JP2007049169A - Group iii-v compound semiconductor light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a group III-V compound semiconductor having high crystallinity and high quality, and a light emitting element having high light emitting efficiency using the same. <P>SOLUTION: The compound semiconductor comprises at least a light emitting layer and a charge injection layer on a substrate. The light emitting layer is represented by a formula of In<SB>x</SB>Ga<SB>y</SB>Al<SB>z</SB>N, wherein 0<x≤1, 0≤y<1, 0≤z<1, x+y+z=1. The charge injection layer is represented by a formula of In<SB>X'</SB>Ga<SB>Y'</SB>Al<SB>Z'</SB>N, wherein 0≤x'≤1, 0≤y'≤1, 0≤z'≤1, x'+y'+z'=1. The compound semiconductor has a band gap larger than that of the light emitting layer, and a substrate layer having at least three layers between the light emitting layer and the substrate. The substrate layer is a compound semiconductor represented by a formula of In<SB>u</SB>Ga<SB>v</SB>Al<SB>w</SB>N, wherein 0≤u≤1, 0≤v≤1, 0≤w≤1, u+v+w=1. At least one layer of the substrate layer is sandwiched between the two layers having a smaller InN crystal mixing ratio than that of the one layer. The InN crystal mixing ratio of one layer is at least 0.05 or more larger than the InN crystal mixing ratio of the layer brought into contact with the layer from the substrate side. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a group 3-5 compound semiconductor represented by the general formula In _u Ga _v Al _w N (where u + v + w = 1, 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, 0 ≦ w ≦ 1) and The present invention relates to a light emitting element used.

As material for the light emitting element such as ultraviolet or blue light emitting diodes or ultraviolet or blue laser diode, the general formula In _x Ga _y Al _z N (provided that, x + y + z = 1,0 <x ≦ 1,0 ≦ y <1,0 A Group 3-5 compound semiconductor represented by ≦ z <1) is known. Hereinafter, x, y, and z in the general formula may be referred to as InN mixed crystal ratio, GaN mixed crystal ratio, and AlN mixed crystal ratio, respectively. Among these Group 3-5 compound semiconductors, those containing 10% or more of InN in the mixed crystal ratio are particularly important for display applications because the emission wavelength in the visible region can be adjusted according to the InN mixed crystal ratio.

The Group 3-5 compound semiconductor has been tried to be deposited on various substrates such as sapphire, GaAs, ZnO, etc., but the lattice constant and chemical properties are greatly different from the compound semiconductor, so that the quality is sufficiently high. The crystal is not obtained. Therefore, an attempt has been made to obtain an excellent crystal by first growing a GaN crystal having a lattice constant and chemical properties similar to those of the compound semiconductor, and then growing the compound semiconductor thereon. No. 55-3834). Recently, in a light-emitting element using a semiconductor represented by In _x Ga _y N (where x + y = 1, 0 <x <1, 0 <y <1) as an active layer, the thickness of the light-emitting layer is 20 mm. It has been reported that a high-efficiency light-emitting element can be realized by adjusting the degree (Japanese Journal of Applied Physics, 1995, 34, L797). However, even in this case, it has been reported that the luminous efficiency decreases as the InN mixed crystal ratio of the light emitting layer is increased.

  An object of the present invention is to provide a high-quality group 3-5 compound semiconductor having high crystallinity and a light-emitting element having high light emission efficiency using the same.

As a result of diligent study in view of such a situation, the inventors of the present invention have provided a specific underlayer consisting of at least three layers between the light emitting layer and the substrate, whereby the crystallinity of the layer grown on the underlayer is determined. Has been found to be remarkably improved, leading to the present invention.
That is, the present invention includes (1) at least a light emitting layer and a charge injection layer on a substrate, and the light emitting layer has the general formula In _x Ga _y Al _z N (where 0 <x ≦ 1, 0 ≦ y <1, 0 ≦ z <1, x + y + z = 1), which is a non-doped group 3-5 compound semiconductor, and the charge injection layer has a general formula of In _{x ′} Ga _{y ′} Al _{z ′} N (wherein 0 ≦ x ′ ≦ 1, 0 ≦ y ′ ≦ 1, 0 ≦ z ′ ≦ 1, x ′ + y ′ + z ′ = 1), and a group 3-5 compound semiconductor having a larger band gap than the light emitting layer The light emitting layer is a group 3-5 compound semiconductor sandwiched between and in contact with two charge injection layers, and has a base layer composed of at least three layers between the light emitting layer and the substrate. layer (where, 0 ≦ u ≦ 1,0 ≦ v ≦ 1,0 ≦ w ≦ 1, u + v + w = 1) the general formula in _u Ga _v Al _w N to form a 3-5 group compound represented by It is a semiconductor, and at least one layer in the underlayer is sandwiched between and in contact with two layers having a smaller InN mixed crystal ratio, and the InN mixed crystal ratio of the at least one layer is 3-5 compound semiconductor characterized in that it is 0.05 or more larger than the InN mixed crystal ratio of the layer in contact with.
The present invention also relates to (2) a light emitting device using the Group 3-5 compound semiconductor described in (1).

