JP2006324279A - Semiconductor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor element that reduces polarization generated by the lamination of two semiconductor layers having different composition each other, has a mesa section for enabling a carrier to move smoothly, and has low electric resistance. <P>SOLUTION: A band gap change layer of which the composition changes is arranged between the two semiconductor layers that are laminated at the mesa section and have different composition each other in a lamination direction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor element formed by stacking a plurality of semiconductor layers.

  In recent years, high-frequency devices and semiconductor light-emitting elements used in high-speed communication devices that have been developed are formed by laminating a plurality of semiconductor thin films on a substrate. In order to separate a plurality of semiconductor elements formed by stacking semiconductor thin films on a substrate in this manner from adjacent semiconductor elements, a mesa shape may be used (see, for example, Non-Patent Document 1). For example, compound semiconductors such as InAlAs and InGaAs are stacked on an InP substrate by epitaxial growth, then gate, source, and drain electrodes are made of a metal such as Ti / Al or Ni / Al, and a mesa shape is formed by dry etching or the like. Then, element isolation is performed.

  In addition, in order to concentrate carriers from the electrodes at specific locations of the semiconductor element, a part of the semiconductor element may be formed in a mesa shape to narrow the carrier movement path. For example, in a semiconductor light emitting device, in order to improve the unimodality of the light intensity distribution (transverse mode) and improve the coupling efficiency between the semiconductor light emitting device and an external device such as an optical pickup, a part of the semiconductor light emitting device is mesa. The carrier flow is narrowed and concentrated in the active layer (see, for example, Patent Document 1).

  In the following description, “a part of a semiconductor element formed in a mesa shape” is abbreviated as “mesa portion”. In addition, “near the surface where the junction between the contact layer and the first semiconductor layer appears inside the mesa part” is described as “near the side wall of the mesa part”, and “the inside away from the side wall of the mesa part”. It is described as “the center of the mesa”.

A conceptual diagram of a cross section of a conventional semiconductor element 107 is shown in FIG. The semiconductor element 107 is configured by laminating an electrode 11, a substrate 12, a first semiconductor layer 15, a second semiconductor layer 17, a contact layer 18 and an electrode 19. Further, the mesa portion 7 is formed in a mesa shape from the electrode 19 to a part of the width in the stacking direction of the first semiconductor layer 15.
http: //www3.fed.or.jp/pub/review/FEDreviewV1N12E1SanoE.pdf Japanese Patent Application Laid-Open No. 11-177175.

  However, two semiconductor layers having different compositions may be stacked adjacent to each other due to device requirements. For example, when the first semiconductor layer 15 and the second semiconductor layer 17 are group III nitride-based compounds and have different elemental compositions as in the semiconductor element 107 of FIG. 7, the first semiconductor layer 15 and the second semiconductor layer If the mesa portion 7 including the layer 17 is formed, the spontaneous polarization or piezo polarization caused by lattice strain (hereinafter referred to as “piezo polarization caused by spontaneous polarization or lattice strain”) is formed between the first semiconductor layer 15 and the second semiconductor layer 17. Is abbreviated as “polarization”). In particular, the polarization charge appeared remarkably at the heterointerface of the III-nitride compound heterostructure laminated in the C-axis direction. When a polarization charge is generated between the first semiconductor layer 15 and the second semiconductor layer 17, the carriers moving the mesa portion 7 from the second semiconductor layer 17 to the first semiconductor layer 15 in the stacking direction are generated from the electric field due to the polarization charge. In response to the repulsive force, the carrier moves in a concentrated manner in the vicinity of the side wall of the mesa portion 7 as in the carrier flow 91 of FIG. However, there is a problem that the vicinity of the side wall of the mesa portion 7 has poor crystallinity due to the influence of the formation of the mesa portion 7, the carrier transport is hindered, and the electric resistance of the semiconductor element 107 is increased.

  The present invention has been made to solve the above-described problems, and provides a semiconductor element in which carriers can move smoothly in a mesa portion in which two semiconductor layers having different compositions are stacked, and thus has low electrical resistance. Objective.

  In order to achieve the above object, according to the present invention, a band gap changing layer whose composition changes in the stacking direction is arranged between two semiconductor layers having different compositions stacked in the mesa portion.

Specifically, the first invention of the present application is laminated on a substrate and has a composition formula of Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1). A first semiconductor layer of a group III nitride compound represented by the following formula: a first semiconductor layer adjacent to a side opposite to the substrate side of the first semiconductor layer, and a composition formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1), a band gap changing layer of a group III nitride compound whose composition continuously changes monotonously in the stacking direction, and the band The gap change layer is laminated adjacent to the side opposite to the first semiconductor layer side, and the composition formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ a second semiconductor layer of a group III nitride compound represented by x + y ≦ 1), and the band gap changing layer side of the second semiconductor layer; An electrode for applying a voltage from the outside to the pair side, and in the stacking direction, from the electrode to the second semiconductor layer or the first semiconductor layer is a mesa shape, The band gap of the band gap change layer is substantially equal to the band gap of the second semiconductor layer from the band gap substantially equal to the band gap of the first semiconductor layer from the first semiconductor layer toward the second semiconductor layer. It is a semiconductor element characterized by continuously monotonously changing to a band gap.

The group III nitride compound represented by the composition formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) is changed by changing the composition of the band. It is a semiconductor whose gap can be adjusted. Therefore, the band gap of the band gap changing layer can be monotonously changed by monotonically changing the composition designated by x and y in the group III nitride compound.

  In the first invention of the present application, the band gap changing layer that continuously and monotonously changes from the composition of the second semiconductor layer to the composition of the first semiconductor layer is set to the second semiconductor layer on the side equal to the composition of the second semiconductor layer. By adjoining the first semiconductor layer on a side that is adjacent to the layer and that is equal to the composition of the first semiconductor layer, avoiding a sharp composition change from the second semiconductor layer to the first semiconductor layer, the second semiconductor layer The band gap can be continuously and monotonously changed from the semiconductor layer to the first semiconductor layer. Therefore, the polarization charge can be dispersed between the second semiconductor layer and the first semiconductor layer by the band gap change layer, and the repulsive force from the electric field of the polarization charge is reduced. It can move smoothly from the two semiconductor layers to the first semiconductor layer. Therefore, in the stacking direction, a carrier from the electrode to the second semiconductor layer or the first semiconductor layer has a mesa shape, so that carriers can smoothly move in the central portion of the mesa portion having good crystallinity. .

  Therefore, the first invention of the present application can provide a semiconductor element in which carriers can move smoothly in a mesa portion in which two semiconductor layers having different compositions are stacked, and thus has low electrical resistance.

The second invention of the present application is laminated on a substrate and represented by the composition formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1). A first semiconductor layer of a group nitride compound and a layer adjacent to the side of the first semiconductor layer opposite to the substrate side, and a composition formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1), and the band gap changing layer of the group III nitride compound whose composition monotonously changes in a stepwise manner in the stacking direction, and the band gap changing layer Stacked adjacent to the side opposite to the first semiconductor layer side, the composition formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) A second semiconductor layer of the group III nitride compound represented, and an outer side of the second semiconductor layer opposite to the band gap changing layer side. And an electrode for applying a voltage from the electrode to the second semiconductor layer or the first semiconductor layer in the stacking direction, the band gap changing layer The band gap is stepped from the first semiconductor layer toward the second semiconductor layer from a band gap substantially equal to the band gap of the first semiconductor layer to a band gap substantially equal to the band gap of the second semiconductor layer. The semiconductor element is characterized by monotonously changing.

The group III nitride compound represented by the composition formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) is changed by changing the composition of the band. It is a semiconductor whose gap can be adjusted. Accordingly, the band gap changing layer is formed by stacking a plurality of group III nitride compound thin films having compositions specified by different values of x and y in the composition formula, thereby forming a band gap of the band gap changing layer. Can be monotonously changed stepwise.

  In the second invention of the present application, the band gap changing layer that monotonously changes in a stepwise manner from the composition of the second semiconductor layer to the composition of the first semiconductor layer is set on the side that is equal to the composition of the second semiconductor layer. By adjoining the first semiconductor layer on a side that is adjacent to the layer and that is equal to the composition of the first semiconductor layer, avoiding a sharp composition change from the second semiconductor layer to the first semiconductor layer, the second semiconductor layer The band gap can be monotonously changed stepwise from the semiconductor layer to the first semiconductor layer. Therefore, the polarization charge can be dispersed between the second semiconductor layer and the first semiconductor layer by the band gap change layer, and the repulsive force from the electric field of the polarization charge is reduced. It can move smoothly from the two semiconductor layers to the first semiconductor layer. Therefore, in the stacking direction, a carrier from the electrode to the second semiconductor layer or the first semiconductor layer has a mesa shape, so that carriers can smoothly move in the central portion of the mesa portion having good crystallinity. .

