JP4519693B2 - Nitride semiconductor - Google Patents

Nitride semiconductor Download PDF

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JP4519693B2
JP4519693B2 JP2005093162A JP2005093162A JP4519693B2 JP 4519693 B2 JP4519693 B2 JP 4519693B2 JP 2005093162 A JP2005093162 A JP 2005093162A JP 2005093162 A JP2005093162 A JP 2005093162A JP 4519693 B2 JP4519693 B2 JP 4519693B2
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nitride semiconductor
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哲也 赤坂
康之 小林
俊樹 牧本
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Nippon Telegraph and Telephone Corp
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本発明は、窒化物半導体に関し、より詳細には、可視光から紫外領域で発光する発光デバイスや、高電力・高周波数・高温動作の電子デバイスに適用することができ、ＩＩＩ族元素として少なくともホウ素（Ｂ）を含有する窒化物半導体に関する。   The present invention relates to a nitride semiconductor, and more specifically, can be applied to a light-emitting device that emits light in the visible to ultraviolet region, and an electronic device that operates at high power, high frequency, and high temperature, and includes at least boron as a group III element. The present invention relates to a nitride semiconductor containing (B).

窒化物半導体とは、ホウ素（Ｂ）、アルミニウム（Ａｌ）、ガリウム（Ｇａ）、あるいは、インジウム（Ｉｎ）等のＩＩＩ族元素のうち少なくとも１つ以上の元素と、Ｖ族元素である窒素との化合物である。一般式は、ＡｌａＢｂＧａｃＩｎｄＮ（０≦ａ≦１，０≦ｂ≦１，０≦ｃ≦１，０≦ｄ≦１，ａ＋ｂ＋ｃ＋ｄ＝１）で表され、以下、組成の範囲の表示は省略する。 A nitride semiconductor is a combination of at least one element among group III elements such as boron (B), aluminum (Al), gallium (Ga), or indium (In) and nitrogen that is a group V element. A compound. General formula is represented by Al a B b Ga c In d N (0 ≦ a ≦ 1,0 ≦ b ≦ 1,0 ≦ c ≦ 1,0 ≦ d ≦ 1, a + b + c + d = 1), or less, of the composition The range display is omitted.

Ｂを含まない窒化物半導体、すなわち、ＡｌａＧａｃＩｎｄＮは、電界効果トランジスタ等の電子デバイス、または、可視光領域から近紫外領域の短波長帯の発光材料として、近年盛んに研究および技術開発が行われている。窒化物半導体薄膜を用いた発光ダイオードは、橙色から紫外領域の発光が得られる（例えば、非特許文献１参照）。窒化物半導体を用いたレーザダイオードは、４５０ｎｍから３７０ｎｍ前後の発振波長で、室温連続発振を達成している（例えば、非特許文献２参照）。短波長の紫外領域で発光する発光ダイオードやレーザダイオードを実現するためには、Ｂを含有するバンドギャップのより大きな窒化物半導体を用いる必要がある。 B-containing nitride semiconductors, that is, Al a Ga c In d N, have been actively researched and developed in recent years as electronic devices such as field effect transistors, or as light emitting materials in the short wavelength band from the visible light region to the near ultraviolet region. Technology development is underway. A light emitting diode using a nitride semiconductor thin film can emit light in an orange to ultraviolet region (see, for example, Non-Patent Document 1). A laser diode using a nitride semiconductor achieves room temperature continuous oscillation at an oscillation wavelength of about 450 nm to about 370 nm (see, for example, Non-Patent Document 2). In order to realize a light emitting diode or a laser diode that emits light in a short wavelength ultraviolet region, it is necessary to use a nitride semiconductor containing B and having a larger band gap.

中村修二、「ＧａＮ系発光素子の現状と将来」、応用物理、第６５巻、第７号、第６７６〜６８６頁、１９９６年Shuji Nakamura, “Current Status and Future of GaN-based Light Emitting Elements”, Applied Physics, Vol. 65, No. 7, pp. 676-686, 1996 I.Akasaki, H.Amano, ”Crystal Growth and Conductivity Control of Group III Nitride Semiconductors and Their Application to Short Wavelength light Emitters”, Jpn. J. Appl. Phys. vol.36 pp.5393-5408 (1997)I. Akasaki, H. Amano, “Crystal Growth and Conductivity Control of Group III Nitride Semiconductors and Their Application to Short Wavelength light Emitters”, Jpn. J. Appl. Phys. Vol. 36 pp. 5393-5408 (1997)

しかしながら、以下に述べる理由により、Ｂを含有する窒化物半導体は、良好な結晶性を示す高品質な結晶を得ることが難しく、発光材料や電子デバイスへの応用は実現していない。   However, for the reasons described below, it is difficult for a nitride semiconductor containing B to obtain high-quality crystals exhibiting good crystallinity, and application to light-emitting materials and electronic devices has not been realized.

