JP2000223741A - Nitride semiconductor light emitting device - Google Patents

Abstract

(57) [Problem] To improve a light emitting characteristic and an electric characteristic of a light emitting element made of a nitride semiconductor and realize a high output operation and a low power consumption operation. SOLUTION: As a means for forming a p-type conductor layer in a nitride semiconductor such as GaN or InGaN, a growth layer having a high hole concentration formed by introducing as a donor type impurity together with an acceptor type impurity during crystal growth. And a light-emitting element comprising:

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blue / ultraviolet light emitting device using a nitride semiconductor, and more particularly to a light emitting device having excellent light emitting characteristics and electrical characteristics by obtaining a high concentration of hole concentration.

[0002]

2. Description of the Related Art InGaN, GaN, AlGaN, InGaN
A nitride semiconductor such as AlGaN is a material that has a direct transition and can change the band gap in the range of 1.95 to 6.2 eV by controlling composition and has high thermal stability. In particular, expectations as materials for blue / ultraviolet light emitting diodes and semiconductor lasers are increasing. Originally, this nitride semiconductor material was difficult to obtain a low-resistance layer even if it was mainly doped with a p-type impurity, and became a high-resistance layer.

[0003] This is because nitride compound semiconductors,
For example, in a gallium nitride-based compound semiconductor, when a crystal is grown by a vapor growth method, an n-type conductive layer is generally easily formed. Therefore, for the purpose of forming the p-type conductive layer, Be, Mg, Ca, Zn,
There is a problem that a sufficiently high carrier concentration cannot be obtained even if impurities such as Cd are doped as a dopant. The main cause is that the crystal is exposed to a relatively high growth temperature of around 1000 ° C., and if the nitrogen partial pressure of the atmosphere is low, nitrogen is dissociated from the crystal, and a vacancy is formed at the nitrogen lattice point, This vacancy acts as a donor. The amount generated varies greatly depending on the growth conditions, but is approximately 1 × 10 ¹⁷ / cm ³ to 1 × 10 ²² /.
It is said to be cm ^3. According to studies by the inventors, under normal growth conditions in the MO-CVD method, the donor concentration caused by nitrogen vacancies can be easily reduced to 4 × 10 ¹⁶ / cm.
^The number reaches ³ units, and especially InN reaches 10 ¹⁸ / cm ³ .
As described above, in at least a gallium nitride-based compound semiconductor, the generation density of nitrogen vacancies varies depending on the magnitude of the nitrogen partial pressure of the growth source gas and the composition of the material during crystal growth, and generally, when the nitrogen partial pressure is low, The formation of nitrogen vacancies increased.

[0004] This donor is compensated by the acceptor by the addition of a p-type dopant, so that the donor concentration should decrease and eventually the acceptor concentration should increase.
In practice, the acceptor concentration reaches saturation on the order of 10 ¹⁸ / cm ³ and then gradually decreases. The reason that it is difficult to obtain a p-type conductive layer having a high hole concentration is that not only the original activation rate of the acceptor impurity in the crystal is not so large, but also the hydrogen contained in the growth source gas and the carrier gas. It is possible to form a compound by combining with a crystal constituent atom or an impurity, thereby preventing the intrinsic activation of the impurity.
In order to realize a p-type conductive layer having a high hole concentration, it is necessary to suppress the formation of these donors and the formation of the composite so as not to proliferate, and to generate a desired acceptor concentration.

[0005] As a result of efforts to overcome such problems, Japanese Patent Application Laid-Open Nos. Hei 2-257679 and Hei 5-183189 have been proposed.
A technology for realizing a low-resistance p-type layer disclosed in Japanese Unexamined Patent Publication (Kokai) No. H10-260, has been found. In the former, a technique of irradiating the i-type gallium nitride-based compound semiconductor layer with an electron beam, and in the latter, a technique of annealing the i-type gallium nitride-based compound semiconductor layer at 400 ° C. or more can realize a low-resistance p-type layer. is suggesting. The reason that a low-resistance p-type layer can be obtained by these techniques is that, when a gallium nitride-based compound semiconductor crystal is grown by a vapor phase growth method, generally, ammonia is used as a nitrogen source and hydrogen or a compound containing hydrogen is used as a carrier gas. It is described that since the ionized hydrogen at the time of the reaction is combined with the p-type dopant doped in the gallium nitride-based compound semiconductor, the p-type dopant hinders the function of acting as an acceptor. ing.

