JP2003017747A - Photoelectric conversion function element and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric conversion function element which uses a laminated structure having an ZnTe-based semiconductor contact layer as a substrate, where ohmic contact with an electrode can be realized, and to provide its manufacturing method. SOLUTION: This photoelectric conversion function element is provided with electrodes on the front and rear surfaces of a II-VI group compound semiconductor crystal having at least pn junction, and it is also provided with a contact layer between an n-type semiconductor layer and an n-type electrode, and furthermore at least a part of the contact layer is made of n-type semiconductor containing an In element as an n-type impurity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric conversion function element using a II-VI group compound semiconductor crystal having a laminated structure having a pn junction as a substrate and a method for manufacturing the same.

[0002]

2. Description of the Related Art II-VI group compound semiconductors are semiconductors having a wide band gap among compound semiconductors, and thus can emit yellow, green and blue light. In recent years, attempts have been made to develop a high-efficiency and long-life photoelectric conversion functional element using a II-VI group compound semiconductor crystal as a substrate.

In order to manufacture a highly efficient photoelectric conversion functional element, it is necessary that the conductivity type of a semiconductor can be controlled to be a p-type or an n-type. Generally, a II-VI group compound semiconductor is a conductivity type. Is difficult to control. For example, ZnSe
It is relatively easy to control the n-type semiconductor with low resistance, but it is difficult to control it to the p-type. Conversely, ZnT
Although it is easy to control e to be p-type, it is difficult to control it to be n-type.

In general, Z used for photoelectric conversion functional elements
The nSe-based semiconductor crystal has a p-type ZnSe layer formed by a method of irradiating ZnSe at a high concentration with highly reactive active nitrogen obtained by plasma-exciting nitrogen using a molecular beam epitaxial growth method. This p-type ZnSe layer is used as a contact layer with the electrode.

However, since it is difficult for ZnSe to obtain a high p-type carrier concentration, the contact resistance between the electrode and the p-type ZnSe contact layer cannot be sufficiently reduced. Therefore, a photoelectric conversion function element using a ZnSe-based semiconductor crystal having a pn junction has a problem that its operating voltage becomes high, power consumption increases, and that the element deteriorates quickly due to heat generation.

Therefore, a photoelectric conversion functional element has been proposed in which a ZnTe layer to which a p-type impurity can be added at a high concentration is laminated on a pn junction of a ZnSe-based semiconductor, and the p-type ZnTe layer is used as a contact layer with an electrode. . However, if the ZnSe layer and the ZnTe layer were directly laminated, the resistance was increased due to the large discontinuity of the valence band at the interface, and it was not possible to realize a low voltage.

A photoelectric conversion element using a crystal having a laminated structure in which a ZnSeTe layer in which the composition ratio of Se and Te is gradually changed is formed on the ZnSe layer, and an n-type ZnTe layer is formed thereon. Alternatively, a photoelectric conversion functional element using a crystal having a laminated structure in which a superlattice layer of ZnSe and ZnTe is formed between a ZnSe layer and a ZnTe layer has been developed to lower the voltage.

As described above, the photoelectric conversion functional element using the ZnSe type semiconductor has been mainstream, and the photoelectric conversion element using the II-VI group compound semiconductor other than the ZnSe type semiconductor has not been put into practical use.

However, as described above, a crystal having a laminated structure including a ZnSeTe layer having a varied composition ratio or a superlattice layer of ZnSe and ZnTe is produced with high crystallinity because the lattice constants of ZnTe and ZnSe are significantly different. It is difficult to do so, and there is a drawback that the characteristics of the photoelectric conversion element are adversely affected. That is, although the photoelectric conversion device using the ZnSe-based semiconductor has been put to practical use, the operating voltage cannot be made sufficiently low, and the problems of power consumption and device deterioration have not been sufficiently improved.

On the other hand, a photoelectric conversion functional element using a ZnTe-based semiconductor has not been developed so far because it has not been possible to easily grow a ZnTe single crystal. However, in recent years, the present inventors have succeeded in growing a p-type ZnTe single crystal, and as a result, it has become possible to stably obtain a p-type ZnTe single crystal substrate. Along with this, development of photoelectric conversion functional devices using ZnTe-based semiconductors has become widespread.

However, since it is difficult to obtain a high n-type carrier concentration in the ZnTe-based semiconductor, the contact resistance between the electrode and the n-type ZnTe layer cannot be sufficiently reduced. Therefore, the photoelectric conversion functional element using the ZnTe-based semiconductor has a problem that the operating voltage increases and the power consumption increases, and that the element deteriorates quickly due to heat generation.