第１に、Ｂを含まない窒化物半導体ＡｌａＧａｃＩｎｄＮとＢＮとは、格子定数が著しく異なるので、ＡｌａＢｂＧａｃＩｎｄＮにおけるＢ組成ｂを増やしていくと、大きなミッシビリティギャップにより相分離が起こり、結晶中のＢ組成に不均一が生じてしまう。 First, a not a nitride semiconductor Al a Ga c In d N and BN which contains B, since the lattice constants are different significantly, when gradually increasing the Al a B b Ga c In d N B composition in b, large Phase separation occurs due to the miscibility gap, resulting in non-uniformity in the B composition in the crystal.

第２に、化学的気相成長法（Chemical Vapor Deposition:ＣＶＤ）や物理的気相成長法における典型的な成長条件である摂氏千数百度以下および常圧以下の環境において、ＡｌａＧａｃＩｎｄＮの安定な結晶構造は、ウルツ鉱型六方晶である。これに対して、ＢＮはグラファイト型六方晶であり、お互いに異なる結晶構造を有する。このように異なる結晶構造を有するために、ＡｌａＢｂＧａｃＩｎｄＮの結晶性を損なう原因となっている。 Second, a chemical vapor deposition: in (Chemical Vapor Deposition CVD) and physical vapor typical Celsius thousand several hundred degrees under the following and normal pressure the growth conditions in the growth process environment, Al a Ga c In stable crystal structure of the d N is the wurtzite hexagonal. On the other hand, BN is a graphite-type hexagonal crystal and has different crystal structures. Such a different crystal structure causes the crystallinity of Al a B b Ga c In d N to be impaired.

図１に、従来のＢを含む窒化物半導体薄膜の表面の光学顕微鏡写真を示す。この試料は、（０００１）面を主方位とする窒化珪素基板上に、ＭＯＣＶＤ装置を用いて、厚さが５００ｎｍのＡｌ0.94Ｂ0.06Ｎ薄膜が形成されている。Ｂ組成が０．０６と比較的小さいにもかかわらず、表面が砂粒状に荒れているのが分かる。 FIG. 1 shows an optical micrograph of the surface of a conventional nitride semiconductor thin film containing B. In this sample, an Al 0.94 B 0.06 N thin film having a thickness of 500 nm is formed on a silicon nitride substrate having a (0001) plane as a main orientation by using an MOCVD apparatus. Although the B composition is 0.06, which is relatively small, it can be seen that the surface is roughened into sand particles.

図２に、従来のＢを含む窒化物半導体のＸ線回折チャートを示す。Ｘ線回折チャートには、相分離によりウルツ鉱型のＡｌＢＮ（０００２）の回折ピークが２つ見られる。このように品質の低い窒化物半導体薄膜を、発光材料や電子デバイスに用いることはできなかった。特に、Ｂ組成ｂが大きくなるにつれて、結晶性が著しく劣化するという問題もあった。   FIG. 2 shows an X-ray diffraction chart of a conventional nitride semiconductor containing B. In the X-ray diffraction chart, two diffraction peaks of wurtzite AlBN (0002) are observed due to phase separation. Such a low quality nitride semiconductor thin film could not be used for a light emitting material or an electronic device. In particular, as the B composition b is increased, there is a problem that the crystallinity is remarkably deteriorated.

本発明は、このような問題に鑑みてなされたもので、その目的とするところは、可視光から紫外領域で発光する発光デバイスや、高電力・高周波数・高温動作の電子デバイスに適用することができ、結晶品質の高い窒化物半導体を提供することにある。   The present invention has been made in view of such problems, and its object is to apply to light-emitting devices that emit light in the ultraviolet region from visible light, and electronic devices that operate at high power, high frequency, and high temperature. It is possible to provide a nitride semiconductor with high crystal quality.

本発明は、このような目的を達成するために、請求項１に記載の発明は、（０００１）面からのずれが±１０度以下の主方位面を有する炭化珪素結晶からなる基板の前記主方位面上に結晶成長した多層構造を有する窒化物半導体であって、前記多層構造は、ウルツ鉱型の結晶構造であり、（１）ホウ素の組成が０．０５未満であって、前記基板と格子整合している第１のＡｌＢＧａＩｎＮ層と、（２）厚さが１０ｎｍ未満で、ホウ素の組成が０．０５以上０．５未満であって、前記第１のＡｌＢＧａＩｎＮ層と格子整合している第２のＡｌＢＧａＩｎＮ層とが交互に積層され、前記第２のＡｌＢＧａＩｎＮ層を前記第１のＡｌＢＧａＩｎＮ層で挟んだ多層構造であり、前記第１のＡｌＢＧａＩｎＮ層および前記第２のＡｌＢＧａＩｎＮ層のインジウムの組成が０．０１以上であることを特徴とする。 In order to achieve such an object, the present invention provides the main structure of a substrate made of a silicon carbide crystal having a main orientation plane whose deviation from the (0001) plane is ± 10 degrees or less. A nitride semiconductor having a multilayer structure in which crystals are grown on an orientation plane , wherein the multilayer structure is a wurtzite crystal structure, and (1) a boron composition is less than 0.05 , A first AlBGaInN layer that is lattice-matched ; (2) a thickness of less than 10 nm and a boron composition of 0.05 to less than 0.5 that is lattice-matched to the first AlBGaInN layer; a second AlBGaInN layer are laminated alternately, and the second AlBGaInN layer a multilayer structure is sandwiched between said first AlBGaInN layer, of the first AlBGaInN layer and the second AlBGaInN layer The composition of indium is characterized in that at least 0.01.

