JP2002016287A - Semiconductor element and optical semiconductor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the characteristics of an optical semiconductor element formed of GaAs semiconductor. SOLUTION: This optical semiconductor element includes an N-type GaAsP semiconductor layer 5, a P-type GaAsP semiconductor layer 5a, formed on the layer 5, a first electrode 21 formed to an N-type GaAs semiconductor substrate 1, a ZnO layer 15 (second electrode), which is formed to the P-type GaAsP semiconductor layer 5a and contains group III B, Al, Ga or In of 2-8 at% as dopant, and further an upper part electrode 17 formed in a part region on the layer 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for a GaAs compound semiconductor device having a pn junction, and more particularly to an optical semiconductor device having excellent optical and electrical characteristics.

[0002]

2. Description of the Related Art Various functional elements can be manufactured by forming a pn junction using a GaAs-based semiconductor material. For example, a light emitting diode (Light Emittin)
g Diode: LED) generally has a pn junction composed of an n-type GaAs-based semiconductor layer and a p-type GaAs-based semiconductor layer, and further has an electrical connection to each of the n-type and p-type semiconductor layers. A metal electrode for contacting the substrate is formed.

When a current is applied between the metal electrodes so as to be in a forward direction with respect to the pn junction, a light emission phenomenon caused by recombination of electrons and holes occurs in a region near the pn junction interface. Occurs. The generated light is, for example, on the p-type semiconductor surface side
(Optical surface) and used for various purposes.

In order to improve the luminous efficiency and luminous characteristics of the LED, the quality of the semiconductor crystal and the structure and shape of the p-type or n-type semiconductor layer are important. Similarly, the structure of a metal electrode for electrically contacting the p-type or n-type forming the optical surface is also extremely important.

The structure of a GaAs-based optical semiconductor device, for example, an LED, generally has at least two types of structures, a first structure and a second structure.

The LED having the first structure is mainly composed of pn
The junction has a homozygous structure and is manufactured as in the following steps.

For example, an n-type GaAs substrate is
After P is vapor-grown, an anti-diffusion film is formed by silicon nitride (SiN _x ). An opening is formed in a partial region of SiN _x .

[0008] By thermally diffusing Zn, a p-type GaAsP layer is formed in a part of the region through the opening. Since it is difficult to extract light from the n-type GaAs substrate side, generally, the surface of the p-type GaAsP layer is often used as an optical surface.

On the n-type GaAs substrate, a metal ohmic electrode made of, for example, AuSn, which is in electrical contact, is formed. The p-type side used as the optical surface is p-type GaAs
For example, Al electrically contacted only in a partial region of the P layer
And the like.

The LED having the second structure mainly has a pn
The junction has a single or double hetero junction structure, and is manufactured by the following steps.

For example, an n-type GaAs substrate is formed on an n-type GaAs substrate.
s buffer layer, n-type AlGaInP cladding layer, AlG
The aInP active layer, the p-type AlGaInP clad layer, and the p-type GaAs layer are sequentially formed by a metal organic chemical vapor deposition method (MO-CV
D) or the like. On the n-type GaAs substrate, a metal ohmic electrode made of, for example, AuGe, which is electrically contacted, is formed.
A metal ohmic electrode made of, for example, Al is formed in electrical contact with a part of the type GaAs layer.

In order to inject a sufficient current from the electrode into each of the p-type and n-type semiconductor layers for either LED in the first structure or the second structure, the distance between the semiconductor layer and the electrode is reduced. Is a necessary condition that the contact resistance is sufficiently low. Therefore, the contact resistance is improved by changing the electrode area, shape, and metal material. However, on the other hand, an opaque metal electrode blocks light generated near the pn junction, so it is not desirable to form the electrode area large.

In view of the above, an LED using the transparent conductive film for improving the optical characteristics of the LED having the first structure has been considered. The manufacturing process is described below.

For example, an n-type GaAs substrate is
After P is vapor-grown, an anti-diffusion film is formed with silicon nitride (SiNx). An opening is formed in a partial region of SiNx. By thermally diffusing Zn, a p-type GaAsP layer is formed in a partial region through the opening. A transparent conductive film is formed of, for example, indium tin oxide (ITO) on a wide region covering at least a partial region where the p-type GaAsP layer is formed. An upper electrode for wire bonding is formed of, for example, Al in a region avoiding the partial region.

An LED whose optical surface is covered by a transparent electrode with respect to the pn junction can be manufactured, and the emitted light is not blocked by an opaque metal electrode or the like, and the light is emitted at the pn junction interface. On the other hand, current can be injected with a uniform distribution. Therefore, the emission intensity distribution is uniform near the optical surface, and an increase in the amount of light can be expected.

