JPH077182A - Gallium nitride based compound semiconductor light emitting element - Google Patents

Abstract

PURPOSE:To enhance the luminance and the emission output of a light emitting element by interposing an n-type layer doped with n-type dopant and p-type dopant, as an emission layer, between an n-type layer and a p-type layer. CONSTITUTION:After growth of a buffer layer 2 and an n-type GaN layer 3 on a saphire substrate 1, an n-type Ga1-XAlXN (0<=X<1, X<Y, X<Z) doped with n-type and p-type dopants is grown, as an emission layer, between an n-type clad layer Ga1-YAlYN (0<Y<1) layer 4 and a p-clad layer Ga1-ZAlZN (0<Z<1) layer. Furthermore, the n-type clad layer 4 is laminated on the n-type GaN layer to obtain an emission layer excellent in the crystallinity thus realizing a light emitting element excellent in emission intensity and emission efficiency. When the value of X is increased in the Al mixed crystal ratio of n-type and p-type clad layers, emission output from a preferable double heterostructure can be enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device using a gallium nitride compound semiconductor, and more particularly to a gallium nitride compound semiconductor light emitting device having a double hetero structure having a pn junction.

[0002]

2. Description of the Related Art GaN, GaAlN, InGaN, In
Since gallium nitride-based compound semiconductors such as AlGaN have a direct transition and the bandgap changes from 1.95 eV to 6 eV, they are regarded as promising materials for light emitting devices such as light emitting diodes and laser diodes. At present, a light emitting device using this material is a so-called MIS in which a high-resistance i-type gallium nitride compound semiconductor doped with a p-type dopant is stacked on an n-type gallium nitride compound semiconductor.
Blue light emitting diodes with a structure are known.

As a light-emitting element having a MIS structure, for example, in JP-A-4-10665, JP-A-4-10666 and JP-A-4-10667, n-type GaA is disclosed.
On the 1N layer, i-type Ga doped with Si and Zn
A technique is disclosed in which an AlN layer is laminated and the i-type layer is used as a light emitting layer. According to these techniques, the emission color can be changed to blue, white, or red by changing the doping ratio of Si to Zn.

[0004]

However, as in the above-mentioned technique, the p-type dopant Zn and the n-type dopant Si are further doped to obtain a high resistance i.
The light emitting device having the MIS structure using the GaAlN layer as a light emitting layer has low brightness and low light emission output, and is still insufficient for practical use as a light emitting device.

Therefore, the present invention has been made in view of such circumstances, and an object of the present invention is to improve the brightness and the light emission output of a light emitting device by using a gallium nitride-based compound semiconductor having a pn junction. To improve.

[0006]

We have decided not to use GaAlN as an i-type light emitting layer having a high resistance as in the past, but as an n-type having a low resistance, and newly using this n-type GaAlN layer as a light emitting layer.
The above problems have been solved by realizing a light emitting device having an n-junction double hetero structure. That is, the gallium nitride-based compound semiconductor light emitting device of the present invention is an n-type Ga _{1 -Y} Al _Y N
N _- type Ga _1-X Al doped with an n-type dopant and a p-type dopant between the (0 <Y <1) layer and the p-type Ga _1-Z Al _Z N (0 <Z <1) layer _X N (0 ≦ X <1, X <Y, X <Z)
A layer is provided as a light emitting layer.

In the gallium nitride-based compound semiconductor light emitting device of the present invention, the n-type Ga _{1 -Y} Al _Y N layer (hereinafter referred to as the n-clad layer), which is the cladding layer, means GaAlN such as Si, Ge, Se, It is a layer doped with an n-type dopant such as Te and grown to exhibit n-type characteristics. In addition, GaAlN has a property of becoming n-type even if it is not doped.