請求項２に記載の発明は、（０００１）面からのずれが±１０度以下の主方位面を有する炭化珪素結晶からなる基板の前記主方位面上に結晶成長した多層構造を有する窒化物半導体であって、前記多層構造は、ウルツ鉱型の結晶構造であり、（１）ホウ素の組成が０．０５未満であって、前記基板と格子整合している第１のＡｌＢＧａＩｎＮ層と、（２）厚さが１分子層以下で、ホウ素の組成が０．５以上であって、前記第１のＡｌＢＧａＩｎＮ層と格子整合している第２のＡｌＢＧａＩｎＮ層とが交互に積層され、前記第２のＡｌＢＧａＩｎＮ層を前記第１のＡｌＢＧａＩｎＮ層で挟んだ多層構造であり、前記第１のＡｌＢＧａＩｎＮ層および前記第２のＡｌＢＧａＩｎＮ層のインジウムの組成が０．０１以上であることを特徴とする。 The invention according to claim 2 is a nitride semiconductor having a multilayer structure in which a crystal is grown on the main orientation plane of a substrate made of a silicon carbide crystal having a main orientation plane whose deviation from the (0001) plane is ± 10 degrees or less. a is, the multilayer structure is a wurtzite crystal structure, (1) a composition of boron is less than 0.05, the first AlBGaInN layer in the substrate lattice-matched, (2 ) is equal to or smaller than one molecular layer thick, there is the composition of the boron 0.5 or more, said the first AlBGaInN layer lattice matched to that second AlBGaInN layer are laminated alternately, the second A multilayer structure in which an AlBGaInN layer is sandwiched between the first AlBGaInN layers, and the indium composition of the first AlBGaInN layer and the second AlBGaInN layer is 0.01 or more.

請求項３に記載の発明は、Ｃ面からのずれが±１０度以下の主方位面を有するサファイア基板の前記主方位面上に結晶成長した多層構造を有する窒化物半導体であって、前記多層構造は、ウルツ鉱型の結晶構造であり、（１）ホウ素の組成が０．０５未満であって、前記基板と格子整合している第１のＡｌＢＧａＩｎＮ層と、（２）厚さが１０ｎｍ未満で、ホウ素の組成が０．０５以上０．５未満であって、前記第１のＡｌＢＧａＩｎＮ層と格子整合している第２のＡｌＢＧａＩｎＮ層とが交互に積層され、前記第２のＡｌＢＧａＩｎＮ層を前記第１のＡｌＢＧａＩｎＮ層で挟んだ多層構造であり、前記第１のＡｌＢＧａＩｎＮ層および前記第２のＡｌＢＧａＩｎＮ層のインジウムの組成が０．０１以上であることを特徴とする。
請求項４に記載の発明は、Ｃ面からのずれが±１０度以下の主方位面を有するサファイア基板の前記主方位面上に結晶成長した多層構造を有する窒化物半導体であって、前記多層構造は、ウルツ鉱型の結晶構造であり、（１）ホウ素の組成が０．０５未満であって、前記基板と格子整合している第１のＡｌＢＧａＩｎＮ層と、（２）厚さが１分子層以下で、ホウ素の組成が０．５以上であって、前記第１のＡｌＢＧａＩｎＮ層と格子整合している第２のＡｌＢＧａＩｎＮ層とが交互に積層され、前記第２のＡｌＢＧａＩｎＮ層を前記第１のＡｌＢＧａＩｎＮ層で挟んだ多層構造であり、前記第１のＡｌＢＧａＩｎＮ層および前記第２のＡｌＢＧａＩｎＮ層のインジウムの組成が０．０１以上であることを特徴とする。 The invention according to claim 3 is a nitride semiconductor having a multilayer structure in which crystals are grown on the main azimuth plane of a sapphire substrate having a main azimuth plane whose deviation from the C plane is ± 10 degrees or less. The structure is a wurtzite crystal structure, (1) a first AlBGaInN layer having a boron composition less than 0.05 and lattice-matched with the substrate, and (2) a thickness less than 10 nm. And second AlBGaInN layers having a boron composition of 0.05 or more and less than 0.5 and lattice-matched with the first AlBGaInN layers are alternately stacked, and the second AlBGaInN layers are A multilayer structure sandwiched between first AlBGaInN layers, wherein the composition of indium in the first AlBGaInN layer and the second AlBGaInN layer is 0.01 or more .
The invention according to claim 4 is a nitride semiconductor having a multilayer structure in which a crystal is grown on the main azimuth plane of a sapphire substrate having a main azimuth plane whose deviation from the C plane is ± 10 degrees or less. The structure is a wurtzite crystal structure, (1) a first AlBGaInN layer having a boron composition of less than 0.05 and lattice-matched with the substrate, and (2) a thickness of one molecule. The second AlBGaInN layer having a boron composition of 0.5 or more and having a boron composition of 0.5 or more and lattice-matched with the first AlBGaInN layer are alternately stacked, and the second AlBGaInN layer is formed as the first AlBGaInN layer. The AlBGaInN layer has a multilayer structure, and the indium composition of the first AlBGaInN layer and the second AlBGaInN layer is 0.01 or more.