The Group 3-5 compound semiconductor of the present invention has high crystallinity and high quality, and a light-emitting element using the same has high luminous efficiency and great industrial value.
Next, the present invention will be described in detail.

The group 3-5 compound semiconductor in the present invention has a layer composed of an underlayer and a quantum well structure in this order on a substrate. Here, the quantum well structure, the general formula In _x Ga _y Al _z N (provided that, x + y + z = 1,0 <x ≦ 1,0 ≦ y <1,0 ≦ z <1) layer, represented by (hereinafter , May be referred to as a light emitting layer.) Is a general formula In _{x ′} Ga _{y ′} Al _{z ′} N (where 0 ≦ x ′ ≦ 1, 0 ≦ y ′ ≦ 1, 0 ≦ z ′ ≦ 1, x It is expressed by '+ y' + z '= 1) and is in contact with being sandwiched by a layer having a larger band gap than the light emitting layer (hereinafter sometimes referred to as a charge injection layer). Note that x ′, y ′, and z ′ in the general formula representing the two charge injection layers may be the same as or different from each other.

Then, the underlying layer in the present invention consists of at least three layers, in any layer also general formula In _u Ga _v Al _w N (wherein, 0 ≦ u ≦ 1,0 ≦ v ≦ 1,0 ≦ w ≦ 1, u + v + w = 1). Note that u, v, and w in the general formula representing at least three layers in the underlayer may be the same as or different from each other.
In the underlayer in the present invention, at least one layer in the underlayer is in contact with two layers having an InN mixed crystal ratio smaller than the InN mixed crystal ratio of this layer.
A layer sandwiched between layers having a small InN mixed crystal ratio in the underlayer in the present invention may be hereinafter referred to as a strained layer.

Comparing the strained layer with the layer in contact with the strained layer from the substrate side, the difference in InN mixed crystal ratio between the strained layer and the layer in contact with the strained layer from the substrate side is 0.05 or more. More preferably, it is 0.1 or more, Most preferably, it is 0.2 or more. When the mixed crystal ratio difference is smaller than 0.05, the effect of the present invention is not sufficient.
The thickness of the strained layer is preferably 5 mm or more. When the thickness of the strained layer is less than 5 mm, the effect is not sufficient.
Further, since the strain layer has lattice strain, if the thickness is too large, a new defect may be generated. In this case, the crystallinity of the layer grown on the strained layer is lowered, which is not preferable. The preferable upper limit of the thickness of the strained layer depends on the difference in the InN mixed crystal ratio between the strained layer and the layer grown before the strained layer. That is, when the difference in InN mixed crystal ratio is 0.3 or less, the product of the difference in mixed crystal ratio and the thickness (Å) is preferably 30 or less with respect to the thickness of the strained layer. However, when the difference in InN mixed crystal ratio exceeds 0.3, the thickness of the strained layer is preferably 100 mm or less. Specifically, when the difference in InN mixed crystal ratio is 0.05, the thickness of the strained layer is preferably 600 mm or less. When the difference in InN mixed crystal ratio is 0.3, the thickness of the strained layer is preferably 100 mm or less.
Although the number of strain layers is one and the effect of the present invention can be obtained, there are cases where a greater effect can be obtained by using a plurality of strain layers. As an example of such an underlayer, a structure composed of (2m + 1) layers in which m layers having a large InN mixed crystal ratio and (m + 1) layers having a small InN mixed crystal ratio are alternately stacked. Can be mentioned. However, m is a positive integer of 2 or more.
In such an underlayer having a multilayer structure including a plurality of strained layers, the InN mixed crystal ratio may be changed little by little while the thickness of each strained layer is kept constant. In addition, the InN mixed crystal ratio of each strained layer may be changed little by little in a range not exceeding the critical film thickness while keeping constant.
A layer having an InN mixed crystal ratio smaller than that of the strained layer may be changed little by little, or may be the same.

