JP2006024582A - Semiconductor device, semiconductor layer and its production process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that an environment-proof semiconductor device utilizing boron phosphide (BP) and BP based mixed crystal cannot be provided because a process for forming a BP crystal layer having a band gap around 3 eV is not disclosed. <P>SOLUTION: The semiconductor device comprising a boron phosphide (BP) layer having a band gap of 2.8-3.4 eV under room temperature or a boron phosphide (BP) based mixed crystal layer represented by general formula B<SB>α</SB>Al<SB>β</SB>Ga<SB>γ</SB>In<SB>1-α-β-γ</SB>P<SB>δ</SB>As<SB>ε</SB>N<SB>1-δ-ε</SB>(0<α≤1, 0≤β<1, 0≤γ<1, 0<α+β+γ≤1, 0<δ≤1, 0≤ε<1, 0<δ+ε≤1) containing that boron phosphide is produced using vapor phase epitaxial growth method. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention provides a boron phosphide (BP) layer having a forbidden band width at room temperature of 2.8 electron volts (eV) or more and 3.4 eV or less, or a general formula B containing the boron phosphide._αAl_βGa_γIn_{1- α - β - γ}P_δAs_εN_{1- δ - ε}Boron phosphide represented by (0 <α ≦ 1, 0 ≦ β <1, 0 ≦ γ <1, 0 <α + β + γ ≦ 1, 0 <δ ≦ 1, 0 ≦ ε <1, 0 <δ + ε ≦ 1) The present invention relates to a (BP) mixed crystal layer, a semiconductor element including the BP layer or the BP mixed crystal layer, and a method for manufacturing the BP layer or the BP mixed crystal layer.
[0002]
[Prior art]
Examples of III-V compound semiconductors composed of boron (B) belonging to group III of the periodic table and group V elements include boron nitride (BN), boron phosphide (BP), and boron arsenide (BAs). For example, hexagonal boron nitride (BN) is an indirect transition semiconductor with a band gap of 7.5 electron volts (eV) at room temperature (Satoru Teramoto, “Introduction to Semiconductor Devices” (( (See page 28, Baifukan Co., Ltd., first published on March 30, 1995, page 28.) Boron arsenide (BAs) is an indirect transition group III-V compound with a forbidden band width of about 0.85 eV at room temperature. Is known (see "Introduction to Semiconductor Devices" above).
[0003]
On the other hand, boron phosphide (BP) is a kind of group III-V compound semiconductor (see Nature, 179 (No. 4569) (1957), page 1075), and several types of forbidden bands of indirect transition type semiconductors. The value of is reported. For example, B.I. Stone et al. Obtained a room-temperature band gap of about 6 eV for a polycrystalline BP film deposited on a quartz plate by an optical absorption method (Phys. Rev. Lett., Vol. 4, No. 6 (1960). ), Pages 282-284). In addition, in J. L. According to Peret, the forbidden bandwidth of BP is summarized as 6.0 eV (see J. Am. Ceramic Soc., 47 (1) (1964), pages 44 to 46). N. Sclar gave 6.20 eV as the forbidden band width at absolute zero (= 0 K) based on the ionic radius value and the shared radius value (J. Appl. Phys., 33 (10) (1962), 2999-3002). According to Manca, a forbidden bandwidth of 4.2 eV is proposed (see J. Phys. Chem. Solids, 20 (1961), pages 268-273).
[0004]
On the other hand, R.I. J. et al. Archer et al. Obtained 2 eV as a room-temperature band gap of cubic BP from a single crystal BP grown from a nickel phosphide melt (Phys. Rev. Lett., 12 (19) (1964). ) See pages 538-540). In addition, a band gap of 2.1 eV is given by theoretical calculation based on the binding energy value (see J. Appl. Phys., 36 (1965), pages 330 to 331). Although there is a large difference in the forbidden band width of boron phosphide (BP) as described above (see J. Phys. Chem. Solids, 29 (1968), pages 1025 to 1032), the forbidden band width of BP is about 2 eV. (1) RCA Review, 25 (1964), pages 159 to 167, (2) Z. anorg.allg.chem., 349 (1967), pages 151 to 157 , (3) J. Appl. Phys., 36 (1965), (5) "Semiconductor device overview", and (6) Akazaki Isao, "III-V group compound semiconductor" (Baifukan Co., Ltd.) , May 20, 1994, first edition, page 150).
[0005]
Boron phosphide (BP) and composition formula B_XAl_YGa_1-XYN_1-ZP_ZA BP mixed crystal represented by (0 <X ≦ 1, 0 ≦ Y <1, 0 ≦ X + Y ≦ 1, 0 <Z ≦ 1) is used as a functional layer constituting a semiconductor light emitting element. For example, a single layer (single layer) made of BP is in a short wavelength visible light emitting diode (LED) or a laser diode (LD), and there is a conventional example used for forming a buffer layer (Japanese Patent Laid-Open No. 2-275682). ). BP single layer and B_XAl_YGa_1-XYN_1-ZP_ZAn example in which a light emitting portion of a pn junction type heterojunction structure is formed from a superlattice structure with a mixed crystal single layer is known (see Japanese Patent Laid-Open No. 10-242514). B_XAl_YGa_1-XYN_1-ZP_ZThere is a technique for forming a clad (barrier) layer from a superlattice structure with a mixed crystal single layer (see Japanese Patent Laid-Open No. 2-288371). Boron phosphide (BP) having a forbidden band width of 2 eV at room temperature cannot exert a barrier effect on the light emitting layer. Therefore, in the above-described conventional example, BP and aluminum nitride (AlN) are mixed. A nitrogen-containing mixed crystal layer that has been crystallized to increase the room temperature forbidden band width to, for example, 2.7 eV is used (see the above-mentioned JP-A-2-288371).
[0006]
In addition, an example in which a heterobipolar transistor (HBT) is configured using a BP single layer is known (see J. Electrochem. Soc., 125 (4) (1978), pages 633 to 637). This conventional HBT includes diborane (B₂H₆) / Phosphine (PH_ThreeBP single layer grown on a silicon (Si) crystal substrate having a (100) plane by means of a system vapor deposition method and having a forbidden band width of 2.0 eV is used (see J. Electrochem. Soc described above). , 125 (1978)). Further, a technique for constructing a solar cell using a BP single layer having a forbidden band width of 2.0 eV as a window layer is disclosed (the above-mentioned J. Electrochem. Soc., 125 (1978)). reference).
[0007]
As described above, conventionally, a semiconductor element has been composed of boron phosphide (BP) having a forbidden band width of about 2 eV or a mixed crystal containing BP having the forbidden band width. In the above solar cell configured with Si as a base material having a room temperature forbidden band width of 1.1 eV, even in a BP layer having a forbidden band width of 2.0 eV, the forbidden band width is larger than that of the base Si. Therefore, it is disclosed that it can be effectively used as a window layer (see J. Electrochem. Soc., 125 (1978) above). On the other hand, however, it has been reported that the forbidden bandwidth is narrowed depending on the plane orientation of the Si single crystal used as the substrate in the prior art for forming the BP layer using Si as the substrate (Akira Nishinaga, “Applied Physics” 45, No. 9 (1976), pages 891-897). Compared to a BP layer formed on a Si substrate having a (100) plane, it is formed on a Si substrate having a (111) plane because it has a higher surface defect density on the Si substrate having a (111) plane. The BP layer has been reported to be opaque (see "Applied Physics" above, pages 895-896).
[0008]
In addition, it is reported that the lattice constant becomes large due to the large amount of surface defects, and the band gap becomes narrower (see “Applied Physics”, page 896). It has been known that there is a correlation between the lattice constant and the forbidden band width from the past, and it is well known that the forbidden band width increases as the lattice constant decreases (the above-mentioned “III-V”). Group compound semiconductor ”, page 31). That is, according to the conventional research example, it is taught that a BP layer having a band gap smaller than about 2 eV, which is used as a BP forbidden band width, is resulted depending on the formation condition of the BP layer. ing. Due to the low forbidden band width, there has been a drawback that it is not possible to simply construct a high-voltage environment-resistant semiconductor element from a boron phosphide (BP) crystal layer.
[0009]
[Problems to be solved by the invention]
For example, a light-emitting layer having a room temperature forbidden band width of 2.8 eV is used for a heterojunction blue LED or LD having an emission wavelength of 450 nanometers (nm) at room temperature. Further, in order to exert a clad action on the light emitting layer, it is necessary to form the barrier layer from a semiconductor material having a room temperature forbidden band of at least about 2.8 eV. For this reason, when forming a heterojunction light emitting portion of a conventional boron phosphide (BP) -based light emitting device, there is a drawback that a cladding layer cannot be formed from boron phosphide (BP) having a room temperature forbidden band width of about 2 eV. It was. Therefore, a mixed crystal containing BP is formed as described above, for example, B_XAl_YGa_1-XYN_1-ZP_ZConventionally, a barrier layer having a high forbidden band width as a multi-element mixed crystal has been used (see the above-mentioned JP-A-2-288371). However, it is well known that advanced techniques are required for mixed crystals with a large number of constituent elements, control of the composition ratio of constituent elements, etc., and it becomes more difficult to obtain a good quality crystal layer (see above). (See "Introduction to Semiconductor Devices", page 24). Therefore, conventionally, there has been a problem in the film formation technology that the BP mixed crystal layer as the barrier layer cannot be easily formed.
[0010]
Further, for example, in a conventional npn type HBT, a BP layer having a forbidden band width of 2.0 eV is used as an n-type emitter (the above-mentioned J. Electrochem. Soc., 125 (1978)). On the other hand, a p-type Si layer is used for the p-type base layer (see J. Electrochem. Soc., 125 (1978) above). The band gap of Si is about 1.1 eV, so the difference in band gap between the heterojunction structures of the BP emitter layer and the Si base layer is only 0.9 eV. If the emitter layer is composed of a BP layer that has a larger difference in the forbidden band width from the base layer than before, leakage of the base current from the base layer to the emitter layer is further suppressed, and the current transmission rate (= emitter current / The collector current characteristics are improved (see the above edited by Isao Akasaki, “III-V Group Compound Semiconductor”, pages 239 to 242), and it is thought that an HBT having excellent characteristics is brought about.
[0011]
Zinc blend crystal type, more precisely cubic zinc sulfide type (spherlite) (by Phillips, "Semiconductor Bonding Theory" (Yoshioka Shoten, July 25, 1985, 3rd edition), The lattice constant of boron phosphide (BP) single crystal which is 14 to 15) is 4.538４．５ (see “Introduction to Semiconductor Devices”, page 28). On the other hand, cubic gallium nitride mixed crystal (composition formula) GaN with a nitrogen (N) composition ratio of 0.97_0.97P_0.03Or gallium nitride / indium Ga with an indium (In) composition ratio of 0.10_0.90In_0.10There is a group III nitride semiconductor having a lattice constant of 4.538 の such as N. Accordingly, if a BP layer and a group III nitride semiconductor as described above are used, for example, a lattice-matched stacked two-dimensional electron field effect transistor (TEGFET) (K) that has an advantage in manifesting high electron mobility. By Sieger, "Semiconductor Physics (Part 2)" (see Yoshioka Shoten Co., Ltd., June 25, 1991, first edition, pages 352 to 353). A TEGFET can be formed by using a group nitride semiconductor as a two-dimensional electron (TEG) electron transit layer and using an indirect transition type BP layer as a spacer layer or an electron supply layer. In the TEGFET, the spacer layer or the electron supply layer that is hetero (heterogeneous) bonded to the electron transit layer is composed of boron phosphide (BP) that has a larger forbidden band width than before. Therefore, the barrier difference at the heterojunction interface with the electron transit layer can be increased, which is advantageous for accumulating two-dimensional electrons in the region in the electron transit layer near the heterojunction interface, and high electron mobility. A group III nitride semiconductor TEGFET exhibiting a high degree of temperature can be provided.
[0012]
If a BP layer having a large room temperature forbidden band width can be used, the discontinuity of conduction band with other semiconductor layers can be further increased. A heterojunction structure having a large band discontinuity and a large barrier difference can efficiently accumulate two-dimensional electrons, and is effective in developing high electron mobility. If a structure having a large electron mobility is used in a Hall element which is a magnetoelectric conversion element, it is advantageous to obtain an element having higher sensitivity to magnetism (Akiei Kataoka, “Magnetoelectric Conversion Element”). (Refer to Nikkan Kogyo Shimbun Co., Ltd., issued on February 1, 1986, 4th printing, pages 56-58.) Therefore, the realization of a heterojunction structure having a BP layer with a forbidden band width larger than before is It is expected to contribute to the construction of a high-sensitivity Hall element that exhibits high product sensitivity (refer to the above-mentioned “magnetoelectric conversion element”, page 56).
