JP5451320B2 - ZnO-based compound semiconductor device - Google Patents

Description

  The present invention relates to a ZnO-based compound semiconductor device, and more particularly to a ZnO-based compound semiconductor light emitting device.

  Zinc oxide (ZnO) is a direct transition type semiconductor having a band gap energy of 3.37 eV at room temperature, and the exciton binding energy is 60 meV, which is relatively large compared to other semiconductors. In addition, since the raw materials are inexpensive and harmless to the environment and the human body, it is expected to realize a light-emitting element with high efficiency, low power consumption, and excellent environmental characteristics.

  A light emitting device such as an LED requires a p-type layer and an n-type layer. As a dopant for producing an n-type with a ZnO-based compound semiconductor, a group III atom or an O site that substitutes a Zn site is used. VII atoms are considered, and many n-type conductivity controls using group III atoms such as Ga and Al have been reported.

For example, Patent Document 1 proposes a method for producing a ZnO-based transparent conductive film ZnO: Al, ZnO: Ga doped with a group III atom. Further, according to Non-Patent Document 1, it is reported that Ga concentration and carrier concentration in a single crystal ZnO film are sufficiently controllable in the range of 10 ¹⁷ to 10 ²⁰ cm ⁻³ .

  By the way, when manufacturing light emitting elements, such as LED, if a dopant diffuses into other than a desired layer, element characteristics will fall remarkably. In the case of a GaAs-based semiconductor light emitting device, diffusion of a p-type dopant into the active layer is a problem. For example, an n-type diffusion stopper layer is provided between the p-type cladding layer and the active layer. A method of suppressing the diffusion of the p-type dopant by providing it is disclosed (for example, see Patent Document 2). Patent Document 3 discloses a method of suppressing the diffusion of a p-type dopant by forming the p-type layer from at least two layers doped with different dopants.

  Thus, in the case of a GaAs-based semiconductor light emitting device, several methods for preventing dopant diffusion are shown.

  On the other hand, with respect to ZnO-based compound semiconductors, there are almost no reports on dopant diffusion, and the present inventor has found that Ga, which is an n-type dopant, diffuses in a semiconductor element.

  FIG. 13 is a cross-sectional view showing an example of a ZnO-based LED element structure according to a conventional manufacturing method.

  A general LED includes an n-type semiconductor layer, an active layer, and a p-type semiconductor layer in an element. In this conventional technique, the n-type semiconductor layer of a ZnO-based LED is doped with Ga atoms as a dopant.

  The inventors actually manufactured a ZnO-based LED element shown in FIG. 13 as Comparative Example 1 using a conventional manufacturing method.

  First, an undoped ZnO buffer layer (buffer layer) 2 was formed on the cleaned n-type + c ZnO substrate 1. The buffer layer 2 was grown to a thickness of about 30 nm at 300 ° C. Next, annealing was performed to improve the quality of the buffer layer (buffer layer) 2. The annealing temperature was 900 ° C. and the annealing time was 20 minutes.

Next, the n-type semiconductor layer 3 was formed on the surface of the buffer layer (buffer layer) 2. The n-type semiconductor layer is Ga-doped Mg _0.2 Zn _0.8 O, and the Ga concentration is about 2 × 10 ¹⁸ cm ⁻³ . The growth temperature was 900 ° C.

Thereafter, an undoped ZnO active layer 4 was formed on the surface of the n-type semiconductor layer 3. The growth temperature was 900 ° C. A p-type semiconductor layer (N-doped Mg _0.2 Zn _0.8 O) doped with nitrogen (N) was formed on the surface of the active layer 4. The growth temperature was 650 ° C.

  Subsequent to the layer formation (film formation) step, an electrode was produced. An n-type electrode (for example, a 300-500 nm aluminum layer on a 2-10 nm thick titanium layer) 8 is formed on the surface of the substrate 1, and a p-type translucent electrode (for example, thickness 0) is formed on the p-type semiconductor layer surface. A 5 to 5 nm nickel layer and a 1 to 20 nm thick gold layer formed on the surface thereof, and a bonding pad electrode (for example, a 100 nm thick nickel layer) on the p-type translucent electrode 6 , 1000 nm thick gold) 7. In the step of forming the electrode, for example, a lithography technique using a resist film or the like is used.

  Thereafter, an electrode alloying process is performed in an oxidizing gas atmosphere at 300 to 800 ° C., for example. The alloy processing time is, for example, about 30 seconds to 10 minutes. As described above, a ZnO-based compound semiconductor light emitting device (ZnO-based LED) was manufactured.

Japanese Patent No. 3040373 JP-A-9-260776 JP 2006-19695 A JP 2002-261321 A

Applied Physics Society 120th Crystal Engineering Subcommittee Meeting (2004) p. 27-34

  FIG. 14 is a graph showing the profile in the depth direction of the N concentration and the Ga concentration of a ZnO-based LED manufactured by the conventional method as shown in FIG. This figure is based on a SIMS (Secondary Ion-microprobe Mass Spectrometer) analysis.

  According to this, it can be seen that Ga which should have been doped only in the n-type semiconductor layer 3 has diffused to a part of the active layer 4 and the p-type semiconductor layer 5. In such a case, the crystal quality of the active layer 4 is lowered, and accordingly, defects acting as non-radiative recombination centers are introduced, leading to a reduction in luminous efficiency. In the p-type layer 5, n-type carriers are formed due to the introduction of defects accompanying the deterioration of the crystal quality and the incorporation of Ga, leading to a decrease in p-type carrier density and n-type formation, and high output and reliable semiconductor light emission. It adversely affects the formation of the device. The diffusion of Ga from the n-type layer seems to proceed simultaneously with the growth of the active layer 4 and the p-type layer 5 that maintain a high substrate temperature.

  FIG. 15 is a graph showing an example of current-voltage characteristics of the ZnO-based LED whose SIMS analysis results are shown in FIG.

  The vertical axis indicates the current of 2 mA / 1 memory, and the horizontal axis indicates the voltage of 2 V / 1 memory. When a pn junction is made of a ZnO-based material, the threshold voltage in the current-voltage characteristics should be about 3 V, but the ZnO-based LED in the above figure is about 1 V, which is It shows that the characteristic is a Schottky. This is considered to be because the element characteristics of the LED are remarkably deteriorated because the dopant Ga diffuses from the n-type semiconductor layer 3 to the p-type semiconductor layer 5. For this reason, no light emission is observed from the ZnO-based LED fabricated by the conventional method.

  Ga diffusion can be suppressed by setting the substrate temperature (growth temperature) at the time of forming the active layer and the p-type semiconductor layer on the n-type ZnO-based semiconductor layer to a low temperature, at least 500 ° C. or less. However, if the growth temperature is too low, the unevenness of the growth film surface becomes severe. In MBE growth, a three-dimensional growth film with severe irregularities is formed unless the distance (for example, Zn or O) supplied to the substrate surface at the time of growth by migration on the substrate surface is sufficient. Since the distance moved by this migration is short when the substrate temperature is low, three-dimensional growth occurs.

