JPH11307811A - Ultraviolet light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the presence of N atom holes and emit ultraviolet rays with high luminance by doping an activated layer with at least one kind selected from the group consisting of In, P, and As at a predetermined concentration. SOLUTION: A buffer layer 2, then a lower barrier layer 3, and further a lower clad layer 4 are laminated sequentially on a substrate 1. An activated layer 5 comprised of a GaN compound semiconductor into which a dopant has been doped is laminated on the layer 4. As the GaN compound semiconductor, a GaN composition or an AlGaN composition having a smaller band gap than the layer 4 is suitable. A dopant to be doped into the GaN compound semiconductor is at least one kind selected from the group consisting of In, P, and As, and the doping concentration of the dopant in the layer 5 is set between 1×10<18> and 1×10<21> cm<-3> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultraviolet light emitting device, and more particularly, to an ultraviolet light emitting device having an active layer made of a GaN-based compound semiconductor in which the presence of vacancies in a crystal is suppressed, and The present invention relates to an ultraviolet light-emitting element capable of emitting light.

[0002]

2. Description of the Related Art In recent years, attempts have been made to develop light-emitting elements that emit ultraviolet light. In particular, an ultraviolet light emitting device having an active layer made of a GaN-based compound semiconductor has attracted attention, and has been actively studied for practical use. This ultraviolet light emitting element is made of, for example, silicon, sapphire, Si
On a predetermined substrate such as C, GaAs, or GaP, each layer made of a predetermined semiconductor material epitaxially grown by applying a gas source MBE method or MOCVD method is sequentially laminated, and further, electrodes are loaded at predetermined positions. It has a structure.

[0003] Specifically, there is an element having the following structure. That is, on the substrate, a buffer layer made of GaN, a lower barrier layer made of AlGaN, a composition controlled so that the band gap is smaller than the lower barrier layer and larger than an active layer described later, N- doped with an n-type dopant such as
A lower cladding layer made of AlGaN, an active layer made of a GaN-based compound semiconductor having a smaller band gap than the lower cladding layer, for example, GaN, or an AlGaN or the like whose composition is controlled as described above, and a band gap larger than the active layer. Is a composition controlled to be
P-AlG doped with a p-type dopant such as Mg
an upper cladding layer made of aN, a composition controlled so that a band gap is larger than that of the upper cladding layer, and p-type doped with a p-type dopant such as Mg.
An upper barrier layer made of AlGaN is laminated in this order from the bottom, and an n-type electrode made of, for example, Ti / Al is placed on the lower barrier layer, and a p-type electrode made of, for example, Au / Ni is made of the upper barrier layer. Above are the elements loaded respectively.

[0004]

By the way, in the ultraviolet light emitting device thus constituted, Ga as an active layer is used.
There is a problem that N atom vacancies exist in the crystal of the N-based compound semiconductor. This is because, in a device having an active layer in which a large amount of N atom vacancies exist, the vacancy location becomes a non-emission center, so that band edge emission becomes low in luminance and luminous efficiency becomes low.

[0005] Therefore, in order to emit light at a high band edge and emit light with high luminous efficiency, the Ga of the active layer must be used.
An N-based compound semiconductor having good crystallinity, ie, N
It is necessary to form a crystal in which the presence of atomic vacancies is suppressed. The present invention suppresses the presence of N atom vacancies, and furthermore, Ga doped with a dopant acting as an emission center.
It is an object of the present invention to provide an ultraviolet light-emitting device having an active layer made of an N-based compound semiconductor and capable of emitting ultraviolet light with high luminance.

[0006]

According to the present invention, there is provided an active layer comprising a GaN-based compound semiconductor, wherein the active layer is selected from the group consisting of In, P, and As. At least one type is 1 × 10 ¹⁸ to 1 × 10
An ultraviolet light emitting device is provided, which is doped at a concentration of ²¹ cm ^-3 .

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an ultraviolet light emitting device of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view illustrating an example of the layer structure of the light emitting device of the present invention. In FIG. 1, a buffer layer 2 is first stacked on a substrate 1. The substrate 1 is not particularly limited, and preferable examples include a silicon substrate, a sapphire substrate, a SiC substrate, a GaAs substrate, and a GaP substrate.