[0013]
Further, for example, in a Schottky barrier diode using a Si single crystal as a substrate, if a BP layer having a room temperature forbidden band exceeding about 2 eV can be formed, a Schottky barrier diode having high withstand voltage is provided. Can contribute to the composition of The larger the forbidden band width, the lower the intrinsic carrier density in the material properties of the semiconductor (see the above “III-V group compound semiconductor”, pages 172 to 174). It is thought that it will be superior to the construction of the environment-resistant element.
[0014]
As in the above-described conventional example, it is usual that a semiconductor element is configured using a BP layer having a forbidden band width of about 2 eV. If a BP layer having a larger forbidden band width can be formed, it is conceivable that improvement and improvement of semiconductor element characteristics can be achieved. In past research examples, there is also known an example in which a BP layer having a high forbidden band width of about 6 eV is formed as described above (see Phys. Rev. Lett., 4 (6) (1960) above). However, this is a polycrystalline layer and is not necessarily suitable for forming an active layer or a functional layer of a semiconductor element. However, in a wide gap semiconductor having such a large forbidden band width, it is difficult to control the conductivity type and the carrier density by impurity doping. A BP crystal layer having a room temperature forbidden band width of about 3 eV is suitable for constituting a functional layer of a semiconductor element such as a spacer layer in TEGFET, an electron supply layer, or an emitter layer in HBT.
[0015]
According to past studies on the forbidden band width of compound semiconductors, it is known that the forbidden band width tends to become larger when the average atomic number of the constituent elements becomes smaller (Kazuo Fueki et al., “Applied Chemistry Series”). 3 “Chemistry of Electronic Materials” (Maruzen Co., Ltd., issued on July 20, 1981), pages 26-29). The average atomic number is an arithmetic average value of atomic numbers of elements constituting the compound semiconductor. FIG. 1 shows the relationship between the forbidden band width and the average atomic number of various III-V compound semiconductors at room temperature. For example, the room temperature band gap of gallium arsenide (GaAs) (average atomic number = 32) composed of gallium (Ga) (atomic number = 31) and arsenic (atomic number = 33) is 1.43 eV. (See “Introduction to Semiconductor Devices” above, page 28). On the other hand, gallium phosphide (GaP) (average atomic number = 23) having an average atomic number smaller than that of GaAs has a large room-temperature band gap of 2.26 eV (see “Overview of Semiconductor Devices” on page 28 above). ). This relationship is also applicable to II-VI group compound semiconductors, and it is taught that the band gap tends to increase as the average atomic number of the constituent atoms decreases (see “Physics of Semiconductors” by K. Sieger). Gaku (above) "(Yoshioka Shoten Co., Ltd., June 10, 1991, first print), see page 36).
[0016]
From the tendency of the room temperature forbidden band width related to the average atomic number, it is said that the forbidden band width of a III-V group compound semiconductor having a relatively large ionic bond can be estimated. Assuming that this tendency is small in the difference in electronegativity between constituent elements and is applicable to BP crystals having strong covalent bonds, the band gap of the BP single crystal layer is estimated to be about 3 eV. . Also, according to the “dielectric method” proposed by VanVechten (1) JA Van Vechten, Phys. Rev. Lett., 182 (1969, 891.) and 2) Akasaki Akira, “ Group III nitride semiconductor "(Baifukan Co., Ltd., first published on December 8, 1999, pages 19 to 21), the band gap of the BP single crystal is calculated to be 2.98 eV. In the calculation, the lattice constants of carbon (diamond) (C) and silicon (Si) single crystals are 3.567Å and 4.531Å, respectively, and the closest interatomic distances of C (diamond) and Si are respectively 1.54 and 2.34 (refer to “Basic Manual of Chemical Handbook” (Maruzen Co., Ltd., issued on August 20, 1970, 3rd edition), page 1259) Other values required for calculation Is the suggested value (See “Group III nitride semiconductor” above, pages 20-21).
[0017]
Currently, boron phosphide (BP) having a room temperature forbidden band width of about 3 eV and a boron phosphide (BP) mixed crystal including the BP crystal in a single layer that is convenient for such a semiconductor device configuration. It has not been disclosed. This is because the formation method of the BP crystal layer having excellent crystallinity is not clear. That is, when forming a semiconductor element, a formation method for producing a BP mixed crystal having a suitable forbidden band width is not clear. In order to improve the characteristics of a semiconductor device using a BP crystal layer, it is necessary to create a method for forming a BP crystal layer with a forbidden band width of about 3 eV. However, although a BP crystal layer is conventionally formed using a vapor phase growth method or the like, a method for forming a BP crystal layer that provides a forbidden band width of about 3 eV has not been disclosed yet. The present invention has been made against the background of the prior art described above, and a boron phosphide (BP) layer having a forbidden band width at room temperature of 2.8 electron volts (eV) or more and 3.4 eV or less, or phosphation thereof. General formula B containing boron_αAl_βGa_γIn_{1- α - β - γ}P_δAs_εN_{1- δ - ε}Boron phosphide represented by (0 <α ≦ 1, 0 ≦ β <1, 0 ≦ γ <1, 0 <α + β + γ ≦ 1, 0 <δ ≦ 1, 0 ≦ ε <1, 0 <δ + ε ≦ 1) The structure of the (BP) mixed crystal layer, the semiconductor device including the BP layer or the BP mixed crystal layer, and the manufacturing method of the BP layer or the BP mixed crystal layer is clarified, and the semiconductor device characteristics are improved and improved. An object of the present invention is to provide a semiconductor device to be achieved, a semiconductor layer therefor, and a manufacturing method thereof.
[0018]
[Means for Solving the Problems]
That is, the present invention
(1) A semiconductor element comprising a semiconductor layer made of boron phosphide (BP) having a forbidden band width at room temperature of 2.8 electron volts (eV) to 3.4 eV.
(2) The semiconductor element according to (1), comprising a heterojunction between a semiconductor layer made of boron phosphide (BP) and another semiconductor layer having a different band gap from the semiconductor layer.
(3) The semiconductor element according to (2), wherein the semiconductor layer made of boron phosphide (BP) and the semiconductor layer forming a heterojunction with the semiconductor layer are lattice-matched.
(4) The semiconductor layer forming a heterojunction with the semiconductor layer made of boron phosphide (BP) is GaN._0.97P_0.03(3) The semiconductor element according to (3).
(5) The semiconductor element according to any one of (1) to (4), wherein a semiconductor layer made of boron phosphide (BP) is stacked on a crystal substrate.
It is.
[0019]
The present invention also provides
(6) General formula B including boron phosphide (BP) having a forbidden band width at room temperature of 2.8 electron volts (eV) to 3.4 eV._αAl_βGa_γIn_{1- α - β - γ}P_δAs_εN_{1- δ - ε}Boron phosphide represented by (0 <α ≦ 1, 0 ≦ β <1, 0 ≦ γ <1, 0 <α + β + γ ≦ 1, 0 <δ ≦ 1, 0 ≦ ε <1, 0 <δ + ε ≦ 1) (BP) A semiconductor element comprising a semiconductor layer made of a mixed crystal.
(7) Boron phosphide (BP) mixed crystal is an aluminum phosphide / boron mixed crystal (B_XAl_1-XP: 0 <X <1), gallium phosphide / boron mixed crystal (B_XGa_1-XP: 0 <X <1) or indium phosphide / boron mixed crystal (B_XIn_1-XThe semiconductor element according to (6), wherein P: 0 <X <1).
(8) A semiconductor layer comprising a boron phosphide (BP) mixed crystal and a heterojunction between the semiconductor layer and another semiconductor layer having a different forbidden band width (6) or (7) The semiconductor element as described in.
(9) The semiconductor element according to (8), wherein the semiconductor layer formed of a boron phosphide (BP) -based mixed crystal and the semiconductor layer forming a heterojunction with the semiconductor layer are lattice-matched.
(10) The semiconductor element according to any one of (6) to (9), wherein a semiconductor layer made of a boron phosphide (BP) mixed crystal is stacked on a crystal substrate.
It is.
[0020]
The present invention also provides
(11) The semiconductor element according to any one of (1) to (10), wherein the semiconductor element has a pn junction structure.
(12) The semiconductor element according to (11), which is a light emitting element.
(13) The semiconductor element according to any one of (1) to (10), wherein the semiconductor element is a light receiving element.
(14) The semiconductor element according to any one of (1) to (10), which is a transistor.
(15) The semiconductor device as described in (14), which is a field effect transistor (FET).
(16) The semiconductor element according to (14), which is a heterobipolar transistor (HBT).
(17) The semiconductor element according to any one of (1) to (10), which is a Hall element.
It is.
[0021]
The present invention also provides
(18) A semiconductor layer made of boron phosphide (BP) whose forbidden band width at room temperature is 2.8 electron volts (eV) or more and 3.4 eV or less.
(19) The semiconductor layer according to (18), wherein a semiconductor layer made of boron phosphide (BP) is stacked on a crystal substrate.
(20) General formula B including boron phosphide (BP) whose forbidden band width at room temperature is 2.8 electron volts (eV) or more and 3.4 eV or less_αAl_βGa_γIn_{1- α - β - γ}P_δAs_εN_{1- δ - ε}Boron phosphide represented by (0 <α ≦ 1, 0 ≦ β <1, 0 ≦ γ <1, 0 <α + β + γ ≦ 1, 0 <δ ≦ 1, 0 ≦ ε <1, 0 <δ + ε ≦ 1) (BP) A semiconductor layer made of a mixed crystal.
(21) The boron phosphide (BP) mixed crystal is an aluminum phosphide / boron mixed crystal (B_XAl_1-XP: 0 <X <1), gallium phosphide / boron mixed crystal (B_XGa_1-XP: 0 <X <1) or indium phosphide / boron mixed crystal (B_XIn_1-XThe semiconductor layer according to (20), wherein P: 0 <X <1).
(22) The semiconductor layer according to (20) or (21), wherein a semiconductor layer made of a boron phosphide (BP) -based mixed crystal is laminated on a crystal substrate.
It is.
[0022]
The present invention also provides
(23) The method for growing a semiconductor layer according to any one of (18) to (22), wherein the semiconductor layer is grown by a vapor phase growth method.
(24) The method for growing a semiconductor layer according to (23), wherein the semiconductor layer is grown at a temperature higher than 750 ° C. and not higher than 1200 ° C.
(25) The method for growing a semiconductor layer according to (23) or (24), wherein the vapor phase growth method is a metal organic chemical vapor deposition method (MOCVD method).
(26) The ratio of the total supply amount of the group V element source containing phosphorus (P) to the total supply amount of the group III element source containing boron (B) during the growth of the semiconductor layer is 15 or more and 60 or less. The method for growing a semiconductor layer according to (25), wherein the growth rate of the semiconductor layer is 20 to 300 mm / min.
It is.
[0023]
The present invention also provides
(27) A buffer layer composed of amorphous boron phosphide (BP) or boron phosphide (BP) based mixed crystal is formed on a crystal substrate by a MOCVD method at a temperature of 250 ° C. to 750 ° C. A method for growing a semiconductor layer, comprising growing a semiconductor layer made of boron phosphide (BP) having a forbidden band width at room temperature of 2.8 electron volts (eV) to 3.4 eV on the buffer layer.
(28) A buffer layer made of amorphous boron phosphide (BP) or boron phosphide (BP) mixed crystal is formed on the crystal substrate by MOCVD at a temperature of 250 ° C. or higher and 750 ° C. or lower. And B containing boron phosphide (BP) having a forbidden band width of 2.8 electron volts (eV) or more and 3.4 eV or less on the buffer layer._αAl_βGa_γIn_{1- α - β - γ}P_δAs_εN_{1- δ - ε}Boron phosphide represented by (0 <α ≦ 1, 0 ≦ β <1, 0 ≦ γ <1, 0 <α + β + γ ≦ 1, 0 <δ ≦ 1, 0 ≦ ε <1, 0 <δ + ε ≦ 1) (BP) A semiconductor layer growth method for growing a semiconductor layer made of a mixed crystal.
(29) Boron phosphide (BP) mixed crystal is an aluminum phosphide / boron mixed crystal (B_XAl_1-XP: 0 <X <1), gallium phosphide / boron mixed crystal (B_XGa_1-XP: 0 <X <1) or indium phosphide / boron mixed crystal (B_XIn_1-XThe method for growing a semiconductor layer according to (28), wherein P: 0 <X <1).