  Therefore, the substrate temperature at which Ga diffusion does not occur (about 500 ° C. or lower) is too low, and a three-dimensional growth film is formed. A three-dimensionally grown film with severe irregularities is not preferable because it has many dislocations and point defects, leading to a reduction in luminous efficiency and lifetime in the light emitting element.

  For example, Patent Document 4 is a light-emitting element made of a GaAs-based compound semiconductor in which an n-cladding layer, an active layer, and a p-type cladding layer are sequentially stacked, and a GaAs-based compound semiconductor between the p-type cladding layer and the active layer. And a diffusion suppressing layer containing carbon atoms. This suppresses the diffusion of Zn, Mg, Cd, Be, etc. used as dopants in the p-type cladding layer into the active layer.

  Although the installation of such a diffusion suppression layer or diffusion prevention layer is effective for element diffusion, an extra layer is provided as an additional layer for the original device configuration. In order to obtain a desired luminance, it is necessary to apply a high voltage.

  An object of the present invention is to prevent the crystal quality of the active layer of the ZnO-based compound semiconductor element from being deteriorated by the diffusion of the n-type dopant.

  Another object of the present invention is to prevent the conductivity of the p-type semiconductor layer of the ZnO-based compound semiconductor element from being deteriorated by the diffusion of the n-type dopant.

According to one aspect of the present invention, a ZnO-based compound semiconductor element includes an n-type semiconductor layer doped with nitrogen (N) together with a group III element, and a p-type semiconductor layer formed above the n-type semiconductor layer. , look including the formed active layer between the p-type semiconductor layer and the n-type semiconductor layer, the concentration of nitrogen (n) doped into the n-type semiconductor layer, or the concentration of the group III element It is 3 × 10 ²⁰ cm ⁻³ or less .

  According to the present invention, the crystal quality of the active layer of the ZnO-based compound semiconductor element can be prevented from being deteriorated by the diffusion of the n-type dopant.

  Moreover, according to this invention, it can prevent that the conductivity of the p-type semiconductor layer of a ZnO type compound semiconductor element deteriorates by the diffusion of an n-type dopant.

It is the schematic of the manufacturing apparatus of a ZnO type compound semiconductor. 1 is a schematic cross-sectional view for explaining an element structure and a manufacturing method of a ZnO-based light emitting diode according to a first embodiment of the present invention. It is a graph which shows the current-voltage characteristic of a general LED element. It is a graph which shows the current-voltage characteristic of the light emitting diode produced in the 1st Example. It is a graph which shows the emission spectrum of the light emitting diode produced in the 1st Example. It is a schematic sectional drawing for demonstrating the element structure and preparation method of the sample of the n-type ZnO type compound semiconductor layer by the 2nd Example of this invention. It is a graph which shows the analysis result by SIMS regarding the sample of the n-type ZnO type compound semiconductor layer of the 2nd example and comparative example 2. It is a schematic sectional drawing for demonstrating the element structure and preparation method of the sample of the n-type ZnO type compound semiconductor layer by the 3rd Example of this invention. It is a graph which shows the analysis result by SIMS regarding the sample of the n-type ZnO type compound semiconductor layer of the 3rd example and comparative example 3. It is a photograph showing the observation result by AFM (atomic force microscope) of the N dope ZnO layer grown at the substrate temperature of 700 ° C. on the ZnO substrate and the Ga · N compound dope ZnO layer grown at the substrate temperature of 900 ° C. FIG. It is a schematic sectional drawing which shows an example of the light-emitting device structure formed on an insulating substrate. It is a schematic sectional drawing which shows an example of the semiconductor light-emitting device which has the n-type semiconductor layer which maintained desired impurity concentration distribution by N compound doping by the Example of this invention. It is sectional drawing which shows an example of the ZnO type LED element structure by the conventional preparation methods. It is a graph which shows the profile of the depth direction of N density | concentration and Ga density | concentration of ZnO type LED produced by the conventional method like FIG. It is a graph which shows an example of the current-voltage characteristic of ZnO type LED which showed the SIMS analysis result in FIG.

  FIG. 1 is a schematic view of a ZnO-based compound semiconductor manufacturing apparatus.

  Hereinafter, a ZnO-based compound semiconductor using ZnO and MgZnO will be described.

  As a method of manufacturing a ZnO-based compound semiconductor, for example, an oxygen radical beam radicalized in an electrodeless discharge tube using a high frequency of 13.56 MHz and a zinc beam from a Knudsen cell (K cell) are grown up to a growth temperature. There is a molecular beam epitaxy (MBE) method in which a substrate whose temperature is increased is simultaneously irradiated and ZnO is grown on the substrate.

  For example, a ZnO substrate is used as the substrate. As a method for epitaxially growing a ZnO-based compound semiconductor layer on a ZnO substrate, a ZnO buffer layer is formed on a ZnO substrate at a low temperature, and then annealed at a high temperature, and then a ZnO layer is grown at a predetermined temperature. There is a method of growing a ZnO layer directly on a substrate without a buffer layer. The growth temperature (substrate temperature during growth) of the ZnO-based compound semiconductor layer is preferably high from the viewpoint of improving crystallinity, and is preferably at least 500 ° C. or higher, preferably 700 ° C. or higher. When the substrate temperature is less than 500 ° C., the flatness and crystallinity are remarkably deteriorated.

  A substrate heater 16 is disposed in the ultra-high vacuum container 11, and the substrate 17 is held by the substrate heater 16. The ultra-high vacuum container 11 includes a zinc (Zn) source gun 14, an oxygen (O) radical source gun 15, a magnesium (Mg) source gun 18, a nitrogen (N) radical source gun 19, and a gallium (Ga) source gun 20. Is provided. The zinc source gun 14, the magnesium source gun 18, and the gallium source gun 20 each include a Knudsen cell that contains solid sources of Zn, Mg, and Ga, and emit a zinc beam, a magnesium beam, and a gallium beam, respectively. .

  The oxygen radical source gun 15 and the nitrogen radical source gun 19 each include an electrodeless discharge tube that uses a high frequency (for example, 13.56 MHz). The oxygen radical source gun 15 and the nitrogen radical source gun 19 radicalize oxygen gas and nitrogen gas in an electrodeless discharger, respectively, and emit an oxygen radical beam and a nitrogen radical beam. By supplying a desired beam at a desired timing on the substrate 17, a ZnO-based compound semiconductor layer having a desired composition can be grown.

The magnesium source gun 18, the nitrogen radical source gun 19, and the gallium source gun 20 are provided as necessary when manufacturing a light emitting diode (LED), for example. Further, instead of the nitrogen radical source gun 19, an NH ₃ source gun or the like may be used, and the substrate surface may be irradiated with the NH ₃ gas as it is.