[0006]

Although this technique has a remarkable effect in realizing the formation of a low-resistance gallium nitride-based compound, the ratio of activation as an acceptor to the total amount of the p-type dopant doped in the crystal is considered. most about 4% p-type dopant concentration 10 ¹⁷ / cm ^3, 10 ¹⁹
/ Cm ³ , which is about 0.1%, and the obtained hole carrier concentration is at most about 5 × 10 ¹⁸ / cm ³ . Under normal growth conditions, 3-8 × 10 ¹⁷ / cm ³ after growth
And the formation of a pn junction, an ohmic electrode, and the like becomes insufficient, and there is a problem that sufficient element characteristics cannot be obtained. The reason why the hole carrier concentration cannot be sufficiently mentioned is that, as described above, activation inhibition by a compound generated from the bond between an impurity and hydrogen and formation of a donor by a nitrogen vacancy are mentioned.

The problem of activation inhibition due to the bond between the impurity and hydrogen is that the bond with hydrogen is broken by annealing in nitrogen at 400 to 500 ° C. or higher as disclosed in Japanese Patent Application Laid-Open No. 5-183189 to function as an acceptor. As is well known, the recovery can be solved to some extent at least by the annealing process. For example, Ga
In the case of N, AlGaN, InGaN, and the like, when a p-type conductive layer is grown, Mg having a level of 160 meV is generally doped as an impurity for the purpose of forming a shallower acceptor level. This accept (Mg ⁺ ) When it associates with protons (H ⁺ ) that have entered the crystal during crystal growth, it is electrically coupled to form a Mg—H complex. JP-A-5-183189 discloses that Mg-
It is disclosed that the problem can be solved by annealing at a temperature of 400 ° C. or higher at which the H compound decomposes. However, this technique cannot sufficiently decompose and remove the Mg-H complex,
Since Mg is not sufficiently activated as an acceptor, the activation rate is as good as about 1%, which is an issue for lowering the resistance. Further, device construction of a semiconductor laser or the like that requires a high current injection mechanism is still insufficient, and further higher concentration is demanded.

Accordingly, the present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a pn junction associated with the realization of a high-concentration p-type conductive layer in a nitride compound semiconductor. , Related to the formation of ohmic electrodes,
It is an object of the present invention to improve the performance of light-emitting elements such as visible light-emitting diodes and visible semiconductor lasers mainly composed of blue, which are constructed by these technologies, such as light output characteristics and electric characteristics.

[0009]

According to the first aspect of the present invention, the semiconductor device is characterized by having a p-type conductive layer containing a p-type dopant and an n-type dopant. Since the p-type conductive layer is easily formed, the performance of the semiconductor device constituted by this layer is significantly improved. In the light emitting diode, the driving power, which was conventionally large, could be reduced by about 30 to 40% without optimizing the element structure.

According to the second aspect of the present invention, a layer having an unconventional hole carrier concentration can be obtained by applying the means for forming a p-type conductive layer to the formation of a p-type AlGaN layer or an InGaN layer. An excellent light emitting element such as a light emitting diode having a high power or a semiconductor laser withstanding a high output operation can be realized.

According to the third aspect of the present invention, the InGaN layer and the Al layer, which have had to increase the series resistance in the conventional method,
The construction of a semiconductor device composed of a horizontal GaN layer and a stock layer could be facilitated. That is, a high hole carrier concentration AlGaN layer could be formed at a lower temperature than the conventional method.

According to the fourth aspect, the hole carrier concentration suitable for each semiconductor element is in a relatively wide range, but the donor level and the acceptor level are electrically paired to form a static state. The electric energy is stabilized, and the acceptor atoms are less likely to be displaced from lattice points. Since the configuration in which atoms acting as acceptors are further arranged at symmetric positions via the donor in this atom pair is considered to be stable,
By co-doping the amount of atoms acting as donors with about half the desired hole carrier concentration, the hole carrier concentration can be controlled over a wide range with little compensation. Therefore, the practical use of various semiconductor devices such as field effect transistors / bipolar transistors and semiconductor lasers has become a reality.

According to the fifth aspect of the present invention, unlike the amphoteric impurities, the use of a VI group element such as O, S, Se, or Te as an atom forming the donor level limits the formation of the donor level. Therefore, the possibility of replacing nitrogen vacancies is high, so that the control of the hole concentration is facilitated.

[0014]

Embodiments of the present invention will be described below. However, the examples described below illustrate means for embodying the technical idea of the present invention, and the method of the present invention may be implemented in terms of the composition of material crystals, crystal growth conditions, the type of vapor-phase growth gas, etc. It is not specific to the example.

