JP2006237129A - Semiconductor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor element of a practical double hetero structure having a sufficiently high photo-electric conversion efficiency by incorporating an iron silicide layer as an active layer. <P>SOLUTION: The semiconductor element is constituted by forming the iron silicide layer on a predetermined substrate, and forming a cap layer which is made of a silicon germanium or a silicon of crystal grain of 50 nm or less of a mean particle diameter on the above iron silicide layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor device including an iron silicide layer as an active layer.

Unlike iron silicide of α-Fe ₂ Si ₂ which is a tetragonal structure metal, iron silicide, in particular β-FeSi _2, is a semiconductor having an orthorhombic structure and a forbidden band width of about 0.85 eV. β-FeSi ₂ has a much larger absorption coefficient than crystalline silicon (wavelength 1.1 μm, absorption coefficient 10 ⁵ cm ⁻¹ ) and high photoelectric conversion efficiency. It is expected to be an infrared light receiving material such as an efficient solar cell. In addition, unlike compound semiconductors such as GaAs, β-FeSi ₂ does not require use of As or the like that is difficult to handle in the environment. 3).

Therefore, based on the characteristics of iron silicide such as β-FeSi ₂ described above, in recent years, research and development of optical semiconductor elements using the iron silicide as an active layer has been actively conducted.

JP 2003-318493 A JP 2003-243426 A JP 2003-183812 A

  However, in the light emitting device including iron silicide as an active layer, it is difficult to prevent carrier recombination in the silicon portion around the iron silicide when current is injected. It is difficult to realize the increase. In addition, non-radiative recombination of electrically conductive carriers or photon carriers occurs on the surface of the iron silicide layer, thereby reducing the direct light-electricity conversion efficiency.

  In view of such a problem, it has been attempted to realize a so-called double hetero structure by providing a silicon layer as a cap layer on the iron silicide layer. According to this double heterostructure, non-radiative recombination of photon carriers on the iron silicide layer surface due to the provision of the cap layer can be suppressed, and the confinement effect of photon carriers can be increased. Therefore, it is expected that the photoelectric conversion efficiency can be increased, and as a result, sufficient light emission intensity can be realized.

  However, even in such a double heterostructure, crystal defects such as dislocations are formed due to internal strain of the cap layer (silicon layer) due to lattice mismatch between the iron silicide layer and the cap layer (silicon layer). The disappearance of injected carriers and photon carriers due to these defects has been a factor of reducing the direct optical-electric conversion efficiency. As a result, a practical double heterostructure including an iron silicide layer as an active layer has not yet been achieved.

  It is an object of the present invention to provide a practical double heterostructure semiconductor device having an iron silicide layer as an active layer and having sufficiently high photoelectric conversion efficiency.

In order to achieve the above object, the present invention provides:
A predetermined substrate;
An iron silicide layer formed on the substrate;
A cap layer made of silicon germanium formed on the iron silicide layer;
The present invention relates to a semiconductor element (first semiconductor element).

The present invention also provides:
A predetermined substrate;
An iron silicide layer formed on the substrate;
A first buffer layer made of silicon germanium formed on the iron silicide layer;
A cap layer made of silicon formed on the first buffer layer;
The present invention relates to a semiconductor element (second semiconductor element).

Furthermore, the present invention provides
A predetermined substrate;
An iron silicide layer formed on the substrate;
A cap layer made of silicon made of fine crystal grains having an average grain size of 50 nm or less, formed on the iron silicide layer;
The present invention relates to a semiconductor element (third semiconductor element).

  The inventors of the present invention have intensively studied to achieve the above object. As a result, in a conventional double heterostructure including an iron silicide layer as an active layer, the cap layer is made of silicon germanium instead of silicon, so that the lattice mismatch between the iron silicide layer and the cap layer is achieved. It has been found that the rate can be reduced, and introduction of dislocations into the cap layer can be reduced as much as possible (first semiconductor element).