  Accordingly, the second invention of the present application can provide a semiconductor element in which carriers can move smoothly in a mesa portion in which two semiconductor layers having different compositions are laminated, and thus has low electrical resistance.

  The second semiconductor layer of the semiconductor element according to the present invention is preferably p-type.

  When the second semiconductor layer is p-type, the carriers moving through the mesa portion are holes. Holes having a large effective mass compared to electrons are difficult to move near the side wall of the mesa having poor crystallinity. Therefore, the electric resistance of the p-type mesa portion where holes move near the side wall of the mesa portion due to the polarization charge was high. Therefore, the holes move smoothly around the center of the mesa portion by the band gap changing layer, so that the electric resistance of the mesa portion is lowered.

  Therefore, the present invention can provide a semiconductor element in which carriers can move smoothly in a mesa portion in which two semiconductor layers having different compositions are stacked, and thus has low electrical resistance.

  The width in the stacking direction of the band gap changing layer of the semiconductor element according to the present invention is preferably 3 (nm) or more and less than 100 (nm).

  The bandgap changing layer inserted for the purpose of alleviating a steep composition change between the first semiconductor layer and the second semiconductor layer has a width in the stacking direction (hereinafter referred to as “stacking direction” for achieving the above purpose). ”Is abbreviated as“ film thickness. ”) Is required to be 3 (nm) or more. On the other hand, since the electric resistance increases in proportion to the distance in the laminating direction of the mesa portion, the film thickness of the band gap changing layer is preferably less than 100 (nm).

  Therefore, the present invention can provide a semiconductor element in which carriers can move smoothly in a mesa portion in which two semiconductor layers having different compositions are stacked, and thus has low electrical resistance.

  The semiconductor device according to the present invention includes a stacking direction of the first semiconductor layer, the band gap change layer, and the second semiconductor layer, a crystal of a group III nitride compound of the first semiconductor layer, and a band gap change layer. It is preferable that the crystal of the Group III nitride compound and the C-axis direction of the Group III nitride compound crystal of the second semiconductor layer are parallel to each other.

  Even when the crystal of the group III nitride compound in which the polarization charge appears remarkably is laminated in the C-axis direction, the first semiconductor layer, the band gap change layer, and the second semiconductor layer are sequentially formed. By laminating, the polarization charge is reduced, and carrier transport between the first semiconductor layer and the second semiconductor layer can be facilitated.

  Therefore, the present invention can provide a semiconductor element in which carriers can move smoothly in a mesa portion in which two semiconductor layers having different compositions are stacked, and thus has low electrical resistance.

In the semiconductor device according to the present invention, the charge density of polarization generated at the adjacent interface between the group III nitride compound of the first semiconductor layer and the group III nitride compound of the second semiconductor layer is represented by ρ (cm ⁻² ), When the width of the band gap change layer in the stacking direction is expressed as d (cm), the impurity concentration n (cm ⁻³ ) of the impurity added to the band gap change layer is 0.5ρ / d ≦ n. ≦ 3ρ / d is preferable.

  In order to reduce the electrical resistance of the semiconductor element, it is preferable to add an impurity to the band gap change layer. On the other hand, when the impurity concentration is high, crystal defects increase, and it becomes impossible to reduce the electrical resistance of the semiconductor element. Furthermore, when the semiconductor element is used as a light emitting element, the amount of light absorbed by the crystal defects increases and the light emission efficiency decreases. Further, when Mg is added as an impurity, the semiconductor element deteriorates due to Mg diffusion, and the reliability decreases. Therefore, the impurity concentration of the band gap changing layer is preferably within the above range.

  The semiconductor device according to the present invention further comprises an active layer that generates light by recombination of electrons and holes between the substrate and the first semiconductor layer, wherein the first semiconductor layer has the composition formula X = 0 and 0.95 ≦ y ≦ 1, and functions as a light guide layer for guiding the light generated in the active layer, and the second semiconductor layer has x = m (0.05 in the composition formula). ≦ m ≦ 0.1) and x + y = 1, function as a clad layer for supplying carriers to the active layer, and the band gap change layer is 0 ≦ x ≦ m and x + y = 1 in the composition formula It is preferable that the entire structure has a function as a semiconductor laser.

The composition of the group III nitride compound of the second semiconductor layer is x = m (0.05 ≦ m ≦ 0.1) and x + y = 1 in the composition formula, that is, Al _m Ga _1-m N. By setting the composition of the group III nitride compound of the first semiconductor layer to x = 0 and y = 1 in the composition formula, that is, GaN, the band gap of the second semiconductor layer is the first semiconductor layer. It becomes larger than the band gap of the semiconductor layer. Accordingly, carriers can smoothly move from the second semiconductor layer through the band gap changing layer to the first semiconductor layer, and the second semiconductor layer functions as a cladding layer for supplying carriers.

  Moreover, the refractive index is reduced by setting the composition of the group III nitride compound of the first semiconductor layer to x = 0 and 0.95 ≦ y ≦ 1 in the composition formula, that is, GaN or InGaN compound. Light generated in the active layer is reflected by the first semiconductor layer. Therefore, the light generated in the active layer guides the first semiconductor layer and stimulates emission, and the first semiconductor layer functions as a light guide layer.

  Therefore, the present invention can provide a semiconductor element that can smoothly move carriers in a mesa portion in which two semiconductor layers having different compositions are stacked and thus functions as a semiconductor laser having low electrical resistance.

  According to the present invention, it is possible to provide a semiconductor element in which carriers can move smoothly in a mesa portion in which two semiconductor layers having different compositions are stacked, and the electrical resistance is low.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to embodiment shown below.

(Embodiment 1)
The present embodiment is a group III nitride layered on a substrate and represented by the composition formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1). A first compound layer of a physical compound and a layer adjacent to the side of the first semiconductor layer opposite to the substrate side are stacked, and the composition formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1) , 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1), and the band gap changing layer of the group III nitride compound whose composition continuously changes monotonously in the stacking direction, and the first of the band gap changing layer It is laminated adjacent to the side opposite to the semiconductor layer side, and is expressed as a composition formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1). A second semiconductor layer of a group III nitride compound and a side of the second semiconductor layer opposite to the band gap changing layer side An electrode for applying a voltage, and a mesa shape from the electrode to the second semiconductor layer or the first semiconductor layer in the stacking direction, and the band gap changing layer The band gap is continuously from the first semiconductor layer toward the second semiconductor layer, from a band gap substantially equal to the band gap of the first semiconductor layer to a band gap substantially equal to the band gap of the second semiconductor layer. It is a semiconductor element characterized by monotonous change.

  The conceptual diagram of the cross section of the semiconductor element 101 which is one embodiment which concerns on 1st invention of this application is shown in FIG. The semiconductor element 101 includes an electrode 11, a substrate 12, a first semiconductor layer 15, a band gap change layer 16, a second semiconductor layer 17, a contact layer 18, and an electrode 19. In the semiconductor element 101, each semiconductor layer is stacked on the substrate 12.

  In the stacking direction, from the electrode to the first semiconductor layer, from the electrode to a part of the first semiconductor layer, or from the electrode to the entire first semiconductor layer is mesa-shaped. Also good.

  The semiconductor element 101 forms a mesa portion from the electrode 19 to a part of the width in the stacking direction of the first semiconductor layer 15 as a mesa portion 1.

  The electrode 11 and the electrode 19 are arranged for applying a voltage to the semiconductor element 101. Since the efficiency as a semiconductor element is impaired if rectification occurs when the electrode and the semiconductor come into contact with each other, it is desirable that the electrode 11 and the electrode 19 be made of a material that can make ohmic contact with the semiconductor. Furthermore, it is desirable that the material has a small contact resistance with a wiring with an external power supply or other device. Therefore, a structure in which a material serving as a buffer is sandwiched between a material in contact with a semiconductor and a material connected to a wiring is preferable. For example, Ti / Al / Ti / Au and Al / Au are exemplified as the material of the electrode that contacts the n-type semiconductor. Examples of the electrode material in contact with the p-type semiconductor include Ni / Au, Pd / Au, and Pt / Au.

