JP2009177029A - Method of manufacturing semiconductor film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a compound semiconductor film with high carrier density. <P>SOLUTION: The disclosed method includes: a step S103 of forming a first semiconductor layer 47b, by supplying first and second dopants 17a, 19a and the raw material of constitutive elements of a group-III nitride semiconductor 47; a step S101 of forming a second semiconductor layer 47a; and a step S107 of repeatedly forming the first semiconductor layer 47b and the second semiconductor layer 47a. The second dopant 19a acts as a dopant of the same conduction type as the first dopant 17a. The second semiconductor layer 47a is an undoped layer or a lightly-doped layer. In the lightly-doped layer, the first and second dopants 17a, 19a are doped at a density lower than the density of the first semiconductor layer 47b. The atomic radius of constitutive elements substituted in the semiconductor layer 47b is greater than that of the first dopant 17a and smaller than that of the second dopant 19a. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a semiconductor film.

Non-Patent Document 1 discloses a technique of co-doping a semiconductor film with a donor and an acceptor for realizing a low-resistance semiconductor film. When both the donor and acceptor are co-doped, each impurity atom forms a one-to-one (1: 1) pair. Another acceptor impurity is coordinated around the atomic pair and functions as an acceptor as a whole. For example, when the donor and acceptor impurities are highly doped at a ratio of 1: 2 (1: 2), an acceptor having a difference concentration can be formed. According to this method, a high hole concentration of about 10 ¹⁹ -10 ²¹ cm ^-3 , which has been difficult in the past, can be realized. For example, when beryllium (Be) is used as an acceptor and silicon (Si) is used as a donor for a GaN semiconductor film, a hole concentration that is three times or more that of doping with Be alone is realized. A hole density of × 10 ¹⁸ cm ⁻³ is obtained.
Yamamoto, T. Katayama-Yoshida, H .; Materials design for the Fabrication of low-resistivity p-type GaN using a codoping method.Jpn.J.Appl.Phys. 36,1997, p.L180-L183.

  In order to improve the performance of semiconductor devices such as realizing low resistance ohmic contact in various semiconductor devices and reducing forward resistance in semiconductor light emitting devices, it is necessary to realize low resistance semiconductor films. Since the resistance value of a semiconductor depends on the carrier density in the semiconductor, it is necessary to increase the carrier density by adding a dopant to the semiconductor film at a high concentration in order to realize a low resistance semiconductor film.

  When the GaN semiconductor film is co-doped with Si as a donor and Be as an acceptor as in the conventional technique described above, a part of Ga in the GaN semiconductor film is replaced with Be and Si. Here, the atomic radius of Si and the atomic radius of Ga are close, but the atomic radius of Be is considerably smaller than the atomic radius of Ga. Therefore, when Be and Si are highly doped, local lattice distortion occurs in the GaN crystal. As a result, donor-type defects are generated in the GaN crystal, and holes are trapped there, so that these donor-type defects reduce the hole density.

  This invention is made | formed in view of such a subject, and it aims at providing the method of manufacturing a compound semiconductor film with a high carrier density.

  A method of manufacturing a semiconductor film according to the present invention includes supplying first and second dopants acting as dopants to a group III nitride semiconductor, and a raw material of a constituent element of the group III nitride semiconductor, to form a group III nitride A step of forming a first semiconductor layer that is a doped layer of a physical semiconductor, a step of forming a second semiconductor layer made of a group III nitride semiconductor, a step of repeating the formation of the first semiconductor layer and the second semiconductor layer, The first semiconductor layer includes a first dopant and a second dopant, and the second dopant acts as a dopant of the same conductivity type as the first dopant with respect to the group III nitride semiconductor, and the second dopant The semiconductor layer is an undoped layer or a lightly doped layer of a group III nitride semiconductor, and at least one of the first and second dopants in the lightly doped layer is a first semiconductor layer with respect to the group III nitride semiconductor. Than concentration in The first and second dopants are substituted with at least one constituent element of the constituent elements of the group III nitride semiconductor in the first semiconductor layer and the lightly doped layer. The atomic radius of the constituent element to be substituted in the semiconductor layer is larger than the atomic radius of the first dopant and smaller than the atomic radius of the second dopant.

  According to the method for manufacturing a semiconductor film of the present invention, the atomic radius of the first dopant is smaller than the constituent element of the host semiconductor that is substituted for the first dopant, and the atomic radius of the second dopant is Since it is larger than the constituent element of the host semiconductor replaced with the dopant of 2, the local lattice distortion in the host semiconductor can be reduced in the doped layer that is the first semiconductor layer. Further, when the second semiconductor layer is an undoped layer, the second semiconductor layer has no lattice distortion due to the addition of the dopant. When the second semiconductor layer is a lightly doped layer, the concentration of the first and / or second dopant doped in the second semiconductor layer is higher than the concentration of the first and / or second dopant in the first semiconductor layer. Since it is low, the lattice strain due to the dopant addition of the second semiconductor layer is smaller than the lattice strain due to the dopant addition of the first semiconductor layer. Since the first semiconductor layer and the second semiconductor layer are alternately formed, the lattice strain of the entire semiconductor film is further reduced. As a result, the decrease in carrier density due to lattice strain is reduced, and thus a group III nitride semiconductor film having a high carrier density can be obtained.

