JP3598591B2 - Method for manufacturing group 3-5 compound semiconductor - Google Patents

Description

【００３３】
【発明の効果】
本発明によれば、ｐ型の３−５族化合物半導体層を成長する前に、ｐ型ドーパント原料を供給し、３族原料は供給しない工程を設けることによって、輝度および発光効率の向上した、発光素子が作製できるため、きわめて有用であり工業的価値が大きい。
【図面の簡単な説明】
【図１】本発明における空流し工程の概念図。
【図２】本発明の実施例１に示す３−５族化合物半導体の構造を示す図。
【図３】実施例１〜３、比較例１、２におけるＭｇ原料の空流し工程の時間とＬＥＤの輝度との関係を示す図。
【符号の説明】
１……サファイア基板
２……ＧａＮバッファー層
３……ｎ型ＧａＮ：Ｓｉ層
４……ノンドープＧａＮ層
５……第１の層であるｎ型ＧａＮ層
６……第３の層であるＩｎＧａＮ層
７……保護層であるＡｌＧａＮ層
８……第２の層であるｐ型ＧａＮ：Ｍｇ層[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a Group 3-5 compound semiconductor by a vapor phase growth method. In particular, the present invention relates to a method for manufacturing a Group 3-5 compound semiconductor used for a light emitting element.
[0002]
[Prior art]
Conventionally, 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) as a blue light emitting diode 3-5 group compound represented by Semiconductor devices are used. Since the group 3-5 compound semiconductor is a direct transition type, it has high luminous efficiency, and can emit light at an emission wavelength from yellow to violet and ultraviolet depending on the In concentration, and is particularly useful for short wavelength light emitting devices. It is.
[0003]
Examples of the method for producing the Group 3-5 compound semiconductor include a molecular beam epitaxy (hereinafter, sometimes referred to as MBE) method, a metal organic chemical vapor deposition (hereinafter, sometimes referred to as MOVPE) method, and a hydride gas phase. A growth (hereinafter sometimes referred to as HVPE) method or the like is used.
Of these methods, the MOVPE method involves heating a substrate placed under normal pressure or reduced pressure, supplying an organometallic compound containing a Group 3 element and a raw material containing a Group 5 element in a gaseous phase, This is a method of causing a decomposition reaction to grow a semiconductor film. The MOVPE method is important in that the uniform and high-quality Group 3-5 compound semiconductor can be grown over a large area.
[0004]
By the way, as a method for increasing the luminous efficiency of a light-emitting element, a structure in which a light-emitting layer is interposed between p-type and n-type semiconductor layers, and a layer having a band gap larger than the band gap of the light-emitting layer is in contact with both sides of the light-emitting layer. It is widely known to use a so-called double heterostructure.
However, it is very difficult to form a steep pn junction interface with a group III-V compound semiconductor produced by the MOVPE method, so that even in a device having a double hetero structure, the luminance and the luminous efficiency have not been sufficient.
[0005]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for manufacturing a group 3-5 compound semiconductor that can increase the luminance and the luminous efficiency of a light emitting element.
[0006]
[Means for Solving the Problems]
The present inventors have made various studies on the light emitting device having a double hetero structure of the group 3-5 compound semiconductor, and found that the light emitting device before growing the p-type layer was used for the purpose of improving the sharpness at the growth interface of the p-type layer. It is found that when a step of supplying a p-type dopant material and not supplying a group 3 material is provided (hereinafter sometimes referred to as an emptying step), the luminous efficiency of the light emitting element is drastically improved. Reached.
[0007]
That is, the present invention is the following invention.
[1] contains a formula _{In x Ga y Al z N (} x + y + z = 1,0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ z ≦ 1) 3-5 group compound semiconductor multilayer structure represented by A group III-V compound semiconductor having at least one p-type layer in the laminated structure is reacted with a group III organometallic compound and a compound having N in a molecule by a metalorganic vapor phase epitaxy method. A method for producing a group 3-5 compound semiconductor by growing in a tube, comprising a step of supplying a p-type dopant material and not supplying a group 3 material before a step of growing a p-type layer. A method for producing a Group 3-5 compound semiconductor.
[2] The method for producing a Group 3-5 compound semiconductor according to [1], wherein the p-type dopant is Mg.
[0008]
[3] the group 3-5 compound semiconductor includes an n-type first layer, a p-type second layer, and at least one third layer sandwiched between the two layers; The method for producing a Group 3-5 compound semiconductor according to [1] or [2], wherein the third layer is in contact with two layers having a larger band gap on both sides of the third layer.