  In order to reduce the contact resistance with the substrate 12, the electrode 11 has a side opposite to the side on which the first semiconductor layer 15 is laminated (hereinafter referred to as "the side opposite to the side on which the first semiconductor layer 15 is laminated" of the substrate 12). (Abbreviated as “rear surface of substrate 12”).

The substrate 12 is disposed to physically support the semiconductor element 101 composed of a semiconductor thin film. A material on which a semiconductor thin film is favorably grown is selected as the substrate of the semiconductor element 101. For example, a group III nitride compound represented by the composition formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) (hereinafter “composition formula”) “Group III nitride compound represented by Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1”) is referred to as “Al _x Ga _y In ₁₋ abbreviated as “ _xy N compound”.) When thin films are laminated, sapphire (Al ₂ O ₃ ), gallium nitride (GaN) or silicon carbide (SiC) is exemplified.

The second semiconductor layer 17 is a semiconductor layer of an Al _x Ga _y In _1-xy N compound. The second semiconductor layer 17 has a relation of x = m (0.01 ≦ m ≦ 0.15, preferably 0.05 ≦ m ≦ 0.10) and x + y = 1 in the composition formula, that is, the composition formula is Al _m Ga. _1-m group III represented as N nitride compound (hereinafter, the "group III nitride based compound composition formula is represented as _{Al m Ga 1-m} N"_{"Al m Ga 1-m} N compound" For example). The second semiconductor layer 17 is preferably p-type. When the second semiconductor layer 17 is p-type, a p-type impurity is added to increase the carrier density. An example of the impurity added to the second semiconductor layer 17 is Mg, and the impurity concentration is 5 × 10 ¹⁸ (cm ⁻³ ) or more and 1 × 10 ²⁰ (cm ⁻³ ) or less. The film thickness of the second semiconductor layer 17 is preferably not less than 100 (nm) and not more than 2000 (nm), and more preferably not less than 200 (nm) and not more than 500 (nm).

The first semiconductor layer 15 is a semiconductor layer of an Al _x Ga _y In _1-xy N compound. The band gap of the first semiconductor layer 15 is preferably narrower than the band gap of the second semiconductor layer 17. Specifically, the composition of the first semiconductor layer 15 is set to x = 0 and y = 1 in the composition formula, that is, a group III nitride compound (hereinafter, “composition formula is represented as GaN”). "Group III nitride compound" is abbreviated as "GaN compound"). The composition of the first semiconductor layer 15 may be x = 0 and 0.95 ≦ y ≦ 1 in the composition formula, that is, a GaInN compound. The film thickness of the first semiconductor layer 15 is preferably 20 (nm) or more and 200 (nm) or less, and more preferably 50 (nm) or more and 150 (nm) or less. When the second semiconductor layer 17 is p-type, the first semiconductor layer 15 is designed to have an impurity concentration that is lower than the p-type impurity concentration that is not doped or added to the second semiconductor layer 17.

The band gap changing layer 16 is an Al _x Ga _y In _1-xy N compound layer whose composition continuously changes monotonously in the stacking direction. That is, the band gap change layer 16 has a composition in which the values of x and y in the composition formula continuously and monotonously change from one side of the band gap change layer 16 to the other side in the stacking direction. For example, the band gap changing layer 16 is a GaN compound in which one side of the band gap changing layer 16 with respect to the stacking direction is x = 0 and y = 1 in the composition formula, and the other side is x = 0. Al _0.08 Ga _0.92 N compound in which 08 and y = 0.92, and the value of x is continuous from 0 to 0.08 in the composition formula from the one side to the other side And a composition in which the value of y continuously monotonously changes from 1 to 0.92 while maintaining the relationship of x + y = 1. Since the composition of the band gap changing layer 16 continuously and monotonously changes, the polarization charge can be reduced in the band gap changing layer 16.

  The film thickness of the band gap changing layer 16 is preferably 3 (nm) or more and less than 100 (nm), and more preferably 3 (nm) or more and 50 (nm) or less.

When the second semiconductor layer 17 is p-type, a p-type impurity such as Mg may be added to the band gap change layer 16 in order to make it p-type. For example, the impurity concentration can be 1 × 10 ¹⁸ (cm ⁻³ ) or more and 1 × 10 ¹⁹ (cm ⁻³ ) or less.

The charge density of polarization generated at the adjacent interface between the group III nitride compound of the first semiconductor layer and the group III nitride compound of the second semiconductor layer is ρ (cm ⁻² ), and the band gap change When the width in the stacking direction of the layer is expressed as d (cm), the impurity concentration n (cm ⁻³ ) of the impurity added to the band gap changing layer is in the range of Formula 1, that is, the charge density ρ is changed in the band gap. It is preferably in the range of 50% to 300% of the quotient divided by the layer thickness d.

Furthermore, it is preferable that it is the range of several 2 for smooth carrier transport, and it is more preferable that it is the range of several 3.

The impurity concentration of the band gap change layer disposed between the GaN compound and the Al _0.08 Ga _0.92 N compound is exemplified below. The polarization charge density generated at the interface between the GaN compound and the Al _0.08 Ga _0.92 N compound is ρ = 3 × 10 ¹² (cm ⁻² ). When the film thickness of the band gap changing layer is 10 (nm), the impurity concentration n of the impurity added to the band gap changing layer is 1.5 × 10 ¹⁸ (cm ⁻³ ) or more and 9 × 10 ¹⁸ (cm ^{− 3} ) The following range is preferable.

  The contact layer 18 is a semiconductor layer for making ohmic contact with the electrode 19. For example, a GaN compound having a film thickness of 10 (nm) to 100 (nm) can be exemplified. Impurities may be added to the contact layer 18 to reduce the electrical resistance. When the contact layer 18 is a GaN compound and the second semiconductor layer 17 is p-type, Mg is exemplified as the p-type impurity to be added.

  Each semiconductor layer of the semiconductor element 101 is stacked using a metal organic vapor phase epitaxy method (hereinafter, “metal organic vapor phase epitaxy” is abbreviated as “MOCVD method”). The MOCVD method is a method in which a reaction gas is introduced into a reaction furnace (chamber) and fixed in the chamber, and the reaction gas is thermally decomposed and reacted on a substrate maintained at 600 to 1100 degrees Celsius to epitaxially grow a thin film. is there. By controlling manufacturing parameters such as the flow rate and concentration of the reaction gas, the reaction temperature and time, and the type of dilution gas, semiconductor layers having different compositions and film thicknesses can be easily stacked and manufactured.

When the first semiconductor layer 15, the band gap changing layer 16, the second semiconductor layer 17, and the contact layer 18 are Al _x Ga _y In _1-xy N compound thin films, the MOCVD method uses Ga (CH ₃ ) as a group III element. ₃ (trimethylgallium, hereinafter abbreviated as “TMG”), In (C ₂ H ₅ ) ₃ (triethylindium, abbreviated as “TMI” hereinafter) and Al (CH ₃ ) ₃ (trimethylaluminum, hereinafter “TMA”). ) Is used as a raw material gas and ammonia vapor is used to form a nitride. In addition, the impurity may be CP ₂ Mg (cyclopentadienyl magnesium) as a p-type dopant or SiH ₄ (silane) as a source gas as an n-type dopant. The source gas is introduced into the chamber by hydrogen or nitrogen carrier gas. The MOCVD method is a desired Al _x Ga _y In _{1-x based on} the manufacturing parameters of the mixed gas flow rate and the substrate temperature obtained by mixing CP ₂ Mg or SiH ₄ , TMG, TMI, TMA and ammonia source gases at a predetermined ratio. _-Y N compounds can be grown. The MOCVD method can control the film thickness of the Al _x Ga _y In _1-xy N compound by the reaction time. Moreover, the Al _x Ga _y In _1-xy N compounds having different compositions can be successively stacked by sequentially changing the production parameters at a predetermined reaction time.

  In the semiconductor element 101, a first semiconductor layer 15, a band gap change layer 16, a second semiconductor layer 17, and a contact layer 18 are sequentially stacked on a substrate 12. One or more semiconductor layers may be stacked between the substrate 12 and the first semiconductor layer 15. Specifically, the semiconductor element 101 is created as follows. The substrate 12 is introduced into the chamber, the inside of the chamber is replaced with a carrier gas, and the temperature of the substrate 12 is raised to about 600 to 1100 ° C.