  The ultra-high vacuum vessel 11 is also provided with a reflection high-energy electron diffraction (RHEED) gun 12 and a screen 13 for displaying a RHEED diffraction image. From the RHEED diffraction image, the crystallinity of the ZnO-based compound semiconductor layer formed on the substrate 17 can be evaluated. When the ZnO-based compound semiconductor layer is a single crystal having a flat surface (two-dimensionally grown), the RHEED diffraction image shows a streak pattern, and is a single crystal having a non-flat surface (three-dimensionally grown) Shows a spot pattern in the RHEED diffraction image. When the ZnO-based compound semiconductor layer is polycrystalline, the RHEED diffraction image shows a ring pattern.

An exhaust pump exhausts the inside of the ultra-high vacuum container. In the present specification, the ultra-high vacuum means that the degree of vacuum is 1 × 10 ⁻⁷ Torr or less.

  When growing an n-type layer in a ZnO-based compound semiconductor device, a radicalized oxygen radical beam, a zinc beam from a K cell, and a gallium beam are simultaneously irradiated onto the substrate 1 that has been heated to the growth temperature. .

  In addition, when a hole carrier injection layer (p-type layer) is grown in manufacturing a ZnO-based compound semiconductor light emitting device, for example, a nitrogen radical beam gun 19 obtained by radicalizing nitrogen gas is used to form a cladding layer. For example, a desired layer is laminated with a desired composition using, for example, a magnesium gun 18 that emits a magnesium (Mg) beam.

As a substrate used for manufacturing a ZnO-based compound semiconductor, a zinc oxide substrate (ZnO), a sapphire substrate (Al ₂ O ₃ ), a silicon carbide substrate (SiC), a gallium nitride substrate (GaN), a hexagonal Mg _x Zn ₁ There are a −xO substrate (0 <x ≦ 0.5), a cubic Mg _x Zn ₁ -xO substrate (0.5 <x ≦ 1), a Si substrate, and the like. In order to obtain a zinc oxide (ZnO) layer having good crystallinity, a substrate having a smaller lattice mismatch is better, and a zinc oxide (ZnO) substrate is particularly preferable. In the case of manufacturing a light-emitting element, Mg _x Zn ₁ − having a larger band gap than ZnO so that the substrate does not absorb the emitted light from the active layer and the extraction efficiency of the emitted light from the element is not lowered. It is also preferable to use an xO substrate (0 <x ≦ 1).

  As the substrate, various surfaces such as a + c plane, a −c plane, an a plane, and an m plane can be used, and a ZnO-based compound semiconductor layer can be grown thereon. Furthermore, for example, for the + c plane substrate, various substrates having an off angle in the m direction or the a direction can be used. Alternatively, a template in which an MgZnO, ZnO, or GaN film of 1 μm or more is formed on the substrate may be used.

  Next, the definition of the flux amount of zinc (Zn) and oxygen (O) will be described. In the embodiment of the present invention, the Zn beam flux amount is defined as Kzn · Jzn, and the O radical beam flux amount is defined as Ko · Jo.

  The Zn flux strength is Jzn, and the O radical flux strength is Jo. In addition, a coefficient indicating the ease of Zn deposition on the O termination surface of the ZnO crystal (Zn deposition coefficient) is Kzn, and a coefficient indicating the ease of O deposition on the Zn termination surface (O adhesion coefficient). ) Is Ko. At this time, Kzn · Jzn, which is the product of the Zn adhesion coefficient Kzn and the flux strength Jzn, corresponds to the number of Zn atoms deposited per unit time on the unit area of the substrate. In addition, Ko · Jo, which is the product of the adhesion coefficient Ko of O and the flux strength Jo, corresponds to the number of O atoms deposited per unit area of the substrate. Here, Ko · Jo / Kzn · Jzn, which is the ratio of the product Ko · Jo to the product Kzn · Jzn, is defined as the flux ratio. When the flux ratio is greater than 1, it is called the O-rich condition, and the flux ratio is less than 1. The case is called Zn rich condition.

  In “J. Crystal Growth 265 (2004) p375-381”, it is described that ZnO grows two-dimensionally and an epitaxial film can be obtained when the flux ratio is extremely 5.6 and an O-rich condition.

Further, the growth rate G of the ZnO growth film can be obtained by the following (Equation 1).
G = [(Kzn · Jzn) ^-1 + (Ko · Jo) ^-1 ] ^-1 -RZnO (Formula 1)
Here, RZnO is a term for re-evaporation of ZnO and can be almost ignored when the substrate temperature is 800 ° C. or lower. However, when it exceeds 900 ° C., RDZnO is on the order of several tens of nm / hr, which affects the growth rate.

Regarding Kzn · Jzn, the Zn adhesion coefficient Kzn is 1, and the value obtained using a film thickness monitor or the like can be applied to Jzn. As for Ko · Jo, a growth rate G is obtained by actually growing a ZnO film under the conditions known by Kzn · Jzn and a substrate temperature of 800 ° C. or less where RNZnO can be ignored. By substituting the obtained growth rate G and Kzn · Jzn into the above equation, it is possible to derive Ko · Jo under the set O radical gun conditions (O ₂ flow rate, RF power, etc.).

  The inventors actually fabricated a ZnO-based light emitting diode according to the first embodiment of the present invention, measured the current-voltage characteristics, and confirmed the light emission state. Moreover, the depth direction analysis regarding Ga density | concentration and N density | concentration by SIMS was performed. Hereinafter, a ZnO-based light emitting diode (ZnO-based LED) according to the first embodiment of the present invention will be described.

  FIG. 2 is a schematic cross-sectional view for explaining an element structure and a manufacturing method of a ZnO-based light emitting diode according to the first embodiment of the present invention.

  The device structure and the ZnO-based compound semiconductor film according to the embodiment of the present invention are produced by, for example, the molecular beam epitaxy (MBE) method shown in FIG. In addition to the MBE method, for example, a known epitaxial growth method such as PLD (Pulsed Laser Deposition) or MOVPE (Metal Organic Vapor Phase Epitaxy) can also be used.

First, the ZnO substrate 1 was subjected to thermal annealing to clean the substrate surface. Thermal annealing was performed at 900 ° C. for 30 minutes under a high vacuum of 1 × 10 ⁻⁹ Torr.

  Subsequently, the ZnO buffer layer 2 was produced by irradiating the ZnO substrate 1 with a Zn beam and an O radical beam at a substrate temperature of 350 ° C. Subsequently, in order to improve the crystallinity of the buffer layer 2, the substrate temperature was raised to 800 ° C., and annealing was performed for 20 minutes. The thickness of the buffer layer 2 was about 10 nm.