[4] The method for producing a Group 3-5 compound semiconductor according to [3], wherein the thickness of the third layer is 5 ° or more and 90 ° or less.
[5] Each of the concentrations of Si, Ge, Mg, Zn and Cd contained in the third layer is 1 × 10 ¹⁹ cm ⁻³ or less. A method for producing a Group V compound semiconductor.
[0009]
Next, the present invention will be described in detail.
Since a good crystal cannot be obtained by bulk growth of the Group 3-5 compound semiconductor, it is difficult to perform homoepitaxial growth using the Group 3-5 compound semiconductor itself as a substrate. For this reason, sapphire, ZnO, GaAs, Si, SiC, or the like is used as the substrate for crystal growth of the group III-V compound semiconductor. In particular, sapphire is preferable since a group III-V compound semiconductor having good crystallinity can be grown by using a buffer layer such as AlN.
[0010]
In the present invention, the following raw materials can be used.
As a Group 3 raw material, trimethylgallium [(CH ₃ ) ₃ Ga, hereinafter referred to as TMG may be used. ], Triethylgallium [(C ₂ H ₅ ) ₃ Ga, hereinafter sometimes referred to as TEG. A trialkylgallium represented by a general formula R ₁ R ₂ R ₃ Ga (where R ₁ , R ₂ , and R ₃ represent a lower alkyl group); trimethylaluminum [(CH ₃ ) ₃ Al]; Triethylaluminum [(C ₂ H ₅ ) ₃ Al, hereinafter sometimes referred to as TEA. ], Is represented by triisobutyl aluminum _{[(i-C 4 H 9} ) formula 3 Al], etc. _R 1 _R 2 _R 3 Al (wherein _{R 1,} R 2, _{R 3} is a lower alkyl group.) Trialkylaluminum; trimethylamine alane [(CH ₃ ) ₃ N: AlH ₃ ]; trimethyl indium [(CH ₃ ) ₃ In; ], Triethylindium [(C ₂ H ₅ ) ₃ In], etc., and a trialkyl represented by a general formula R ₁ R ₂ R ₃ In (where R ₁ , R ₂ , and R ₃ represent a lower alkyl group). Indium and the like can be mentioned. These are used alone or as a mixture.
[0011]
Next, as a Group 5 raw material, ammonia, hydrazine, methylhydrazine, 1,1-dimethylhydrazine, 1,2-dimethylhydrazine, t-butylamine, ethylenediamine, and the like can be given. These are used alone or as a mixture. Among these raw materials, ammonia and hydrazine do not contain a carbon atom in the molecule, and thus are suitable because the carbon is not easily contaminated in the semiconductor.
As the p-type dopant of the Group 3-5 compound semiconductor, a Group 2 element is preferable. Specific examples include Mg, Zn, Cd, Hg, and Be. Of these, Mg, which is easy to produce a low-resistance p-type, is preferable.
[0012]
As a raw material of the Mg dopant, biscyclopentadienyl magnesium (hereinafter sometimes referred to as Cp ₂ Mg), bismethylcyclopentadienyl magnesium, bisethylcyclopentadienyl magnesium, bis n-propylcyclopentadiene magnesium enyl, organic represented by the general formula such as bis-i- propyl-cyclopentadienyl magnesium _{(RC 5 H 4) 2 Mg} ( wherein R represents H or having 1 to 4 carbon atoms or less of a lower alkyl group.) Metal compounds are preferred because they have a suitable vapor pressure.
[0013]
As the n-type dopant of the Group 3-5 compound semiconductor, a Group 4 element and a Group 6 element are preferable. Specific examples include Si, Ge, and O. Among them, Si that can easily form an n-type with low resistance and obtains a material having a high material purity is preferable. As a raw material of the Si dopant, SiH ₄ , Si ₂ H _{6 and the} like are preferable.
[0014]
The method for producing a Group 3-5 compound semiconductor of the present invention is characterized in that a step of supplying a p-type dopant material and not supplying a Group 3 material is provided before the step of growing a p-type semiconductor layer. Sinking step).
As shown in the conceptual diagram of FIG. 1, this idle flow step is a step performed before the step of growing a p-type layer, and is a step of supplying a p-type dopant material and not supplying a group 3 material.
The emptying step and the subsequent growth step of the p-type layer may be performed continuously or at intervals (in the case of FIG. 1). Is preferably as short as possible, and is preferably performed continuously.
