JP2007042771A - P-type wide gap semiconductor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a p-type wide gap semiconductor having a new structure. <P>SOLUTION: The p-type wide gap semiconductor has an aligned lamination of a layer 12 formed of a second semiconductor showing the p-type electrical characteristic on the layers 11, 11' formed of a first semiconductor having the forbidden band width of 2.8 eV or more. Here, "aligned lamination" means that the first semiconductor and the second semiconductor are laminated without disturbance in crystal structure of both first and second semiconductors. The p-type wide gap semiconductor has the wide gap near the forbidden band width of the first semiconductor, and also functions as a p-type wide gap semiconductor through injection of holes due to the second semiconductor. As the first semiconductor, ZnO, MgO and mixed crystals of these elements may be used, and as the second semiconductor, Cu<SB>2</SB>O, CuAlO<SB>2</SB>, CuGaO<SB>2</SB>, CulnO<SB>2</SB>may be used having the crystal structure similar to that of the first semiconductor and the mixed crystals of two or three kinds of CuAlO<SB>2</SB>, CuGaO<SB>2</SB>, CulnO<SB>2</SB>. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a p-type wide gap semiconductor having a forbidden bandwidth of 2 eV or more.

  Various light-emitting elements using zinc oxide (ZnO) have been proposed. ZnO is a semiconductor with a wide forbidden band of 3.37 eV and is called a “wide gap semiconductor”. Thereby, the light emitting element using ZnO emits purple light having a wavelength of 365 nm. If such a light-emitting element using ZnO is put into practical use, the price is lower than that of a light-emitting element using gallium nitride (GaN), which is currently in practical use for emitting light of the same wavelength. It is expected that it can be made more efficient and more efficient.

  Patent Document 1 describes a ZnO-based compound semiconductor light emitting device having a semiconductor stacked portion including an n-type semiconductor layer made of a ZnO-based compound and a p-type semiconductor layer also made of a ZnO-based compound. Here, the ZnO-based compound refers to an oxide containing a Group IIA and / or Group IIB element and Zn in addition to ZnO. In the ZnO-based compound, a negative charge is applied so as to maintain electrical neutrality. Therefore, it is difficult to obtain a p-type ZnO-based compound semiconductor simply by injecting an acceptor into a ZnO-based compound.

Patent Documents 2 to 4 describe a production method for obtaining a p-type ZnO-based compound semiconductor.
Among these, Patent Document 2 describes that a crystal of a ZnO-based compound semiconductor containing acceptor impurities is grown while intermittently supplying donor impurities. This document states that this method suppresses lattice defects and provides a p-type ZnO-based compound semiconductor with a high activation rate.
Patent Document 3 describes manufacturing a p-type ZnO semiconductor layer doped with nitrogen atoms by growing a ZnO thin film on a GaN-based thin film in a [0001] direction in a nitrogen atmosphere. According to this document, such a configuration can increase the doping amount of nitrogen atoms and obtain a high-quality crystal.
Patent Document 4 discloses a rapid heat treatment in which a ZnO thin film implanted with P ₂ O ₅ (phosphorus oxide) is heated at a rate of 50 to 100 ° C. per second and held at 600 to 950 ° C. for 1 to 3 minutes. It is described that a p-type ZnO semiconductor can be obtained by performing.

Patent Document 4 discloses a heterostructure in which a light emitting layer made of undoped ZnO into which holes and electrons are not injected is sandwiched between injection layers made of p-type and n-type ZnO-based compound semiconductors, or a heterostructure thereof. Furthermore, a light-emitting element having a double hetero structure sandwiched between injection layers made of other p-type and n-type ZnO-based compound semiconductors is described. In a heterostructure light-emitting element, it is necessary to use p-type and n-type semiconductors having a wider band gap than the semiconductor of the light-emitting layer in the injection layer. Therefore, in Patent Document 4, MgZnO (Mg _x Zn _1-x O (0 <x <1)) whose forbidden band width is 3.4 eV to 4.0 eV is used as such a p-type and n-type semiconductor. .