  In addition, as another aspect of the method for producing a semiconductor film according to the present invention, the first and second dopants acting as dopants for the group III nitride semiconductor, the raw materials for the constituent elements of the group III nitride semiconductor, Forming a first semiconductor layer which is a doped layer of a group III nitride semiconductor, forming a second semiconductor layer made of a group III nitride semiconductor, a first semiconductor layer, and a second semiconductor The first semiconductor layer includes a first dopant and a second dopant, and the second dopant has the same conductivity type as the first dopant with respect to the group III nitride semiconductor. The second semiconductor layer is an undoped layer or a lightly doped layer of a group III nitride semiconductor, and the lightly doped layer is a first dopant and a second dopant for the group III nitride semiconductor. At least one is first The first and second dopants are substituted with at least one of the constituent elements of the group III nitride semiconductor in the first semiconductor layer and the lightly doped layer. The atomic radius of the first dopant is smaller than the atomic radius of the second dopant.

  According to the method for manufacturing a semiconductor film of the present invention, since the atomic radius of the first dopant is smaller than the atomic radius of the second dopant, the first semiconductor layer is compared with the case where only the first dopant is doped. In the doped layer, the local lattice distortion in the host semiconductor can be reduced. Further, when the second semiconductor layer is an undoped layer, the second semiconductor layer has no lattice distortion due to the addition of the dopant. When the second semiconductor layer is a lightly doped layer, the concentration of the first and / or second dopant doped in the second semiconductor layer is higher than the concentration of the first and / or second dopant in the first semiconductor layer. Since it is low, the lattice strain due to the dopant addition of the second semiconductor layer is smaller than the lattice strain due to the dopant addition of the first semiconductor layer. Since the first semiconductor layer and the second semiconductor layer are alternately formed, the lattice strain of the entire semiconductor film is further reduced. As a result, since the decrease in carrier density due to lattice strain is reduced, a group III nitride semiconductor film having a high carrier density can be obtained.

  Furthermore, the second semiconductor layer is preferably an undoped layer of a group III nitride semiconductor. Thereby, the lattice distortion due to the addition of the dopant is eliminated in the second semiconductor layer. As a result, the effect of reducing the lattice strain of the entire semiconductor film by alternately forming the first semiconductor layer and the second semiconductor layer is particularly strong.

  The second semiconductor layer is preferably a lightly doped layer of a group III nitride semiconductor. Thereby, the specific resistance of the second semiconductor layer is reduced. As a result, the resistance value of the entire semiconductor film can be reduced, and the electrical characteristics of the semiconductor film can be improved.

  Further, the group III nitride semiconductor is preferably any one of GaN, InN, and AlN. Alternatively, the group III nitride semiconductor is preferably a mixed crystal composed of at least two of GaN, InN, and AlN.

  Furthermore, it is preferable that the first dopant is beryllium and the second dopant is magnesium. These dopants replace gallium atoms in the GaN semiconductor. The atomic radius of gallium atoms is between the atomic radii of magnesium and beryllium. Therefore, the effect of reducing the lattice strain of the host semiconductor can be sufficiently obtained.

  Furthermore, the thickness of the first semiconductor layer is preferably 0.5 nm or more and 10 nm or less, and the thickness of the second semiconductor layer is preferably 0.5 nm or more and 10 nm or less. Thereby, the effect of reducing the lattice strain of the entire semiconductor film caused by alternately forming the first semiconductor layer and the second semiconductor layer is sufficiently increased. As a result, a group III nitride semiconductor film having a higher carrier density can be obtained.

Further, the doping concentration in the first semiconductor layer of beryllium is 5 × 10 ¹⁸ or more and 1 × 10 ²¹ cm ⁻³ or less, and the doping concentration in the first semiconductor layer of magnesium is 5 × 10 ¹⁸ or more and 1 × 10 ²¹ cm ^−3. The following is preferable. As a result, the effect of reducing local lattice distortion of the host semiconductor due to the above-described doping is particularly effectively exhibited.

  Furthermore, it is preferable that the first semiconductor layer and the second semiconductor layer are formed by molecular beam epitaxy. According to the molecular beam epitaxy method, the constituent elements of the semiconductor can be easily replaced with the first dopant and the second dopant. Therefore, a semiconductor film with a higher carrier density can be obtained.

