JP2011146572A - Epitaxial wafer for infrared led and infrared led - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an epitaxial wafer for an infrared LED and an infrared LED, capable of improving an output. <P>SOLUTION: An epitaxial wafer 20b for an infrared LED includes: an Al<SB>y</SB>Ga<SB>(1-y)</SB>As substrate (0≤y≤1) 10 including an Al<SB>x</SB>Ga<SB>(1-x)</SB>As layer 11 (0≤x≤1) having a major surface 11a and a rear face 11b on the reverse side of the major surface 11a; an epitaxial layer 21 formed on the major surface 11a of the Al<SB>x</SB>Ga<SB>(1-x)</SB>As layer 11 and including an active layer; and a transparent conductive film 26 formed on the epitaxial layer 21. In the Al<SB>x</SB>Ga<SB>(1-x)</SB>As layer 11, a composition ratio x of Al of the rear face 11b is greater than a composition ratio x of Al of the major surface 11a. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an infrared wafer for an infrared LED and an infrared LED.

LED (Light Emitting Diode) using Al _a Ga _(1-a) As (0 ≦ a ≦ 1) (hereinafter also referred to as AlGaAs (aluminum gallium arsenide)) and a GaAs (gallium arsenide) compound semiconductor material Is widely used as an infrared light source. Infrared LEDs as an infrared light source are used in optical communications, spatial transmission, projectors, etc., and output increases with the increase in data transmission capacity, transmission distance, and illumination distance. Improvement is demanded.

  Semiconductor light emitting devices using such AlGaAs compound semiconductors are disclosed in, for example, Japanese Patent Application Laid-Open No. 2002-335008 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2002-335007 (Patent Document 2).

JP 2002-335008 A JP 2002-335007 A

  In Patent Documents 1 and 2, the Al composition ratio of the AlGaAs support substrate is made substantially uniform. As a result of intensive studies, the present inventor has found that when the Al composition ratio is high, there is a problem that the characteristics of an infrared LED manufactured using this AlGaAs support substrate deteriorate. Further, as a result of intensive studies, the present inventor has found that when the Al composition ratio is low, there is a problem that the transmission characteristics of the AlGaAs support substrate are poor. For this reason, the present inventor has found that there is a problem that the outputs of the semiconductor light emitting devices of Patent Documents 1 and 2 are not sufficient. Further, in order to solve this output problem, in Patent Documents 1 and 2, it is necessary to remove all of the GaAs substrate.

  Then, the objective of this invention is providing the epitaxial wafer and infrared LED for infrared LED which can improve an output.

Infrared-LED epitaxial wafer of the present invention, Al _y Ga ₍₁ including a main _{surface, Al x Ga (1-x} ) As layer having an opposed rear surface and a main surface (0 ≦ x ≦ 1) _-y) As substrate (0 ≦ y ≦ 1), an epitaxial layer formed on the main surface of the Al _x Ga _(1-x) As layer and including an active layer, and a transparent conductive layer formed on the epitaxial layer In the Al _x Ga _(1-x) As layer, the Al composition ratio x on the back surface is higher than the Al composition ratio x on the main surface.

  In the infrared LED epitaxial wafer, the transparent conductive film is preferably ITO (Indium Tin Oxide).

  In the infrared LED epitaxial wafer, the layer in contact with the transparent conductive film in the epitaxial layer is preferably p-type.

Preferably, in the epitaxial wafer for infrared LEDs, the epitaxial layer includes another layer formed on the active layer, and the other layer is 1 × 10 ¹⁷ cm ⁻³ or more and 2 × 10 ¹⁸ cm ⁻³ or less. The layer has a p-type cladding layer formed on the active layer, or a p-type cladding layer formed on the active layer and a p-type cladding layer formed on the p-type cladding layer. With the window layer.

  In the epitaxial wafer for infrared LEDs, the active layer preferably has a thickness of 1.5 μm or less.

  In the infrared LED epitaxial wafer, the active layer preferably has 3 to 20 well layers (quantum well layers).