Japanese Patent Laid-Open No. 2001-044499 ([0020], FIG. 1) JP 2002-289918 A ([0009] to [0012]) Japanese Unexamined Patent Publication No. 2004-304166 ([0011], FIGS. 5 to 6) JP 2005-039172 A ([0024] to [0032])

  Although all of the ZnO-based p-type semiconductors described in Patent Documents 2 to 4 have been devised in various ways, they are the same as conventional ones in that many impurities are added to the ZnO-based compound. Cannot be completely eliminated, and addition of impurities deteriorates the crystal quality. In order to obtain a p-type wide gap semiconductor that is not affected by the self-compensation effect and has excellent crystal quality, it is necessary to realize a ZnO-based p-type semiconductor that does not require addition of impurities.

  An object of the present invention is to provide a p-type wide gap semiconductor having a novel configuration that does not necessarily require addition of impurities. Such a p-type wide gap semiconductor realizes a forbidden bandwidth that is the same as or wider than that of ZnO, which is an n-type semiconductor.

  The p-type wide gap semiconductor according to the present invention, which has been made to solve the above-mentioned problems, is a second layer having p-type electrical characteristics on a layer made of a first semiconductor having a forbidden band width of 2.8 eV or more. These semiconductors are characterized by being laminated in a matched manner.

In the present application, “matched lamination” means that both the first semiconductor and the second semiconductor are laminated without disturbing the crystal structure, particularly in the vicinity of the boundary surface.
“Matched stacking” includes the case where the first semiconductor and the second semiconductor have the same crystal system, and the case where the first semiconductor and the second semiconductor have the same kind of lattice structure even if the crystal systems are different. It is. Here, the “same kind of lattice structure” includes a case where both have a triangular lattice structure or both have a square lattice structure on the surface where the first semiconductor and the second semiconductor are in contact. For example, if either one of the two semiconductors is a hexagonal crystal and the other is a cubic crystal having a face-centered cubic lattice, the atoms are both triangular lattice-shaped on the hexagonal (0001) plane and the (111) plane of the face-centered cubic lattice. Therefore, if the lattice constants of the triangular lattice are close to each other in both semiconductors, both the semiconductors can be matched and laminated without disturbing the crystal structure.

Embodiments and effects of the invention

A wide gap semiconductor having a forbidden band width of 2.8 eV or more is used as the first semiconductor. As this semiconductor, an intrinsic semiconductor or an n-type semiconductor can be used. A p-type semiconductor can also be used as the first semiconductor. In that case, the hole concentration in the semiconductor can be made higher than in the case of using only the p-type semiconductor used for the first semiconductor. Typical examples of the first semiconductor include ZnO and MgO, or MgZnO (Mg _x Zn _1-x O (0 <x <1)) which is a solid solution thereof. ZnO has a hexagonal crystal structure. In addition, MgO often shows a rock salt structure, but when it is formed on a buffer layer made of a material having a lattice constant close to that of ZnO or ZnO and having a hexagonal crystal structure, MgO also has a hexagonal crystal structure. Show. The a-axis lattice constant is 3.249% for ZnO and 4.212% for hexagonal MgO.

A p-type semiconductor is used for the second semiconductor layer. The second semiconductor does not need to have a wider forbidden band as the first semiconductor. For example, any one of Cu ₂ O, CuAlO ₂ , CuGaO _2, and CulnO ₂ can be used for the second semiconductor. Further, for example, as in CuAl _x Ga _1-x O ₂ (0 <x <1), two or three mixed crystals of CuAlO ₂ , CuGaO ₂ , and CulnO ₂ can be used.

Of these second semiconductors, Cu ₂ O has a cubic face-centered cubic lattice. Since the lattice constant of the triangular lattice on the (111) face of Cu ₂ O is 3.01Å and the difference from the lattice constant of the a-axis of ZnO is only -7.4%, Cu ₂ O is on hexagonal crystals such as ZnO. Matched stacking can be performed. The forbidden band width of Cu ₂ O is 2.0 eV, which is smaller than ZnO or the like, but this is not a problem in the present invention.
Note that Cu ₂ O crystals often lack some Cu atoms, but even those having such defects have cubic face-centered cubic lattices and p-type electrical characteristics. As long as it is sufficient, it can be used as the second semiconductor.

