JP3756575B2 - Group III nitride semiconductor device - Google Patents

Description

しかし、これらの応力緩和層材料は全て酸化物であるため、成膜時におけるSiやSiC 表面の酸化が懸念される。仮に、基板表面が酸化したときには、多くの場合、基板と酸化物材料との界面に非晶質層が形成され、その上に形成された膜の結晶性が悪化する。このため、基板上に酸化抑制のための酸化防止層T として、Al_x Ga_y In_1-x-y N を極薄く(10nm 程度) 形成し、その上に応力緩和層S を形成する。そして最後に、Al_x Ga_y In_1-x-y N からなるダブルヘテロ構造や量子井戸構造など、目的の半導体装置用の多層AlGaInN 層Ntを形成する。成膜方法として分子線エピタキシャル（MBE)または有機金属気相成長法などが適用できる。
実施例１
先ず、Si単結晶の (1,1,1)面の基板上に直接、厚さ100nm のZnO 層を形成した。スパッタ条件としては、基板温度を250 ℃とし、スパッタガスはArとしその圧力を1Pa とした。ターゲットにはAlを2wt%添加したZnO 焼結体を用いた。Alの添加は応力緩和層に導電性を持たせるためである。
【００１６】
得られたZnO 膜は、Ｘ線回折パターンからｃ軸配向していることが確認できた。図２はSi基板上に直接形成されたZnO 膜の反射高速電子線回折(RHEED) 像を示し、（ａ）は電子線入射が (1,-1,1) 方向の場合のパターンの図、（ｂ）は電子線入射が(1,0,0) 方向の場合であり（ａ）に対してｃ面内で30°回転させた場合のパターンの図である。図２から、単結晶のパターン（（ｂ）における高輝度（大きい白点）のみ) と低輝度（淡い白点）のみのパターン）がずれて重なっていることから、ZnO 膜のｃ面内でａ軸の向きが回転した多結晶膜であることが判った。
【００１７】
図３はSi基板上に直接形成されたZnO 膜のオージェ電子分光による深さ方向の元素分析の結果を示す図である。Si基板の領域にも大量の酸素が検出され、Si基板表面が酸化されていることが判る。このため、ZnO の多結晶化は、ZnO を形成するときにSi表面が酸化されたことに起因していることが想定できる。
このZnO 膜上に、多層のAl _x Ga _y In_1-x-y N 膜を窒素ラジカルを使った分子線エピタキシャル（MBE)により形成した。層構成はAlN の第 1のバッファ層、その上にGaN の第 2のバッファ層、n 型AlGaN のクラッド層、GaN の活性層、p 型AlGaN のクラッド層からなるダブルヘテロ構造としたが、亀裂は観測されず、ZnO の応力緩和層の効果が確認できた。
【００１８】
Si基板表面の酸化を抑制するため、酸化防止層としてSi基板上にn 型GaN 膜を10nm形成した。その上にZnO 応力緩和層を100nm 形成した。図４はSi基板にGaN 膜を形成されたZnO 膜のオージェ電子分光による深さ方向の元素分析の結果を示す図である。図３と比較して、図４からGaN 膜がSiの酸化を防止していることが確認できる。
【００１９】
図５はSi基板上のGaN 膜上に形成されたZnO 膜のRHEED 像を示し、（ａ）は電子線入射が (1,-1,1) 方向の場合のパターンの図、（ｂ）は電子線入射が(1,0,0) 方向の（（ａ）に対してｃ面内で30°回転させた）場合のパターンの図である。酸化防止層の形成されない場合（図２）と異なり、パターンは二重構造になっていず、ZnO のｃ面内のａ軸の回転は観測されない。このことから、酸化抑制のための GaN層を導入することにより、Si基板の酸化が抑制され、ZnO はエピタキシャル成長（単結晶成長）することが判った。
【００２０】