By providing the base layer including the strained layer between the light emitting layer and the substrate, the crystallinity of the layer grown on the base layer can be remarkably improved. This effect is recognized even when the compound semiconductor is grown at normal pressure using the metal organic vapor phase epitaxy method described later, but the effect is particularly remarkable when grown at a reduced pressure.
Crystallinity can be confirmed by the density of etch pits generated on the surface of the compound semiconductor treated with a mixed acid of heated phosphoric acid and sulfuric acid. Since the effect of the underlayer appears as a decrease in the etch pit density, it is considered that the underlayer suppresses the propagation of dislocations existing in the compound semiconductor crystal.

Furthermore, in the present invention, at least one layer between the substrate-side layer and the light emitting layer among the two layers having a small InN mixed crystal ratio in the underlayer is doped with an n-type impurity. To do. Specifically, a strained layer or a layer having a small InN mixed crystal ratio grown on the strained layer is doped with an n-type impurity.
By doing so, since the InN mixed crystal ratio of the strained layer is higher than the InN mixed crystal ratio of the layer bonded thereto, the band gap of the strained layer is smaller than the band gap of the layer bonded thereto. Even if there is, it can be avoided that the injected carriers are recombined in the strained layer and the recombination efficiency in the light emitting layer is lowered.
A preferable carrier concentration of the n-type doped layer is 1 × 10 ¹⁷ cm ⁻³ or more, more preferably 1 × 10 ¹⁸ cm ⁻³ or more.

One example of the structure of the Group 3-5 compound semiconductor of the present invention is shown in FIG. The example shown in FIG. 1 is a layer having a quantum well structure in which a strained layer 2 and an underlayer composed of an n-type layer 1 and an n-type layer 3 and two charge injection layers 4 and 6 are in contact with each other with a light-emitting layer 5 interposed therebetween. And a p-type layer 7 are laminated in this order.
An n-type layer 1 or an n-type layer 3 is provided with an n-electrode, and a p-type layer 7 is provided with a p-electrode. When a voltage is applied in the forward direction, current is injected and light emission from the light-emitting layer 5 is obtained. An element is obtained.

When the n-type carrier concentration in the charge injection layer 4 is sufficiently high, an n electrode may be formed in the charge injection layer 4.
When the band gap of the n-type layer 3 is larger than the light emitting layer, the n-type layer 3 and the charge injection layer 4 function as a charge injection layer without separating the n-type layer 3 and the charge injection layer 4 as separate layers. Thus, the charge injection layer 4 may not be grown.
When the p-type carrier concentration in the charge injection layer 6 is sufficiently high, an electrode may be formed on the charge injection layer 6. In this case, the p-type layer 7 may not be formed.
However, if the charge injection layer 4 or the charge injection layer 6 is doped at a high concentration, the crystallinity of these layers may be lowered. In such a case, the light emission characteristics or the electrical characteristics deteriorate, which is not preferable. In such a case, it is necessary to reduce the impurity concentration in the charge injection layer 4 or the charge injection layer 6. The impurity concentration range that does not lower the crystallinity is preferably 1 × 10 ¹⁸ cm ⁻³ or less, more preferably 1 × 10 ¹⁷ cm ⁻³ or less.

  By the way, it is known that a compound semiconductor that does not contain In can be obtained with a relatively high quality by using an appropriate buffer layer as compared with those that contain In. For this reason, it is preferable that a layer containing no In is first grown on a substrate, and then a charge injection layer and a light emitting layer are formed. However, when a layer containing In is used as the charge injection layer, defects may occur in the charge injection layer due to lattice mismatch with a layer not containing In that has been grown on the substrate in advance. In such a case, the occurrence of defects in the charge injection layer can be suppressed by inserting the base layer in the present invention between the layer not containing In grown in advance and the charge injection layer.