CuAlO ₂ , CuGaO ₂ , CulnO _2, or a mixed crystal thereof has a delafossite-type crystal structure having a triangular lattice. The lattice constants of the triangular lattices of CuAlO ₂ , CuGaO ₂ , and CulnO ₂ are 2.857 Å, 2.975 3.2, and 3.292 そ れ ぞ れ, respectively, and the difference between these lattice constants and the lattice constant of the a-axis of ZnO is -12.1%, -8.4, respectively. % And + 1.32%, so these second semiconductors can be stacked in conformity on a hexagonal crystal such as ZnO.

Thus, the laminated body in which the first semiconductor layer and the second semiconductor layer are aligned and laminated has a wide gap close to the forbidden band width of the first semiconductor, and holes are injected by the second semiconductor, Functions as a single p-type wide gap semiconductor. In the present invention, since no impurity is directly added to the first semiconductor having a wide gap, the self-compensation effect does not occur.
In addition, if the second semiconductor layer can be aligned and stacked on the first semiconductor layer, a p-type wide gap semiconductor can be formed regardless of the material of the first semiconductor layer. Therefore, a p-type wide gap semiconductor having a forbidden band width close to ZnO or wider than ZnO can be obtained by matching and laminating the second semiconductor layer on the first semiconductor layer made of MgZnO or MgO.

  As described above, by using a first semiconductor having a forbidden band width of 2.8 eV or more, the p-type wide gap semiconductor of the present invention can obtain a forbidden band width of 2 eV or more. In order to emit ultraviolet light (wavelength of 400 nm or less) in the light emitting element using the p-type wide gap semiconductor, it is desirable that the forbidden band width of the first semiconductor is 3.2 eV or more.

Matching stacking becomes difficult as the second semiconductor layer becomes thicker, and the second semiconductor layer develops its own electrical characteristics, making it impossible to form a wide gap as a whole. Therefore, the second semiconductor layer needs to be thinned to some extent. The appropriate thickness varies depending on the materials of the first semiconductor layer and the second semiconductor layer, but can be determined in advance by theoretical calculation or preliminary experiment. For example, when the calculation was performed for MgO as the first semiconductor and Cu ₂ O as the second semiconductor, if the thickness of the Cu ₂ O layer is about 0.2 nm or less, it is the same as or higher than that of ZnO. It was revealed that a p-type wide gap semiconductor with a large forbidden bandwidth can be obtained. If the thickness of the Cu ₂ O layer is about 0.8 nm or less, a p-type wide gap semiconductor having a forbidden band width of 2.0 eV or more larger than Cu ₂ O can be obtained.

Since the second semiconductor layer cannot be made too thick as described above, the amount of holes that can be injected into the p-type wide gap semiconductor when only one first semiconductor layer and one second semiconductor layer are provided. There is a limit. Therefore, the amount of hole injection can be increased by alternately laminating a plurality of first semiconductor layers and second semiconductor layers (multiple lamination).
When a plurality of first semiconductor layers are used, two or more types of layers made of materials having different forbidden bandwidths may be combined. For example, ZnO can be used for some of the first semiconductor layers, and MgO can be used for the other first semiconductor layers. The forbidden band width of the p-type wide gap semiconductor can be controlled by adjusting the ratio or thickness of the two or more first semiconductor layers.

An atom (acceptor atom for generating holes) for further increasing the hole concentration may be added to the second semiconductor. In addition, acceptor atoms may be added to the first semiconductor in order to generate holes and lower the original electron density. Of course, such acceptor atoms may be added to the first semiconductor at a concentration showing p-type electrical conduction. For example ZnO in the first semiconductor, in the case of using Cu ₂ O in the second semiconductor, the addition of nitrogen atoms on either or both of the ZnO or Cu ₂ O, i.e. ZnO and / or Cu ₂ O A part of the oxygen atom of can be replaced with a nitrogen atom. As a result, electrons of ZnO and / or Cu ₂ O are trapped by nitrogen atoms, thereby generating holes in ZnO and / or Cu ₂ O, so that the hole concentration can be further increased.