(30) The method for growing a semiconductor layer according to any one of (27) to (29), wherein the semiconductor layer is grown at a temperature higher than 750 ° C. and not higher than 1200 ° C. by a vapor phase growth method.
(31) The method for growing a semiconductor layer according to any one of (27) to (30), wherein the semiconductor layer is grown by an MOCVD method.
It is.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
The semiconductor element having a semiconductor layer made of boron phosphide (BP) or boron phosphide (BP) mixed crystal of the present invention includes, for example, silicon (silicon), gallium phosphide (GaP), gallium arsenide (GaAs), and the like. The semiconductor single crystal can be configured as a substrate. For example, in the case of an LED, LD, or light receiving element, if these semiconductor single crystals having conductivity are used as a substrate, the electrodes can be easily arranged, so that there is an advantage that the element can be configured easily as a light emitting / receiving element. . Silicon (Si single crystal), which has a higher melting point than Group III-V compound semiconductors, can be suitably used as a substrate crystal because it has heat resistance even at an epitaxial growth temperature around 1000 ° C. Further, even when various elements are integrated, it can be suitably used as a substrate. Sapphire (α-Al₂O_ThreeAn oxide single crystal such as a single crystal exhibits, for example, an effect of preventing leakage of element operating current due to its electrical insulation. For this reason, it can be preferably used, for example, for field effect transistor (FET) applications in which the amount of drain current leakage is suppressed. In addition, diamond or silicon carbide (SiC) has a relatively high thermal conductivity, and therefore is particularly suitable as a substrate for power FETs that require cooling of the element.
[0025]
The surface orientation suitable for the substrate is a low order mirror index surface such as {100}, {110} or {111}. An Si single crystal having a surface inclined at an angle in the range of several degrees to several tens of degrees from these low mirror index surfaces can also be used as a substrate. In the {111} crystal plane of a zinc-blend type crystal such as Si, GaP, or GaAs, atoms constituting the crystal are denser than the {100} crystal plane. For this reason, this is effective in suppressing diffusion and penetration of atoms constituting the epitaxial growth layer into the substrate. Single crystals having higher-order Miller index planes such as {311} and {511} are also channeled (RG WILSON and GR BREWER, “ION BEAMS With Application to Ion Implantation” (John Wiley & Sons, Inc., 1973), see pages 263 to 265), which is effective in suppressing the intrusion of the growth layer constituent elements into the single crystal substrate. However, reflecting the plane orientation of the substrate surface, the growth orientation of the upper epitaxial growth layer is also higher, which may cause inconveniences such as complicated cutting into individual elements.
[0026]
A semiconductor element comprising a semiconductor layer made of boron phosphide (BP) according to the present invention is characterized by comprising a boron phosphide (BP) semiconductor layer having a specific band gap. In addition, a semiconductor element including a semiconductor layer composed of a boron phosphide (BP) mixed crystal according to the present invention includes a BP mixed crystal including a BP having a specific band gap. It is said. The BP mixed crystal layer is a III-V group compound semiconductor mixed crystal containing boron (B) and phosphorus (P) as constituent elements. For example, the general formula B_αAl_βGa_γIn_{1- α - β - γ}P_δAs_εN_{1- δ - ε}(0 <α ≦ 1, 0 ≦ β <1, 0 ≦ γ <1, 0 <α + β + γ ≦ 1, 0 <δ ≦ 1, 0 ≦ ε <1, 0 <δ + ε ≦ 1) is there. More specifically, aluminum phosphide and boron (B_XAl_1-XP: 0 ≦ X ≦ 1), gallium phosphide / boron (B_XGa_1-XP: 0 ≦ X ≦ 1) and indium phosphide / boron (B_XIn_1-XP: 0 ≦ X ≦ 1) Mixed crystal. Boron nitride phosphide (BP_YN_1-Y: 0 <Y ≦ 1) and boron arsenide (BP)_YAs_1-Y: 0 <Y ≦ 1) or boron phosphide / gallium (B_XGa_1-XP_YAs_1-Y: 0 <X ≦ 1, 0 <Y ≦ 1).
[0027]
The mechanical or electrical specifications of boron phosphide (BP) or BP mixed crystal layer are appropriately selected depending on the device. In the electron supply layer of an n-channel TEGFET having an n-type electron transit layer, for example, the layer thickness is set to about 10 nm to about 50 nm, and the carrier concentration is set to about 1 × 10 10.¹⁸cm^-3~ About 5 × 10¹⁸cm^-3An n-type BP layer is used. In a light emitting diode (LED), a window layer for efficiently extracting emitted light to the outside is an n-type or a p-type corresponding to the conductivity type of the underlayer with the cladding layer, for example, , About 1 × 10¹⁸cm^-3It is composed of a highly conductive BP layer or BP mixed crystal layer exceeding the above. In the laser diode (LD), the current confinement layer is composed of a conductive layer having a conductivity type opposite to that of the underlayer such as the upper clad layer, or a high resistance BP or BP mixed crystal layer. The boron phosphide (BP) binary semiconductor is an in-direct transition type semiconductor (see “Semiconductor Device Overview” above, page 28). On the other hand, BP has a small ionic bond of Philips (0.006) (see "Semiconductor Bonding Theory" above, pages 49-51). Therefore, it is easy to obtain a BP crystal layer having a high electrical activation rate of a dopant, a high carrier concentration, and a low resistance. In the present invention, such a low-resistance BP layer is preferably used as, for example, an LED current diffusion layer and an LD or FET ohmic contact layer to constitute a BP-based semiconductor element. Further, in a BP-based semiconductor element that requires a conductive buffer layer, it is preferably used to construct a conductive buffer layer.
[0028]
The BP crystal layer and the BP mixed crystal layer according to the present invention may be formed by, for example, a well-known metal organic chemical vapor deposition (MOCVD) method (Inst. Phys. Conf. Ser., No. 129 (IOP Publishing Ltd., 1993), pp. 157-162), molecular beam epitaxy (MBE) method (see J. Solid State Chem., 133 (1997), pp. 269-272), halide method, hydride method, etc. It is grown by the vapor phase growth method. The metalorganic chemical vapor deposition method is a one-vapor deposition method using an organic compound of boron (B) as a boron (B) source. In the MOCVD method, for example, boron phosphide / gallium (B_XGa_1-XP: 0 ≦ X ≦ 1) mixed crystal is triethylboron ((C₂H_Five)_ThreeB), trimethylgallium ((CH_Three)_ThreeGa) or triethylgallium ((C₂H_Five)_ThreeGa), phosphine (PH_Three) Or a raw material system composed of an organic phosphorus compound such as trialkyl phosphorus. In the vapor phase growth of boron phosphide (BP) crystal layer by the halide method (halide method), for example, boron trichloride (BCl)_ThreeBoron (B) halide such as)) as a boron (B) source, and phosphorus trichloride (PCl)_Three) And the like can be used as a phosphorus (P) source (see “The Crystal Growth Society of Japan”, Vol. 24, No. 2 (1997), page 150). Boron tribromide (BCl_Three) Is a boron (B) source (see J. Appl. Phys., 42 (1) (1971), pages 420 to 424). In the hydride method, for example, borane (BH_Three) Or diborane (B₂H₆) And other boron hydrides as a boron (B) source and phosphine (PH_Three) Can be grown using a phosphorus hydride such as (1) J. Crystal Growth, 24/25 (1974), pp. 193-196, and (2) J. Crystal Growth, 132 (1993), pages 611-613).
[0029]
According to the vapor phase growth method, for example, a so-called liquid for growing boron phosphide (BP) crystals from a conventional nickel (Ni) -phosphorus (P) melt or copper (Cu) -phosphorus (P) melt. Compared with the phase growth means (see J. Electrochem. Soc., 120 (6) (1973), pages 802 to 806), the control of the thickness and composition ratio of the BP mixed crystal layer is easier and easier. There are advantages that can be implemented. Further, according to the vapor phase growth means, there is an advantage that a heterojunction structure of a BP layer or a BP mixed crystal layer and another semiconductor crystal layer can be easily formed. In particular, according to the MOCVD means equipped with a piping system capable of instantaneously changing the gas source species supplied to the growth reaction furnace, the composition of the crystal layer can be rapidly changed. A so-called steep heterojunction interface structure in which the composition is abruptly changed at the hetero (heterogeneous) junction interface becomes efficient in accumulating low-dimensional electrons. Therefore, a steep heterojunction interface structure with a BP layer or a BP mixed crystal layer formed by MOCVD has an effect of bringing about a BP semiconductor element such as TEGFET having excellent electron mobility.
[0030]
The temperature for growing the BP layer or the BP mixed crystal layer is determined in consideration of the vapor phase growth method, the crystal material used as the substrate, and the crystal form of the target BP layer or BP mixed crystal layer. In order to obtain a single crystal BP layer, a high temperature exceeding 750 ° C. is generally required without depending on the above-mentioned vapor phase growth means. Triethyl boron ((C₂H_Five)_ThreeB) / phosphine (PH_Three) / Hydrogen (H₂) In order to obtain a single crystal BP layer by means of atmospheric pressure (substantially atmospheric pressure) or reduced pressure MOCVD using a reaction system, a temperature higher than 750 ° C. and lower than 1200 ° C. is suitable (US Pat. No. 6,069,021). reference). In other words, it is necessary to select the substrate material from such a heat-resistant crystal that does not deteriorate at such a high temperature. As a substrate material having heat resistance in this high temperature region, boron phosphide (BP) single crystal (1) Z. anorg. Allg. Chem., 349 (1967), (2) Kristall und Technik, 2 (4) (1967), pages 523-534, (3) Kristall untechnik, 4 (4) (1969), pages 487-493, and (4) J. Electrochem. Soc., 120 (1973) above. ), Sapphire (α-Al₂O_Three), Silicon carbide (SiC) (see J. Appl. Phys., 42 (1) (1971) above), and silicon (silicon single crystal). At high temperatures above 1200 ° C, molecular formula B₆P or B₁₃P₂(Refer to J. Am. Ceram. Soc., 47 (1) (1964), pages 44 to 46), and monomeric boron phosphide (boron monophosphide). It is inconvenient to obtain a single crystal layer consisting of From the single crystal BP layer or the BP mixed crystal layer, for example, an electron supply layer of TEGFET can be configured. Further, a clad layer of LED or LD can be formed. The crystal form (structure) of the grown BP layer or mixed crystal layer thereof is known from a diffraction pattern obtained by a general X-ray diffraction method (XRD) or electron beam diffraction method. A single crystal results in a spot-like diffraction point (see J. Crystal Growth, 70 (1984), pages 507-514).
[0031]
In addition, a relatively low temperature of 250 ° C. to 750 ° C. is suitable for obtaining an amorphous or polycrystalline BP crystal layer depending on the MOCVD means of the same reaction system (see US Pat. No. 6,069,021 above). . Amorphous BP layer or BP mixed crystal layer forms a layered structure for phosphorus-based semiconductor devices including a growth layer that has a large lattice mismatch with the crystal forming the substrate on the substrate. In doing so, it has the effect of relaxing the lattice mismatch and providing a growth layer with excellent crystallinity. Further, it effectively works to prevent the growth layer from peeling off from the substrate surface, which is mainly caused by the difference in thermal expansion coefficient between the substrate material and the growth layer. Therefore, for example, a BP layer mainly composed of amorphous material can be used as a buffer layer constituting a phosphorus-based semiconductor element. The buffer layer is also composed of, for example, a multilayer structure in which a single crystal layer of boron phosphide (BP) grown at a higher temperature is stacked on an amorphous boron phosphide layer grown at a low temperature. (See US-6,029,021 above). Even when a substrate having a lattice mismatch with BP is used, a BP single crystal layer having excellent crystallinity can be easily obtained by interposing an amorphous BP layer. For example, in a boron phosphide-based semiconductor light-emitting device, the buffer layer having a multilayer structure has an advantage that a light-emitting portion that provides high-intensity light emission can be configured. Further, for example, in a boron phosphide-based HBT, a high-quality collector layer or subcollector having a small crystal defect such as misfit dislocation due to lattice mismatch on the buffer layer having a multilayer structure. This can contribute to obtaining a (sub-collector) layer or the like.