Next, the light emitting layer will be described.
Since the lattice constant of the Group 3-5 compound semiconductor varies greatly depending on the mixed crystal ratio, when there is a large difference in the lattice constant between the light emitting layer and the charge injection layer of the Group 3-5 compound semiconductor, It is preferable to reduce the thickness of the light emitting layer in accordance with the magnitude of strain due to matching.
The preferred thickness range of the light emitting layer depends on the magnitude of the strain. A light emitting layer having an InN mixed crystal ratio of 10% or more is stacked on a layer represented by Ga _a Al _b N (where a + b = 1, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1) as _a charge injection layer. In this case, the preferred thickness of the light emitting layer is 5 mm or more and 90 mm or less. When the thickness of the light emitting layer is less than 5 mm, the light emission efficiency is not sufficient. On the other hand, if it is larger than 90 mm, defects are generated and the luminous efficiency is not sufficient.

In addition, by reducing the thickness of the light emitting layer, charges can be confined in the light emitting layer with high density, so that the light emission efficiency can be improved. For this reason, even when the difference in lattice constant is smaller than that in the above example, the thickness of the light emitting layer is preferably the same as that in the above example.
When the light emitting layer contains Al, impurities such as O are easily taken in, and the light emission efficiency may be lowered. In such a case, as the light emitting layer, a material represented by the general formula In _x Ga _y N not containing Al (where x + y = 1, 0 <x ≤ 1, 0 ≤ y <1) is used. can do.

The difference in band gap between the charge injection layer and the light emitting layer is preferably 0.1 eV or more. When the difference in band gap between the charge injection layer and the light emitting layer is smaller than 0.1 eV, the carriers are not sufficiently confined in the light emitting layer, and the light emission efficiency is lowered. More preferably, it is 0.3 ev or more. However, if the band gap of the charge injection layer exceeds 5 eV, the voltage required for charge injection becomes high. Therefore, the band gap of the charge injection layer is preferably 5 eV or less.
The thickness of the charge injection layer is preferably 10 to 5000 mm. Even if the thickness of the charge injection layer is smaller than 5 mm or larger than 5000 mm, the luminous efficiency is lowered, which is not preferable. More preferably, it is 10 to 2000 cm.
The light emitting layer may be a single layer or a plurality of light emitting layers. An example of such a structure is a stacked structure of (2n + 1) layers in which n light emitting layers and layers having a larger band gap than (n + 1) light emitting layers are alternately stacked. Here, n is a positive integer, preferably 1 or more and 50 or less, more preferably 1 or more and 30 or less. When n is 50 or more, the light emission efficiency is lowered and it takes time to grow, which is not preferable. Such a structure having a plurality of light emitting layers is particularly useful in the case of manufacturing a semiconductor laser that requires a strong light output.

  By doping the light emitting layer with an impurity, light can be emitted at a wavelength different from the band gap of the light emitting layer. Since this is light emission from impurities, it is called impurity light emission. In the case of impurity emission, the emission wavelength is determined by the composition of the Group 3 element in the light emitting layer and the impurity element. In this case, the InN mixed crystal ratio of the light emitting layer is preferably 5% or more. When the InN mixed crystal ratio is less than 5%, the emitted light is almost ultraviolet rays, and a sufficient brightness cannot be felt. As the InN mixed crystal ratio increases, the emission wavelength becomes longer, and the emission wavelength can be adjusted from purple to blue and green.

As an impurity suitable for impurity light emission, a group 2 element is preferable. Among group 2 elements, doping with Mg, Zn, and Cd is preferable because of high luminous efficiency. Zn is particularly preferable. The concentration of these elements is preferably 10 ¹⁸ to 10 ²² cm ⁻³ . The light emitting layer may be simultaneously doped with Si or Ge together with these Group 2 elements. A preferable concentration range of Si and Ge is 10 ¹⁸ to 10 ²² cm ⁻³ .