In the nitride semiconductor light emitting device of the present invention,
FIG. 1 shows a cross-sectional structure of a gallium nitride-based compound semiconductor light emitting device of one embodiment. Sapphire, SiC, M
Materials such as gAl ₂ O ₄ , GaN, MgO, Si, ZnO can be used, but usually sapphire is used. M
According to the O-CVD method, the GaN buffer layer 2 is grown on the substrate by using ammonia (NH ₄ ) and trimethylgallium (TMG), which are source gases, with hydrogen as a carrier gas, and further, Subsequently, the n ⁺ -type GaN layer 3,
n-type GaAlN layer 4, n-type InGaN layer 5, p-type GaAs
It grows continuously as the 1N layer 6 and the p ⁺ -type GaN layer 7 as a layer having a carrier concentration and a thickness suitable for the light emitting element, respectively. In the present invention, the p-type GaAlN layer 6 which is a p-type conductive layer is used.
And a method relating to carrier concentration control of the p ⁺ -type GaN layer 7, characterized in that, in order to form a high-concentration p-type conductive layer, an impurity serving as a donor is added to the growth layer in addition to an impurity serving as an acceptor. And

In a gallium nitride-based compound semiconductor, a nitrogen blanket vapor pressure during crystal growth is high, so that a nitrogen vacancy is easily formed. The amount is about 1 × 10 ¹⁷ / cm ³ -1 × 10 ²⁰
/ Cm ^3, and generally exhibits n-type conduction unless a specific impurity is added. In order to reduce the number of generated nitrogen vacancies as much as possible, it is necessary to control the vapor pressure of NH ₄ as a nitrogen source to obtain a balanced vapor pressure, and this means is usually employed. In order to convert the conduction type of the growth layer having such properties to p-type, the donor may be compensated by adding an impurity serving as an acceptor. However, the acceptor atoms doped into the growth layer from the crystal growth atmosphere may be used. Binds to H ⁺ present around it and inhibits activation of the dopant.
When the acceptor (A ⁺ ) exists solely electrically,
The electrostatic energy is unstable, and the acceptor moves toward minimization of free energy by displacement or formation of a compound, and a compensation effect appears. This prevents the acceptor concentration from increasing. However, in the present invention, p-type Ga
_In doping the _1-z Al _z N layer 6 and the P-type GaN layer 7, for example, as a dopant gas in a source gas of TMG and TMA and ammonia or TMG and ammonia,
By supplying Cp ₂ Mg (cyclopentagenyl magnesium) and SiH ₄ (silane) at a flow rate ratio of about 3: 1, the carrier concentration of the p-type conductive layer is reduced to 6%.
It became easy to control up to × 10 ²⁰ / cm ³ . The reason why such an effect was obtained is that some of the doped S
i substitutes for a nitrogen lattice position to form a shallow acceptor,
Most of which are substituted at group III atoms to form shallow donors, and which are also substituted at group III elements.
Becomes a shallow acceptor, and the acceptor (Mg ⁺ ) and the donor (Si ⁻ ) form a pair, so that the electrostatic energy becomes stable. It is thought that one Mg coordinated around this pair of atoms acts as an acceptor, resulting in activation to a high concentration. Further, the donor which is not electrostatically coupled to the acceptor and has an effect of neutralizing H ⁺ in the crystal has an effect of increasing the conductivity of the p-type conductive layer.

Example 1 A method of manufacturing the gallium nitride-based compound semiconductor light emitting device of the present invention by a normal MOCVD method will be described.

A sufficiently cleaned sapphire substrate 1 is placed in a reaction vessel and heated to 1100 ° C. using hydrogen as a carrier gas to thermally clean the sapphire substrate. After this treatment, the temperature was lowered to 500 ° C., and hydrogen was used as a carrier gas, and TMG (trimethylgallium) and ammonia were used as source gases to form a 200 ° G.
The aN buffer layer 2 is grown. Thereafter, the TMG gas was stopped, the substrate temperature was raised to 1030 ° C., and the source gas was TMG.
Then, an n + GaN layer having a carrier concentration of 1 × 10 ¹⁹ / cm ³ for the cathode contact is grown to a thickness of 3.5 μm by using silane gas as a dopant gas for the purpose of doping Si with ammonia and Si.

Subsequently, the flow rate of the silane gas is reduced to reduce the doping of Si, and the carrier concentration is reduced to 1 × 10 ¹⁸ /
An n-type GaN layer of 0.5 μm in cm ³ was grown to form a GaN clad layer 3 having a two-layer structure. After the growth of the n-type GaN cladding layer 3, the raw material gas and the dopant gas are both stopped, the substrate temperature is lowered to 850 ° C., the carrier gas is switched to nitrogen, and the raw material gases are TMG, TMI (trimethylindium) and ammonia. Using silane gas as a dopant gas, 100-nm thick n-type In _0.15
A Ga _0.85 N layer 5 is grown. Subsequently, the source gas and the dopant gas are interrupted to raise the substrate temperature to 1030 ° C., and the source gas TMG, ammonia and T
MA (trimethyl aluminum Niu beam), the dopant gas as Cp ₂ Mg (cyclopentadienyl magnesium) as the silane gas from about 3: used in a proportion of 1, Mg and S
The p-type Al _0.1 Ga _0.9 N layer 6 doped with i
m.

