JP3491375B2 - Light emitting device and manufacturing method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to gallium nitride (GaN).
The present invention relates to a light emitting device including a nitrogen-containing III-V group compound layer containing nitrogen, such as aluminum nitride (AlN) and mixed crystals thereof, as a light emitting layer. The present invention relates to a light emitting device including a nitrogen-containing III-V group compound layer doped with an element that becomes a recombination center of light emission.

[0002]

2. Description of the Related Art In a conventional short-wavelength light emitting diode (LED) such as blue or blue-green, a III-V group compound semiconductor containing nitrogen (element symbol: N) (nitrogen-containing III-V group compound semiconductor) emits light. Used as a layer. For example, in conventional blue LEDs, gallium nitride (GaN) or a gallium nitride / indium (GaInN) mixed crystal composed of GaN and indium nitride (InN) is used as a light emitting layer material (Kuki Kato, "Toyoda Gosei Co., Ltd." Report ", Vol.35,
No. 2 (1993), page 91 and S.H. Nakamur
a et al., Appl. Phys. Lett. , 64 (13)
(1994), 1687. ).

A conventional light emitting layer for a short-wavelength LED composed of these nitrogen-containing III-V group compound semiconductor layers is doped with zinc (Zn) belonging to a Group II element of the periodic table of elements. (For example, Appl. Phys.
Lett. , 64 (1994), 1687. ). In GaN having a bandgap of about 3.4 eV at room temperature, zinc forms an impurity level at a relatively deep energy position of about 0.4 eV from the valence band (VonH.G.GRIMMEI).
SS et al., Z. Nature forsh. , 15 (196
0), 799. ). The reason for doping zinc into a nitrogen-containing III-V compound semiconductor having a relatively wide band gap such as GaN is that the recombination center (recombina) formed by zinc is formed.
This is because short-wavelength light emission is obtained by utilizing indirect recombination due to the ion center.

Impurities which are the recombination centers of luminescence in GaN include cadmium (Cd), mercury (Hg), and gold (A).
u), copper (Cu), lithium (Li), etc. (Z.Nat
urforsh. , 15 (1960), 799. ), Silicon (Si) (F. KAREL et al., Phys.st
at. sol. , 3 (1963), K78. ). AlN
, Manganese (Mn) is known as a luminescent impurity that forms recombination centers (GA Wolff et al., P.
hys. Rev. , 114 (5) (1959), 126
2. ). Further, for GaN, boron (B), magnesium (Mg), which is doped by an ion implantation method,
In addition to phosphorus (P), calcium (Ca), and arsenic (As), the impurities described in the next section are mentioned as impurities that cause light emission (J. I. Pankov et al., J. Appl.
Phys. , 47 (12) (December 1976), 53.
87. ).

That is, beryllium (Be), carbon (C),
Oxygen (O), sodium (Na), Al, sulfur (S),
Chlorine (Cl), potassium (K), scandium (S
c), iron (Fe), cobalt (Co), nickel (N
i), germanium (Ge), selenium (Se), krypton (Kr), strontium (Sr), zirconium (Zr), silver (Ag), tin (Sn), tellurium (T).
e), barium (Ba), dysporodium (Dy), erbium (Er), etc. can be used.

In addition, a supplementary center is an isoelectronic trap.
LEDs utilizing pseudo-indirect transitions according to p) are also known. For example, a typical example is a III-V group compound semiconductor LED having gallium phosphide (GaP) doped with nitrogen as an isoelectronic trap as a light emitting layer ("Semiconductor Engineering" (Supervised by Toshiji Fukami, Tokyo, 1993). (Published by Denki University), p. 195). As with phosphorus, doping with nitrogen, which is a Group V element of the Periodic Table of Elements, produces strong luminescence due to pseudo-indirect transition centered on nitrogen based on the difference in the number of extra-shell electrons between nitrogen and phosphorus. is there. Nitrogen-doped gallium arsenide phosphide (Ga) is used for the light emitting layer utilizing the isoelectronic trap.
PAs) and gallium indium phosphide (GaInP) (“Semiconductor Engineering”, p. 195). When isoelectronic trap impurities are used as a light emitting layer, an LED with excellent strength can be obtained.

The three primary colors of light are red, blue and green. Even in the case of manufacturing a multicolor display (display) or the like that mixes the three primary colors and exhibits various colors, it is preferable to combine light by combining light emitting elements having the same luminous intensity of these three colors. desirable. In the present situation, high brightness exceeding 1 (candela) has been achieved for blue and red LEDs. On the other hand, the light emission intensity of an LED that emits green, which is one of the three primary colors, which is absolutely necessary in light mixing for multicolor display, remains low at about 0.3 candela. In order to realize a multicolor LED display device, it is necessary to sufficiently increase the emission intensity of a short-wavelength LED that emits green light.

If an element constituting a semiconductor layer and belonging to the same group of the periodic table of elements but different in the number of extra-shell electrons is an isoelectronic impurity, GaN is used.
For Al, In for GaN, thallium (Tl) for GaN, etc. can be isoelectronic impurities. Thallium is also the recombination center of the emission, and GaN doped with thallium gives green emission with a wavelength of about 525 nm (Z.
urforsh. , 15 (1960), 799. ). From this, if it is used as a nitrogen-containing III-V group compound semiconductor light emitting layer containing gallium, aluminum, or indium which is a group III element other than thallium doped with thallium, a green band of higher brightness can be obtained. LEDs are expected.

However, for the main purpose of increasing the emission intensity, a nitrogen-containing nitrogen doped with thallium, which can be an isoelectric trap and a recombination center of emission, can be obtained.
A light emitting device including a III-V group compound semiconductor layer as a light emitting layer has not yet been realized. Therefore, in order to obtain an LED having a light emitting layer made of a nitrogen-containing III-V group compound semiconductor doped with thallium, a nitrogen-containing III-V group compound semiconductor doped with thallium is obtained in order to obtain a light emitting device with high emission intensity. The quality requirement that the light emitting layer made of is to have, for example: The concentration should be unknown. This is mainly due to the fact that the problems in the conventional growth technique that hinder the stable formation of the nitrogen-containing III-V group compound semiconductor layer doped with thallium have not been sufficiently solved.

Conventionally, a nitrogen-containing III-V group compound layer such as GaN or AlN for use as a light emitting device has been mainly produced by a vapor phase growth method such as VPE method or MBE method. Among vapor phase growth methods, pyrolysis vapor phase growth methods (MOCVD, MOVPE (or OMVPE)) using an organic metal compound as a raw material
It is abbreviated as. ) Is the conventional main vapor phase growth method. Taking MOCVD growth of GaN as an example, trialkylgallium compounds such as trimethylgallium ((CH ₃ ) ₃ Ga) and triethylgallium ((CH ₃ CH ₂ ) ₃ Ga) are typical gallium feed materials. It's being used. Regarding organic compounds of thallium, trimethylthallium ((CH ₃ ) ₃ Tl) and triethylthallium ((CH ₃ CH ₂ ) ₃ Tl) have already been proposed as constituent elements or dopant sources in MOCVD growth.