  In another aspect of the method for producing a semiconductor film according to the present invention, the first and second dopants acting as dopants for the compound semiconductor and the raw material of the constituent element of the compound semiconductor are supplied. A step of forming a first semiconductor layer that is a doped layer; a step of forming a second semiconductor layer made of a compound semiconductor; a step of repeating the formation of the first semiconductor layer and the second semiconductor layer; The layer includes a first dopant and a second dopant. The second dopant acts as a dopant of the same conductivity type as the first dopant with respect to the compound semiconductor, and the second semiconductor layer is an undoped layer of the compound semiconductor. Or a lightly doped layer, wherein the lightly doped layer is such that at least one of the first and second dopants is lower in concentration than the concentration in the first semiconductor layer with respect to the compound semiconductor. The first dopant and the second dopant are substituted with at least one constituent element of the constituent elements of the compound semiconductor in the first semiconductor layer and the lightly doped layer, and the atomic radius of the first dopant is It is characterized by being smaller than the atomic radius of the dopant of 2.

  According to the method for manufacturing a semiconductor film of the present invention, since the atomic radius of the first dopant is smaller than the atomic radius of the second dopant, the first semiconductor layer is compared with the case where only the first dopant is doped. In the doped layer, the local lattice distortion in the host semiconductor can be reduced. Further, when the second semiconductor layer is an undoped layer, the second semiconductor layer has no lattice distortion due to the addition of the dopant. When the second semiconductor layer is a lightly doped layer, the concentration of the first and / or second dopant doped in the second semiconductor layer is higher than the concentration of the first and / or second dopant in the first semiconductor layer. Since it is low, the lattice strain due to the dopant addition of the second semiconductor layer is smaller than the lattice strain due to the dopant addition of the first semiconductor layer. Since the first semiconductor layer and the second semiconductor layer are alternately formed, the lattice strain of the entire semiconductor film is further reduced. As a result, a decrease in carrier density due to lattice strain is reduced, and a compound semiconductor film having a high carrier density can be obtained.

  According to the present invention, a method for producing a compound semiconductor film having a high carrier density is provided.

Hereinafter, a method for producing a compound semiconductor film according to an embodiment will be described in detail with reference to the accompanying drawings. In addition, in each drawing, the same code | symbol is used for the same element and the overlapping description is abbreviate | omitted. In addition, the dimensional ratios in the components in the drawings and between the components are arbitrary for easy viewing of the drawings.
[First embodiment]

  FIG. 1 is a flowchart showing main steps of a method for producing a compound semiconductor film according to the first embodiment of the present invention. FIG. 2 is a drawing showing an example of a crystal growth apparatus for manufacturing a compound semiconductor film. As shown in the flowchart 100 of FIG. 1, the method of manufacturing the compound semiconductor film according to the present embodiment includes a substrate installation step S101, an undoped layer formation step (step of forming a second semiconductor layer) S103, and a doped layer formation. Step (step of forming the first semiconductor layer) S105, and further includes an undoped layer forming step S103 and a doped layer forming step S105 that are repeated a predetermined number of times S107.

  In the substrate installation step S101, a substrate 31 for forming a compound semiconductor film is installed in a crystal growth apparatus. As a crystal growth apparatus, a molecular beam epitaxy apparatus 13 as shown in FIG. 2 can be used.

  The molecular beam epitaxy apparatus 13 includes a chamber 13a, a substrate holder 13b, a source 13c, an RHEED apparatus 13d as a monitor apparatus, and an exhaust port 13e to which a vacuum pump is connected. Specifically, the source 13c is the dopant sources 17, 19, and 29 and the raw material sources 21, 23, 25, and 27. The dopant sources 17, 19, 29 and the raw material sources 21, 25, 27 are provided in the respective cells 17K, 19K, 29K, 21K, 25K, and 27K. The raw material source 23 is a gaseous raw material source and is introduced into the chamber 13a via the cell 23K. Each of the cells 17K, 19K, 29K, 21K, 23K, 25K, and 27K has a shutter 17S, 19S, 29S, 21S, 23S, 25S, and 27S, respectively. Each of the cells 17K, 19K, 29K, 21K, 25K, and 27K includes a resistance heater 17R, 19R, 29R, 21R, 25R, and 27R, respectively.

  The molecular beam epitaxy apparatus 13 can selectively supply each dopant source and each material source onto the substrate 31 by heating the dopant source or source cell with a resistance heater and opening the shutter of the cell. Is possible. Further, it is possible to supply a high-frequency magnetic field to the nitrogen 23 a using an RF radical gun and supply the plasma-ized nitrogen 23 a onto the substrate 31.

  The dopant sources 17 and 19 provide first and second dopants 17a and 19a that function as dopants of the same conductivity type in the compound semiconductor, respectively. The source sources 21 and 23 provide constituent atoms 21a and 23a of the compound semiconductor. In the present embodiment, the dopant sources 17, 19, 29 and the source sources 21, 23, 25, 27 are beryllium, magnesium, silicon, gallium, nitrogen, aluminum, and indium, respectively. The first dopant 17a is beryllium, and the second dopant 19a is magnesium. The raw material 21a is gallium, and the raw material 23a is nitrogen (N).

