JP4786481B2 - Semiconductor device and manufacturing method of semiconductor device - Google Patents
Semiconductor device and manufacturing method of semiconductor device Download PDFInfo
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本発明は導体装置と半導体装置の製造法に関する。 The present invention relates to a conductor device and a method for manufacturing a semiconductor device.
窒化物半導体は、Ａｌ、Ｇａ、Ｉｎ等のIII族元素のうち少なくとも一つ以上の元素と、Ｖ族元素である窒素との化合物であり、例えば、一般式Ａｌ１−ａ−ｂＧａａＩｎｂＮで表される。窒化物半導体は、直接遷移型であり、その組成により最大６．２ｅＶから０．８ｅＶまでの幅広い禁止帯幅を有する。また、広い禁止帯幅を有する組成においては、熱的安定性、絶縁破壊電界、飽和電子速度が大きい。以上の特性から、窒化物半導体を用いて、遠赤外から紫外領域での受光・発光デバイス、および、耐高温・高出力・高周波トランジスタ等の電子デバイスヘの応用が期待され、開発が進められている。 A nitride semiconductor is a compound of at least one element among group III elements such as Al, Ga, and In and nitrogen that is a group V element. For example, the nitride semiconductor has a general formula of Al 1-ab Ga a In. b Represented by N. Nitride semiconductors are of direct transition type and have a wide band gap from a maximum of 6.2 eV to 0.8 eV depending on the composition. In addition, a composition having a wide band gap has a large thermal stability, breakdown electric field, and saturation electron velocity. The above characteristics are expected to be applied to light-receiving / light-emitting devices in the far-infrared to ultraviolet region and electronic devices such as high-temperature / high-power / high-frequency transistors using nitride semiconductors. Yes.
例えば、発光デバイスとして、紫外・深紫外発光ダイオード（ＬＥＤ）のさらなる短波長化が様々な研究機関において検討されている（下記非特許文献１参照）。紫外・深紫外ＬＥＤの実用化のためには、発光効率の向上が必要である。
For example, as a light emitting device, further shortening of the wavelength of an ultraviolet / deep ultraviolet light emitting diode (LED) has been studied by various research institutions (see Non-Patent
上記で述べた紫外ＬＥＤ用のエピ構造（エピタキシャル構造）を図１１に示す。この構造は従来構造の一例であるが、ＡｌｆＧａ１−ｆＮ/ＡｌｇＧａ１−ｇＮ超格子層を活性層として有し、ｐ型ＡｌｈＧａ１−ｈＮ層とｎ型ＡｌｅＧａ１−ｅＮ層をその上下に有していること、結晶方位はｃ軸が上方向になっていることは他の例でも同様である。 The epi structure (epitaxial structure) for the ultraviolet LED described above is shown in FIG. This structure is an example of a conventional structure, but has an Al f Ga 1-f N / Al g Ga 1-g N superlattice layer as an active layer, a p-type Al h Ga 1-h N layer, and an n-type Al to have e Ga 1-e N layer above and below, the crystal orientation is also true in other examples that is in the upward direction c axis.
この時、活性層であるＡｌｆＧａ１−ｆＮ/ＡｌｇＧａ１−ｇＮ超格子層のバンドダイアグラムは図１２のようになる。窒化物半導体のヘテロ構造では、自発分極とピエゾ分極がｃ軸方向に発生するため、内部電界が生じる。この内部電界により、価電子帯と伝導帯は図１２に示したように傾く。そのため、ＡｌｆＧａ１−ｆＮ/ＡｌｇＧａ１−ｇＮ超格子層にキャリアが送り込まれた場合、電子はＡｌｇＧａ１−ｇＮ井戸層の伝導帯の表面側に局在し、正孔はＡｌｇＧａ１−ｇＮ井戸層の価電子帯の表面側に局在する。この空間的な分離のために、電子と正孔の再結合が生じにくくなるために、発光効率はバンドが傾いていない構造と比較し低下する。ＡｌｆＧａ１−ｆＮ障壁層とＡｌｇＧａ１−ｇＮ井戸層のＡｌ組成を近づければ、自発分極とピエゾ分極は滅少するのでバンドの傾きは小さくなる。しかし、この場合、障壁層の高さも小さくなるために、井戸層でのキャリア閉じ込めが弱くなり、この場合も発光効率が低下する。 At this time, the band diagram of the Al f Ga 1-f N / Al g Ga 1-g N superlattice layer as the active layer is as shown in FIG. In a nitride semiconductor heterostructure, spontaneous polarization and piezoelectric polarization occur in the c-axis direction, and an internal electric field is generated. Due to this internal electric field, the valence band and the conduction band are inclined as shown in FIG. Therefore, when carriers are sent into the Al f Ga 1-f N / Al g Ga 1-g N superlattice layer, the electrons are localized on the surface side of the conduction band of the Al g Ga 1-g N well layer, Holes are localized on the surface side of the valence band of the Al g Ga 1-g N well layer. Due to this spatial separation, recombination of electrons and holes is less likely to occur, so that the luminous efficiency is reduced as compared with a structure in which the band is not inclined. If the Al compositions of the Al f Ga 1-f N barrier layer and the Al g Ga 1-g N well layer are brought close to each other, the spontaneous polarization and the piezo polarization are reduced, and the slope of the band is reduced. However, in this case, since the height of the barrier layer is also reduced, carrier confinement in the well layer becomes weak, and in this case also, the light emission efficiency is lowered.