Also, an LED using the transparent conductive film to improve the optical characteristics of the LED having the second structure has been considered. The manufacturing process is described below.

For example, an n-type GaAs substrate is formed on an n-type GaAs substrate.
s buffer layer, n-type AlGaInP cladding layer, AlG
An aInP active layer, a p-type AlGaInP cladding layer, and a p-type GaAs layer are sequentially formed by using a metal organic chemical vapor deposition method (MO-CVD) or the like.

On a p-type GaAs layer used as an optical surface,
For example, a transparent conductive film is formed by ITO or the like. An upper electrode for wire bonding is formed of, for example, Al on a partial region of the transparent conductive film. On the n-type GaAs substrate side, an ohmic electrode made of a metal such as AuGe, which is in electrical contact, is formed.

A transparent conductive film such as ITO having a low resistance can have a current diffusion function. The applied current is diffused widely in the transparent conductive film via the upper electrode, and is uniformly injected into the p-type GaAs layer.

However, the p-type GaAs on the optical surface
It is known that the interface between the s layer and the transparent conductive film such as ITO has an electrically large contact resistance.

Therefore, a metal layer such as AuZn is formed as an ohmic contact auxiliary film with the p-type GaAs layer and the IT layer.
Improvements such as insertion between transparent conductive films such as O have been made.

However, since the AuZn layer is an optically opaque metal, an attempt is made to improve the light transmittance by forming the AuZn layer as an extremely thin film having a thickness of 10 nm or less.

In a GaAs-based semiconductor device, for example, an LED which is a semiconductor light emitting device, in particular, the ITO formed on the optical surface in the first structure or the second structure.
There is a possibility that the optical characteristics can be improved by using such a transparent conductive film as an electrode or a current diffusion layer.

Here, the transparent conductive film formed on the semiconductor surface on the p-type or n-type optical surface means not only ITO but also Z
It includes a thin film of nO, In ₂ O ₃ , and SnO ₂ .

[0025]

SUMMARY OF THE INVENTION As described above, GaAs
It is a well-known fact that in a device structure of a system optical semiconductor device, optical characteristics can be improved by using a transparent conductive film as an electrode or a current diffusion layer. As a transparent conductive film,
In addition to ITO, ZnO, In ₂ O ₃ , SnO _{2, and the} like are mainly included, and many researches and developments have been made on these.

However, ZnO, In ₂ O ₃ or SnO ₂
Is difficult to use for a current injection type semiconductor light emitting device, for example, an LED or the like, because the material itself has a high resistivity. Further, ZnO, In ₂ O _{3 is formed} on the GaAs-based semiconductor layer.
Alternatively, there is no report that an ohmic contact with a GaAs-based semiconductor was obtained when SnO ₂ was formed.

[0027] In the transparent electrode film, ITO is considered to be promising as a current diffusion layer having a sufficiently low low resistivity of 10 ^-4 Ω · cm depending on the forming method.
Ohmic contact with the system semiconductor has not been obtained. It is known to have very large contact resistance.

As a technique for partially solving the above problem, p
There has been proposed an element structure in which an extremely thin metal layer such as AuZn is inserted as an ohmic contact auxiliary film between a type GaAs-based semiconductor layer and a transparent conductive film. Some logical interpretations are that the metal film is extremely thin, for example, 10 nm.
It is possible to improve the light transmittance by setting the thickness to the following thickness, and the p-type GaAs-based semiconductor layer and the AuZn
Ohmic contact is obtained with the layer, and Au
It is stated that an ohmic contact can be obtained between the Zn layer and the transparent conductive film.

However, when a metal layer such as AuZn is inserted, the transmittance is reduced to a considerable extent even if it is thin. Variations in transmittance due to variations in film thickness also occur, making it difficult to control variations in the amount of light. In particular, there is an example in which the forward driving voltage of the semiconductor light emitting element is increased,
It cannot be said that a sufficient ohmic contact with the base semiconductor layer has been obtained. Further, there is no mention of electrical contact between the n-type GaAs-based semiconductor layer and the transparent conductive film.

Therefore, there has been no transparent electrode or transparent current diffusion layer having excellent optical and electrical characteristics using a transparent conductive film that can be formed on a GaAs-based semiconductor.

In general, the junction interface between a semiconductor and another substance is varied by taking into account the band structure on the semiconductor side, particularly the Fermi level, the acceptor level or the donor level, and the work function of a metal or the like. Is understood.