このZnO 膜上に、上記と同じ層構成の多層のAl _x Ga _y In_1-x-y N のダブルヘテロ構造を形成し、さらにキャップ層を形成した。図６はSi基板上のGaN 膜、ZnO 膜の二重層上の Al _x Ga_y In_1-x-y N 膜の電子顕微鏡観察による結晶の状態を示す図である。図から、その表面は平滑であり、亀裂は生じていないことが判る。この状態の AlGaInN膜を用いて、特に精細な構造を必要としないフォトダイオード等のIII 族窒化物半導体装置は成立する。
【００２１】
上記のダブルヘテロ構造を含む層構成のIII 族窒化物半導体装置の１例としてレーザダイオードを作製した。図７は本発明に係るレーザダイオードのへき開面に垂直な面での断面図である。基板1 は(1,1,1) 面Siであり、酸化防止層11、応力緩和層12が順次積層されている。厚さ50nmのAlN の第1 のバッファ層２を形成し、その上に厚さ0.5 μm のGaN の第２のバッファ層、厚さ150nm のn 型AlGaN のクラッド層４、厚さ50nmのGaN の活性層５、厚さ150nm のp 型AlGaN のクラッド層6 からなるダブルヘテロ構造を形成し、さらに厚さ100nm p 型GaN キャップ層７を形成してある。基板1 の電極8aはAl、キャップ層7 の電極9 はAu/Cr である。
【００２２】
Si基板1 をへき開することによりIII 族窒化物半導体層は（1,-1,0,0) 面がへき開面となり、光共振器が形成できる。このレーザダイオードにパルス電流を流し、電流密度約10kA/cm²以上でレーザ発振させることができた。
また、酸化防止層として、Ga_1-x Al_x N (0 ＜x ≦1)も実施したが、同様に酸化防止の効果があり、応力緩和層は単結晶であり、III 族窒化物半導体層は良好に成膜できた。
実施例２
基板としてSi単結晶の (1,1,1)面を用い、応力緩和層にマグネトロンスパッタにより形成したサファイア (α−Al₂O₃)を用いた。なお、基板温度は５００℃、ターゲットにはAl₂O₃ の焼結体を用い、スパッタガスにはArを使い、圧力は1Pa 、膜厚は120nm とした。
【００２３】
サファイア応力緩和層の場合も、ZnO 応力緩和層の場合と同様、酸化防止層がない場合、Si(1,1,1) 基板上でｃ軸配向に成長はするが、ｃ面内でのａ軸方向の回転が見られた。ところが、酸化防止層を導入することにより、サファイアおよびその上に形成したダブルへテロ構造ともにエピタキシャル成長し、亀裂も観測されなかった。
実施例３
基板としてSi単結晶の (1,1,1)面を用い、応力緩和層にマグネトロンスパッタリングにより形成したマグネシア (MgO)を用いた。なお、基板温度は400 ℃、ターゲットにはMgO の焼結体を用い、スパッタガスはArを使い、圧力は1Pa 、膜厚は100nm とした。MgO の場合も、酸化防止層がない場合、Si(1,1,1) 基板上でｃ軸配向ではあるが、ｃ面内でのａ軸方向の回転が見られた。ところが、酸化防止層を導入することにより、MgO およびその上に形成したダブルへテロ構造ともにエピタキシャル成長し、亀裂も観測されなかった。
実施例４
基板としてSi単結晶の (1,1,1)面を用い、応力緩和層にマグネトロンスパッタリングにより形成したスピネル (MgAl₂ O₄) を用いた。なお、基板温度は600 ℃、ターゲットにはMgAl₂ O₄焼結体を用い、スパッタガスにはArを使い、圧力は1Pa 、膜厚は120nm とした。スピネルの場合も、酸化防止層がない場合、Si(1,1,1) 基板上でｃ軸配向ではあるが、ｃ面内でのａ軸方向の回転が見られた。ところが、酸化防止層を導入することにより、スピネルおよびその上に形成したダブルへテロ構造ともにエピタキシャル成長し、亀裂も観測されなかった。
実施例５
基板としてSi単結晶の (1,1,1)面を用い、応力緩和層にマグネトロンスパッタリングにより形成したネオジガレイト (NdGaO₃) を用いた。なお、基板温度は700 ℃、ターゲットにはNdGaO₃焼結体を用い、スパッタガスにはArを使い、圧力は1Pa 、膜厚は120nm とした。ネオジガレイトの場合も、酸化防止層がない場合、Si(1,1,1) 基板上でｃ軸配向ではあるが、ｃ面内でのａ軸方向の回転が見られた。ところが、酸化防止層を導入することにより、ネオジガレイトおよびその上に形成したダブルへテロ構造ともにエピタキシャル成長し、亀裂も観測されなかった。