[0032]
From the BP mixed crystal layer, a growth layer lattice-matched with the single crystal substrate can be formed. For example, a boron phosphide / gallium mixed crystal having a boron composition ratio of 0.02 (boron phosphide mixed crystal ratio = 2%) (B_0.02Ga_0.98P) (see JP-A-11-266006) is a BP mixed crystal layer having a lattice constant of 5.4309 定 数. Therefore, B_0.02Ga_0.98From P (see the above-mentioned JP-A-11-266006), a growth layer lattice-matched to a Si single crystal (lattice constant = 5.4309３０) can be formed. The growth layer lattice-matched to the Si single crystal used as the substrate is an indium boron phosphide mixed crystal (B_0.33In_0.67P). For example, a high quality buffer layer can be formed from the BP mixed crystal growth layer that is lattice-matched with the substrate. In addition, a magnetosensitive layer exhibiting high electron mobility suitable for obtaining a Hall element with high product sensitivity can be configured. Moreover, it can utilize suitably for the light transmissive layer (window layer) etc. of a light receiving element.
[0033]
A semiconductor element comprising a semiconductor layer made of boron phosphide (BP) according to the present invention is a boron phosphide (BP) semiconductor having a forbidden band width of 2.8 electron volts (eV) or more and 3.4 eV or less at room temperature. Configure using layers. In addition, a semiconductor element having a semiconductor layer made of a boron phosphide (BP) -based mixed crystal according to the present invention has a BP that has a forbidden band width of 2.8 electron volts (eV) or more and 3.4 eV or less at room temperature. A BP-based mixed crystal semiconductor layer is used and configured. Room temperature is approximately 20 ° C. That is, it exceeds 2 eV, which is the forbidden bandwidth of the conventional BP, and is not as high as 4.2 eV to 6.0 eV, which has been reported in the past, and has an intermediate forbidden bandwidth that has not been conventionally known. A BP-based semiconductor element is configured using a BP layer or a BP mixed crystal layer. A boron phosphide (BP) layer having a forbidden band width of 2.8 eV or more and 3.4 eV or less at room temperature can be formed by defining the growth conditions. In particular, it can be formed by setting both the growth rate and the raw material supply ratio within a prescribed range. The growth rate of the boron phosphide (BP) layer or the BP mixed crystal layer is preferably 20 to 300 Å per minute. If the growth rate is set to a slow rate of less than 20 ｍｉｎ / min, phosphorus (P) constituent elements or their compounds from the growth layer surface may not be sufficiently desorbed and volatilized, and film formation may not be achieved. If a high growth rate exceeding 300 Å / min is set, the obtained band gap value becomes unstable, which is not preferable. Further, if the growth rate is increased rapidly, it tends to be a polycrystalline crystal layer, which is inconvenient for obtaining a single crystal layer.
[0034]
In addition to the growth rate, the feed ratio of the raw material is preferably defined in the range of 15 to 60. In the case of forming the BP layer, the raw material supply ratio is the ratio of the supply amount of the phosphorus (P) source to the supply amount of the boron (B) source to the growth reaction system. In the case of forming a BP-based mixed crystal, the ratio of the total supply amount of the group V element source including phosphorus (P) to the total supply amount of the group III element source including boron (B) is used. is there. Boron phosphide / indium (B_XIn_1-XFor example, in the case of forming a mixed crystal of P: 0 ≦ X ≦ 1, the amount of phosphorus (P) source supplied relative to the total amount of gallium (Ga) source and indium (In) source supplied to the growth reaction system It is a ratio. That is, the so-called V / III ratio. If the V / III ratio is as small as less than 15, the growth layer surface is undesirably disturbed. On the other hand, when the III / V ratio exceeds 60 and is extremely large, a growth layer in which phosphorus (P) is rich in terms of stoichiometry is easily formed. Excess phosphorus (P) enters the position where boron (B) should occupy in the crystal lattice and acts as a donor (Katsufusa Shono, “Semiconductor Technology Collection 100 in the VLSI Age [5] (Ohm Co., Ltd., issued May 1, 1984, see the electronic magazine Electronics Vol. 29, No. 5 (May 1984) Appendix, p. 121). The flash to which BP or BP mixed crystals belong. Zinc ore-type crystals originally have a condensed valence band structure that makes it easy to obtain p-type semiconductor layers (Toshiaki Ikoma and Hideaki Ikoma, “Introduction to Basic Physical Properties of Compound Semiconductors”) (See Baifukan, first edition published on September 10, 1991, pages 14-17.) Despite this, if the stoichiometric composition shifts to the rich side of phosphorus (P), a low-resistance p-type crystal layer This is inconvenient because it interferes with the formation of
[0035]
In order to omit the conditions for forming the BP layer in the conventional vapor phase growth means, diborane (B₂H₆) / Phosphine (PH_Three) / Hydrogen (H₂) In the hydride method, a growth rate of about 120 Å / min to about 700 Å / min is described (see Jpn. J. Appl. Phys., 13 (3) (1974) above). On the other hand, in this hydride growth means, the V / III ratio (= PH)_Three/ B₂H₆) Must be about 50 or more (see Jpn. J. Appl. Phys., 13 (1974) above). In particular, it is stated that the V / III ratio needs to be increased to 250 in order to obtain a single crystal BP layer (see Jpn. J. Appl. Phys., 13 (1974) above). In another example of forming a BP layer using diborane and phosphine as raw materials, the growth rate is set to at least 400 cm / min (by Shono Shobo, “Semiconductor Technology (above)” (University of Tokyo). Publishing, June 25, 1992, 9th edition), see pages 74-77). Further, in order to obtain a BP layer exhibiting semiconductor properties, V / III needs to be 100 times or more (see “Semiconductor Technology (above)”, pages 76 to 77). Therefore, the conventional B₂H₆/ PH_Three/ H₂In the system hydride method, the low growth rate of the present invention can be adopted, but at the same time, the V / III ratio does not satisfy the specified range of the present invention.
[0036]
In the halogen method using chloride as a raw material, the V / III ratio was set so as to satisfy the scope of the present invention, and it was grown by the halide generated due to decomposition during vapor phase growth of the raw material halide. The BP layer inside or the Si substrate itself is etched, and it is difficult to obtain a flat BP layer. The MOCVD method is suitable for growing a BP layer or a BP-based mixed crystal layer under conditions satisfying both the growth rate and the V / III ratio specified in the present invention. In particular, the MOCVD method using a trialkyl boron compound as a boron (B) source can be suitably used (see the above Inst. Phys. Conf. Ser., No. 129). Among trialkylboron compounds, triethylboron ((C₂H_Five)_ThreeAccording to the MOCVD means using B), it is possible to easily form an amorphous BP layer or a BP-based mixed crystal layer at a low temperature, or a single crystal layer at a high temperature. Trimethylboron ((CH_Three)_ThreeB) is a gas at room temperature, like borane and diborane, and is not as suitable as triethyl boron for forming a BP layer or a BP mixed crystal layer at a low temperature. For the formation of a BP layer or a BP crystal layer at a low temperature, it is suitable to use a boron (B) source of an organic boron compound which is liquid at room temperature having a low boiling point.
[0037]
For example, the growth temperature when forming a boron phosphide (BP) single crystal layer using a triethylboron / phosphine / hydrogen MOCVD reaction system is preferably 850 ° C. or higher and 1150 ° C. or lower. More desirably, the growth temperature is 900 ° C. or higher and 1100 ° C. or lower. Particularly preferred is a temperature of 950 ° C to 1050 ° C. For example, if the V / III ratio is set to 30 at 950 ° C., a boron phosphide (BP) single crystal layer having a forbidden band width of about 2.9 eV can be stably obtained. The forbidden band width (= Eg) is, for example, the general photoluminescence (PL) method, cathodoluminescence (CL), or the relationship between the absorption coefficient and the photon energy (by the above-mentioned Zieger, “Semiconductor Physics ( Lower) ”, page 390-400). FIG. 2 illustrates the photon energy dependence of the absorption coefficient for an undoped BP layer formed on the surface of a Si single crystal substrate having a (111) plane and doped with boron (B) under the above conditions. . Absorption coefficient (α: cm^-1) And photon energy (hν: eV), the forbidden band width at room temperature is about 3.1 eV. Incidentally, for the BP crystal, the rate of change (temperature coefficient) depending on the temperature of the forbidden band width is minus (−) 4.5 × 10 6 per unit absolute temperature.^-FoureV is known (see Z. anorg. allg. chem., 349 (1967) above). The negative sign in this temperature coefficient means that the band gap increases as the temperature decreases. Therefore, for example, the forbidden band width of the BP layer at the liquid nitrogen temperature (= 77 K) is about 3.2 eV. Thus, the BP layer of the present invention can be obtained by setting the growth rate and the V / III ratio within the range defined by the present invention.
[0038]
FIG. 3 shows magnesium (Mg) grown using the same MOCVD reaction system as described above, at a temperature of 950 ° C., with a growth rate of 100 Å / min, and a V / III ratio of 60. 2 illustrates a CL spectrum of a doped p-type boron phosphide (BP) layer. The spectrum was measured at a temperature of 30K. Since boron phosphide (BP) is an indirect transition semiconductor, the CL spectrum is suitable for acquisition at 77 K or lower. The carrier concentration of the sample p-type BP layer is about 8 × 10¹⁸cm^-3It is. The layer thickness is about 2.2 μm. The component of the CL spectrum illustrated in FIG. 3 is a spectrum having a peak wavelength of about 3785 mm according to analysis using a general peak separation method (indicated by the symbol “SP1” in FIG. 3). And a spectrum having a peak wavelength of about 5696Å (indicated by the symbol “SP2”). “SP2” is considered a spectrum due to “deep” impurity levels. Further, the spectrum feature indicated by “SP2” is characterized in that a decrease in emission intensity over time is observed. On the other hand, “SP1” is a spectrum estimated to be band edge absorption, and a forbidden bandwidth of about 3.2 eV is calculated from its peak wavelength (3785 mm).
[0039]
Triethyl boron ((C₂H_Five)_ThreeB) / phosphine (PH_Three) / Hydrogen (H₂For example, in the case of an undoped boron phosphide (BP) layer grown by a system MOCVD means, the band gap is generally high in an amorphous layer. In particular, for example, the room-temperature forbidden band width of a BP amorphous layer that inherently contains strain due to lattice mismatch with the underlying layer may be as large as 3.0 eV to 3.4 eV. In a BP polycrystalline layer grown at a high growth rate, the band gap generally tends to be small. In particular, in a thick film having a thickness exceeding about 2 to 3 μm, the forbidden band width may decrease from about 2.8 eV to about 3.0 eV at room temperature, for example. In addition, in the single crystal BP layer grown under the conditions of the growth rate and V / III ratio in the above preferred range, an intermediate band gap between the amorphous layer and the polycrystalline layer can be taken.
[0040]
If boron phosphide (BP) having a forbidden bandwidth described in the present invention is used, a general formula B having a forbidden bandwidth that has not existed in the past is used._αAl_βGa_γIn_{1- α - β - γ}P_δAs_εN_{1- δ - ε}(0 <α ≦ 1, 0 ≦ β <1, 0 ≦ γ <1, 0 <α + β + γ ≦ 1, 0 <δ ≦ 1, 0 ≦ ε <1, 0 ≦ δ + ε ≦ 1) Crystals can be formed. For example, when boron phosphide (BP) according to the present invention having a forbidden band width of 2.8 eV or more and 3.4 eV or less is used, the forbidden band width at room temperature exceeds about 1.5 V and is less than 3.4 eV. Boron arsenide mixed crystal (BP)_δAs_ε: 0 <δ <1, 0 <ε <1, δ + ε = 1). When a conventional BP crystal having a forbidden band width of about 2.0 eV is used, it exceeds about 1.5 eV, which is a forbidden band width of boron arsenide (BAs) (the “III-V group compound semiconductor” described above). 150, and BP having a narrow band gap of about 2.0 eV, which is the band gap of boron phosphide (BP)._δAs_εOnly mixed crystals (0 <δ <1, 0 <ε <1, δ + ε = 1) are formed.
[0041]
For example, if boron phosphide (BP) according to the present invention having a forbidden band width of 2.8 eV to 3.4 eV is used, the forbidden band width at room temperature exceeds 2.3 eV and less than 3.4 eV. Boron phosphide / gallium mixed crystal (B_XGa_1-XP: 0 <X <1) can be formed. Since the band gap of gallium phosphide (GaP) at room temperature is 2.3 eV (see “Introduction to Semiconductor Devices”, page 28), mixed crystals of BP are formed by mixed crystallization with boron phosphide (BP). If the ratio is increased, that is, by increasing the boron (B) composition ratio (= X), B of 2.3 eV or more_XGa_1-XP (0 <X <1) mixed crystals can be formed. Incidentally, B formed using a conventional BP whose forbidden band width is about 2.0 eV._XGa_1-XIn a P (0 <X <1) mixed crystal, B having a narrow band gap of about 2.0 eV or more and 2.3 eV or less._XGa_1-XOnly P (0 <X <1) mixed crystals can be formed. B_XGa_1-XA boron phosphide-based semiconductor element in which consideration is given to prevent environmental pollution can be configured from a BP-based mixed crystal that does not contain arsenic (As) as a constituent element, such as a P (0 <X <1) mixed crystal. Benefits are born.