Incidentally, many transparent conductive films such as ITO mainly show n-type conductive characteristics. Many oxide transparent conductive films, such as an electrical band structure, are not yet well understood. In particular, since it has both a semiconductor property and a metal property, even when it has a bond with another metal, a semiconductor, or another substance, its interface state is hardly understood.

Phenomena related to the bonding between the GaAs-based semiconductor and the transparent conductive oxide film have been hardly investigated.

An object of the present invention is to form a novel transparent conductive film serving as a current injection layer on the surface of a GaAs-based semiconductor used as an optical semiconductor device, and to improve the electrical and optical characteristics of a semiconductor light-emitting device formed of a GaAs-based semiconductor. To improve it.

[0035]

According to one aspect of the present invention, there is provided a GaAs-based semiconductor layer, and 2 at% to 8 at% of group III B, A formed on the GaAs-based semiconductor layer.
and a ZnO layer containing at least one of l, Ga and In as a dopant.

2 to 8 at% of group III B, A
A ZnO layer containing at least one of l, Ga and In as a dopant is provided as a novel transparent electrode or transparent current spreading layer.

The carrier concentration in ZnO can be increased by adding at least one of Group B, Al, Ga or In of ZnO of 2 to 8 at% as a dopant. Rate can be reduced. In a GaAs semiconductor,
ZnO containing Zn as an element that contributes as a p-type dopant
Layers can reduce contact resistance at the interface and improve electrical and optical properties.

[0038]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing an embodiment of the present invention, when a transparent conductive film is used as a transparent electrode or a transparent current diffusion layer for a semiconductor light emitting device LED, L
The effects on the optical and electrical characteristics of the ED are summarized below.

(1) Uniform Current Injection Since a transparent conductive film having high conductivity can be formed so as to widely cover the pn junction, a sufficiently uniform current can be applied to the pn junction surface. Can be injected. In particular, local current concentration can be prevented, element deterioration due to current is suppressed, and the life of the element is prolonged.

(2) Emission intensity near uniform optical surface A uniform current distribution can be injected into the pn junction, so that a uniform emission intensity distribution can be obtained from the pn junction. Similarly, a uniform emission intensity distribution can be obtained on the optical surface.

(3) Control of emitted light immediately below the electrode The current injected from the electrode to the pn junction has the highest density immediately below the electrode. The light emission intensity from the pn junction in that region is also large in proportion to the current density. However, when an opaque metal electrode is formed on the optical surface, the emitted light having the highest emission intensity from the pn junction is absorbed or reflected into the element by the opaque electrode.

By forming the transparent conductive film as a transparent electrode, a metal electrode required for wire bonding or flip chip can be formed at a position where light emitted from the pn junction is not blocked.

Further, when the transparent conductive film is formed as a transparent current diffusion layer, the current injected from the electrode is sufficiently concentrated without being locally concentrated, so that more light is emitted from the region other than immediately below the electrode. Strength is obtained and external quantum efficiency is improved.

In the semiconductor light emitting device, the external quantum efficiency refers to the efficiency of light that can be extracted outside the semiconductor device by a light emitting phenomenon obtained through a recombination process of electrons and holes by a certain injection current. This is an index indicating how much the injected energy (current) can be extracted outside as light energy.

(4) Reduction in Drive Voltage Since the transparent conductive film can be formed so as to cover almost the entire pn junction, it is possible to occupy a large area of the junction between the transparent conductive film and the semiconductor layer. . When the contact resistances per unit area have substantially the same value, the larger the bonding area, the lower the overall contact resistance. Therefore, the driving voltage of the light emitting element can be reduced, and power consumption can be suppressed.

(5) Use of refractive index difference When the interface is formed of materials having different refractive indexes,
The critical angle is determined from Nell's law. The magnitude of the critical angle is
Determined by the refractive index difference, especially the direction of light travel is the refractive index
When going from a high-substance substance to a low-substance substance, the refractive index difference
The larger the is, the smaller the critical angle is. At an angle greater than the critical angle
The incident light is totally reflected at the interface. For example, LED smell
When discussing light emission from a pn junction,
Rate is about n _s= 3.7, a GaAs-based semiconductor having
The outside has a refractive index of n_airFinger refers to air with = 1
You. Because of the large refractive index difference, the light emitted from the pn junction is
The ratio of reflection at the interface is large. Sky
Transparent conductive film having refractive index between GaAs and semiconductor
In the case of using, the refractive index difference becomes small and the critical angle becomes large.
Become. Therefore, light emitted from the pn junction is reflected inside the device.
The rate of irradiation is reduced, and the external takeout efficiency is improved.

