JP3713751B2 - Group 3-5 compound semiconductor and light emitting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a group 3-5 compound semiconductor represented by the general formula In _x Ga _y Al _z N (where x + y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1) and It relates to the light emitting element used.
[0002]
[Prior art]
As a material of a light emitting element such as an ultraviolet or blue light emitting diode (hereinafter referred to as LED) or an ultraviolet or blue laser diode, a general formula In _x Ga _y Al _z N (where x + y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1; hereinafter referred to as InGaAlN)) is known. In particular, when the mixed crystal ratio of InN (hereinafter sometimes referred to as “In composition”, “Al composition” or the like may be similarly described)) is 10% or more, light emission in the visible region depends on the In composition. Since the wavelength can be adjusted, it is particularly important for display applications.
[0003]
Incidentally, in order to manufacture a light emitting element that can be driven at a low voltage, it is necessary to have a structure in which the light emitting layer is sandwiched between p-type and n-type current injection layers. As for the structure, a structure in which the p-type carrier concentration and / or the n-type carrier concentration decreases as the light emitting layer is approached has been proposed (Japanese Patent Laid-Open No. 7-15041).
However, the fact is that a light emitting element having high luminous efficiency has not been obtained yet.
[0004]
[Problems to be solved by the invention]
The objective of this invention is providing the 3-5 group compound semiconductor and light emitting element which are used for the light emitting element which has high luminous efficiency.
[0005]
[Means for Solving the Problems]
As a result of various studies on the Group 3-5 compound semiconductor, the present inventors have found that when the p-layer side layer in contact with the light-emitting layer has a band gap larger than that of the light-emitting layer and the p-type impurity concentration is low, the light emission efficiency is improved. The improvement was found and the present invention was achieved.
[0006]
That is, the present invention is the invention described below.
[1] Laminated structure of Group 3-5 compound semiconductor represented by general formula In _x Ga _y Al _z N (where x + y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1) The stacked structure includes a first layer which is an n-type semiconductor layer, and a second layer doped with a p-type impurity, and between the first layer and the second layer, A third layer that functions as a light-emitting layer; and a fourth layer. The third layer and the fourth layer are in direct contact with each other. The third layer is on the first layer side. The fourth layer is on the second layer side, the fourth layer has a larger band gap than the third layer, is an undoped layer that is not doped with impurities, and the Mg concentration is 10 ¹⁷ cm ⁻³ or less. A Group 3-5 compound semiconductor.
[2] The Group 3-5 compound semiconductor according to [1] above is represented by the general formula Ga _a Al _b A group 3-5 compound semiconductor laminated on a group 3-5 compound semiconductor represented by N (where a + b = 1, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1).
[ 3 ] The first layer is made of a group 3-5 compound semiconductor represented by the general formula Ga _a Al _b N (where a + b = 1, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1). [3] The group 3-5 compound semiconductor according to any one of [1] to [2] .
[4] The group 3-5 compound semiconductor according to any one of [1] to [3], wherein the third layer has a thickness of 10 to 500 mm.
[ 5 ] The concentration of each element of Si, Ge, Mg, Zn, and Cd contained in the third layer is 10 ¹⁹ cm ⁻³ or less, and any one of [1] to [4] 3-5 compound semiconductor of description.
[6] The group 3-5 compound semiconductor according to any one of [1] to [5], wherein the third layer is a non-doped layer that is not doped with impurities.
[ 7 ] A light emitting device using the Group 3-5 compound semiconductor according to any one of [1] to [6] .
[0007]
Next, the present invention will be described in detail.
The Group 3-5 compound semiconductor of the present invention has a structure in which a first semiconductor layer that is an n-type semiconductor layer and a second semiconductor layer that is doped with a p-type impurity sandwich a third semiconductor layer that is a light emitting layer. Have. The first layer and the second layer are layers in contact with the n electrode and the p electrode, respectively. Charges can be injected from the first layer and the second layer, and the charges can be recombined in the third layer to emit light. In particular, a so-called double heterostructure in which the third layer is in contact with two layers having a larger band gap is important because it has an effect of confining electric charges in the third layer, so that the light emission efficiency can be increased.
When the band gap exceeds 5 eV, the group 3-5 compound semiconductor has high resistance and it becomes difficult to transfer charges. Therefore, any layer of the stacked structure in the group 3-5 compound semiconductor of the present invention has a band gap of 5 eV or less. It is preferable that
In the group 3-5 compound semiconductor of the present invention, in order to confine charges in the third layer efficiently by the double heterostructure, the band gap of the two layers in contact with the third layer is 0.1 eV from the third layer. It is preferable that it is larger. More preferably, it is 0.3 eV or more.