[0042]
The BP mixed crystal composed of the BP crystal of the present invention having a forbidden band width of 2.8 eV or more and 3.4 eV or less is high in a wide range that is not found in the conventional BP mixed crystal as in the above example. Has forbidden bandwidth. For this reason, for example, it is particularly useful for constructing a barrier layer for the light emitting layer provided for emitting short-wavelength light. For example, B with a boron composition ratio (= X) of 0.90_0.90Al_0.10From the P mixed crystal, cubic gallium nitride / indium mixed crystal (Ga_0.75In_0.25A cladding layer for the light emitting layer consisting of N) can be constructed. Boron phosphide (BP) or BP mixed crystals are zinc-blende photo-type crystals, and a p-type layer can be obtained from the band structure of the valence band (see "Introduction to basic properties of compound semiconductors" above). It ’s easy. Therefore, for example, the situation is different from that of hexagonal gallium nitride (h-GaN), and a p-type low-resistance cladding layer can be easily formed. Cubic Ga_0.75In_0.25From the N light-emitting layer, blue-violet near-ultraviolet light having an emission wavelength of 4430 mm is emitted._0.90Al_0.10P mixed crystal and Ga_0.75In_0.25From the heterojunction structure made of N, there is an advantage that a pn junction type light-emitting portion that provides blue band light emission of a single or double heterojunction structure can be formed. In addition, B_0.90Al_0.10P mixed crystal and Ga_0.75In_0.25N has the same lattice constant (= 4.628Å) (the lattice constant of cubic indium nitride (InN) is calculated as 4.98Å: “III-V compound semiconductor” above, page 330 reference). That is, from the BP mixed crystal of the present invention, a clad layer lattice-matched to the light-emitting layer can be formed, so that a lattice-matched light-emitting portion can be formed. Crystal layers having a lattice matching relationship with each other are high-quality crystal layers with few crystal defects due to lattice mismatch. For this reason, high intensity light emission is emitted from the lattice-matching light-emitting portion, which can contribute to providing a high-luminance boron phosphide-based semiconductor light-emitting element. Note that a crystal layer having a lattice matching relationship with each other means a crystal layer having a lattice mismatch degree of ± 0.4% or less.
[0043]
Further, when the boron phosphide (BP) layer or the BP mixed crystal layer of the present invention is used, it is convenient to form a lattice matching type light emitting section suitable for forming an LED or LD. For example, a clad layer made of n-type or p-type boron phosphide (BP: lattice constant = 4.538Å) and gallium nitride phosphide (GaN) with a phosphorus (P) composition ratio of 0.03_0.97P_0.03Lattice constant = 4.538Å) A lattice matching system, for example, a pn junction type light emitting portion can be formed from a light emitting layer made of a mixed crystal. In addition, cubic GaN with a phosphorus composition ratio of 0.10_0.90P_0.10Cubic boron phosphide / gallium (B) with a light emitting layer made of gallium (Ga) and a gallium (Ga) composition ratio of 0.07_0.93Ga_0.07The light emitting part of the lattice matching system can be simply configured from the clad layer made of P). Similarly, gallium arsenide nitride (GaN_1-XAs_X: 0 ≦ X ≦ 1) can also be used as the light emitting layer to form a lattice-matched light emitting portion. However, the production energy of gallium nitride (GaN) is (−) 26.2 kcal / mol. On the other hand, the formation energy of GaAs is (−) 19.2 kcal / mol. (See JP-A-10-53487). On the other hand, the formation energy of GaP is (−) 29.2 kcal / mol. And smaller than the generation energy of GaN (see the above-mentioned JP-A-10-53487). For this reason, GaN_1-XAs_XGaN compared to mixed crystals_1-XP_XConveniently, mixed crystals can be formed more easily. The cladding layer is GaN_1-XP_XThe light emitting layer is composed of a BP layer or a BP mixed crystal layer having a larger band gap at room temperature. From a BP layer or a BP mixed crystal layer having a high forbidden band width of about 0.1 eV or more, most preferably 0.3 eV or more, a cladding layer that can sufficiently exert a barrier action on the light emitting layer can be formed.
[0044]
Further, the boron phosphide (BP) or BP mixed crystal according to the present invention has a large forbidden band width that can transmit visible light having a short wavelength as described above. For this reason, for example, B in which the boron composition ratio (= X) is adjusted to give a forbidden band width of 2.7 eV or more._XGa_1-XFrom P (when a BP crystal having a room temperature forbidden band width of 3.0 eV is used, 0.4 ≦ X <1), an emission transmission layer (window) of an LED having an emission wavelength longer than about 4590 mm is used. ) Layer can be suitably configured. In addition, a boron phosphide / indium mixed crystal having a band gap exceeding 2.8 eV and less than 3.4 eV (B_XIn_1-XP) From mixed crystals, LEDs or surface-emitting LDs that can transmit light having a wavelength longer than about 4430 mm (Iga, Koyama, “Surface emitting laser” (Ohm Co., Ltd., published on September 25, 1990) , 1st edition, 1st printing) and 4-5 pages). Moreover, it can utilize for comprising the reflecting mirror of LED or a surface emitting laser (surface emitting laser) use (refer said "surface emitting laser", pages 118-119).
[0045]
GaN that can be generated more easily_1-XP_XFrom the laminated structure composed of the mixed crystal and the BP layer or BP-based mixed crystal of the present invention, a light receiving portion for use in a light receiving element can be configured. For example, a bonded structure of boron phosphide (BP) or a BP mixed crystal layer and a semiconductor layer having a lattice mismatch degree of ± 0.4% or less with those is a signal / noise intensity ratio, so-called S / S. A light receiving portion for use in a light receiving element having a large N ratio and excellent light receiving sensitivity can be configured. In particular, for example, a boron phosphide (BP) layer and a semiconductor layer lattice-matched thereto, for example, the above GaN_1-XP_XBy using a light-receiving part composed of a heterojunction structure with a layer, a light-receiving part for use with a high-sensitivity light-receiving element that has a low dark current and excellent light-receiving sensitivity can be configured. In addition, the BP layer or BP mixed crystal of the present invention is useful as a light transmission layer that can efficiently introduce a photometric object into the light receiving layer. In particular, since a BP layer or a BP mixed crystal layer having a relatively high forbidden bandwidth exceeding 2.8 eV, which has not been conventionally used, can efficiently transmit short-wavelength visible light such as blue, It can be effectively used as a window layer of a light receiving element for measuring visible light.
[0046]
A heterojunction structure composed of a boron phosphide (BP) layer or a BP mixed crystal layer and a semiconductor layer lattice-matched therewith has an advantage that carriers, for example, electrons can be transported at high speed. For example, BP layer or BP mixed crystal layer and GaN_1-XP_XA heterojunction structure with a mixed crystal is suitable for forming a functional layer of a TEGFET that requires high-speed electron mobility. In this case, direct transition type GaN_1-XP_XSince a mixed crystal layer can exhibit high electron mobility, it is particularly suitable for constituting an electron transit layer of a TEGFET. Further, an electron supply layer that forms a heterojunction with the electron transit layer and supplies electrons into the electron transit layer can be configured from the BP layer or the BP mixed crystal layer. In addition, a spacer layer that may be disposed between the electron supply layer and the electron transit layer can be configured from the BP layer or the BP mixed crystal layer of the present invention. The electron transit layer or spacer layer has a general formula B in which the forbidden band width is larger than the constituent material of the electron transit layer by 0.2 eV or more, preferably about 0.3 eV or more._αAl_βGa_γIn_{1- α - β - γ}P_δAs_εN_{1- δ - ε}(0 <α ≦ 1, 0 ≦ β <1, 0 ≦ γ <1, 0 <α + β + γ ≦ 1, 0 <δ ≦ 1, 0 ≦ ε <1, 0 <δ + ε ≦ 1) It is preferable to configure. In particular, GaN_1-XP_XThe mixed crystal layer is easier to form than the arsenic compound for the above reasons.
[0047]
GaN_1-XP_XIf the banding of the forbidden band depending on the phosphorus (P) composition ratio of the mixed crystal is used (see Appl. Phys. Lett., 60 (20) (1992), pages 2540-2542), the region of direct transition Thus, the forbidden band width can be changed by changing the phosphorus (P) composition by about several percent. For example, if the phosphorus (P) composition ratio is 5%, the forbidden band width can be reduced from 3.2 eV to about 2.8 eV. Further, if the phosphorus (P) composition ratio is 10%, it can be lowered to about 2.0 eV. That is, GaN_1-XP_XFrom the mixed crystal, the band gap with the spacer layer or the electron supply layer made of the BP layer or the BP-based mixed crystal layer corresponds to the phosphorus (P) composition ratio, and the electron capable of revealing the above-mentioned preferable band gap difference. There is an advantage that the traveling layer can be simply configured.
[0048]
For example, as schematically illustrated in FIG. 4, on a substrate 401 made of sapphire having a plane orientation of (0001) (c-plane), for example,
(1) Undoped high-resistance boron phosphide / aluminum (B) with a forbidden band of preferably 3 eV or more within a range of 2.8 eV or more and 3.4 eV or less and a layer thickness (= d) of about 100 mm._XAl_1-XLow-temperature buffer layer 402 mainly composed of amorphous material consisting of P: 0 <X <1)
(2) It is formed at a temperature higher than that of the low-temperature buffer layer 402, and preferably has a forbidden band width of 3 eV or more. For example, the carrier concentration (= n) is about 5 × 10¹⁵cm^-3And a high-temperature buffer layer 403 made of undoped n-type BP with d = 3000 Å
(3) For example, cubic undoped n-type GaN lattice-matched with BP forming the high-temperature buffer layer 403 and having a smaller band gap_0.97P_0.03(For example, n = 5 × 10¹⁶cm^-3, D = 250 Å)
(4) Preferably, the forbidden band width is set to 3 eV or higher and has a higher forbidden band width than the electron transit layer 104. For example, the carrier concentration (= n) is about 5 × 10¹⁵cm^-3The spacer layer 405 made of undoped n-type BP with d = 50Å
(5) Preferably, the forbidden band width is set to 3 eV or more, for example, the carrier concentration (= n) is about 2 × 10¹⁸cm^-3The electron supply layer 406 made of silicon (Si) -doped n-type BP with d = 250Å
(6) Preferably, the forbidden band width is set to be equal to or smaller than the electron supply layer 406, for example, the carrier concentration (= n) is about 5 × 10¹⁸cm^-3And an ohmic electrode contact layer 407 made of silicon (Si) -doped n-type BP with d = 150Å
These layers are sequentially stacked to form a stacked structure 41 for TEGFET 40 use. Next, a recess process is performed on a part of the contact layer 407, and a Schottky junction gate electrode 408 is provided there. Further, an ohmic source electrode 409 and a drain electrode 410 are formed on the surface of the contact layer 407 left on both sides of the recess 411 to constitute the TEGFET 40.
[0049]
Also, for example, GaN laminated on boron phosphide (BP) or BP mixed crystal_1-XP_XThe mixed crystal layer can be used as a magnetic sensitive part of the Hall element. In particular, a direct transition type rather than an indirect transition type, for example, GaN_1-XP_XThe mixed crystal layer can be used as a magnetic sensitive layer (magnetic sensitive layer) of the Hall element. GaN_1-XP_XThe mixed crystal layer is composed of indium antimonide (InSb, forbidden band width = 0.18 eV), indium arsenide (InAs, forbidden band width = 0.36 eV), or gallium arsenide (GaAs, GaAs, which constitutes a magnetosensitive layer of a conventional Hall element. Forbidden band width = 1.43 eV) (For the value of room-temperature forbidden band width, see "III-V compound semiconductor" above, page 150). (See Appl. Phys. Lett., 60 (1992) above). Semiconductor materials with a large forbidden band can operate at high temperatures because the temperature at which they reach the intrinsic region in conductivity is higher (see “Semiconductor Physics (above), pages 5-10” above). For example, GaN_1-XAs_XFor example, GaN, which can take a higher forbidden bandwidth than mixed crystals_1-XP_XFrom the mixed crystal, a magnetosensitive layer capable of operating the device at a higher temperature can be formed. Therefore, GaN_1-XP_XA heterojunction structure composed of a mixed crystal layer and a BP layer or a BP mixed crystal layer has an advantage that an environment-resistant Hall element that operates even at high temperatures can be configured. In particular, direct-transition n-type GaN lattice-matched with the BP layer or BP mixed crystal layer_1-XP_XSince the mixed crystal layer results in improved electron mobility, it can contribute to obtaining an environment-resistant Hall element that is highly sensitive and that can operate at a high temperature.