Further, it is more preferable that the n-clad layer is laminated on the n-type GaN layer. This is because a light emitting element having a light emitting layer with excellent crystallinity has higher emission intensity and luminous efficiency, and in order to obtain a light emitting layer with excellent crystallinity, light is emitted on the n-clad layer excellent in crystallinity. This is because it is necessary to stack layers. According to our experiments, the crystallinity of gallium nitride-based compound semiconductor tends to deteriorate as the ternary and quaternary mixed crystals are formed. Therefore, in order to obtain an n-clad layer of a ternary mixed crystal or a quaternary mixed crystal having excellent crystallinity, the n-clad layer is formed by n-type GaN.
By stacking on the layer, the n-clad layer having the highest crystallinity can be obtained.

Also, a p-type Ga that is also a clad layer
_{The 1-Z} Al _Z N layer (hereinafter referred to as the p-clad layer) means G
It is a layer grown by doping aAlN with a p-type dopant such as Zn, Mg, Cd, Be, or Ca to show p-type characteristics. Furthermore, a GaAlN layer grown by doping with a p-type dopant was applied to the Japanese Patent Application No. 3-357 filed previously by the applicant.
As disclosed in Japanese Patent No. 046, by performing an annealing treatment at a temperature of 400 ° C. or higher, a p with a resistivity of 100 Ω · cm or less is obtained.
A mold can be realized, which is more preferable.

Furthermore, the Al mixed crystal ratio of the n-clad layer and the p-clad layer, that is, the Y value and the Z value must be larger than the X value. By making those values larger than the X value, it is possible to improve the light emission output as a preferable double hetero structure.

On the other hand, the electron carrier concentration in the n-type Ga _1-x Al _x N layer (hereinafter referred to as the n-emitting layer) which is the emitting layer is 1 ×.
It is preferable to adjust it in the range of 10 ¹⁷ / cm ³ to 1 × 10 ²² / cm ³ . If the electron carrier concentration is lower than 1 × 10 ¹⁷ / cm ³ or higher than 1 × 10 ²² / cm ³ , a practically sufficient light emission output tends not to be obtained. Further, the electron carrier concentration and the resistivity are inversely proportional, and when the concentration is about 1 × 10 ¹⁵ / cm ³ or less, the n light emitting layer has a high resistance i.
It tends to become a mold, and it becomes impossible to measure the electron carrier concentration. The electron carrier concentration can be adjusted by appropriately adjusting the doping amounts of the n-type dopant and the p-type dopant with which the n light emitting layer is doped, or by appropriately adjusting the growth conditions. The effect of the electron carrier concentration of the n light emitting layer will be described later in detail. In addition, the n-type dopant is p
By doping more than the type dopant, the n light emitting layer can be preferably made to be n type. Needless to say, the types of n-type dopant and p-type dopant with which the light emitting layer is doped are the same as the above-mentioned dopants.

Further, by forming a p-type GaN layer (hereinafter referred to as a p-contact layer) as a contact layer on the p-clad layer, ohmic contact between the positive electrode and the p-contact layer is easily obtained, and light emission is achieved. It is possible to reduce the forward voltage applied to the device and improve the light emission efficiency. Because, according to our experiments, the GaN layer not containing Al tends to obtain ohmic contact with the electrode more easily than the GaAlN layer. Therefore, by stacking the GaN layer on the p-clad layer, Ohmic characteristics are improved. The p-type dopant of this p-type GaN layer is no different from the above-mentioned p-type dopant, and, similarly to the p-clad layer, the GaN layer grown by doping the p-type dopant is annealed at 400 ° C. or higher. ,
A p-type having a resistivity of 100 Ω · cm or less can be realized, which is more preferable.

[0013]

In FIG. 1, an n-type GaN layer, an Si-doped n-type Ga0.9Al0.2N layer as an n-clad layer, and a Zn, Si-doped n-type Ga0.99Al0.01N layer as an n-light emitting layer are formed on a substrate. , Mg-doped p-type Ga0.9Al0.1 as the p-clad layer
When a light emitting device having a double hetero structure with a pn junction in which an N layer and an Mg-doped p-type GaN layer as a p contact layer are sequentially laminated is manufactured and the light emitting device is caused to emit light, the n-type Ga0. The relationship between the electron carrier concentration of the 99Al0.01N layer and the relative light emission output of the light emitting element is shown.