  Further, even when the cap layer is made of silicon as in the prior art, by introducing a buffer layer (first buffer layer) made of silicon germanium between the iron silicide layer and the cap layer, the iron layer is similarly formed. It has been found that the lattice mismatch rate between the silicide layer and the cap layer can be reduced, and introduction of dislocations into the cap layer can be reduced as much as possible (second semiconductor element).

  Furthermore, even when the cap layer is made of silicon as in the prior art, the lattice mismatch rate between the iron silicide layer and the cap layer is also reduced by setting the average grain size of the crystal grains to 50 nm or less. It was found that the introduction of dislocations into the cap layer can be reduced as much as possible (third semiconductor element).

  In the third semiconductor element, the cap layer is made of silicon as in the conventional case, but the average grain size of the crystal grains is 50 nm or less, so that the lattice mismatch rate is 1.4% to 5.5. Although the junction area of each crystal grain with the iron silicide layer can be kept small in spite of being as large as%, the substantial lattice mismatch rate can be reduced, and the dislocation into the cap layer can be reduced. Can be suppressed.

  Like the silicon cap layer, the silicon germanium cap layer can suppress non-radiative recombination of photon carriers on the surface of the iron silicide layer, and can increase the confinement effect of photon carriers. The photoelectric conversion efficiency can be increased, and as a result, sufficient light emission intensity can be realized (first semiconductor element).

  Further, in the second semiconductor element and the third semiconductor element, since the cap layer is made of silicon as in the conventional case, the same high light-electricity conversion efficiency as in the conventional case can be obtained, and sufficient light emission. Strength can be realized.

  In the first semiconductor element and the second semiconductor element described above, the germanium concentration in the interface with the iron silicide layer in the cap layer or in the buffer layer is 50 atomic% to 90 atomic%. It is preferable that Thereby, the lattice mismatch rate between the cap layer or the buffer layer and the iron silicide layer can be further reduced. Specifically, the lattice mismatch rate can be reduced to 0% to 2%.

  The concentration of 50 atomic% to 90 atomic% of the cap layer and the buffer layer at the interface of the iron silicide layer can be set over the entire thickness direction of these layers, or the thickness direction of the layers. It is also possible to provide a composition gradient so that the concentration of germanium (silicon) increases (decreases) toward the interface with the iron silicide. In this case, since the relative silicon concentration in the cap layer can be increased, it is possible to obtain the same function and effect as when the cap is made of silicon. Further, since the silicon concentration on the cap layer side of the buffer layer can be increased, the lattice mismatch rate between the buffer layer and the cap layer composed of silicon can be reduced, and the cap layer The introduction of dislocations into can be further reduced.

  In one embodiment of the present invention, a buffer layer (second buffer layer) made of silicon germanium can be provided between the substrate and the iron silicide layer. Thereby, the lattice mismatch ratio between the substrate and the iron silicide layer can be reduced, and introduction of dislocations into the iron silicide layer can be suppressed.

  In this case as well, the germanium concentration in the interface with the iron silicide layer in the buffer layer is preferably 50 atomic% to 90 atomic%. Thereby, the lattice mismatch rate between the buffer layer and the iron silicide layer can be further reduced. Further, a composition gradient can be provided in the thickness direction so that the germanium (silicon) concentration increases (decreases) toward the interface with the iron silicide. In this case, particularly when the substrate is made of silicon, the lattice mismatch ratio between the substrate and the buffer layer can be reduced, and the buffer effect of the buffer layer can be further increased.

  As described above, according to the present invention, a practical double heterostructure semiconductor element having an iron silicide layer as an active layer and having a sufficiently high photoelectric conversion efficiency can be provided.

  Hereinafter, details of the present invention, other features and advantages will be described based on the best mode for carrying out the invention.

  FIG. 1 is a block diagram showing an example of a preferred embodiment of an optical semiconductor element comprising the semiconductor element of the present invention.

