JP2004047847A - Manufacturing method for boron phosphate layer, and boron phosphate semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing high resistance boron phosphate layer useable for an electric field effect transistor (FET) and a light emitting device, etc., on a crystal substrate. <P>SOLUTION: When a high resistance boron phosphate (BP) layer is formed directly on a crystal substrate with the aid of gas phase growing means, the high resistance boron phosphate layer is formed by keeping temperature of the crystal substrate in a range of from 1000 °C or higher to 1200 °C or lower, and doping magnesium (Mg) is added into the boron phosphate layer exhibiting p-type conductivity in an undoped state. When it is formed by being joined with an amorphous base layer formed on the crystal substrate, the temperature of the crystal substrate is kept at 750 °C or higher, and at temperature or lower where the amorphous base layer is subjected to gas phase growth. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
INDUSTRIAL APPLICABILITY The present invention can be effectively used for, for example, blocking leakage of operating current when configuring a field effect transistor (FET), or a current blocking layer or the like when configuring a light emitting element such as a light emitting diode (LED). The present invention relates to a novel technique for producing a high-resistance boron phosphide layer by a vapor phase growth means, which can be suitably used as a semiconductor device.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a high-resistance group III-V compound semiconductor layer exhibiting electrical insulation and having high resistance has been used as, for example, a buffer layer of a Schottky junction field effect transistor (MESFET). (See J. Crystal Growth, 55 (1981), pp. 255-262). For example, in a gallium nitride (GaN) -based MESFET, monomeric boron phosphide (BP), which is made to have a high resistance by intentionally adding oxygen (O) belonging to a group VI element of the element periodicity, is used. There is a technology example in which is used as a buffer layer. Further, in a light emitting diode (LED) in a blue band, oxygen is doped (doped) instead of a pn junction composed of n-type and p-type boron phosphide layers (see JP-A-10-242569). There is an example in which a current confinement layer is simply formed from the obtained high-resistance boron phosphide layer.
[0003]
Conventionally, a high-resistance boron phosphide layer doped with Group VI oxygen is conventionally formed of a boron compound containing an oxygen atom, for example, triethoxyborane ((C ₂ H ₅ O) ₃ It is formed by vapor phase growth means using B)) as a boron source. Alternatively, it is formed by a metal organic chemical vapor deposition (MOCVD) means in a gaseous atmosphere containing a small amount of oxygen. The resistivity (specific resistance) at room temperature of the oxygen-added boron phosphide layer obtained by these conventional vapor phase growth techniques is 1 × 10 ⁴ It remains below ohm-cm (unit: Ω-cm).
[0004]
In addition to means for forming a high-resistance semiconductor layer by adding an impurity capable of forming a deep level in a III-V group compound semiconductor such as oxygen or chromium (Cr), a shallow level ( There may be a means for forming a shallow level, adding an impurity imparting conductivity, and forming a high-resistance layer by an electric compensation effect. For example, a p-type impurity imparting p-type conductivity is added to an n-type III-V compound semiconductor layer to electrically compensate for a residual donor by using an acceptor. This is a means for obtaining a high-resistance layer. Conversely, means for adding an n-type impurity to the p-type III-V compound semiconductor layer and compensating for the residual acceptor with a donor to form a high-resistance layer can also be considered. In addition, after the III-V compound semiconductor layer is vapor-phase grown, there may be a means for increasing the resistance by implanting ions of impurities of the opposite conductivity type to the layer.
[0005]
[Problems to be solved by the invention]
In the conventional technical means for obtaining a high-resistance boron phosphide layer by adding oxygen, the obtained resistivity is 1 × 10 3 as described above. ⁴ Ω · cm or less. The leakage of the operating current is further suppressed, and a high trans-conductance (g) is obtained. _m In order to construct the FET of (1), it is necessary to use a boron phosphide layer having a higher resistance. In the FET, an impurity such as oxygen which forms a deep impurity level acts as a trap center and causes a temporal change in the drain current. . That is, the means for increasing the resistance by adding oxygen cannot sufficiently suppress the leakage of the drain current, is excellent in pinch-off characteristics, and has a high g-value. _m However, a high-resistance boron phosphide layer that provides a high-FET with sufficient stability has not been achieved.