Further, the flow rate of the p-type dopant material in the emptying step may be the same as or different from the flow rate of the p-type dopant material in the growth step of the p-type layer. It is preferable that there is no fluctuation in the flow rate because fluctuations in the flow rate may cause deterioration in crystal quality.
[0015]
The temperature in the reaction tube in the emptying step may be the same as or different from the growth temperature of the p-type layer performed later, but the same temperature is more preferable. If the temperature of the airflow step is different from the growth temperature of the p-type layer, the growth time is extended by the time required for raising or lowering the temperature, and the temperature is changed before the airflow step. It is not preferable because the quality of the grown crystal may be deteriorated.
The pressure in the reaction tube in the idling step may be the same as or different from the pressure during the subsequent growth of the p-type layer. In the more preferred emptying step, the group V source gas may or may not be supplied at the same time because the complexity of the process can be reduced. However, if the temperature of the emptying step is 650 ° C. or higher, the quality of the crystal grown before this step may be reduced unless the group V source gas is supplied. Are preferably supplied simultaneously.
[0016]
The main control factors in the emptying process include the type, flow rate, supply time, temperature and pressure of the p-type dopant material. Since the preferable range of these control factors varies depending on the growth apparatus, the preferable range cannot be specified without limitation. However, as the growth apparatus increases, the supply time increases in the direction in which the flow rate in the preferable range increases. Change in direction.
[0017]
As an example of a preferable range of the flow rate of the Mg raw material, the range in the apparatus used by the present inventors is as follows. When biscyclopentadienyl magnesium is used, the carrier gas flow rate is maintained while the raw material bubbler is maintained at 30 ° C. It is 50 sccm or more and 500 sccm or less. If it is less than 50 sccm or more than 500 sccm, the effect of providing this step is not obtained, which is not preferable. Here, sccm is a unit of gas flow rate, and indicates that a gas weighing 1 cc per minute in a standard state flows per minute.
[0018]
As a preferable example of the Mg raw material supply time, a range in the apparatus used by the present inventors is as follows. When performing an idle flow process using biscyclopentadienyl magnesium at 1100 ° C., normal pressure, and a flow rate of 200 sccm, It is 1 second or more and less than 3 minutes, and more preferably 10 seconds or more and 2 minutes or less. If the time is shorter than 1 second or longer than 3 minutes, the effect of this step cannot be obtained, which is not preferable.
The preferred temperature range of the emptying step is from 600 ° C to 1200 ° C. If the temperature is lower than 600 ° C. or higher than 1200 ° C., the effect of this step cannot be obtained, which is not preferable.
[0019]
As a Group 3-5 compound semiconductor obtained by the method for producing a Group 3-5 compound semiconductor of the present invention, an n-type first layer and a second layer doped with a p-type dopant, and a third light-emitting layer One having a structure in which a layer is interposed is given. Electric charge can be injected from the first layer and the second layer, and the electric charge can be recombined in the third layer to emit light. In particular, a so-called double hetero structure in which the third layer is sandwiched between two layers having larger band gaps is preferable because it has an effect of confining charges in the third layer and thus can increase luminous efficiency. However, when there is an n-type layer between two or more p-type layers in the laminated structure, or when there is a p-type layer between two or more n-type layers, Since pn junctions in opposite directions are formed, the electrical characteristics of the diode deteriorate, which is not preferable.
When the band gap of the Group 3-5 compound semiconductor exceeds 5 eV, the resistance becomes high and the movement of charges becomes difficult. Therefore, any of the layers of the layered structure of the Group 3-5 compound semiconductor has a band gap of 5 eV or less. Preferably, there is.
In order to efficiently confine charges in the third layer by the double hetero structure in the group III-V compound semiconductor of the present invention, the band gap of the two layers in contact with the third layer is set to be smaller than the band gap of the third layer by 0. It is preferably greater than or equal to .1 eV. More preferably, it is 0.3 eV or more.
[0020]
The third layer may be a layer including a plurality of layers functioning as a light emitting layer. Specifically, an example in which a layer including 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.
[0021]
As the third layer which is a light-emitting layer, the group III-V compound semiconductor having an In composition of 10% or more is preferable for display use because the band gap can be made visible. Those containing Al tend to take in impurities such as oxygen, and when used as a light-emitting layer, the luminous efficiency may decrease. In such a case, as the light-emitting layer does not contain Al general formula _In x _Ga y N (provided that, x + y = 1,0 <x ≦ 1,0 ≦ y <1) be used those represented by Can be.