  In the undoped layer forming step S103, first, preparation such as heating and plasma generation is performed in the source 13c. The substrate 31 is heated to about 700 ° C. Further, the gallium 21a and the nitrogen 23a are supplied on the substrate 31 by substantially the same number of atoms by adjusting the heating temperature of the raw material sources 21 and 23 or the like. In addition, a predetermined amount of beryllium 17a and magnesium 19a is supplied onto the substrate 31 by adjusting the heating temperature of the dopant sources 17 and 19 or the like. Then, the shutters 21S and 23S of the raw material sources 21 and 23 are opened, and gallium 21a and nitrogen 23a are supplied onto the substrate 31. Then, GaN, which is a group III nitride semiconductor, is epitaxially grown on the substrate 31. Further, the surface during the epitaxial growth of GaN is observed with the RHEED apparatus 13d. Specifically, surface state information can be obtained by making an electron beam incident on the substrate 31 at a low angle by the RHEED device 13d and observing the reflected diffraction image.

  The thickness of the undoped layer is preferably 0.5 nm or more. This is because when the undoped layer is greater than this thickness, the effect of reducing the lattice strain of the entire GaN film manufactured by the method of manufacturing the compound semiconductor film according to the present embodiment (details will be described later) is particularly remarkable. This is because the present inventors have confirmed by experiment. Moreover, it is preferable that the film thickness of an undoped layer is 10 nm or less. This is because if the undoped layer is more than this thickness, the effect of reducing the lattice strain of the entire GaN film is improved, but electrical connection is hindered between the doped layers described later. That is, when a current is passed in the stacking direction of the GaN film manufactured by the method for manufacturing the compound semiconductor film according to the present embodiment, a tunnel current flows in the undoped layer having a high specific resistance due to the quantum mechanical effect. This is because the present inventors have confirmed through experiments that a sufficient current can flow in the GaN film and the electrical characteristics of the GaN film are improved when the thickness is 10 nm or less. The undoped layer becomes the second semiconductor layer.

In the doped layer forming step S105, with the shutters 21S and 23S of the source sources 21 and 23 opened, the shutters 17S and 19S of the dopant sources 17 and 19 are further opened, and gallium 21a, nitrogen 23a, and the first dopant beryllium. 17a and the second dopant magnesium 19a are supplied onto the substrate 31. Then, a GaN layer (doped layer) containing beryllium 17a as the first dopant and magnesium 19a as the second dopant is formed on the undoped layer. At this time, the doping concentration in the doped layer of beryllium 17a is preferably 1 × 10 ¹⁸ or more. This is because if the doping concentration in the doped layer of beryllium 17a is higher than this value, the interaction between beryllium 17a and magnesium 19a becomes sufficiently large. That is, the effect of offsetting the lattice strain of the doped layer due to the addition of beryllium 17a and the lattice strain of the doped layer due to the addition of magnesium 19a is sufficiently exerted, and the effect of reducing the lattice strain of the entire GaN film as described later is sufficiently exhibited. It is because it is demonstrated. The doped layer becomes the first semiconductor layer.

The doping concentration in the doped layer of beryllium 17a is preferably 1 × 10 ²¹ cm ⁻³ or less. This is because if the doping concentration in the doped layer of beryllium 17a is higher than this value, the crystallinity of the doped layer tends to deteriorate and the carrier density tends to decrease regardless of the doping concentration in the doped layer of magnesium 19a. is there.

Similarly, the doping concentration in the doped layer of magnesium 19a is preferably 1 × 10 ¹⁸ or more. This is because the interaction between the beryllium 17a and the magnesium 19a becomes sufficiently large when the doping concentration in the doped layer of the magnesium 19a is higher than this value. That is, the effect of offsetting the lattice strain of the doped layer due to the addition of beryllium 17a and the lattice strain of the doped layer due to the addition of magnesium 19a is sufficiently exerted, and the effect of reducing the lattice strain of the entire GaN film as described later is sufficiently exhibited. It is because it is demonstrated.

The doping concentration in the doped layer of magnesium 19a is preferably 1 × 10 ²¹ cm ⁻³ or less. This is because if the doping concentration in the doped layer of magnesium 19a is higher than this value, the crystallinity of the doped layer tends to deteriorate and the carrier density tends to decrease regardless of the doping concentration in the doped layer of beryllium 17a. is there.

  Moreover, it is preferable that the film thickness of a dope layer is 0.5 nm or more. This is because if the thickness of the doped layer is less than this value, there are the following drawbacks. That is, in order to effectively exhibit the effect of reducing the lattice strain of the entire GaN layer as will be described later, it is preferable that the doped layer and the undoped layer have the same film thickness. Therefore, if the thickness of the doped layer is 0.5 nm or less, it is necessary to form a large number of very thin doped layers and undoped layers alternately in order to form the entire GaN layer. It takes time to open and close the shutter for switching the formation of the layers (see FIG. 2), and the throughput in manufacturing the entire GaN layer is greatly reduced.

  Moreover, it is preferable that the film thickness of a dope layer is 10 nm or less. This is because if the thickness of the doped layer is greater than this value, a large amount of lattice strain accumulates in the doped layer, so that the lattice strain of the entire GaN can be reduced by alternately laminating doped layers and undoped layers as described later. This is because the effect of reducing tends not to be sufficiently exhibited.