[0006]
Also, a technique of adding an impurity for imparting conductivity can be considered as one means for forming a high-resistance boron phosphide layer. However, boron phosphide grown in a vapor phase already has 10 ²⁰ cm ^-3 There is a large amount of vacancies to the extent or more. For example, a large amount of phosphorus vacancies are present in an undoped boron phosphide layer grown at a high temperature exceeding 1000 ° C., and boron occupies these vacancies. Is formed as a low resistance layer. It is actually difficult to electrically compensate the acceptor involved in the phosphorus vacancies present at a high concentration by adding an n-type impurity to form a high resistance layer. 10 ²⁰ -10 ²¹ cm ^-3 In order to generate high-concentration donors, it is necessary to add at least a higher n-type impurity, which only results in disordered crystals. A so-called counter-doping method of adding a large amount of n-type impurities to the p-type conductive layer and conversely adding p-type impurities to the n-type conductive layer is a method of counter-doping of boron or phosphorus existing at a high concentration. The specific boron phosphide in which the holes dominantly determine the conductivity type cannot be a sufficiently effective technical means for forming a high-resistance boron phosphide layer.
[0007]
SUMMARY OF THE INVENTION The present invention solves the problems of the prior art in view of the unique properties of boron phosphide semiconductors which contain boron and phosphorus as constituent elements, each of which is likely to generate volatile substances at high temperatures. It is an object of the present invention to provide a method for manufacturing a high-resistance boron phosphide layer which can be used for a (FET), a light-emitting element, and the like on a crystal substrate.
[0008]
[Means for Solving the Problems]
That is, the present invention
(1) In a method for manufacturing a boron phosphide layer in which a boron phosphide (BP) layer is formed directly on a crystal substrate by vapor phase growth means, the temperature of the crystal substrate is maintained in a range of 1000 ° C. to 1200 ° C. And forming a high-resistance boron phosphide layer by adding magnesium (Mg) to the boron phosphide layer exhibiting p-type conductivity in an undoped state. Production method.
(2) In a method for producing a boron phosphide layer formed by bonding a boron phosphide layer to an amorphous underlayer formed on a crystal substrate by a vapor phase growth means, the temperature of the crystal substrate is set to 750 ° C. or higher. In addition, while maintaining the temperature of the amorphous underlayer at a temperature equal to or lower than the vapor growth temperature, magnesium (Mg) is added to the boron phosphide layer exhibiting p-type conductivity in an undoped state to provide high-resistance phosphide. A method for producing a boron phosphide layer, comprising forming a boron layer.
(3) An amorphous underlayer containing boron (B) and phosphorus (P), which is directly grown on a crystal substrate at a temperature of 750 ° C. or more and 1200 ° C. or less, and has a layer thickness of 2 nanometers ( (2) The method for producing a boron phosphide layer according to the above (2), wherein the layer is not less than 50 nm and not more than 50 nm.
(4) The production of the boron phosphide layer according to the above (2) or (3), wherein the high resistance boron phosphide layer and the amorphous underlayer are formed by the same vapor phase growth means. Method.
(5) A boron phosphide-based semiconductor device comprising a high-resistance boron phosphide layer formed by the method according to any one of the above (1) to (4).
(6) The phosphorus according to (5), wherein the boron phosphide-based semiconductor element is a field effect transistor (FET) in which an active layer is provided above a high resistance boron phosphide layer. Boronide semiconductor element.
(7) The boron phosphide-based semiconductor element is a Schottky junction field effect transistor in which a Schottky-junction metal gate electrode is provided by being joined to a high-resistance boron phosphide layer. The boron phosphide-based semiconductor device according to the above (5) or (6).
(8) The boron phosphide-based semiconductor element is a light-emitting element in which an ohmic electrode made of a metal material having ohmic contact is provided above a high-resistance boron phosphide layer. A boron phosphide-based semiconductor device according to 5).
(9) The boron phosphide-based semiconductor element includes a high-resistance boron phosphide layer as a current confinement layer for narrowing a flow path of an element operation current supplied from the ohmic contact electrode to the light emitting layer. The boron phosphide-based semiconductor device according to the above (8), which is a laser diode.
(10) The light-emitting diode in which the boron phosphide-based semiconductor element includes a high-resistance boron phosphide layer as a current blocking layer for preventing a forward current from flowing to a projection region of the ohmic contact electrode. (8) The boron phosphide-based semiconductor device according to the above (8).
It is.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
The boron phosphide layer of the present invention is grown on a substrate made of a conductive or insulating crystal having heat resistance at a high temperature. For a boron phosphide-based light-emitting element such as an LED or LD, a conductive crystal such as silicon (Si) single crystal, silicon carbide (SiC), or gallium nitride (GaN) is preferably used as a substrate because of easy arrangement of ohmic electrodes. Available to Insulating sapphire (α-Al ₂ O ₃ Single crystals) and other oxide single crystals can be used as a crystal substrate for FET applications. Means for vapor-phase growing a boron phosphide layer on these crystal substrates include a halogen method, a hydride method, a molecular beam epitaxial (MBE) method, and a MOCVD method. Triethyl boron ((C ₂ H ₅ ) ₃ The MOCVD method using an organic boron compound such as B) as a boron source is a convenient means because an amorphous boron phosphide layer can be vapor-phase grown at a relatively low temperature.