実施例６
また、6H-SiC基板を用いて、実施例1 と同様に、ZnO を応力緩和層、GaN 酸化防止層とした実験を行ったが、実施例1 と同様に応力緩和層、酸化防止層の効果が確認できた。
【００２４】
【発明の効果】
本発明によれば、Al_x Ga_y In_1-x-y N(0 ≦x 、y かつ 0≦x+y ≦1)結晶の熱膨張係数より小さな熱膨張係数を持つ結晶からなる基板上に形成されたAl_x Ga_y In_1-x-y N 層を含むIII 族窒化物半導体装置において、前記基板と前記Al_x Ga_y In_1-x-y N 層との間に基板材料およびAl_x Ga_y In_1-x-y N 結晶の熱膨張係数より大きな熱膨張係数を持つ材料からなる応力緩和層を介在させて、Al_x Ga_y In_1-x-y N に生ずる応力を緩和したため、熱膨張係数がAl_x Ga_y In_1-x-y N 膜より小さい基板上のAl_x Ga_y In_1-x-y N からなる多層膜を有するIII 族窒化物半導体装置には亀裂がなく、またへき開性を利用して個別化が簡単にできる。
【００２５】
さらに、応力緩和層と基板との間に、Al_x Ga_y In_1-x-y N (0≦x 、y かつ 0≦x+y ≦1)からなる酸化防止層を介在させ、応力緩和層およびその上に形成されるAl_x Ga_y In_1-x-y N 膜の結晶性の悪化を防止するようにしたので、精細な層構成の発光ダイオードやレーザダイオードを形成できる。
【図面の簡単な説明】
【図１】本発明に係るIII 族窒化物半導体装置の層構成の断面図
【図２】 Si基板上に直接形成されたZnO 膜の反射高速電子線回折(RHEED) 像を示し、（ａ）は電子線入射が(1,-1,1)方向の場合の結晶構造の写真、（ｂ）は電子線入射が(1, 0, 0) 方向の場合であり(a) に対してc 面内で30°回転させた場合の結晶構造の写真
【図３】 Si基板上に直接形成されたZnO 膜のオージェ電子分光による深さ方向の元素分析の結果を示す図
【図４】 Si基板にGaN 膜を形成されたZnO 膜のオージェ電子分光による深さ方向の元素分析の結果を示す図
【図５】 Si基板上のGaN 膜上に形成されたZnO 膜の反射高速電子線回折(RHEED) 像を示し、（ａ）は電子線入射が(1,-1,1)方向の場合の結晶構造の写真、（ｂ）は電子線入射が(1, 0, 0) 方向の（(a) に対してc 面内で30°回転させた）場合の結晶構造の写真
【図６】 Si基板上のGaN 膜、ZnO 膜の二重層上のAl_x Ga_y In_1-x-y N 膜の電子顕微鏡観察による結晶の状態を示す顕微鏡写真
【図７】本発明に係るレーザダイオードのへき開面に垂直な面での断面図
【図８】従来のIII 族窒化物半導体装置の１例であるレーザダイオードの断面図
【図９】 Si結晶基板上に直接形成されたAl_x Ga_y In_1-x-y N 膜の表面の走査型電子顕微鏡観察による結晶の状態を示す顕微鏡写真
【符号の説明】
１ 基板
２ バッファ層
２ａ 第１のバッファ層
２ｂ 第２のバッファ層
３ コンタクト層
４ クラッド層
５ 活性層
６ クラッド層
７ キャップ層
８ 第１の電極層
８ａ 第１の電極層
９ 第２の電極層
Ｓ 応力緩和層
Ｔ 酸化防止層
Ｎｔ AlGaInN 層[0001]
BACKGROUND OF THE INVENTION
Group III nitride semiconductor _{(Al x Ga y In 1-} xy N (0 ≦ x, y and relates III nitride semiconductor device such as a laser diode or light emitting diode using a 0 ≦ x + y ≦ 1) .