以上説明したように、本発明によれば、厚さが１０ｎｍ未満でホウ素の組成が０．０５以上０．５未満、または厚さが１分子層以下でホウ素の組成が０．５以上の窒化物半導体層を、ホウ素の組成が０．０５未満の窒化物半導体層で挟む多層構造を備えたので、結晶品質の高い窒化物半導体を提供することが可能となる。 As described above, according to the present invention, nitriding with a thickness of less than 10 nm and a boron composition of 0.05 or more and less than 0.5, or a thickness of one molecular layer or less and a boron composition of 0.5 or more. Since the multilayer semiconductor structure in which the nitride semiconductor layer is sandwiched between the nitride semiconductor layers having a boron composition of less than 0.05, a nitride semiconductor with high crystal quality can be provided.

また、本発明によれば、窒化物半導体層のいずれかに、組成が０．０１以上のインジウムを含むことにより、さらに結晶欠陥を減少させることが可能となる。   In addition, according to the present invention, it is possible to further reduce crystal defects by including indium having a composition of 0.01 or more in any of the nitride semiconductor layers.

以下、図面を参照しながら本発明の実施形態について詳細に説明する。   Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

図３に、本発明の実施例１にかかる窒化物半導体の多層構造を示す。窒化物半導体の多層構造は、Ｓｉ面炭化珪素（ＳｉＣ）基板１１上に、Ａｌ0.8Ｂ0.04Ｇａ0.1Ｉｎ0.06Ｎ層（第１窒化物半導体層）１２を形成し、その上に、Ａｌ0.32Ｂ0.1Ｇａ0.62Ｉｎ0.06Ｎ（第２窒化物半導体層）１３とＡｌ0.8Ｂ0.04Ｇａ0.1Ｉｎ0.06Ｎ層（第３窒化物半導体層）１４とを交互に合計１０層積層する。 FIG. 3 shows a multilayer structure of a nitride semiconductor according to Example 1 of the present invention. In the multilayer structure of nitride semiconductor, an Al 0.8 B 0.04 Ga 0.1 In 0.06 N layer (first nitride semiconductor layer) 12 is formed on a Si-plane silicon carbide (SiC) substrate 11, and Al 0.32 B is formed thereon. A total of 10 layers of 0.1 Ga 0.62 In 0.06 N (second nitride semiconductor layer) 13 and Al 0.8 B 0.04 Ga 0.1 In 0.06 N layer (third nitride semiconductor layer) 14 are alternately stacked.

ＳｉＣ基板１１は、主方位面が（０００１）面から０．５度だけ＜１−１００＞方向（以下、−１は結晶方位の１バーを示す）に傾いている。第１窒化物半導体層１２は、厚さ２００ｎｍであり、第２窒化物半導体層１３は、厚さ９ｎｍである。第３窒化物半導体層１４は、厚さ４１ｎｍであり、第１窒化物半導体層１２と同じ組成である。   The SiC substrate 11 is inclined in the <1-100> direction (hereinafter, -1 indicates one bar of the crystal orientation) by 0.5 degrees from the (0001) plane. The first nitride semiconductor layer 12 has a thickness of 200 nm, and the second nitride semiconductor layer 13 has a thickness of 9 nm. The third nitride semiconductor layer 14 has a thickness of 41 nm and the same composition as the first nitride semiconductor layer 12.