[0010]
The temperature at which the boron phosphide layer is directly vapor-grown on a crystal substrate as described above is in the range of 1000 ° C. or more and 1200 ° C. or less. In the present invention, it is based on vapor-phase growth of a boron phosphide layer having p-type conductivity in an undoped state in which impurities are not intentionally added. At high temperatures above 1200 ° C, B ₁₃ P ₂ (See J. Am. Ceramic Soc., 47 (1) (1964), pp. 44-46), which is inconvenient for obtaining monomeric boron phosphide. The main vapor growth conditions of the vapor growth temperature and the V / III ratio are 1 × 10 ¹⁹ cm ^-3 ~ 1 × 10 ²⁰ cm ^-3 It is preferable to set so that a carrier (hole) concentration within the range described above can be obtained. The higher the vapor phase growth temperature, the higher the obtained carrier (hole) concentration. The V / III ratio is the concentration ratio of the phosphorus source to the boron source during vapor phase growth. The carrier concentration can be measured by the usual Hall effect.
[0011]
In the present invention, a high-resistance boron phosphide layer is vapor-deposited by intentionally doping magnesium (Mg) under the condition that a p-type boron phosphide layer can be vapor-phase grown in an undoped state. Magnesium is a typical p-type impurity for III-V compound semiconductors (see "III-V compound semiconductors" (May 20, 1994, first edition issued by Baifukan Co., Ltd.), pp. 73-77). . The present invention is completely different from the method of forming a high-resistance semiconductor layer by counterdoping magnesium (Mg) into an n-type III-V compound semiconductor layer. A high resistance boron phosphide layer is vapor-phase grown by doping magnesium (Mg) which is a p-type impurity. As a source of addition of magnesium (Mg) to the p-type boron phosphide layer, bis-cyclopentadienyl magnesium (bis- (C ₅ H ₅ ) ₂ Mg). Bis- (C to boron phosphide layer ₅ H ₅ ) ₂ In doping using Mg, the concentration of Mg atoms in the boron phosphide layer increases substantially linearly as shown in FIG. 1 according to the supply amount of the magnesium (Mg) source. In order to form a high-resistance boron phosphide layer, the concentration of Mg atoms in the boron phosphide layer is 1 × 10 ¹⁹ Atom / cm ^-3 ~ 1 × 10 ²⁰ Atom / cm ^-3 It is preferable to dope Mg so that 10 ¹⁸ Atom cm ^-3 Doping with magnesium (Mg) at a low concentration of about / only leaves a p-type boron phosphide layer that is not sufficiently high in resistance, even though Mg acts as an acceptor. The atomic concentration of Mg in the boron phosphide layer can be determined by general secondary ion mass spectrometry (SIMS), Auger spectroscopy, or the like.
[0012]
Of the Group II elements that are p-type impurities for Group III-V compound semiconductors, magnesium (Mg) is most effective in providing a high resistance boron phosphide layer. Magnesium (Mg) is boron and has the chemical formula: MgB ₂ Or the chemical formula: MgB ₆ (See "Data Book Handbook of High Melting Compounds" (December 20, 1977, published by Nippon Soso Communication Co., Ltd.), p. 122). reference). Therefore, by adding magnesium (Mg) at the same time as the vapor phase growth of the boron phosphide layer, Mg is combined with the boron constituting the boron phosphide layer and volatilizes together with boron. As a result, a large amount of boron is removed. Voids can be created in the boron phosphide layer. Then, a large amount of donors are generated due to the occupation of the generated boron vacancies by the phosphorus atoms, and the donors combine the acceptor existing in the boron phosphide layer in an undoped state with the acceptor generated due to the addition of Mg. It electrically compensates and contributes to providing a high resistance boron phosphide layer. According to the magnesium (Mg) doping means according to the present invention, the specific resistance (= resistivity) at room temperature is 1 × 10 ⁴ A high-resistance boron phosphide layer having a resistance of Ω · cm or more can be vapor-phase grown.