また、ａ面等の無極性面方向に紫外ＬＥＤ用のエピ構造を積層する構造も開発されている。しかし、無極性方向への窒化物半導体の成長は困難であり、転位、点欠陥、不純物等の欠陥密度は、ｃ軸方向への成長時と比べ、１桁から３桁ほど多いのが現状である。これらの高密度の欠陥は、非発光再結合中心となるので、平坦なバンドダイアグラムは得られるものの、発光効率はｃ軸方向成長の場合と比べ低い。 A structure in which an epi structure for an ultraviolet LED is laminated in a nonpolar plane direction such as a-plane has been developed. However, it is difficult to grow nitride semiconductors in the nonpolar direction, and the density of defects such as dislocations, point defects, and impurities is about one to three digits higher than that in the c-axis direction. is there. Since these high-density defects become non-radiative recombination centers, a flat band diagram can be obtained, but the luminous efficiency is lower than that in the case of growth in the c-axis direction.
以上のように、紫外ＬＥＤに用いられるＡｌＧａＮ層からなる従来構造においては、ｃ軸方向では分極効果により、バンドが傾斜する傾向の影響で発光効率が低い。ａ面等の無極性面に沿ったＡｌＧａＮ層の結晶品質は、ｃ軸方向へのＡｌＧａＮ層と比べ、大幅に低く、発光効率が低い。そのため、実用化に必要な強い輝度を有する紫外ＬＥＤは現在得られていないのが現状である。
上述のように、紫外ＬＥＤでは、分極効果による井戸層内での電子と正孔の空間分離のため、発光効率が低く、実用化に必要な強い輝度が得られていないという課題がある。 As described above, the ultraviolet LED has a problem that the luminous efficiency is low due to the spatial separation of electrons and holes in the well layer due to the polarization effect, and the strong luminance necessary for practical use is not obtained.
本発明は、上記課題に鑑みてなされたものであり、本発明が解決しようとする課題は、超格子層における電子と正孔の空間分離を抑制することを可能とする半導体装置と半導体装置の製造法を提供することである。 The present invention has been made in view of the above problems, and the problem to be solved by the present invention is a semiconductor device and a semiconductor device capable of suppressing the space separation of electrons and holes in the superlattice layer. It is to provide a manufacturing method.
上記課題を解決するために、本発明においては、請求項１に記載したように、
超格子層を有する半導体装置において、前記超格子層の障壁層が、０．６４≦ｘ≦１．０としたときに、Ｉｎ １−ｘ Ａｌ ｘ Ｎで表される窒化物半導体であり、前記超格子層の井戸層が、０≦ｙ≦０．９６としたときに、Ａｌ ｙ Ｇａ １−ｙ Ｎで表される窒化物半導体であり、かつ、前記障壁層のＡｌ組成が、前記井戸層のＡｌ組成に対してピエゾ分極電界の差が 0.005C/m２ 以下となる組成であることを特徴とする半導体装置を構成する。
In order to solve the above problems, in the present invention, as described in
In the semiconductor device having a superlattice layer, the barrier layer of the superlattice layer is a nitride semiconductor represented by In 1-x Al x N when 0.64 ≦ x ≦ 1.0 , When the well layer of the superlattice layer is 0 ≦ y ≦ 0.96, it is a nitride semiconductor represented by Al y Ga 1-y N, and the Al composition of the barrier layer is the well layer difference piezoelectric polarization field in the semiconductor device, characterized in that the composition to be 0.005 C / m 2 or less with respect to the Al content.
また、本発明においては、請求項２に記載したように、
前記超格子層が紫外発光ダイオードの活性層であることを特徴とする請求項１記載の半導体装置を構成する。
In the present invention, as described in
The superlattice layer constituting a semiconductor device according to claim 1 Symbol mounting, characterized in that the active layer of the ultraviolet light-emitting diode.