As a supply source of the group V element in the MOCVD method, a hydride of the group V element is generally used. In MOCVD growth of a nitrogen-containing III-V compound layer, ammonia (NH ₃ ) is a typical nitrogen supply source. No. I
Trialkyl compounds of Group II elements are Lewis acidic. Conversely, hydrides of Group V elements such as ammonia generally exhibit Lewis basicity. The Lewis base and the Lewis acid molecule bond very easily based on the electron-accepting / supplying reaction between the molecules to form a refractory substance having a higher melting point. For example, an example is given in which a trimethylgallium-amine complex formed by the association of trimethylgallium and ammonia forms a bisamino derivative (complex) having a melting point of 97 ° C. through the route shown in the following chemical reaction formula (1). To be In organometallic compounds of Group III elements, the
Group III elements have a strong tendency to have a valence of four (GE.
COATES, Organo-Metallic Co
mounds, 2nd. edi. , (1960) (M
ETHUEN & CO LTD), p. 88). Trialkyl thallium compounds typified by trimethyl thallium and triethyl thallium have a smaller degree of accepting electrons from other molecules as compared with trialkyl compounds of Al, Ga and In (Organo-Metalli).
c Compounds, p. 158), forming a complex by association with ammonia which is a Lewis base. MO
The conventional trialkyl thallium compound proposed for CVD cannot completely avoid a complexation reaction with a hydride of a Group V element such as ammonia which exhibits Lewis basicity. Doping nitrogen
It has been a main cause that the growth of the III-V compound semiconductor layer is not carried out with sufficient stability.

If the raw material of thallium is consumed unnecessarily due to the complexing reaction, the intended amount or concentration of thallium cannot be accurately supplied to the growth reactor. As a result, a polymer-like product is generated by the complexing reaction, and as a result, (a) the surface state is impaired, and (b) sufficient controllability of the thallium concentration in the growth layer is obtained. It is causing problems such as not being.

In the MOCVD method, normal pressure (atmospheric pressure)
Film formation by utilizing thermal decomposition of an organometallic compound raw material such as trimethylgallium ((CH ₃ ) ₃ Ga) containing an element that constitutes a semiconductor, such as an aliphatic compound or an aromatic compound Carry out. In the thermal decomposition of the organometallic compound raw material, the metal element that constitutes it is released, and carbon (C) is generated due to the decomposition of the hydrocarbon group such as an aliphatic group or an aromatic group added to the metal atom. It is released at the same time. For example, in the case of a methyl metal compound, the main cause of carbon contamination in the growth layer is the methyl group (CH ₃
-) Or a pyrolysis fragment thereof.
Also in the thermal decomposition of trimethyl thallium, which is an example of a conventional thallium source, thallium is released into the growth system, and carbon is decomposed and released from the methyl group and its fragments. In addition to the background carbon concentration, the carbon concentration accompanying the decomposition of trimethylthallium further increases the carbon atom concentration in the growth layer. In the MOMBE method, a trimethyl or triethyl compound may be used as a raw material, but in the usual VPE method or MBE method, an organometallic compound is used as a starting material for growing a nitrogen-containing III-V group compound semiconductor. Things are rare. But,
Nitrogen-containing material grown by conventional VPE method or MBE method III
Carbon is also contained in the -V compound semiconductor growth layer, for example, as a medium of the residue of the organic solvent used for cleaning the surface of the substrate crystal, or monoxide and carbon dioxide adsorbed on the substrate surface. The carbon concentration as the background is MOCV
There is no extreme difference from the case of D.

The growth temperature required to obtain a nitrogen-containing Group III-V compound semiconductor MOCVD layer of good quality is 8
In the range of around 00 ° C to 1200 ° C, the background concentration of carbon atoms increases with the growth temperature.
GaNM at 800 ° C, the lowest at a practical growth temperature
The background concentration of carbon atoms in the OCVD growth layer is about 4
It is about 10 ¹⁶ cm ^-3 . At the growth temperature of 950 ° C., the background carbon atom concentration of the undoped GaN MOCVD film rises to about 7 × 10 ¹⁶ cm ⁻³ . In a GaN MOCVD growth layer obtained by using a conventional trialkyl thallium compound as a thallium doping source, the concentration of carbon atoms is significantly increased from the background concentration in almost proportion to the amount of thallium doping in the growth layer. Normal pressure type M using trimethyl thallium as a thallium doping source
FIG. 4 illustrates the relationship between the concentration of thallium atoms and the concentration of carbon atoms of the thallium-doped GaN layer grown at a temperature of 950 ° C. by the OCVD method. At the growth temperature of 950 ° C., the atomic concentration of carbon in the thallium-doped GaN MOCVD layer that makes the atomic concentration of thallium 5 × 10 ¹⁷ cm ⁻³ or more becomes approximately 1 × 10 ¹⁸ cm ⁻³ or more. Regardless of the nitrogen-containing III-V group compound semiconductor material doped with thallium, a typical growth temperature is from about 800 ° C. to 1200 ° C.
Within the range of ° C, the carbon atom concentration at the same thallium atom concentration increases with the growth temperature. For example, the thallium atom concentration obtained when the growth temperature is 1050 ° C. is 5 ×
The atomic concentration of carbon in the AlN layer, which is 10 ¹⁷ cm ⁻³ , is about 2
It is × 10 ¹⁸ cm ^-3, which is about four times that when the growth temperature is 800 ° C. As long as conventional trimethyl thallium is used as a thallium source, a nitrogen-containing III-V compound semiconductor layer in which the atomic concentration of thallium grown at a conventional general temperature is about 5 × 10 ¹⁷ cm ⁻³ However, it has been difficult to reduce the atomic concentration of carbon to about 10 ¹⁸ cm ^-3 or less. Since this increase in carbon atom concentration is essential to the thermal decomposition of the trialkyl thallium compound, it cannot be sufficiently avoided even by changing the growth method as long as the conventional thallium doping source is used.

Increasing the carbon concentration in the nitrogen-containing III-V compound semiconductor layer hinders the increase in the emission intensity of the LED.
For example, excessive concentration of carbon promotes non-emissive defects related to carbon impurities inside the nitrogen-containing III-V compound semiconductor layer. Nitrogen-containing III-V containing a large amount of non-luminous defects
When the group compound semiconductor layer is used for a light emitting element, it absorbs light emitted from the light emitting structure, which is inconvenient for increasing the brightness of the light emitting element. Therefore, in order to obtain a nitrogen-containing III-V group compound semiconductor layer doped with thallium having a low density of non-radiative centers and the like that hinders the increase of the emission intensity of the LED, the amount of carbon contamination in the layer can be reduced. It is necessary to select a doping source of thallium. At present, no doping source of thallium suitable for suppressing carbon contamination in place of the conventional trialkyl thallium compound has been proposed. These are obstacles to obtaining a high-brightness green LED comprising a thallium-doped nitrogen-containing III-V group compound semiconductor.