[0008]
In the group 3-5 compound semiconductor of the present invention, a third layer and a fourth layer are included between the first layer and the second layer, and the third layer and the fourth layer are directly In contact, the third layer is on the first layer side and the fourth layer is on the second layer side. The fourth layer has a larger band gap than the third layer.
In the Group 3-5 compound semiconductor of the present invention, the concentration of Mg contained in the fourth layer is 10 ¹⁸ cm ⁻³ or less, preferably 10 ¹⁷ cm ⁻³ or less. If the Mg concentration exceeds 10 ¹⁸ cm ⁻³ , the luminous efficiency is lowered, which is not preferable.
The film thickness of the fourth layer is preferably 10 to 1 μm. More preferably, it is 50 to 5000 inches. If the thickness of the fourth layer is less than 10 mm, sufficient effects cannot be obtained. On the other hand, when it is larger than 1 μm, the luminous efficiency is decreased, which is not preferable.
When the third layer contains In, thermal stability is not sufficient, and deterioration may occur during crystal growth or a semiconductor process. The fourth layer can have a function of protecting the deterioration of the third layer. For this purpose, the In composition of the fourth layer is preferably 10% or less, and the Al composition is preferably 5% or more. More preferably, the In composition is 5% or less and the Al composition is 10% or more.
The fourth layer is in direct contact with the third layer, but when the layer in contact with the fourth layer on the opposite side of the third layer is a p-type semiconductor, the band gap of the fourth layer is It is preferably larger than the band gap of the p-type layer with which the fourth layer is in contact. This is because the fourth layer has a barrier property against electrons with respect to the p-type layer. The preferred band gap difference between the fourth layer and the p-type layer in contact therewith is preferably 0.1 eV or more, more preferably 0.3 eV or more.
[0009]
Examples of the Group 3-5 compound semiconductor of the present invention further include those having a structure in which the Group 3-5 compound semiconductor is grown on Ga _a Al _b N (a and b are the same as described above). The Group 3-5 compound semiconductor grown on Ga _a Al _b N has higher crystallinity. This is preferable because the luminous efficiency is further increased. The reason is considered as follows. The injected charge is recombined non-radiatively due to crystal defects or the like in addition to recombining radiatively in the light emitting layer. Therefore, it is considered that the smaller the number of crystal defects, the lower the ratio of non-radiative recombination and the higher the light emission efficiency. An example of this structure is shown in FIG.
The first layer may be Ga _a Al _b N (a and b are the same as described above). An example of this is shown in FIG.
[0010]
In the example of FIGS. 1 and 2, the second layer and the fourth layer are in direct contact with each other. However, the other layers are not limited to the extent that the object of the present invention is not impaired. There may be one or more layers. However, when there is an n-type layer between two or more p-type layers in the stacked structure, or when there is a p-type layer between two or more n-type layers, Since pn junctions opposite to each other can be formed, the electrical characteristics as a diode are deteriorated, which is not preferable.
Further, the third layer may be a layer composed of a plurality of layers functioning as a light emitting layer. Specifically, an example in which a layer composed of a plurality of layers functions as a light emitting layer includes a structure in which two or more light emitting layers are stacked with a layer having a larger band gap.
[0011]
As the third layer which is a light emitting layer, a Group 3-5 compound semiconductor having an In composition of 10% or more is important for display applications because the band gap can be made visible. Those containing Al can easily take in impurities such as oxygen, and when used as a light emitting layer, the light emission efficiency may decrease. In such a case, the light emitting layer is preferably one represented by the general formula In _x Ga _y N (where x + y = 1, 0 <x ≦ 1, 0 ≦ y <1) not containing Al.
The lattice constant of the compound semiconductor varies greatly depending on the composition. In particular, the lattice constant of InN is about 12% or more larger than that of GaN or AlN. For this reason, depending on the composition of each layer of the compound semiconductor, there may be a large difference in the lattice constant between the layers. When there is a large lattice mismatch, a defect may occur in the crystal, which causes a decrease in crystallinity. In order to suppress the occurrence of defects due to lattice mismatch, the thickness of the layer must be reduced according to the magnitude of strain due to lattice mismatch. The preferred thickness range depends on the magnitude of the strain. When the compound semiconductor containing 10% or more of In is stacked on Ga _a Al _b N (a and b are the same as above), the preferred thickness of the layer containing In is 10 to 500 mm. A more preferable thickness range is 10 to 100 mm, particularly preferably 10 to 90 mm. When the thickness of the layer containing In is less than 10 mm, the light emission efficiency is not sufficient. On the other hand, if it is larger than 500 mm, defects are generated and the luminous efficiency is not sufficient.