また、本発明においては、請求項３に記載したように、
前記超格子層がｎ型半導体層とｐ型半導体層との間に挟まれ、前記ｎ型半導体層の組成が、０≦ａ≦１、０≦ｂ≦１、０≦ａ＋ｂ≦１としたときに、Ａｌ１−ａ−ｂＧａａＩｎｂＮで表され、前記ｐ型半導体層の組成が、０≦ｃ≦１、０≦ｄ≦１、０≦ｃ＋ｄ≦１としたときに、Ａｌ１−ｃ−ｄＧａｃＩｎｄＮで表されることを特徴とする請求項１または２記載の半導体装置を構成する。
In the present invention, as described in claim 3 ,
When the superlattice layer is sandwiched between an n-type semiconductor layer and a p-type semiconductor layer, and the composition of the n-type semiconductor layer is 0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1 in, represented by Al 1-a-b Ga a in b N, when the composition of the p-type semiconductor layer, which is a 0 ≦ c ≦ 1,0 ≦ d ≦ 1,0 ≦ c + d ≦ 1,
また、本発明においては、請求項４に記載したように、
半導体装置の製造法において、障壁層の組成が、０．６４≦ｘ≦１．０としたときに、Ｉｎ １−ｘ Ａｌ ｘ Ｎで表され、井戸層の組成が、０≦ｙ≦０．９６としたときに、ＡｌｙＧａ１−ｙＮで表され、かつ前記障壁層のＡｌ組成が、前記井戸層のＡｌ組成に対してピエゾ分極電界の差が 0.005C/m ２ 以下となる組成である超格子層を形成する工程を有することを特徴とする半導体装置の製造法を構成する。
In the present invention, as described in claim 4 ,
In the method of manufacturing a semiconductor device, when the composition of the barrier layer is 0.64 ≦ x ≦ 1.0 , it is represented by In 1-x Al x N , and the composition of the well layer is 0 ≦ y ≦ 0. when the 96 is represented by Al y Ga 1-y N, and Al composition of the barrier layer, the difference in piezoelectric polarization field is 0.005 C / m 2 or less with respect to the Al composition of the well layer composition constituting a method for producing a semiconductor device characterized by comprising the step of forming a der Ru superlattice layer.
本発明の特徴は、超格子層を有する半導体装置において、前記超格子層の障壁層の組成と井戸層の組成とが相異なり、前記障壁層がＡｌ又はＩｎを含む窒化物半導体であり、前記井戸層がＡｌ又はＧａを含む窒化物半導体であることにあり、それによって、超格子層における電子と正孔の空間分離を抑制することを可能とする半導体装置と半導体装置の製造法を提供することができる。 A feature of the present invention is that in a semiconductor device having a superlattice layer, the composition of the barrier layer of the superlattice layer is different from the composition of the well layer, and the barrier layer is a nitride semiconductor containing Al or In, Provided is a semiconductor device and a method for manufacturing the semiconductor device, in which the well layer is a nitride semiconductor containing Al or Ga, thereby enabling to suppress spatial separation of electrons and holes in the superlattice layer. be able to.
本発明を紫外発光ダイード（ＬＥＤ）に適用すれば、活性層である超格子層における電子と正孔の空間分離を抑制することが可能となり、その結果として、ＬＥＤの輝度が向上する。 When the present invention is applied to an ultraviolet light emitting diode (LED), it is possible to suppress the space separation of electrons and holes in the superlattice layer which is an active layer, and as a result, the brightness of the LED is improved.
上記の課題を解決するために、本発明では、エピ構造（エピタキシャル構造）として、障壁層の組成と井戸層の組成とが相異なり、障壁層がＡｌ又はＩｎを含む窒化物半導体であり、井戸層がＡｌ又はＧａを含む窒化物半導体である超格子構造を構成するという手段をとっている。 In order to solve the above problems, in the present invention, as an epi structure (epitaxial structure), the composition of the barrier layer and the composition of the well layer are different, the barrier layer is a nitride semiconductor containing Al or In, and the well A measure is taken to form a superlattice structure in which the layer is a nitride semiconductor containing Al or Ga.
本発明によれば、結晶品質の制御が比較的容易なｃ軸方向への成長を行いつつ、活性層内のピエゾ分極と自発分極により発生する内部電界を従来構造に比べ抑制することが可能である。その結果として、紫外ＬＥＤにおける発光効率の向上が可能である。 According to the present invention, it is possible to suppress the internal electric field generated by piezo polarization and spontaneous polarization in the active layer as compared with the conventional structure, while performing growth in the c-axis direction in which the control of crystal quality is relatively easy. is there. As a result, the luminous efficiency of the ultraviolet LED can be improved.
以下の説明においては、本発明に係る半導体装置の超格子層が紫外ＬＥＤにおける活性層である場合について説明するが、本発明は、これに限られるものではない。 In the following description, the case where the superlattice layer of the semiconductor device according to the present invention is an active layer in an ultraviolet LED will be described, but the present invention is not limited to this.