[0016]

Nitrogen-containing material doped with thallium, which is an isoelectric element and which can be a recombination center of light emission, for the purpose of increasing the light emission intensity.
In order to stably obtain a high-luminance LED that emits light of a short wavelength, especially green, which includes a group V compound semiconductor, it is necessary to solve the following problems. (1) Nitrogen-containing material required to increase the emission intensity I
Atomic concentration of thallium in II-V compound semiconductor layer (2) Atomic concentration of carbon in nitrogen-containing III-V compound semiconductor layer that can suppress the generation of defects such as non-radiative centers that cause a decrease in emission intensity ( 3) Further, by vapor phase growth method such as MOCVD method,
Adopting a doping source of thallium, which is required for stably forming a thallium-doped nitrogen-containing III-V group compound semiconductor light-emitting layer with excellent surface condition and low carbon concentration.

[0017]

The present invention solves the problems by the following means and provides a high-luminance green light emitting device. That is, according to the present invention, (a) boron (B), aluminum (Al), gallium (Ga) or indium (I)
The present invention provides a light emitting device comprising a nitrogen-containing III-V group compound semiconductor layer doped with thallium, containing any one of the group III elements of n) and nitrogen as a constituent element of group V. In particular, the nitrogen-containing III-V group compound semiconductor layer doped with (b) thallium has an atomic concentration of thallium of 5 × 10 ¹⁷ cm ⁻³ or more and an atomic concentration of carbon of 2 × 10 ¹⁶ cm 3. ^-3 or less, and also
(C) The nitrogen-containing III-V compound semiconductor layer described in (b) above is characterized by doping thallium with a cyclopentadienyl thallium compound.

The nitrogen-containing III-V group compound semiconductor layer to be doped with thallium is at least one group III element selected from boron (B), aluminum (Al), gallium (Ga) and indium (In). Is included as a constituent element. III-V group 2 corresponding to this
The original compounds include boron nitride (BN), aluminum nitride (AlN), gallium nitride (GaN) and indium nitride (InN). Nitrogen-containing ternary III-V group compound crystals include aluminum nitride / gallium (AlGaN), gallium nitride / indium (GaInN), aluminum nitride / indium (AlInN), boron nitride / gallium (BGaN), boron nitride / indium. (BInN)
Etc. Further, the nitrogen-containing quaternary III-V group compound crystal contains aluminum nitride / gallium / indium (AlG
aInN), boron nitride, gallium, indium (BG
aInN) and the like. The thallium doping layer is
A nitrogen-containing III-V group compound semiconductor layer containing nitrogen and a group V element other than nitrogen may be used. Examples of the nitrogen-containing III-V group compound semiconductor containing nitrogen and a group V element other than nitrogen include aluminum gallium phosphide / gallium nitride (AlGaNP) and gallium arsenide / indium nitride (GaInNAs).

Nitrogen-containing III-V doping with thallium
The conduction type of the group compound semiconductor layer is p-type, n-type or high-resistance i-type. P-type thallium-doped nitrogen-containing III-V
The group compound semiconductor layer is formed on the periodic table II of the periodic table of elements during vapor phase growth.
It can be obtained by doping with zinc, magnesium, beryllium, etc. belonging to the group. N-type thallium-doped nitrogen-containing
The III-V group compound semiconductor layer can be obtained by doping silicon or tin which is a group IV element or sulfur, selenium or tellurium which is a group VI element. For example, in vapor phase growth by MOCVD, if a nitrogen-containing III-V compound semiconductor layer containing thallium and magnesium is simultaneously doped, a p-type nitrogen-containing III-V compound semiconductor layer doped with thallium is obtained. be able to. An example of a magnesium doping source is biscyclopentadienyl magnesium ((C ₅ H ₅ ) ₂ Mg) and the like (CR LEWIS et al., Electron. L).
ett. , 18 (13) (1982), 569. ). First
Conventional silane (SiH ₄ ), disilane (Si ₂ H ₆ ), hydrogen sulfide (H ₂
S), hydrides such as hydrogen selenide (H2 Se) can be used. Further, an organic compound containing these elements can also be used as a doping source. In a growth method such as a vapor phase growth method, if the above n-type and p-type elements are doped so that the donor concentration and the acceptor concentration, which represent the amount of electrical activity, are substantially equal, the n-type is obtained. By compensating for the p-type carrier, a nitrogen-containing III-V group compound semiconductor layer having high resistance can be obtained.

Nitrogen-containing III-V doped with thallium
When the group compound semiconductor layer is used as a light emitting layer, the carrier concentration of the thallium-doped layer is in the range of about 1 × 10 ¹⁵ cm ⁻³ to about 1 × 10 ¹⁷ cm ^{−3 for} the n-type layer. , And preferably in the vicinity of 1 × 10 ¹⁶ cm ^-3 . The carrier concentration of the p-type layer is about 1 × 10 ¹⁵ cm ⁻³ to about 1 ×.
And 10 ¹⁷ cm ^-3, is preferably 1 × 10 ¹⁷ cm ^-3 and forth. In vapor phase growth methods such as MOCVD method, for example, nitrogen-containing dopant III-V which becomes n-type or p-type
The carrier concentration can be set to the above preferable value by adjusting the doping amount to the group compound semiconductor layer.

N for forming a light emitting layer by doping thallium
The thickness of the p-type or p-type nitrogen-containing compound semiconductor layer is generally about 0.01 μm or more and several μm or less, preferably about 0.1 μm. Layer thickness of about 0.01 μm or more and several μm
The light emitting layer described below can be obtained by adjusting the growth (deposition) time under vapor phase growth conditions in which the deposition rate of the nitrogen-containing III-V compound semiconductor layer is known.

When the atomic concentration of thallium in the light emitting layer is relatively low, the emission intensity increases almost linearly in proportion to the atomic concentration of thallium. When the atomic concentration of thallium exceeds a certain concentration, the emission intensity tends to be saturated.
As an example, FIG. 5 shows the dependence of the photoluminescence emission intensity of the magnesium-doped p-type GaN layer doped with thallium on the thallium atom concentration. When the atomic concentration of thallium is 5 × 10 ¹⁷ cm ⁻³ or more, the emission intensity tends to be saturated. Further, thallium has an atomic concentration of 5 × 10 5.
^If the doping exceeds ¹⁹ cm ⁻³ , the surface condition is significantly deteriorated and the emission intensity is decreased. The similar relationship between the atomic concentration of thallium and the emission intensity is recognized regardless of the material forming the light emitting layer. This tendency can be obtained almost without depending on the conduction type and carrier concentration of the nitrogen-containing III-V group compound semiconductor layer doped with thallium. If a thallium-doped nitrogen-containing III-V group compound semiconductor layer capable of obtaining a high photoluminescence intensity is used as a light emitting layer, it becomes advantageous in obtaining a high-brightness LED. Therefore, the atomic concentration of thallium is set to a range in which a large photoluminescence emission intensity is stably provided. Therefore, the atomic concentration of thallium doped in the light emitting layer is set to 5 × 10 ¹⁷ cm ⁻³ or more, and 5 × 10 ¹⁹ cm which does not deteriorate the surface state of the growth layer.
^-3 or less. Outside this concentration range, the effect of increasing the emission intensity due to the doping of thallium is not always sufficient as compared with the case where the thallium concentration is within the above range.