[0022]
The lattice constant of the group III-V compound semiconductor greatly changes 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 Group 3-5 compound semiconductor, a large difference may occur in the lattice constant between the layers. When there is a large lattice mismatch, a defect may be generated 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 Group III-V compound semiconductor containing 10% or more of In is stacked on Ga _x Al _1-xN (where 0 ≦ x ≦ 1), the preferable thickness of the layer containing In is 5 ° or more and 500 ° or less. is there. When the thickness of the layer containing In is less than 5 °, the luminous efficiency becomes insufficient. On the other hand, if it is larger than 500 °, a defect occurs, and the luminous efficiency is also insufficient. A more preferable thickness range is 5 ° to 90 °.
[0023]
By doping the third layer with an impurity, light can be emitted at a wavelength different from the band gap of the third layer. Since this is light emission from an impurity, 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 in 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. The emission wavelength becomes longer as the In composition is increased, and the emission wavelength can be adjusted from purple to blue and green.
As an impurity suitable for impurity emission, a Group 2 element is preferable. Among the group II elements, Mg, Zn, and Cd are preferably used because of high luminous efficiency. Particularly, Zn is preferable. The concentration of these elements is preferably from 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 preferred concentration range of Si and Ge is 10 ¹⁸ to 10 ²² cm ⁻³ .
[0024]
In the case of impurity light emission, the light emission spectrum generally becomes broad, and the light emission spectrum shifts as the amount of injected charge increases, or a peak of band edge light emission appears. Difficult to raise. Therefore, when high color purity is required, when emission power needs to be concentrated in a narrow wavelength range, or when an element with high emission efficiency is required, it is more advantageous to use band edge emission. . In order to realize a light-emitting element using band-edge light emission, the amount of impurities contained in the third layer must be reduced. Specifically, the concentration of each element of Si, Ge, Mg, Cd and Zn is preferably 10 ¹⁹ cm ⁻³ or less, more 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 emitting light in the visible region, the In composition is preferably 10% or more. If 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 increases, and the emission wavelength can be adjusted from purple to blue and green.
[0025]
When the third layer, which is a light emitting layer, contains In, thermal stability is not sufficient, and deterioration may occur during crystal growth or in a semiconductor process. A protective layer may be inserted between the light emitting layer and the p-type layer for the purpose of preventing such deterioration of the light emitting layer. In order to provide a sufficient protective function, the protective layer preferably has an In composition of 10% or less and an Al composition of 5% or more. More preferably, the In composition is 5% or less and the Al composition is 10% or more.
The thickness of the protective layer is preferably from 10 ° to 1 μm. More preferably, it is 50 ° or more and 5000 ° or less. If the thickness of the protective layer is less than 10 °, a sufficient effect cannot be obtained. On the other hand, when the thickness is larger than 1 μm, the luminous efficiency decreases, which is not preferable.
[0026]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.
Example 1
A Group 3-5 compound semiconductor having the structure shown in FIG. 2 was produced by MOVPE, and a light emitting device was produced therefrom.
The substrate used was a mirror-polished sapphire C surface which was organically washed and used. The growth was based on a two-step growth method using a low-temperature growth buffer layer. At a substrate temperature of 550 ° C., hydrogen was used as a carrier gas, and TMG and ammonia were supplied to form a GaN buffer layer 2 having a thickness of 500 °. Next, the substrate temperature is raised to 1100 ° C., and TMG, ammonia and silane gas are supplied onto the buffer layer 2 to provide an n-type carrier concentration of 1 × 10 ¹⁹ / cm ³ using Si as a dopant and a film thickness of about 3 μm. Was grown, and TMG and ammonia were supplied at the same temperature to grow a non-doped GaN layer 4 at 1500 °.
[0027]
Next, the substrate temperature is lowered to 785 ° C., changing the carrier gas to nitrogen, TEG, TMI and ammonia, respectively 0.04 sccm, 0.08Sccm, and 4slm supply, _{an In} 0.3 _{Ga 0.7} which is a light-emitting layer An N layer 5 was grown for 70 seconds. Further, at the same temperature, TEG, TEA, and ammonia were supplied at 0.032 sccm, 0.008 sccm, and 4 slm, respectively, and the Ga _0.8 Al _0.2 N layer 6 as the protective layer was grown for 10 minutes. Here, slm is a unit of gas flow rate, and 1 slm corresponds to 1000 sccm.
Regarding the thicknesses of these two layers, the growth rates obtained from the thicknesses of the layers grown for a longer time under the same conditions are 43 ° / min and 30 ° / min. They are 50 ° and 300 ° respectively.