  In the repeating step S107, the undoped layer forming step S103 and the doped layer forming step S105 are repeated a predetermined number of times in order. As a result, the doped layer and the undoped layer are alternately stacked repeatedly a predetermined number of times. In addition, prior to the undoped layer formation S103, a doped layer formation step S105 can also be performed.

  FIG. 3 is a view schematically showing the structure of an epitaxial substrate having a GaN film manufactured by the method according to the present embodiment. As shown in FIG. 3, the epitaxial substrate E <b> 1 has a substrate 31 and a GaN film 47 formed on the substrate 31. The GaN film 47 is a laminated film in which undoped layers 47a and doped layers 47b are alternately and repeatedly laminated a predetermined number of times. Further, the undoped layer 47a and the doped layer 47b form a homojunction 47c with each other.

  In the GaN film 47 manufactured as described above, beryllium 17a as the first dopant and magnesium 19a as the second dopant are both substituted with Ga atoms in the doped layer 47b. The beryllium 17a and the magnesium 19a both function as p-type dopants in the doped layer of the GaN film 47. The atomic radius of Ga is larger than beryllium 17a and smaller than magnesium 19a. Therefore, in the doped layer 47b, local lattice distortion caused by doping is reduced. In addition, lattice strain due to dopant addition does not occur in the undoped layer 47a. Since the undoped layer 47a and the doped layer 47b are alternately and repeatedly formed, the lattice strain of the entire GaN film is further reduced. As a result, it is possible to suppress a decrease in carrier density due to lattice distortion, and thus a GaN film 47 having a high carrier density can be obtained.

In the present embodiment, the preferred doping concentration in the doped layer 47b of beryllium 17a is 5 × 10 ¹⁸ or more and 1 × 10 ²¹ cm ⁻³ or less, and the preferred doping concentration in the doped layer 47b of magnesium 19a is 5 ×. 10 ¹⁸ or more and 1 × 10 ²¹ cm ⁻³ or less. When the doping concentration of the beryllium 17a and the magnesium 19a is within such a range, the effect of reducing the local lattice distortion of the GaN film 47 due to the doping of the beryllium 17a and the magnesium 19a as described above is exhibited particularly effectively. As a result, a GaN film 47 having a higher carrier density is obtained.

  In the present embodiment, the thickness of the undoped layer 47a is preferably 0.5 nm to 10 nm, and the thickness of the doped layer 47b is preferably 0.5 nm to 10 nm. When the thickness of the undoped layer 47a and the doped layer 47b is within such a range, the effect of reducing the lattice strain of the GaN film 47 as a whole as described above is particularly effectively exhibited. As a result, a GaN film 47 having a higher carrier density is obtained.

  Further, the undoped layer 47a in the present embodiment can be replaced with a low doped layer 47a in which at least one of the dopants of beryllium 17a and magnesium 19a is doped at a lower concentration than the concentration in the doped layer 47b. In this case, the above-described undoped layer forming step S103 is replaced with a low doped layer forming step (step of forming a second semiconductor layer) S103, and the repeating step S107 includes undoped layer forming step S103, low doped layer forming step S105, and Is a step of repeating a predetermined number of times in order. Further, the lightly doped layer 47a becomes the second semiconductor layer. In the lightly doped layer forming step S103, the lightly doped layer 47a is formed by the same method as the formation of the doped layer 47b in the doped layer forming step S105. At this time, the beryllium 17a and / or the magnesium 19a is formed. The supply amount is decreased from the supply amount in the dope layer forming step S105. The lightly doped layer 47a may contain both beryllium 17a and magnesium 19a as dopants, or may contain only one of them.

The doping concentration of beryllium 17a in the lightly doped layer 47a is preferably less than 5 × 10 ¹⁸ cm ⁻³ . This is because if the doping concentration is 5 × 10 ¹⁸ cm ⁻³ or more, the lattice strain of the low doped layer 47a increases, and a GaN film is formed by alternately laminating doped layers 47b and low doped layers 47a as described later. This is because the effect of reducing the lattice strain of the entire 47 tends not to be sufficiently exhibited. Further, the measurement limit of the doping concentration of beryllium 17a in the lightly doped layer 47a by the SIMS method is 5 × 10 ¹⁴ cm ⁻³ , but the doping concentration of beryllium 17a in the lightly doped layer 47a is less than this measurement limit. May be.

The doping concentration of magnesium 19a in the lightly doped layer 47a is preferably less than 5 × 10 ¹⁸ cm ⁻³ . This is because if the doping concentration is 5 × 10 ¹⁸ cm ⁻³ or more, the lattice strain of the low doped layer 47a increases, and a GaN film is formed by alternately laminating doped layers 47b and low doped layers 47a as described later. This is because the effect of reducing the lattice strain of the entire 47 tends not to be sufficiently exhibited. The measurement limit of the doping concentration of magnesium 19a in the lightly doped layer 47a by the SIMS method is 5 × 10 ¹⁴ cm ⁻³ , but the doping concentration of magnesium 19a in the lightly doped layer 47a is less than this measurement limit. May be.