[0013]
As another method of manufacturing a boron phosphide layer on a crystal substrate, a p-type boron phosphide layer for forming a high-resistance layer is formed by forming an amorphous layer containing boron and phosphorus formed on a crystal substrate underneath. The ground layer can be formed by bonding to the amorphous layer. The amorphous layer eliminates the lattice mismatch between the crystal substrate and the p-type boron phosphide layer, and has good crystallinity p-type boron phosphide having a low density of crystal defects such as misfit dislocations. Has the effect of providing a layer. Further, boron and phosphorus constituting the amorphous layer are used as a “growth nucleus” for vapor phase growth of a p-type boron phosphide layer (Akira Nishinaga, “Basics of Crystal Growth” (Baifukan Co., Ltd., 1997) The first edition published on June 23), see Chapter 2), and can contribute to providing a continuous p-type boron phosphide layer without gaps. In particular, an amorphous layer containing boron in a stoichiometrically rich amount compared to phosphorus is particularly suitable for vapor-phase growth of a p-type boron phosphide layer. The amorphous layer enriched with boron has a stoichiometrically insufficient amount of phosphorus, and therefore contains an excessive amount of phosphorus vacancies that can act as acceptors. Therefore, the amorphous layer containing boron abundantly can sufficiently exert the action of alleviating the lattice mismatch with the crystal substrate, and also continuously brings excess phosphorus vacancies to the upper boron phosphide layer, This is effective in reliably providing a p-type boron phosphide layer in an undoped state. The amorphous layer containing excess boron can be formed particularly stably at a temperature of 750 ° C. to 1200 ° C. The thickness of the amorphous layer is preferably 2 nm or more and 50 nm or less. The concentration of phosphorus vacancies present in excess as compared with boron vacancies involved in the generation of donors is measured, for example, as a p-type carrier (hole) concentration in Hall effect measurement. The amorphous layer containing boron and phosphorus includes boron phosphide, boron phosphide / gallium (B _X Ga _1-X P: 0 <X <1), boron phosphide / aluminum / indium (B _X Al _Y In _1-XY P: 0 <X <1, 0 ≦ Y <1, 0 <X + Y ≦ 1).
[0014]
It is convenient to obtain a high-resistance boron phosphide layer by forming a high-resistance boron phosphide layer by the same vapor-phase growth means after vapor-phase growth of an amorphous layer on a crystal substrate. . For example, triethyl boron ((C ₂ H ₅ ) ₃ B) as a boron source and phosphine (PH ₃ The amorphous layer and the boron phosphide layer are successively vapor-phase grown by the atmospheric pressure (substantially atmospheric pressure) or reduced pressure MOCVD method using) as a phosphorus source. In particular, after the amorphous layer containing boron and phosphorus is vapor-phase grown by the MOCVD method, subsequently, the same MOCVD vapor-phase growth apparatus as used for the vapor-phase growth of the amorphous layer is used. The technique of vapor-phase growing a boron phosphide layer is convenient. If the high-resistance boron phosphide layer is formed at a temperature of 750 ° C. or higher and a temperature lower than the temperature at which the amorphous underlayer is vapor-phase grown, the single crystal boron phosphide layer is vapor-phase grown. It will be convenient. When the temperature is lower than 750 ° C., a polycrystalline boron phosphide layer tends to be easily obtained. In addition, according to the technique of growing the high-resistance boron phosphide layer at a temperature equal to or lower than the temperature at which the amorphous layer is vapor-phase grown, the amorphous layer can be prevented from being thermally damaged and denatured, Therefore, there is an advantage that a high-resistance boron phosphide layer having excellent crystallinity can be grown in a vapor phase.
[0015]
The high-resistance boron phosphide layer of the present invention can be used to form various semiconductor devices. For example, a high-resistance boron phosphide layer provided on an insulating crystal substrate can be used as a high-resistance buffer layer for suppressing leakage of a drain current when forming a MESFET. Further, when configuring a field effect transistor (TEGFET) using a two-dimensional electron gas, it can be used as a gate electrode forming layer for forming a Schottky gate electrode in addition to a buffer layer. Since the high-resistance boron phosphide layer according to the present invention utilizes magnesium (Mg) which forms a relatively shallow level, a conventional III-V group which has a high resistance by adding a deep impurity is used. Unlike a compound semiconductor layer, a high-resistance layer which is superior in suppressing a temporal change (drift) of a drain current or the like can be provided.