Generally, a ZnTe-based semiconductor crystal used as a substrate for a photoelectric conversion function element can be obtained by the method described below. For example, a group III element is arranged on the surface of a p-type ZnTe single crystal substrate, and heat treatment is performed to perform the above-mentioned I
An n-type Z is formed by diffusing a group II element as an n-type impurity into the substrate.
An nTe layer is formed to obtain a laminated structure.

An n-type ZnTe thin film is formed on a p-type ZnTe single crystal substrate by an epitaxial growth method to obtain a laminated structure.

In addition, a p-type ZnTe single crystal substrate is provided with a p-type Z
nTe buffer layer and Mg containing Mg, Cd, Se, etc.
A p-type clad layer of quaternary mixed crystal such as ZnSeTe and CdZnSeTe, a ZnTe active layer, and an n-type clad layer of quaternary mixed crystal are sequentially formed by epitaxial growth to obtain a laminated structure.

[0015]

However, the n-type semiconductor layer (n-type ZnTe layer, n-type clad layer of quaternary mixed crystal) in the above-mentioned laminated structure is less likely to make ohmic contact with the n-type electrode and has a contact resistance. I couldn't lower it. That is, n-type ZnTe formed by the conventional method
Since the carrier concentration of the layer is limited to 10 ¹⁷ / cm ⁻³ , ohmic contact with the electrode cannot be obtained at this level of carrier concentration. Therefore, currently p
A photoelectric conversion functional element using a ZnTe-based semiconductor crystal having an n-junction as a substrate has not reached a practical use level,
There is no report that the voltage could be effectively reduced.

The present invention has been made to solve the above problems, and provides a photoelectric conversion functional element using as a substrate a ZnTe based semiconductor crystal having at least a contact layer capable of making ohmic contact with an electrode, and a method for manufacturing the same. The purpose is to

[0017]

The present invention is a photoelectric conversion functional element comprising an II-VI group compound semiconductor crystal having at least a pn junction and electrodes provided on the front surface and the back surface thereof, respectively. A contact layer is provided between the mold electrode and at least a part of the contact layer is composed of an n-type semiconductor containing an In element as an n-type impurity.

As a result, since the n-type electrode and the contact layer are in ohmic contact with each other, the operating voltage of the photoelectric conversion function element is lowered, the power consumption can be reduced, and the element life can be prevented from being shortened due to internal heat generation.

Specifically, the contact layer is the n-type.
It is formed by thermally diffusing In into the type semiconductor layer. For example,
In can be thermally diffused into the n-type semiconductor layer by disposing In on the n-type semiconductor layer and irradiating an energy beam such as a laser beam in an inert gas or a nitrogen gas. Thereby, n-type ZnTe can be easily formed.
A contact layer can be formed.

An ITO layer may be provided between the In-diffused layer and the n-type electrode. According to such a photoelectric conversion function element, there is an effect that the light emitting area can be widened by the ITO layer. Since the light absorption by the ITO layer is very small, the decrease in emission intensity can be suppressed very little.

Further, since the ITO layer is formed by bringing indium oxide into contact with the surface of the In-doped n-type ZnTe contact layer, there is no adverse effect such as formation of a barrier layer due to the film formation, good interface adhesion and contact. Sex is obtained. Since ITO is a transparent film with high conductivity,
It can also be used as a mold electrode.

Furthermore, n-type ZnT is formed on the p-type ZnTe substrate.
Homostructure with e layer formed or Zn on p-type substrate
Element and a Te element, at least a single heterostructure in which a p-type layer and an n-type semiconductor layer made of a II-VI group compound semiconductor are sequentially stacked, or a Zn element and a T element are formed on a p-type substrate.
Photoelectric conversion based on a crystal having at least one of a structure in which a p-type clad layer made of a II-VI group compound semiconductor containing at least an e element, an active layer, and an n-type clad layer are sequentially stacked In the case of a functional element, forming the contact layer according to the present invention can effectively reduce the power consumption.

The process leading to the completion of the present invention will be described below. In general, it has been considered difficult to increase the n-type carrier concentration in a ZnTe-based semiconductor, but the present inventors have utilized an energy beam such as an excimer laser beam to irradiate the n-type semiconductor with an n-type. Impurity n
The carrier concentration in the n-type semiconductor layer was successfully increased by diffusing into the n-type semiconductor layer.

Specifically, In is arranged on a high-resistance ZnTe substrate having a resistivity of about 1000 Ω · cm by a vapor deposition method, and an excimer laser beam is irradiated as an energy beam in an inert atmosphere to obtain the high resistance. In was diffused into the ZnTe substrate.