The relationship between the atomic concentration of carbon in the thallium-doped p-type GaN layer and the photoluminescence emission intensity when the atomic concentration of thallium is about 1 × 10 ¹⁸ cm ^-3 in the region where a large emission intensity is obtained. Is shown in FIG. When the atomic concentration of carbon exceeds 2 × 10 ¹⁶ cm ⁻³ , the photoluminescence emission intensity sharply decreases. This is because the density of non-luminous crystal defects increases as the carbon atom concentration increases, and the light scattering increases as the surface state of the growth layer deteriorates. Similarly, the relationship between the atomic concentration of carbon and the emission intensity hardly depends on the type, conduction type and carrier concentration of the nitrogen-containing III-V group compound semiconductor doped with thallium. To form the light emitting layer, it is convenient to use a nitrogen-containing III-V group compound semiconductor layer that stably exhibits high photoluminescence intensity, and therefore the carbon atom concentration is set to 2 × 10 ¹⁶ cm ^-3 or less. . In reality, the atomic concentration of carbon in the nitrogen-containing III-V compound semiconductor layer does not become lower than the background carbon concentration. Therefore, the carbon concentration in the nitrogen-containing III-V group compound semiconductor layer is actually 2 × 10 5 or more when the background concentration is higher than the background concentration.
^{It is} less than ¹⁶ cm ^-3 . The concentration of carbon contained in the light emitting layer can be easily measured and controlled by, for example, secondary ion mass spectrometry.

As long as a conventional trialkyl thallium compound that is a thallium source is used, the atomic concentration of carbon is defined in the present invention within the atomic concentration range of thallium defined in the present invention as shown in FIG. A thallium-doped nitrogen-containing III-V group compound semiconductor layer having a value not more than the value cannot be obtained.
In particular, in the vapor phase growth method, in order to dope the nitrogen-containing III-V group compound semiconductor layer with thallium without the complexation reaction and to suppress the carbon concentration to 2 × 10 ¹⁶ cm ⁻³ or less, In the present invention, a cyclopentadienyl thallium compound is used as a thallium doping source. A typical example of a cyclopentadienyl thallium compound has a valency of 1
Valent cyclopentadienyl thallium (I) (C ₅ H
_{There is 5} Tl (I). Thallium has three valence electrons because it is a group III element. However, in cyclopentadienyl thallium (I), only one electron contributes to the bond, and two other electrons that do not contribute to the bond exist around the thallium atom. The presence of these isolated electrons dilutes Lewis acidity, making it difficult for electron supply / accept reactions with Lewis bases to occur. Thereby, M of the nitrogen-containing III-V group compound semiconductor layer
In OCVD growth, a lone electron pair existing around a nitrogen atom that constitutes ammonia, which is often used as a nitrogen source, and a non-bonding electron pair existing around thallium, electrically repel each other. However, there is an advantage that it is not easily complexed to form a complex. Therefore, a growth layer having an excellent smooth surface condition can be obtained.

Cyclopentadienyl thallium (I) (C
₅ H ₅ Tl (I) decomposes at relatively low temperatures of about 300 ° C. Upon decomposition, the cyclopentadienyl ring (C ₅ H ₅ −) bonded to the thallium atom is released, and is not dissociated into carbon atom and hydrogen atom to become cyclopentadiene. Cyclopentadiene is highly vaporizable and is easily discharged into the growth reaction system. Therefore, there is an advantage that the concentration of the thermal decomposition product, which is a carbon pollution source, in the growth environment can be reduced. Cyclopentadienyl thallium (I) (C ₅ H ₅ Tl) in combination with biscyclopentadienyl magnesium ((C ₅ H ₅ ) ₂ Mg), which is one of the above-mentioned p-type dopants obtained by adding a cyclopentadiene ring. When used together with (I)), nitrogen-containing nitrogen which exhibits p-type conduction doped with thallium having a carbon concentration equal to or lower than the value specified in the present invention III
A -V compound semiconductor layer can be obtained. The combination of raw materials with cyclopentadienyl ring added is nitrogen-containing III
In the growth of the group-V compound semiconductor layer, it has an advantage in reducing the background concentration of carbon atoms, and suppresses the incorporation of carbon atoms into the nitrogen-containing group III-V compound semiconductor layer accompanying the doping of thallium. Is superior to.

The thallium-doped nitrogen-containing III-V group compound semiconductor layer using cyclopentadienyl thallium (I) as a thallium doping material is, for example, MOCVD.
It can be formed by a vapor phase growth method such as a method. MOCVD
The growth method may be a normal pressure method or a reduced pressure method. The growth temperature is about 3 regardless of the pressure at which the growth is performed.
It can be set in the range of about 00 ° C to about 1200 ° C. If the temperature is within this range, the thallium atom concentration is 5 × 10 ¹⁵
Within the range of not less than cm ^{−3 and not} more than 5 × 10 ¹⁹ cm ^−3, a thallium-doped nitrogen-containing III-V group compound semiconductor layer having a carbon concentration of not more than 2 × 10 ¹⁶ cm ⁻³ can be obtained. This is because in this temperature range, the doping efficiency of thallium into the nitrogen-containing III-V compound semiconductor layer is good, the atomic concentration of thallium is easily controlled, and the thallium-doped light emitting layer is stably formed. Further, it is because the mixing of carbon into the layer is sufficiently suppressed. FIG. 4 shows the thallium atom concentration dependence of the carbon atom concentration of the GaN layer grown at a growth temperature of 950 ° C. using cyclopentadienyl thallium (I) as a thallium doping source, together with the conventional example.

The nitrogen-containing III-V group compound semiconductor layer doped with thallium can also be obtained by implanting thallium ions. The atomic concentration of thallium can be set to 5 × 10 ¹⁷ cm ⁻³ or more by adjusting the dose amount of thallium ions to the implanted body.
On the other hand, when the thallium-doped nitrogen-containing III-V group compound semiconductor layer is obtained by implanting thallium ions, the carbon atom concentration of the implanted body does not change. The carbon atom concentration of the thallium-doped nitrogen-containing III-V compound semiconductor layer obtained by the ion implantation method is almost the background carbon atom concentration of the layer. The background carbon atom concentration of the nitrogen-containing III-V compound semiconductor layer at the conventional practical growth temperature is at least about 4 ×.
It is 10 ¹⁶ cm ^-3 . Even if thallium ions are implanted into the body to be implanted in which the background concentration of carbon atoms is increased, it is difficult to keep the atom concentration of carbon within the range specified by the present invention.

Nitrogen-containing III-V doped with thallium
An LED including a light emitting layer made of a group compound semiconductor can be manufactured by, for example, processing a laminated structure including a clad layer that heterojunctions with the light emitting layer. As an example of a laminated structure for an LED, an n-type buffer layer, an n-type lower clad layer, a p-type thallium-doped light emitting layer, and a p-type upper clad layer are sequentially deposited on a crystal substrate. Can be mentioned. Depending on the conductivity type of the thallium-doped light emitting layer, if the conductivity type of the cladding layer or the like to be heterojunction therewith is changed, a pn junction type light emitting device can be obtained. When a thallium-doped light emitting layer having a high resistance is used, a pn junction type light emitting device having a structure in which a p-type layer and an n-type layer are arranged on both sides of the light-emitting layer can be obtained. The high resistance thallium-doped III-V group compound semiconductor layer can also be used to obtain a MIS type light emitting device.