[0016]
The high-resistance boron phosphide layer of the present invention can be used as a high-resistance layer constituting a current confinement layer of an LD in a light-emitting element. In the LED, the short-circuit flow of the element operating current to the light emitting portion is prevented, and the LED can be suitably used as a current blocking layer for diffusing the current over substantially the entire surface of the light emitting portion. For example, a gallium nitride (GaN) layer serving as an upper clad layer is vapor-phase grown while doping with magnesium (Mg), and then a high-resistance boron phosphide layer is formed while also doping with Mg. Next, processing is performed so as to leave a high-resistance boron phosphide layer only in a region where an ohmic electrode is to be arranged. Next, the exposed surface of the upper clad layer and the surface of the remaining high-resistance boron phosphide layer are covered with a highly conductive transparent conductive film such as an indium-tin composite oxide (ITO) film. Next, an ohmic electrode is provided above the remaining high resistance boron phosphide layer in contact with the transparent conductive film. With this configuration, the operating current supplied from the electrode is prevented from flowing in the vertical direction to the light emitting portion below by the high-resistance boron phosphide layer, and preferentially flows in the horizontal direction via the transparent conductive film. Is done. For this reason, the operating current can be spread over a wide range of the light emitting section, and an LED with high light emission intensity can be provided.
[0017]
Further, the boron phosphide layer of the present invention which is doped with magnesium (Mg) to have a high resistance is used for forming a stripe type LD, for example, in "Structure LD" (edited by Ryoichi Ito and Michiharu Nakamura, "Semiconductor Laser"). (See Baifukan Co., Ltd., first edition, sixth edition, published on October 30, 1997), pp. 118-121), which can be effectively used as a current constriction layer. An LD including a magnesium-doped high-resistance boron phosphide layer as a current confinement layer is formed, for example, by the following procedure. First, a boron phosphide layer is vapor-grown on the surface of the upper cladding layer on the light emitting layer composed of single or multiple quantum wells (QW) while doping with magnesium. The vapor-grown high-resistance boron phosphide layer is removed in a strip shape only in a region where an electrode to be in ohmic contact with the upper cladding layer is to be formed. The area to be strip-shaped is generally 3 × 10 ^-4 cm ~ 3 × 10 ^-3 cm and is a stripe-shaped region whose length is substantially equal to the length of the resonator. Next, an LD is formed by covering the surface of the high-resistance boron phosphide layer including the region opened in a stripe shape with an ohmic electrode. The element operating current supplied from the ohmic electrode for driving the LD is narrowed in the region through which the high-resistance boron phosphide layer flows, and intensively flows only in the region opened in a stripe shape. A current of a density is injected into the light emitting layer via the upper cladding layer. In particular, in the present invention, the lattice spacing (the spacing between the {110} crystal planes of boron phosphide) which is substantially equal to the a-axis lattice constant ({0.319 nm) of gallium nitride (GaN) is substantially equal to about 0.321 nm. ), The current confinement layer is composed of a boron phosphide layer, so that a current confinement layer having few crystal defects such as misfit dislocations can be formed on the upper cladding layer made of aluminum / gallium nitride. In addition, it is possible to provide an LD with less withstand voltage failure involving dislocations in the layer.
[0018]
[Action]
In the means for vapor-phase growing a high-resistance boron phosphide layer while adding magnesium (Mg) according to the present invention, Mg added to the boron phosphide layer contains undoped p-type boron phosphide inside the layer. It has the function of generating boron vacancies capable of electrically compensating for acceptors involving phosphorus vacancies.
[0019]
【Example】
(First embodiment)
The content of the present invention will be specifically described by taking, as an example, a case where a high-resistance boron phosphide layer doped with magnesium (Mg) is used as a buffer layer to form a stacked structure for a gallium nitride (GaN) -based MESFET. explain.
[0020]
FIG. 2 schematically shows a cross-sectional structure of a laminated structure 1A that can be used for forming a GaN-based MESFET. Crystal substrate 101 was an undoped high-resistance silicon (Si) single crystal having a {111} plane with a resistivity of 10 Ω · cm or more. On the surface of the substrate 101, triethyl boron ((C ₂ H ₅ ) ₃ B) / phosphine (PH ₃ ) / Hydrogen (H ₂ A) Amorphous layer 102 containing boron and phosphorus was formed at 1025 ° C. using MOCVD growth means at normal pressure (substantially atmospheric pressure). V / III ratio (= PH) when the amorphous layer 102 is grown by vapor phase ₃ / (C ₂ H ₅ ) ₃ B supply concentration ratio) was set to 16. The thickness of the amorphous layer 102 was about 10 nm. The supply of triethylboron as a boron source to the vapor phase growth region was once stopped to terminate the vapor phase growth of the amorphous layer 102.