[0008] The buffer layer 2 is a layer provided for the purpose of, for example, relaxing lattice mismatch with a layer grown thereon to prevent misfit dislocations. Buffer layer 2
Examples of the material include GaN and AlN. The lower barrier layer 3 is stacked on the buffer layer 2. As a material of the lower barrier layer 3, an n-type GaN-based compound semiconductor having a larger band gap than that of the lower cladding layer 4 described later is selected. For example, AlGa
N and GaN can be given. Of these, the former is preferable because it has a larger band gap and, therefore, allows more materials to be selected as the material of the lower cladding layer 4.

Then, a lower cladding layer 4 is laminated on the lower barrier layer 3. As a material of the lower cladding layer 4, an n-type GaN-based compound semiconductor having a band gap smaller than that of the lower barrier layer 4 and larger than an active layer 5 described later is selected. Specifically, the lower barrier layer 3
Is different from the composition of AlGaN, and n-AlGaN doped with an n-type dopant such as Si is preferable.

The lower barrier layer 3 and the lower cladding layer 4 are made of Al
When composed of GaN, the lower barrier layer 3
_0.2 Ga _0.8 constituted by N, the lower cladding layer 4, for example Al
_It may be made of _0.1 Ga _0.9 N to express a band gap difference between the two. On the lower cladding layer 4, an active layer 5 made of a GaN-based compound semiconductor doped with a dopant for suppressing the presence of N atom vacancies is laminated.

The GaN compound semiconductor is not particularly limited as long as it emits light having a wavelength in the ultraviolet region and has a smaller band gap than the lower cladding layer 4 and an upper cladding layer 6 described later. Specifically, Ga
N or AlGaN having a composition whose band gap is smaller than that of the lower cladding layer 4 is preferable. As the dopant doped into the GaN-based compound semiconductor, In,
At least one selected from the group consisting of P and As is used. The dopant forms a solid solution in the crystal of the GaN-based compound semiconductor and suppresses the presence of N atom vacancies. Further, as will be described later, it itself also serves as a luminescence center together with surrounding Ga atoms and N atoms. These are G
Since it becomes electrically neutral in the aN-based compound semiconductor crystal, it does not act as a donor or an acceptor.

The doping concentration of the dopant in the active layer is set to 1 × 10 ¹⁸ to 1 × 10 ²¹ cm ^-3 . If the doping concentration is lower than 1 × 10 ¹⁸ cm ⁻³ ,
This is because the effect of suppressing the existence of N atom vacancies is poor.
On the other hand, if it is higher than 1 × 10 ²¹ cm ⁻³ , the active layer will be GaN
This is because a mixed crystal of InN and InN is formed, and as a result, the band gap of the active layer becomes small, and the emission wavelength becomes longer than the wavelength in the ultraviolet region. The active layer is other G
The same applies to the case of an aN-based compound semiconductor or the case where the dopant is P or As.

The active layer 5 may be doped with an n-type dopant such as Si, in addition to the above dopant. Then, on the active layer 5, the upper clad layer 6
Are laminated. The material of the upper cladding layer is p
A GaN-based compound semiconductor having a larger band gap than the active layer 5 is selected. Specifically, p-AlG doped with a p-type dopant such as Mg
aN is preferred.

On the upper cladding layer 6, an upper barrier layer 7 is laminated. As the material of the upper barrier layer 7, a p-type GaN-based compound semiconductor having a larger band gap than the upper cladding layer 6 is selected. For example, p-AlGaN, p-GaN, or the like having a different composition from p-AlGaN constituting the upper cladding layer 6 can be given, and the former has a larger band gap, and thus is more suitable as the material of the upper cladding layer 6. This is preferred because many things can be selected.

The upper cladding layer 6 and the upper barrier layer 7 are
When composed of AlGaN, the upper cladding layer 6 is composed of, for example, Al _0.1 Ga _0.9 N, and the upper barrier layer 7 is composed of, for example, A.
composed of l _{0. 2} Ga _0.8 N, it is sufficient to express the band gap difference between them. An n-type electrode E1 made of, for example, Ti / Al is provided on the lower barrier layer 3.
On the barrier layer 7, a p-type electrode E2 made of, for example, Au / Ni is loaded.