As shown in this figure, p-type dopant and n
Double with n-emissive layer doped with type dopant
In the case of terror structure gallium nitride compound semiconductor light emitting device,
n Light-emission output of light-emitting device depending on electron carrier concentration in light-emitting layer
Changes. The emission output depends on the electron carrier concentration of the n emission layer.
10¹⁶/cm³It increases sharply from the vicinity and is approximately 1 × 10^{1 9}
-10²⁰/cm³It becomes the maximum near, and when it exceeds it again
It tends to decrease sharply. N type currently in practical use
Emitting a MIS structure light emitting device composed of GaN and i-type GaN
The light output depends on the maximum light emission output of the light emitting device of the present invention.
Only 1/100 or less, and considering the practical range
As a result, the electron carrier concentration is 1 x 10¹⁷/cm ³~ 5 x 10
^{twenty two}/cm³Is preferred. In addition, this figure shows Zn, Si
It is shown about doped Ga0.99Al0.01N.
However, other p-type dopants and n-type dopants are doped at the same time.
The same applies to the n-type Ga0.99Al0.01N light emitting layer
Relative emission output was obtained. Furthermore, increase the Al mixed crystal ratio.
With GaAlN, which has been messed up, the emission wavelength is shortened.
With respect to the relative light emission output, similar results were obtained. this
As described above, in the light emitting device of the present invention, the electronic key of the n light emitting layer is
The light emission output changes as follows depending on the carrier concentration.
It is presumed that this is the reason.

It is known that when GaN grows undoped (no addition), it exhibits n-type due to the formation of nitrogen vacancies. The residual electron carrier concentration of this non-doped n-type GaN is about 1 × 10 ¹⁷ / cm ³ to 1 depending on the growth conditions.
It shows a value of approximately 10 ²² / cm ³ . Furthermore, this n-type G
Doping the aN layer with a p-type dopant (Zn in the case of FIG. 1) that serves as the emission center reduces the electron carrier concentration in the n-type GaN layer. For this reason, if the p-type dopant is doped so that the electron carrier concentration is extremely reduced, the n-type GaN becomes i-type with high resistance. The emission output changes by adjusting the electron carrier concentration, suggesting the possibility of DA pair emission in which the emission center of Zn, which is a p-type dopant, forms a pair with a donor impurity to emit light. , I'm not sure about the detailed mechanism. Importantly, donor impurities (eg, n-type dopant, non-doped GaAl) that create some electron carriers are used.
N-type GaAlN in which both N) and a p-type dopant that is an acceptor impurity are present significantly increases the intensity of the emission center in a light emitting device having a double hetero structure.

[0016]

FIG. 2 is a sectional view showing the structure of a gallium nitride-based compound semiconductor light emitting device according to an embodiment of the present invention. The light emitting device of the present invention will be manufactured by the metal organic chemical vapor deposition method based on this drawing. Describe how to do.

Example 1 The sapphire substrate 1 was placed in a reaction vessel, the sapphire substrate 1 was cleaned, the growth temperature was set to 510 ° C., hydrogen was used as a carrier gas, and ammonia and TMG ( Trimethylgallium) is used to grow the GaN buffer layer 2 on the sapphire substrate to a film thickness of about 200 Å.

After growing the buffer layer 2, stop only TMG,
The temperature is raised to 1030 ° C. When the temperature reached 1030 ° C, n-type G doped with Si using TMG and ammonia gas as the source gas and silane gas as the dopant gas.
The aN layer 3 is grown to 4 μm.

After the growth of the n-type GaN layer 3, T is used as a source gas.
MG, TMA (trimethylaluminum) and ammonia, silane gas as a dopant gas, and Si-doped Ga0.8Al0.2N layer of 0.15 as the n-clad layer 4.
Grow μm.