The resulting layer has a carrier concentration of 1 × 10 ¹⁸
/ Cm ³ . After the growth of the p-type AlGaN layer 6, T
After stopping MA, the flow rate ratio between Cp ₂ Mg and silane was increased at the same rate, and a p ⁺ -type GaN layer 7 doped simultaneously with Mg and Si was grown to a thickness of 0.3 μm.

After the growth of the p ⁺ -type GaN layer, the growth substrate taken out of the reaction vessel was subjected to a heat treatment at 700 ° C. for 20 minutes in a nitrogen atmosphere to promote a reduction in the resistance of the p-type conductive layer. The resistivity of the resulting p-type conductive layer was 0.040-cm, and the hole carrier concentration was 8 × 10 ¹⁹ / cm ³ .

[0022] In the above process the through-obtained grown layer well known methods, the anode into P ⁺ -type Kuratsudo layer, the cathode to the n ⁺ -type cladding layer to form, respectively, to form a light-emitting diode of 500μm square.

When a forward current of 20 mA was applied, a forward voltage of 3.8 V, an emission output of 1.5 mW, and an emission wavelength of 410 nm were used.
And uniform light emission was obtained.

[Embodiment 2] In the growth of the p-type AlGaN layer 6 of Embodiment 1, Cp ₂ Mg was used as a P-type dopant.
(Cyclopentagenenylmagnesium) gas, hydrogen sulfide (H ₂ S) as an n-type dopant, and a flow ratio thereof at a ratio of 3: 1 to flow p-type Al _0.1 Ga _0.9 doped with Mg and S. The N layer 6 was grown to a thickness of 0.2 μm.
The carrier concentration of the obtained layer was 2 × 10 ¹⁹ / cm ³ . After growing the p-type AlGaN layer 6, the TMA gas is interrupted, and dopant gases Cp ₂ Mg and H ₂ S are
While maintaining the ratio, increase the amount of p ⁺ -type GaN layer 7 to 0.1.
It grew to a thickness of 3 μm. The carrier concentration in this layer is 5 × 1
0 ²⁰ / cm ³ .

In the other steps, a light emitting diode was prepared in the same manner. The light emitting output was 1.9 m with a forward current of 20 mA.
W, a forward voltage of 3.1 V, and an emission wavelength of 410 nm provided uniform characteristics.

[0026]

As described above, according to the present invention, by realizing a high concentration p-type conductive layer in a pn junction of a nitride compound semiconductor, an ohmic electrode, etc., a visible light emitting diode mainly comprising blue light, A useful nitride semiconductor device having improved performance such as light output characteristics and electric characteristics of a light emitting device such as a semiconductor laser can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a light emitting device according to one embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 1 substrate 2 buffer layer 3 n ⁺ -type GaN layer 4 n-type AlGaN layer 5 n-type InGaN layer 6 p-type AlGaN layer 7 P ⁺ -type GaN layer 8 cathode 9 anode

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 5F041 AA03 AA04 CA03 CA12 CA34 CA40 CA46 CA49 CA53 CA54 CA56 CA57 CA65 CB13 5F045 AA04 AB14 AB17 AC01 AC08 AC12 AC19 AD09 AD12 AD14 AF02 AF03 AF04 AF09 BB16 CA11 CA12 DA53 EB15 EE15 CA17 CB05 CB19 DA05 DA35 EA24

Claims (5)

[Claims] 1. A nitride semiconductor device comprising a p-type conductive layer containing a p-type dopant and an n-type dopant. 2. The nitride according to claim 1, wherein the p-type conductive layer is a gallium nitride semiconductor layer containing Al and / or a gallium nitride semiconductor layer containing In as a light emitting layer or a cladding layer. Semiconductor light emitting device. 3. The nitride semiconductor light emitting device according to claim 2, further comprising the p-type conductive layer made of AlGaN as a cladding layer on the light emitting layer made of InGaN. 4. The p-type conductive layer according to claim 1, wherein the p-type dopant and the n-type dopant are simultaneously doped so as to be approximately 3: 1. 3. The nitride semiconductor device according to item 1. 5. The nitride semiconductor device according to claim 1, comprising a p-type conductive layer formed using a group VI element as an n-type dopant added simultaneously with the p-type dopant.