By applying a voltage of a predetermined value between the electrodes E1 and E2 of the device thus constructed, the active layer 5 emits ultraviolet light of a predetermined wavelength, and the entire device emits ultraviolet light. Functions as an element. The light emitting device of the present invention shown in FIG. 1 can be manufactured by applying a known epitaxial growth method such as a gas source MBE method or a MOCVD method.

An example of the case of manufacturing by the gas source MBE method will be described below. First, a substrate made of the above-described material, for example, a silicon substrate 1 is placed in a predetermined crystal growth apparatus.
Is set. Then, for example, metal Ga or trimethylgallium is supplied as a Ga source, and dimethylhydrazine, ammonia, plasma nitrogen, or radical nitrogen is supplied as an N source, and a GaN buffer layer 2 is formed on the substrate 1.

While supplying the above-mentioned Ga source and N source, an Al source is further supplied, and AlGa is supplied on the buffer layer 2.
A lower barrier layer 3 made of N is formed. Examples of the Al source include metal Al or trimethyl aluminum. While supplying the above-mentioned Ga source, N source and Al source, an n-type dopant source is further supplied, and a lower clad made of n-AlGaN having a composition smaller in band gap than the lower barrier layer 3 is formed on the lower barrier layer 3. The layer 4 is formed. As the n-type dopant source, for example, metal Si
Alternatively, a Si source such as silane may be used.

Next, on the lower cladding layer 4, In,
An active layer 5 made of a GaN-based compound semiconductor doped with at least one selected from the group consisting of P and As is formed.
When GaN is used as the GaN-based compound semiconductor, supply of the above-mentioned Al source and Si source is cut off, and the In source, P source
Source and at least one source selected from As source. As the In source, metal In or trimethylindium, as the P source, metal P, phosphine, or an organic phosphorus compound such as trimethyl phosphorus or dimethylamino phosphorus, and as the As source, metal As, arsine, or trimethyl arsenic or dimethyl Organic arsenic compounds such as amino arsenic are preferred examples.
When two or more dopants are used, two or more dopants may be selected from the above-mentioned In source, P source, and As source, and these may be supplied simultaneously or one by one.

By adjusting various conditions such as the type of the dopant source and the supply pressure of each source gas, the active layer 5 is formed.
Can be adjusted. Therefore, the film forming conditions are set so that the dopant concentration falls within the above range. Next, the supply of only the dopant source is stopped, and the above-described Al source and p-type dopant source are further supplied to form an upper clad layer 6 made of p-AlGaN on the active layer 5. Examples of the p-type dopant source include a Mg source such as metallic Mg or biscyclopentadienyl magnesium.

Next, for example, the supply pressure of the Al source is made higher than that in the case of forming the upper clad layer 6, and the p-Al having a composition larger in band gap than the upper clad layer 6 is formed.
An upper barrier layer 7 made of GaN is formed on the upper clad layer 6. Then, the entire surface of the thus-obtained laminated structure is masked with a masking material, and predetermined patterning and etching of each layer are performed.

Finally, an n-type electrode E1 made of, for example, Ti / Al is formed on the lower barrier layer 3 whose surface is exposed.
A p-type electrode E2 made of, for example, Au / Ni is loaded on the upper barrier layer 7, respectively. Thus, the light emitting device having the structure shown in FIG. 1 is manufactured. In the case of the above-described manufacturing example, the supply of the Al source and the Si source was cut off during the formation of the active layer 5, and the active layer 5 was changed to GaN. An active layer is obtained.
In this case, for example, by adjusting the supply pressure of the Al source, A
l _0.08 Ga _0.92 lower cladding layer of N 4 or the like and it is needless to say than the upper cladding layer 6, a small composition of the bandgap.

The n-type dopant such as Si is GaN
Since it does not cancel out the effect of suppressing the existence of N vacancies of In, P, and As in the system compound semiconductor crystal, the supply of the Si source may be continued when the active layer 5 is formed.
Further, the above-mentioned production example is performed by the gas source MBE method. However, using the above-mentioned various organometallic compounds as a source, each layer is formed by the MOCVD method, and then, etching and loading of each electrode are performed. The light emitting device of FIG. 1 can also be manufactured by performing the above. In this method, although not an organometallic compound, ammonia may be used as the N source, and silane may be used as the Si source.