The nitrogen-containing III-V group compound semiconductor layers forming the stack may all be made of the same material or different materials. If all the layers forming the stack are made of GaN, a stack structure made of the same material can be obtained. GaN is an example of a nitrogen-containing III-V group compound semiconductor layer, and a layered structure can be formed using a material appropriately selected from the nitrogen-containing III-V group compound semiconductors described above. An example of a laminated structure made of different nitrogen-containing III-V group compound semiconductor materials is an AlN layer / a thallium-doped AlGaN light emitting layer / InN layer.

There is no limitation on the combination of conduction types of the nitrogen-containing III-V group compound semiconductor layers constituting the laminated structure. LE
In obtaining a double heterojunction structure having a pn junction for D use, each layer located below the light emitting layer is
There is an example in which the light emitting layer is composed of n-type layers, and the layers arranged above the light emitting layer in the film thickness direction of the light emitting layer are inverted to p-type.

There are various methods for forming electrodes, materials for electrodes, and shapes of electrodes when manufacturing light-emitting elements such as LEDs.
There are materials and shapes. Examples of the method for forming the electrodes include physical deposition methods such as vacuum deposition method and sputtering method, and chemical deposition methods such as CVD method. The electrodes may be formed using a plurality of forming methods. For example, if a thin gold (Au) vapor deposition film having a thickness of about several thousand angstroms is formed by a vacuum vapor deposition method and a gold plating film is further deposited on the gold vapor deposition film by a plating method or the like, lead wire bonding or a circuit board It is possible to form an electrode having a large layer thickness that can withstand mounting. The material of the electrodes is, for example, a pn junction type LED.
In this case, a material that can obtain ohmic contact with the layer forming the electrode is particularly preferable. In the MIS type light emitting element, it is not always necessary to form the electrode from a material that can obtain ohmic characteristics. Known magnesium, A
l and Au (G. LEWICKI et al., J. Phys. Ch.
em. Solids, 29 (1968), 1255. )
And Ag (Yoichiro Uemura, "Applied Physics", Vol. 40, No. 5 (1971), page 572) can be used as the electrode material. The electrode can be formed not only by a single layer film of metal but also by a structure in which metal films are laminated in multiple layers. The electrode can be composed of an inorganic compound such as indium tin oxide, which is abbreviated as ITO, or a conductive organic compound film. The shape of the electrodes may be circular, rectangular, polygonal, or the like. The shape of the electrode may be determined in consideration of the processability in obtaining the light emitting element such as the bonding property of the lead wire. Further, the electrodes can be formed by combining metal films having different shapes. For example, the electrode may be a combination of a conductive film having a circular planar shape and a cross-shaped conductive film formed by intersecting rectangles at a right angle. The final thickness of the metal film used as the electrode is preferably about several thousand angstroms to 5 μm.

[0032]

The function utilizes that thallium acts as an element to further increase the intensity of light emitted from the light emitting layer.

[0033]

【Example】

(Example 1) Hereinafter, the present invention will be described based on examples. In this example, a layered structure including a plurality of nitrogen-containing III-V group compound semiconductor layers provided with a thallium (Tl) -doped gallium nitride (GaN) light-emitting layer deposited on a substrate was used.
An example of configuring the ED will be given. A schematic plan view and a vertical sectional view of the manufactured LED are shown in FIGS. 1 and 2, respectively. In constructing the laminated structure, 5N (9
Plate-shaped aluminum (Al) having a purity of 9.999% or more was used. Used aluminum substrate (10
1) is a disc with a diameter of 50 ± 1 mm and a thickness of about 0.5 m.
It was m. The substrate may be selected from other materials.
For example, sapphire or the like conventionally used for depositing a nitrogen-containing III-V compound semiconductor layer may be used. The surface of the aluminum substrate (101) was treated with a dilute acid, washed with ultrapure water having a specific resistance of about 18 mega ohm centimeters (MΩ · cm), and then dried at room temperature. After drying, it was loaded into a reaction furnace of an atmospheric pressure type MOCVD growth apparatus and placed on a mounting table.

Next, high-purity hydrogen gas purified by a palladium (Pd) membrane permeation type hydrogen purification apparatus is supplied as a carrier gas from above the aluminum substrate (101), and the surface of the substrate (101) is supplied with about 10 atoms. Hydrogen gas was blown at a flow rate of 1 / min. Hydrogen gas substrate (10
While continuously spraying onto 1), the temperature of the substrate (101) was heated to about 300 ° C. by using a resistance heating type heater for about 20 minutes, and the temperature was maintained for 15 minutes. While the substrate (101) was kept at the same temperature, no gas other than the above hydrogen carrier gas was supplied into the reaction furnace. Then, immediately before the temperature was increased to 600 ° C., which is a so-called growth temperature of the substrate (101) for depositing the nitrogen-containing III-V compound semiconductor layer by the same heater, the nitrogen source was vaporized. 1,4-diazabicyclo [2,2,2] octane (1,4-Diazabicy
Doping of [clo [2,2,2] octane) into the hydrogen carrier gas was started. This nitrogen source has a temperature of about 60
1,4-diazabicyclo [2
2,2] octane was entrained and doped with hydrogen gas purified as described above. The reason for choosing 1,4-diazabicyclo [2,2,2] octane as the nitrogen source is that it is a low-temperature decomposable nitrogen compound that decomposes at about 450 ° C in a state of almost equilibrium. by. As a result, aluminum (A
l) Allows the material to be used as a substrate.

After raising the temperature of the substrate (101) to 600 ° C. which is a growth temperature by raising the temperature, it was held at the same growth temperature for 20 minutes in order to stabilize the temperature of the substrate (101).
After the holding time of 20 minutes has elapsed, doping of trimethylgallium ((CH ₃ ) ₃ Ga) used as a gallium (Ga) source into the hydrogen carrier gas is started, and the Al substrate (10
An n-type GaN layer (102) was deposited on 1). n-type G
The aN layer (102) was obtained by doping a hydrogen carrier gas with a silane (SiH ₄ ) gas containing silicon (Si) already known as an n-type dopant. The doping amount of silane gas into the hydrogen carrier gas is such that the carrier concentration of the n-type GaN layer (102) is about 1 × 1.
It was adjusted to be 0 ¹⁸ cm ^-3 . When the doping silane gas diluted with high-purity hydrogen gas to a volume concentration of 5 ppm was used, the flow rate of the silane doping gas required to obtain the carrier concentration was 12 cc / min. G
Although the film thickness of the aN layer (102) is about 2 μm in this embodiment, the film thickness and the carrier concentration are not limited to the numerical values of this embodiment.