In the case of impurity emission, the emission spectrum is generally broad, and the emission spectrum may shift as the amount of injected charge increases. For this reason, when high color purity is required or when it is necessary to concentrate light emission power in a narrow wavelength range, it is advantageous to use band edge light emission. In order to realize a light emitting element using band edge light emission, the amount of impurities contained in the light emitting layer must be kept low. Specifically, the concentration of each element of Si, Ge, Mg, Cd, and Zn is preferably 10 ¹⁹ cm ⁻³ or less. More preferably, it is 10 ¹⁸ cm ⁻³ or less.
When band edge emission is used, the light emission efficiency depends on the defects in the light emitting layer, and decreases as the number of defects increases. Therefore, it is necessary to reduce the defects in the light emitting layer as much as possible. Therefore, the underlayer in the present invention has a great effect on improving the light emission efficiency of the light emitting element using the band edge.
As the InN mixed crystal ratio of the light emitting layer increases and the light emission wavelength becomes longer, the light emission efficiency may decrease. In this case, by increasing the AlN mixed crystal ratio of the charge injection layer 4 on the substrate side, it is possible to increase the InN mixed crystal ratio while suppressing a decrease in light emission efficiency.

In the Group 3-5 compound semiconductor, when the InN mixed crystal ratio of the light emitting layer is high, the thermal stability is not sufficient, and the crystal may grow during the crystal growth or in the semiconductor process. For the purpose of preventing such deterioration, a charge injection layer 6 having a low InN mixed crystal ratio can be laminated on a light emitting layer having a high InN mixed crystal ratio, and this layer can have a function as a protective layer. (Hereinafter, the charge injection layer in this case may be referred to as a protective layer.
). In order to provide the protective layer with a sufficient protective function, the protective layer preferably has an InN mixed crystal ratio of 10% or less and an AlN mixed crystal ratio of 5% or more. More preferably, the InN mixed crystal ratio is 5% or less, and the AlN mixed crystal ratio is 10% or more.

  In order to provide the protective layer with a sufficient protective function, the thickness of the protective layer is preferably 10 to 1 μm. If the thickness of the protective layer is less than 10 mm, a sufficient effect cannot be obtained. On the other hand, when it is larger than 1 μm, the luminous efficiency is decreased, which is not preferable. More preferably, it is 50 to 5000 inches.

Next, the substrate and growth method used in the present invention will be described.
As the substrate for crystal growth of the Group 3-5 compound semiconductor, sapphire, ZnO, GaAs, Si, SiC, NGO (NdGaO ₃ ), spinel (MgAl ₂ O ₄ ) and the like are used. In particular, sapphire is important because it is transparent and high quality crystals with a large area can be obtained.

  Examples of the method for producing the Group 3-5 compound semiconductor include molecular beam epitaxy (hereinafter sometimes referred to as MBE) method, metal organic vapor phase epitaxy (hereinafter also referred to as MOVPE) method, and hydride vapor phase. Examples include a growth (hereinafter sometimes referred to as HVPE) method. When the MBE method is used, the nitrogen source is a gas source molecular beam epitaxy (hereinafter sometimes referred to as GSMBE) method, which is a method of supplying nitrogen gas, ammonia, and other nitrogen compounds in a gaseous state. Commonly used. In this case, the nitrogen raw material may be chemically inert and nitrogen atoms may not be easily taken into the crystal. In that case, the nitrogen uptake efficiency can be increased by exciting the nitrogen raw material with microwaves and supplying it in an activated state.

Next, the manufacturing method by the MOVPE method of the 3-5 group compound semiconductor of this invention is demonstrated.
In the case of the MOVPE method, the following raw materials can be used.
That is, the Group 3 raw material may be described as trimethylgallium [(CH ₃ ) ₃ Ga, hereinafter TMG. ], Triethylgallium [(C ₂ H ₅ ) ₃ Ga, hereinafter sometimes referred to as TEG. ] Trialkylgallium represented by the general formula R ₁ R ₂ R ₃ Ga (where R ₁ , R ₂ and R ₃ represent lower alkyl groups); trimethylaluminum [(CH ₃ ) ₃ Al] , Triethylaluminum [(C ₂ H ₅ ) ₃ Al, hereinafter referred to as TEA. ], General formula R ₁ R ₂ R ₃ Al such as triisobutylaluminum [(i-C ₄ H ₉ ) ₃ Al] (wherein R ₁ , R ₂ and R ₃ are the same as defined in the previous term) Trimethylaluminum [(CH ₃ ) ₃ N: AlH ₃ ]; trimethylindium [(CH ₃ ) ₃ In, hereinafter sometimes referred to as TMI. ], General formula R ₁ R ₂ R ₃ In such as triethylindium [(C ₂ H ₅ ) ₃ In] (where R ₁ , R ₂ and R ₃ are the same as defined in the previous term). And trialkylindium. These may be used alone or in combination.