Then, as an n-type electrode, I was formed on the In diffusion layer.
n is formed in the shape of a circular dot by vapor deposition to form the electrical characteristics of the n-type layer.
A sample for sex evaluation was prepared. About this sample n
As a result of measuring the electric resistance on the mold electrode side, ohmic characteristics
And shows a resistivity of 5 × 10 ^-3It was Ω · cm. Well
As a result of the hole measurement, the carrier concentration of the In diffusion layer was
Degree is 8 × 10¹⁹cm^-3Met.

From this result, it is possible to make an ohmic contact between the ZnTe-based n-type semiconductor layer and the n-type electrode by irradiating an energy beam to diffuse In into the n-type ZnTe layer to form a contact layer. The present invention has been completed based on the feeling that it can be obtained.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1) FIG. 1 is an explanatory diagram showing the configuration of a photoelectric conversion functional element according to the first embodiment of the present invention.
The base of this photoelectric conversion functional element is a p-type ZnTe substrate 11
An n-type ZnTe layer 12 and an n-type contact layer 13 are sequentially stacked on the top of the n-type ZnTe layer 12. A method for manufacturing the photoelectric conversion functional element having such a structure will be described below.

First, an Al element is arranged on the p-type ZnTe substrate 11 and Al is thermally diffused into the p-type ZnTe substrate 11 as an n-type impurity to form an n-type ZnTe layer (Al diffusion layer) 12
Was formed to a thickness of 0.3 to 1.2 μm. p-type ZnTe
The carrier concentration of the substrate 11 is, for example, 2 × 10 ¹⁸ / cm
^It is preferably about ^-3 . The n-type ZnTe layer 1
The n-type impurity for forming 2 is not limited to the Al element and may be an In element or a Ga element.

Next, Al remaining on the surface of the n-type ZnTe layer 12 was removed by light etching. Then, In was arranged on the n-type ZnTe layer 12 by a vapor deposition method. Then, the In arranged on the surface of the n-type ZnTe layer 12 is irradiated with an excimer laser in an inert atmosphere to produce the n-type ZnT.
In was diffused into the e layer 12 to form an n-type contact layer (In diffusion layer) 13 with a thickness of 50 to 250 nm. The irradiation output of the excimer laser at this time is 30 to 120 mJ.
/ Cm ² is recommended.

After that, In was placed on the n-type contact layer 13 by vapor deposition to form an n-type electrode of 130 μmφ. Further, an Au electrode was formed on the back surface of the p-type ZnTe single crystal substrate to manufacture a photoelectric conversion functional element having the structure shown in FIG.

The photoelectric conversion function element thus manufactured can flow a current of 50 mA required for the operation of the photoelectric conversion function element with an applied voltage of 4.3 V, and is a general LED.
The current-voltage characteristics were similar to those of (light emitting diode).

(Embodiment 2) FIG. 2 is an explanatory diagram showing the configuration of a photoelectric conversion functional element according to a second embodiment of the present invention. The base body of this photoelectric conversion function element is configured by sequentially stacking a p-type ZnTe layer 15, an n-type ZnTe layer 12, and an n-type contact layer 13 on a p-type ZnTe substrate 11. Below, the manufacturing method of the photoelectric conversion functional element which has such a structure is demonstrated.

First, the p-type ZnTe layer 15 was formed on the p-type ZnTe single crystal substrate 11 by the epitaxial growth method. At this time, nitrogen was used as the p-type impurity. Then, the n-type ZnTe layer 12 was formed on the p-type ZnTe layer 15 by an epitaxial growth method. At this time, Al was used as the n-type impurity.

Next, In was placed on the n-type ZnTe layer 12 by a vapor deposition method. Then, in an inert atmosphere, n-type Zn
The In arranged on the surface of the Te layer 12 is irradiated with an excimer laser to diffuse In into the n-type ZnTe layer 12 and n
Type contact layer (In diffusion layer) 13 of 50 to 250 nm
Formed with a thickness of. The irradiation output of the excimer laser at this time may be 30 to 120 mJ / cm ² .

After that, In is arranged on the n-type contact layer 13 by a vapor deposition method to form an n-type electrode of 130 μmφ. Further, an Au electrode was formed on the back surface of the p-type ZnTe single crystal substrate to fabricate a photoelectric conversion functional element having the structure shown in FIG.