On the GaN layer (102), trimethylgallium was added as a gallium source and 1,4-diazabicyclo [2,2].
2,2] octane is used as a nitrogen source, and cyclopentadienyl thallium (I) (C ₅ H ₅ Tl (I)) is used as a thallium doping source to deposit a light emitting layer made of p-type GaN doped with thallium. did. The growth temperature was continuously set to 600 ° C. The doping amount of thallium is the doping amount of cyclopentadienyl (I) to the hydrogen carrier gas so that the concentration of thallium in the GaN light emitting layer (103) becomes about 9 × 10 ¹⁷ cm ^{−3 in} atomic concentration. It was adjusted. When the temperature of the container (127) accommodating the thallium source (126) described above is adjusted to 80 ° C. by the thallium source constant temperature bath (128), this atomic concentration is the raw material flowing to the thallium source (126). It was obtained by setting the flow rate of the carrier gas (117) to 120 cc / min. The p-type thallium-doped light-emitting layer (103) is a biscyclopentadienylmagnesium to which a cyclopentadienyl ring (C ₅ H ₅ −) similar to cyclopentadienyl (I) which is a thallium doping source is additionally bonded. ((C ₅ H ₅ ) ₂
Mg) was utilized as a p-type dopant source. p-type G
The carrier concentration of the aN light emitting layer (103) is about 1 × 10 ¹⁷ c
m ^−3, and the deposition conditions were set so that the film thickness was about 0.1 μm. According to a general SIMS analysis, the concentration of carbon impurities in the p-type GaN light emitting layer (103) is about 2 × 10 ¹⁶ c.
It was quantified as m ^-3 .

On the p-type GaN light emitting layer (103), trimethyl gallium was used as a gallium source and 1,4-diazabicyclo [2,2,2] octane was used as a nitrogen source, and biscyclopentadienyl magnesium was used as a p-type dopant. A p-type GaN layer (104) was deposited as a doping source. The film thickness is about 0.1 μm and the carrier concentration is about 3 × 10 ¹⁷ c
m ^-3 . The growth temperature was maintained at 600 ° C., and the flow rate of the hydrogen carrier gas was continuously set to 10 liters / minute. Ga
During the deposition of the N layers ((102) to (104)), the pressure in the reaction furnace was constantly maintained near 760 Torr.

By the above growth operation, L consisting of a total of three GaN layers including the thallium-doped light emitting layer on the substrate.
A laminated structure for ED use was obtained. An LED was produced by the following method using the obtained laminated structure as a base material.

The surface of the p-type GaN layer (104), which is the outermost layer of the laminated structure, was covered with a silicon oxide film (105) by a usual plasma CVD method. Next, a silicon oxide film (10
The surface of 5) was coated with a general photoresist material. Next, using a known photolithography method, the region where the surface electrode (106) is to be formed was patterned, and the above photoresist material was removed only in the region where the electrode (106) was to be formed. This exposed the surface of the p-type GaN layer (104) only in the formation region of the electrode (106). Then, the p-type G exposed through the above patterning process is exposed.
High-purity (6N) aluminum was deposited on the surface of the photoresist material remaining on the surface of the aN layer (104) and the surface of the silicon oxide film (105) by a normal vacuum deposition method.
After the vacuum deposition of aluminum, the aluminum vacuum deposition film deposited on the surface of the photoresist material was removed by a lift-off method using the photoresist material remaining on the silicon oxide film (105). By this lift-off method, the aluminum vacuum deposition film remains only in the region where the photoresist material is peeled off, that is, in the electrode formation region, and the surface electrode (106) is formed from this. The surface electrode (106) was a circular electrode having a diameter of about 130 μm. The thickness of the surface electrode (106) was about 700 nm.

The other counter electrode (107) necessary for driving the LED is also used as the substrate (101) since aluminum, which is a light metal having conductivity, is used for the substrate (101) in this embodiment. . By this. An LED was prepared in which electrodes were arranged above and below the laminated structure including the substrate and the chip size was about 300 μm □.

A DC voltage was applied between the electrodes ((106) and (107)) of the manufactured LED, and a forward operating current of 20 mA was passed to drive the LED. The main electrical and optical characteristics obtained are listed in Table 1. The emission color was deep green, and the central wavelength of emission was about 527 nm.
In comparison with the conventional GaP green LED having a central wavelength of light emission of about 555 nm, the conventional device has a brightness of about 100 millicandelas (mcd), whereas the LED provided with the thallium-doped light emitting layer of the present embodiment. About 80
An improvement of 0 mcd was recognized. The forward voltage (Vf) when the forward current is 20 mA is about 3.2 V, which is about 10% of Vf when compared to about 3.5 V of the conventional blue LED made of a nitrogen-containing III-V group compound semiconductor. Reduction was recognized.

[0042]

[Table 1]

After sealing with a general semiconductor element encapsulating epoxy resin, an operation reliability test was performed in a high temperature and high humidity environment while continuously applying a forward operating current of 20 mA to the element. . The temperature in the reliability test (high-temperature high-humidity storage test) was + 60 ° C., and the relative humidity was kept at 80%. In the LED of the present embodiment, after 1000 hours have passed since the start of energization, the decrease in the emission brightness of more than 5% compared to the initial emission brightness before the test is performed is due to the fact that almost the same number of LEs as the LEs are tested.
No confirmation was made for D, indicating that the LED has excellent operation reliability.

Example 2 In this example, aluminum gallium nitride (AlG) formed by doping thallium is used.
An explanation will be given by taking as an example a method of forming aN) mixed crystal layer using a vapor phase growth method. FIG. 3 is a schematic view of an atmospheric pressure (atmospheric pressure) MOCVD vapor phase growth apparatus used in this example.

In MOCVD growth of the AlGaN mixed crystal layer, in the present example, trimethylgallium ((CH ₃ ) ₃ Ga) was used as the gallium (Ga) source (108) and trimethylaluminum (109) was used as the aluminum (Al) source (109). (CH ₃ ) ₃ Al) was used, and ammonia (NH ₃ ) was used as a nitrogen (N) source.

The gallium source (108) and aluminum source (109) were contained in separate stainless steel containers ((111) and (112)). Stainless steel container ((1
11) and (112)) were kept at a constant temperature by using their own thermostats ((114) and (115)). The stainless steel bubbling container (111) for the gallium source (108) was set at 0 ° C., and the stainless steel bubbling container (112) containing the aluminum source (109) was set at 20 ° C.

The gallium source (108) and the aluminum source (109) were purified by a palladium membrane permeation type purification device and a low temperature adsorption type purification device, and the dew point was from -95 ° C to -110.
Bubbling was carried out with a raw material carrying gas (117) for carrying vapor of each source consisting of high-purity hydrogen gas in the range of ° C. Bubbling flow rate to the gallium source (108) is 10c
The flow rate of bubbling to the aluminum source (109) was 25 cc / min. Raw material after bubbling ((1
The raw material carrying gas (117) accompanied by the steam of (08) and (109) is airtight piping ((118) and (11)
9)), which has a piping configuration that allows circulation in either the main pipe (121) or the exhaust pipe (122) leading to the reaction furnace (123) for depositing the AlGaN mixed crystal layer. Before starting the deposition of the AlGaN mixed crystal layer, the raw material carrying gas accompanied by the vapor of the raw material that has been circulated in the pipes ((118) and (119)) is a valve ((13
It was introduced into the exhaust pipe (122) by operating the opening and closing of 0-1) to (130-4)).