  A light emitting element can be formed using the p-type wide gap semiconductor according to the present invention. This light-emitting element has a heterostructure in which a layer made of the p-type wide gap semiconductor of the present invention, a light-emitting layer, and an n-type semiconductor are stacked in this order. Furthermore, a p-type wide gap semiconductor layer and an n-type semiconductor layer are formed from two p-type wide gap semiconductor layers and n-type semiconductor layers made of two different materials, respectively. It can also be formed.

  For the light emitting layer, ZnO or a laminate of ZnO and MgO can be used. In this case, if ZnO, MgO, or MgZnO is used for the p-type wide gap semiconductor, both the light emitting layer and the p-type wide gap semiconductor layer have the same crystal structure, so that both can be reliably bonded. For the same reason, when ZnO or a laminate of ZnO and MgO is used for the light emitting layer, MgZnO can be used for the n-type semiconductor layer.

  Since the light-emitting element according to the present invention uses a p-type wide gap semiconductor having a wide forbidden band similar to that of ZnO or the like used for the light-emitting layer, it can emit blue light or violet light.

An embodiment of a p-type wide gap semiconductor according to the present invention will be described with reference to FIGS.
FIG. 1A is a cross-sectional view of a p-type wide gap semiconductor in which a first semiconductor layer 11 and a second semiconductor layer 12 are stacked. ZnO can be used for the first semiconductor layer 11, and the second semiconductor layer 12 is made of Cu ₂ O, CuAlO ₂ , CuGaO ₂ , CulnO ₂ , and CuAlO ₂ , CuGaO ₂ , and CulnO _2. Any two or three kinds of mixed crystals can be used. In order to enable matching stacking of the first semiconductor layer 11 and the second semiconductor layer 12, the thickness of the second semiconductor layer 12 is sufficiently reduced. For example, when Cu ₂ O is used as the material of the second semiconductor layer 12, it is possible to realize a matching stack sufficiently if the thickness of the second semiconductor layer 12 is 1 nm or less. In the present embodiment, the thickness of the Cu ₂ O layer 12 is about 0.1 nm, and the thickness of the ZnO layer 11 is about 0.2 to ₂ nm, which is thicker than that.

  FIG. 1B shows another embodiment of a p-type wide gap semiconductor. In this embodiment, either MgO or MgZnO is used for the first semiconductor layer 11 '. The same material as the above material can be used for the second semiconductor layer 12. A ZnO buffer layer 13 is provided on the first semiconductor layer 11 ′. By providing the first semiconductor layer 11 ′ on the ZnO buffer layer 13, MgO and MgZnO of the first semiconductor layer 11 ′ have the same hexagonal crystal structure as ZnO.

FIGS. 2A to 2C show examples of p-type wide gap semiconductors having a multiple stacked structure in which first semiconductor layers and second semiconductor layers are stacked alternately and repeatedly. Each of the second semiconductor layers is made of Cu ₂ O. In the p-type wide gap semiconductor 20a shown in (a), the first semiconductor layer 211a, the second semiconductor layer 221, the first semiconductor layer 212a, the second semiconductor layer 222, the first semiconductor layer 213a, the second semiconductor layer 223,. Each layer is stacked in the order. ZnO is used for the material of the first semiconductor layers 211a, 212a, 213a,. In the p-type wide gap semiconductor 20b shown in (b), MgO is used as the material of the first semiconductor layers 211b, 212b, 213b,. In the p-type wide gap semiconductor 20c shown in (c), ZnO is used as the material of the first semiconductor layers 211c, 213c, 215c,..., and MgO is used as the material of the first semiconductor layers 212c, 214c, 216c,. , Respectively. That is, focusing on only the first semiconductor layer in (c), the layers 211c, 213c, 215c,... Made of ZnO and the layers 212c, 214c, 216c,.