The photoelectric conversion function element thus manufactured can flow a current of 50 mA required for the operation of the photoelectric conversion function element with an applied voltage of 4.4 V, and is a general LED.
The current-voltage characteristics were similar to those of

(Embodiment 3) FIG. 3 is an explanatory diagram showing the structure of a photoelectric conversion function element according to a third embodiment of the present invention. The base of this photoelectric conversion function element is a p-type ZnMb substrate with a p-type ZnTe buffer layer 16 and a p-type ZnMg layer.
SeTe clad layer 17, ZnTe active layer 18, n
The type ZnMgSeTe cladding layer 19 is sequentially laminated and configured. Below, the manufacturing method of the photoelectric conversion functional element which has such a structure is demonstrated.

First, p on the p-type ZnTe single crystal substrate 11
The type ZnTe buffer layer 16 was formed to a thickness of 400 nm, and the p type ZnMgSeTe cladding layer 17 was formed to a thickness of 300 nm on the buffer layer 16 by an epitaxial growth method. Lastly, nitrogen was used as a p-type impurity.

Next, on the p-type ZnMgSeTe clad layer 17, a ZnTe active layer 1 was formed by an epitaxial growth method.
8 is formed to a thickness of 8 nm, and n-type ZnMgSe is formed thereon.
The Te clad layer 19 was formed to a thickness of 300 nm. At this time, Al was used as the n-type impurity.

Next, the n-type ZnMgMgSeTe clad layer 1
In was placed on 9 by vapor deposition. Then, the In arranged on the surface of the n-type ZnMgSeTe layer 12 is irradiated with an excimer laser in an inert atmosphere to produce the n-type ZnMgS
In is diffused into the eTe layer 12 to form an n-type contact layer (I
The n diffusion layer 13 was formed to a thickness of 50 to 250 nm.
The irradiation output of the excimer laser at this time is 30 to 120.
It is good to set it to mJ / cm ² .

Then, In was placed on the n-type contact layer 13 by a vapor deposition method to form an n-type electrode. Furthermore, p
Of an Au electrode on the back surface of the ZnTe single crystal substrate of FIG.
A photoelectric conversion functional element having the structure shown in was produced.

The photoelectric conversion function element thus manufactured can flow a current of 50 mA required for the operation of the photoelectric conversion function element with an applied voltage of 4.8 V, and is a general LED.
The current-voltage characteristics were similar to those of

The n-type ZnMgMgSeTe clad layer 1
9, an n-type ZnTe layer is laminated on the n-type ZnTe layer, In is placed on the n-type ZnTe layer, and the n-type contact layer is formed by diffusing In in the ZnTe layer by irradiating an excimer laser. May be.

(Comparative Example 1) FIG. 4 is an explanatory view showing an example of a laminated structure used as a substrate of a conventional photoelectric conversion functional element. It differs from the laminated structure described in the first embodiment in that the n-type contact layer 13 is not formed.

The laminated structure shown in FIG. 4 is obtained by diffusing Al (n-type impurities) in the p-type ZnTe substrate 11 and then n-type ZnTe.
The Al remaining on the surface of the Te layer 12 is removed by light etching, and electrodes are formed by a vapor deposition method. The carrier concentration, the thickness of each layer, etc. were made in the same manner as in the first embodiment.

In the photoelectric conversion function element in which this n-type contact layer is not formed, only a current of 0.8 mA flows at an applied voltage of 4.5 V, and it is possible to obtain a sufficient current necessary for the photoelectric conversion function element. could not. Therefore,
Since it is necessary to apply a higher voltage in order to operate it as a photoelectric conversion function element, it has not been possible to reduce the power consumption.

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the above embodiments.

For example, in Examples 2 and 3, a ZnTe single crystal substrate was used as the p-type substrate for epitaxial growth, but a substrate other than ZnTe may be used, and II- containing at least one of Zn element and Te element may be used. It is considered that any substrate can be used as long as it can be epitaxially grown with a Group VI compound semiconductor.

Further, in the above embodiment, E was deposited on the n-type contact layer 13 in which In was thermally diffused by an excimer laser.
ITO (Indium Tin Oxide) is formed by the B vapor deposition method,
In may be vapor-deposited on the ITO layer to form an n-type electrode. According to the photoelectric conversion functional element having such a laminated structure, the ITO layer has an effect of expanding the light emitting area. In addition, since the light absorption by the ITO layer is very small, the decrease in emission intensity is very small. actually,
By forming the ITO layer, the light emitting area was more than doubled.

Further, p for epitaxial growth
Nitrogen, phosphorus and arsenic are suitable as the type impurities, and group III elements such as Al or group VII elements such as Cl are suitable as the n-type impurities.