[0050]
The Hall element according to the present invention is composed of a laminated structure including a substrate, for example, a buffer layer and a magnetosensitive layer. An example of a laminated structure for use in an environment-resistant Hall element according to the present invention is shown in the sectional view of FIG. For the substrate 501, for example, a single crystal such as silicon, sapphire, or silicon carbide (SiC) is used. The first buffer layer 502 provided on the single crystal substrate 501 is composed of, for example, an amorphous n-type boron phosphide (BP) layer grown at a low temperature. The second buffer layer 503 is composed of, for example, a silicon (Si) -doped n-type BP single crystal layer grown at a higher temperature than the first buffer layer 502. The magnetosensitive layer 504 is made of, for example, boron phosphide (BP: melting point = 3000 ° C. (see the above “Introduction to Semiconductor Devices”, page 28), high melting point gallium nitride (GaN: melting point of hexagonal h-GaN> 1700). ° C (see "Introduction to Semiconductor Devices" above, page 28)) or gallium nitride phosphide (GaN_1-XP_X: 0 <X <1). The magnetosensitive layer 504 is preferably made of a material that has little lattice mismatch and lattice matching with the underlying layer (the second buffer layer 503 in the stacked structure system of FIG. 5). The absolute value of the degree of lattice mismatch (Δ: unit%) is the lattice constant (= a₀) And the lattice constant of the deposited layer (= a).
Δ (%) = | (aa₀/ A₀| × 100
BP single crystal with cubic GaN (a = 4.510４．５) (a₀= 4.538cm) is only 0.6%, which is a material suitable for forming the magnetosensitive layer. In addition, the buffer layer (first 502 in FIG. 5) mainly composed of amorphous material in the as-grown state described in this configuration example has an action of relaxing lattice mismatch, and further improves the crystallinity of the upper layer. To contribute to.
[0051]
Further, gallium nitride phosphide (GaN with a nitrogen composition ratio of 0.03)_0.97P_0.03) Is 4.538Å which is consistent with the BP single crystal. The magnetosensitive layer made of such a lattice-matching material has a low density of crystal defects such as misfit transition caused by lattice mismatch and becomes a high-quality crystal layer. Therefore, since a higher mobility can be expressed, a highly sensitive Hall element having excellent heat resistance is provided. For example, triethyl boron ((C₂H_Five)_ThreeB) / phosphine (PH_Three) / Ammonia (NH_Three) / Hydrogen (H₂The following growth layers are sequentially stacked on the surface of a phosphorus (P) -doped n-type Si single crystal substrate 501 having a plane orientation of (100) by a normal atmospheric pressure MOCVD method.
(1) First buffer layer 502 made of an undoped n-type BP layer having a layer thickness (= d) of about 70 mm and a forbidden band width of about 3.1 eV at room temperature
(2) Carrier concentration (= n) is about 6 × 10¹⁵cm^-3And a second buffer layer 503 (d = 0.7 μm) made of an n-type BP layer having a room temperature forbidden band width of about 3.0 eV
(3) d = 0.1 μm, n = 2 × 10¹⁶cm^-3The electron mobility at room temperature is about 850 cm.²/ V ・ s cubic n-type GaN_0.97P_0.03Next, for example, methane (CH_Four) / Argon (Ar) / Hydrogen (H₂) Mesa processing is performed on the magnetosensitive layer 504 by the system plasma etching means. Further, ohmic electrodes made of, for example, gold (Au) or an Au alloy are laid on the four end portions of the magnetosensitive layer 504 left in a cross shape as the magnetosensitive portion (Hall cross portion). Such a configuration provides a high-sensitivity Hall element for environment resistance with a product sensitivity of about 15 mV / mA · kG at room temperature.
[0052]
The boron phosphide (BP) according to the present invention has a large forbidden band width exceeding the conventional forbidden band width (about 2 eV). A mixed crystal can be formed. Therefore, when configuring a heterojunction structure with another semiconductor layer having a different forbidden band width, the degree of freedom can be expanded, and various heterojunction structures can be manifested. For example, in the conventional small band gap BP (band gap 2 eV), GaN lattice-matched with BP_0.97P_0.03A heterojunction structure for exerting a barrier action on (forbidden band width 3 eV) cannot be formed. On the other hand, in the BP according to the present invention, in particular, from a BP having a forbidden bandwidth exceeding 3 eV, GaN_0.97P_0.03Therefore, a lattice-matched heterojunction structure that exhibits a “confinement” effect of carriers can be formed. Such a heterojunction is useful for providing a heterojunction device such as an environment-resistant TEGFET or a Hall element as described above. In the TEGFET, if the BP or BP mixed crystal having a large forbidden bandwidth according to the present invention is used as a buffer layer, leakage of gate current can be suppressed in particular, so that a TEGFET excellent in mutual conductance (gm) is obtained. Further, in the Hall element, if the buffer layer is composed of BP or BP mixed crystal having a large forbidden band described in the present invention, it is possible to suppress leakage of operating current, and to provide a Hall element with high product sensitivity. Play.
[0053]
Since the semiconductor layer made of BP or BP mixed crystal described in the present invention can exhibit a larger forbidden band width as compared with the conventional semiconductor layer, various semiconductor layers and band-offsets are widely used. It is possible to create a heterojunction structure that is extremely large. Since the heterojunction structure using the semiconductor layer made of BP or BP mixed crystal described in the present invention is a heterojunction structure having a large band discontinuity as described above, it can be used particularly advantageously as a barrier layer. . .
[0054]
【Example】
(Example 1)
In Example 1, the present invention will be described in detail by taking a group III nitride semiconductor LED using the BP semiconductor layer of the present invention as an example. FIG. 6 schematically shows a cross-sectional structure of the pn junction LED 60 according to the first embodiment.
[0055]
The laminated structure 61 for use in the LED 60 is composed of a boron (B) -doped p-type Si single crystal having a (111) plane as a substrate 601. The low-temperature buffer layer 602 on the substrate 601 was made of boron phosphide (BP) mainly composed of amorphous material in an as-grown state. The low-temperature buffer layer 602 includes triethylboron ((C₂H_Five)_ThreeB) / phosphine (PH_Three) / Hydrogen (H₂) It was grown at 350 ° C. by a system atmospheric pressure MOCVD method. The layer thickness of the low temperature buffer layer 602 was about 12 nm.
[0056]
On the surface of the low-temperature buffer layer 602, a p-type BP layer doped with magnesium (Mg) at 950 ° C. was laminated as the lower cladding layer 603 using the MOCVD vapor phase growth means. Magnesium doping sources include bis-cyclopentadienyl magnesium (bis- (C_FiveH_Five)₂Mg) was used. The carrier concentration of the lower cladding layer 603 is about 7 × 10.¹⁸cm^-3It was. The layer thickness was about 0.8 μm.
[0057]
FIG. 7 shows the wavelength dependence of the refractive index at room temperature and the extinction coefficient of the BP layer forming the lower cladding layer 603. There is a tendency for the extinction coefficient (= k) to rapidly increase at a wavelength shorter than about 450 nm. Further, the refractive index (= n) also tends to increase on the short wavelength side. For example, the refractive index at a wavelength of 450 nm is about 3.12, and the extinction coefficient is about 0.0029, whereas at a wavelength of 380 nm, α = 3.28 and k = 0.1120 is measured. Imaginary part of complex permittivity (ε₂= 2 · n · k) (refer to the above “III-V compound semiconductor”, pages 168 to 171) and the photon energy are shown in FIG. Ε with increasing photon energy₂The value exhibits a decreasing behavior. Also, ε₂The photon energy obtained from the intercept of the value was about 3.1 eV. From this, it was shown that the room temperature forbidden band width of the boron phosphide (BP) crystal forming the lower cladding layer 603 is about 3.1 eV.
[0058]
On the BP lower cladding layer 603 having a room temperature forbidden band width of about 3.1 eV, a magnesium-doped phosphorus (P) composition ratio lattice-matched to boron phosphide (BP) is 0.03 (= 3%). p-type gallium phosphide (GaN)_0.97P_0.03) Layer as a light emitting layer 604. BP forming the lower cladding layer 603 and GaN_0.97P_0.03The difference in the forbidden band width from the light-emitting layer composed of (forbidden band width at room temperature: 2.9 eV) was about 0.2 eV. Cubic GaN_0.97P_0.03The light emitting layer 604 made of trimethylgallium ((CH_Three)_ThreeGa) / PH_Three/ H₂It was grown at 950 ° C. by the system atmospheric pressure MOCVD method. The carrier concentration of the light emitting layer 604 is about 3 × 10.¹⁷cm^-3The layer thickness was about 0.3 μm.
[0059]
On the light emitting layer 604, n-type boron phosphide (BP) having a layer thickness of about 0.3 μm was laminated as an upper clad layer 605. The upper cladding layer 605 is made of (C₂H_Five)_ThreeB / PH_Three/ H₂It was grown at 950 ° C. by the system atmospheric pressure MOCVD method. The lattice constant of the light emitting layer 605 is 4.538 mm, and the lattice constants of the upper cladding layer 605 and the light emitting layer 604 are made to coincide. The upper clad layer 605 was also made of a BP crystal having a forbidden band width of about 3.1 eV at room temperature, like the lower clad layer 603. The carrier concentration of the upper cladding layer 605 is about 2 × 10¹⁸cm^-3It was. A lower clad layer 603 and an upper clad layer 605 made of a BP semiconductor layer having a forbidden band width of about 3.1 eV, and GaN_0.97P_0.03A light emitting portion 606 having a pn junction type double hetero (DH) junction structure type is formed from the light emitting layer 604.
[0060]
On the upper cladding layer 605, a current diffusion layer 607 made of n-type boron phosphide (BP) having a forbidden band width of about 3.1 eV was laminated. The Si-doped BP layer forming the current spreading layer 607 is (C₂H_Five)_ThreeB / PH_Three/ H₂It was grown at 950 ° C. by the system atmospheric pressure MOCVD method. The thickness of the current spreading layer 607 is about 50 nm and the carrier concentration is about 8 × 10 10.¹⁸cm^-3Set to.
[0061]
A p-type ohmic electrode 609 made of aluminum (Al) was formed on the back surface of the p-type Si single crystal substrate 601. In addition, an n-type ohmic electrode 608 made of a gold / germanium (Au · Ge) alloy is disposed at the center of the surface of the current diffusion layer 607. The diameter of the n-type ohmic electrode 608 was about 130 μm. Thereafter, the Si single crystal serving as the substrate 601 was cut in a direction parallel to and perpendicular to the [211] direction to obtain an LED chip (chip) 60 having a side of about 300 μm.
[0062]
A drive current was passed between the ohmic electrodes 608 to 609 in the forward direction to emit light. The current-voltage (IV characteristic) showed a normal rectifying characteristic based on the good pn junction characteristic of the light emitting unit 606. Forward voltage obtained from IV characteristics (so-called V_f) Was about 3.1 V (forward current = 20 mA). The reverse voltage was about 10 V (reverse current = 5 μA). When an operating current of 20 milliamperes (mA) was passed in the forward direction, blue light having an emission center wavelength of about 430 nm was emitted. The half width of the emission spectrum was about 23 nm. The emission intensity in a chip state measured using a general integrating sphere was about 14 microwatts (μW), and a BP compound semiconductor LED having a high emission intensity was provided.
[0063]
(Example 2)
In the second embodiment, the contents of the present invention will be described in detail by taking a pn junction diode provided with a boron phosphide (BP) layer according to the present invention as an example. FIG. 9 schematically shows a cross-sectional structure of a pn junction diode 90 of the second embodiment.