In this case, the GaN film 47 is a laminated film in which lightly doped layers 47a and doped layers 47b are alternately laminated. Then, the lattice strain caused by the addition of the dopant generated in the lightly doped layer 47a is smaller than the lattice strain caused by the addition of the dopant generated in the doped layer 47b. Therefore, similarly to the case where the undoped layers 47a and the doped layers 47b are alternately stacked, it is possible to reduce the lattice strain of the GaN film by alternately stacking the low doped layers 47a and the doped layers 47b. . Furthermore, the specific resistance of the lightly doped layer 47a is smaller than that of the undoped layer 47a. Therefore, the resistance value of the entire GaN film can be reduced, and the electrical characteristics of the GaN film can be improved.
[Second Embodiment]

  FIG. 4 is a flowchart showing main steps of a method of manufacturing a compound semiconductor film and a method of manufacturing an epitaxial substrate having an LED structure according to the second embodiment of the present invention. FIG. 5 is a diagram schematically showing an LED structure manufactured by the method according to the present embodiment. Epitaxial substrate E2 includes a stack of films corresponding to LED structure 33. As shown in the flowchart 100a of FIG. 4, the method for manufacturing the epitaxial substrate E2 having the LED structure according to the present embodiment mainly includes the following steps.

Step S105:
This is the same process as the substrate installation process S101 (see FIG. 1) in the first embodiment. That is, a substrate 31 (in this embodiment, a GaN substrate) for forming a semiconductor film is placed in the molecular beam epitaxy apparatus 13.

Step S107:
The shutters 21S, 29S, and 23S of the cells 21K, 29K, and 23K are opened, and gallium 21a as a raw material, nitrogen 23a, and silicon 29 as a dopant are supplied onto the GaN substrate 31. Thereby, the n-type GaN buffer layer 35 is formed on the GaN substrate 31. The thickness of the n-type GaN buffer layer 35 is, for example, 500 nm.

Step S109:
Further, the shutter 25S of the cell 25K is opened, and alumina is further supplied from the alumina 25 which is a raw material source. Thereby, the n-type AlGaN cladding layer 37 is formed on the n-type GaN buffer layer 35. The thickness of the n-type AlGaN cladding layer 37 is, for example, 500 nm.

Step S111:
The shutters 25S and 29S of the cells 25K and 29K are closed, and the first GaN guide layer 39 is formed. The thickness of the first GaN guide layer 39 is, for example, 10 nm.

Step S113:
The shutter 27S of the cell 27K is opened, and the InGaN active layer 41 is formed. The thickness of the InGaN active layer 41 is 3 nm, for example.

Step S115:
The second GaN guide layer 43 is formed by closing the shutter 27S of the cell 27K. The thickness of the second GaN guide layer 43 is, for example, 10 nm.

Step S117:
The shutters 25S and 17S of the cell 25K and the cell 17K and the shutter (not shown) of the Te cell are opened, and the p-type AlGaN cladding layer 45 is formed. The thickness of the p-type AlGaN cladding layer 45 is, for example, 500 nm.

Step S119:
The shutters 25S and 17S of the cell 25K and the cell 17K and the shutter of the Te cell are closed, and a part of the p-type GaN contact layer 47 is formed. A suitable film thickness of the undoped layer 47a is not less than 0.5 nm and not more than 10 nm.

Step S121:
The shutters 17S and 19S of the cell 17K and the cell 19K are opened, and a doped layer 47b that is a part of the p-type GaN contact layer 47 is formed. A suitable thickness of the doped layer 47b is not less than 0.5 nm and not more than 10 nm. Further, the preferable doping concentration in the doped layer 47b of beryllium 17a is 1 × 10 ¹⁸ or more and 1 × 10 ²¹ cm ⁻³ or less, and the preferable doping concentration in the doped layer 47b of magnesium 19a is 1 × 10 ¹⁸ or more and 1 × 10 6. ²¹ cm- ³ or less.

Step S123:
The undoped layer 47a forming step S119 and the doped layer 47b forming step S121 are repeated a predetermined number of times in order. As a result, the undoped layer 47a and the doped layer 47b are alternately and repeatedly stacked a predetermined number of times to form the p-type GaN contact layer 47.

Step S125:
After lowering the substrate temperature, the epitaxial substrate E2 is taken out of the growth chamber.

  As shown in FIG. 5, the epitaxial substrate E <b> 2 has an LED structure 33 formed on the main surface 31 a of the GaN substrate 31. As a specific configuration of the LED structure 33, an InGaN active layer 41 is provided between an n-type AlGaN cladding layer 37 and a p-type AlGaN cladding layer 45. A p-type GaN contact layer 47 is formed on the p-type AlGaN cladding layer 45. A first GaN guide layer 39 is provided between the InGaN active layer 41 and the n-type AlGaN cladding layer 37, and a second GaN guide is interposed between the InGaN active layer 41 and the p-type AlGaN cladding layer 45. A layer 43 is provided. A first electrode such as an anode is provided on the p-type GaN contact layer 47, and a second electrode such as a cathode is provided on the back surface 31 b of the GaN substrate 31.