  An optical semiconductor device 10 shown in FIG. 1 includes a buffer layer 12, an iron silicide active layer 13, and a cap layer 14 which are sequentially formed on a predetermined substrate 11. An electrode 15 is formed on the back side of the substrate 11, and an electrode 16 is formed on the cap layer 14.

  According to the present invention, the cap layer 14 needs to be composed of a silicon germanium layer or a silicon layer made of crystal grains having an average grain size of 50 nm or less. Thereby, the lattice mismatch rate between the iron silicide layer 13 and the cap layer 14 can be reduced, and introduction of dislocations into the cap layer 14 can be reduced as much as possible.

  The lower limit of the size of the silicon crystal grains constituting the cap layer 14 is not particularly limited, but is currently about 10 nm depending on the manufacturing method.

  Also, the buffer layer 12 needs to be composed of a silicon germanium layer according to the present invention. Thereby, the lattice mismatch rate between the substrate 11 and the iron silicide layer 13 can be reduced, and the introduction of dislocations into the iron silicide layer 13 can be suppressed.

  When the cap layer 14 is composed of a silicon germanium layer, the germanium concentration at the interface 14A with the iron silicide layer 13 is preferably 50 atomic% to 90 atomic%. Thereby, the lattice mismatch rate between the cap layer 14 and the iron silicide layer 13 can be further reduced, and specifically, the lattice mismatch rate can be reduced to 0% to 2%.

  In addition, while realizing the above-described germanium concentration at the interface 14A, the concentration can be set over the entire thickness direction of the layer, but preferably, a composition gradient is provided in the thickness direction of the layer, The concentration of germanium (silicon) may be increased (decreased) toward the interface 14A with the iron silicide layer 13. In this case, since the relative silicon concentration in the cap layer 14 can be increased, the same effect as when the cap layer 14 is made of silicon can be obtained.

  Further, since the optical semiconductor element 10 shown in FIG. 1 includes the buffer layer 12 as described above, the lattice mismatch rate between the substrate 11 and the iron silicide layer 13 can be reduced thereby, and the iron silicide can be reduced. Introduction of dislocations into the layer 13 can be suppressed.

  Also in this case, it is preferable that the germanium concentration in the interface with the iron silicide layer 13 in the buffer layer 11 is 50 atomic% to 90 atomic%. Thereby, the lattice mismatch rate between the buffer layer 11 and the iron silicide layer 13 can be further reduced. Further, a composition gradient can be provided in the thickness direction so that the concentration of germanium (silicon) increases (decreases) toward the interface with the iron silicide 13. In this case, particularly when the substrate is made of silicon, the lattice mismatch rate between the substrate 11 and the buffer layer 13 can be reduced, and the buffer effect of the buffer layer 12 can be further increased.

The iron silicide layer 13 can be composed of, for example, a β-FeSi ₂ layer exhibiting good semiconductor properties. Further, the iron silicide layer 13 may contain n-type impurities such as Co, Ni, Pt, Pd, P, As, and Sb as required, and Mn, Cr, V, Ti, Al, Zn, A p-type impurity such as In, Ga, or Cu may also be included. Further, the iron silicide layer 13 may have a laminated structure in which these n-type iron silicide layer and p-type iron silicide layer are laminated.

The substrate 11 can typically be (100) silicon crystal or (111) silicon crystal, but other STO (strontium titanate substrate), MgO (magnesia substrate), YSZ (yttria stabilized zirconia substrate). ), Al ₂ O ₃ (sapphire substrate), or the like can also be used. The silicon crystal can be formed by, for example, the CZ method or the FZ method.

  The buffer layer 12 and the iron silicide layer 13 can be formed using a known method such as MOCVD, vapor deposition, sputtering, and pulsed laser ablation. The cap layer 14 can also be formed by the same method as described above when the cap layer 14 is made of silicon germanium.