Next, a mixed gas (mixed gas G) having a mixed ratio of TMG, TMI, TMA, ammonia and CP ₂ Mg on which the first semiconductor layer 15 is grown is introduced and reacted on the substrate 12 for a predetermined time. Layer 15 is laminated. For example, when the first semiconductor layer 15 is a non-doped GaN compound, a mixed gas G of TMG and ammonia is used.

  Next, the band gap changing layer 16 is stacked on the first semiconductor layer 15. The reaction gas for laminating the band gap change layer 16 will be described later.

Next, a mixed gas (mixed gas H) having a mixed ratio of TMG, TMI, TMA, ammonia and CP ₂ Mg on which the second semiconductor layer 17 is grown is introduced and reacted on the band gap changing layer 16 for a predetermined time. A second semiconductor layer 17 is stacked. For example, when the second semiconductor layer 17 is a p-type Al _0.08 Ga _0.92 N compound, a mixed gas H of TMG, TMA, ammonia and CP ₂ Mg is used.

In the growth of the band gap change layer 16, the mixture ratio of TMG, TMI, TMA, and ammonia is continuously changed monotonously from the mixed gas G to the mixed gas H according to the reaction time. It is possible to obtain a semiconductor layer whose composition monotonously changes in the stacking direction up to the semiconductor layer 17 and has no steep change in band gap. Further, the band gap change layer 16 can be made p-type by adding CP ₂ Mg to the mixed gas.

After the second semiconductor layer 17 is stacked, a mixed gas (mixed gas I) having a mixed ratio of TMG, ammonia, and CP ₂ Mg on which the contact layer 18 grows is introduced and reacted on the second semiconductor layer 17 for a predetermined time. Then, the contact layer 18 is laminated.

  As a method for growing the group III nitride compound on the substrate 12, a molecular beam epitaxial growth method (MBE method) may be used.

  After the contact layer 18 is stacked, the material of the electrode 19 and the material of the electrode 11 are stacked on the contact layer 18 and the back surface of the substrate 12. A sputtering method or a vacuum deposition method can be used as a method for laminating the electrode material.

  After laminating the electrode materials, the mesa portion 1 is formed. Examples of the means for forming the mesa unit 1 are described below. After laminating the material of the electrode 19, a striped resist pattern is formed on the material of the electrode 19 by photolithography. Next, etching is performed by dry etching from the material of the electrode 19 exposed without the resist pattern to a desired position of the second semiconductor layer 16 or the first semiconductor layer 15 in the stacking direction. Subsequently, the resist pattern is removed, and the mesa portion 1 is completed. Since the etching is performed up to a part of the film thickness of the second semiconductor layer 16 or the first semiconductor layer 15, the end point, that is, the height of the mesa portion 1 is controlled by the etching time.

When the composition of the one side of the band gap changing layer 16 is equal to the composition of the first semiconductor layer 15 and the composition of the other side is equal to the composition of the second semiconductor layer 17, the band gap changing layer 16 The band gap changing layer 16 is laminated so that one side is adjacent to the first semiconductor layer 15 and the other side is adjacent to the second semiconductor layer 17. Since the composition continuously changes monotonically from the first semiconductor layer 15 to the second semiconductor layer 17, the band gap also changes monotonously continuously from the first semiconductor layer 15 to the second semiconductor layer 17. For example, when the first semiconductor layer 15 is a GaN compound and the second semiconductor layer 17 is an Al _0.08 Ga _0.92 N compound, the composition of the one side of the band gap change layer 16 is GaN, By setting the composition of the other side to Al _0.08 Ga _0.92 N, between the first semiconductor layer 15 and the band gap change layer 16 and between the band gap change layer 16 and the second semiconductor layer 17. The sharp composition change disappears, and the composition continuously and monotonously changes from the first semiconductor layer 15 to the second semiconductor layer 17.

  Accordingly, it is possible to disperse the polarization charge that has hindered carrier transport, and carriers are located near the center of the mesa portion 1 from the second semiconductor layer 17 to the first semiconductor layer 15 or from the first semiconductor layer 15 to the second semiconductor layer. 17 can be moved smoothly. For example, when the second semiconductor layer 17 is p-type, holes can smoothly move from the second semiconductor layer 17 to the first semiconductor layer 15 near the center of the mesa portion 1.

  A conceptual diagram of a band diagram of the semiconductor element 101 is shown in FIG. In FIG. 2, 11a is a region of the electrode 11, 12a is a region of the substrate 12, 15a is a region of the first semiconductor layer 15, 16a is a region of the band gap changing layer 16, 17a is a region of the second semiconductor layer 17, and 18a is a contact. The region 18 a and the layer 19 a indicate the band gap of the electrode 19 region. 21 is the top level of the valence band, and 22 is the bottom level of the conduction band. In FIG. 2, a part of the band gap from the electrode 11 to the substrate 12 and from the contact layer 18 to the electrode 19 is omitted. In the following description, the second semiconductor layer 17 and the contact layer 18 are p-type.

  The holes injected from the electrode 19 can smoothly move in the direction of the substrate 12 through the p-type contact layer 18 and the second semiconductor layer 17 in which majority carriers are holes. The band gap of the first semiconductor layer 15 is narrower than the band gap of the second semiconductor layer 17, and the band gap changing layer 16 causes the top level 21 of the valence band of the first semiconductor layer 15 and the valence band of the second semiconductor layer 17. The top level 21 is gently connected, and holes can move along the top level 21 of the valence band to the first semiconductor layer 15 that is energetically stable.

  Accordingly, since the hole gap between the second semiconductor layer 17 and the first semiconductor layer 15 is facilitated by the band gap changing layer 16 of the mesa portion 1, the holes of the semiconductor element 101 are formed in the mesa portion 1 having good crystallinity. The center vicinity can be moved like a carrier flow 91, and the electrical resistance of the mesa unit 1 can be reduced.

  That is, in the mesa portion, the band gap change layer is disposed between the second semiconductor layer and the first semiconductor layer, so that carriers can smoothly move in the central portion of the mesa portion having good crystallinity. Can do.

  Therefore, according to the first invention of the present application, it is possible to provide a semiconductor element in which carriers can move smoothly in a mesa portion in which two semiconductor layers having different compositions are stacked, and the electrical resistance is low.

  Further, since the electric resistance is low, the built-in voltage is low, and the driving voltage applied to the semiconductor element 101 can be lowered.

  Further, the reaction with the passivation material that covers the mesa portion 1 can be reduced by reducing the number of carriers moving in the vicinity of the side wall of the mesa portion 1, and the reliability of the semiconductor element 101 can be improved.

  Note that when the two group III nitride compound crystals having different compositions are laminated in the C-axis direction, the polarization charge appears remarkably. Accordingly, the stack direction of the first semiconductor layer 15, the band gap change layer 16 and the second semiconductor layer 17, the group III nitride compound crystal of the first semiconductor layer 15, and the group III nitride of the band gap change layer 16. The effect of the band gap changing layer 16, that is, the effect of dispersion of the polarization charge is maximized when the crystal of the compound compound and the C-axis direction of the crystal of the group III nitride compound of the second semiconductor layer 17 are parallel. .

  Therefore, according to the first invention of the present application, in the mesa portion in which crystals of two group III nitride compounds having different compositions are aligned in the C-axis direction, carriers can move smoothly, and thus a semiconductor element having low electrical resistance. Can be provided.

(Embodiment 2)
The present embodiment is a group III nitride layered on a substrate and represented by the composition formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1). A first compound layer of a physical compound and a layer adjacent to the side of the first semiconductor layer opposite to the substrate side are stacked, and the composition formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1) , 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1), and the band gap changing layer of the group III nitride compound whose composition monotonously changes in a stepwise manner in the stacking direction, and the first of the band gap changing layer It is laminated adjacent to the side opposite to the semiconductor layer side, and is expressed as a composition formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1). A second semiconductor layer of a group III nitride compound and a side of the second semiconductor layer opposite to the band gap changing layer side An electrode for applying a voltage, and a mesa shape from the electrode to the second semiconductor layer or the first semiconductor layer in the stacking direction, and the band gap changing layer The band gap is stepped from the first semiconductor layer toward the second semiconductor layer, from a band gap substantially equal to the band gap of the first semiconductor layer to a band gap substantially equal to the band gap of the second semiconductor layer. It is a semiconductor element characterized by monotonous change.