  Next, examples of the Group 5 materials include ammonia, hydrazine, methyl hydrazine, 1,1-dimethylhydrazine, 1,2-dimethylhydrazine, t-butylamine, ethylenediamine, and the like. These may be used alone or in combination. Among these raw materials, ammonia and hydrazine are preferable because they do not contain carbon atoms in their molecules and thus cause less carbon contamination in the semiconductor.

Group 2 elements are important as the p-type dopant of the Group 3-5 compound semiconductor. Specific examples include Mg, Zn, Cd, Hg, and Be. Among these, Mg that is easy to produce a low-resistance p-type is preferable.
Mg dopant materials include biscyclopentadienyl magnesium, bismethylcyclopentadienyl magnesium, bisethylcyclopentadienyl magnesium, bis-n-propylcyclopentadienyl magnesium, bis-i-propylcyclopentadienyl In order that the organometallic compound represented by the general formula (RC ₅ H ₄ ) ₂ Mg (eg, R represents hydrogen or a lower alkyl group having 1 to 4 carbon atoms) such as magnesium has an appropriate vapor pressure Is preferred.

As the n-type dopant of the Group 3-5 compound semiconductor, the Group 4 element and the Group 6 element are important. Specific examples include Si, Ge, and O. Among these, Si is preferable because it can easily produce a low-resistance n-type and can provide a material with high purity. As a raw material for the Si dopant, silane (SiH ₄ ), disilane (Si ₂ H ₆ ), and the like are suitable.

  Examples of the growth apparatus based on the MOVPE method that can be used for the production of the Group 3-5 compound semiconductor include a normal single-piece or multi-piece type. In the case of multiple wafers, it is desirable to grow under reduced pressure in order to ensure the uniformity of the epi film within the wafer surface. A preferable growth pressure range in the multi-sheet taking apparatus is 0.001 atm or more and 0.8 atm or less.

  As the carrier gas, a gas such as hydrogen, nitrogen, argon, helium or the like can be used alone or in combination. However, when hydrogen is included in the carrier gas, sufficient crystallinity may not be obtained when the compound semiconductor having a high InN mixed crystal ratio is grown. In this case, it is necessary to reduce the hydrogen partial pressure in the carrier gas. A preferable partial pressure of hydrogen in the carrier gas is 0.1 atm or less.

  Among these carrier gases, hydrogen and helium are mentioned in that they have a large kinematic viscosity coefficient and hardly cause convection. However, helium is more expensive than other gases, and when hydrogen is used, the crystallinity of the compound semiconductor is not good as described above. Since nitrogen and argon are relatively inexpensive, they can be suitably used when a large amount of carrier gas is used.

EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to these.
Example 1
A Group 3-5 compound semiconductor having the structure of FIG. 2 was prepared by the MOVPE method.
A substrate 8 having a mirror-polished sapphire C surface was used after organic cleaning. As a growth method, a two-stage growth method using GaN as a low temperature growth buffer layer was used. GaN buffer layer 9 having a thickness of about 300 mm at 550 ° C. at 1/8 atm, n-type layer 1 made of GaN doped with Si having a thickness of about 2.5 μm at 1050 ° C. Grew as a carrier gas.

Next, the substrate temperature is 750 ° C., the carrier gas is nitrogen, carrier gas, TEG, TMI, silane and ammonia diluted to 1 ppm with nitrogen are respectively supplied at 4 slm, 0.04 sccm, 0.6 sccm, 5 sccm, 4 slm, A strained layer 2 doped with Si-doped In _0.3 Ga _0.7 N was grown for 70 seconds. After maintaining the state of supplying only nitrogen and ammonia as growth interruption for 5 minutes, TEG, TEA, the above-mentioned silane and ammonia were further supplied at the same temperature by 0.032 sccm, 0.008 sccm, 5 sccm and 4 slm, An n-type layer 3 made of Ga _0.8 Al _0.2 N doped with Si was grown for 10 minutes.
However, slm and sccm are units of gas flow rate. 1 slm indicates that a gas having a weight occupying a volume of 1 liter in a standard state flows per minute, and 1000 sccm corresponds to 1 slm.
It should be noted that the film thicknesses of the layer 2 and the layer 3 are obtained from the above growth time because the growth rates obtained from the thickness of the layer grown for a longer time under the same conditions are 43 Å / min and 30 Å / min, respectively. The resulting film thicknesses can be calculated as 50 mm and 300 mm, respectively.