  On the other hand, when the cap layer 14 is made of silicon, the cap layer 14 is preferably formed using a plasma CVD method, more preferably an ECR plasma CVD method. Thus, the cap layer 14 made of silicon having an average grain size of 50 nm or less can be easily formed. In this case, the substrate 11 can be appropriately heated as necessary, but it is preferable that no bias voltage is applied to the substrate 11 (in addition to the buffer layer 12 and the iron silicide layer 13). When a bias voltage is applied, the orientation in the cap layer 14, and thus the crystallization, becomes insufficient, and the function as the cap layer may not be sufficiently exhibited.

  The electrode 15 can be made of, for example, Al, and the electrode 16 can be made of, for example, AuGe.

  In the optical semiconductor device 10 shown in FIG. 1, a voltage is applied between the electrodes 15 and 16 and a current accompanying this is injected into the iron silicide layer 13 to excite the current to produce a predetermined light emission. Can be used as In addition, a predetermined light is incident and introduced into the iron silicide layer 13, a predetermined voltage (current) is generated by photoexcitation, and taken out through the electrodes 15 and 16 to be used as a semiconductor light receiving element. be able to.

  In the optical semiconductor element 10 shown in FIG. 1, light emission and light reception are performed from the cap layer 14 side, but can also be performed from the substrate 11 side.

  The thickness of each layer depends on the material composition to be used and the use of the obtained semiconductor element. For example, the buffer layer 12 can be 10 nm to 2000 nm, and the iron silicide layer 13 can be 10 nm to 200 nm. The cap layer 14 can be 10 nm to 500 nm.

  FIG. 2 is a block diagram showing another example of a preferred embodiment of an optical semiconductor element comprising the semiconductor element of the present invention. In the semiconductor element shown in FIG. 2, the same reference numerals are used for the same components as those of the semiconductor element shown in FIG.

  An optical semiconductor element 20 shown in FIG. 2 includes a second buffer layer 12, an iron silicide active layer 13, a first buffer layer 17, and a cap layer 14 which are sequentially formed on a predetermined substrate 11. An electrode 15 is formed on the back side of the substrate 11, and an electrode 16 is formed on the cap layer 14.

  The first buffer layer 17 needs to be made of silicon germanium according to the present invention, and the cap layer 14 needs to be made of silicon as usual. Thereby, the lattice mismatch rate between the iron silicide layer 13 and the cap layer 14 can be reduced, and introduction of dislocations into the cap layer 14 can be reduced as much as possible.

  The germanium concentration at the interface 17A of the first buffer layer 17 with the iron silicide layer 13 is preferably 50 atomic% to 90 atomic%. Thereby, the lattice mismatch rate between the cap layer 14 and the iron silicide layer 13 can be further reduced, and specifically, the lattice mismatch rate can be reduced to 0% to 2%.

  Further, in order to realize the above-described germanium concentration at the interface 17A, the concentration can be set over the entire thickness direction of the layer, but preferably, a composition gradient is given in the thickness direction of the layer, The concentration of germanium (silicon) may be increased (decreased) toward the interface 17A with the iron silicide layer 13. In this case, the lattice mismatch rate between the first buffer layer 17 and the cap layer 14 made of silicon can be reduced, and the introduction of dislocations into the cap layer 14 can be further reduced.

  The second buffer layer 12 in this example is the same as the buffer layer 12 shown in FIG. 1, and the other substrate 11 and iron silicide layer 13 are the same as those shown in FIG. Therefore, the substrate 11 and the iron silicide layer 13 of this example can be the same as those shown in FIG. 1 and can be formed by the same manufacturing method and manufacturing conditions. Note that the thickness of the first buffer layer 17 is, for example, 20 nm to 2000 nm.

  Further, the optical semiconductor element shown in this example can also be used as a semiconductor light emitting element and a semiconductor light receiving element as in the case shown in FIG.

  The present invention has been described in detail with specific examples. However, the present invention is not limited to the above contents, and various modifications and changes can be made without departing from the scope of the present invention.