  FIG. 3 shows a conceptual diagram of a cross section of a semiconductor element 103 according to an embodiment of the second invention of the present application. The semiconductor element 103 is configured by laminating the electrode 11, the substrate 12, the first semiconductor layer 15, the band gap change layer 36, the second semiconductor layer 17, and the electrode 19. In the semiconductor element 103, each semiconductor layer is stacked on the substrate 12.

  In the stacking direction, from the electrode to the first semiconductor layer, from the electrode to a part of the first semiconductor layer, or from the electrode to the entire first semiconductor layer is mesa-shaped. Also good.

  The semiconductor element 103 forms a mesa portion from the electrode 19 to a part of the film thickness of the first semiconductor layer 15 as a mesa portion 3.

  The same reference numerals as those used in FIG. 1 have the same configuration and the same function. The difference between the semiconductor element 103 and the semiconductor element 101 of FIG. 1 is that the band gap changing layer 36 is disposed between the first semiconductor layer 15 and the second semiconductor layer 17 instead of the band gap changing layer 16. .

  Note that one or more semiconductor layers may be stacked between the substrate 12 and the first semiconductor layer 15 as in the semiconductor element 101.

The band gap changing layer 36 is an Al _x Ga _y In _1-xy N compound layer whose composition monotonously changes in a stepwise manner in the stacking direction. That is, the band gap changing layer 36 has a composition in which the values of x and y in the composition formula monotonously change in a stepwise manner from one side of the band gap changing layer 36 to the other side in the stacking direction. Specifically, the band gap changing layer 36 is formed by laminating a plurality of Al _x Ga _y In _1-xy N compound thin films having different band gaps in order of increasing or decreasing band gap width. For example, the band gap changing layer 36 is a GaN compound thin film, Al _0.02 Ga _0.98 N compound having a thickness of 10 nm from the one side in the stacking direction to the other side in the stacking direction. A thin film, an Al _0.04 Ga _0.96 N compound thin film, an Al _0.06 Ga _0.94 N compound thin film, and an Al _0.08 Ga _0.92 N compound thin film are sequentially stacked. The band gap of the band gap changing layer 36 is stepped from the narrowest band gap of the GaN compound thin film to the widest band gap of the Al _0.08 Ga _0.92 N compound thin film from the one side to the other side. Changes monotonously. The composition of the compound thin film may be changed unevenly, and the film thickness of the compound thin film may also be uneven. Since the composition of the band gap change layer 36 changes monotonously in a stepped manner, the polarization charge can be reduced in the band gap change layer 36.

  The film thickness of the band gap changing layer 36 is preferably 3 (nm) or more and less than 100 (nm), and more preferably 3 (nm) or more and 50 (nm) or less.

When the second semiconductor element 17 is p-type, a p-type impurity may be added to the band gap changing layer 36 in the impurity concentration range described with reference to the band gap changing layer 16 in FIG. Specifically, Mg is exemplified as the p-type impurity, and the impurity concentration n is exemplified by a range of 1 × 10 ¹⁸ (cm ⁻³ ) to 1 × 10 ¹⁹ (cm ⁻³ ). The range of the impurity concentration of the band gap changing layer 36 is the charge density and band of polarization generated at the interface between the first semiconductor layer 15 and the second semiconductor layer 17 as described in the band gap changing layer 16 in FIG. It is preferable to calculate from the width of the gap change layer 36 in the stacking direction.

  The semiconductor element 103 is created as described below. The first semiconductor layer 15, the band gap change layer 36, the second semiconductor layer 17, and the contact layer 18 are sequentially stacked on the substrate 12 using the MOCVD method described in the first embodiment. The band gap changing layer 36 is formed by changing the manufacturing parameters in a stepped manner every predetermined time. Next, as described for the semiconductor element 101 in FIG. 1, the electrode 11 and the electrode 19 are stacked by sputtering or vacuum deposition, and the mesa portion 3 is formed by using lithography and dry etching to form the semiconductor element 103. be able to.

  By changing the composition of the one side of the band gap changing layer 36 to be equal to the composition of the first semiconductor layer 15 and making the composition of the other side equal to the composition of the second semiconductor layer 17, the band gap change of FIG. The same effect as that of the layer 16 can be obtained. That is, the band gap changing layer 36 is laminated so that the one side of the band gap changing layer 36 and the first semiconductor layer 15 are adjacent to each other, and the other side and the second semiconductor layer 17 are adjacent to each other. In addition, there is no steep composition change between the first semiconductor layer 15 and the band gap change layer 36 and between the band gap change layer 36 and the second semiconductor layer 17. Therefore, the polarization charge that hinders the transport of carriers can be dispersed, and the carriers can smoothly move from the second semiconductor layer 17 to the first semiconductor layer 15 in the vicinity of the center of the mesa portion 3. For example, when the second semiconductor layer 17 is p-type, holes can smoothly move from the second semiconductor layer 17 to the first semiconductor layer 15 near the center of the mesa portion 3.

  A conceptual diagram of a band diagram of the semiconductor element 103 is shown in FIG. In FIG. 4, the same reference numerals as those used in FIG. 2 are the same laminated film regions and have the same functions. 4 is different from the band diagram of the semiconductor element 101 in FIG. 2 between the region 15a of the first semiconductor layer 15 and the region 17a of the second semiconductor layer 17 in the band diagram. That is, the area 16a of the band gap changing layer 36 is displayed without the area 16a. In FIG. 4, a part of the band gap from the contact layer 18 to the electrode 19 and from the substrate 12 to the electrode 11 is omitted. In the following description, the second semiconductor layer 17 and the contact layer 18 are p-type.

  The holes injected from the electrode 19 move to the second semiconductor layer 17 as described in the band diagram of the semiconductor element 101 in FIG.

  The band gap changing layer 36 connects the top level 21 of the valence band of the first semiconductor layer 15 and the top level 21 of the valence band of the second semiconductor layer 17 in a stepped manner, and the holes are in the valence band. It can move to the first semiconductor layer 15 that is stable in energy along the top level 21.

  Therefore, the hole gap between the second semiconductor layer 17 and the first semiconductor layer 15 is facilitated by the band gap changing layer 36 of the mesa portion 3, so that the holes of the semiconductor element 103 are formed in the mesa portion 3 having good crystallinity. It is possible to move around the center like a carrier flow 91, and to reduce the electrical resistance of the mesa unit 3.

  That is, in the mesa portion, the band gap change layer is disposed between the second semiconductor layer and the first semiconductor layer, so that carriers can smoothly move in the central portion of the mesa portion having good crystallinity. Can do.

  Therefore, according to the second invention of the present application, in the mesa portion in which two semiconductor layers having different compositions are laminated, carriers can move smoothly, and a semiconductor element having low electrical resistance can be provided.

  Further, like the semiconductor element 101, the semiconductor element 103 can obtain the effect of reducing the driving voltage and improving the reliability.

  The semiconductor element 103 is similar to the semiconductor element 101 when the first semiconductor layer 15, the band gap changing layer 36 and the second semiconductor layer 17 are stacked when the C-axis of the group III nitride compound crystal is aligned. The effect of the gap change layer 36, that is, the effect of dispersion of the polarization charge is maximized.

  Therefore, according to the second invention of the present application, in the mesa portion in which crystals of two group III nitride compounds having different compositions are aligned in the C-axis direction, carriers can move smoothly, and thus a semiconductor element having low electrical resistance. Can be provided.

(Embodiment 3)
The semiconductor element according to the first or second invention of the present application further includes an active layer that generates light by recombination of electrons and holes between the substrate and the first semiconductor layer, The semiconductor layer has x = 0 and 0.95 ≦ y ≦ 1 in the composition formula, and functions as a light guide layer that guides light generated in the active layer, and the second semiconductor layer has x in the composition formula = M (0.05 ≦ m ≦ 0.1) and x + y = 1, function as a clad layer for supplying carriers to the active layer, and the band gap change layer is 0 ≦ x in the composition formula ≦ m and x + y = 1, and the structure as a whole preferably has a function as a semiconductor laser.