図４に、実施例１の窒化物半導体多層構造の表面の光学顕微鏡写真を示す。凹凸がまったくない滑らかな鏡面状の表面が得られていることが分かる。また、原子間力顕微鏡（ＡＦＭ）で表面を詳細に観察すると、原子層レベルで平坦な表面であることが分かる。さらに、Ｘ線回折の測定から非常に高い結晶性を有していることも分かった。ここで、第２窒化物半導体層１３と第３窒化物半導体層１４とは、共にウルツ鉱型の結晶構造を有し、ａ軸の格子定数が０．３１２ｎｍと等しく、格子整合している。ｃ軸は、ＳｉＣ基板１１のｃ軸に一致している。   FIG. 4 shows an optical micrograph of the surface of the nitride semiconductor multilayer structure of Example 1. It can be seen that a smooth mirror-like surface having no irregularities is obtained. Further, when the surface is observed in detail with an atomic force microscope (AFM), it can be seen that the surface is flat at the atomic layer level. Furthermore, it was found from the measurement of X-ray diffraction that it has very high crystallinity. Here, both the second nitride semiconductor layer 13 and the third nitride semiconductor layer 14 have a wurtzite type crystal structure, and the lattice constant of the a-axis is equal to 0.312 nm and is lattice-matched. The c axis coincides with the c axis of the SiC substrate 11.

格子定数がほぼ一致している場合に、Ｂを含まない第２窒化物半導体層１３と第３窒化物半導体層１４とを用いれば、それぞれの層の厚さは任意に設計することができる。しかしながら、Ｂを比較的多量に含む窒化物半導体の場合には、ウルツ鉱型の結晶構造が不安定相であるため、第２窒化物半導体層１３のＢの組成は、０．０５以上で０．５未満であって、膜厚が１０ｎｍを超えないようにする必要がある。加えて、Ｂの組成が０．０５未満の第３窒化物半導体層１４によって、第２窒化物半導体層１３をサンドイッチ状に挟むこと（最下層の第２窒化物半導体層１３は、第１窒化物半導体層１２と第３窒化物半導体層１４とによって挟む）が、良好な結晶性を得るために不可欠である。すなわち、Ｂ組成の大きな窒化物半導体層を、Ｂ組成の小さな窒化物半導体層により挟むことにより、格子定数や結晶構造の相違による結晶品質の劣化を防ぐことができる。   If the second nitride semiconductor layer 13 and the third nitride semiconductor layer 14 that do not contain B are used when the lattice constants are substantially the same, the thickness of each layer can be arbitrarily designed. However, in the case of a nitride semiconductor containing a relatively large amount of B, since the wurtzite crystal structure is an unstable phase, the composition of B in the second nitride semiconductor layer 13 is 0.05 or more and 0. It is necessary that the film thickness does not exceed 10 nm. In addition, the second nitride semiconductor layer 13 is sandwiched between the third nitride semiconductor layers 14 having a B composition of less than 0.05 (the lowermost second nitride semiconductor layer 13 is the first nitride). Sandwiched between the semiconductor semiconductor layer 12 and the third nitride semiconductor layer 14) is indispensable for obtaining good crystallinity. That is, by sandwiching a nitride semiconductor layer having a large B composition between nitride semiconductor layers having a small B composition, it is possible to prevent deterioration in crystal quality due to a difference in lattice constant or crystal structure.

図５に、実施例１の窒化物半導体多層構造の表面粗さと第２窒化物半導体層のＢ組成との関係を示す。図３に示した多層構造において、第２窒化物半導体層１３の厚さを９ｎｍに固定し、第２窒化物半導体層１３のＢ組成を変えたときの、窒化物半導体多層構造の表面粗さを示す。表面粗さは、ＡＦＭで測定した平均二乗根粗さであり、対数スケールで縦軸に示す。なお、第２窒化物半導体層１３と第３窒化物半導体層１４のａ軸の格子定数差が５％以内に収まるように、第２窒化物半導体層１３のＡｌ，ＧａおよびＩｎ組成を適宜調整している。   FIG. 5 shows the relationship between the surface roughness of the nitride semiconductor multilayer structure of Example 1 and the B composition of the second nitride semiconductor layer. In the multilayer structure shown in FIG. 3, the surface roughness of the nitride semiconductor multilayer structure when the thickness of the second nitride semiconductor layer 13 is fixed to 9 nm and the B composition of the second nitride semiconductor layer 13 is changed. Indicates. The surface roughness is the mean square root roughness measured by AFM and is shown on the vertical axis on a logarithmic scale. The Al, Ga, and In compositions of the second nitride semiconductor layer 13 are appropriately adjusted so that the difference in lattice constant between the a-axes of the second nitride semiconductor layer 13 and the third nitride semiconductor layer 14 is within 5%. is doing.

第２窒化物半導体層１３のＢ組成が０．５を超えない場合には、表面粗さは０．２５ｎｍと原子層レベルで非常に滑らかな表面が得られている。ところが、第２窒化物半導体層１３のＢ組成が０．５を超えると、結晶性の劣化により表面粗さが急激に大きくなっているのが分かる。   When the B composition of the second nitride semiconductor layer 13 does not exceed 0.5, the surface roughness is 0.25 nm, and a very smooth surface is obtained at the atomic layer level. However, it can be seen that when the B composition of the second nitride semiconductor layer 13 exceeds 0.5, the surface roughness rapidly increases due to deterioration of crystallinity.