[0012]
By doping impurities in the third layer, light can be emitted at a wavelength different from the band gap of the third layer. Since this is light emission from impurities, it is called impurity light emission. In the case of impurity light emission, the emission wavelength is determined by the composition of the Group 3 element of the third layer and the impurity element. In this case, the In composition of the third layer is preferably 5% or more. When the In composition is less than 5%, the emitted light is almost ultraviolet light, and sufficient brightness cannot be felt. As the In composition increases, the emission wavelength becomes longer, and the emission wavelength can be adjusted from purple to blue to 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. In particular, Zn is preferable. The concentration of these elements is preferably 10 ¹⁸ to 10 ²² cm ⁻³ . The third 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 .
[0013]
In the case of impurity emission, the emission spectrum is generally broad. For this reason, band edge emission is used when high color purity is required or when it is necessary to concentrate the emission power in a narrow wavelength range. In order to realize a light-emitting element using band edge light emission, the amount of impurities contained in the third 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. Furthermore, it is preferably 10 ¹⁸ cm ⁻³ or less.
In the case of band edge emission, the emission color is determined by the composition of the Group 3 element in the third layer. When light is emitted in the visible region, the In composition is preferably 10% or more. When the In composition is less than 10%, the emitted light is almost ultraviolet light, and sufficient brightness cannot be felt. As the In composition increases, the emission wavelength becomes longer, and the emission wavelength can be adjusted from purple to blue to green.
[0014]
As a method for producing a Group 3-5 compound semiconductor of the present invention, molecular beam epitaxy (hereinafter sometimes referred to as MBE) method, metal organic vapor phase epitaxy (hereinafter also referred to as MOVPE) method, hydride. Examples include a vapor phase growth (hereinafter sometimes referred to as HVPE) method. When using the MBE method, the nitrogen source is generally 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. Has been 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.
[0015]
In general, since a group 3-5 compound semiconductor cannot obtain good crystals by bulk growth, homoepitaxial growth using the compound semiconductor itself as a substrate is difficult. For this reason, sapphire, ZnO, GaAs, Si, SiC, or the like is used as a substrate for crystal growth of the compound semiconductor. In particular, sapphire is particularly important because it can grow the compound semiconductor having good crystallinity when used in combination with a buffer layer such as AlN.
In the case of MOVPE, 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 referred to as TEG. ], A trialkyl gallium 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 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 represent lower alkyl groups). Trialkylaluminum; trimethylamine allane [(CH ₃ ) ₃ N: AlH ₃ ]; trimethylindium [(CH ₃ ) ₃ In, hereinafter sometimes referred to as TMI. ], Triethylindium [(C ₂ H ₅ ) ₃ In] and other general formulas R ₁ R ₂ R ₃ In (where R ₁ , R ₂ and R ₃ represent lower alkyl groups). Examples include alkyl indium. These may be used alone or in combination.
[0016]
Next, examples of the Group 5 raw material include ammonia, hydrazine, methyl hydrazine, 1,1-dimethylhydrazine, 1,2-dimethylhydrazine, t-butylamine, and ethylenediamine. 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.
[0017]
【Example】
Hereinafter, the present invention will be described in detail by way of examples, but the present invention is not limited thereto.
Example 1
A Group 3-5 compound semiconductor having a structure shown in FIG. 3 was produced by vapor phase growth by the MOVPE method. A substrate obtained by mirror-polishing the sapphire C surface was used for organic cleaning. The growth was performed by a two-step growth method using a low temperature growth buffer layer. GaN, which is a first layer doped with Si at 1100 ° C. using TMG, ammonia, and silane (SiH ₄ ) as a dopant after forming 500 GaN of TMG and ammonia at 600 ° C. as the buffer layer 2 9) was formed to a thickness of 3 μm, and non-doped GaN (number 10) was formed to a thickness of 1500 mm in this order.
Next, after the temperature is lowered to 785 ° C., the carrier gas is changed from hydrogen to nitrogen, and TEG, TMI, and ammonia are supplied at 0.04 sccm, 0.08 sccm, and 4 slm, respectively, and the third layer 11 is In _0.3 Ga _0.7 N. Was grown for 90 seconds, and TEG, TEA, and ammonia were supplied at 0.032 sccm, 0.008 sccm, and 4 slm, respectively, and Ga _0.8 Al _0.2 N as the fourth layer 6 was grown for 10 minutes. However, sccm and slm are units of gas flow rate, and 1 sccm indicates that a gas having a weight occupying a volume of 1 cc in a standard state per minute flows, and 1 slm is 1000 sccm.
The growth rates obtained from the relationship between the growth time and the film thickness in the thick films of these layers are 33 Å / min and 25 Å / min, respectively, and the thicknesses of the respective layers obtained from these are 50 Å and 250 各 々, respectively.