  The conceptual diagram of the cross section of the semiconductor element 105 which is other embodiment which concerns on this invention 1st invention is shown in FIG. The semiconductor element 105 includes an electrode 51, an n-type substrate 52, an n-type underlayer 53, an n-side first semiconductor layer 55, an n-side band gap changing layer 56, an n-type second semiconductor layer 57, an active layer 54, and a p-side first. A semiconductor layer 65, a p-side band gap changing layer 66, a p-type second semiconductor layer 67, a p-type contact layer 68, and an electrode 19 are provided. 5, the same reference numerals as those used in FIG. 1 are the same laminated films and have the same functions. The semiconductor element 105 functions as a semiconductor laser.

The n-type substrate 52 is disposed to physically support the semiconductor element 105 composed of a semiconductor thin film. A material on which a semiconductor thin film can be favorably grown is selected as the substrate of the semiconductor element 105. For example, sapphire is exemplified when an Al _x Ga _y In _1-xy N compound is laminated.

The n-type underlayer 53 can improve the crystallinity of the n-side first semiconductor layer 55. For example, a GaN compound having n-type Si with a film thickness of 1 μm or more and 5 μm or less can be exemplified. The impurity concentration is exemplified to be 5 × 10 ¹⁷ (cm ⁻³ ) or more and 1 × 10 ¹⁹ (cm ⁻³ ) or less.

  The electrode 51 has a function as a cathode for applying a voltage to the semiconductor element 105. The material of the electrode 51 is exemplified by Ti / Al / Ti / Au and Al / Au as in the description of the electrode 11 in FIG.

The active layer 54 is a layer that emits light by recombination of electrons and holes. The wavelength of the emitted light is determined by the band gap of the material used for the active layer 54. The material employed for the active layer 54 is preferably a direct transition type semiconductor with high luminous efficiency. By using the Al _x Ga _y In _1-xy N compound thin film, a wide band gap can be created by changing the composition, and a semiconductor light emitting device having a desired wavelength can be manufactured. Further, the active layer 54 is formed by alternately arranging at least two types of semiconductor thin films having different band gaps, so that the semiconductor thin film having the wider band gap is used as the barrier layer, and the semiconductor thin film having the smaller band gap is used as the well layer. A multiple quantum well structure (MQW) can also be used. By setting the active layer 54 to the MQW, electrons can be concentrated in a specific energy state, and light can be efficiently emitted even with a small current. When MQW is used, the wavelength of light emitted by the band gap of the well layer is determined. Note that both ends of the MQW may be barrier layers or well layers. For example, as the barrier layer, x = 0, y = q (0.95 ≦ q ≦ 1, preferably 0.97 ≦ q ≦ 1) in the composition formula, that is, the composition formula is expressed as Ga _q In _1-q N. In the composition formula, the group III nitride compound thin film and the well layer are formed with x = 0, y = p (p <q and 0.80 ≦ p ≦ 0.95, preferably 0.85 ≦ q ≦ 0. 9), that the composition formula is a combination of an III nitride compound film represented as _{Ga p In 1-p} N MQW are illustrated. Incidentally, the "composition formula III nitride compound represented as _{Ga q In 1-q} N" is abbreviated to _{"Ga q In 1-q} N compound" in the following description, "a composition formula _Ga p an In _1-p N a group III nitride-based compound represented "product is referred to as" _{Ga p In 1-p} N compound ".

  The thickness of the barrier layer is preferably 5 (nm) or more and 20 (nm) or less, and more preferably 7 (nm) or more and 15 (nm) or less.

  The thickness of the well layer is preferably 1 (nm) to 10 (nm), and more preferably 3 (nm) to 5 (nm).

  Of the film thickness of the active layer 54, the MQW film thickness (the total film thickness of the barrier layer and the well layer) is preferably 380 nm or more and 480 nm or less.

Further, Al _x Ga _y In _1-x prevents the phenomenon of carrier overflow, in which electrons receiving heat energy due to heat generated by light emission of the semiconductor element move to the p-type side semiconductor layer beyond the barrier of the quantum well. An electron barrier layer of _-yN compound may be disposed at the end of the MQW on the p-type side with respect to the MQW. Since the electron barrier layer has a wide band gap and the bottom level of the transmission band is high, even electrons having obtained the thermal energy can pass through the electron barrier layer and move to the p-type semiconductor layer. Can not. For example, x = s and x + y = 1 (0.1 ≦ s ≦ 0.3, preferably 0.15 ≦ s ≦ 0.25) in the composition formula as the electron barrier layer, that is, the composition formula is Al _s Ga _1. group III represented as _-s N nitride compound (hereinafter, the "group III nitride based compound composition formula is represented as _{Al s Ga 1-s} N", _{"Al s Ga 1-s} N compound" Abbreviated.) A thin film is illustrated. The film thickness of the electron barrier layer is 10 (nm) or more and 30 (nm) or less, preferably 15 (nm) or more and 25 (nm) or less. In the p-type semiconductor layer, carriers overflowing electrons become ineffective carriers that do not participate in light emission and reduce the light emission efficiency of the semiconductor element. Therefore, the active layer 54 can reduce the number of ineffective carriers by having the electron barrier layer. In addition, the luminous efficiency of the semiconductor element can be increased.

In order to make the semiconductor element 105 into a highly efficient semiconductor laser, the active layer 54 has the MQW well layer with p = 0.87 in the composition formula, that is, Ga _0.87 In _0.13 N compound, and the MQW barrier. Preferably, the layer is q = 1 in the composition formula, that is, the GaN compound and the electron barrier layer is s = 0.2 in the composition formula, that is, the Al _0.2 Ga _0.8 N compound. The well layer preferably has a thickness of 3 nm, the barrier layer has a thickness of 10 nm, and the electron barrier layer has a thickness of 20 nm. Mg is added as an impurity to make the electron barrier layer p-type. The impurity concentration is, for example, in the range of 1 × 10 ¹⁹ (cm ⁻³ ) to 1 × 10 ²⁰ (cm ⁻³ ) and preferably 5 × 10 ¹⁹ (cm ⁻³ ).

The n-type second semiconductor layer 57 is a semiconductor layer of an Al _x Ga _y In _1-xy N compound. The Al _m Ga _1-m N compound described in the second semiconductor layer 17 in FIG. 1 is exemplified. In order to make the semiconductor element 105 a highly efficient semiconductor laser, it is desirable to use an Al _0.08 Ga _0.92 N compound. In order to make the active layer 54 function as a clad layer for supplying electrons, an n-type impurity for increasing the carrier density is added to the n-type second semiconductor layer 57. Si is exemplified as the impurity added to the n-type second semiconductor layer 57. The impurity concentration of the n-type second semiconductor layer 57 is exemplified to be 5 × 10 ¹⁷ (cm ⁻³ ) or more and 1 × 10 ¹⁹ (cm ⁻³ ) or less. The film thickness of the n-type second semiconductor layer 57 is preferably 300 (nm) or more and 2000 (nm) or less, and more preferably 400 (nm) or more and 1200 (nm) or less.

In order to make the semiconductor element 105 a highly efficient semiconductor laser, the impurity concentration of the n-type second semiconductor layer 57 is 3 × 10 ¹⁸ (cm ⁻³ ) and the film thickness is 1000 (nm). Further preferred.

The n-side first semiconductor layer 55 is an Al _x Ga _y In _1-xy N compound semiconductor layer that functions as a light guide layer that reflects and guides light generated in the active layer 54. The composition of the Al _x Ga _y In _1-xy N compound is designed so that the refractive index of the n-side first semiconductor layer 55 is smaller than the refractive index of the active layer 54. For example, the GaN compound or GaInN compound exemplified in the first semiconductor layer 15 of FIG. To prevent the impurities from diffusing into the active layer 54, no impurity is added to the n-side first semiconductor layer 55, or a concentration lower than that of the impurity added to the n-type second semiconductor layer 57 is designed. The band gap of the n-side first semiconductor layer 55 is designed to be wider than the band gap of the active layer 54 and narrower than the band gap of the n-type second semiconductor layer 57. When the active layer 54 is the MQW, the band gap of the n-side first semiconductor layer 55 is wider than the band gap of the barrier layer constituting the MQW and narrower than the band gap of the n-type second semiconductor layer 57. The thickness of the n-side first semiconductor layer 55 is preferably in the range exemplified by the first semiconductor layer 15 in FIG.

In order to make the semiconductor element 105 a highly efficient semiconductor laser, the n-side first semiconductor layer 55 is a non-doped GaN compound or a low-doped GaN compound having an impurity Si concentration of 1 × 10 ¹⁸ (cm ⁻³ ) or less. The film thickness is preferably 100 (nm).