After growing the n-type layer 3, the growth pressure is 1 atm, the substrate temperature is 785 ° C., the non-doped In _0.3 Ga _0.7 N light emitting layer 5 is 50 mm, and the non-doped Ga _0.8 Al _0.2 N charge injection layer 6 is 300 mm. grown.
After the charge injection layer 6 was grown, the temperature of the substrate was set to 1100 ° C., and a p-type layer 7 made of GaN doped with Mg was grown 5,000 mm. The sample thus prepared was heat-treated at 800 ° C. for 20 minutes in nitrogen at 1 atm to make the Mg doped layer low resistance.
In the above example, the layers 9, 1, 10, 2, and 3 are the underlayers. The layer 3 also functions as a charge injection layer.

  The sample thus obtained was formed into an LED by forming an electrode according to a conventional method. Ni-Au alloy was used as the p electrode, and Al was used as the n electrode. When a current of 20 mA was passed through the LED in the forward direction, clear blue light emission was exhibited and the luminance was 860 mcd.

Comparative Example 1
An LED was fabricated in the same manner as in Example 1 except that after the non-doped GaN layer 10 was grown, the light-emitting layer 5, the charge injection layer 6, and the p-type layer 7 made of Mg-doped GaN were grown. When this was evaluated in the same manner as in Example 1, although it emitted blue light, the luminance was 390 mcd.

Example 2
An LED was fabricated in the same manner as in Example 1 except that the layer 3 was GaN doped with Si. When this was evaluated in the same manner as in Example 1, the luminance was 630 mcd, the central wavelength of the emission peak was 4600 mm, and the external quantum efficiency was 0.8%.

Example 3
The LED was fabricated in the same manner as in Example 1 except that the light emitting layer 5 and the charge injection layer 6 were grown at 1/8 atm and then the Mg-doped GaN layer 7 was grown at a growth pressure of 1 atm. did. When this was evaluated in the same manner as in Example 1, the luminance was 520 mcd and the center wavelength of the emission peak was 4600 mm.

Comparative Example 2
After growing the non-doped GaN layer 10, except that the light-emitting layer 5, the charge injection layer 6, and the Mg-doped GaN layer 7 were grown without growing the strained layer 2 and the Ga _0.8 Al _0.2 N layer 3. Produced an LED in the same manner as in Example 3. When this was evaluated in the same manner as in Example 1, the emission was very weak and the luminance was 10 ⁻⁴ cd or less.

Example 4
After growing the non-doped GaN layer 10, the strained layer 2 and the Ga _0.8 Al _0.2 N layer 3 were grown twice, and the LED was fabricated in the same manner as in Example 3 except that the structure had two strained layers. Produced. When this was evaluated in the same manner as in Example 1, the luminance was 240 mcd.

Example 5
An LED was fabricated in the same manner as in Example 3 except that after the strained layer 2 was grown, the Ga _0.7 Al _0.3 N layer 3 was grown instead of the Ga _0.8 Al _0.2 N layer 3. When this was evaluated in the same manner as in Example 1, the central wavelength of the emission peak was 5050 mm, and the luminance was 320 mcd. The emission wavelength was longer than that in Example 3.

Example 6
A Group 3-5 compound semiconductor shown in FIG. 3 is grown by vapor phase growth by the MOVPE method, and an LED having an emission wavelength of 5100 nm is manufactured.
On the sapphire (0001) substrate 8, GaN is grown as a buffer layer 9 with TMG and ammonia at a growth temperature of 600 ° C. and a pressure of 1/8 atm, and then a Si-doped GaN layer 1 is grown to 3 μm at 1100 ° C.
Next, a total of 6 layers of an In _0.3 Ga _0.6 Al _0.1 N layer doped with Si and a Ga _0.8 Al _0.2 N layer doped with Si were repeatedly grown as a base layer, and then an In _0.3 Ga _0.6 Al _0.1 N layer doped with Si A charge injection layer 4 made of is grown.
Next, a light-emitting layer 5 made of 150 Ｉｎ In _0.5 Ga _0.5 N layer is grown, and then a Ga _0.8 Al _0.2 N layer 6 is grown Å 300 Å.
Next, a GaN layer 7 doped with Mg is grown by 5000 mm. After the growth is completed, the substrate is taken out and heat-treated at 800 ° C. in nitrogen to reduce the resistance of the Mg-doped GaN layer.
An LED having a sharp emission spectrum can be produced by forming an electrode from the sample thus obtained according to a conventional method to form an LED.