  As described above, the p-type GaN contact layer 47 has the same configuration as the GaN film 47 (see FIG. 3) in the first embodiment. Therefore, the p-type GaN contact layer 47 of the present embodiment is a layer having a high carrier density and a low resistance. As a result, the operating voltage and light emission characteristics of the LED structure 33 are improved. In this embodiment, the p-type GaN contact layer 47 is formed by repeating the undoped layer 47a and the doped layer 47b. However, another p-type semiconductor layer can be formed by the same method.

Hereinafter, in order to further clarify the effects of the present invention, description will be made using examples. 6 and 7 are tables showing the relationship between the hole density and the conditions of the laminated film configuration according to Examples 1 to 4 and 5. FIG. Examples 1 to 4 are stacked films in which undoped layers of GaN semiconductors and doped layers of GaN semiconductors are alternately stacked on a GaN substrate as in the first embodiment described above. Example 5 is a laminated film in which lightly doped layers of GaN semiconductors and doped layers of GaN semiconductors are alternately laminated on a GaN substrate. In any of the examples, the undoped layer and the doped layer were repeatedly formed so that the total film thickness of the laminate including the undoped layer and the doped layer was 500 nm. Further, magnesium and beryllium were used as dopants. In Examples 1 to 4, the doping density in the doped layers of magnesium and beryllium was 5.00 × 10 ¹⁹ cm ⁻³ . In Example 5, the doping density in the low-doped layer of magnesium and beryllium is both 3.00 × 10 ¹⁸ cm ^−3, and the doping density in the doped layer of magnesium and beryllium is 5.00 × 10 ¹⁹ cm ⁻³ .

  In Examples 1 to 4, the combination of the thicknesses of the undoped layer and the doped layer was different for each example. Specifically, the thicknesses of the undoped layer and the doped layer in Example 1 were both set to 0.5 nm. Moreover, the thickness of the undoped layer and doped layer of Example 2 was 1 nm. Moreover, the thickness of the undoped layer and doped layer of Example 3 was 5 nm. Moreover, the thickness of the undoped layer and doped layer of Example 4 was 10 nm. In Example 5, the thicknesses of the undoped layer and the doped layer were both 5 nm. Moreover, in Examples 1-5, all the layers were formed using the molecular beam epitaxy apparatus.

As shown in FIG. 6, the hole densities of Examples 1 to 5 are 1.0 × 10 ¹⁸ cm ⁻³ , 1.5 × 10 ¹⁸ cm ⁻³ , 4.5 × 10 ¹⁸ cm ⁻³ , 1, respectively. The results were 0.8 × 10 ¹⁸ cm ⁻³ and 5.5 × 10 ¹⁸ cm ⁻³ , and each example showed high hole density.

  The present invention is not limited to the above embodiment, and various modifications can be made.

  For example, in the above-described embodiment, a GaN semiconductor is used as the group III nitride semiconductor, but a semiconductor film of InN or AlN can be formed instead of GaN. Alternatively, the semiconductor film can be formed using a mixed crystal composed of at least two of GaN, InN, and AlN. Examples of these mixed crystals include AlGaN, InGaN, and AlInN.

  When InN is used as the group III nitride semiconductor, for example, beryllium and magnesium can be used as the first and second dopants, respectively. When AlN is used as the group III nitride semiconductor, for example, beryllium and magnesium can be used as the first and second dopants, respectively.

  Moreover, in the above-mentioned embodiment, the atomic radius of the atom (Ga) substituted by the dopant in the host semiconductor was larger than the first dopant (beryllium) and smaller than the second dopant (magnesium). However, it is not limited to such a mode. For example, if the atomic radii of the first dopant and the second dopant are different from each other, the average atomic radius of the dopant in the host semiconductor is a value between the atomic radii of the two dopants, and the small atomic radius dopant. The lattice distortion caused by

Further, the host semiconductor is not limited to a group III nitride semiconductor, for example, ZnO, ZnMgO.
Even so, it is possible to implement the present invention.

FIG. 1 is a flowchart showing main steps of a method for manufacturing a compound semiconductor film according to the first embodiment. FIG. 2 is a drawing showing an example of a crystal growth apparatus for manufacturing a compound semiconductor film. FIG. 3 is a diagram conceptually showing the structure of an epitaxial substrate having a GaN film manufactured by the method according to the first embodiment. FIG. 4 is a flowchart showing main steps of a method for manufacturing a compound semiconductor film and a method for manufacturing an epitaxial substrate having an LED structure according to the second embodiment. FIG. 5 is a diagram schematically showing an LED structure manufactured by the method according to the second embodiment. FIG. 6 is a diagram showing the film configuration and hole density of the example of the present invention. FIG. 7 is a diagram showing the film configuration and hole density of the example of the present invention.