The n-side band gap changing layer 56 is an Al _x Ga _y In _1-xy N compound layer whose composition continuously changes monotonously in the stacking direction. That is, the n-side band gap changing layer 56 has a composition in which the values of x and y in the composition formula continuously and monotonously change from one side to the other side in the stacking direction. For example, the n-side band gap change layer 56 can be exemplified by a group III nitride compound having the same composition as the band gap change layer 16 described in FIG. Since the composition of the n-side band gap changing layer 56 continuously monotonously changes, the polarization charge can be reduced in the n-side band gap changing layer 56.

  The film thickness of the n-side band gap changing layer 56 is preferably 3 (nm) or more and less than 100 (nm), and more preferably 3 (nm) or more and 50 (nm) or less.

An n-type impurity may be added to the n-side band gap changing layer 56 to make it n-type. Specifically, Si is exemplified as the n-type impurity, and the impurity concentration n is exemplified by a range of 5 × 10 ¹⁷ (cm ⁻³ ) to 5 × 10 ¹⁸ (cm ⁻³ ). The impurity concentration range of the n-side band gap change layer 56 is generated at the interface between the n-side first semiconductor layer 55 and the n-type second semiconductor layer 57 as described in the band gap change layer 16 of FIG. It is preferable to calculate from the charge density of polarization and the width of the n-side band gap changing layer 56 in the stacking direction.

Further, in order to make the semiconductor element 105 a highly efficient semiconductor laser, the film thickness of the n-side band gap changing layer 56 is 10 (nm), and the impurity concentration n to be added is 1.5 × 10 ¹⁸ (cm ⁻³ ). The range is 9 × 10 ¹⁸ (cm ⁻³ ) or less, and preferably 3 × 10 ¹⁸ (cm ⁻³ ).

The p-type second semiconductor layer 67 is a semiconductor layer of Al _x Ga _y In _1-xy N compound. The Al _m Ga _1-m N compound described in the second semiconductor layer 17 in FIG. 1 is exemplified. In order to make the semiconductor element 105 a highly efficient semiconductor laser, it is desirable to use an Al _0.08 Ga _0.92 N compound. In order to function as a cladding layer for supplying holes to the active layer 54, the p-type second semiconductor layer 67 is added with a p-type impurity such as Mg for increasing the carrier density. The impurity concentration and film thickness of the p-type second semiconductor layer 67 are preferably in the ranges exemplified for the second semiconductor layer 17 in FIG.

In order to make the semiconductor element 105 into a highly efficient semiconductor laser, the impurity concentration of the second semiconductor layer 57 is more preferably 3 × 10 ¹⁹ (cm ⁻³ ) and the film thickness is more preferably 500 (nm).

The p-side first semiconductor layer 65 is an Al _x Ga _y In _1-xy N compound semiconductor layer that functions as a light guide layer in the same manner as the n-side first semiconductor layer 55. For example, the GaN compound exemplified in the first semiconductor layer 15 of FIG. To prevent the impurities from diffusing into the active layer 54, no impurities are added to the p-side first semiconductor layer 65, or the concentration is lower than the concentration of impurities added to the p-type second semiconductor layer 67. Further, the band gap of the p-side first semiconductor layer 65 is designed to be wider than the band gap of the active layer 54 and narrower than the band gap of the p-type second semiconductor layer 67. When the active layer 54 is the MQW, the band gap of the p-side first semiconductor layer 65 is wider than the band gap of the barrier layer constituting the MQW and narrower than the band gap of the p-type second semiconductor layer 67. The thickness of the p-side first semiconductor layer 65 is preferably in the range exemplified by the first semiconductor layer 15 in FIG.

In order to make the semiconductor element 105 a highly efficient semiconductor laser, the p-side first semiconductor layer 65 is a non-doped GaN compound or a low-doped GaN compound having an impurity Mg concentration of 1 × 10 ¹⁹ (cm ⁻³ ) or less. The film thickness is preferably 100 (nm).

The p-side band gap changing layer 66 is a layer of an Al _x Ga _y In _1-xy N compound whose composition continuously changes monotonously in the stacking direction. This has the same configuration and effect as the band gap changing layer 16 of FIG. For example, the p-side band gap changing layer 66 may be a group III nitride compound having the same composition as that of the band gap changing layer 16 described with reference to FIG. In order to make the p-side band gap changing layer 66 p-type, a p-type impurity such as Mg may be added in the impurity concentration range described in the band gap changing layer 16 of FIG. The film thickness of the p-side band gap changing layer 66 is preferably in the range exemplified by the band gap changing layer 16 in FIG.

Further, in order to make the semiconductor element 105 a highly efficient semiconductor laser, the thickness of the p-side band gap changing layer 66 is 10 (nm), and the impurity concentration n to be added is 1.5 × 10 ¹⁸ (cm ⁻³ ). The range is 9 × 10 ¹⁸ (cm ⁻³ ) or less, and preferably 3 × 10 ¹⁸ (cm ⁻³ ).

  The configuration and effect of the p-type contact layer 68 are the same as those of the contact layer 18 of FIG. In order to make the semiconductor element 105 a highly efficient semiconductor laser, the thickness of the p-type contact layer 68 is desirably 50 (nm).

  The semiconductor element 105 is created as described below. Using the MOCVD method described in the first embodiment, an n-type base layer 53, an n-side first semiconductor layer 55, an n-side band gap changing layer 56, an n-type second semiconductor layer 57, and an active layer are formed on the n-type substrate 52. 54, a p-side first semiconductor layer 65, a p-side band gap changing layer 66, a p-type second semiconductor layer 67, and a p-type contact layer 68 are laminated in this order. Thereafter, the mesa portion 5 is formed as described in the semiconductor element 101 of FIG.

  Thereafter, in order to remove the semiconductor layer of the negative electrode portion M where the electrode 51 is to be formed, a resist pattern that covers the upper layer of the positive electrode portion P is formed again using a lithography technique, and the p-type of the negative electrode portion M is formed by dry etching. The semiconductor layer from the contact layer 68 to a part of the thickness of the n-type underlayer 53 is removed. Since the etching is performed up to a part of the thickness of the n-type underlayer 53, the end point, that is, the thickness of the n-type underlayer 53 left in the negative electrode portion M is controlled by the etching time.

  After forming the negative electrode portion M, the electrode 51 is formed using the MOCVD method, the lithography technique, and dry etching.

  On the side of the p-type polarity with respect to the active layer 54 of the semiconductor element 105, the first semiconductor layer 15, the band gap changing layer 16, the second semiconductor layer 17 and the contact layer 18 of the semiconductor element 101 of FIG. This is a substitute for the one semiconductor layer 65, the p-side band gap changing layer 66, the p-type second semiconductor layer 67 and the p-type contact layer 68.

  A conceptual diagram of a band diagram of the semiconductor element 105 is shown in FIG. In FIG. 6, 51 a is a region of the electrode 51, 53 a is a region of the n-type underlayer 53, 55 a is a region of the n-side first semiconductor layer 55, 57 a is a region of the n-type second semiconductor layer 57, and 54 a is the active layer 54. The region 65a is the region of the p-side first semiconductor layer 65, 66a is the region of the p-side band gap changing layer 66, 67a is the region of the p-type second semiconductor layer 67, 68a is the region of the p-type contact layer 68, and 19a is The band gap of the stripe-shaped electrode 19 is shown. 21 is the top level of the valence band, and 22 is the bottom level of the conduction band. In the band diagram of FIG. 6, the active layer 54 of the semiconductor element 105 has an MQW structure, and has an electron barrier layer at the end of the MQW on the p-type side with respect to the MQW. In the region 54a of the active layer 54, 54b represents a well layer region, 54c represents a barrier layer region, and 54d represents an electron barrier layer region. In FIG. 6, a part of the band gap from the electrode 51 to the n-type underlayer 53 and from the p-type contact layer 68 to the electrode 19 is omitted.

  By applying a voltage with the electrode 19 as an anode and the electrode 51 as a cathode, electrons are injected from the electrode 51 and holes are injected from the electrode 19 into the semiconductor element 105.