The p-type wide gap semiconductor of this example can be manufactured by, for example, a molecular beam epitaxy (MBE) method. Here, the p-type wide gap semiconductor 20a is taken as an example and a manufacturing method thereof is described with reference to FIG. As the substrate, a commercially available sapphire single crystal substrate 33 having the A surface as the surface was used. Sapphire has a hexagonal crystal structure like ZnO, and Al, which is the main component, is arranged on the lattice points of the triangular lattice on the A plane.
First, the sapphire single crystal substrate 33 is heated to 940 ° C. to clean the substrate surface (a). Next, the temperature of the sapphire single crystal substrate 33 is set to 500 ° C., and molecular beams of Zn atoms and O atoms are respectively irradiated onto the substrate to form an LT (low temperature) -ZnO layer 34 (b). Then, heat up to 920 ° C. and anneal (c). Next, while maintaining the substrate temperature at 900 ° C., the ZnO layer 311 is formed by irradiating the LT-ZnO layer 34 with molecular beams of Zn atoms and O atoms, respectively (d). Subsequently, a Cu ₂ O layer 321 is formed by irradiating the ZnO layer 311 with molecular beams of Cu atoms and O atoms (f) while maintaining the substrate temperature (g). Here, when Cu atom supply amount (flux amount) is 1.2 × 10 ⁻⁷ Torr or more and O atom supply amount (O ₂ gas flow rate) is 0.4 sccm or less, impurity CuO is generated. And a layer made of Cu ₂ O can be formed. Thereafter, ZnO layers 312, 313,... And Cu ₂ O layers 322, 323,... Are alternately formed by the same method (h). In addition, the thickness of each layer can be adjusted by controlling the supply rate and supply time of the molecular beam based on the results of preliminary experiments conducted in advance.
Further, even when the substrate temperature was maintained at 700 ° C. in the step (d), the p-type wide gap semiconductor 20a could be manufactured similarly.

  The p-type wide gap semiconductors 20b and 20c can be manufactured by a similar method. In this case, the layer made of MgO (the first semiconductor layers 211b, 212b,... Of the p-type wide gap semiconductor 20b and the first semiconductor layers 212c, 214c,... Of the p-type wide gap semiconductor 20c) has a substrate temperature. Can be formed by irradiating the ZnO layer with molecular beams of Mg atoms and O atoms, respectively, in a state of being fixed between 700 ° C. and 900 ° C.

FIG. 4A shows the result of calculating the forbidden band width of the p-type wide gap semiconductor 20a, and FIG. 4B shows the size of the forbidden bandwidth. The vertical axis of the graph represents the forbidden band width, and the horizontal axis represents the thickness per Cu ₂ O layer. The calculation was performed when the number of stacked ZnO layers or MgO layers was 1, 2, 3, 5, and 20. As a result, in the p-type wide gap semiconductor 20b, the forbidden band width wider than that in the case of ZnO (3.37 eV) can be obtained by setting the thickness per Cu ₂ O layer to about 0.2 nm or less (3.37 eV) ( It was found that the broken line portion in FIG. The forbidden band width of the p-type wide gap semiconductor 20a is narrower than that of ZnO, but is 2.0 eV or more wider than Cu ₂ O by making the thickness per Cu ₂ O layer about 0.8 nm or less. The forbidden band width can be obtained (FIG. 4A, broken line portion).

FIG. 5 shows the result of measuring the light transmittance of the p-type wide gap semiconductors 20a and 20b. The forbidden bandwidth estimated from this transmittance is 1.8 eV for the p-type wide gap semiconductor 20a and 3.0 eV for the p-type wide gap semiconductor 20b.
In addition, as a result of measuring the electrical resistivity of the p-type wide-gap semiconductor 20b, was 10 ⁴ Ωcm.