Next, a Ga · N composite doped n-type ZnO layer 31 was further grown on the ZnO buffer layer 2. The substrate 1 was irradiated with a Zn beam, an O radical beam, a Ga beam, and an N radical beam simultaneously at a substrate temperature of 900 ° C. In the irradiation of the Zn beam, Zn having a purity of 7N was used as a solid source, and the Zn beam flux intensity (Jzn) was set to 2 × 10 ¹⁵ atoms / (cm ² s). Irradiation with the O radical beam was performed by introducing a pure oxygen gas with a purity of 6 N into an electrodeless discharge tube at 2 sccm and plasmatizing with a high frequency power of 300 W. The amount of O radical (KoJo) is controlled to 1 × 10 ¹⁵ atoms / (cm ² s) based on the oxygen flow rate and the high frequency power. In addition, Ga beam irradiation uses 7N purity Ga as a solid source. The Ga beam flux intensity was controlled by the heating temperature of the Knudsen cell, and the temperature was 450 ° C. The N radical beam was irradiated by introducing a pure nitrogen gas having a purity of 7N into an electrodeless discharge tube at 0.5 sccm and converting it to plasma with a high frequency power of 90 W. The Ga concentration in the grown film is 3 × 10 ¹⁷ cm ⁻³ or more, and the nitrogen (N) concentration is 1 × 10 ²⁰ cm ⁻³ or more. The film thickness of the Ga · N composite doped n-type ZnO layer 31 was 100 nm.

Subsequently, a Ga · N composite doped n-type Mg _x Zn _1-x O (x = 0.25) layer (n-type cladding layer) 32 was grown on the Ga · N composite doped n-type ZnO layer 31. The substrate was irradiated with a Zn beam, Mg beam, O radical beam, Ga beam and N radical beam simultaneously at a substrate temperature of 900 ° C. In the irradiation of the Zn beam, 7N purity Zn was used as a solid source, and the flux intensity was set to 2 × 10 ¹⁵ atoms / (cm ² s). For the Mg beam irradiation, 6N purity Mg was used as the solid source, and the flux intensity was 1.7 × 10 ¹⁴ atoms / (cm ² s). The O radical beam was irradiated by introducing a pure oxygen gas having a purity of 6N into an electrodeless discharge tube at 2 sccm and converting it to plasma with a high frequency power of 300 W. This condition corresponds to 1 × 10 ¹⁵ atoms / (cm ² s) as the amount of O radical beam.

The Ga beam flux intensity was controlled by the heating temperature of the Knudsen cell, and the temperature was 450 ° C. The N radical beam was irradiated by introducing a pure nitrogen gas having a purity of 7N into an electrodeless discharge tube at 0.5 sccm and converting it to plasma with a high frequency power of 90 W. The Ga concentration in the grown film is 3 × 10 ¹⁷ cm ⁻³ or more, and the nitrogen (N) concentration is 1 × 10 ²⁰ cm ⁻³ or more. The Ga · N composite doped Mg _x Zn _1-x O (x = 0.25) layer 32 had a thickness of 30 nm.

In the first embodiment, the Ga · N composite doped n-type ZnO layer 31 and the Ga · N composite doped Mg _x Zn _1-x O (x = 0.25) layer 32 are combined to form the n-type layer 3. Call.

Next, the ZnO active layer 4 was grown on the Ga · N composite-doped n-type Mg _x Zn _1-x O (x = 0.25) layer 32. The growth of the ZnO active layer 4 was performed by irradiating the substrate with a Zn beam and an O radical beam at a substrate temperature of 900 ° C. In the irradiation of the Zn beam, the flux intensity was set to 1.6 × 10 ¹⁴ atoms / (cm ² s). Irradiation with the O radical beam was performed by introducing a pure oxygen gas having a purity of 6N into an electrodeless discharge tube at 3 sccm and converting it to plasma with a high frequency power of 300 W. This condition corresponds to 1.2 × 10 ¹⁵ atoms / (cm ² s) as the amount of O radical beam. The thickness of the ZnO active layer 4 was 10 nm.

The active layer 4 has, for example, a DH structure or an MQW structure. In the case of a DH structure, an undoped or appropriate conductivity ZnO layer is formed as the active layer 4. In the case of the MQW structure, the active layer 4 has, for example, a thin-film (MgZnO / ZnO) _n / MgZnO stacked structure. In this case, the ZnO layer or the like constitutes a well, and the MgZnO layer constitutes a barrier.

Next, a p-type Mg _x Zn _1-x O (x = 0.25) layer (p-type MgZnO layer) 5 doped with nitrogen (N) was grown on the ZnO active layer 4. The growth of the p-type MgZnO layer 5 was performed by irradiating the substrate with a Zn beam, Mg beam, O radical beam and N radical beam at a substrate temperature of 700 ° C. In the irradiation of the Zn beam, Zn having a purity of 7N was used as a solid source, and the flux amount was set to 2 × 10 ¹⁵ atoms / (cm ² s).

The Mg beam was irradiated with Mg having a purity of 7N as a solid source and a flux amount of 1.7 × 10 ¹⁴ atoms / (cm ² s). The O radical beam was irradiated by introducing a pure oxygen gas having a purity of 6N into an electrodeless discharge tube at 2 sccm and converting it to plasma with a high frequency power of 300 W. This condition corresponds to 1 × 10 ¹⁵ atoms / (cm ² s) as the amount of O radical beam. The N radical beam was irradiated by introducing a pure nitrogen gas having a purity of 7N into an electrodeless discharge tube at 0.5 sccm and converting it to plasma with a high frequency power of 90 W. The thickness of the p-type Mg _x Zn _1-x O (x = 0.25) layer 5 was 30 nm. The nitrogen (N) concentration in the film grown as described above is 1 × 10 ²⁰ cm ⁻³ or more.

  In addition, the p-type semiconductor layer 5 can also use P and As which are V group elements as a p-type dopant instead of nitrogen (N). In addition, a group I element such as Li, Na, Cu, or Ag can be used as the p-type dopant instead of the group V element. Further, a combination of these may be used to simultaneously dope two or more elements such as N and P.

The N element substitutes a part of the O site of ZnO to become an acceptor. Among various group V elements, N has an ionic radius close to that of O and can be stably substituted. As a source used for doping N, various sources such as N ₂ , N ₂ O, NO, N ₂ + O ₂ , and NH ₃ may be used as long as they contain N element.

The concentration (hole carrier density) of active nitrogen (N) in the p-type semiconductor layer 5 is required to be 1 × 10 ¹⁶ cm ⁻³ or more when a light emitting device such as an LED is manufactured. ZnO and N element doped as an acceptor in ZnMgO have a low activation rate, and effective hole carriers cannot be obtained unless N of 1 × 10 ¹⁸ cm ⁻³ or more is doped.

In addition, if the concentration of N is more than 5 × 10 ²⁰ cm ⁻³ , many defects are generated in the p-type ZnMgO layer and the p-type ZnO film, causing a leak when a current is passed through the device. It may become. Therefore, the concentration of N is preferably in the range of 1 × 10 ¹⁸ cm ^{−3 to} 5 × 10 ²⁰ cm ⁻³ . More preferably, in the range of ^{1 × 10 19 cm -3 ~3 ×} 10 20 cm -3.

  Next, an n-type electrode (500 nm aluminum layer on a 10 nm thick titanium layer) 8 is formed on the n-ZnO substrate 1, and a p-type transparent electrode (1 nm thick nickel layer) is formed on the surface of the p-ZnO layer. Then, a bonding electrode (gold having a thickness of 500 nm) 7 is formed on the p-type electrode 6 and a gold layer having a thickness of 10 nm formed on the surface thereof. Thereafter, an electrode alloying process is performed in an oxygen atmosphere at 400 ° C., for example. The alloy processing time is 2 minutes. Thus, a ZnO-based light emitting diode according to the first example was manufactured.