  The electrons injected from the electrode 51 can smoothly move in the direction of the active layer 54 through the n-type n-type underlayer 53 and the n-type second semiconductor layer 57 in which majority carriers are electrons. The band gap of the n-side first semiconductor layer 55 is narrower than the band gap of the n-type second semiconductor layer 57, and the n-side band gap changing layer 56 and the bottom level 22 of the conduction band of the n-side first semiconductor layer 55 and the n-type. The second semiconductor layer 57 is gently connected to the bottom level 22 of the conduction band, and electrons can move along the bottom level 22 of the conduction band to the n-side first semiconductor layer 55 that is energetically stable. In addition, since there is no steep composition change between the n-side first semiconductor layer 55 and the n-type second semiconductor layer 57 and the polarization charge that has hindered electron transport is dispersed, the electrons are n-type second semiconductor. It can move smoothly from the layer 57 to the n-side first semiconductor layer 55. The electrons are concentrated in each well layer of the active layer 54 that is narrower than the band gap of the n-side first semiconductor layer 55.

  On the other hand, the holes injected from the electrode 19 pass through the p-type contact layer 68, the p-type second semiconductor layer 67, and the p-side band gap changing layer 66 as described in the band diagram of the semiconductor element 101 of FIG. It moves to the p-side first semiconductor layer 65. The holes that have moved to the p-side first semiconductor layer 65 are concentrated in each well layer of the active layer 54 that is narrower than the band gap of the p-side first semiconductor layer 65. Although the electron barrier layer of the active layer 54 has a wide band gap, the electron barrier layer has little influence on the movement of holes because the top level 21 of the valence band is high.

  The active layer 54 is expressed between the top level 21 of the valence band of the quantum well and the bottom level 22 of the conduction band by recombination of the electrons and holes concentrated in each well layer of the active layer 54. The light of the wavelength according to the band gap to be emitted is emitted.

  Therefore, according to the present invention, it is possible to provide a semiconductor element that functions as a semiconductor laser having low electrical resistance, in which carriers can smoothly move in a mesa portion in which two semiconductor layers having different compositions are stacked.

  Further, like the semiconductor element 101, the semiconductor element 105 can obtain an effect of reducing driving voltage and improving reliability.

In the semiconductor element 105, the same effect can be obtained even if the band gap changing layer 36 described with reference to FIG. 3 is provided as an alternative to the p-side band gap changing layer 66. Further, as an alternative to the n-side band gap changing layer 56, the same effect can be obtained even if an Al _x Ga _y In _1-xy N compound layer whose composition monotonously changes in the stacking direction is arranged. it can.

  The configuration of the semiconductor element of the present invention can be used as a light emitting element and a light receiving element. Moreover, it can utilize also for electronic devices, such as a transistor and a diode, and a compound high frequency electronic device represented by HEMT.

1 is a configuration conceptual diagram of a semiconductor element 101 according to an embodiment of the first invention of the present application. It is a conceptual diagram of the band diagram of the semiconductor element 101 which is one embodiment according to the first invention of the present application. It is a composition conceptual diagram of semiconductor element 103 which is one embodiment concerning the 2nd invention of this application. It is a conceptual diagram of the band diagram of the semiconductor element 103 which is one embodiment according to the second invention of the present application. It is a composition conceptual diagram of semiconductor element 105 which is other embodiments concerning the 1st invention of this application. It is a conceptual diagram of the band diagram of the semiconductor element 105 which is other embodiment which concerns on 1st invention of this application. It is a composition conceptual diagram of the conventional semiconductor element 107.

Explanation of symbols

101, 103, 105, 107 Semiconductor element 1, 3, 5, 7 Mesa portion 11, 19, 51 Electrode 12 Substrate
DESCRIPTION OF SYMBOLS 15 1st semiconductor layer 16, 36 Band gap change layer 17 2nd semiconductor layer 18 Contact layer 52 n-type substrate 53 n-type base layer 54 Active layer 55 n-side first semiconductor layer 56 n-side band gap change layer 57 n-type first Two semiconductor layers 65 p-side first semiconductor layer 66 p-side band gap change layer 67 p-type second semiconductor layer 68 p-type contact layer 11a region of electrode 11 12a region of substrate 12 15a region of first semiconductor layer 15 16a band gap Change layer 16 region 17a Second semiconductor layer 17 region 18a Contact layer 18 region 19a Electrode 19 region 36a Band gap change layer 36 region 51a Electrode 51 region 53a N-type underlayer 53 region 54a Active layer 54 region Region 54b Well layer region 54c of active layer 54c Barrier layer region 54d of active layer 54d Active layer 54 Region of electron barrier layer 55a region of n-side first semiconductor layer 55a region of n-side band gap changing layer 56a region of n-type second semiconductor layer 57a region of p-side first semiconductor layer 65 66a p-side band Region of gap changing layer 66a Region of p-type second semiconductor layer 67 68a Region of p-type contact layer 68 21 Top level of valence band 22 Bottom level of conduction band 91 Carrier flow M Negative electrode portion P Positive electrode Part

Claims (7)

A group III nitride compound stacked on a substrate and represented by the composition formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1). A semiconductor layer;
The first semiconductor layer is laminated adjacent to the side opposite to the substrate side, and the composition formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y). ≦ 1), a band gap changing layer of a group III nitride compound whose composition continuously changes monotonously in the stacking direction;
The band gap change layer is stacked adjacent to the side opposite to the first semiconductor layer side, and the composition formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, A second semiconductor layer of a group III nitride compound represented by 0 ≦ x + y ≦ 1),
An electrode for applying a voltage from the outside to the side opposite to the band gap changing layer side of the second semiconductor layer;
A semiconductor device comprising:
In the stacking direction, from the electrode to the second semiconductor layer or the first semiconductor layer is a mesa shape,
The band gap of the band gap change layer is substantially equal to the band gap of the second semiconductor layer from the band gap substantially equal to the band gap of the first semiconductor layer from the first semiconductor layer toward the second semiconductor layer. A semiconductor element characterized by continuously monotonously changing to a band gap. A group III nitride compound stacked on a substrate and represented by the composition formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1). A semiconductor layer;
The first semiconductor layer is laminated adjacent to the side opposite to the substrate side, and the composition formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y). ≦ 1), a band gap changing layer of a group III nitride compound whose composition monotonously changes stepwise in the stacking direction;
The band gap change layer is stacked adjacent to the side opposite to the first semiconductor layer side, and the composition formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, A second semiconductor layer of a group III nitride compound represented by 0 ≦ x + y ≦ 1),
An electrode for applying a voltage from the outside to the side opposite to the band gap changing layer side of the second semiconductor layer;
A semiconductor device comprising:
In the stacking direction, from the electrode to the second semiconductor layer or the first semiconductor layer is a mesa shape,
The band gap of the band gap change layer is substantially equal to the band gap of the second semiconductor layer from the band gap substantially equal to the band gap of the first semiconductor layer from the first semiconductor layer toward the second semiconductor layer. A semiconductor element characterized by monotonically changing to a band gap in a stepped manner.   The semiconductor element according to claim 1, wherein the second semiconductor layer is p-type.   4. The semiconductor element according to claim 1, wherein the width of the band gap change layer in the stacking direction is 3 (nm) or more and less than 100 (nm). 5.   The stacking direction of the first semiconductor layer, the band gap change layer, and the second semiconductor layer and the crystal of the group III nitride compound of the first semiconductor layer, the crystal of the group III nitride compound of the band gap change layer 5. The semiconductor element according to claim 1, wherein the C-axis direction of the group III nitride compound crystal of the second semiconductor layer is parallel. The charge density of polarization generated at an adjacent interface between the group III nitride compound of the first semiconductor layer and the group III nitride compound of the second semiconductor layer is ρ (cm ⁻² ), and the band gap change layer When the width in the stacking direction is expressed as d (cm), the impurity concentration n (cm ⁻³ ) of the impurity added to the band gap change layer is in the range of 0.5ρ / d ≦ n ≦ 3ρ / d. The semiconductor device according to claim 1, wherein the semiconductor device is a semiconductor device. An active layer that generates light by recombination of electrons and holes between the substrate and the first semiconductor layer;
The first semiconductor layer has x = 0 and 0.95 ≦ y ≦ 1 in the composition formula, and functions as a light guide layer for guiding light generated in the active layer,
The second semiconductor layer has a relationship of x = m (0.05 ≦ m ≦ 0.1) and x + y = 1 in the composition formula, and functions as a clad layer for supplying carriers to the active layer,
And the band gap change layer is in the range of the relationship of 0 ≦ x ≦ m and x + y = 1 in the composition formula,
7. The semiconductor device according to claim 3, wherein the entire structure has a function as a semiconductor laser.

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