Explanation of symbols

17a ... first dopant (beryllium), 19a ... second dopant (magnesium), 21a ... group III nitride semiconductor element (gallium), 23a ... group III nitride semiconductor Constituent element (nitrogen), 47... Group III nitride semiconductor (GaN), 47a... Undoped layer (low doped layer, second semiconductor layer), 47b... Doped layer (first semiconductor layer), S101 ... Substrate installation step, S103 ... Undoped layer (low doped layer) forming step, S105 ... Doped layer forming step, S107 ... Repeating step.

Claims (10)

A method for manufacturing a semiconductor film, comprising:
The first and second dopants acting as dopants for the group III nitride semiconductor and a material for the constituent elements of the group III nitride semiconductor are supplied to form a first doped layer of the group III nitride semiconductor. Forming a semiconductor layer;
Forming a second semiconductor layer comprising the group III nitride semiconductor;
Repeating the formation of the first semiconductor layer and the second semiconductor layer;
With
The first semiconductor layer includes the first dopant and the second dopant;
The second dopant acts as a dopant of the same conductivity type as the first dopant with respect to the group III nitride semiconductor,
The second semiconductor layer is an undoped layer or a lightly doped layer of the group III nitride semiconductor,
In the lightly doped layer, at least one of the first and second dopants is doped at a lower concentration than the concentration in the first semiconductor layer with respect to the group III nitride semiconductor,
The first and second dopants are substituted with at least one constituent element among the constituent elements of the group III nitride semiconductor in the first semiconductor layer and the lightly doped layer,
The atomic radius of the constituent element to be substituted in the first semiconductor layer is larger than the atomic radius of the first dopant and smaller than the atomic radius of the second dopant. A method for manufacturing a semiconductor film, comprising:
The first and second dopants acting as dopants for the group III nitride semiconductor and a material for the constituent elements of the group III nitride semiconductor are supplied to form a first doped layer of the group III nitride semiconductor. Forming a semiconductor layer;
Forming a second semiconductor layer comprising the group III nitride semiconductor;
Repeating the formation of the first semiconductor layer and the second semiconductor layer;
With
The first semiconductor layer includes the first dopant and the second dopant;
The second dopant acts as a dopant of the same conductivity type as the first dopant with respect to the group III nitride semiconductor,
The second semiconductor layer is an undoped layer or a lightly doped layer of the group III nitride semiconductor,
In the lightly doped layer, at least one of the first and second dopants is doped at a lower concentration than the concentration in the first semiconductor layer with respect to the group III nitride semiconductor,
The first and second dopants are substituted with at least one constituent element among the constituent elements of the group III nitride semiconductor in the first semiconductor layer and the lightly doped layer,
The method of claim 1, wherein the atomic radius of the first dopant is smaller than the atomic radius of the second dopant.   The method according to claim 1, wherein the second semiconductor layer is an undoped layer of the group III nitride semiconductor.   The method according to claim 1, wherein the second semiconductor layer is a lightly doped layer of the group III nitride semiconductor.   The group III nitride semiconductor is GaN, InN, AlN, or a mixed crystal composed of at least two of GaN, InN, and AlN. the method of.   The method according to claim 1, wherein the first dopant is beryllium and the second dopant is magnesium. The doping concentration of the beryllium in the first semiconductor layer is 5 × 10 ¹⁸ or more and 1 × 10 ²¹ cm ⁻³ or less, and the doping concentration of the magnesium in the first semiconductor layer is 5 × 10 ¹⁸ or more and 1 × 10 ²¹ cm. The method according to claim 6, wherein the method is ³ or less.   8. The thickness of the first semiconductor layer is 0.5 nm to 10 nm, and the thickness of the second semiconductor layer is 0.5 nm to 10 nm. The method according to one item.   The method according to claim 1, wherein the formation of the first semiconductor layer and the second semiconductor layer is performed by a molecular beam epitaxy method. A method for manufacturing a semiconductor film, comprising:
Supplying a first and second dopant acting as a dopant to the compound semiconductor and a raw material of a constituent element of the compound semiconductor to form a first semiconductor layer which is a doped layer of the compound semiconductor;
Forming a second semiconductor layer made of the compound semiconductor;
Repeating the formation of the first semiconductor layer and the second semiconductor layer;
With
The first semiconductor layer includes the first dopant and the second dopant;
The second dopant acts as a dopant of the same conductivity type as the first dopant with respect to the compound semiconductor,
The second semiconductor layer is an undoped layer or a lightly doped layer of the compound semiconductor,
In the lightly doped layer, at least one of the first and second dopants is doped to the compound semiconductor at a concentration lower than the concentration in the first semiconductor layer,
The first and second dopants are substituted with at least one constituent element among the constituent elements of the compound semiconductor in the first semiconductor layer and the lightly doped layer,
The method of claim 1, wherein the atomic radius of the first dopant is smaller than the atomic radius of the second dopant.

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