  FIG. 3 is a graph showing current-voltage characteristics of a general LED element.

  In general, regarding the current-voltage characteristics of LED elements, the characteristics shown in FIG. 3 can be considered. The characteristic indicated by the solid line in FIG. 3 is an ideal diode characteristic, and there is no leakage current in both the forward bias characteristic and the reverse bias characteristic, and the threshold voltage is at least 3 V or more. The characteristic indicated by the broken line has a low withstand voltage in the reverse bias characteristic, and in the forward bias characteristic, a minute current starts to flow from a voltage lower than the threshold voltage, and can be said to have a leak current.

  FIG. 4 is a graph showing current-voltage characteristics of the light-emitting diode fabricated in the first example.

  As shown in FIG. 15, the conventional light emitting diode (Comparative Example 1) exhibits Schottky characteristics and has a low withstand voltage when a reverse voltage is applied. However, as shown in FIG. 4, in this sample (first embodiment), the threshold voltage is 3 V or more, there is no leakage current, and good diode characteristics with high withstand voltage when applying reverse voltage are obtained. ing.

  FIG. 5 is a graph showing an emission spectrum of the light emitting diode produced in the first example.

  Regarding the light emission characteristics, light emission at 380 nm was obtained unlike the conventional light emitting diode (Comparative Example 1) shown in FIG. This is considered to be due to the fact that Ga is doped with N in the Ga doped layer to suppress the diffusion of Ga. By suppressing the diffusion of Ga, the crystallinity deterioration of the active layer and the p-type layer is suppressed, the generation of defects serving as non-emission centers in the active layer is suppressed, and the generation of n-type carriers accompanying the formation of defects in the p-type layer. It is thought that it had the effect of suppressing.

  In the first embodiment, both the n-type layer (n-ZnO layer 31 and n-MgZnO layer 32) 3 and the p-type layer (p-MgZnO layer) 5 are doped with nitrogen (N). The influence on the conductivity of N is different.

  In the p-type layer 5, N atoms substitute a part of the O site to become acceptors, and give p-type conductivity to MgZnO. However, the growth temperature when doping N must be 300 ° C. ≦ Tg <800 ° C., preferably 500 ° C. ≦ Tg ≦ 700 ° C. If the growth temperature is too higher than this temperature, the doped N will not replace the O site and p conductivity will not be imparted. On the other hand, if the growth temperature is too low, the growth film grows three-dimensionally and becomes a film with severe irregularities. In the three-dimensional growth film, donor-type defects such as dislocations and point defects are formed, and thus p-type conductivity is not exhibited.

On the other hand, the growth of the n-type layer 3 needs to be 800 ° C. <Tg ≦ 1100 ° C., and preferably 900 ° C. ≦ Tg ≦ 1100 ° C. Since N doped at a growth temperature higher than 800 ° C. takes the form of N ₂ molecules in the film, it is considered that no acceptor is generated, and the film does not exhibit p-type conductivity.

  Next, as a second embodiment (embodiment 2), a buffer layer 2 is grown on a ZnO substrate 1, a Ga · N composite doped n-type ZnO layer 31 is grown by 200 nm thereon, and further undoped thereon. A ZnO layer 33 was grown to 200 nm. As Comparative Example 2, a Ga-doped n-type ZnO layer grown to 200 nm instead of the Ga · N composite-doped n-type ZnO layer 31 was produced. In this structure, the presence or absence of diffusion of gallium (Ga) from the Ga · N composite-doped n-type ZnO layer 31 or the Ga-doped n-type ZnO layer 33 to the undoped ZnO layer 33 by performing a depth direction analysis on the Ga concentration by SIMS It was confirmed.

  FIG. 6 is a schematic cross-sectional view for explaining an element structure and a manufacturing method of a sample of an n-type ZnO-based compound semiconductor layer according to a second embodiment of the present invention.

  Similar to the first embodiment, it is fabricated by a molecular beam epitaxy (MBE) method. First, as in the first example, the surface of the ZnO substrate 1 was washed to produce a ZnO buffer layer 2.

Next, a Ga · N composite doped n-type ZnO layer 31 was grown on the ZnO buffer layer 2. The substrate 1 was irradiated with a Zn beam, an O radical beam, a Ga beam, and an N radical beam simultaneously at a substrate temperature of 900 ° C. In the irradiation of the Zn beam, Zn having a purity of 7N was used as a solid source, and the Zn beam flux intensity (Jzn) was set to 2 × 10 ¹⁵ atoms / (cm ² s). Irradiation with the O radical beam was performed by introducing a pure oxygen gas with a purity of 6 N into an electrodeless discharge tube at 2 sccm and plasmatizing with a high frequency power of 300 W. The amount of O radical (KoJo) is controlled to 1 × 10 ¹⁵ atoms / (cm ² s) based on the oxygen flow rate and the high frequency power. In addition, Ga beam irradiation uses 7N purity Ga as a solid source. The Ga beam flux intensity was controlled by the heating temperature of the Knudsen cell, and the temperature was 450 ° C. The N radical beam was irradiated by introducing a pure nitrogen gas having a purity of 7N into an electrodeless discharge tube at 0.5 sccm and converting it to plasma with a high frequency power of 90 W. The Ga concentration in the grown film is 3 × 10 ¹⁷ cm ⁻³ or more, and the nitrogen (N) concentration is 1 × 10 ²⁰ cm ⁻³ or more. The film thickness of the Ga · N composite doped n-type ZnO layer 31 was 200 nm.

  Subsequently, an undoped ZnO layer 33 was grown on the Ga · N composite-doped n-type ZnO layer 31 at a substrate temperature of 900 ° C. The growth was performed under the same conditions as the Ga · N composite-doped n-type ZnO layer 31 except that the irradiation of the Ga beam and the N radical beam was stopped. The film thickness was 200 nm.

  As indicated by the dotted line in the figure, the active layer 4 and the p-type layer 5 are stacked and the p-type transparent electrode 6, the bonding electrode 7 and the n-type electrode 8 are produced as in the first embodiment. A ZnO-based light emitting diode according to Example 2 can be manufactured.

  In Comparative Example 2, the Ga · N composite doped n-type ZnO layer 31 in the second embodiment is replaced with a Ga-doped n-type ZnO layer. The growth was performed under the same conditions as the Ga · N composite-doped n-type ZnO layer 31 except that the irradiation of the N radical beam was stopped. The film thickness was also 200 nm.

  FIG. 7 is a graph showing the analysis results by SIMS regarding the samples of the n-type ZnO-based compound semiconductor layers of the second example and the comparative example 2.

