated in <FIG> or <FIG> may be composed of any type such as n-type, p-type or i-type. Furthermore, AlGaN layer <NUM> may also be composed of any type such as n-type, p-type or i-type.

That is, the present disclosure provides a group III nitride semiconductor including a GaN layer composed of AlxGa<NUM>-xN (<NUM> ≤ x < <NUM>), an InGaN layer disposed on the GaN layer and composed of InGaN, an AlGaN layer including a dopant, the layer being disposed on the InGaN layer and composed of AlyGa<NUM>-yN (<NUM> ≤ y < <NUM>), and a functional layer disposed on the AlGaN layer, wherein the concentration of Mg in the GaN layer is higher than the concentration of Mg in the AlGaN layer, and the concentration of the dopant in the AlGaN layer is higher than the concentration of Mg in the AlGaN layer.

In the case where the GaN layer includes a dopant, as described above, the GaN layer preferably has a first region that is located closer to the InGaN layer and has a higher concentration of the dopant than the concentration of Mg, and a second region that is located opposite to the first region and has a lower concentration of the dopant than the concentration of Mg. In such a case, the dopant may also be a p-type dopant.

As described above, the dopant included in AlGaN layer <NUM> is preferably an n-type dopant. Furthermore, the n-type dopant is preferably Si.

As one example of the functional layer, has been described above a light-emitting diode provided with InGaN light-emitting layer <NUM>. The functional layer, however, is not limited to such an InGaN light-emitting layer, and can be any functional layer or the like for various semiconductors. One example of such semiconductors includes a power device (Embodiment <NUM> described below) including a channel layer as such a functional layer.

A power device according to an example not forming part of the present invention includes a GaN layer composed of AlxGa<NUM>-xN (<NUM> ≤ x < <NUM>), an InGaN layer disposed on the GaN layer and composed of InGaN, an AlGaN layer disposed on the InGaN layer and composed of AlyGa<NUM>-yN (<NUM> ≤ y < <NUM>), and a channel layer as one example of a functional layer disposed on the AlGaN layer, wherein the concentration of Mg in the GaN layer is higher than the concentration of Mg in the AlGaN layer, and the concentration of the dopant in the AlGaN layer is higher than the concentration of Mg in the AlGaN layer.

<FIG> (right drawing) illustrates a power device according to an example not forming part of the present invention. First GaN buffer layer <NUM> as one example of a GaN layer is disposed on ScAlMgO<NUM> substrate <NUM>, and InGaN diffusion suppression layer <NUM> as one example of an InGaN layer is disposed thereon. Furthermore, second GaN buffer layer <NUM> and AlGaN back barrier layer <NUM> (the composition of Al is, for example, <NUM>%, and the thickness is, for example, <NUM>) are disposed thereon, and GaN channel layer <NUM> (the thickness is, for example, <NUM>) as one example of a functional layer is disposed thereon. Furthermore, AlGaN barrier layer <NUM> (the composition of Al is, for example, <NUM>%, and the thickness is, for example, <NUM>) is disposed thereon. Such a stacked structure is sequentially formed by the MOCVD method as in Embodiments <NUM> and <NUM>. Furthermore, respective electrodes required for transistor operation, including source electrode <NUM>, gate electrode <NUM> on p-type GaN layer <NUM>, and drain electrode <NUM>, are disposed on AlGaN barrier layer <NUM>.

GaN channel layer <NUM> is required to be a high-quality and high-resistivity layer having few impurities and defects, for the purpose of an enhancement in mobility of a two-dimensional electron gas. The reason is because the presence of impurities and defects in GaN channel layer <NUM> causes a two-dimensional electron gas to be thus scattered, thereby not allowing any desired functions to be performed. Such a presence of impurities and defects in GaN channel layer <NUM> also causes the problem of the occurrence of current collapse, for example, an increase in on-resistance due to capturing of any electron accelerated by the voltage stress in operation of the power device.

<FIG> (left drawing) illustrates the concentration of Mg between first GaN buffer layer <NUM> and AlGaN barrier layer <NUM> in the power device of the present Embodiment by a solid line. The concentration of Mg is measured by the same method as described above. As illustrated in the left drawing (graph) of <FIG>, diffusion of Mg from ScAlMgO<NUM> substrate <NUM> is suppressed in InGaN diffusion suppression layer <NUM>. Such suppression can be seen from a very lower concentration of Mg in second GaN buffer layer <NUM> than the concentration of Mg in first GaN buffer layer <NUM>. In other words, the power device of the present example can allow GaN channel layer <NUM> to be kept as a high-quality layer including no impurities and to maximally perform the function of a channel layer.