[0002]
[Prior art]
Group III nitride (Al _x Ga _y In _1-xy N (0 ≤ x, y and 0 ≤ x + y ≤ 1)) with direct transition and controllable optical gap in the range of 1.9 to 6.2 eV Group III nitride semiconductor devices, such as laser diodes and light-emitting diodes using silicon, have been prototyped. Hereinafter, a group III nitride abbreviated as _{Al x Ga y In 1-xy} N or AlGaInN. Group III nitride semiconductor devices have been mainly formed on sapphire substrates because of the good matching of crystal lattices and thermal expansion coefficients. And by controlling the optical gap by changing the composition (x, y) of Al _x Ga _y In _1-xy N, by controlling the valence electrons to n-type and p-type by adding Si and magnesium (Mg), Double heterostructure (MCYoo, KHShim, et al .: Proceedings of International Symposium on Blue Laser and Light Emitting Diodes, Chiba Univ., Japan, March 5-7, 1996, p554-557) or quantum well structure (S. Nakamura, Group III nitride semiconductor devices such as et al, J. Japanese Journal of Applied Physics, vol 35, part 2, No 2B (1996), L217 to L220) have been reported.
[0003]
FIG. 8 is a cross-sectional view of a laser diode which is an example of a conventional group III nitride semiconductor device. An AlN buffer layer 2 and a GaN contact layer 3 are formed on a substrate 1 made of sapphire (c-plane). In addition, a double heterostructure composed of an n-type AlGaN cladding layer 4, a GaN active layer 5 and a p-type AlGaN cladding layer 6 is formed. A p-type GaN cap layer 7 is formed thereon, and the double heterostructure and the cap layer 7 are collectively photo-etched, and the side surfaces are perpendicular to the substrate surface. Due to the low conductivity of sapphire, the contact layer 3 extends outside the double heterostructure for the electric lead on the substrate side, and a first electrode layer 8 made of Au / Cr is formed on the surface thereof. Yes. A second electrode layer 9 made of Al / Ti is formed on the cap layer 7.
[0004]
In _{Al x Ga y In 1-xy} N film metal organic vapor phase epitaxy (hereinafter referred to as MOCVD), for raising the temperature of the substrate to about 1000 ° C., in addition to the matching of the lattice constant on the choice of substrate It is also necessary to consider the consistency of the thermal expansion coefficient. Even if the substrate has a good lattice constant matching, if a substrate material with a thermal expansion coefficient smaller than Al _x Ga _y In _1-xy N is used, Al _x Ga _y In _1-xy N will be applied during cooling after film formation. It is known that tensile stress occurs in the film, and in some situations, the film cracks (A. Kuramata, K. Horino, et al .; Proceedings of International Symposium on Blue Laser and Light Emitting Diodes, Chiba Univ., Japan, March 5-7, 1996, p80-85).
[0005]
The al _x Ga deposition substrate material _y In _1-xy N sapphire have been used. The sapphire substrate _{Al x Ga y In 1-xy} N crystal lattice matching stability, and moreover, the thermal expansion coefficient of sapphire, alpha (sapphire) is 7.5 × 10 ^-6 / K (hereinafter, alpha (substance name) Represents the thermal expansion coefficient of the material), Al _x Ga _y In _1-xy N is larger than α (Al _x Ga _y In _1-xy N) = 5.6 × 10 ^-6 / K, so no cracks occur .
[0006]
However, the sapphire substrate has the following drawbacks. 1. Since there is no cleavage, an optical resonator in a laser diode cannot be formed by simple cleavage. 2. Conductivity is small and electrodes cannot be taken from the substrate surface.
[0007]
[Problems to be solved by the invention]
On the other hand, if the substrate of Si crystal or 6H-SiC crystal is used, the above two drawbacks are solved, but the coefficient of thermal expansion is α (Si) = 3.59 × 10 ^-6 / K, α (6H-SiC ) = 4.2 for less than × 10 ^-6 / K and _{Al x Ga y in 1-xy} N -based coefficient of thermal expansion (e.g., alpha (GaN) = 5.6 × 10 ^-6 / K), the deposition temperature after the deposition When cooling from (about 1000 ° C.) to room temperature, the film shrinks more than the substrate, but since the substrate is thicker than the film, tensile stress is generated on the film side. As a result, the film may crack. Therefore, a semiconductor device cannot be manufactured. Figure 9 is a diagram showing a state of a crystal by scanning electron microscopy of the surface of the _{Al x Ga y In 1-xy} N film is directly formed on the Si crystal substrate. It can be seen that a crack has occurred.