In the infrared LED epitaxial wafer, the Al _y Ga _(1-y) As substrate preferably includes a GaAs substrate in contact with the back surface of the Al _x Ga _(1-x) As layer.

  The infrared LED of the present invention comprises the above infrared LED epitaxial wafer and an electrode formed on the epitaxial wafer.

  The infrared LED preferably has a rise time and a fall time in pulse application of 5 nsec to 100 nsec.

  In the infrared LED, the cutoff frequency in applying a pulse is preferably 10 MHz or more.

  According to the infrared-LED epitaxial wafer and the infrared LED of the present invention, the output can be improved.

It is sectional drawing which shows schematically the epitaxial wafer for infrared LED in Embodiment 1 of this invention. It is a figure for demonstrating the Al composition ratio x of the AlGaAs layer in Embodiment 1 of this invention. It is a figure for demonstrating the Al composition ratio x of the AlGaAs layer in Embodiment 1 of this invention. It is a figure for demonstrating the Al composition ratio x of the AlGaAs layer in Embodiment 1 of this invention. It is a figure for demonstrating the carrier concentration of the AlGaAs layer in Embodiment 1 of this invention. It is a figure for demonstrating the carrier concentration of the AlGaAs layer in Embodiment 1 of this invention. It is a figure for demonstrating the carrier concentration of the AlGaAs layer in Embodiment 1 of this invention. It is sectional drawing which shows schematically the epitaxial wafer for infrared LED in Embodiment 2 of this invention. It is sectional drawing which shows roughly infrared LED in Embodiment 3 of this invention. It is sectional drawing which shows roughly the infrared LED in Embodiment 4 of this invention. FIG. 4 is a diagram showing the output of each sample in Example 1. It is a figure which shows the rise time and fall time of each sample in Example 1. FIG. It is a figure which shows the cutoff frequency of each sample in Example 2. FIG. It is a figure which shows the relationship between the number of MQW layers in Example 5, and rise time. It is a figure which shows the relationship between the number of MQW layers in Example 5, and fall time. It is a figure which shows the relationship between the thickness of the active layer in Example 6, and rise time. It is a figure which shows the relationship between the thickness of the active layer in Example 6, and fall time.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
First, an infrared LED epitaxial wafer 20a in the present embodiment will be described with reference to FIG.

With reference to FIG. 1, epitaxial wafer 20a in the present embodiment will be described. As shown in FIG. 1, the epitaxial wafer 20a includes the AlGaAs substrate _{(Al y Ga (1-y} ) As substrate (0 ≦ y ≦ 1)) 10, an epitaxial layer 21 formed on the AlGaAs substrate 10, an epitaxial And a transparent conductive film 26 formed on the layer 21.

  The AlGaAs substrate 10 includes a GaAs substrate 13 and an AlGaAs layer 11 formed on the GaAs substrate 13.

  The GaAs substrate 13 may or may not have an off angle. For example, the GaAs substrate 13 has a {100} plane or a main surface inclined from 0 ° to 2 ° or less from {100}. It is preferable. The surface of the GaAs substrate 13 may be a mirror surface or a rough surface. In addition, {} indicates a collective surface.

  The AlGaAs layer 11 has a main surface 11a and a back surface 11b opposite to the main surface 11a. The main surface 11 a is a surface opposite to the surface in contact with the GaAs substrate 13. The back surface 11 b is a surface in contact with the GaAs substrate 13.

The AlGaAs layer 11 is represented by Al _x Ga _(1-x) As (0 ≦ x ≦ 1). In the AlGaAs layer 11, the Al composition ratio x of the back surface 11b is higher than the Al composition ratio x of the main surface 11a. The composition ratio x is the molar ratio of Al. The composition ratio (1-x) is a molar ratio of Ga.

  Here, the molar ratio of the AlGaAs layer 11 will be described with reference to FIGS. 2 to 4, the vertical axis indicates the position in the thickness direction from the back surface to the main surface of the AlGaAs layer 11, and the horizontal axis indicates the Al composition ratio x at each position.