[0021]
On the other hand, the phosphine (PH ₃ ) And hydrogen (H ₂ ), The temperature of the Si single crystal substrate 101 was lowered from 1025 ° C. to 850 ° C. Thereafter, the boron source was again supplied to the vapor phase growth region, and joined to the amorphous layer 102 to start vapor phase growth of the high resistance boron phosphide layer 103 serving as a buffer layer. During the vapor phase growth of the boron phosphide layer 103, about 2.0 × 10 ¹⁹ cm ^-3 The V / III ratio was set to 1296 so as to obtain a p-type conductive layer having a carrier (hole) concentration of 1296. Magnesium (Mg) was doped in order to obtain a high resistance layer under the vapor growth conditions. The doping source of Mg is biscyclopentadienyl magnesium (bis- (C ₅ H ₅ ) ₂ Mg) was used. The concentration of Mg atoms in the boron phosphide layer is about 1 × 10 5 in order to generate a high concentration of boron vacancy-related donors due to the formation of a volatile compound with boron. ²⁰ Atom / cm ³ Magnesium was added so that Thus, the resistivity at room temperature is about 2 × 10 ⁴ A high resistance boron phosphide layer 103 having a resistance of Ω · cm was obtained. The layer thickness of the high-resistance boron phosphide layer 103 was about 100 nm. The supply of the boron source, the phosphorus source, and the magnesium source to the vapor phase growth region was stopped, and the vapor phase growth of the high-resistance boron phosphide layer was terminated. Hydrogen gas was continuously circulated in the vapor phase growth region.
[0022]
Next, while maintaining the temperature of the Si single crystal substrate 101 at 850 ° C., the amorphous layer 102 and the high-resistance boron phosphide layer 103 were undoped in the same MOCVD vapor deposition apparatus as used for vapor phase growth. An n-type gallium nitride (GaN) layer 104 was grown by vapor phase. The gallium nitride layer 104 is made of trimethylgallium ((CH ₃ ) ₃ Ga) / ammonia (NH ₃ ) / H ₂ The reaction system was vapor-phase grown by atmospheric pressure MOCVD. The lattice spacing ({0.321 nm) of {110} -crystal plane of boron phosphide intersecting the {111} -crystal plane forming the surface of the high-resistance boron phosphide layer 103 and the wurtzite crystal form (Wurtzite) Since the a-axis lattice constant (≒ 0.319 nm) of GaN substantially matched, the gallium nitride layer 104 was a crystal layer composed of a {0001} -crystal plane. In consideration of the use as the active layer (channel) of the MESFET, the V / III ratio is about 1.2 × 10 4 to obtain the n-type gallium nitride layer 104 having a low carrier (electron) concentration. ⁴ Set to. The carrier concentration of the undoped n-type gallium nitride layer 104 is about 2 × 10 ¹⁶ cm ^-3 The layer thickness was set to about 50 nm. In addition, due to good lattice spacing matching with the magnesium (Mg) -doped high-resistance boron phosphide layer 103 of the buffer layer, the electron mobility of the gallium nitride layer 104 at room temperature is about 660 cm. ² / V · s.
[0023]
The supply of trimethylgallium to the vapor phase growth region was stopped, and the vapor phase growth of the gallium nitride layer 104 was terminated. Thereafter, a magnesium (Mg) -doped high-resistance boron phosphide layer 105 was formed again at 850 ° C. using the same MOCVD vapor deposition apparatus. The vapor-phase growth conditions for the high-resistance boron phosphide layer 105 were the same as those for the high-resistance boron phosphide layer 103 used as a buffer layer. The atomic concentration of magnesium (Mg) in the layer is also about 1 × 10 4 in order to obtain substantially the same resistivity as the high-resistance boron phosphide layer 103. ²⁰ Atom / cm ³ And However, the layer thickness was 50 nm. Thereafter, the supply of the boron source to the vapor phase growth region was stopped, and the vapor phase growth of the high-resistance boron phosphide layer 105 was terminated. Until the temperature of the Si single crystal substrate 101 dropped to about 600 ° C., phosphine was kept flowing, thereby suppressing the volatilization of phosphorus from the surface of the high-resistance boron phosphide layer 105. The supply of phosphine was stopped at about 600 ° C., and the mixture was naturally cooled to a temperature near room temperature in a hydrogen gas atmosphere. Accordingly, the high-resistance boron phosphide layer 103 doped with magnesium is used as a buffer layer, the n-type gallium nitride layer 104 is used as an active layer, and the high-resistance boron phosphide layer 105 is used as a gate of a Schottky junction field effect transistor. A laminated structure 1A used as an electrode forming layer was formed.
[0024]
The boron phosphide layer 103 serving as a high-resistance buffer layer has no gap because the amorphous layer 102 containing boron and phosphorus is used as a base layer and is vapor-phase grown at a lower temperature than the amorphous layer 102. It became a continuous layer with a flat surface. Reflecting the continuity of the boron phosphide layer 103 and the flatness of the surface, the gallium nitride layer 104 has a void (“Lattice Mismatched Thin Films” (The Minerals, Metals & Materials Society, 1999) (ISBN No. 0). 87339-444-5), see pages 177-182). In addition, since the vapor phase growth is performed with the gallium nitride layer 104 having a good surface state interposed therebetween, the smoothness of the surface of the boron phosphide layer 105 is represented by rms (root mean square); (Square root value of average value) was as good as about 0.5 nm.