また、格子定数や結晶構造の相違のために生ずる結晶欠陥を防ぐためには、第２窒化物半導体層１３と第３窒化物半導体層１４のＩｎ組成を、少なくとも０．０１以上にすることが重要である。これは、Ｉｎを多く含むことによって、特に点欠陥の密度を減少させることができるからである。この効果は、ＢとＩｎの電気陰性度の差が大きいため、Ｂを含む窒化物半導体の場合に特に効果が高い。   In order to prevent crystal defects caused by differences in lattice constants and crystal structures, it is important that the In composition of the second nitride semiconductor layer 13 and the third nitride semiconductor layer 14 is at least 0.01 or more. It is. This is because the density of point defects can be particularly reduced by containing a large amount of In. This effect is particularly high in the case of a nitride semiconductor containing B because the difference in electronegativity between B and In is large.

図３に示した窒化物半導体多層構造において、第２窒化物半導体層１３の膜厚を、１分子層以下にすると、第２窒化物半導体層１３のＢ組成を０．５以上に増やしても良好な結晶性を得られることができる。これは、第２窒化物半導体層１３の膜厚を極端に薄く１分子層以下とすることにより、第２窒化物半導体層１３および第３窒化物半導体層１４の安定なウルツ鉱型の積層シーケンス、すなわちｃ軸方向のＡＢＡＢＡＢ・・・・という積層の繰り返しが確実に引き継がれるからである。従って、第３窒化物半導体層１４によるサンドイッチ効果が大きくなり、第２窒化物半導体層１３のウルツ鉱型の結晶構造がより安定化される。このため、第２窒化物半導体層１３は、ＢＮ（Ｂ組成が１）であっても構わない。 In the nitride semiconductor multilayer structure shown in FIG. 3, if the film thickness of the second nitride semiconductor layer 13 is one molecular layer or less, the B composition of the second nitride semiconductor layer 13 can be increased to 0.5 or more. Good crystallinity can be obtained. This is because the second nitride semiconductor layer 13 is extremely thin and has a molecular layer or less, so that a stable wurtzite stacking sequence of the second nitride semiconductor layer 13 and the third nitride semiconductor layer 14 is achieved. That is, the repetition of the stacking of ABABAB in the c-axis direction is surely taken over. Therefore, the sandwich effect by the third nitride semiconductor layer 14 is increased, and the wurtzite crystal structure of the second nitride semiconductor layer 13 is further stabilized. For this reason, the second nitride semiconductor layer 13 may be BN (B composition is 1).

図６に、実施例２の窒化物半導体多層構造の表面粗さと第２窒化物半導体層のＢ組成との関係を示す。図３に示した多層構造において、第２窒化物半導体層１３の厚さを１分子層相当に固定し、第２窒化物半導体層１３のＢ組成を変えたときの、窒化物半導体多層構造の表面粗さを示す。表面粗さは、ＡＦＭで測定した平均二乗根粗さであり、対数スケールで縦軸に示す。なお、第２窒化物半導体層１３と第３窒化物半導体層１４のａ軸の格子定数差ができるだけ小さくなるように、第２窒化物半導体層１３のＡｌ，ＧａおよびＩｎ組成を適宜調整している。 FIG. 6 shows the relationship between the surface roughness of the nitride semiconductor multilayer structure of Example 2 and the B composition of the second nitride semiconductor layer. In the multilayer structure shown in FIG. 3, the thickness of the second nitride semiconductor layer 13 is fixed to one molecular layer, and the B composition of the second nitride semiconductor layer 13 is changed. Indicates surface roughness. The surface roughness is the mean square root roughness measured by AFM and is shown on the vertical axis on a logarithmic scale. The Al, Ga, and In compositions of the second nitride semiconductor layer 13 are adjusted as appropriate so that the difference in lattice constant between the a-axes of the second nitride semiconductor layer 13 and the third nitride semiconductor layer 14 is as small as possible. Yes.

第２窒化物半導体層１３の厚さを１分子層相当とすると、Ｂ組成が１（すなわちＢＮ）であっても原子層レベルで平坦な表面を有することがわかる。
When the thickness of the second nitride semiconductor layer 13 is equivalent to one molecular layer, it can be seen that even if the B composition is 1 (that is, BN), it has a flat surface at the atomic layer level.

実施例１，２では、基板１１として、主方位面が（０００１）面から０．５度だけ＜１−１００＞方向に傾いたＳｉ面ＳｉＣ基板を用いた。（０００１）面からのずれが任意の方位に±１０度以下の主方位面を有するＳｉＣ基板を用いた場合でも、同様の効果を得ることができる。   In Examples 1 and 2, as the substrate 11, a Si surface SiC substrate having a main azimuth plane tilted in the <1-100> direction by 0.5 degrees from the (0001) plane was used. Even when a SiC substrate having a main azimuth plane whose deviation from the (0001) plane is ± 10 degrees or less in an arbitrary direction is used, the same effect can be obtained.