図１は、Ａｌ０．５８Ｇａ０．４２Ｎを井戸層として、障壁層にＩｎＡｌＮ層とＡｌＧａＮ層とを用いた場合の、バンド不連続量と分極電界の関係を比較して示したグラフである。同じバンド不連続量であれば、ＩｎＡｌＮ障壁層はＡｌＧａＮ障壁層よりも分極電界が小さい。同じバンド不連続量であれば、分極が小さい方が発光効率は高く、本発明のＩｎＡｌＮ/ＡｌＧａＮ超格子はＡｌＧａＮ/ＡｌＧａＮ超格子よりも発光効率が高いことが期待できる。なお、図中の点線で示した、バンド不連続量 0.05eV(分極電界 -0.003C/m２)以上、バンド不連続量 0.25eV(分極電界 0.005C/m２)以下の範囲が望ましい。 FIG. 1 is a graph showing a comparison between the relationship between the band discontinuity and the polarization electric field when Al 0.58 Ga 0.42 N is used as a well layer and an InAlN layer and an AlGaN layer are used as a barrier layer. is there. For the same band discontinuity, the InAlN barrier layer has a smaller polarization electric field than the AlGaN barrier layer. If the band discontinuity is the same, the light emission efficiency is higher when the polarization is smaller, and the InAlN / AlGaN superlattice of the present invention can be expected to have higher light emission efficiency than the AlGaN / AlGaN superlattice. In addition, the range of the band discontinuity 0.05 eV (polarization electric field −0.003 C / m 2 ) or more and the band discontinuity 0.25 eV (polarization electric field 0.005 C / m 2 ) or less shown by the dotted line in the figure is desirable.
なお、図１においては、一例としてＡｌ０．５８Ｇａ０．４２Ｎ井戸層の場合を示したが、ＡｌＧａＮ井戸層のＡｌ組成に対しＩｎＡｌＮ障壁層のバンドギャッブが高い図２に示した点線より上の範囲において、本発明は有効である。なお、バンド不連続量 0.05eV(分極電界 -0.003C/m２)以上、バンド不連続量 0.25eV(分極電界 0.005C/m２)以下となる、図２において塗りつぶした範囲が望ましい。 In FIG. 1, the Al 0.58 Ga 0.42 N well layer is shown as an example, but the band gap of the InAlN barrier layer is higher than the dotted line shown in FIG. 2 with respect to the Al composition of the AlGaN well layer. In this range, the present invention is effective. The range shown in FIG. 2 is preferably a band discontinuity of 0.05 eV (polarization electric field −0.003 C / m 2 ) or more and a band discontinuity of 0.25 eV (polarization electric field 0.005 C / m 2 ) or less.
なお、分極電界は、上記非特許文献２に記載の物性定数を基に算出を行った。
The polarization electric field was calculated based on the physical constants described in
上述の量子井戸構造において、井戸層の膜厚が １.5nm、障壁層の膜厚が 1.5nm以上の時に、分極電界による電子と正孔の空間分離が観測される。また、井戸層の膜厚が 10nm 以下の時に量子効果がみられる。したがって、本発明においては、井戸層の膜厚が 1.5nm 以上 10nm 以下の範囲で有効である。また、障壁層の上限の厚さは、井戸層と障壁層の格子定数が異なること（格子不整合）により制限される。この格子不整を有する結晶においては、結晶の膜厚の増加に伴い結晶内に発生する歪が増加して、膜厚が臨界膜厚を超えると結晶に欠陥や転位が導入され、結晶の品質が劣化する。 In the above quantum well structure, when the thickness of the well layer is 1.5 nm and the thickness of the barrier layer is 1.5 nm or more, spatial separation of electrons and holes due to the polarization electric field is observed. In addition, the quantum effect is observed when the well layer thickness is 10 nm or less. Therefore, the present invention is effective when the thickness of the well layer is in the range of 1.5 nm to 10 nm. The upper limit thickness of the barrier layer is limited by the difference in lattice constant between the well layer and the barrier layer (lattice mismatch). In a crystal having this lattice irregularity, the strain generated in the crystal increases as the crystal film thickness increases. When the film thickness exceeds the critical film thickness, defects and dislocations are introduced into the crystal, and the crystal quality is improved. to degrade.
図３に、井戸層にＡｌＧａ(Ｉｎ)Ｎ、障壁層にＩｎＡｌ(Ｇａ)Ｎを用いた場合の臨界膜厚の格子不整依存性を示す。ここで、(Ｉｎ)、(Ｇａ)は、それぞれ、Ｉｎ、Ｇａが含まれていない場合があることを示す。格子不整は井戸層、障壁層の組成によって決まる。例えば、上述の図２における本発明の適用領域（塗りつぶし領域）において、井戸層ＡｌＧａＮのＡｌ組成が 0.0(すなわちＧａＮ）かつ障壁層ＩｎＡｌＮのＡｌ組成が 0.64 の時が格子不整 +2.4% に相当し、この適用領域において最大の格子不整となる。図３より、格子不整 +2.4% の時の膜厚が 5nm であることから、井戸層ＡｌＧａＮのＡｌ組成が 0.0(すなわちＧａＮ）かつ障壁層ＩｎＡｌＮのＡｌ組成が 0.64 の時の障壁層厚の上限は 5nm であることがわかる。また、この領域において、井戸層ＡｌＧａＮのＡｌ組成が 0.96 かつ障壁層ＩｎＡｌＮのＡｌ組成が 1.0 の時に格子不整が -0.1% になり、通常量子井戸構造の障壁層に用いられる膜厚が 100nm 以下であることを考慮すれば、井戸層ＡｌＧａＮのＡｌ組成が 0.96 かつ障壁層ＩｎＡｌＮのＡｌ組成が 1.0 の時に格子不整による障壁層の膜厚の制限はほぼなくなることがわかる。 FIG. 3 shows the lattice mismatch dependence of critical film thickness when AlGa (In) N is used for the well layer and InAl (Ga) N is used for the barrier layer. Here, (In) and (Ga) indicate that In and Ga may not be included, respectively. The lattice irregularity is determined by the composition of the well layer and the barrier layer. For example, in the application area (filled area) of the present invention in FIG. 2 described above, when the Al composition of the well layer AlGaN is 0.0 (that is, GaN) and the Al composition of the barrier layer InAlN is 0.64, this corresponds to the lattice irregularity + 2.4%. In this application area, the maximum lattice irregularity is obtained. Figure 3 shows that the upper limit of the barrier layer thickness when the Al composition of the well layer AlGaN is 0.0 (ie, GaN) and the Al composition of the barrier layer InAlN is 0.64 because the film thickness when the lattice irregularity is + 2.4% is 5 nm. It can be seen that is 5nm. In this region, when the Al composition of the well layer AlGaN is 0.96 and the Al composition of the barrier layer InAlN is 1.0, the lattice irregularity is -0.1%, and the film thickness normally used for the barrier layer of the quantum well structure is 100 nm or less. Considering that, when the Al composition of the well layer AlGaN is 0.96 and the Al composition of the barrier layer InAlN is 1.0, it is understood that there is almost no restriction on the thickness of the barrier layer due to lattice mismatch.