[0008]
In view of the above problems, an object of the present invention is to provide a III-nitride semiconductor device comprising a _{Al x Ga y In 1-xy} N crystal causing no crack on a substrate of Si crystal or 6H-SiC crystals It is in.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, Al _x Ga _y In _1-xy N (0 ≤ x, y and 0 ≤ x + y ≤ 1) on a substrate made of a crystal having a thermal expansion coefficient smaller than that of the crystal. in group III nitride semiconductor device comprising _{Al x Ga y in 1-xy} N layer formed, said substrate and said _{Al x Ga y in 1-xy} N layer and the substrate material and the Al _x Ga _y in between _1-xy N with a stress relieving layer composed of a material having a larger thermal expansion coefficient than the thermal expansion coefficient is interposed crystal, and relieving the stress generated in the _{Al x Ga y in 1-xy} N.
[0010]
The substrate material may be silicon (Si) crystal or carbonized silicon (SiC) crystal.
The stress relaxation layer is made of at least one of zinc oxide (ZnO), magnesium oxide (MgO), sapphire (α-Al ₂ O ₃ ), spinel (MgAl ₂ O ₄ ), or neodymium gallate (NdGaO ₃ ). good.
[0011]
An anti-oxidation layer made of Al _x Ga _y In _1-xy N (0 ≦ x, y and 0 ≦ x + y ≦ 1) is interposed between the stress relaxation layer and the substrate, and the stress relaxation layer and the upper layer _{Al x Ga y in 1-xy} N film may prevent the crystalline deterioration of formed.
The group III nitride semiconductor device may be a light emitting diode or a laser diode.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a cross-sectional view of the layer structure of a group III nitride semiconductor device according to the present invention. Substrate 1 antioxidant layer on the T, the stress relaxation layer S, then _{Al x Ga y In 1-xy} N layer Nt is laminated.
The surface of the substrate 1 is a (1,1,1) plane of Si crystal or a (0,0,0,1) plane of SiC crystal. _{Al x Ga y In 1-xy} N layer Nt consists composition (x, y) and a plurality of layers of different doping. For example, a double heterostructure diode is the same as the buffer layer 2 to the cap layer 7 in FIG. Other semiconductor layers or electrode layers are further stacked depending on the application.
[0013]
The stress relaxation layer S will be described below.
Since the thermal expansion coefficient of the substrate material is smaller than the thermal expansion coefficient of the AlGaInN crystal, the AlGaInN film shrinks more than the substrate when it cools from the deposition temperature (approximately 1000 ° C) after deposition of AlGaInN to room temperature. However, since the substrate is thicker than the AlGaInN film, tensile stress is generated on the AlGaInN film side. As a result, cracks may occur in the AlGaInN film. However, if a layer of material having a thermal expansion coefficient greater than the thermal expansion coefficient of these two materials is inserted between the substrate and the AlGaInN film, this insertion layer tends to shrink the substrate, ie, the substrate Since the apparent thermal expansion coefficient is increased to approach that of the AlGaInN film, the tensile force applied to the AlGaInN film is relaxed, and cracking of the AlGaInN film is prevented. Therefore, this insertion layer is called a stress relaxation layer.
[0014]
A material suitable for the stress relaxation layer must also have a low lattice mismatch rate. Table 1 lists these materials. Table 1 shows the coefficient of thermal expansion of the material suitable for the stress relaxation layer and the lattice mismatch ratio for the GaN crystal.
[0015]
[Table 1]

However, since all of these stress relaxation layer materials are oxides, there is a concern about oxidation of Si and SiC surfaces during film formation. If the substrate surface is oxidized, in many cases, an amorphous layer is formed at the interface between the substrate and the oxide material, and the crystallinity of the film formed thereon deteriorates. For this reason, Al _x Ga _y In _1-xy N is formed extremely thin (about 10 nm) as an antioxidant layer T for suppressing oxidation on the substrate, and a stress relaxation layer S is formed thereon. Finally, a multilayer AlGaInN layer Nt for a target semiconductor device, such as a double hetero structure or a quantum well structure made of Al _x Ga _y In _1-xy N, is formed. As a film formation method, molecular beam epitaxy (MBE) or metal organic vapor phase epitaxy can be applied.
Example 1
First, a ZnO layer having a thickness of 100 nm was directly formed on a (1,1,1) plane substrate of a Si single crystal. As sputtering conditions, the substrate temperature was 250 ° C., the sputtering gas was Ar, and the pressure was 1 Pa. A ZnO sintered body added with 2 wt% Al was used as the target. The addition of Al is for imparting conductivity to the stress relaxation layer.
