JP3637662B2 - Group 3 nitride semiconductor light emitting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light emitting device using a group III nitride semiconductor with improved band edge emission efficiency.
[0002]
[Prior art]
Conventionally, as a light-emitting element according to the band edge emission using group III nitride semiconductor, an In _0.08 Ga _0.92 N or Si is used an added In _0.08 Ga _0.92 N elements are known in the emission layer. In this device, light having a wavelength of 380 nm is emitted by electron-hole recombination between the Si donor level and the valence band, or between the valence band and the conduction band.
[0003]
[Problems to be solved by the invention]
However, a light-emitting element having this structure has a low concentration of carriers injected into the light-emitting layer, electron-hole recombination hardly occurs, and light emission efficiency is not good.
[0004]
The present invention has been made to solve the above-described problems, and an object of the present invention is to improve the light emission efficiency of band edge emission in a group 3 nitride compound semiconductor light emitting device.
[0005]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a light emitting device having a p layer, an n layer, a light emitting layer sandwiched between the p layer and the n layer, and each layer made of a group III nitride semiconductor. Are added at a concentration of 1 × 10 ¹⁷ to 5 × 10 ¹⁸ / cm ³ , the thickness of the light emitting layer is 15 to 200 nm, and the output light is the donor impurity level and valence band, conduction band and acceptor impurity It is characterized by the emission wavelength due to the transition of electrons between the levels or between the conduction band and the valence band. By setting the thickness of the light emitting layer to 15 to 200 nm, the confinement effect of injected carriers is improved. As a result, depending on the presence of the impurity level, the transition of electrons between the donor impurity level and the valence band, between the conduction band and the acceptor impurity level, between the conduction band and the valence band increases, and between the impurity level and the band edge. Alternatively, the emission intensity and emission efficiency between bands increase. When the thickness of the light emitting layer is less than 1 nm, the crystallinity is not good, which is not desirable. However, if it is thinner than 15 nm, it is difficult to obtain good uniformity of the interface, so a thickness of 15 nm or more is more desirable. Further, if the thickness of the light emitting layer is greater than 200 nm, the effect of confining injected carriers is lowered, which is not desirable.
[0006]
Further, the light emitting layer is quaternary, ternary, binary, i.e., the general formula _{Al x Ga y In 1-xy} N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ It is possible to use a group III nitride semiconductor represented by 1). The composition ratio may be appropriately selected from the viewpoint of the relationship between the emission wavelength and the forbidden band width and the lattice matching. Moreover, it is good also as a quantum well structure of at least 1 period or more. In particular, in order to obtain light emission around 380 nm, it is desirable that the light emitting layer is Ga _x In _1-x N (0 ≦ x ≦ 1).
[0007]
When the thickness of the light emitting layer is set to 15 to 200 nm and both the donor impurity and the acceptor impurity are added, the transition between the donor impurity level and the valence band is larger than when only the donor impurity is added. It has been confirmed that
[0008]
Silicon (Si), tellurium (Te), sulfur (S), or selenium (Se) can be used as the donor impurity, and magnesium (Mg) or zinc (Zn) can be used as the acceptor impurity. . These may be selected based on the relationship between the emission wavelength and the forbidden bandwidth.
[0009]
【Example】
[First embodiment]
In FIG. 1, a light emitting diode 10 has a sapphire substrate 1, and a 500 Å AlN buffer layer 2 is formed on the sapphire substrate 1. Of On the buffer layer 2, in turn, a film thickness of about 5.0 .mu.m, a concentration 5 × 10 ¹⁸ / cm high carrier concentration comprising a silicon-doped GaN of ³ n ⁺ layer 3, a thickness of about 0.5 [mu] m, the concentration 5 × 10 ¹⁷ / cm ³ n layer 4 made of GaN of silicon doped, thickness silicon and zinc at about 50nm, respectively, 5 × 10 ¹⁸ / cm ³ emitting layer 5 made of doped in _0.08 Ga _0.92 n, the membrane Thickness of about 0.5 μm, hole concentration of 5 × 10 ¹⁷ / cm ³ , p layer 61 of Al _0.08 Ga _0.92 N doped with magnesium at a concentration of 5 × 10 ²⁰ / cm ³ , film thickness of about 1 μm, hole concentration of 7 × 10 ^A contact layer 62 made of GaN doped with magnesium having a density of ¹⁸ / cm ³ and a magnesium concentration of 5 × 10 ²¹ / cm ³ is formed. An electrode 7 made of Ni that is bonded to the contact layer 62 is formed on the contact layer 62. Further, a part of the surface of the high carrier concentration n ⁺ layer 3 is exposed, and an electrode 8 made of Ni bonded to the layer 3 is formed on the exposed portion.