図４に、一例として、従来構造での紫外ＬＥＤの活性層の構造を示す。図において、Ａｌ０．６５Ｇａ０．３５Ｎ障壁層とＡｌ０．５８Ｇａ０．４２Ｎ井戸層の超格子構造となっている。堆積方向はｃ軸を向く結晶方位となっている。Ａｌ０．６５Ｇａ０．３５Ｎの禁止帯幅はおよそ 5.17eV であり、Ａｌ０．５８Ｇａ０．４２Ｎの禁止帯幅はおよそ 4.97eV であり、バンド不連続量はおよそ 0.2eV である。この時、障壁層と井戸層の分極電界の差はおよそ 0.007C/m２である。 As an example, FIG. 4 shows a structure of an active layer of an ultraviolet LED having a conventional structure. In the figure, an Al 0.65 Ga 0.35 N barrier layer and an Al 0.58 Ga 0.42 N well layer have a superlattice structure. The deposition direction is a crystal orientation that faces the c-axis. The band gap of Al 0.65 Ga 0.35 N is about 5.17 eV, the band gap of Al 0.58 Ga 0.42 N is about 4.97 eV, and the band discontinuity is about 0.2 eV. . At this time, the difference in polarization electric field between the barrier layer and the well layer is approximately 0.007 C / m 2 .
図５に、一例として、本発明構造での紫外ＬＥＤの活性層の構造を示す。図において、Ｉｎ０．１３Ａｌ０．８７Ｎ障壁層とＡｌ０．５８Ｇａ０．４２Ｎ井戸層の超格子構造という形態をとっている。堆積方向がｃ軸を向く結晶方位となっている。本実施の形態例におけるＩｎ０．１３Ａｌ０．８７Ｎの禁止帯幅はおよそ 5.20eV であり、Ａｌ０．５８Ｇａ０．４２Ｎの禁止帯幅はおよそ 4.97eV であり、バンド不連続量はおよそ 0.23eV である。この時、障壁層と井戸層の分極電界の差は 0.004C/m２ である。超格子のバンド不連続量が大きく、分極電界の差が小さいほど発光効率は向上する。本発明構造は、図４で示した従来構造に比べ超格子のバンド不連続量が大きく、分極電界の差が小さいため、従来構造に比べて発光効率を向上させられることが分かる。 FIG. 5 shows, as an example, the structure of the active layer of the ultraviolet LED in the structure of the present invention. In the figure, a superlattice structure of an In 0.13 Al 0.87 N barrier layer and an Al 0.58 Ga 0.42 N well layer is employed . The crystal orientation is such that the deposition direction faces the c-axis. In this embodiment, In 0.13 Al 0.87 N has a forbidden band width of about 5.20 eV, and Al 0.58 Ga 0.42 N has a forbidden band width of about 4.97 eV. Is about 0.23eV. At this time, the difference in polarization electric field between the barrier layer and the well layer is 0.004 C / m 2 . Luminous efficiency improves as the band discontinuity of the superlattice increases and the difference in polarization electric field decreases. It can be seen that the structure of the present invention has a larger band discontinuity of the superlattice and a smaller difference in polarization electric field than the conventional structure shown in FIG.