[0016]
It was confirmed from the X-ray diffraction pattern that the obtained ZnO film was c-axis oriented. Fig. 2 shows a reflection high-energy electron diffraction (RHEED) image of a ZnO film directly formed on a Si substrate. (A) is a pattern diagram when the electron beam incidence is in the (1, -1,1) direction. (B) is a diagram of a pattern when the electron beam incidence is in the (1,0,0) direction and is rotated by 30 ° in the c plane with respect to (a). From FIG. 2, the single crystal pattern (only the high brightness (large white point) in (b)) and the low brightness (light white point) pattern) are shifted and overlapped, and therefore, within the c-plane of the ZnO film. It was found that the film was a polycrystalline film in which the direction of the a-axis was rotated.
[0017]
FIG. 3 is a diagram showing the results of elemental analysis in the depth direction by Auger electron spectroscopy of a ZnO film directly formed on a Si substrate. A large amount of oxygen is also detected in the region of the Si substrate, indicating that the surface of the Si substrate is oxidized. For this reason, it can be assumed that the polycrystallization of ZnO is caused by the oxidation of the Si surface when forming ZnO.
This on the ZnO film, and the _{Al x Ga y In 1-xy} N film multilayer is formed by molecular beam epitaxy using nitrogen radical (MBE). The layer structure is a double heterostructure consisting of a first buffer layer of AlN, a second buffer layer of GaN, a clad layer of n-type AlGaN, an active layer of GaN, and a clad layer of p-type AlGaN. Was not observed, and the effect of the stress relaxation layer of ZnO was confirmed.
[0018]
In order to suppress oxidation of the surface of the Si substrate, an n-type GaN film having a thickness of 10 nm was formed on the Si substrate as an antioxidant layer. A ZnO stress relaxation layer was formed to 100 nm thereon. FIG. 4 is a diagram showing the results of elemental analysis in the depth direction by Auger electron spectroscopy of a ZnO film having a GaN film formed on a Si substrate. Compared with FIG. 3, it can be confirmed from FIG. 4 that the GaN film prevents oxidation of Si.
[0019]
Fig. 5 shows the RHEED image of the ZnO film formed on the GaN film on the Si substrate. (A) is a pattern diagram when the electron beam incidence is in the (1, -1,1) direction. It is a figure of a pattern in case an electron beam incidence is (1,0,0) direction (rotated 30 degrees in c plane with respect to (a)). Unlike the case where the antioxidant layer is not formed (FIG. 2), the pattern does not have a double structure, and rotation of the a-axis in the c-plane of ZnO is not observed. From this, it was found that by introducing a GaN layer to suppress oxidation, oxidation of the Si substrate was suppressed and ZnO was epitaxially grown (single crystal growth).
[0020]
This on the ZnO film, to form a double heterostructure multilayered _{Al x Ga y In 1-xy} N having the same layer structure as described above, further form a cap layer. 6 is a diagram showing a state of a crystal by electron microscopy of _{Al x Ga y In 1-xy} N film on bilayer GaN film, ZnO film on the Si substrate. From the figure, it can be seen that the surface is smooth and no cracks have occurred. By using the AlGaInN film in this state, a group III nitride semiconductor device such as a photodiode that does not require a particularly fine structure is established.
[0021]
A laser diode was fabricated as an example of a group III nitride semiconductor device having a layer structure including the above-described double heterostructure. FIG. 7 is a sectional view taken along a plane perpendicular to the cleavage plane of the laser diode according to the present invention. The substrate 1 is a (1,1,1) plane Si, and an antioxidant layer 11 and a stress relaxation layer 12 are sequentially laminated. A first buffer layer 2 of AlN having a thickness of 50 nm is formed, and a second buffer layer of GaN having a thickness of 0.5 μm, a clad layer 4 of n-type AlGaN having a thickness of 150 nm, and a GaN having a thickness of 50 nm are formed thereon. A double heterostructure comprising an active layer 5 and a 150 nm thick p-type AlGaN cladding layer 6 is formed, and a 100 nm thick p-type GaN cap layer 7 is further formed. The electrode 8a of the substrate 1 is Al, and the electrode 9 of the cap layer 7 is Au / Cr.