[0025]
(Second embodiment)
In the second embodiment, the contents of the present invention will be specifically described by taking as an example a case where a MESFET is formed from a laminated structure having a high-resistance boron phosphide layer as a buffer layer.
[0026]
FIG. 3 schematically shows a cross-sectional structure of the MESFET according to the second embodiment. The same components as those already shown in FIG. 2 are denoted by the same reference numerals in FIG.
[0027]
After taking out the laminated structure 1A produced in the first embodiment from the MOCVD vapor deposition apparatus, the surface of the high-resistance boron phosphide layer 105 is processed using a general photolithography technique, and the gate ( gate) Only the region where the electrode 107 is to be formed is left. Next, the laminated structure 1A thus processed is placed again in the MOCVD vapor deposition apparatus, and an undoped n-type boron phosphide layer 106 is deposited as an ohmic contact layer for forming an ohmic electrode. did. The n-type boron phosphide layer 106 corresponds to the above (C ₂ H ₅ ) ₃ B / PH ₃ / H ₂ Vapor-phase growth was performed at 850 ° C. using a reactive MOCVD method. The carrier (electron) concentration of the n-type boron phosphide layer 106 is about 1 × 10 ¹⁹ cm ^-3 And the layer thickness was about 150 nm. After the supply of the boron source to the vapor phase growth region is stopped and the growth of the n-type boron phosphide layer 106 is completed, the boron source is cooled to room temperature by the same method as in the case of the high-resistance boron phosphide layer 105. A laminated structure 1B for MESFET 10 was formed.
[0028]
After cooling, the n-type boron phosphide layer 106 covering the remaining high-resistivity boron phosphide layer 105 is applied to the laminated structure 1B taken out of the MOCVD vapor deposition apparatus using a general photolithography technique. And a recessed portion 108 exposing the surface of the high-resistance boron phosphide layer 105 was formed. The height difference (step) between the high resistance boron phosphide layer 105 doped with magnesium (Mg) for forming a gate electrode and the n-type boron phosphide layer 106 on the bottom surface of the recess 108 was set to about 150 nm. The width of the recess 108 is about 1 × 10 ^-3 cm.
[0029]
A gate electrode 107 having a Schottky contact slightly closer to the source electrode 109 than the center of the surface of the high-resistance boron phosphide layer 105 on the bottom surface of the recess 108 is formed by a general patterning technique and lift-off. Formed by technique. The gate electrode 107 has a three-layer structure of Ti / platinum (Pt) / gold (Au) in which the side in contact with the surface of the high-resistance boron phosphide layer 105 is titanium (Ti). Gate length is about 1.5 × 10 ^-4 cm. Further, on the surface of the n-type boron phosphide layer 106 left opposite to the region except for the recessed portion 108, a gold-germanium (Au.Ge) alloy film is formed on the side in contact with the n-type boron phosphide layer 106. , A source electrode 109 and a drain electrode 110 having an ohmic contact with a three-layer structure of Au.Ge/nickel (Ni) / Au. Thus, a MESFET was formed. The horizontal distance between the source electrode 109 and the drain electrode 110 is about 1 × 10 ^-3 cm.
[0030]
In the MESFET fabricated in the second embodiment as described above, the active layer composed of the n-type gallium nitride layer 104 is provided on the boron phosphide layer 103 doped with magnesium (Mg) to have a high resistance. Therefore, leakage of the drain current to the buffer layer was suppressed. For this reason, the saturated source-drain current (so-called I _dss ) Was not observed, and the gate pinch-off voltage was about 12.4 volts (V) (however, the source-drain current (the so-called I- _ds ) Is 5 × 10 ^-6 A). In addition, since the high resistance boron phosphide layer 103 doped with magnesium (Mg), which is assumed to form a relatively “shallow” acceptor level in the group III-V compound semiconductor, is used as the buffer layer, the drain current has a reduced relaxation time. No long-term drift was observed. The mutual conductance at room temperature obtained when the drain voltage is 5 V (so-called g _m ) Reached as high as about 10 milliSiemens (mS) / mm per unit gate length (mm). In the vicinity of the gate pinch-off voltage due to an increase in the gate voltage (so-called Vg), g _m However, a high performance MESFET capable of maintaining a high value of 8 mS / mm was provided.