In the power device of the present example, the concentration of each dopant is higher than the concentration of Mg diffused in the stacked structure, except for a region of first GaN buffer layer <NUM>, in contact with ScAlMgO<NUM> substrate <NUM>. Also in the power device of the present example, a second region of first GaN buffer layer <NUM>, located closer to ScAlMgO<NUM> substrate <NUM>, having the concentration of the dopant lower than the concentration of Mg, and a first region of first GaN buffer layer <NUM>, located closer to InGaN diffusion suppression layer <NUM>, having the concentration of the dopant higher than the concentration of Mg are formed.

<FIG> (left drawing) here also illustrates the concentration profile of Mg in a power device having the same structure except for no formation of InGaN diffusion suppression layer <NUM> (Comparative Example), by a dashed line. In the Comparative Example, Mg is diffused into GaN channel layer <NUM>, resulting in degradations in characteristics, such as an increase in on-resistance.

Also in the power device of the present example, Mg can be diffused from ScAlMgO<NUM> substrate <NUM> into first GaN buffer layer <NUM> to result in an increase in lattice constant of GaN, as in the light-emitting diodes of Embodiment <NUM> and Embodiment <NUM>. Accordingly, a lattice mismatch slightly present between ScAlMgO<NUM> substrate <NUM> and a layer grown thereon (for example, GaN channel layer <NUM>) can be reduced to result in a reduction in such distortion.

Atypical thickness of first GaN buffer layer <NUM> on ScAlMgO<NUM> substrate <NUM> is here about <NUM>, and the defect density calculated from the dark spot density according to a cathode luminescence (CL) method is about <NUM> × <NUM><NUM> cm-<NUM>. On the other hand, the defect density in the case of use of a Si substrate conventionally frequently used as a substrate for power devices is <NUM><NUM> to <NUM><NUM> cm-<NUM>. In other words, the defect density is significantly lowered in the present Embodiment as compared with the case of use of a conventional Si substrate.

For example, the entire region or a partial region of AlGaN back barrier layer <NUM> is not necessarily doped with n-type impurities such as Si in order that the power device of the present example ensures a high withstanding pressure.

A main group III elemental metal constituting group III nitride is most preferably gallium (Ga), and such a main group III elemental metal may be, for example, aluminum (Al), indium (In), or thallium (Tl). Such metals may be used singly or in combinations of two or more kinds thereof. For example, in the case where indium is contained, the composition thereof is represented by AlsGatIn{<NUM> - (s + t)}N (wherein <NUM> ≤ s < <NUM>, <NUM> ≤ t < <NUM>, and s + t < <NUM>).

Claim 1:
A group III nitride semiconductor light-emitting device (<NUM>, <NUM>), comprising:
a substrate (<NUM>, <NUM>);
a GaN layer (<NUM>) disposed on the substrate and composed of AlxGa<NUM>-xN (<NUM> ≤ x < <NUM>)
an InGaN layer (<NUM>) disposed on the GaN layer and composed of InGaN;
an AIGaN layer (<NUM>) disposed on the InGaN layer and composed of AlyGa<NUM>-yN (<NUM> ≤ y < <NUM>) comprising a dopant; and
a functional layer (<NUM>) being a light-emitting layer and disposed on the AIGaN layer;
wherein
the substrate is a RAMgOa substrate made of a single crystal body represented by general formula RAMgO<NUM>, wherein R represents one or more trivalent elements selected from the group consisting of Sc, In, Y, and lanthanoids, and A represents one or more trivalent elements selected from the group consisting of Fe (III), Ga, and Al;
wherein
a concentration of Mg in the GaN layer is higher than a concentration of Mg in the AIGaN layer,
wherein
a concentration of the dopant in the AIGaN layer is higher than the concentration of Mg in the AIGaN layer,
wherein
the GaN layer comprises a dopant, and includes
a first region that is located closer to the InGaN layer and has a higher concentration of the dopant than the concentration of Mg, and
a second region that is located opposite to the first region and has a lower concentration of the dopant than the concentration of Mg, and
wherein the second region of the GaN layer has a thickness of <NUM> or more and <NUM> or less.