[0018]
Next, the temperature is raised to 1100 ° C., and TMG, ammonia, and biscyclopentadienylmagnesium [(C ₅ H ₅ ) ₂ Mg, hereinafter referred to as Cp ₂ Mg may be used as a dopant. , GaN doped with Mg as the second layer 7 was grown by 5000 mm. After completion of the growth, the substrate was taken out and heat-treated at 800 ° C. in nitrogen.
An electrode was formed on the sample thus obtained according to a conventional method, and an LED by band edge emission was obtained. 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 400 mcd.
[0019]
Comparative Example 1
When growing the fourth layer 6, the LED was supplied in the same manner as in Example 1 except that 100 sccm of nitrogen was supplied to a Cp ₂ Mg bubbler maintained at 30 ° C., and this was added to the raw material to dope Mg. Was made. The brightness in the forward direction of 20 mA of the LED produced by the band edge emission was 20 mcd.
Similarly, a sample was grown after the fourth layer was grown. This sample does not have the second layer 7 of the sample of Comparative Example 1, and the fourth layer 6 is the outermost layer. The photoluminescence spectrum of this sample at room temperature (hereinafter sometimes referred to as PL spectrum) was measured using 325 nm light of a He—Cd laser as excitation light, and the weakness from Mg of the fourth layer 6 was found to be 420 nm. Broad luminescence was seen. This light emission indicates that the compound semiconductor is doped with a Mg concentration of at least 2 × 10 ¹⁹ cm ⁻³ or more.
[0020]
【The invention's effect】
By using the Group 3-5 compound semiconductor of the present invention, the performance of a light-emitting element such as an ultraviolet or blue LED or an ultraviolet or blue laser diode can be enhanced, and thus industrial value is great.
[Brief description of the drawings]
FIG. 1 shows _a group 3-5 compound semiconductor according to the present invention in which a group 3-5 compound semiconductor is stacked on Ga _a Al _b N (where a + b = 1, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1). Sectional view of an example.
FIG. 2 is _a cross-sectional view of an example of a Group 3-5 compound semiconductor of the present invention in which the first layer is Ga _a Al _b N (where a + b = 1, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1). .
3 is a cross-sectional view of a Group 3-5 compound semiconductor of the present invention manufactured in Example 1. FIG.
[Explanation of symbols]
1 ... substrate 2 ... buffer layer 3 ··· Ga _a Al _b N (provided that, a + b = 1,0 ≦ a ≦ 1,0 ≦ b ≦ 1) is a layer 4 ... first layer In _x Ga _y Al _z N (where x + y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1) Layer 5... In _x Ga _y Al _z N which is the third layer (However, x + y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1) Layer 6... The fourth layer, Ga _a Al _b N (where a + b = 1, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1) Layer 7... p-type GaN as the second layer
8 ... Ga _a Al _b N (where a + b = 1, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1) layer 9 GaN doped with Si as the first layer Layer 10... Non-doped GaN layer 11... In _x Ga _y Al _z N as a third layer (where x + y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1) layer

Claims (7)

It consists of a laminated structure of a Group 3-5 compound semiconductor represented by the general formula In _x Ga _y Al _z N (where x + y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1), The stacked structure includes a first layer that is an n-type semiconductor layer and a second layer doped with a p-type impurity, and a light-emitting layer is provided between the first layer and the second layer. A third layer that functions, and a fourth layer, wherein the third layer and the fourth layer are in direct contact, the third layer is on the first layer side, and the fourth layer Is on the second layer side, the fourth layer is a non-doped layer having a larger band gap than that of the third layer and is not doped with impurities, and the Mg concentration is 10 ¹⁷ cm ⁻³ or less. Group 3-5 compound semiconductor. The group 3-5 compound semiconductor according to claim 1 is a group 3-5 compound semiconductor represented by a general formula Ga _a Al _b N (where a + b = 1, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1). A Group 3-5 compound semiconductor stacked on top. The first layer is made of a group 3-5 compound semiconductor represented by _a general formula Ga _a Al _b N (where a + b = 1, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1). Item 3-5 compound semiconductor according to any one of Items 1 and 2 . 4. The group 3-5 compound semiconductor according to claim 1, wherein the third layer has a thickness of 10 to 500 mm. 5. The concentration of each element of Si, Ge, Mg, Zn, and Cd contained in the third layer is 10 ¹⁹ cm ^-3 or less, and 3-5 according to any one of claims 1 to 4 Group compound semiconductors. The group 3-5 compound semiconductor according to any one of claims 1 to 5 , wherein the third layer is a non-doped layer not doped with impurities. The light emitting element using the 3-5 group compound semiconductor in any one of Claims 1-6 .

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