FIG. 6 shows an embodiment of a light emitting device according to the present invention. The light emitting element 40a has a charge between a layer 41 made of the p-type wide gap semiconductor 20c of this embodiment and a layer 42 made of Mg _x Zn _1-x O (0 <x <1) which is an n-type semiconductor. A light emitting layer 43 made of ZnO into which no silicon ions are implanted is arranged, and a pair of electrodes 44 and 45 are arranged so as to sandwich a laminated body made of these layers 41 to 43. Here, the p-type wide gap semiconductor layer 41 has a forbidden band width determined by the thickness of the Cu ₂ O layer (second semiconductor layer) wider than the forbidden band width of ZnO that is the light emitting layer 43 (wider than 3.37 eV). ) Is used.
When a voltage is applied between the electrode 44 and the electrode 45 such that the electrode 44 (p-type wide gap semiconductor layer 41) side is positive and the electrode 45 (n-type semiconductor layer 42) side is negative, the p-type wide gap semiconductor layer 41 is positive. In the holes, electrons are injected from the n-type semiconductor layer 42 into the light emitting layer 43, and the holes and electrons recombine to obtain purple light emission.

Sectional drawing which shows one Example of the p-type wide gap semiconductor based on this invention. Sectional drawing which shows the Example of the p-type wide gap semiconductor which has the multiple laminated structure concerning this invention. Sectional drawing which shows one Example of the manufacturing method of the p-type wide gap semiconductor which has the multiple laminated structure concerning this invention. Graph showing the results of the forbidden band width was calculated the p-type wide gap semiconductor of the present embodiment (ZnO / Cu ₂ O semiconductor and MgO / Cu ₂ O Semiconductor). Graph showing the result of the transmittance of light was measured for ZnO / Cu ₂ O semiconductor and MgO / Cu ₂ O semiconductor of the present embodiment. Sectional drawing which shows the Example of the light emitting element which concerns on this invention.

Explanation of symbols

11 ... 1st semiconductor layer (ZnO layer)
11 '... 1st semiconductor layer (MgO layer or MgZnO layer)
12, 22 ... second semiconductor layer (Cu ₂ O layer)
13 ... ZnO buffer layers 20a, 20b, 20c ... p-type wide gap semiconductors 211a, 212a, 213a, ...... first semiconductor layer (ZnO layer)
211b, 212b, 213b, .... First semiconductor layer (MgO layer)
211c, 213c, 215c, .... First semiconductor layer (ZnO layer)
212c, 214c, 216c, .... First semiconductor layer (MgO layer)
311, 312 ... ZnO layers 321, 322 ... Cu ₂ O layer 33 ... sapphire single crystal substrate 34 ... LT-ZnO layer 40a ... light emitting element 41 ... p-type wide gap semiconductor layer 42 ... n-type semiconductor layer 43 ... light emitting layer 44, 45 ... Electrode

Claims (10)

  A p-type wide gap semiconductor characterized in that a second semiconductor exhibiting p-type electrical characteristics is laminated on a layer made of a first semiconductor having a forbidden band width of 2.8 eV or more. 2. The p-type wide gap semiconductor according to claim 1, wherein the first semiconductor layer is made of any one of ZnO, MgO, and Mg _x Zn _1-x O (0 <x <1). The second semiconductor layer is made of any one of Cu ₂ O, CuAlO ₂ , CuGaO ₂ , CulnO ₂ , and CuAlO ₂ , CuGaO ₂ , and CulnO _2. The p-type wide gap semiconductor according to claim 1, wherein the p-type wide gap semiconductor is formed.   The p-type wide gap semiconductor according to claim 1, wherein a plurality of first semiconductor layers and second semiconductor layers are alternately stacked.   5. The p-type wide gap semiconductor according to claim 4, comprising two or more types of first semiconductor layers made of materials having different forbidden bandwidths.   6. The p-type wide gap semiconductor according to claim 5, comprising two kinds of first semiconductor layers of ZnO and MgO.   The p-type wide gap semiconductor according to claim 1, wherein acceptor atoms for generating holes are added to the first semiconductor layer and / or the second semiconductor layer.   A light emitting device comprising: a layer made of the p-type wide gap semiconductor according to claim 1, a light emitting layer, and an n type semiconductor layer, which are laminated in this order.   The light emitting device according to claim 8, wherein the light emitting layer is made of ZnO or a laminate of ZnO and MgO. The light emitting device according to claim 9, wherein the n-type semiconductor layer is made of Mg _x Zn _1-x O (0 <x <1).

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