Ammonia having a concentration of 100% was used as the nitrogen source. Liquefied ammonia is stored in a steel cylinder container (11
Stored in 3). The vaporized ammonia is decompressed (1
The pressure was reduced to approximately 1 atm by a gauge pressure via 16) and then introduced into the main pipe (121).

Cyclopentadienyl thallium (I) (C ₅ H ₅ Tl (I)) was used as the thallium source (126). The thallium source (126) is a stainless steel container (1
27), and the container (127) is a thermostat (12).
It was kept constant at 75 ° C. according to 8). Each source ((108)
The temperatures of (110) and (126)) were kept constant about 2 hours before the deposition and growth of the AlGaN layer doped with thallium described later. Thallium source (1
In the container (127) containing 26), high-purity hydrogen gas was previously passed as a raw material carrying gas (117) for carrying the sublimated thallium source. Before carrying out the deposition growth of the AlGaN layer, the raw material carrying gas accompanied by the vapor of the thallium source was introduced into the exhaust pipe (122) using the pipe (129).

Sapphire (alumina single crystal) was used for the substrate (101). The substrate (101) was surface-treated with dilute acid and then dried. The substrate (101) which has undergone the pretreatment is placed on the surface of the heating body (124) which also serves as a substrate mounting table placed at a substantially horizontal center position in the reactor (123) having a circular cross section. . Board (101)
After mounting, the inside of the reaction furnace (123) was evacuated to a vacuum of about 10 ⁻³ Torr using a normal vacuum pump. After evacuation, an argon gas was introduced into the reaction furnace (123) to bring the pressure in the reaction furnace (123) to almost atmospheric pressure.

The pressure in the reaction furnace (123) was set to about 760T.
After setting the atmospheric pressure to orr, the gas introduced into the reaction furnace (123) was switched to hydrogen purified to a higher purity than argon. High-purity hydrogen was introduced as a carrier gas (110) into the reaction furnace (123) through the main pipe (121).
The flow rate of the carrier gas (110) was set to 10 l / min. The carrier gas introduced into the reaction furnace (123) is a nozzle (125) provided in the reaction furnace (123).
And sprayed onto the surface of the substrate (101).

Carrier gas (110) reactor (12)
3) The inside of the reaction furnace (123) is continuously circulated and the pressure inside the reaction furnace (123) is maintained at about atmospheric pressure, while the resistance heating type heating element (1) is used.
24), the temperature of the substrate (101) placed on the surface of the heating body (124) was once heated to 400 ° C. 40
After reaching 0 ° C., the substrate (101) was held at the same temperature for 20 minutes. While holding the substrate (101) at the same temperature,
No source gas other than the high-purity hydrogen carrier gas (110) was allowed to flow in the reaction furnace (123).

After that, a carrier gas reaction furnace (123)
Ammonia gas, which is a nitrogen source decompressed by the decompression device (116), is introduced into the main pipe (121) through the pipe (120) without changing the supply flow rate to the reactor and the pressure in the reaction furnace (123). did. The supply rate of ammonia gas was 2 liters / minute. About 10 minutes after starting the doping of the nitrogen source, the temperature of the substrate (101) was raised to the growth temperature of 950 ° C. After heating, the hydrogen carrier gas (110) was supplied and the nitrogen source gas nozzle (12)
The substrate (101) was kept at the same temperature for 20 minutes while continuing the supply to the surface of the substrate (101) via the inside of 5).

The temperature of the substrate (101) was used as the growth temperature 9
After the temperature was maintained at 50 ° C., while maintaining the pressure in the reaction furnace (123) at about atmospheric pressure, the raw material carrying gas containing the vapors of the gallium source (108) and the aluminum source (109) was valved ((130-1 )-(130-4)), the high-purity hydrogen carrier gas (110) continuously flowing in the main pipe (121) was doped. At the same time, the doping of the source carrier gas (117) containing the vapor of the thallium source (126) into the hydrogen carrier gas (110) is controlled by the valve ((130-5).
And (130-6)) were opened and closed. Thereby, the growth of the AlGaN mixed crystal layer doped with thallium was started.

A hydrogen carrier gas (110) doped with each raw material is passed through a nozzle (125) to a substrate (10).
Continued on the surface of 1) for 1 hour. During this time, the pressure inside the reaction furnace (123) was maintained at about atmospheric pressure. Thereby, the AlGaAs mixed crystal layer was deposited on the substrate (101) for 1 hour. After 1 hour has passed, the open / closed states of the valves ((130-1) to (130-6)) are switched, and the gallium source (108) and the aluminum source (10) are switched.
9) and the hydrogen carrier gas (11) flowing in the main pipe (121) for the raw material carrying gas containing the thallium source (126).
The doping to 0) was stopped, and it was introduced into the exhaust pipe (122). By this valve operation, the deposition of the AlGaAs mixed crystal layer was completed. In order to prevent nitrogen from volatilizing from the surface of the AlGaN mixed crystal layer, the supply of ammonia gas used as a nitrogen source to the hydrogen carrier gas (110) was continued. At the same time when the above valve operation is performed, the heating element (1
The power supply to 24) was stopped, and the temperature of the substrate (101) was lowered. When the temperature of the substrate (101) has dropped to about 400 ° C., the valve (130-7) is closed to stop the doping of the hydrogen source into the hydrogen carrier gas (110) and introduce it into the exhaust pipe (122). did. Hydrogen carrier gas (11) flowing into the reactor (123) through the main pipe (121)
0) is supplied to the substrate (10) whose temperature has dropped to around room temperature.
It was continued until 1) was taken out from the reaction furnace (123). By the above growth operation, to obtain a thallium doping Al _{0. 15} Ga _0.85 N mixed crystal layer be about 0.7μm film thickness. Therefore, the growth rate was about 0.7 μm / hour.

On the surface of the obtained nitrogen-containing III-V compound semiconductor layer, almost no particulate foreign matter mainly produced by the complexing reaction was observed, and the surface was extremely smooth and flat. According to SIMS analysis, the atomic concentration of thallium is about 1.
2 × 10 ¹⁸ cm ⁻³ , while the carbon concentration is SIMS
According to the analysis, it was about 3 × 10 ¹⁶ cm ⁻³ . By using the thallium doping source according to the invention,
Within the atomic concentration range of thallium, which has an excellent surface condition and provides high-intensity light emission, the atomic concentration of carbon that causes a decrease in emission intensity can be suppressed to an extremely low concentration.