(6) Use of Interference Phenomenon For light of a certain wavelength, conditions for constructing light are determined from the interference phenomenon. Assuming that the film thickness is d, the formula d = (2m-1) λ / 4n
Is led. The transparent conductive film has a refractive index n between air and the GaAs-based semiconductor. By satisfying the above conditional expression as the center wavelength λ, it is possible to make the transparent conductive film function as an anti-reflection film like an optical multilayer film. Here, m is a positive integer.

In the present specification, the group III-V Ga
GaAs-based optical semiconductor devices include GaAs
s, binary crystal of GaP, GaAsP, AlGaAs
ternary mixed crystal such as s, InGaAs, AlGaInP, I
A quaternary mixed crystal such as nAlGaAs is also included.

The optical semiconductor element basically includes a light emitting element and a light receiving element.

The electrical and optical characteristics of ZnO will be briefly described.

ZnO has various electrical and optical characteristics depending on the crystal structure and various dopants. For example, the electric characteristics show a wide range of semiconductor or metallic properties from ferroelectric properties. In particular, ZnO appropriately doped with at least one of Group III B, Al, Ga or In can have low resistivity and high optical transmittance and excellent optical properties.

FIG. 1 shows the effective carrier concentration n,
The relationship between the mobility μ and the resistivity ρ and the content (at%) of, for example, Ga in ZnO is shown.

As shown in FIG. 1, 2 at% (atomic percentage) or more and 20 at% or less, especially 2 at% to 8 a
When a ZnO film containing Ga is formed at a rate up to t%, a film having a high carrier concentration and a relatively high mobility, that is, a film having a low resistivity ρ can be formed. Such films have requirements for use as electrode films or current spreading layers.

FIG. 2 shows the spectral characteristics of the Ga-doped ZnO film. The horizontal axis indicates the wavelength λ, and the vertical axis indicates the light transmittance. In the wavelength region from 400 nm to 800 nm, the thickness of the Ga-doped ZnO film is 240 nm, 50 nm,
80% even if it changes to 0 nm, 870 nm, 990 nm
The above transmittance is shown. Therefore, it can be said that the conductive film has sufficient light transmission characteristics, that is, a transparent conductive film.

Incidentally, when the spectral characteristics shown in FIG.
The Ga content in the O transparent conductive film is about 4 at%.

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 3 shows the structure of the semiconductor light emitting device according to the first embodiment of the present invention. FIG. 3A is a plan view of a semiconductor light emitting device, and FIG. 3B is a view of IIIa-I in FIG.
FIG. 2 shows a sectional view taken along line IIb.

As shown in FIGS. 3A and 3B,
The semiconductor light emitting device A includes an n-type GaAs substrate 1 doped with an n-type impurity, for example, Te, and an n-type GaAs formed thereon, for example, doped with Te or Si.
aAsP layer 5.

The first region which is a part of the n-type GaAsP layer 5
The region C has, for example, a p-type GaAsP layer 5 a doped with Zn (p-type impurity) and an opening O in a region corresponding to the first region C, and is formed on the surface of the n-type GaAsP layer 5. Diffusion-preventing silicon nitride film (SiNx) 11
And a ZnO film, such as a Ga-doped ZnO film, which is appropriately doped with at least one of group III B, Al, Ga or In formed on the second region E including the first region C and wider than the first region. 15 is included.

N-type GaAsP layer 5 and p-type GaAsP layer 5
a forms a pn junction.

An electrode for wire bonding or flip chip, for example, an upper electrode 17 made of Al is formed on the third area F near the end of the second area E and not including the first area C. The upper electrode 17 does not cover the opening O (first region C).

On the back surface of the n-type GaAs substrate 1, for example, Au
A lower electrode 21 containing Sn is formed.

Next, the manufacturing process of the light emitting device shown in FIGS. 3A and 3B will be described with reference to FIGS.

As shown in FIG. 4A, an n-type GaAs substrate
Prepare one.

As shown in FIG. 4B, an n-type GaAs substrate
An n-type GaAsP layer 5 is crystal-grown on 1 by, for example, a vapor phase growth method.

As shown in FIG. 4C, n-type GaAsP
An SiNx film 11 is formed on the layer 5 by a thin film forming apparatus, for example, plasma CVD.

As shown in FIG. 4D, a resist pattern PR having an opening O is formed by photolithography.
To form Using the resist pattern PR as a mask, S
The iNx film 11 is etched by a dry etching method to remove the SiNx film in a region corresponding to the opening O. After that, the resist pattern PR is removed.