[0024]

EXAMPLES Example 1 An ultraviolet light emitting device was manufactured by the gas source MBE method as follows. First, the silicon substrate 10 was set in a predetermined crystal growth apparatus. G
Metal Ga (5 × 10 ⁻⁷ Torr) is supplied as a source, dimethylhydrazine (5 × 10 ⁻⁵ Torr) is supplied as N source,
At 40 ° C., a 50 ° -thick GaN buffer layer 20 was formed on the silicon substrate 10.

Once these supplies are stopped, the temperature is reduced to 850.
° C, and then metal Ga (5 × 10 ⁻⁷⁾ as a Ga source.
Torr), ammonia (5 × 10 ⁻⁶ Torr) as N source, A
Metal Al (2 × 10 ⁻⁷ Torr) is supplied as
AlGaN (composition; Al _0.8 Ga) is formed on the N buffer layer 20.
A lower barrier layer 30 of _0.2 N) having a thickness of 1 μm was formed.

The supply pressure of metal Al was changed to 1 × 10 ^-7 Torr while supplying metal Ga and ammonia at the above pressure, and metal Si (5 × 1 Torr) was used as an n-type dopant source.
0 ^-9 Torr) and n-AlGaN (composition: Al _0.1
A lower cladding layer 40 of Ga _0.8 N) having a thickness of 1000 ° was formed on the lower barrier layer 30. Once the supply was stopped and the temperature was set to 800 ° C., metallic Ga (5 × 10 ⁻⁷ Torr) was used as a Ga source, and ammonia (5
× 10 ^-6 Torr) and metal In (1 × 1
0 ^-8 Torr), and an active layer 50 made of In-doped GaN and having a thickness of 500 ° was formed on the lower cladding layer 40.

Once the supply was stopped, the temperature was reduced to 850.
° C, and then metal Ga (5 × 10 ⁻⁷ Tor) as a Ga source
r), ammonia (5 × 10 ⁻⁶ Torr), Al as N source
Metal Al (1 × 10 ⁻⁷ Torr) as a source, metal Mg (1 × 10 ⁻⁸ Torr) as a p-type dopant source, and p-A
Thickness 10 made of lGaN (composition; Al _0.1 Ga _0.8 N)
An upper cladding layer 60 of 00 ° was formed on the active layer 50.

While supplying the metal Ga, ammonia, and metal Mg at the above pressure, the supply pressure of the metal Al was increased to 2 × 10 ^-7 To
rr, p-AlGaN (composition: Al _0.2 Ga
The barrier layer 70 of _0.8 N) having a thickness of 1000 ° was formed on the upper cladding layer 60. FIG. 2 shows a laminated structure manufactured under the above conditions. Active layer 5 of this laminated structure
When the mass spectrometry was performed on 0, the concentration of In doped in GaN constituting the active layer 50 was 1 × 10 ¹⁹ cm
^{Was -3} .

Next, an SiO ₂ mask was applied to the entire surface having the above-mentioned laminated structure by a plasma CVD method. Further, predetermined patterning was performed using a photoresist, and thereafter, each layer was sequentially etched by performing dry etching. Finally, an n-type electrode made of Ti / Al is loaded on the lower barrier layer 30 whose surface is exposed, and a p-type electrode made of Au / Ni is loaded on the upper barrier layer 70 by vapor deposition, as shown in FIG. The light-emitting element had the following structure.

Next, in the above-mentioned gas source MBE method, an element having the same structure was manufactured by changing the supply pressure of metal In variously and changing the doping concentration of In in the GaN active layer. For comparison in electroluminescence (EL) measurement described later, an element having an active layer made of non-doped GaN was also manufactured (hereinafter, referred to as an element).
This element is referred to as a comparative element).

An EL spectrum was measured by applying a voltage of 4 V to each of these devices, and the emission spectrum was examined. This EL
The emission wavelength in the measurement corresponds to the emission wavelength of the device.
The peak intensity corresponds to the luminance, and the higher the peak intensity, the higher the luminance of the light emission. First, in the emission spectrum of the comparative example device, a peak appeared at a wavelength of 380 nm in the ultraviolet region, but the intensity was low, and at other wavelengths, the peak based on the presence of N atom vacancies was ignored. Appeared with inability to do so.