After the growth of the n-clad layer 4, the flow rate of the TMA gas is reduced and silane gas as a dopant gas and DE are added.
Z (Ciethyl zinc) is used as the n light emitting layer 5, and Si,
A Zn-doped Ga0.99Al0.01N layer is grown to 500 Å. The electron carrier concentration of the five n light emitting layers was 1 × 10 ¹⁹ / cm ³ .

Next, the dopant gas is stopped, and TMG, TMA, ammonia as a source gas, and Cp2Mg (cyclopentadienylmagnesium) as a dopant gas are used, and Mg-doped p-type Ga0 is used as the p-clad layer 6. A 0.8 Al 0.2 N layer is grown to 0.2 μm.

After the p-clad layer 6 is further grown, the TMA gas is stopped and the p-contact layer 7 is made of p-doped Mg.
-Type GaN layer is grown by 0.5 μm.

After the growth, the wafer was taken out from the reaction container and was annealed at 700 ° C. for 2 hours in a nitrogen atmosphere.
Annealing is performed for 0 minutes to form the uppermost p-contact layer 7
And the p-clad layer 6 are further reduced in resistance to have a resistivity of 10 Ω · cm or less.

The p-contact layer 7, p-cladding layer 6, n-emissive layer 5, and n-layer of the wafer obtained as described above
A part of the clad layer 4 is removed by etching to expose the n-type GaN layer 3, the p-contact layer 7 and the n-type Ga.
Ohmic electrodes 8 and 9 are provided on the N layer 3 and 50, respectively.
After cutting into a chip of 0 μm square, it was made into a light emitting diode by an ordinary method, and the light emission output was 40 at 20 mA.
The voltage was 0 μW, the forward voltage was 5 V, and the emission wavelength was 490 nm.

Example 2 When growing the n-type Ga0.99Al0.01N layer, which is the n-emissive layer 5 of Example 1, Si and Z were grown.
The electron carrier concentration is adjusted to 2 × 10 by adjusting the doping amount of n.
Except that the ¹⁷ / cm ^3, was obtained a blue light-emitting diodes in the same manner as in Example 1, the light output at 20 mA 40
The μW, forward voltage and emission wavelength were the same as in Example 1.

Example 3 When growing the n-type Ga0.99Al0.01N layer, which is the n-emissive layer 5 of Example 1, Si and Z were grown.
The electron carrier concentration is adjusted to 2 × 10 by adjusting the doping amount of n.
Except that the ²¹ / cm ^3, was obtained a blue light-emitting diodes in the same manner as in Example 1, the light output at 20 mA 40
The μW, forward voltage and emission wavelength were the same as in Example 1.

Example 4 When growing the n-type Ga0.99Al0.01N layer, which is the n-emissive layer 5 of Example 1, Si and Z were grown.
The electron carrier concentration is adjusted to 1 × 10 by adjusting the doping amount of n.
¹⁷ / addition to the cm ³ is where to obtain a blue light-emitting diodes in the same manner as in Example 1, the light output at 20 mA 10
The μW, forward voltage and emission wavelength were the same as in Example 1.

Example 5 When growing the n-type Ga0.99Al0.01N layer, which is the n-emission layer 5 of Example 1, Si and Z are grown.
The electron carrier concentration is adjusted to 1 × 10 by adjusting the doping amount of n.
²² / addition to the cm ³ is where to obtain a blue light-emitting diodes in the same manner as in Example 1, the light output at 20 mA 10
The μW, forward voltage and emission wavelength were the same as in Example 1.

[Embodiment 6] A light emitting diode is manufactured in the same manner as in Embodiment 1, except that the n-type GaN layer 3 of Embodiment 1 is not grown and the n-clad layer 4 is grown directly on the GaN buffer layer 2. The emission output was 100 at 20 mA.
The μW, forward voltage and emission wavelength were the same as in Example 1. Needless to say, the electrode 9 is formed on the n-clad layer 4.