As shown in FIG. 4E, the SiNx film 11
Is used as a mask to thermally diffuse Zn as a p-type impurity. S
The iNx film 11 functions as a diffusion prevention film for preventing the diffusion of Zn. A p-type GaAsP 5a is formed in a region of the n-type GaAsP layer 5 corresponding to the opening.

N-type GaAsP layer 5 and p-type GaAsP layer 5
a forms a pn junction to form a light emitting region.

Next, as shown in FIG.
Group III B, Al, Ga or In is formed on the AsP layer 5a.
At least one of which is appropriately doped Zn
O, for example, a Ga-doped ZnO film 15 is formed. The Ga-doped ZnO film 15 sufficiently covers the first region C and is formed widely.

The method for forming the Ga-doped ZnO film 15 will be described later.

As shown in FIG. 5G, the ZnO film 15 is separated for each light emitting element using a photolithography technique and a dry etching or wet etching method, and the Ga-doped ZnO film 15 is left in the region E.

As shown in FIG. 5H, Ga-doped Zn
An upper electrode 17 for wire bonding is formed in the region F above the end of the O film 15 using Al or the like. Upper electrode 1
7 does not cover the first area C.

The lower electrode 21 is formed on the back surface of the n-type GaAs substrate 1 using AuSn or the like. In this way, a semiconductor light emitting device having the upper surface as the light emitting surface (optical surface) is formed.

It is also possible to form a semiconductor light receiving element having the upper surface as a light receiving surface by the same steps as described above.

Next, group III B, Al, Ga or In
Containing at least one of them as a dopant
A manufacturing apparatus and a manufacturing method for forming a film will be described.

The ZnO film is formed of at least group III B, A
At least one of l, Ga and In is contained as a dopant, and these dopants need to be sufficiently activated in the ZnO film and function as carriers.
Examples of an apparatus capable of forming a ZnO film satisfying the above conditions include an ion plating apparatus and a sputtering apparatus.

In particular, here, using an ion plating apparatus X as shown in FIG.
An example in which a ZnO film is formed using a as a dopant will be described. The ion plating apparatus X is an apparatus capable of forming a high-quality transparent electrode film by arc discharge.

As shown in FIG. 6, the ion plating apparatus X includes a vacuum chamber 31, a vacuum pump 33 for evacuating the vacuum chamber 31, and a vacuum chamber 3.
1, an substrate 37, a substrate heater 35a, an anode 37 and a cathode 41 (plasma gun) disposed below the substrate holder 35, and an Ar gas into the vacuum chamber 31. Valve 42 for
And

The flow rate of the Ar gas can be adjusted by a mass flow controller. The vacuum pump 33 is provided with a valve 33a capable of adjusting the pumping speed.

The plasma P emitted from the plasma gun 41 and converged on the anode 37 is irradiated on the ZnO solid source 47 on the anode 37 to which an appropriate amount of Ga has been added. The heated solid source 47 forms a highly crystalline transparent conductive film on the substrate through an evaporation and ionization process.

FIG. 7 shows, as a comparative example, a general semiconductor light emitting element B in which a transparent conductive film is not formed in the element structure of Example 1, and FIG.

Comparative Example and Example 1 are LEDs having the first structure, in which the pn junction has a homojunction structure.

FIG. 7A is a plan view, and FIG.
It is a VIIa-VIIb line sectional view of (a).

The semiconductor light emitting device B according to the comparative example shown in FIG. 7 is formed on an n-type GaAs substrate 71 doped with n-type impurities, for example, Te, and is formed on the n-type GaAs substrate 71, for example.
n-type GaAsP layer 7 doped with e or Si
5 is included.

For example, a p-type GaAsP layer 75a doped with Zn (p-type impurity) and an opening in a region corresponding to the first region G are formed in the first region G, which is a partial region of the n-type GaAsP layer 75. Silicon nitride film (SiN) having a portion O2 and formed on the surface of the n-type GaAsP layer 75 to prevent diffusion.
x) The second upper electrode 85 is formed of, for example, Al so as to cover 81 and a part of the opening O2 on the first region G.

The shape of the second upper electrode 85 made of Al on the optical surface does not necessarily have to be the shape shown in FIG. 7, and it is sufficient that the second upper electrode 85 has a junction in a partial region of p-type GaAsP.

The pn junction is formed by the n-type GaAsP layer 75 and the p-type GaAsP layer 75a.

On the back surface of the n-type GaAs substrate 71, for example,
A lower electrode 91 containing uSn is formed.

FIG. 8 shows a forward current-voltage characteristic graph of the semiconductor light emitting devices of Example 1 and Comparative Example.