[0010]
Next, a method for manufacturing the light emitting diode 10 having this structure will be described.
The light emitting diode 10 was manufactured by vapor phase epitaxy using an organometallic compound vapor phase epitaxy (hereinafter referred to as “M0VPE”).
The gases used were NH ₃ and carrier gas H ₂ or N ₂ , trimethylgallium (Ga (CH ₃ ) ₃ ) (hereinafter referred to as “TMG”) and trimethylaluminum (Al (CH ₃ ) ₃ ) (hereinafter referred to as “TMA”). ), Trimethylindium (In (CH ₃ ) ₃ ) (hereinafter referred to as “TMI”), silane (SiH ₄ ), and cyclopentadienyl magnesium (Mg (C ₅ H ₅ ) ₂ ) (hereinafter referred to as “CP ₂ ”). Mg ”) and diethylzinc (Zn (C ₂ H ₅ ) ₂ ) (hereinafter referred to as“ DEZ ”).
[0011]
First, a single-crystal sapphire substrate 1 having a thickness of 100 to 400 μm and having a surface a cleaned by organic cleaning and heat treatment is mounted on a susceptor mounted in a reaction chamber of an M0VPE apparatus. Next, the sapphire substrate 1 was vapor-phase etched at a temperature of 1100 ° C. while flowing H ₂ into the reaction chamber at a flow rate of ₂ Liter / min at normal pressure.
[0012]
Next, the temperature is lowered to 400 ° C., H ₂ is supplied at 20 Liters / minute, NH ₃ is supplied at 10 Liters / minute, and TMA is supplied at 1.8 × 10 ⁻⁵ mol / minute, and the AlN buffer layer 2 is about 500 mm thick. Formed. Next, the temperature of the sapphire substrate 1 was kept at 1150 ° C., and H ₂ was diluted to 20 Liter / min, NH ₃ was 10 Liter / min, TMG was 1.7 × 10 ⁻⁴ mol / min, and diluted to 0.86 ppm with H ₂ gas. Silane was supplied at 200 ml / min for 70 minutes to form a high carrier concentration n ⁺ layer 3 made of silicon-doped GaN having a film thickness of about 5 μm and a concentration of 5 × 10 ¹⁸ / cm ³ .
[0013]
Next, the temperature of the sapphire substrate 1 is maintained at 1100 ° C., N ₂ or H ₂ is 10 Liter / min, NH ₃ is 10 Liter / min, TMG is 1.12 × 10 ⁻⁴ mol / min, and H ₂ gas is 0.86. Si-diluted ppm was supplied at 10 × 10 ⁻⁹ mol / min for 30 minutes to form an n-layer 4 made of silicon-doped GaN with a film thickness of about 0.5 μm and a concentration of 5 × 10 ¹⁷ / cm ³ . .
[0014]
Subsequently, the temperature is maintained at 850 ° C., N ₂ or H ₂ is 20 Liter / min, NH ₃ is 10 Liter / min, TMG is 1.53 × 10 ⁻⁴ mol / min, and TMI is 0.02 × 10 ⁻⁴ mol / min. Silane diluted to 0.86 ppm with H ₂ gas at 10 × 10 ⁻⁸ mol / min and DEZ at 2 × 10 ⁻⁴ mol / min for 15 minutes to supply silicon and zinc with a thickness of 50 nm, Each of the active layers 5 made of In _0.08 Ga _0.92 N doped to 5 × 10 ¹⁸ / cm ³ was formed.
[0015]
Subsequently, the temperature is maintained at 1100 ° C., N ₂ or H ₂ is 20 Liter / min, NH ₃ is 10 Liter / min, TMG is 1.12 × 10 ⁻⁴ mol / min, TMA is 0.47 × 10 ⁻⁴ mol / min, Then, CP ₂ Mg was introduced at 2 × 10 ⁻⁴ mol / min for 30 minutes to form a p-layer 61 composed of magnesium (Mg) -doped Al _0.08 Ga _0.92 N with a film thickness of about 0.5 μm. The concentration of magnesium in the p layer 61 is 5 × 10 ²⁰ / cm ³ . In this state, the p layer 61 is still an insulator having a resistivity of 10 ⁸ Ωcm or more.