なお、図５に示した構造は、あくまでも本発明における実施の形態の一例である。ＩｎｘＡｌ１−ｘＮ層とＡｌｙＧａ１−ｙＮ層の各組成を変えても、それは、図２に示した範囲においては、本発明の効果が現れることに何ら影響を与えるものではない。また、ＩｎｘＡｌ１−ｘＮ層とＡｌｙＧａ１−ｙＮ層の各膜厚を変えても、それは、本発明の効果が現れることに何ら影響を与えるものではない。 Note that the structure shown in FIG. 5 is merely an example of an embodiment of the present invention. Even if each composition of the In x Al 1-x N layer and the Al y Ga 1-y N layer is changed, this does not affect the effect of the present invention in the range shown in FIG. Absent. Moreover, even if the film thicknesses of the In x Al 1-x N layer and the Al y Ga 1-y N layer are changed, it does not affect the effect of the present invention.
図６の（ａ）と（ｂ）は、各々、従来構造であるＡｌｆＧａ１−ｆＮ/ＡｌｇＧａ１−ｇＮ超格子構造のバンドギャップダイアグラムと、井戸層に蓄積される電子と正孔の分布を示す。図７の（ａ）と（ｂ）は、各々、本発明構造であるＩｎｘＡｌ１−ｘＮ/ＡｌｙＧａ１−ｙＮ超格子構造のバンドギャップダイアグラムと、井戸層に蓄積される電子と正孔の分布を示す。井戸層と障壁層のバンド不連続量が等しいとき、本発明においては分極電界によるバンドの傾きが、従来構造と比較し、抑制されている。そのため、キャリアが注入された時、井戸層での電子と正孔の空間分離が抑制されるため、発光効率を向上させることが可能である。ここで、電子と正孔の空間分離による電子の分布のピークと正孔の分布のピークの位置が層方向において、従来構造においては 4nm 程度離れており、本発明構造においてはほぼ一致する。この電子の分布のピークと正孔の分布のピークの位置は一致するか又は 2nm 以内の範囲内にあれば、本発明の効果が現れる。 FIGS. 6A and 6B show a band gap diagram of the Al f Ga 1-f N / Al g Ga 1-g N superlattice structure, which is a conventional structure, and electrons accumulated in the well layer, respectively. The distribution of holes is shown. FIGS. 7A and 7B show the band gap diagram of the In x Al 1-x N / Al y Ga 1-y N superlattice structure, which is the structure of the present invention, and the electrons accumulated in the well layer, respectively. And the distribution of holes. When the band discontinuities of the well layer and the barrier layer are the same, in the present invention, the band inclination due to the polarization electric field is suppressed as compared with the conventional structure. Therefore, when carriers are injected, space separation of electrons and holes in the well layer is suppressed, so that light emission efficiency can be improved. Here, the positions of the electron distribution peak and the hole distribution peak due to the space separation of electrons and holes are about 4 nm apart in the layer direction in the conventional structure, and are almost the same in the structure of the present invention. If the positions of the electron distribution peak and the hole distribution peak coincide with each other or are within a range of 2 nm or less, the effect of the present invention appears.
図８に、本発明による紫外ＬＥＤのエピ構造を示す。基板の上に、ＡｌＮ核形成層、ｎ型のＡｌ０．８Ｇａ０．２Ｎ層を有し、その上にＩｎ０．１３Ａｌ０．８７Ｎ層とＡｌ０．５８Ｇａ０．４２Ｎ層の超格子層を有し、その上に、ｐ型のＡｌ０．８Ｇａ０．２Ｎ層を有する形態となっている。なお、ｎ型のＡｌ０．８Ｇａ０．２Ｎ層は、一般に、Ａｌ１−ａ−ｂＧａａＩｎｂＮ層（０≦ａ≦１、０≦ｂ≦１、０≦ａ＋ｂ≦１）であり、超格子層は、一般に、ＩｎｘＡｌ１−ｘＮ（０≦ｘ≦１）層とＡｌｙＧａ１−ｙＮ（０≦ｙ≦１）層の超格子層であり、ｐ型のＡｌ０．８Ｇａ０．２Ｎ層は、一般に、Ａｌ１−ｃ−ｄＧａｃＩｎｄＮ層（０≦ｃ≦１、０≦ｄ≦１、０≦ｃ＋ｄ≦１）であってもよい。 FIG. 8 shows an epi structure of an ultraviolet LED according to the present invention. An AlN nucleation layer and an n-type Al 0.8 Ga 0.2 N layer are provided on the substrate, and an In 0.13 Al 0.87 N layer and an Al 0.58 Ga 0.42 N layer are provided thereon. It has a superlattice layer, and a p-type Al 0.8 Ga 0.2 N layer on the superlattice layer. An n-type Al 0.8 Ga 0.2 N layer is generally an Al 1-ab Ga a In b N layer (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1). The superlattice layer is generally a superlattice layer of an In x Al 1-x N (0 ≦ x ≦ 1) layer and an Al y Ga 1-y N (0 ≦ y ≦ 1) layer, and is p-type 's Al 0.8 Ga 0.2 N layer, generally, be a Al 1-c-d Ga c in d N layer (0 ≦ c ≦ 1,0 ≦ d ≦ 1,0 ≦ c + d ≦ 1) Good.