［ａ］（０００１）面からずれが±１０度以下の主方位面を有するウルツ鉱型の結晶基板、［ｂ］（１１１）面からのずれが±１０度以下の主方位面を有する閃亜鉛鉱型の結晶基板、［ｃ］Ｃ面からのずれが±１０度以下の主方位面を有するサファイア基板、［ｄ］（１１１）面からのずれが±１０度以下の主方位面を有するダイヤモンド型の結晶基板を用いることもできる。   [A] Wurtzite type crystal substrate having a main orientation plane with a deviation of ± 10 degrees or less from the (0001) plane, Zinc flash having a main orientation plane with a deviation from the [b] (111) plane of ± 10 degrees or less Ore-type crystal substrate, [c] sapphire substrate having a main orientation plane with a deviation from the C plane of ± 10 degrees or less, diamond having a main orientation plane with a deviation from the [d] (111) plane of ± 10 degrees or less A type crystal substrate can also be used.

従来のＢを含む窒化物半導体の表面の光学顕微鏡写真である。It is the optical microscope photograph of the surface of the nitride semiconductor containing the conventional B. 従来のＢを含む窒化物半導体のＸ線回折チャートである。3 is an X-ray diffraction chart of a conventional nitride semiconductor containing B. 本発明の実施例１にかかる窒化物半導体の多層構造を示す断面図である。It is sectional drawing which shows the multilayer structure of the nitride semiconductor concerning Example 1 of this invention. 実施例１の窒化物半導体多層構造の表面の光学顕微鏡写真である。2 is an optical micrograph of the surface of the nitride semiconductor multilayer structure of Example 1. FIG. 実施例１の窒化物半導体多層構造の表面粗さと第２窒化物半導体層のＢ組成との関係を示す図である。It is a figure which shows the relationship between the surface roughness of the nitride semiconductor multilayer structure of Example 1, and B composition of a 2nd nitride semiconductor layer. 実施例２の窒化物半導体多層構造の表面粗さと第２窒化物半導体層のＢ組成との関係を示す図である。It is a figure which shows the relationship between the surface roughness of the nitride semiconductor multilayer structure of Example 2, and B composition of a 2nd nitride semiconductor layer.

符号の説明Explanation of symbols

１１ Ｓｉ面炭化珪素（ＳｉＣ）基板
１２ 第１窒化物半導体層
１３ 第２窒化物半導体層
１４ 第３窒化物半導体層
11 Si-plane silicon carbide (SiC) substrate 12 First nitride semiconductor layer 13 Second nitride semiconductor layer 14 Third nitride semiconductor layer

Claims (4)