[0016]
Subsequently, the temperature is maintained at 1100 ° C., N ₂ or H ₂ is 20 Liter / min, NH ₃ is 10 Liter / min, TMG is 1.12 × 10 ⁻⁴ mol / min, and CP ₂ Mg is 4 × 10 ^−3. A contact layer 62 made of GaN doped with magnesium (Mg) having a thickness of about 1 μm was formed by introducing it at a rate of mol / min for 4 minutes. The concentration of magnesium in the contact layer 62 is 5 × 10 ²¹ / cm ³ . In this state, the contact layer 62 is still an insulator having a resistivity of 10 ⁸ Ωcm or more.
[0017]
The wafer thus obtained was irradiated with an electron beam using a reflection electron beam diffractometer. The electron beam irradiation conditions are an acceleration voltage of 10 kv, a sample current of 1 μA, a beam moving speed of 0.2 mm / sec, a beam diameter of 60 μmφ, and a degree of vacuum of 2.1 × 10 ⁻⁵ Torr. By this electron beam irradiation, the contact layer 62 and the p layer 61 became p-conduction type semiconductors having a hole concentration of 7 × 10 ¹⁷ / cm ³ , 5 × 10 ¹⁷ / cm ³ , and resistivity of 2 Ωcm and 0.8 Ωcm, respectively. In this way, a wafer having a multilayer structure was obtained.
[0018]
Next, as shown in FIG. 2, a SiO ₂ layer 9 having a thickness of 2000 mm was formed on the contact layer 62 by sputtering, and a photoresist 10 was applied on the SiO ₂ layer 9. Then, by photolithography, as shown in FIG. 2, the photoresist 10 at the electrode formation site A ′ with respect to the high carrier concentration n ⁺ layer 3 was removed on the contact layer 62. Next, as shown in FIG. 3, the SiO ₂ layer 9 not covered with the photoresist 10 was removed with a hydrofluoric acid etching solution.
[0019]
Next, the contact layer 62, the p layer 61, the light emitting layer 5, and the n layer 4 at portions not covered with the photoresist 10 and the SiO ₂ layer 9 are subjected to a degree of vacuum of 0.04 Torr, a high frequency power of 0.44 W / cm ² , and BCl _3. Gas was supplied at a rate of 10 ml / min for dry etching, followed by dry etching with Ar. In this step, as shown in FIG. 4, a hole A for extracting an electrode from the high carrier concentration n ⁺ layer 3 was formed.
[0020]
Next, Ni is uniformly vapor-deposited on the entire upper surface of the sample, and after applying a photoresist, a photolithography process, and an etching process, as shown in FIG. 1, the high carrier concentration n ⁺ layer 3 and the contact layer 62 are applied. Electrodes 8 and 7 were formed. Thereafter, the wafer processed as described above was cut into each chip to obtain a light emitting diode chip.
[0021]
The light-emitting element thus obtained had a drive current of 20 mA, an emission peak wavelength of 380 nm, and an emission intensity of 2 mW. The luminous efficiency was 3%, which was 10 times higher than that of the conventional configuration.
[0022]
Further, the emission spectrum of the light emitting diode 10 manufactured as described above was measured. This is shown by the curve X1 in FIG. It can be seen that a peak wavelength of 380 nm is obtained. On the other hand, although light emission is also observed in the vicinity of 440 nm corresponding to light emission between the Si donor level and the Zn acceptor level, it is understood that the light emission intensity at 380 nm is about five times larger than the light emission intensity at 440 nm.
[0023]
For comparison, the emission spectrum of a light-emitting diode in which the Si and Zn concentrations in the light-emitting layer 5 were the same as those in the above example and the thickness of the light-emitting layer 5 was 400 nm was measured. The result is shown by a curve X2 in FIG. In this case, conversely, the emission at 440 nm is dominant, and the intensity is about five times larger than the emission intensity at 380 nm. This means that when the thickness of the light emitting layer 5 is 400 nm, there is no effect of increasing the light emission intensity of 380 nm.