[0064]
On a Si single crystal substrate 901 doped with phosphorus (P) and having an n-type (111) surface, diborane (B₂H₆) / (CH_Three)_ThreeGa / H₂Boron phosphide and gallium (B_XGa_1-XA low-temperature crystal layer 902-1 composed of P) was laminated. The boron (B) composition ratio (= X) was 0.02 which lattice matched with the Si single crystal (lattice constant = 5.431５). The low temperature crystal layer 902-1 is about 1.3 × 10^FourGrowth was performed under reduced pressure of Pascal (Pa). The layer thickness of the low-temperature crystal layer 902-1 was about 4 nm.
[0065]
According to the observation by the cross-sectional TEM method, B in an as-grown state during film formation_0.02Ga_0.98In the P low-temperature crystal layer 902-1, the upper region from the joint surface with the Si single crystal substrate 901 to about 1 nm is a single crystal. B_0.02Ga_0.98No peeling was observed between the P low-temperature crystal layer 902-1 and the n-type Si single crystal substrate 901, and good adhesion was maintained. The upper part of the low-temperature crystal layer 902-1 was mainly composed of an amorphous material.
[0066]
B_0.02Ga_0.98On the P low-temperature crystal layer 902-1, Si-doped n-type B in which a composition gradient is imparted to a boron composition (= X) at 950 ° C. using the above-described reduced pressure MOCVD reaction system._XGa_1-XA P high temperature crystal layer 902-2 was laminated. The composition ratio of boron (B) was linearly increased from 0.02 to 1.0 in the increasing direction of the layer thickness of the high-temperature crystal layer 902-2. That is, the surface of the n-type high-temperature crystal layer 902-2 is a boron phosphide (BP) layer with a gradient in the composition of boron (B). N-type B with this composition gradient_XGa_1-XThe P (X = 0.02 → 1.0) layer was based on a BP crystal having a forbidden band width of about 3.0 eV at room temperature, and thus was a crystal layer of about 3.0 eV. The boron (B) composition gradient was applied by uniformly increasing the amount of diborane supplied to the MOCVD reaction system over time and conversely decreasing the amount of trimethylgallium. The layer thickness was about 0.4 μm. The pressure of the reaction system during the growth of the n-type high-temperature crystal layer 902-2 is about 1.3 × 10^FourPa was set. B_XGa_1-XDuring the growth of the P composition gradient (X = 0.02 → 1.0) high-temperature crystal layer 902-2, disilane (Si₂H₆-H₂Si was doped using a mixed gas. Carrier concentration is about 1x10¹⁸cm^-3Set to. According to the analysis by X-ray diffraction analysis, the n-type high-temperature crystal layer 902-2 is a (111) -oriented cubic B_XGa_1-XIt was recognized as a P (X = 0.02 → 1.0) crystal layer.
[0067]
B as n-type high-temperature crystal layer 902-2_XGa_1-XAfter the formation of the P composition gradient layer, B_0.02Ga_0.98Most of the amorphous body in the P low-temperature crystal layer 902-1 was single-crystallized based on the single crystal layer existing in the boundary region with the Si single crystal substrate 901 in the as-grown state. N-type B_XGa_1-XThe P (X = 0.02 → 1.0) high-temperature crystal layer 902-2 is a B having a composition lattice-matched with the Si single crystal substrate 901._0.02Ga_0.98Since it was provided on the low-temperature crystal layer 902-1 made of P (lattice constant = 5.431Å), it was a continuous film that did not peel off. The buffer layer 902 is composed of the multilayer structure of the low-temperature and high-temperature crystal layers 902-1 and 902-2.
[0068]
On the n-type high-temperature crystal layer 902-2, B₂H₆/ PH_Three/ H₂An n-type boron phosphide (BP) layer 903 was bonded at 950 ° C. by a system reduced pressure MOCVD method. During the growth of the n-type BP layer 903, Si₂H₆-H₂Si was doped using a mixed gas. The carrier concentration of the n-type BP layer 903 is about 5 × 10.¹⁷cm^-3The layer thickness was about 0.3 μm. The n-type layer 903 was made of BP crystal having a forbidden band width of about 3.0 eV at room temperature.
[0069]
On the n-type BP layer 903, B₂H₆/ PH_Three/ H₂A p-type BP layer 904 was laminated at 950 ° C. by a system reduced pressure MOCVD method. The p-type BP layer 904 is composed of a magnesium (Mg) -doped BP layer having a forbidden band width of about 3.0 eV. Biscyclopentadienyl Mg (bis- (C_FiveH_Five)₂Mg) was used. Although the p-type layer 904 is a wide band gap semiconductor, it is a zinc blende crystal type and is composed of BP having a low ion binding property, so that the carrier concentration is about 3 × 10 × 10.¹⁸cm^-3And was able to. The layer thickness of the p-type layer 904 was about 0.2 μm. The n-type BP layer 903 and the p-type BP layer 904 described above constitute a pn junction structure.
[0070]
An n-type ohmic electrode 906 made of aluminum (Al) was formed on the back surface of the n-type Si single crystal substrate 901. A p-type ohmic electrode 905 made of gold (Au) is disposed at the center of the surface of the p-type BP layer 904. The diameter of the p-type ohmic electrode 905 was about 110 μm. Thereafter, the Si single crystal serving as the substrate 901 was cut in a direction parallel to and perpendicular to the [211] direction to form a diode 90 chip having a side of about 350 μm.
[0071]
FIG. 10 illustrates current-voltage (IV characteristics) measured by passing a current in the forward direction between the two ohmic electrodes 905 to 906. The pn junction type BP diode of Example 2 exhibited normal rectification characteristics based on good pn junction characteristics. Further, the reverse voltage was about 15 V (reverse current = 10 μA), and a high breakdown voltage compound semiconductor pn junction diode was provided.
[0072]
Example 3
In the third embodiment, the contents of the present invention will be described in detail by taking an npn junction type heterobipolar transistor (HBT) having a BP mixed crystal containing boron phosphide (BP) of the present invention as an example. FIG. 11 is a schematic cross-sectional view of the npn junction type HBT 10 of the third embodiment.
[0073]
On the Si single crystal substrate 101 having the (100) plane of phosphorus (P) -doped n-type, diborane (B₂H₆) / (CH_Three)_ThreeGa / H₂Boron phosphide and gallium (B_XGa_1-XA low temperature buffer layer 102 composed of P) was laminated. The boron (B) composition ratio (= X) was 0.02 which lattice matched with the Si single crystal (lattice constant = 5.431５). The low temperature buffer layer 102 is about 1.3 × 10^FourGrowth was performed under reduced pressure of Pascal (Pa). The layer thickness of the low temperature buffer layer 102 was about 14 nm.
[0074]
B_0.02Ga_0.98On the P low-temperature buffer layer 102, the following functional layers were sequentially laminated by fixing the growth temperature at 850 ° C. using the above-described reduced pressure MOCVD reaction system. The carrier concentration (n (n-type) or p (p-type)) and layer thickness (t) of each functional layer 103 to 108 constituted the laminated structure 11 for HBT10 as follows.
(1) The boron composition ratio (= X) is linearly increased from 0.02 to 1.0 from the bonding interface with the BP low-temperature buffer layer 102 toward the layer surface, that is, the surface is boron phosphide (BP Si-doped n-type B_XGa_1-XCollector layer 103 made of a P composition gradient layer (n = 9 × 10¹⁷cm^-3T = 0.50 μm).
(2) n = 2 × 10¹⁸cm^-3, T = 0.10 μm, a sub collector layer 104 made of Si-doped n-type BP.
(3) n = 3 × 10¹⁸cm^-3, T = 0.05 μm, intermediate layer 105 made of cubic Si-doped n-type gallium nitride (GaN).
(4) p = 3 × 10¹⁹cm^-3, T = 0.01 μm, and a forbidden band width at room temperature of about 3 eV. Magnesium (Mg) doped p-type boron phosphide (BP_0.97N_0.03).
(5) n = 4 × 10¹⁸cm^-3An emitter layer 107 made of Si-doped n-type gallium nitride (GaN) with a forbidden band width of about 3.2 eV at room temperature, t = 0.20 μm.
(6) n = 7 × 10¹⁸cm^-3, T = 0.10 μm, and a contact layer 108 made of Si-doped n-type gallium nitride (GaN) having a forbidden band width of about 3.2 eV at room temperature.
[0075]
Then argon (Ar) / methane (CH_Four) / Hydrogen (H₂) Etching was performed stepwise on the HBT multilayer structure 11 by a general plasma etching means using a mixed gas to expose the surfaces of the functional layers of the contact layer 108, the base layer 106, and the sub-lector layer 104. Since the intermediate layer 105 has an effect of preventing the etching of the subcollector layer 104, the surface of the subcollector layer 104 is clearly exposed.
[0076]
An emitter electrode 109 made of a gold / germanium (Au 97 wt% / Ge 3 wt%) alloy was placed on the surface of the contact layer 108. The planar shape of the emitter electrode 109 was a square with a side length of about 110 μm. On the subcollector layer 104 exposed by the etching process, a collector electrode 110 made of an Au / Ge alloy was installed as described above. The electrodes 109 and 110 for the n-type layer were deposited by a general vacuum vapor deposition means, and then alloyed for 5 minutes at 420 ° C. Thereafter, a band-like base electrode 111 made of a gold / zinc (Au 95 wt% / Zn 5 wt%) alloy was placed on the p-type base layer 106 by a selective patterning method using a well-known photolithography technique. Thereafter, alloying heat treatment of the base electrode 111 was performed at 400 ° C. for 2 minutes. Then, it cut | judged to each semiconductor element.
[0077]
With a voltage of 2.5 V (so-called collector voltage) applied between the emitter electrode 109 and the collector electrode 110 of the obtained HBT, the base current of the base layer 106 with a sheet resistance of about 360 Ω / □ is 0 V. To 50 microamperes (μA). DC current gain (β = I_CE/ V_B) Was substantially constant with respect to the change width of the base current, and was about 95. Thus, according to the present invention, an HBT having a high DC amplification factor and stability is provided.
[0078]
Example 4
In the fourth embodiment, the contents of the present invention will be described in detail by taking, as an example, a photo detector for ultraviolet band having a boron phosphide (BP) semiconductor layer described in the present invention. FIG. 12 is a schematic cross-sectional view showing the configuration of the light receiving element 20 of the fourth embodiment.
[0079]
On a sapphire substrate 201 having (0001) (c-plane), triethylboron (C₂H_Five)_ThreeB / PH_Three/ H₂A low temperature buffer layer 202 made of boron phosphide (BP) was deposited at 380 ° C. by a system normal pressure (substantially atmospheric pressure) MOCVD method. The layer thickness of the low temperature buffer layer 202 was about 5 nm. On the BP low-temperature buffer layer 202, a silicon (Si) -doped n-type boron phosphide (BP) active layer 203 is laminated at 825 ° C. by using the above atmospheric pressure MOCVD means, and is laminated for use in the light receiving element 20. Structure 21 was constructed. The active layer 203 is composed of a BP semiconductor layer having a forbidden band width of about 3.1 eV at room temperature. The carrier concentration of the active layer 203 is about 2 × 10¹⁷cm^-3The layer thickness was about 1.8 μm.
[0080]
The manufactured light-receiving element laminated structure 21 was subjected to plasma etching to etch the central portion of the surface of the active layer 203 into a circular shape. Etching was performed on a circular region having a diameter of about 120 μm, and the etching depth was about 0.1 μm. In this region, a three-layer Schottky electrode 204 made of titanium (Ti) / platinum (Pt) / gold (Au) having a diameter of about 100 μm was formed. In addition, an annular ohmic electrode 205 having a three-layer structure of gold / germanium (Au · Ge)) / nickel (Ni) / gold (Au) is disposed around the outer periphery of the Schottky electrode 204 to place the light receiving element 20. Configured. The annular electrode 205 was formed on a circumference having a diameter of about 220 μm with the center of the Schottky electrode 204 as the center.
[0081]
In the fifth embodiment, since the BP active layer 203 is stacked with the low-temperature buffer layer 202 as the base layer, the active layer 203 becomes a high-quality crystal layer, and therefore, the reverse direction of −2 V is provided between the ohmic electrode 205 and the Schottky electrode 204. The dark current when a voltage is applied is 1 × 10^-8A / cm²Decreased to a degree. Further, the cut-off wavelength is about 400 nm, and according to the present invention, a near-UV light receiving element having excellent dark current characteristics is provided.