  In the sample produced in Comparative Example 2, the diffusion of Ga was confirmed from the Ga-doped n-type ZnO layer to the upper undoped ZnO layer. On the other hand, in the sample of Example 2 in which N was combined with the Ga-doped n-type ZnO layer, almost no Ga diffusion into the undoped ZnO layer 33 was observed, and the Ga diffusion was N-doped ( It is suggested that it can be suppressed by the Ga · N composite doped n-type ZnO layer 31). This is presumably because a bond occurs between Ga and N, and the Ga element is fixed.

In the sample grown up to the Ga-doped n-type ZnO layer in Comparative Example 2, the Ga concentration is 3 × 10 ¹⁷ (cm ⁻³ ), whereas the n-type carrier density is also approximately 3 × 10 ¹⁷ (cm ^-3 ). That is, the activation rate of Ga in the Ga-doped n-type ZnO layer was approximately 1.

In contrast, the Ga concentration in the sample according to the second example grown up to the Ga · N composite-doped ZnO layer 31 is 6 × 10 ¹⁷ (cm ⁻³ ), whereas the n-type carrier density is 5 It was 5 × 10 ¹⁷ (cm ⁻³ ). Therefore, also in the Ga-doped n-type ZnO layer 31 in which N is complex-doped, the activation rate of Ga is 0.9 or more, and it seems that the influence of the N doping on the Ga activation rate is very small.

  Next, as Comparative Example 3, a buffer layer 2 is grown on a ZnO substrate 1, a Ga highly doped n-type ZnO layer is grown on it by 180 nm, and a Ga lightly doped n type ZnO layer is grown by 120 nm thereon. Further, a Ga highly doped n-type ZnO layer was grown to 120 nm thereon, and a Ga lightly doped n-type ZnO layer was grown to 80 nm thereon to prepare a sample of an n-type ZnO-based compound semiconductor layer. In this structure, the presence or absence of diffusion of Ga from the Ga heavily doped n-type ZnO layer to the Ga lightly doped n-type ZnO layer was confirmed.

  FIG. 8 is a schematic cross-sectional view for explaining an element structure and a manufacturing method of a sample of an n-type ZnO-based compound semiconductor layer according to the third embodiment of the present invention.

  As a sample of the n-type ZnO-based compound semiconductor layer of the third example (Example 3), a sample in which N was compositely doped into the entire Ga-doped n-type ZnO layer in Comparative Example 3 was produced. In this structure, the presence or absence of diffusion of Ga from the Ga heavily doped n-type ZnO layer to the Ga lightly doped n-type ZnO layer was confirmed.

  Similar to the first and second embodiments, it is fabricated by molecular beam epitaxy (MBE). First, as in the first example, the surface of the ZnO substrate 1 was washed to produce a ZnO buffer layer 2.

  Next, a Ga high-concentration / N composite-doped n-type ZnO layer 35 was grown on the ZnO buffer layer 2. At a substrate temperature of 900 ° C., a Zn beam, O radical beam, Ga beam, and N radical beam were simultaneously irradiated onto the substrate.

In the irradiation of the Zn beam, Zn having a purity of 7N was used as a solid source, and the Zn beam flux intensity (Jzn) was set to 2 × 10 ¹⁵ atoms / (cm ² s). Irradiation with the O radical beam was performed by introducing a pure oxygen gas with a purity of 6 N into an electrodeless discharge tube at 2 sccm and plasmatizing with a high frequency power of 300 W. The amount of O radical (KoJo) is controlled to 1 × 10 ¹⁵ atoms / (cm ² s) based on the oxygen flow rate and the high frequency power.

In addition, Ga beam irradiation uses 7N purity Ga as a solid source. The Ga beam flux intensity was controlled by the heating temperature of the Knudsen cell, and the temperature was 470 ° C. The Ga concentration in the film grown as described above should be about 3 × 10 ¹⁸ cm ⁻³ . The film thickness was 180 nm.

The N radical beam was irradiated by introducing a pure nitrogen gas having a purity of 7N into an electrodeless discharge tube at 0.5 sccm and converting it to plasma with a high frequency power of 90 W. The Ga concentration in the grown film is 3 × 10 ¹⁷ cm ⁻³ or more, and the nitrogen (N) concentration is 1 × 10 ²⁰ cm ⁻³ or more.

Next, a Ga low concentration / N composite doped n-type ZnO layer 36 was grown on the Ga high concentration / N composite doped n type ZnO layer 35. The growth conditions were the same as those of the Ga high-concentration / N composite-doped n-type ZnO layer 35 except that the Ga Knudsen cell temperature was 450 ° C. The Ga concentration in the film grown as described above should be about 3 × 10 ¹⁷ cm ⁻³ . The film thickness was 120 nm.

  Next, a Ga high concentration / N composite doped n-type ZnO layer 37 was grown on the Ga low concentration / N composite doped n type ZnO layer 36. The growth conditions were the same as the Ga high concentration / N composite doped n-type ZnO layer 35, and the film thickness was 120 nm.

  Next, a Ga low concentration / N composite doped n-type ZnO layer 38 was further grown on the Ga high concentration / N composite doped n type ZnO layer 37. The growth conditions were the same as the Ga low concentration / N composite doped n-type ZnO layer 36, and the film thickness was 80 nm.

  As indicated by the dotted line in the figure, the active layer 4 and the p-type layer 5 are stacked and the p-type transparent electrode 6, the bonding electrode 7 and the n-type electrode 8 are produced as in the first embodiment. A ZnO-based light emitting diode according to the third embodiment can be manufactured.

  In Comparative Example 3, the Ga · N composite doped n-type ZnO layers 35 to 38 in the third example are Ga-doped n-type ZnO layers. The growth was performed under the same conditions as the Ga · N composite-doped n-type ZnO layers 35 to 38 except that the irradiation of the N radical beam was stopped.

  The sample according to the third example and the sample according to Comparative Example 3 are analyzed in the depth direction with respect to the Ga concentration by SIMS, and Ga diffusion from the Ga highly doped n-type ZnO layer to the Ga lightly doped n-type ZnO layer is performed. confirmed.

  FIG. 9 is a graph showing the results of SIMS analysis of the samples of the third example and comparative example 3.

  The Ga concentration of the sample of Comparative Example 3 is indicated by a dotted line, and the Ga concentration of the sample of Example 3 is indicated by a thick line. Further, the N concentration of the sample of Example 3 is shown by a solid line. In the sample in which only Ga of Comparative Example 3 is doped and the Ga concentration is changed, it can be seen that Ga diffuses and the concentration distribution is averaged. On the other hand, the Ga concentration distribution is maintained without being averaged in the N-doped sample of Example 3. This is considered to be the effect of N complex doping.

  In the sample of the conventional semiconductor light emitting device shown in FIG. 13 (Comparative Example 1), Ga is slightly diffused in the p-type layer 5 despite being doped with N as shown in FIG. This is probably because the p-type layer 5 is grown at 700 ° C., so the crystal quality is slightly low, and Ga is diffused through defects formed during the growth. Therefore, in order not to diffuse Ga in the Ga · N composite doped ZnO-based semiconductor layer, it is also preferable that the layer itself is a film with few defects. Specifically, it is necessary to have few pits.