When the forward current-voltage characteristics of Example 1 and the comparative example are compared, the light emission starting voltage shows almost the same value in both the example 1 and the comparative example.

When a large electrical contact resistance is provided at the junction interface between the p-type GaAsP and the Ga-doped ZnO transparent conductive film, the light emission starting voltage is also increased. The fact that the light emission starting voltage showed almost the same value as that of the general LED shown in the comparative example suggests that it has a small contact resistance at the junction interface between the p-type GaAsP and the Ga-doped ZnO transparent conductive film. are doing.

Therefore, p-type GaAsP and Ga-doped Zn
It is considered that the junction with the O transparent conductive film shows the electrical characteristics of the ohmic contact or ohmic-like contact.

Further, in a voltage range larger than the light emission starting voltage, the slope of the forward current-voltage characteristic according to the first embodiment has a larger slope than the slope of the current-voltage characteristic according to the comparative example.

In the case where the junction between the p-type GaAsP and the Ga-doped ZnO transparent conductive film exhibits the characteristics of an ohmic contact or an ohmic-like contact, taking into account both the contact resistance per unit area and the junction area, the overall contact The resistance decreases as the bonding area increases.

Therefore, it can be understood that the contact resistance is reflected on the current-voltage characteristics of the light emitting element, and the slope of the graph increases.

The transparent conductive film can be formed as a current injection electrode with a large junction area on the device without blocking light emitted from the pn junction, so that a reduction in the driving voltage of the device can be expected. The reduction in drive voltage can be linked to the effect of power consumption reduction.

Further, as a comparative experiment, when ITO is formed as a transparent electrode in the structure as in Example 1, since the contact resistance is very large and the slope of the current-voltage characteristic is very small, the accurate electric characteristics are not improved. Could not measure.

When the Ga-doped ZnO transparent conductive film used in the semiconductor light emitting device according to the first embodiment is used, good electrical characteristics of ohmic contact or ohmic-like contact can be obtained for a semiconductor material which cannot be realized by a conventional transparent conductive film. Is obtained.

Thus, the inventor conducted an experiment on the interface between the p-type and n-type GaAs-based semiconductors and the transparent conductive film. In particular, p-type and n-type GaAs-based semiconductors and Group III B, A
The contact resistance with a ZnO layer appropriately doped with at least one of l, Ga and In is determined by TLM (Tr
measurements and calculations were performed according to the Emissions Line Model) theory.

As a result, at the junction interface between the p-type and n-type GaAs-based semiconductor and, for example, a Ga-doped ZnO film,
In each case, the contact resistance value is 10 ^-4 to 10 ^-6
It was confirmed that it was as small as Ω · cm ² . Ohmic contacts were obtained at the respective interfaces with the p-type and n-type GaAs-based semiconductors.

Therefore, even for a structure of a semiconductor light emitting device in which an n-type GaAs-based semiconductor material is used as an optical surface, at least one of Group III B, Al, Ga or In is suitably used similarly to the p-type. It is suggested that the ZnO transparent conductive film doped with P can be used as an electrode or a current diffusion layer.

In addition, the optical characteristics of Example 1 and Comparative Example were measured. Comparing the amount of light with respect to the reference forward current, the first embodiment is 1.5 times more than the comparative example.
As a result, a uniform emission intensity distribution was obtained near the optical surface.

Next, a light emitting device according to a second embodiment of the present invention will be described with reference to the drawings.

FIG. 9A is a plan view of a light emitting device according to a second embodiment of the present invention, and FIG. 9B is a sectional view taken along line IXa-IXb of FIG. 9A.

As shown in FIGS. 9A and 9B, the light emitting device D according to the second embodiment includes an n-type GaAs buffer layer 103, an n-type AlGaInP
Cladding layer 105, AlGaInP active layer 107, p-type AlGaInP cladding layer 111, p-type GaAs layer 11
3. The n-type GaAs current block layer 121 is sequentially formed using a metal organic chemical vapor deposition method (MO-CVD) or the like.

The current block layer 121 is formed only in a partial region H on the p-type GaAs layer 113 by photolithography and etching.

The current block layer 121 is made of n-type AlG
It may be formed of aInP or an insulating film (dielectric material).

Further, Group III B, Al, Ga or I
Zn in which at least one of n is appropriately doped
O, for example, a Ga-doped ZnO transparent conductive film 117 is formed by using an ion plating method or the like, and an O3 opening is formed in the Ga-doped ZnO transparent conductive film 117 similarly by using photolithography and an etching technique.

The ZnO transparent conductive film 117 is made of Ga at 2 at.
% To 8 at% doping. B, A instead of Ga
At least one of l and In may be doped.