図８に示した構造の作製法の一例を示す。ＭＯＣＶＤ法により、サファイア基板上に、核形成層を堆積した後、Ｓｉを１×１０１８ｃｍ−３ドープしたｎ型のＡｌ０．８Ｇａ０．２Ｎ層を 500nm 成長し、3nm のＡｌ０．５８Ｇａ０．４２Ｎ井戸層と 3nm のＩｎ０．１３Ａｌ０．８７Ｎ障壁層からなる超格子を３周期成長した後に、Ｍｇを１×１０１９ｃｍ−３ドーブしたｐ型のＡｌ０．８Ｇａ０．２Ｎ層を 300nm 成長するという手順をとっている。原料としてはトリメチルアルミニウム、トリメチルガリウムとアンモニアを用いた。500℃から 1200℃の範囲内の成長温度において、上記の成長を行った。 An example of a manufacturing method of the structure shown in FIG. After depositing a nucleation layer on a sapphire substrate by MOCVD, an n-type Al 0.8 Ga 0.2 N layer doped with 1 × 10 18 cm −3 of Si was grown to 500 nm, and 3 nm of Al 0 After growing a superlattice consisting of a .58 Ga 0.42 N well layer and a 3 nm In 0.13 Al 0.87 N barrier layer for 3 periods, p-type Al 0 doped with 1 × 10 19 cm −3 of Mg .8 Ga 0.2 N layer is grown to 300 nm. Trimethylaluminum, trimethylgallium and ammonia were used as raw materials. The above growth was performed at a growth temperature in the range of 500 ° C to 1200 ° C.
なお、基板の種類は、本発明の効果が現れることに何ら影響を与えない。また、基板上にＡｌＧａＮ層を堆積するために、核形成層あるいは緩衝層を用いたときでも、それらの種類、作製法は、本発明の効果が現れることに何らの影響を与えるものではない。また、ＡｌＧａＮ層に含まれるＳｉ濃度、ＡｌＧａＮ層に含まれるＭｇ濃度は、本発明の効果が現れることに何ら影響を与えない。また、不純物の種類を変えても、それは、本発明の効果が現れることに何ら影響を与えない。また、各層の膜厚、組成も、本発明の効果が現れることに何ら影響を与えるものではない。 Note that the type of the substrate has no influence on the effects of the present invention. Even when a nucleation layer or a buffer layer is used to deposit an AlGaN layer on a substrate, the type and manufacturing method thereof have no influence on the effects of the present invention. Further, the Si concentration contained in the AlGaN layer and the Mg concentration contained in the AlGaN layer have no influence on the effects of the present invention. Moreover, even if the type of the impurity is changed, it does not affect the effect of the present invention. Also, the film thickness and composition of each layer have no influence on the effects of the present invention.
図９に、本発明による構造を用いた紫外ＬＥＤの模式図を示す。図８のエピ構造より、所定の領域のｐ-Ａｌ０．８Ｇａ０．２Ｎ層とＩｎ０．１３Ａｌ０．８７Ｎ/Ａｌ０．５８Ｇａ０．４２Ｎ超格子構造、ｎ-Ａｌ０．８Ｇａ０．２Ｎ層の上部を除去し、それにより表出したｎ-Ａｌ０．８Ｇａ０．２Ｎ上にＴｉ/Ａｌ/Ｎｉ/Ａｕ電極を堆積し、所定の領域以外の除去されていないｐ-Ａｌ０．８Ｇａ０．２Ｎ上にＰｄ/Ａｕ電極を堆積した形態をとっている。 FIG. 9 shows a schematic diagram of an ultraviolet LED using the structure according to the present invention. From the epi structure of FIG. 8, a p-Al 0.8 Ga 0.2 N layer and an In 0.13 Al 0.87 N / Al 0.58 Ga 0.42 N superlattice structure in a predetermined region, n-Al The upper portion of the 0.8 Ga 0.2 N layer is removed, and a Ti / Al / Ni / Au electrode is deposited on the n-Al 0.8 Ga 0.2 N exposed thereby, and a region other than a predetermined region is deposited. It has a form in which a Pd / Au electrode is deposited on p-Al 0.8 Ga 0.2 N that has not been removed.
図１０に、本発明および従来技術により作製したＬＥＤの特性を示す。この特性は室温でパルス電流注入により測定した。その結果、本発明におけるＬＥＤにおいては、従来技術によるものに比べて２倍程度高い光出力が得られた。 FIG. 10 shows the characteristics of the LED fabricated according to the present invention and the prior art. This property was measured by pulsed current injection at room temperature. As a result, in the LED of the present invention, a light output about twice as high as that obtained by the prior art was obtained.