  FIGS. 10A and 10B show an AFM (atomic force microscope) of an N-doped ZnO layer grown on a ZnO substrate at a substrate temperature of 700 ° C. and a Ga · N composite-doped ZnO layer grown at a substrate temperature of 900 ° C. It is a photograph showing the observation result by. The upper row is a 15 μm square and the lower row is a 1 μm square. The N-doped ZnO layer was produced under the same conditions as the p-type MgZnO layer 5 in the sample according to the second example. The Ga · N composite doped ZnO layer was produced under the same conditions as the Ga · N composite doped MgZnO layer 32 in the sample of the second example.

FIG. 10A shows the observation result by AFM of an N-doped ZnO layer grown on a ZnO substrate at a substrate temperature of 700 ° C. It can be seen that there are innumerable fine pits (3 × 10 ⁷ / cm ² ). This is probably because the growth temperature is 700 ° C. In such a state, even if N is doped, there is a high possibility that Ga diffuses through the pits.

FIG. 10B shows an observation result by AFM of a Ga · N composite doped ZnO layer grown at a substrate temperature of 900 ° C. It can be seen that there are few pits (less than 4 × 10 ⁴ / cm ² ). Since the growth temperature is 900 ° C., Ga is fixed and diffusion is suppressed in such a Ga · N composite doped ZnO-based film.

  As described above, according to the embodiment of the present invention, when forming a Ga-doped n-type ZnO-based semiconductor layer, N is compound-doped with Ga so that other layers other than the Ga-doped n-type ZnO-based semiconductor layer can be formed. Ga diffusion is suppressed. As a result, the deterioration of the crystallinity of other layers due to the diffusion of Ga is suppressed.

  In addition, the generation of defects serving as non-luminescent centers can be suppressed in the active layer. Further, in the p-type layer, the generation of n-type carriers accompanying the formation of defects is suppressed.

  Further, in the light emitting element, the threshold voltage is at least equal to or higher than the band gap of ZnO (about 3.3 V), and the light emission efficiency is improved.

Furthermore, according to the embodiment of the present invention, the surface flatness in the Ga doped layer is improved. The n-type dopant in the n-type ZnO-based semiconductor layer constituting the ZnO-based semiconductor light emitting element, for example, Ga concentration is doped with about 1 × 10 ¹⁷ to 1 × 10 ¹⁹ cm ⁻³ . However, when the Ga concentration exceeds 1 × 10 ¹⁸ cm ⁻³ , the unevenness of the growth film surface becomes intense and three-dimensional growth occurs. When the n-type ZnO-based semiconductor layer grows three-dimensionally, the active layer or the p-type layer grown thereon further grows three-dimensionally. A three-dimensionally grown film with severe irregularities is not preferable because it has many dislocations and point defects, leading to a reduction in luminous efficiency and lifetime in the light emitting element. However, by doping N as a composite dopant into the Ga-doped n-type ZnO-based semiconductor layer, three-dimensional growth is suppressed, and an n-type ZnO-based semiconductor layer having excellent surface flatness can be obtained. This is thought to be the result of the surfactant effect associated with the incorporation of N into the film.

  One of the powerful research techniques for thin film growth in recent years is a surfactant-mediated epitaxy. This method is a technique for artificially changing the growth mode of a thin film by using a surfactant (atom or molecule) called a surfactant, and is a useful means for controlling epitaxial growth. For example, Japanese Patent Application Laid-Open No. 2004-221352 discloses a technique using hydrogen as a surfactant.

  Furthermore, according to the embodiment of the present invention, the Ga concentration distribution intentionally formed in the n-type ZnO semiconductor layer can be maintained without averaging due to diffusion by the N complex doping.

  For example, Japanese Patent No. 2663814 and Japanese Patent Application Laid-Open No. 2004-95649 provide an n-type semiconductor layer constituting a light-emitting diode having an intentional distribution such as a continuous or stepwise gradient in carrier concentration in the film thickness direction. Proposed in the Gazette. This indicates that the light emission luminance of the light emitting diode is greatly improved.

  In particular, Japanese Patent Application Laid-Open No. 2004-95649 discloses that the n-type carrier concentration in the n-type ZnO-based semiconductor layer constituting the ZnO-based semiconductor light-emitting element has a gradient. Specifically, it is disclosed that the active layer of the n-type ZnO-based semiconductor layer has a gradient such that the n-type carrier concentration decreases from the far side to the near side.

  As a result, even if the carrier concentration of the entire ZnO-based semiconductor layer is low, a sufficient current spread can be obtained, and the total doping amount can be kept low, so that a ZnO-based semiconductor layer with good crystallinity is formed without impairing crystallinity. it can. As a result, a light-emitting element with high emission efficiency and excellent reliability can be realized.

  This method of giving an n-type carrier concentration distribution in the n-type ZnO-based semiconductor layer can provide a unique effect even when a light-emitting device structure is formed on an insulating substrate (for example, on a sapphire substrate).

  FIG. 11 is a schematic cross-sectional view showing an example of a light-emitting device structure formed on an insulating substrate.

  In the case of forming a light emitting device structure on an insulating substrate 41 (for example, on a sapphire substrate), the n-type electrode 48 and the p-type electrode 46 must be formed on the same surface, and the current flows in a direction parallel to the semiconductor film surface. There is a part that flows.

  When such a structure is employed in a ZnO-based compound semiconductor device, the specific resistance of the n-type layer 43 is large, current spreading is insufficient, and the current mainly flows through the shortest distance to the active layer 44. Current concentrates on the edge of the mesa structure close to the mold electrode 48, causing a problem that light is emitted only at the outer periphery of the mesa.

  FIG. 12 is a schematic cross-sectional view showing an example of a semiconductor light emitting device having an n-type semiconductor layer that maintains a desired impurity concentration distribution by N complex doping according to an embodiment of the present invention.

  As shown in the figure, the n-type ZnO-based semiconductor layer 53 having a high carrier concentration is impaired as a portion that has a portion in contact with the n-type electrode 48 and a current flows in a direction perpendicular to the stacking direction of the semiconductor. By forming the n-type layer 63 with a low carrier concentration and a good crystal quality on the thin film as much as possible, a surface-emitting device free from current concentration can be obtained.

  In order to give a gradient to the n-type carrier concentration, it is necessary to give a gradient to the n-type impurity concentration of Ga, Al, In or the like. Specifically, there is a method of making the gradient of the n-type impurity concentration continuous. As a result, since there is no sharp change in crystal growth, the occurrence of cracks and other defects can be reduced, and a light emitting element with excellent light emission efficiency and reliability can be realized.

  On the other hand, as another method, there is a method in which a plurality of single layers having a constant n-type impurity concentration are stacked, and the impurity concentration of the single layer is decreased or increased for each adjacent layer to give a stepwise gradient. is there. As a result, even in manufacturing methods where it is difficult to continuously change the impurity concentration, such as laser ablation, the change in crystal growth conditions can be alleviated to some extent, the occurrence of cracks and other defects can be reduced, and light emission with excellent luminous efficiency and reliability is also achieved. An element can be realized.