[Embodiment 7] p-contact layer 7 of Embodiment 1
Was grown, and an electrode 8 was formed on the p-clad layer 6 to form a light emitting diode in the same manner as in Example 1. The light emitting diode had a light emission output of 400 μW and a light emission wavelength of 4 at 20 mA.
Although it was 90 nm, the forward voltage was 10 V.

[Embodiment 8] In Embodiment 1, Cp2Mg (cyclopentadienylmagnesium) gas is used as the p-type dopant of the n-type light emitting layer 5 and germane gas is used as the n-type dopant, and the electron carrier concentration is 1 × 10 ¹⁹ / cm ³
When a light emitting diode was prepared in the same manner except that the Mg and Ge-doped Ga0.99Al0.01N layers were grown, the light emitting output was 400 μW, the forward voltage was 5 V, and the emission wavelength was 480 nm.

[Comparative Example 1] A Zn-doped i-type GaN layer is grown on the n-type GaN layer 3 of Example 1. i type Ga
After growth of the N layer, a part of the i-type GaN layer was etched to expose the n-type GaN layer, and electrodes were provided on the n-type GaN layer and the i-type GaN layer to form a MIS structure light emitting diode. Output is 1 μW at 20 mA, forward voltage 2
There were only 0 V and a brightness of 2 mcd.

Comparative Example 2 A Si-Zn-doped i-type GaN layer is grown on the n-type GaN layer 3 of Example 1. i
After the growth of the GaN layer, electrodes are provided in the same manner as in Comparative Example 1,
MIS structure light emitting diode, the light output is 20m
A, 1 μW, forward voltage 20 V, brightness 0.1 mc
There was only d.

[0034]

As described above, the gallium nitride-based compound semiconductor light emitting device of the present invention has a double hetero structure having an n-type Ga _{1 -X} AlX N layer doped with a p-type dopant and an n-type dopant as a light-emitting layer. Therefore, the conventional M
The light emission output is remarkably increased as compared with the light emitting element having the IS structure. Further, by stacking the p-contact layer on the p-clad layer, the forward voltage of the light emitting element is lowered and the light emission efficiency is improved. As a result, the conventional blue light emitting device, which uses only SiC or MIS structure GaN, is replaced with the light emitting device of the present invention, and a flat display, a full-color light emitting diode or the like can be realized.

[Brief description of drawings]

FIG. 1 is an n-type Ga of a light emitting device according to an embodiment of the present invention.
The figure which shows the relationship between the electron carrier density of an AlN layer, and relative light emission output.

FIG. 2 is a schematic cross-sectional view showing a light emitting device structure according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Sapphire substrate 2 ... GaN buffer layer 3 ... n-type GaN layer 4 ... n cladding layer 5 ... n light emitting layer 6 ... p cladding layer 7 ... p contact layer

Claims (5)

[Claims] 1. An n-type dopant and a p-type layer are provided between an n _- type Ga _{1 -Y} Al _Y N (0 <Y <1) layer and a p-type Ga _{1 -Z} Al _Z N (0 <Z <1) layer. N-type Ga doped with a type dopant
_A gallium nitride-based compound semiconductor light emitting device comprising a _1-X Al _X N (0≤X <1, X <Y, X <Z) layer as a light emitting layer. 2. The electron carrier concentration of the n-type Ga _1-x Al _x N layer is in the range of 1 × 10 ¹⁷ / cm ³ to 1 × 10 ²² / cm ^3. Gallium nitride compound semiconductor light emitting device. 3. The gallium nitride-based compound semiconductor light-emitting device according to claim 1, further comprising a p-type GaN layer stacked on the p-type Ga _{1 -Z} Al _Z N as a contact layer. . 4. The p-type Ga _{1 -Z} Al _Z N and / or the p-type GaN layer is annealed at 400 ° C. or higher and adjusted to have a resistivity of 100 Ω · cm or less. Alternatively, the gallium nitride-based compound semiconductor light emitting device according to claim 3. 5. The n-type Ga _{1 -Y} Al _Y N layer is n-type GaN.
The gallium nitride-based compound semiconductor light emitting device according to claim 1, which is laminated on the layer.