As the n-type impurity diffused into the n-type semiconductor layer by irradiation with an energy beam, Al can be used instead of In. In this case, it is considered that the carrier concentration and the layer thickness of the Al diffusion layer may be set to the same level as when In is used as the impurity.

[0053]

According to the present invention, a pn junction is formed, and Zn
In the photoelectric conversion functional element based on the II-VI group compound semiconductor crystal containing Te as a main component, In is thermally diffused into the n-type semiconductor layer by using the energy beam to form the contact layer. It is possible to make ohmic contact with the n-type electrode, and it is possible to obtain a photoelectric conversion functional element having a low operating voltage. Also, In
According to the photoelectric conversion function element in which the ITO layer is formed on the diffusion layer in which the light is diffused and which is used as the contact layer, the light emitting area is widened and the characteristics as the light emitting element can be improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram illustrating a configuration of a photoelectric conversion functional element according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a configuration of a photoelectric conversion function element according to a second embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a configuration of a photoelectric conversion function element according to a third embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a configuration of a conventional photoelectric conversion functional element.

[Explanation of symbols]

10 Au electrode 11 p-type ZnTe substrate 12 n-type ZnTe layer 13 n-type contact layer (Al diffusion layer) 14 In electrode 15 p-type ZnTe layer 16 p-type ZnTe buffer layer 17 p-type ZnMgSeTe clad layer 18 ZnTe active layer 19 n-type ZnMgSeTe cladding layer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kenji Sato             3-17-35, Shinsōnan, Toda City, Saitama Prefecture Stocks             Company Nikko Materials Toda Factory F term (reference) 4M104 BB09 BB36 CC01 DD22 DD26                       DD34 FF02 FF13 GG02 GG04                       HH15                 5F041 CA02 CA41 CA48 CA57 CA64                       CA72 CA88 CA99

Claims (8)

[Claims] 1. II-VI having at least a pn junction
A photoelectric conversion function element having electrodes on the front and back surfaces of a Group III compound semiconductor crystal, wherein a contact layer is provided between an n-type semiconductor layer and an n-type electrode, and at least a part of the contact layer is an In element. A photoelectric conversion functional element, comprising an n-type semiconductor that contains as an n-type impurity. 2. The photoelectric conversion functional element according to claim 1, wherein the contact layer is an In diffusion layer formed by thermally diffusing In in the n-type semiconductor. 3. The photoelectric conversion functional element according to claim 1, wherein the contact layer has an ITO layer between the In diffusion layer and the n-type electrode. 4. The II-VI compound semiconductor crystal comprises:
A homostructure in which an n-type ZnTe layer is formed on a p-type ZnTe substrate, or a p-type layer and an n-type II-VI compound semiconductor containing at least Zn element and Te element on a p-type substrate
A single hetero structure in which the type semiconductor layers are sequentially stacked, or a p-type clad layer, an active layer, and an n-type clad layer made of a II-VI group compound semiconductor containing at least Zn element and Te element on a p-type substrate. The photoelectric conversion function element according to any one of claims 1 to 3, wherein the photoelectric conversion function element has a laminated structure including at least one of the following structure. 5. II-VI having at least a pn junction
In a method of manufacturing a photoelectric conversion functional element, wherein electrodes are provided on the front surface and the back surface of a group compound semiconductor crystal, a step of arranging an In layer on the surface of an n-type semiconductor layer; A method for manufacturing a photoelectric conversion functional element, comprising at least a step of thermally diffusing In in the layer to form a contact layer, and a step of forming an n-type electrode on the contact layer. 6. The step of forming the contact layer comprises irradiating an In layer arranged on the surface of the n-type semiconductor with an energy beam in an inert gas or a nitrogen gas to perform heat treatment, The method for manufacturing a photoelectric conversion element according to claim 5, wherein In is diffused in the type semiconductor layer. 7. The step of forming the contact layer includes the step of thermally diffusing In into the n-type II-VI semiconductor layer and then forming an ITO film on the diffusion layer. The method for manufacturing a photoelectric conversion function element according to claim 5 or 6. 8. The II-VI group compound semiconductor crystal comprises:
A homostructure in which an n-type ZnTe layer is formed on a p-type ZnTe substrate, or a p-type layer and an n-type II-VI compound semiconductor containing at least Zn element and Te element on a p-type substrate
A single hetero structure in which the type semiconductor layers are sequentially stacked, or a p-type clad layer, an active layer, and an n-type clad layer made of a II-VI group compound semiconductor containing at least Zn element and Te element on a p-type substrate. 8. A method of manufacturing a photoelectric conversion function element according to claim 5, wherein the photoelectric conversion function element has a laminated structure having at least one of the following structure.