The distribution of the n-type impurity amount in the n-type ZnO-based semiconductor layer is 1 × 10 ¹⁸ (cm ⁻³ ) to 1 × 10 ²⁰ (cm ⁻³ ) on the side farther from the active layer, and on the side closer to the active layer. It is about 1 × 10 ¹⁷ (cm ⁻³ ) to 1 × 10 ¹⁹ (cm ⁻³ ), preferably about 1 × 10 ¹⁹ (cm ⁻³ ) on the side farther from the active layer, and 1 × 10 ¹⁸ (cm on the near side. ⁻³ ) is desirable, and the impurity concentration decreases as it approaches the active layer.

  However, in actuality, only by growing while controlling the amount of n-type impurities, after growing other layers (for example, an active layer or a p-type ZnO-based semiconductor layer), the n-type in the n-type ZnO-based semiconductor layer is increased. Impurities are averaged by diffusion, and it is very difficult to maintain the intended dope concentration distribution (carrier concentration distribution).

  As a method for solving this problem, according to the embodiment of the present invention, by n-doping with N-type impurities such as Ga and the like, the diffusion of n-type impurities is suppressed, and the intended impurity concentration distribution is maintained. Type semiconductor layer can be obtained.

The Ga / N composite doped layer according to each embodiment of the present invention requires an N concentration at least equal to the Ga concentration. As the Ga concentration in the n-type layer, about 1 × 10 ¹⁷ to 1 × 10 ¹⁹ cm ⁻³ is doped. If it is lower than 1 × 10 ^{17, the} n-type carrier density is too low for the n-type layer of the semiconductor light emitting device. On the other hand, if it ^exceeds 1 × 10 ¹⁹ cm ⁻³ , the n-type layer grows three-dimensionally and the crystallinity is significantly lowered.

Accordingly, at least the same N concentration is necessary as the N concentration for complex doping, but even higher concentration may be used, and even if it is doped up to about 5 × 10 ²⁰ cm ^{−3, the} crystallinity deteriorates and the n-type carrier density is reduced. There is no influence. From the viewpoint of obtaining a film excellent in Ga diffusion suppression and surface flatness, about 3 × 10 ²⁰ cm ⁻³ is desirable. However, if the N concentration is higher than this, the crystallinity of the n-type layer is significantly lowered.

  In the first to third embodiments, Ga is cited as an element that diffuses from the n-type ZnO-based semiconductor layer to other layers. However, the present invention is not limited to this. Examples of group III elements used as n-type dopants in ZnO-based semiconductors include Al and In, and these are also known to diffuse in ZnO. The effect of suppressing diffusion due to is also seen for this Al and In.

As the Ga · N composite doped n-type ZnO-based semiconductor layer according to the first to third embodiments, in addition to ZnO, for example, [Mg _a Zn _1-a O, Cd _a Zn _1-a O, Be _{a Zn 1-a O, Ca a} Zn 1-a O ( both, 0 <a <1)] _{and, [ZnO 1-b S b} , ZnO 1-b Se b, ZnO 1-b Te b ( both 0 < Various ZnO-based mixed crystal layers such as b <1)] can be used. In this case, a Cd source gun, a Be source gun, a Ca source gun, an S source gun, a Se source gun, a Te source gun, and the like are appropriately added to the ZnO-based compound semiconductor manufacturing apparatus shown in FIG.

  In addition, the embodiment of the present invention includes a short wavelength (ultraviolet to blue wavelength) light emitting diode (LED) or a short wavelength laser diode (LD) and its application products such as indicators, It can be applied to an LED display or the like.

  Moreover, it is applicable also to white LED and its application products, for example, a lighting fixture, each indicator, a display, the backlight of each indicator. Also applicable to ZnO-based electrodes (for example, transparent conductive films) and their applied products, various electronic devices such as ZnO-based transistors and their applied products, ZnO-based sensors (for example, humidity sensors, ultraviolet sensors, etc.) and their applied products. It is.

  In addition to ZnO-based compound semiconductor light-emitting devices, various ZnO-based compound semiconductor devices that include ZnO-based semiconductor layers, such as transistors, transparent conductive films, piezoelectric elements, thermoelectric elements, and ultraviolet sensors, for example. And applicable products of the semiconductor element.

  In addition, the other layer in which the group III element such as Ga diffuses is not limited to the p-type semiconductor layer 5 and the active layer 4, and for example, the embodiment of the present invention is applied to a HEMT (high electron mobility transistor). In some cases, it may be an undoped ZnO layer.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

DESCRIPTION OF SYMBOLS 1 ZnO substrate 2 Buffer layer 3, 43, 53, 63 n-type semiconductor layer 4, 44 Active layer 5, 45 p-type semiconductor layer 6, 46 p-type translucent electrode 7 Bonding pad electrode 8, 48 n-type electrode 11 Ultra-high vacuum vessel 12 Reflection high-energy electron diffraction (RHEED) gun 13 Reflection high-energy electron diffraction (RHEED) screen 14 Zinc (Zn) source gun 15 Oxygen (O) radical source gun 16 Substrate heater 17 Substrate 18 Magnesium ( Mg) source gun 19 Nitrogen (N) radical source gun 20 Gallium (Ga) source gun 31 Ga · N composite doped n-type ZnO layer 32 Ga · N composite doped MgZnO layer 33 Undoped ZnO layer 35, 37 Ga high concentration · N Composite doped n-type ZnO layer 36, 38 Ga low concentration / N composite doped n-type ZnO layer 41 Insulating substrate

Claims (6)

An n-type semiconductor layer doped with nitrogen (N) together with a group III element;
A p-type semiconductor layer formed above the n-type semiconductor layer;
Look including the formed active layer between the p-type semiconductor layer and the n-type semiconductor layer,
A ZnO-based compound semiconductor device , wherein the concentration of nitrogen (N) doped in the n-type semiconductor layer is not less than the concentration of the group III element and not more than 3 × 10 ²⁰ cm ⁻³ . The n-type concentration of group III element is doped into the semiconductor layer, ZnO based compound semiconductor device according to claim 1 Symbol placement has a distribution in the film thickness direction. 3. The ZnO-based compound semiconductor device according to claim 2 , wherein the concentration of the group III element doped in the n-type semiconductor layer decreases as the active layer is approached. The concentration of the group III element doped in the n-type semiconductor layer is 1 × 10 ¹⁸ (cm ⁻³ ) to 1 × 10 ²⁰ (cm ⁻³ ) on the side farther from the active layer, which is close to the active layer. ^{1 × 10 17 (cm -3)} ~1 × 10 19 (cm -3) a ZnO based compound semiconductor device according to claim 3, wherein the side. The concentration of the group III element is doped to the n-type semiconductor layer, ZnO based compound semiconductor device according to any one of claims 2-4 having a continuous gradient. The concentration of the group III element is doped to the n-type semiconductor layer, ZnO based compound semiconductor device according to any one of claims 2-4 having a gradual slope.