As shown in FIG. 9, the Ga-doped ZnO transparent conductive film 117 and the partial region I of the current block layer 121 have:
The upper electrode 123 for wire bonding is formed of Al or the like.

The current blocking layer 121 is formed on the upper electrode 1
23 to prevent current concentration just below
Through the transparent conductive film 117, more light can be extracted from the pn junction region where the light is not blocked by the upper electrode 123. The current block layer 121 is provided to improve the external quantum efficiency, but may be omitted in the structure because it has no direct relation to the present invention.

The p-type (n-type) GaAs layer 113 is often formed mainly as a high-concentration carrier layer, and is formed for the purpose of current diffusion or ohmic contact. Therefore, the p-type GaAs layer 113 is also made of ZnO (B, A
1, Ga, In) layer 117.

As described above, the light emitting device according to the present embodiment (Examples 1 and 2) can form a good ohmic contact with the p-type and n-type GaAs-based semiconductor materials, and also has an external quantum It was found that the efficiency was high and the electrical and optical characteristics were excellent.

When a semiconductor light receiving element is formed instead of a semiconductor light emitting element, the semiconductor light receiving element is made to function as a light receiving surface instead of a light emitting surface as an optical surface.

Specifically, a bias is applied in the reverse direction between the pn junctions. At this point, a minute current (dark current) in the reverse direction is flowing through the pn junction.

When light having an appropriate wavelength is incident on the optical surface (light receiving surface), light having energy equal to or greater than the width of the forbidden band generates electrons and holes. It is separated into p-type regions. The photocurrent flowing thereby adds to the dark current. Since the magnitude of the photocurrent changes depending on the light intensity, it functions as a light receiving element (photodiode).

While the embodiments of the present invention have been described above, it will be apparent to those skilled in the art that various changes, improvements, combinations, and the like can be made.

For example, in the present embodiment, among the semiconductor optical elements, a light emitting element, particularly an LED, has been described as an example. However, the transparent conductive film used in the semiconductor optical element of the present invention may be replaced with another optical element such as an LD. The present invention can be applied to a semiconductor optical element and a light receiving element such as a photodiode. Specifically, in addition to a GaAs-based semiconductor light-emitting diode, a GaAs-based semiconductor laser diode and a ZnO transparent material which is appropriately doped with at least one of Group III B, Al, Ga or In on the optical surface of the GaAs-based semiconductor light receiving element. This is a case where a conductive film is used.

[0120]

According to the present invention, when a junction with a ZnO transparent conductive film containing at least one of Group III B, Al, Ga or In as a dopant is formed for a p-type or n-type in a GaAs-based semiconductor material. It has been found that the electrical contact resistance at the interface is small. It becomes possible to incorporate a transparent electrode and a transparent current diffusion layer into the photoconductor element structure. In a light-emitting element having a pn junction, in particular, effects such as a reduction in current concentration and an improvement in external quantum efficiency can be obtained. Further, the driving voltage can be reduced, and reduction in power consumption can be expected.

Accordingly, it is possible to improve the performance, reduce the power consumption, and increase the reliability of the light emitting element.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the content (at%) of Ga in ZnO, the effective carrier concentration, the mobility, and the resistivity.

FIG. 2 is a graph showing light transmittance with respect to wavelength of a ZnO transparent conductive film.

FIG. 3 shows a structure of a semiconductor light emitting device A according to Example 1 of the present invention. FIG. 3A is a plan view, and FIG.
FIG. 3A is a cross-sectional view taken along line IIIa-IIIb.

FIG. 4 is a diagram showing a manufacturing process of the semiconductor light emitting device A shown in FIG.

5 is a view showing a manufacturing process of the semiconductor light emitting device A shown in FIG. 3, and is a process diagram following the process of FIG. 4;

FIG. 6 is a diagram showing a configuration of an ion plating apparatus used for forming a ZnO transparent conductive film.

FIG. 7 is a diagram illustrating a structure of a semiconductor light emitting device B according to a comparative example. FIG. 7A is a plan view, and FIG.
It is a VIIa-VIIb line sectional view of (a).

FIG. 8 is a graph showing forward current-voltage characteristics of semiconductor light emitting devices according to Example 1 and Comparative Example.

FIG. 9 illustrates a structure of a semiconductor light emitting device according to a second embodiment of the present invention. 9A is a plan view, and FIG. 9B is FIG. 9A.
IXa-IXb line sectional view of FIG.