It is a block diagram which shows an example of the preferable aspect of the optical semiconductor element which consists of a semiconductor element of this invention. It is a block diagram which shows the other example of the preferable aspect of the optical semiconductor element which consists of a semiconductor element of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,20 Optical semiconductor element 11 Substrate 12 (First) buffer layer 13 Iron silicide layer 14 Cap layer 15, 16 Electrode

Claims (23)

A predetermined substrate;
An iron silicide layer formed on the substrate;
A cap layer made of silicon germanium formed on the iron silicide layer;
A semiconductor device comprising:   2. The semiconductor element according to claim 1, wherein a germanium concentration in the interface with the iron silicide layer in the cap layer is 50 atomic% to 90 atomic%.   In the thickness direction of the cap layer, the germanium concentration increases toward the interface with the iron silicide layer, and the silicon and germanium constituting the cap layer are compositionally inclined in the thickness direction. The semiconductor element according to claim 2.   4. The semiconductor device according to claim 1, further comprising a buffer layer made of silicon germanium between the substrate and the iron silicide layer. 5.   5. The semiconductor element according to claim 4, wherein a germanium concentration in an interface with the iron silicide layer in the buffer layer is 50 atomic% to 90 atomic%.   The germanium concentration increases toward the interface with the iron silicide layer in the thickness direction of the buffer layer, and the silicon and germanium constituting the buffer layer are compositionally inclined in the thickness direction. The semiconductor element according to claim 5. The semiconductor element according to claim 1, wherein the iron silicide layer contains β-FeSi ₂ . A predetermined substrate;
An iron silicide layer formed on the substrate;
A first buffer layer made of silicon germanium formed on the iron silicide layer;
A cap layer made of silicon formed on the first buffer layer;
A semiconductor device comprising:   The semiconductor element according to claim 8, wherein a germanium concentration in the interface with the iron silicide layer in the first buffer layer is 50 atomic% to 90 atomic%.   In the thickness direction of the first buffer layer, the germanium concentration increases toward the interface with the iron silicide layer, and the silicon and germanium constituting the first buffer layer have a composition gradient in the thickness direction. The semiconductor element according to claim 9, wherein the semiconductor element is formed.   11. The semiconductor device according to claim 8, further comprising a second buffer layer made of silicon germanium between the substrate and the iron silicide layer. 11.   The semiconductor element according to claim 11, wherein a germanium concentration in the interface with the iron silicide layer in the second buffer layer is 50 atomic% to 90 atomic%.   In the thickness direction of the second buffer layer, the germanium concentration increases toward the interface with the iron silicide layer, and the silicon and germanium constituting the second buffer layer have a composition gradient in the thickness direction. The semiconductor element according to claim 12, wherein the semiconductor element is formed. The semiconductor element according to claim 8, wherein the iron silicide layer includes β-FeSi ₂ . A predetermined substrate;
An iron silicide layer formed on the substrate;
A cap layer made of silicon made of fine crystal grains having an average grain size of 50 nm or less, formed on the iron silicide layer;
A semiconductor device comprising:   The semiconductor device according to claim 15, further comprising a buffer layer made of silicon germanium between the substrate and the iron silicide layer.   The semiconductor element according to claim 12, wherein a germanium concentration in the interface with the iron silicide layer in the buffer layer is 50 atomic% to 90 atomic%.   The germanium concentration increases toward the interface with the iron silicide layer in the thickness direction of the buffer layer, and the silicon and germanium constituting the buffer layer are compositionally inclined in the thickness direction. The semiconductor element according to claim 17. The semiconductor element according to claim 15, wherein the iron silicide layer includes β-FeSi ₂ .   The semiconductor device according to claim 15, wherein the cap layer is formed by a plasma CVD method.   21. The semiconductor device according to claim 20, wherein the plasma CVD method is an ECR plasma CVD method.   The semiconductor device according to claim 20 or 21, wherein the plasma CVD method is performed in a state in which a bias voltage is not applied to the stacked body including the substrate and the iron silicide layer.   The semiconductor device according to claim 1, wherein the semiconductor device is an optical semiconductor device.

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