The figure which shows one example of the 3-5 group compound semiconductor of this invention. FIG. 3 shows a light-emitting element of the present invention manufactured in Example 1. FIG. 6 shows a light-emitting element of the present invention shown in Example 6.

Explanation of symbols

1. . . n-type layer 2, 2 ′, 2 ″. . . Strain layer 3, 3 ', 3''. . . n-type layer 4. . . 4. Charge injection layer . . Light emitting layer 6. . . 6. Charge injection layer . . p-type layer 8. . . Substrate 9. . . Buffer layer 10. . . Non-doped GaN layer

Claims (8)

The substrate has at least a light emitting layer and a charge injection layer on the substrate, and the light emitting layer has a general formula In _x Ga _y Al _z N (where 0 <x ≦ 1, 0 ≦ y <1, 0 ≦ z <1). , X + y + z = 1), which is a non-doped group 3-5 compound semiconductor, and the charge injection layer has a general formula of In _{x ′} Ga _{y ′} Al _{z ′} N (where 0 ≦ x ′ ≦ 1, 0 ≦ y ′ ≦ 1, 0 ≦ z ′ ≦ 1, x ′ + y ′ + z ′ = 1), and a Group 3-5 compound semiconductor having a larger band gap than the light emitting layer. In the group 3-5 compound semiconductor light emitting device sandwiched between and in contact with the charge injection layer, the light emitting layer and the substrate have a base layer composed of at least three layers, and the layer forming the base layer has the general formula (wherein, 0 ≦ u ≦ 1,0 ≦ v ≦ 1,0 ≦ w ≦ 1, u + v + w = 1) in u Ga v Al w N be a 3-5 group compound semiconductor represented by At least one layer in the underlayer is sandwiched between and in contact with two layers having a smaller InN mixed crystal ratio, and the InN mixed crystal ratio of the at least one layer is that of the layer in contact with the layer from the substrate side. A Group 3-5 compound semiconductor light emitting device having a larger than InN mixed crystal ratio by 0.05 or more.   The n-type impurity is doped in at least one layer between the layer on the substrate side and the light emitting layer among the two layers having a small InN mixed crystal ratio in the underlayer. -Group 5 compound semiconductor light emitting device.   The group 3-5 compound semiconductor light emitting device according to claim 1 or 2, wherein the light emitting layer has a thickness of 5 to 90 mm.   The charge injection layer on the substrate side of the charge injection layer in contact with the light emitting layer sandwiched between them emits light of the two layers having a small InN mixed crystal ratio in contact with the layer having a large InN mixed crystal ratio in the underlayer The group 3-5 compound semiconductor light-emitting element according to claim 1, which also serves as a layer on the layer side. 5. The group 3-5 compound according to claim 2, wherein the n-type impurity is Si and / or Ge, and the concentration of the n-type impurity is 1 × 10 ¹⁷ cm ⁻³ or more. Semiconductor light emitting device.   The group 3-5 compound according to any one of claims 1 to 5, wherein a thickness of a layer sandwiched between two layers having a small InN mixed crystal ratio in the underlayer is 5 to 600 mm. Semiconductor light emitting device.   At least one layer in the underlayer is sandwiched between and in contact with two layers having a smaller InN mixed crystal ratio, and the thickness of the layer of the at least one layer is 5 mm or more. When the InN mixed crystal ratio is 0.05 or more and 0.3 or less larger than the InN mixed crystal ratio of the layer in contact with the layer from the substrate side, the difference between the mixed crystal ratios and the thickness (Å) of at least one layer When the product is 30 or less and the InN mixed crystal ratio of the at least one layer exceeds the InN mixed crystal ratio of the layer in contact with the layer from the substrate side by more than 0.3, the thickness of the at least one layer Is a group 3-5 compound semiconductor light-emitting device according to any one of claims 1 to 6. The underlayer comprising at least three layers is grown at a pressure of 0.001 atm or more and 0.8 atm or less by metal organic vapor phase epitaxy. -Group 5 compound semiconductor light emitting device.

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