[0082]
【The invention's effect】
According to the present invention, boron phosphide (BP) having a high forbidden bandwidth within the range of 2.8 eV or more and 3.4 eV or less at room temperature, or a BP obtained by mixed crystallization with the BP crystal. Since the compound semiconductor element is configured using the system mixed crystal, the wide band gap property makes it possible to configure a semiconductor element that can operate at a high temperature and has a high breakdown voltage. In particular, since a zinc blende crystal type BP or BP mixed crystal having a small band-gap and a small ion binding property is used, a p-type conductive layer having a high hole concentration can be easily formed. Therefore, there is an effect that a semiconductor element that uses a low-resistance p-type semiconductor layer as a functional layer can be easily provided.
[0083]
From the pn junction type diode using the semiconductor layer made of BP or the semiconductor layer made of BP-based mixed crystal of the present invention, a normal rectifying characteristic and a high breakdown voltage diode were obtained. Also, a blue light-emitting element with high emission intensity was obtained from an LED using a semiconductor layer made of BP or a semiconductor layer made of a BP mixed crystal of the present invention. Further, from the light receiving element using the semiconductor layer made of BP or the semiconductor layer made of a BP-based mixed crystal of the present invention, a light receiving element used for the near ultraviolet band having excellent dark current characteristics was obtained.
[0084]
In addition, a field effect transistor capable of exhibiting high electron mobility could be obtained from the TEGFET using the semiconductor layer made of BP or the semiconductor layer made of BP-based mixed crystal of the present invention. In addition, the HBT using the semiconductor layer made of BP or the semiconductor layer made of a BP-based mixed crystal of the present invention has a high direct current gain and a stable HBT. Moreover, a highly sensitive Hall element having excellent heat resistance was obtained from the Hall element using the semiconductor layer made of BP or the semiconductor layer made of a BP mixed crystal of the present invention.
[0085]
According to the method for forming a wide band gap BP or BP-based mixed crystal layer of the present invention, boron phosphide having a high forbidden bandwidth within an unprecedented range of 2.8 eV to 3.4 eV at room temperature ( BP) or a BP mixed crystal can be formed stably. For this reason, it is effective in forming various heterojunction structures with other semiconductors. For example, a BP having a forbidden band width in the range described in the present invention has a barrier action on gallium nitride phosphide (GaNP mixed crystal) that could not be constructed from a conventional BP having a forbidden band width of about 2 eV. The effect which can comprise the heterojunction structure to exert is acquired.
[0086]
Further, according to the method for forming a BP or BP mixed crystal layer of the present invention, when a laminated structure for obtaining a compound semiconductor element using a single crystal having a lattice mismatch as a substrate material is constituted. In addition, a buffer layer made of BP or a BP mixed crystal that can alleviate inconsistency between the substrate material and the constituent layers of the laminated structure can be formed. Furthermore, it is possible to form a BP layer or a BP mixed crystal layer having excellent crystallinity on the buffer layer that can alleviate the lattice mismatch. Therefore, according to the formation method of the present invention, it is possible to form a laminated structure including a BP layer or a BP mixed crystal layer having excellent crystallinity and to provide a compound semiconductor element having excellent characteristics.
[Brief description of the drawings]
FIG. 1 is a correlation diagram between a forbidden band width at room temperature and an average atomic number of constituent elements of a III-V group compound semiconductor.
FIG. 2 is a graph showing the photon energy dependence of the absorption coefficient of a BP semiconductor layer according to the present invention.
FIG. 3 is a cathodoluminescence (CL) spectrum of a BP semiconductor layer according to the present invention.
FIG. 4 is a schematic cross-sectional view of a TEGFET configured using a BP semiconductor layer according to the present invention.
FIG. 5 is a schematic cross-sectional view of a laminated structure for use in a Hall element configured using a BP semiconductor layer according to the present invention.
FIG. 6 is a schematic cross-sectional view of a pn junction LED according to Example 1 of the present invention.
7 is a graph showing the wavelength dependence of the refractive index and extinction coefficient of the BP layer according to Example 1 of the present invention. FIG.
FIG. 8 is a relationship diagram between an imaginary part of dielectric constant of a BP layer and photon energy according to Example 1 of the present invention.
FIG. 9 is a schematic cross-sectional view of a pn junction diode according to Example 2 of the present invention.
FIG. 10 is a graph showing current-voltage characteristics of a pn junction diode according to Example 2 of the present invention.
FIG. 11 is a schematic diagram showing a cross-sectional structure of an npn junction type HBT according to Embodiment 3 of the present invention.
FIG. 12 is a schematic cross-sectional view of a light-receiving element according to Example 4 of the present invention.
[Explanation of symbols]
10 HBT
11 Laminated structure for HBT
101 n-type Si single crystal substrate
102 Low temperature buffer layer
103 Collector layer
104 Subcollector layer
105 Middle layer
106 Base layer
107 Emitter layer
108 Contact layer
109 Emitter electrode
110 Collector electrode
111 Base electrode
20 Light receiving element
21 Multilayer structure for light receiving element
201 Sapphire substrate
202 BP low temperature buffer layer
203 BP active layer
204 Schottky electrode
205 Ohmic electrode
40 TEGFET
401 substrate
402 Low temperature crystal layer
403 High temperature crystal layer
404 Electronic traveling layer
405 Spacer layer
406 Electron supply layer
407 Contact layer
408 Gate electrode
409 Source electrode
410 Drain electrode
411 Recess Department
501 substrate
502 1st buffer layer
503 Second buffer layer
504 Magnetosensitive layer
505 Spacer layer
60 LED
61 Laminated structure for LED
601 substrate
602 Low temperature buffer layer
603 Lower cladding layer
604 light emitting layer
605 Upper cladding layer
606 Light emitting unit
607 Current spreading layer
608 n-type ohmic electrode
609 p-type ohmic electrode
90 diodes
901 substrate
902 Buffer layer
902-1 Low temperature crystal layer
902-2 High temperature crystal layer
903 n-type BP layer
904 p-type BP layer
905 p-type ohmic electrode
906 n-type ohmic electrode

Claims (31)

A semiconductor element comprising a semiconductor layer made of boron phosphide (BP) having a forbidden band width at room temperature of 2.8 electron volts (eV) to 3.4 eV. The semiconductor element according to claim 1, further comprising a heterojunction between a semiconductor layer made of boron phosphide (BP) and another semiconductor layer having a different band gap from the semiconductor layer. 3. The semiconductor element according to claim 2, wherein the semiconductor layer made of boron phosphide (BP) and the semiconductor layer forming a heterojunction with the semiconductor layer are lattice-matched. _4. The semiconductor element according to claim 3, wherein the semiconductor layer forming a heterojunction with the semiconductor layer made of boron phosphide (BP) is GaN _0.97 P _0.03 . 5. The semiconductor element according to claim 1, wherein a semiconductor layer made of boron phosphide (BP) is stacked on a crystal substrate. Including boron phosphide (BP) to less 3.4eV a bandgap at room temperature 2.8 electron volts (eV) or more, the formula _{B α Al β Ga γ In 1-} α - β - γ P δ As _ε N _{1- δ - ε} (0 <α ≦ 1, 0 ≦ β <1, 0 ≦ γ <1, 0 <α + β + γ ≦ 1, 0 <δ ≦ 1, 0 ≦ ε <1, 0 <δ + ε ≦ 1 ) A semiconductor element comprising a semiconductor layer made of a boron phosphide (BP) -based mixed crystal. The boron phosphide (BP) mixed crystal is an aluminum phosphide / boron mixed crystal (B _X Al _1-X P: 0 <X <1), a gallium phosphide / boron mixed crystal (B _X Ga _1-X P: 0). <X <1) or indium phosphide-boron mixed crystal _{(B X in 1-X P} : 0 < a semiconductor device according to claim 6, characterized in that the X <1). 8. The semiconductor element according to claim 6, comprising a heterojunction between a semiconductor layer made of boron phosphide (BP) -based mixed crystal and another semiconductor layer having a different band gap from the semiconductor layer. . 9. The semiconductor element according to claim 8, wherein a semiconductor layer made of a boron phosphide (BP) mixed crystal and a semiconductor layer forming a heterojunction with the semiconductor layer are lattice-matched. 10. The semiconductor device according to claim 6, wherein a semiconductor layer made of boron phosphide (BP) -based mixed crystal is stacked on a crystal substrate. The semiconductor device according to claim 1, further comprising a pn junction structure. The semiconductor device according to claim 11, wherein the semiconductor device is a light emitting device. The semiconductor device according to claim 1, wherein the semiconductor device is a light receiving device. The semiconductor device according to claim 1, wherein the semiconductor device is a transistor. The semiconductor device according to claim 14, wherein the semiconductor device is a field effect transistor (FET). 15. The semiconductor device according to claim 14, wherein the semiconductor device is a heterobipolar transistor (HBT). The semiconductor device according to claim 1, wherein the semiconductor device is a Hall device. A semiconductor layer made of boron phosphide (BP) having a band gap at room temperature of 2.8 electron volts (eV) to 3.4 eV. The semiconductor layer according to claim 18, wherein a semiconductor layer made of boron phosphide (BP) is stacked on a crystal substrate. Including boron phosphide (BP) to less 3.4eV a bandgap at room temperature 2.8 electron volts (eV) or more, the formula _{B α Al β Ga γ In 1-} α - β - γ P δ As _ε N _{1- δ - ε} (0 <α ≦ 1, 0 ≦ β <1, 0 ≦ γ <1, 0 <α + β + γ ≦ 1, 0 <δ ≦ 1, 0 ≦ ε <1, 0 <δ + ε ≦ 1 The semiconductor layer which consists of a boron phosphide (BP) type mixed crystal represented by this. The boron phosphide (BP) mixed crystal is an aluminum phosphide / boron mixed crystal (B _X Al _1-X P: 0 <X <1), or a gallium phosphide / boron mixed crystal (B _X Ga _1-X P: 0). <X <1) or indium phosphide-boron mixed crystal _{(B X in 1-X P} : 0 < a semiconductor layer according to claim 20, characterized in that the X <1). The semiconductor layer according to claim 20 or 21, wherein a semiconductor layer made of a boron phosphide (BP) based mixed crystal is laminated on a crystal substrate. The method for growing a semiconductor layer according to any one of claims 18 to 22, wherein the semiconductor layer is grown by a vapor phase growth method. The method for growing a semiconductor layer according to claim 23, wherein the semiconductor layer is grown at a temperature higher than 750 ° C and not higher than 1200 ° C. The method for growing a semiconductor layer according to claim 23 or 24, wherein the vapor phase growth method is a metal organic chemical vapor deposition method (MOCVD method). The ratio of the total supply amount of the group V element source containing phosphorus (P) to the total supply amount of the group III element source containing boron (B) during the growth of the semiconductor layer is 15 to 60, and the semiconductor 26. The method for growing a semiconductor layer according to claim 25, wherein the growth rate of the layer is set to 20 to 300 mm / min. A buffer layer made of amorphous boron phosphide (BP) or boron phosphide (BP) mixed crystal is formed on the crystal substrate by MOCVD at a temperature of 250 ° C. or higher and 750 ° C. or lower. A semiconductor layer growth method for growing a semiconductor layer made of boron phosphide (BP) having a forbidden band width of 2.8 electron volts (eV) or more and 3.4 eV or less on a layer. A buffer layer made of amorphous boron phosphide (BP) or boron phosphide (BP) based mixed crystal is formed on a crystal substrate by MOCVD at a temperature of 250 ° C. or higher and 750 ° C. or lower. including boron phosphide (BP) to less 3.4eV a bandgap at room temperature 2.8 electron volts (eV) or more on the layer, the formula _{B α Al β Ga γ in 1-} α - β - _γ P _δ As _ε N _{1- δ - ε} (0 <α ≦ 1, 0 ≦ β <1, 0 ≦ γ <1, 0 <α + β + γ ≦ 1, 0 <δ ≦ 1, 0 ≦ ε <1, 0 < A semiconductor layer growth method for growing a semiconductor layer made of a boron phosphide (BP) -based mixed crystal represented by δ + ε ≦ 1). The boron phosphide (BP) mixed crystal is an aluminum phosphide / boron mixed crystal (B _X Al _1-X P: 0 <X <1), or a gallium phosphide / boron mixed crystal (B _X Ga _1-X P: 0). <X <1) or indium phosphide-boron mixed crystal _{(B X in 1-X P} : 0 < growing method of a semiconductor layer according to claim 28, characterized in that the X <1). 30. The method for growing a semiconductor layer according to claim 27, wherein the semiconductor layer is grown at a temperature higher than 750.degree. C. and not higher than 1200.degree. C. by a vapor phase growth method. 31. The method for growing a semiconductor layer according to claim 27, wherein the semiconductor layer is grown by MOCVD.

Images