On the other hand, when the In concentration is 1 × 10 ¹⁸ to 1
The emission spectrum of the device having a GaN active layer of × 10 ²¹ cm ⁻³ was found to be 38% in the ultraviolet region.
A peak with extremely high intensity appeared at 0 nm, and no peak was observed at other wavelengths. This is G
By doping aN with In, the existence of N atom vacancies in the crystal is suppressed, and furthermore, the result based on the fact that In acts as an emission center together with surrounding Ga atoms and N atoms. It is believed that there is.

Next, the device having an active layer with an In concentration lower than 1 × 10 ¹⁸ cm ⁻³ had an emission spectrum almost similar to that of the device of the comparative example. That is, the wavelength 380n
m, a peak of low intensity appeared, and also at other wavelengths, peaks appeared with insignificant intensity. Also, in the emission spectrum of an element having an active layer having an In concentration higher than 1 × 10 ²¹ cm ⁻³ , the emission wavelength was shifted to a longer wavelength side and tended to be outside the ultraviolet light range.

Embodiments 2 and 3 Each layer was formed in accordance with Embodiment 1 except that metal P or metal As was used as a dopant source for the active layer, and the laminated structure shown in FIGS. Each was produced. Next, each layer was etched and the electrodes were loaded in accordance with Example 1 to manufacture devices having active layers 51 and 52 made of GaN doped with P or As. In addition, when forming the active layers 51 and 52, the supply pressure of the metal P or the metal As is variously changed so that the GaN
An element having the same structure was manufactured except that the concentration of P or As in the active layer was different.

When an EL measurement was performed on each of these devices, the same result as that in Example 1 was obtained. [Example 4] An InGaN-doped AlGaN according to Example 1 except that a metal Al was supplied as an Al source together with a Ga source and an N source when forming an active layer.
A device having an active layer composed of (composition: Al _0.08 Ga _0.92 N) was manufactured. In addition, the supply pressure of metal In was changed variously during the formation of the active layer, and devices having different In concentrations and devices having a non-doped AlGaN active layer were manufactured.

EL measurement was also performed on each of these devices. The result was the same as the result in Example 1.

[0037]

As is apparent from the above description, the ultraviolet light emitting device of the present invention emits ultraviolet light of a predetermined wavelength with high luminance. This is because it has an active layer made of a GaN-based compound semiconductor doped with a dopant that suppresses generation of atomic vacancies and also acts as a light emission center.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of a layer structure of a light-emitting element of the present invention.

FIG. 2 is a cross-sectional view showing a layered structure of each layer when a light emitting device having an active layer made of GaN doped with In is manufactured.

FIG. 3 is a cross-sectional view showing a layered structure of each layer when a light emitting device having an active layer made of GaN doped with P is manufactured.

FIG. 4 is a cross-sectional view showing a stacked structure of each layer when a light emitting device having an active layer made of GaN doped with As is manufactured.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Substrate 2 Buffer layer 3 Upper barrier layer 4 Lower cladding layer 5 Active layer 6 Upper cladding layer 7 Upper barrier layer 10, 11, 12 Silicon substrate 20, 21, 22 GaN buffer layer 30, 31, 32 AlGaN lower barrier layer 40, 41, 42 n-AlGaN (Si-doped AlG
aN) Lower cladding layer 50 In-doped GaN active layer 51 P-doped GaN active layer 52 As-doped GaN active layer 60, 61, 62 p-AlGaN (Mg-doped AlG)
aN) Upper cladding layer 70, 71, 72 p-AlGaN (Mg-doped AlG
aN) Upper barrier layer E1 n-type electrode E2 p-type electrode

Claims (2)

[Claims] 1. An active layer comprising a GaN-based compound semiconductor
Wherein the active layer is selected from the group consisting of In, P, and As.
At least one is 1 × 10¹⁸~ 1 × 10^{twenty one}cm ^-3No
Ultraviolet light emitting element characterized by being doped at a certain degree
Child. 2. The method according to claim 1, wherein the GaN-based compound semiconductor is GaN,
2. The ultraviolet light emitting device according to claim 1, wherein the ultraviolet light emitting device is AlGaN.