[0028]
Next, after raising the substrate temperature to 1100 ° C. and supplying a Cp ₂ Mg and ammonia to perform an air-flow process for 40 seconds, supplying TMG, Cp ₂ Mg and ammonia to supply the Mg-doped GaN layer 7. Grow by 5000 $.
After the Group 3-5 compound semiconductor sample prepared as described above was taken out of the reaction furnace, annealing treatment was performed at 800 ° C. for 20 minutes in nitrogen to convert the Mg-doped GaN layer into a low-resistance p-type layer. An electrode was formed on the thus obtained sample by a conventional method to obtain an LED. A Ni-Au alloy was used as the p electrode, and Al was used as the n electrode. When a current was applied to this LED in the forward direction, it emitted a clear blue light with an emission wavelength of 4570 °. The luminance at 20 mA was 1240 mcd.
[0029]
Comparative Example 1
A sample for comparison was produced in the same manner as in Example 1 except that the air flow step of supplying Cp ₂ Mg and ammonia was not performed. When a current was applied to the device, blue light emission with a light emission wavelength of 4400 ° was recognized, but the luminance at a forward direction of 20 mA was 390 mcd.
[0030]
Examples 2 and 3
A semiconductor was manufactured in the same manner as in Example 1 except that the time of the air flow step of supplying Cp ₂ Mg and ammonia was changed to 30 seconds (Example 2) and 60 seconds (Example 3) instead of 40 seconds. And LED were produced. When a current was applied to the LED in the forward direction, a clear blue light was emitted. Table 1 shows the luminance, efficiency, and emission wavelength at 20 mA.
[0031]
Comparative Example 2
A sample for comparison was grown in the same manner as in Example 1 except that the time of the idle flow step of supplying Cp ₂ Mg and ammonia was changed to 180 seconds instead of 40 seconds. When a current was applied to this, blue light emission was not visually observed.
FIG. 3 shows the relationship between the time of the idling step and the luminance at 20 mA. From this figure, it can be seen that the brightness is significantly improved by the idle flow for 30 seconds, 40 seconds, and 60 seconds as compared with the case where the idle flow is not performed.
[0032]
[Table 1]

[0033]
【The invention's effect】
According to the present invention, before growing a p-type Group 3-5 compound semiconductor layer, a step of supplying a p-type dopant material and not supplying a Group 3 material is provided, whereby the luminance and the luminous efficiency are improved. Since a light-emitting element can be manufactured, it is extremely useful and has great industrial value.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram of an empty flowing step in the present invention.
FIG. 2 is a diagram showing a structure of a Group 3-5 compound semiconductor shown in Embodiment 1 of the present invention.
FIG. 3 is a diagram showing the relationship between the time of an Mg material emptying step and the luminance of an LED in Examples 1 to 3 and Comparative Examples 1 and 2.
[Explanation of symbols]
1 sapphire substrate 2 GaN buffer layer 3 n-type GaN: Si layer 4 non-doped GaN layer 5 n-type GaN layer 6 as first layer InGaN layer as third layer 7... AlGaN layer as protective layer 8... P-type GaN: Mg layer as second layer

Claims (5)

On a substrate, at least n-type first layer, the third layer as a light emitting layer, the three layers consisting of p-type second layer of the general formula In _x Ga _y Al _z N having in this order ( x + y + z = 1,0 ≦ x ≦ 1,0 ≦ y ≦ a 1,0 ≦ z ≦ 1) 3-5 group compound semiconductor represented by the raw material and a compound having an N in group 3 organometallic compounds and molecules and a process for producing grown in the reaction tube by organometallic vapor phase epitaxy which, before the step of growing a layer of p-type, and supplies the p-type dopant raw material group III material is that it has a step which is not supplied A method for producing a Group 3-5 compound semiconductor, which is characterized in that: 2. The method according to claim 1, wherein the p-type dopant is Mg. 3-5 group compound semiconductor manufacturing method according to claim 1 or 2, wherein the third layer is characterized by being in contact with the large two layers of band gap than that on both sides of the layer. The method for producing a Group 3-5 compound semiconductor according to any one of claims 2 to 3, wherein the thickness of the third layer is not less than 5 ° and not more than 90 °. Si contained in the layer of the third layer, Ge, Mg, according to claim 2-4 or, wherein the respective concentrations of Zn and Cd is 1 × 10 ¹⁹ cm ^-3 or less none A method for producing a Group 3-5 compound semiconductor.

Images