本実施の形態例においては、井戸層にＡｌＧａＮ、障壁層にＩｎＡｌＮを用いたが、これらの層が３種類以上のIII族元素を含んでいても、障壁層の組成と井戸層の組成とが相異なり、障壁層がＡｌ又はＩｎを含む窒化物半導体であり、井戸層がＡｌ又はＧａを含む窒化物半導体であれば、本発明の効果は同様に現れる。例えば、井戸層にＡｌ１−ａ−ｂＧａａＩｎｂＮ（０≦ａ＜１、０≦ｂ＜１、０≦ａ＋ｂ＜１）、障壁層にＡｌ１−ｃ−ｄＧａｃＩｎｄＮ（０≦ｃ＜１、０≦ｄ＜１、０≦ｃ＋ｄ＜１）を用いても同様の効果が得られる。この場合、Ａｌ、Ｇａ、Ｉｎの各組成比は、井戸層のバンドギャップが障壁層のバンドギャップよりも小さくなるように設定される必要がある。例えば、井戸層のＧａ組成比(a)は障壁層のもの(c)より高く、障壁層のＩｎ組成比(d)は井戸層のもの(b)よりも高いようにすればよい。 In this embodiment, AlGaN is used for the well layer and InAlN is used for the barrier layer. However, even if these layers contain three or more group III elements, the composition of the barrier layer and the composition of the well layer are different. In contrast, if the barrier layer is a nitride semiconductor containing Al or In and the well layer is a nitride semiconductor containing Al or Ga, the effects of the present invention are similarly exhibited. For example, Al 1-ab Ga a In b N (0 ≦ a <1, 0 ≦ b <1, 0 ≦ a + b <1) is formed in the well layer, and Al 1-c d Ga c In d N is formed in the barrier layer. The same effect can be obtained by using (0 ≦ c <1, 0 ≦ d <1, 0 ≦ c + d <1). In this case, each composition ratio of Al, Ga, and In needs to be set so that the band gap of the well layer becomes smaller than the band gap of the barrier layer. For example, the Ga composition ratio (a) of the well layer may be higher than that of the barrier layer (c), and the In composition ratio (d) of the barrier layer may be higher than that of the well layer (b).
さらに、本実施の形態例において、超格子構造の上下の層に一定の組成のＡｌＧａＮを用いたが、一定の組成のＡｌＧａＩｎＮを用いても構わない。また、一定の組成のものではなく、層方向にＡｌＧａ(Ｉｎ)Ｎの組成が変化するものであっても構わない。この場合、この層の基板と接する部分がＡｌＧａＮであって、層方向に徐々にＡｌ組成、Ｇａ組成、Ｉｎ組成が変化するＡｌＧａＩｎＮであって、超格子構造の障壁層に接する部分が障壁層と同じ組成のＩｎＡｌＮ又はＡｌＧａＩｎＮであることが望ましい。 Furthermore, in this embodiment, AlGaN having a constant composition is used for the upper and lower layers of the superlattice structure, but AlGaInN having a constant composition may be used. Further, the composition of AlGa (In) N may be changed in the layer direction instead of a constant composition. In this case, the portion of this layer in contact with the substrate is AlGaN, and AlGaInN in which the Al composition, Ga composition, and In composition gradually change in the layer direction, and the portion in contact with the barrier layer of the superlattice structure is the barrier layer. InAlN or AlGaInN having the same composition is desirable.
なお、除去する手段、深さ、領域、形態、電極の種類や構造等を変えても、それらは、本発明の効果が現れることに何ら影響を与えるものではない。 Note that even if the removal means, depth, region, form, electrode type, structure, and the like are changed, they do not affect the effects of the present invention.
Claims (4)
前記超格子層の障壁層が、０．６４≦ｘ≦１．０としたときに、Ｉｎ １−ｘ Ａｌ ｘ Ｎで表される窒化物半導体であり、前記超格子層の井戸層が、０≦ｙ≦０．９６としたときに、Ａｌ ｙ Ｇａ １−ｙ Ｎで表される窒化物半導体であり、
かつ、前記障壁層のＡｌ組成が、前記井戸層のＡｌ組成に対してピエゾ分極電界の差が 0.005C/m２ 以下となる組成であることを特徴とする半導体装置。 In a semiconductor device having a superlattice layer,
When the barrier layer of the superlattice layer is 0.64 ≦ x ≦ 1.0, it is a nitride semiconductor represented by In 1-x Al x N, and the well layer of the superlattice layer is 0 It is a nitride semiconductor represented by Al y Ga 1-y N when ≦ y ≦ 0.96 ,
And the Al composition of the said barrier layer is a composition with which the difference of a piezoelectric polarization electric field is 0.005 C / m < 2 > or less with respect to the Al composition of the said well layer .
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| JP5400001B2 (en) * | 2010-08-23 | 2014-01-29 | 日本電信電話株式会社 | III-nitride semiconductor deep ultraviolet light emitting device structure |
| CN103247728B (en) * | 2013-05-09 | 2016-01-13 | 青岛杰生电气有限公司 | A kind of semiconductive ultraviolet light source device |
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| JP4186306B2 (en) * | 1998-05-06 | 2008-11-26 | 松下電器産業株式会社 | Semiconductor device |
| JP2003086840A (en) * | 2001-09-10 | 2003-03-20 | Mitsubishi Cable Ind Ltd | GaN-BASED SEMICONDUCTOR LIGHT EMITTING DIODE |
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