[0022]
By cleaving the Si substrate 1, the (1, -1,0,0) plane of the group III nitride semiconductor layer becomes a cleavage plane, and an optical resonator can be formed. By applying a pulse current to the laser diode, laser oscillation was possible at a current density of about 10 kA / cm ² or more.
In addition, Ga _1-x Al _x N (0 <x ≦ 1) was also carried out as the anti-oxidation layer, but it also has an anti-oxidation effect, the stress relaxation layer is a single crystal, and the group III nitride semiconductor layer Successfully formed a film.
Example 2
A (1,1,1) plane of Si single crystal was used as the substrate, and sapphire (α-Al ₂ O ₃ ) formed by magnetron sputtering was used for the stress relaxation layer. The substrate temperature was 500 ° C., the target was an Al ₂ O ₃ sintered body, Ar was used as the sputtering gas, the pressure was 1 Pa, and the film thickness was 120 nm.
[0023]
In the case of the sapphire stress relaxation layer, as in the case of the ZnO stress relaxation layer, when there is no anti-oxidation layer, it grows in the c-axis orientation on the Si (1,1,1) substrate, but the a in the c-plane. Axial rotation was seen. However, by introducing the antioxidant layer, both sapphire and the double heterostructure formed thereon were epitaxially grown, and no cracks were observed.
Example 3
The substrate was a (1,1,1) plane of Si single crystal, and magnesia (MgO) formed by magnetron sputtering was used for the stress relaxation layer. The substrate temperature was 400 ° C., the target was a MgO sintered body, the sputtering gas was Ar, the pressure was 1 Pa, and the film thickness was 100 nm. In the case of MgO as well, in the absence of an antioxidant layer, rotation in the a-axis direction within the c-plane was observed although it was in the c-axis orientation on the Si (1,1,1) substrate. However, by introducing the antioxidant layer, both MgO and the double heterostructure formed thereon were epitaxially grown, and no cracks were observed.
Example 4
The substrate was a (1,1,1) surface of Si single crystal, and spinel (MgAl ₂ O ₄ ) formed by magnetron sputtering was used for the stress relaxation layer. The substrate temperature was 600 ° C., the target was an MgAl ₂ O ₄ sintered body, the sputtering gas was Ar, the pressure was 1 Pa, and the film thickness was 120 nm. Also in the case of spinel, when there was no antioxidant layer, rotation in the a-axis direction in the c-plane was observed although it was c-axis orientation on the Si (1,1,1) substrate. However, by introducing the antioxidant layer, both the spinel and the double heterostructure formed thereon were epitaxially grown, and no cracks were observed.
Example 5
The substrate was a (1,1,1) plane of Si single crystal, and neodygallate (NdGaO ₃ ) formed by magnetron sputtering was used for the stress relaxation layer. The substrate temperature was 700 ° C., the target was NdGaO ₃ sintered body, Ar was used as the sputtering gas, the pressure was 1 Pa, and the film thickness was 120 nm. Also in the case of neodigalate, when there was no antioxidant layer, rotation in the a-axis direction in the c-plane was observed although it was c-axis orientation on the Si (1,1,1) substrate. However, by introducing the antioxidant layer, both neodigallate and the double heterostructure formed thereon were epitaxially grown, and no cracks were observed.
Example 6
In addition, using a 6H-SiC substrate, an experiment was conducted using ZnO as a stress relaxation layer and a GaN antioxidant layer in the same manner as in Example 1. However, as in Example 1, the effects of the stress relaxation layer and the antioxidant layer were evaluated. Was confirmed.
[0024]
【The invention's effect】
According to the present invention, Al _x Ga _y In _1-xy N (0 ≦ x, y and 0 ≦ x + y ≦ 1) is formed on a substrate made of a crystal having a thermal expansion coefficient smaller than that of the crystal. and Al _x Ga _y in group III nitride semiconductor device comprising an in _1-xy N layer, the substrate material and Al _x Ga _y in _1-xy between the substrate and _{Al x Ga y in 1-xy} N layer The stress generated in Al _x Ga _y In _1-xy N is relaxed by interposing a stress relaxation layer made of a material having a thermal expansion coefficient larger than that of the N crystal, so that the thermal expansion coefficient is Al _x Ga _y In _{1 -xy} N no cracks in the III-nitride semiconductor device small having a multilayer film composed of _{Al x Ga y in 1-xy} N on a substrate from the film, also individualized by utilizing the cleavage property can be easy.