[0024]
Further, only Si was added to the light emitting layer 5 at the same concentration as in the above example to produce a light emitting diode having a thickness of 300 nm, and the emission spectrum of the light emitting diode was measured. The result is shown by a curve X3 in FIG. In this case, since no Zn was added, no emission of 440 nm was observed, but the emission intensity of 380 nm was obtained to the same extent as the curve X2 when both Si and Zn were added to the light emitting layer 5. Yes. This means that when the thickness of the light emitting layer 5 is 300 nm, the transition between the Si donor level and the valence band is still small. It has been confirmed that when the thickness of the light emitting layer 5 is 200 nm or less, the light emission intensity at 380 nm is increased about 5 times or more.
[0025]
The thickness of the light emitting layer 5 that can increase the confinement effect of the injected carriers is 200 nm or less, and if it becomes thinner than 1 nm, the crystallinity deteriorates, and conversely, the light emission efficiency decreases. Therefore, the thickness of the light emitting layer 5 is desirably in the range of 1 to 200 nm. In order to improve the uniformity of the interface, the range of 15 to 200 nm is more desirable. Furthermore, when the concentration of Si and Zn added to the light emitting layer 5 is 1 × 10 ^{17 to} 5 × 10 ¹⁸ / cm ³ , the light emission intensity in the ultraviolet region of 380 nm or less can be increased.
[0026]
Thus, in the present invention, by setting the thickness of the light emitting layer 5 to 1 to 200 nm, between the donor impurity level and the valence band, between the conduction band and the acceptor impurity level, or between the conduction band and the valence band. By increasing the transition of electrons, it is possible to improve the light emission efficiency and control the light emission wavelength.
[0027]
In _0.08 Ga _0.92 N is used for the light emitting layer 5, but a quaternary group III nitride semiconductor such as Al _0.03 Ga _0.89 In _0.08 N may be used. Further, elements other than Si and Zn can be used as impurities to be added. In short, it may be determined in consideration of the forbidden band width and the type of impurities to be added according to the required emission wavelength. That is, in the above embodiment, the emission wavelength is in the ultraviolet region, but the forbidden bandwidth may be determined so that the emission wavelength is in a visible region such as blue or green. Further, the light emitting layer may be a quantum well structure formed by stacking _{Al x Ga y In 1-xy} N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) at least one or more layers . Further, the light emitting layer 5 is preferably lattice-matched with the other layers 3, 4, 61 and the like.
Although the light emitting diode is shown in the above embodiment, the present invention can be applied to a laser diode.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a configuration of a light emitting diode according to a specific embodiment of the present invention.
FIG. 2 is a cross-sectional view showing a manufacturing process of the light-emitting diode of the same example.
FIG. 3 is a cross-sectional view showing a manufacturing process of the light-emitting diode of the same example.
4 is a cross-sectional view showing a manufacturing process of the light-emitting diode according to the embodiment. FIG.
FIG. 5 is a measurement diagram showing emission spectra of various light emitting diodes in which the thickness of the light emitting layer is changed.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Light emitting diode 1 ... Sapphire substrate 2 ... Buffer layer 3 ... High carrier concentration n ^<+> layer 4 ... n layer 5 ... Light emitting layer 61 ... p layer 62 ... Contact layer 7, 8 ... Electrode

Claims (4)

In a light-emitting element having a p-layer, an n-layer, and a light-emitting layer sandwiched between the p-layer and the n-layer, each layer made of a group 3 nitride semiconductor,
Both the donor impurity and the acceptor impurity are added to the light emitting layer at a concentration of 1 × 10 ¹⁷ to 5 × 10 ¹⁸ / cm ³ ,
The light emitting layer has a thickness of 15 to 200 nm, and the emitted light is emitted by transition of electrons between a donor impurity level and a valence band, between a conduction band and an acceptor impurity level, or between a conduction band and a valence band. A group 3 nitride semiconductor light emitting device characterized by having a wavelength. The light-emitting layer and being a _{Al x Ga y In 1-xy} N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) a quantum well structure formed by laminating at least one layer The group III nitride semiconductor light-emitting device according to claim 1. 2. The group III nitride semiconductor light emitting device according to claim 1, wherein the light emitting layer is Ga _x In _1-x N (0 ≦ x ≦ 1). The donor impurity is silicon (Si), tellurium (Te), sulfur (S), or selenium (Se), and the acceptor impurity is magnesium (Mg) or zinc (Zn). The group III nitride semiconductor light-emitting device according to claim 1.

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