（０００１）面からのずれが±１０度以下の主方位面を有する炭化珪素結晶からなる基板の前記主方位面上に結晶成長した多層構造を有する窒化物半導体であって、
前記多層構造は、ウルツ鉱型の結晶構造であり、（１）ホウ素の組成が０．０５未満であって、前記基板と格子整合している第１のＡｌＢＧａＩｎＮ層と、（２）厚さが１０ｎｍ未満で、ホウ素の組成が０．０５以上０．５未満であって、前記第１のＡｌＢＧａＩｎＮ層と格子整合している第２のＡｌＢＧａＩｎＮ層とが交互に積層され、前記第２のＡｌＢＧａＩｎＮ層を前記第１のＡｌＢＧａＩｎＮ層で挟んだ多層構造であり、
前記第１のＡｌＢＧａＩｎＮ層および前記第２のＡｌＢＧａＩｎＮ層のインジウムの組成が０．０１以上であることを特徴とする窒化物半導体。 A nitride semiconductor having a multilayer structure in which a crystal is grown on the main orientation plane of a substrate made of a silicon carbide crystal having a main orientation plane with a deviation from the (0001) plane of ± 10 degrees or less ,
Wherein the multilayer structure is a wurtzite crystal structure, (1) a composition of boron is less than 0.05, the first AlBGaInN layer in the substrate lattice matched, (2) thickness less than 10 nm, and less than 0.5 the composition of the boron 0.05 or more, the first and the second AlBGaInN layer that AlBGaInN layer lattice matched are alternately stacked, the second AlBGaInN layer a multilayer structure sandwiched between the first AlBGaInN layer,
A nitride semiconductor, wherein a composition of indium in the first AlBGaInN layer and the second AlBGaInN layer is 0.01 or more. （０００１）面からのずれが±１０度以下の主方位面を有する炭化珪素結晶からなる基板の前記主方位面上に結晶成長した多層構造を有する窒化物半導体であって、
前記多層構造は、ウルツ鉱型の結晶構造であり、（１）ホウ素の組成が０．０５未満であって、前記基板と格子整合している第１のＡｌＢＧａＩｎＮ層と、（２）厚さが１分子層以下で、ホウ素の組成が０．５以上であって、前記第１のＡｌＢＧａＩｎＮ層と格子整合している第２のＡｌＢＧａＩｎＮ層とが交互に積層され、前記第２のＡｌＢＧａＩｎＮ層を前記第１のＡｌＢＧａＩｎＮ層で挟んだ多層構造であり、
前記第１のＡｌＢＧａＩｎＮ層および前記第２のＡｌＢＧａＩｎＮ層のインジウムの組成が０．０１以上であることを特徴とする窒化物半導体。 A nitride semiconductor having a multilayer structure in which a crystal is grown on the main orientation plane of a substrate made of a silicon carbide crystal having a main orientation plane with a deviation from the (0001) plane of ± 10 degrees or less ,
Wherein the multilayer structure is a wurtzite crystal structure, (1) a composition of boron is less than 0.05, the first AlBGaInN layer in the substrate lattice matched, (2) thickness The second AlBGaInN layer is alternately laminated with the first AlBGaInN layer and the first AlBGaInN layer having a boron composition of not more than one molecular layer and having a boron composition of 0.5 or more. a multilayer structure sandwiched between the first AlBGaInN layer,
A nitride semiconductor, wherein a composition of indium in the first AlBGaInN layer and the second AlBGaInN layer is 0.01 or more. Ｃ面からのずれが±１０度以下の主方位面を有するサファイア基板の前記主方位面上に結晶成長した多層構造を有する窒化物半導体であって、
前記多層構造は、ウルツ鉱型の結晶構造であり、（１）ホウ素の組成が０．０５未満であって、前記基板と格子整合している第１のＡｌＢＧａＩｎＮ層と、（２）厚さが１０ｎｍ未満で、ホウ素の組成が０．０５以上０．５未満であって、前記第１のＡｌＢＧａＩｎＮ層と格子整合している第２のＡｌＢＧａＩｎＮ層とが交互に積層され、前記第２のＡｌＢＧａＩｎＮ層を前記第１のＡｌＢＧａＩｎＮ層で挟んだ多層構造であり、
前記第１のＡｌＢＧａＩｎＮ層および前記第２のＡｌＢＧａＩｎＮ層のインジウムの組成が０．０１以上であることを特徴とする窒化物半導体。 A nitride semiconductor having a multilayer structure in which a crystal growth is performed on the main orientation plane of a sapphire substrate having a main orientation plane with a deviation from the C plane of ± 10 degrees or less ,
The multilayer structure is a wurtzite crystal structure, (1) a first AlBGaInN layer having a boron composition less than 0.05 and lattice-matched with the substrate, and (2) a thickness of Second AlBGaInN layers alternately stacked with second AlBGaInN layers having a boron composition of less than 10 nm and a boron composition of 0.05 to less than 0.5 and lattice-matched with the first AlBGaInN layers. Is a multilayer structure sandwiched between the first AlBGaInN layers,
The nitride compound semiconductor you wherein the first composition of indium AlBGaInN layer and the second AlBGaInN layer is 0.01 or more. Ｃ面からのずれが±１０度以下の主方位面を有するサファイア基板の前記主方位面上に結晶成長した多層構造を有する窒化物半導体であって、A nitride semiconductor having a multilayer structure in which a crystal growth is performed on the main orientation plane of a sapphire substrate having a main orientation plane with a deviation from the C plane of ± 10 degrees or less,
前記多層構造は、ウルツ鉱型の結晶構造であり、（１）ホウ素の組成が０．０５未満であって、前記基板と格子整合している第１のＡｌＢＧａＩｎＮ層と、（２）厚さが１分子層以下で、ホウ素の組成が０．５以上であって、前記第１のＡｌＢＧａＩｎＮ層と格子整合している第２のＡｌＢＧａＩｎＮ層とが交互に積層され、前記第２のＡｌＢＧａＩｎＮ層を前記第１のＡｌＢＧａＩｎＮ層で挟んだ多層構造であり、The multilayer structure is a wurtzite crystal structure, (1) a first AlBGaInN layer having a boron composition less than 0.05 and lattice-matched with the substrate, and (2) a thickness of The second AlBGaInN layer is laminated alternately with the first AlBGaInN layer having a boron composition of 0.5 or more in one molecular layer and being lattice-matched with the first AlBGaInN layer, A multilayer structure sandwiched between first AlBGaInN layers,
前記第１のＡｌＢＧａＩｎＮ層および前記第２のＡｌＢＧａＩｎＮ層のインジウムの組成が０．０１以上であることを特徴とする窒化物半導体。A nitride semiconductor, wherein a composition of indium in the first AlBGaInN layer and the second AlBGaInN layer is 0.01 or more.
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