[0025]
Further, an anti-oxidation layer composed of Al _x Ga _y In _1-xy N (0 ≦ x, y and 0 ≦ x + y ≦ 1) is interposed between the stress relaxation layer and the substrate, and the stress relaxation layer and its since the deterioration of crystallinity of the _{Al x Ga y in 1-xy} N film formed on the to prevent, to form a light-emitting diode or laser diode of fine layer structure.
[Brief description of the drawings]
FIG. 1 is a sectional view of a layer structure of a group III nitride semiconductor device according to the present invention. FIG. 2 shows a reflection high-energy electron diffraction (RHEED) image of a ZnO film formed directly on a Si substrate. Is a photograph of the crystal structure when the electron beam incidence is in the (1, -1,1) direction. (B) is the case where the electron beam incidence is in the (1, 0, 0) direction. Fig. 3 shows the result of elemental analysis in the depth direction by Auger electron spectroscopy of the ZnO film directly formed on the Si substrate. Fig. 4 shows the result of elemental analysis in the depth direction. Fig. 5 shows the results of elemental analysis in the depth direction by Auger electron spectroscopy of a ZnO film formed with a GaN film. Fig. 5 Reflected high-energy electron diffraction (RHEED) of a ZnO film formed on a GaN film on a Si substrate. (A) is a photograph of the crystal structure when the electron beam is incident in the (1, -1,1) direction, and (b) is the ((a) where the electron beam is incident in the (1, 0, 0) direction. (When rotated 30 ° in the c plane) Crystal structure Photo 6 Si GaN film on a substrate, micrograph Figure 7] present invention showing the state of the crystal by electron microscopy of _{Al x Ga y In 1-xy} N film on bilayer ZnO film FIG. 8 is a cross-sectional view of a laser diode according to the present invention perpendicular to the cleavage plane. FIG. 8 is a cross-sectional view of a laser diode which is an example of a conventional group III nitride semiconductor device. FIG. 9 is formed directly on a Si crystal substrate. Scanning electron microscope observation of the surface of the Al _x Ga _y In _1-xy N film
DESCRIPTION OF SYMBOLS 1 Substrate 2 Buffer layer 2a First buffer layer 2b Second buffer layer 3 Contact layer 4 Cladding layer 5 Active layer 6 Cladding layer 7 Cap layer 8 First electrode layer 8a First electrode layer 9 Second electrode layer S Stress relaxation layer T Antioxidation layer Nt AlGaInN layer

Claims (4)

_{Al x Ga y In 1-x} -y N (0 ≦ x, y and 0 ≦ x + y ≦ 1) having a small thermal expansion coefficient than the thermal expansion coefficient of the crystal, which is formed on the Si crystal or Ranaru substrate Al _{x Ga y in 1-x-} y in group III nitride semiconductor device including an N layer, said substrate and said _{Al x Ga y in 1-x-} y substrate material and _Al between the N layer x _Ga y in ₁ the stress relaxation layer composed of a material having a larger thermal expansion coefficient than the thermal expansion coefficient of the _-x-y N crystal interposed _{therebetween,} as well as relieving the stress generated in the _{Al x Ga y in 1-x} -y N, the stress relaxation An anti-oxidation layer made of Al _x Ga _y In _1-xy N (0 ≦ x, y and 0 ≦ x + y ≦ 1) is interposed between the layer and the substrate, and is formed on the stress relaxation layer. is the _{Al x Ga y in 1-x} -y N film crystallinity of Group III nitride semiconductor device characterized by preventing reduction. The stress relaxation layer is made of at least one of zinc oxide (ZnO), magnesium oxide (MgO), sapphire (α-Al ₂ O ₃ ), spinel (MgAl ₂ O ₄ ), or neodymium gallate (NdGaO ₃ ). The group III nitride semiconductor device according to claim 1. 3. The group III nitride semiconductor device according to claim 1, wherein an electrode is provided on a side of the substrate opposite to the side on which the antioxidant layer is formed and connected to the substrate. 4. 4. The group III nitride semiconductor device according to claim 1, wherein the group III nitride semiconductor device is a light emitting diode or a laser diode.

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