[Explanation of symbols]

A Semiconductor light emitting device 1 n-type GaAs substrate 5 n-type GaAsP layer 5a p-type GaAsP layer O opening 11 silicon nitride film for diffusion prevention (SiNx) C first region E second region 15 second electrode (Ga-doped ZnO) Film: transparent conductive film) 21 First electrode

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuaki Hokota 1-3-1 Edanishi, Aoba-ku, Yokohama-shi, Kanagawa Prefecture Inside Stanley Electric Research Institute (72) Inventor Yoshio Suzuki 1 Edanishi, Aoba-ku, Yokohama-shi, Kanagawa Prefecture 3-1 Stanley Electric Co., Ltd. Technical Research Laboratory F-term (reference) 5F041 CA02 CA35 CA38 CA57 CA58 CA82 CA88 CA98

Claims (12)

[Claims] A GaAs-based semiconductor layer; and 2 at% to 8 at% formed on the GaAs-based semiconductor layer.
% Of Group III B, Al, Ga or In as a dopant. 2. The semiconductor device according to claim 1, wherein the GaAs-based semiconductor layer has p-type conductivity. 3. The semiconductor device according to claim 1, wherein the GaAs-based semiconductor layer has n-type conductivity. 4. A GaAs-based semiconductor having a pn junction composed of an n-type GaAs-based semiconductor layer and a p-type GaAs-based semiconductor layer formed as a main optical surface on the n-type GaAs-based semiconductor layer In the device, a first electrode for electrically forming a contact with the n-type GaAs-based semiconductor layer, and an electrical contact for forming a contact with the p-type GaAs-based semiconductor layer, wherein 2 at% to 8 a
an optical semiconductor device comprising: a second electrode made of a ZnO layer containing at least one of t% group III B, Al, Ga and In as a dopant. 5. A pn structure comprising a p-type GaAs-based semiconductor layer and an n-type GaAs-based semiconductor layer formed as a main optical surface on the p-type GaAs-based semiconductor layer.
A GaAs-based semiconductor element having a junction, wherein a first electrode electrically forming a contact with the p-type GaAs-based semiconductor layer, and an electrical contact with the n-type GaAs-based semiconductor layer; 2at% to 8
an optical semiconductor device comprising: a second electrode formed of a ZnO layer containing at least one of B, Al, Ga, and In as a dopant of at% group III. 6. A GaAs-based semiconductor having a pn junction composed of an n-type GaAs-based semiconductor layer and a p-type GaAs-based semiconductor layer formed in a part of the n-type GaAs-based semiconductor layer In the device, a first electrode for electrically forming a contact with the n-type GaAs-based semiconductor layer and the p-type GaAs-based semiconductor layer are covered, and an electrical contact is formed only for the p-type GaAs-based semiconductor layer. And a second electrode comprising a ZnO layer containing at least one of Group B, Al, Ga, and In as a dopant at 2 at% to 8 at%. 7. An n-type GaAs-based semiconductor layer, and formed in a partial region on the n-type GaAs-based semiconductor layer
A GaAs-based semiconductor device having a pn junction composed of a p-type GaAs-based semiconductor layer, a first electrode electrically forming a contact with the n-type GaAs-based semiconductor layer, From a ZnO layer that covers at least one of Group III B, Al, Ga or In as a dopant in a range of 2 at% to 8 at% that covers the base semiconductor layer and makes electrical contact only with the p-type GaAs base semiconductor layer. An optical semiconductor device comprising: a second electrode. 8. A GaAs-based semiconductor having a pn junction composed of a p-type GaAs-based semiconductor layer and an n-type GaAs-based semiconductor layer formed in a partial region on the p-type GaAs-based semiconductor layer In the semiconductor device, a first electrode for electrically forming a contact with the p-type GaAs-based semiconductor layer; and the n-type GaAs covering the n-type GaAs-based semiconductor layer.
2at to form an electrical contact only with the base semiconductor layer
And a second electrode comprising a ZnO layer containing at least one of Group III B, Al, Ga and In as a dopant. 9. The semiconductor device according to claim 4, wherein a semiconductor layer serving as an active layer is formed between the p-type GaAs-based semiconductor layer and the n-type GaAs-based semiconductor layer. Optical semiconductor device. 10. The optical semiconductor according to claim 4, wherein a part of said second electrode includes a third electrode made of a metal which forms an electrical contact with said second electrode. element. 11. The optical semiconductor device according to claim 4, wherein said second electrode has a refractive index n of between 1.8 and 2.2. 12. The optical semiconductor device according to claim 4, wherein the thickness d of the second electrode is d = (2m−1) λ / 4n. Here, m is a positive number, n is the refractive index, and λ is the center wavelength.