Comparative Example Instead of the cyclopentadienyl thallium of the present invention, triethyl thallium ((CH) ₃ T
l) as a thallium doping source, thallium-doped aluminum gallium nitride (Al _0.15 Ga _0.85
N) A mixed crystal layer was grown. In this comparative example, in the atmospheric pressure type MOCVD apparatus shown in FIG.
Only 6) was changed to triethyl thallium. Other conditions were the same as those in the example. Materials for gallium source (108), aluminum source (109) and nitrogen source (110), temperature at which each raw material is held, flow rate conditions of raw material carrying gas for carrying vapor of each raw material, and flow rate of hydrogen carrier gas, etc. The growth conditions including the conditions were not changed. The operations such as the opening and closing operations of the valve were unified with the method described in Example 2.

A stainless steel bubbler container (1 containing a thallium source (126) made of triethylthallium.
27) was kept at 5 ° C by a thermostat (128). The flow rate of high-purity hydrogen gas to be circulated in the container (127) is 5
It was cc / min. As a result, a thallium-doped Al _0.15 Ga _0.85 N mixed crystal layer having an atomic concentration of thallium of about 1 × 10 ¹⁸ cm ⁻³ and a film thickness of about 0.7 μm was obtained in substantially the same manner as in Example 2. According to SIMS analysis, the obtained Al _0.15
The atomic concentration of carbon in the Ga _0.85 N mixed crystal layer is about 5 × 10 ¹⁸ cm
It was ^-3 . Under the same conditions as above, the doping amount of thallium was kept constant and thallium-doped Al _0.15 Ga
_When the growth of the _0.85 N mixed crystal layer was continuously repeated 10 times, the maximum concentration of carbon atoms was 8 × 10 ¹⁸ cm ⁻³ and the minimum concentration was 3 × 10 ¹⁸ cm ^−3. Fluctuated within. The insufficient reproducibility of carbon atom concentration was presumed to be mainly due to the instability of the complexation reaction between the conventional thallium source, triethylthallium, and the nitrogen source, ammonia. In contrast, in the method for forming a thallium-doped Al _0.15 Ga _0.85 N mixed crystal layer according to the present invention described in Example 2, the carbon atom concentration is reproducibly suppressed to less than 4 × 10 ¹⁶ cm ^-3. Further, the thallium atom concentration was stored in a range of ± 6% centering on 1.2 × 10 ¹⁸ cm ⁻³ . In this Comparative Example, the particulate deposited in the central region of the partial region, in particular the surface of the surface of the Al _{0. 15} Ga _0.85 N mixed crystal layer grown on the same Al substrate as described in Example 2 It was difficult to obtain a growth layer having a flat surface due to the concentration of objects.

As is clear from the comparison between the results obtained in Example 2 and the comparative example, the method of forming the nitrogen-containing III-V group compound semiconductor layer using cyclopentadienyl thallium as the doping source of thallium is as follows. The carbon atom concentration in the growth layer is significantly reduced by about two orders of magnitude as compared with the conventional method. Further, by sufficiently suppressing the complexation reaction with ammonia, which is a nitrogen source which has been frequently used, in the gas phase, thallium-doped nitrogen-containing III
The effect of improving the reproducibility of the carbon atom and thallium atom concentrations in the -V compound semiconductor layer is recognized. The effect of sufficiently suppressing the complexing reaction further suppresses the deposition of fine particles generated on the surface of the growth layer, which is mainly caused by this reaction. Therefore, the method for forming a thallium-doped nitrogen-containing III-V group compound semiconductor layer using cyclopentadienyl thallium as a thallium doping source has the effect of stably providing a growth layer having a flat and transparent surface state. . The optically transparent thallium-doped nitrogen-containing III-V compound semiconductor layer produced by defining the carbon atom concentration at a low concentration is used as a colored growth layer when used as a layer constituting a light emitting structure such as a light emitting layer. By comparison, it is clear that it does not hinder the transmission of the light emission from the light emitting structure, and thus is advantageous in obtaining a light emitting element having excellent light emission intensity. Therefore, the method for forming a nitrogen-containing III-V group compound semiconductor layer doped with thallium of the present invention is
There is a ripple effect in which improvement in device characteristics such as increase in light emission intensity is dominant.

[0060]

Effect of the Invention Nitrogen-containing material doped with thallium III-
By using a group V compound semiconductor as a light emitting layer,
The green LED provides improved emission intensity. A method of forming a thallium-doped nitrogen-containing III-V group compound semiconductor layer using cyclopentadinyl thallium as a thallium doping source is provided by avoiding a complexation reaction between starting materials of a group III element and a group V element. This brings about an effect of stably providing a nitrogen-containing III-V group compound semiconductor layer which is excellent in state and is suppressed in a low carbon atom concentration.

[Brief description of drawings]

FIG. 1 is a schematic plan view of an LED according to a first embodiment of the present invention.

FIG. 2 is a schematic sectional view of a central portion of the LED shown in FIG.

FIG. 3 is a schematic view of a vapor phase growth apparatus used for carrying out the present invention.

FIG. 4 is a diagram showing a relationship between a thallium atom concentration and a carbon atom concentration of a GaN layer doped with thallium.

FIG. 5 is a diagram showing the relationship between the thallium atom concentration of a GaN layer doped with thallium and the photoluminescence intensity.

FIG. 6 is a graph showing the relationship between the carbon atom concentration of a GaN layer doped with thallium and the photoluminescence intensity.

[Explanation of symbols]

(101) Substrate (102) n-type GaN layer (103) GaN light-emitting layer (104) p-type GaN layer (105) silicon oxide film (106) surface electrode (107) counter electrode (108) gallium source (109) aluminum source (110) Hydrogen carrier gas (111) Stainless steel container for storing gallium source (112) Stainless steel container for storing aluminum source (113) Steel cylinder for storing nitrogen source (114) Constant temperature tank for gallium source (115) Aluminum Constant temperature bath for source (116) Decompressor for nitrogen source (117) Gas for raw material transport (118) Pipe for flowing raw material transport gas containing gallium source (119) Passing raw material transport gas containing aluminum source Piping (120) Piping for flowing nitrogen source (121) Main piping (122) leading to growth reaction vessel Exhaust pipe (123) Reactor (124) Heater (125) Nozzle (126) Thallium source (127) Thallium source storage stainless steel container (128) Thallium source constant temperature bath (129) Raw material transfer including thallium source Piping (130-1) Valve (130-2) Valve (130-3) Valve (130-4) Valve (130-5) Valve (130-6) Valve (130-7) Valve (131) Curve showing carbon atom concentration when trimethyl thallium is used as a thallium doping source (132) Curve showing carbon atom concentration when using a thallium doping source according to the present invention

Claims (3)

(57) [Claims] 1. Boron (B), aluminum (Al),
At least one of gallium (Ga) or indium (In) is a group III constituent element, and a nitrogen-containing III-V group compound semiconductor layer doped with thallium (Tl) is provided as a light emitting layer. A light emitting element characterized by the above. 2. The atomic concentration of thallium is 5 × 10 ¹⁷ cm ^−3.
And the atomic concentration of carbon (C) is 2 × 10 ¹⁶ cm
^-3 or less, The light emitting device according to claim 1, wherein 3. A method of manufacturing a light emitting device, which comprises doping thallium with a cyclopentadienyl thallium compound as a doping source.