[0031]
【The invention's effect】
According to the present invention, in a method for manufacturing a high-resistance boron phosphide layer in which a high-resistance boron phosphide layer is directly formed on a crystal substrate by a vapor phase growth means, the temperature of the crystal substrate is set to 1000 ° C. or higher and 1200 Magnesium which forms a "shallow" impurity level while vapor-phase growing a boron phosphide layer exhibiting p-type conduction in an undoped state in which impurities are not intentionally added while being kept at a temperature of not more than ℃. (Mg) is added to form a high-resistance boron phosphide layer. For example, if it is used as a buffer layer, leakage of drain current is small, pinch-off characteristics are excellent, and high mutual conductance is obtained. The effect can be improved in configuring a MESFET having the following.
[0032]
Further, a high-resistance boron phosphide layer doped with magnesium (Mg) is formed on a crystal substrate at a temperature of 750 ° C. or more and 1200 ° C. or less, and contains boron and phosphorus and has a layer thickness of 2 nm or more and 50 nm or less. Since it is formed by bonding to an amorphous underlayer, a continuous high-resistance boron phosphide layer having no gap can be formed.
[Brief description of the drawings]
FIG. 1 is a diagram showing a relationship between a supply amount of a magnesium (Mg) source and a Mg atom concentration in a boron phosphide layer.
FIG. 2 is a schematic sectional view of a laminated structure according to a first embodiment of the present invention.
FIG. 3 is a schematic sectional view of a MESFET according to a second embodiment of the present invention.
[Explanation of symbols]
1A laminated structure
1B MESFET laminated structure
101 silicon single crystal substrate
102 Amorphous layer
103 High resistance boron phosphide layer (buffer layer)
104 Gallium nitride layer (active layer)
105 High resistance boron phosphide layer (gate electrode formation layer)
106 n-type boron phosphide layer (ohmic contact layer)
107 Gate electrode
108 Recess
109 Source electrode
110 drain electrode

Claims (10)

In a method for manufacturing a boron phosphide layer in which a boron phosphide (BP) layer is formed directly on a crystal substrate by a vapor phase growth means, the temperature of the crystal substrate is kept in a range of 1000 ° C. or more and 1200 ° C. or less, and undoped. A method for producing a boron phosphide layer, comprising adding magnesium (Mg) to a boron phosphide layer exhibiting p-type conductivity in an (undoped) state to form a high-resistance boron phosphide layer. In a method for manufacturing a boron phosphide layer formed by bonding a boron phosphide layer to an amorphous underlayer formed on a crystal substrate by a vapor phase growth means, the temperature of the crystal substrate is set to 750 ° C. or higher and the amorphous (Mg) is added to a boron phosphide layer exhibiting p-type conductivity in an undoped state while maintaining a high temperature under the temperature at which the high quality underlayer is vapor-phase grown. Forming a boron phosphide layer. An amorphous underlayer containing boron (B) and phosphorus (P), which is directly grown on a crystal substrate at a temperature of 750 ° C. or more and 1200 ° C. or less, and has a layer thickness of 2 nanometers (nm) or more. The method for producing a boron phosphide layer according to claim 2, wherein the layer is 50 nm or less. 4. The method for producing a boron phosphide layer according to claim 2, wherein the high resistance boron phosphide layer and the amorphous underlayer are formed by the same vapor phase growth means. A boron phosphide-based semiconductor device comprising a high-resistance boron phosphide layer formed by the method according to claim 1. 6. The boron phosphide-based semiconductor according to claim 5, wherein the boron phosphide-based semiconductor element is a field effect transistor (FET) in which an active layer is provided above a high-resistance boron phosphide layer. element. The boron phosphide-based semiconductor element is a Schottky junction field-effect transistor having a Schottky junction metal gate electrode joined to a high-resistance boron phosphide layer. Item 7. The boron phosphide-based semiconductor device according to item 5 or 6. 6. The light emitting device according to claim 5, wherein the boron phosphide-based semiconductor device is a light emitting device in which an ohmic electrode made of an ohmic contact metal material is provided above the high-resistance boron phosphide layer. Boron phosphide-based semiconductor device. A laser diode in which a boron phosphide-based semiconductor element includes a high-resistance boron phosphide layer as a current confinement layer for narrowing a flow path of an element operation current supplied from an ohmic contact electrode to a light emitting layer. 9. The boron phosphide-based semiconductor device according to claim 8, wherein: The boron phosphide-based semiconductor element is a light-emitting diode including a high-resistance boron phosphide layer as a current blocking layer for preventing a forward current from flowing to a projection region of the ohmic contact electrode. The boron phosphide-based semiconductor device according to claim 8.

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