  2 to 4, in the AlGaAs layer 11, the Al composition ratio x of the back surface 11b is higher than the Al composition ratio x of the main surface 11a. As shown in FIG. 2, in the AlGaAs layer 11, the Al composition ratio x preferably monotonously decreases from the back surface 11b to the main surface 11a. The monotonic decrease means that the composition ratio x is always the same or decreasing from the back surface 11b of the AlGaAs layer 11 toward the main surface 11a (in the growth direction), and the main surface 11a is more composing than the back surface 11b. It means that the ratio x is low. That is, the monotonic decrease does not include a portion where the composition ratio x increases toward this growth direction.

  As shown in FIG. 3 or 4, the AlGaAs layer 11 may include a plurality of layers (two layers in FIGS. 3 and 4). In this case, as shown in FIG. 3, the AlGaAs layer 11 preferably includes a layer in which the Al composition ratio x monotonously decreases from the back surface 11b toward the main surface 11a. Thereby, the curvature which arises in the AlGaAs substrate 10 can be relieved.

  The Al composition ratio x of the AlGaAs layer 11 is not limited to the above. For example, as shown in FIG. 4, the Al composition ratio x of each layer of the AlGaAs layer 11 may be uniform, and the layer on the back surface 11b side may be higher than the Al composition ratio x on the main surface 11a side.

  In the AlGaAs layer 11, the Al composition ratio x is preferably 0 or more and 0.45 or less. In this case, formation of an oxide layer on the AlGaAs layer 11 can be effectively suppressed and high transmission characteristics can be maintained.

  Next, the carrier concentration of the AlGaAs layer 11 will be described with reference to FIGS. 5 to 7, the vertical axis indicates the position in the thickness direction from the back surface to the main surface of the AlGaAs layer 11, and the horizontal axis indicates the carrier concentration at each position.

  As shown in FIGS. 5 to 7, the AlGaAs layer 11 preferably has a carrier concentration that changes from the back surface 11 b side toward the main surface 11 a side.

  Further, as shown in FIGS. 5 and 6, it is preferable to include a layer in which the carrier concentration monotonously increases or monotonously decreases from the back surface 11b side to the main surface 11a side. The layer in which the carrier concentration is monotonously increased is that the carrier concentration is always the same or increased from the back surface 11b side of the AlGaAs layer 11 to the main surface 11a side (in the growth direction). This means that the surface of the main surface 11a has a higher carrier concentration than the surface on the back surface 11b side. That is, the layer in which the carrier concentration monotonously increases does not include a portion in which the carrier concentration decreases in the growth direction. The layer in which the carrier concentration is monotonously decreased is that the carrier concentration is always the same or decreased from the back surface 11b side of the AlGaAs layer 11 to the main surface 11a side (in the growth direction). This means that the main surface 11a side surface has a lower carrier concentration than the back surface 11b side surface. That is, the layer in which the carrier concentration monotonously decreases does not include a portion in which the carrier concentration increases in the growth direction in this layer.

  As shown in FIGS. 6 and 7, the AlGaAs layer 11 may include a plurality of layers (two layers in FIGS. 6 and 7). In this case, the AlGaAs layer 11 may include a layer that does not monotonously increase or monotonously decrease, as shown in FIG.

  The AlGaAs layer 11 includes a layer in which the carrier concentration monotonously increases from the back surface 11b side to the main surface 11a side, and a layer in which the carrier concentration monotonously decreases from the back surface 11b side to the main surface 11a side. Is preferably not included. That is, the AlGaAs layer 11 includes only a layer whose carrier concentration monotonously increases from the back surface 11b side to the main surface 11a side, or the carrier concentration monotonously increases from the back surface 11b side to the main surface 11a side. Or a layer having a uniform carrier concentration, or a layer in which the carrier concentration monotonously decreases from the back surface 11b toward the main surface 11a, or a carrier concentration monotonously decreases from the back surface 11b toward the main surface 11a. And a layer having a uniform carrier concentration. In this case, since it can manufacture easily, cost can be reduced.

  Note that “the AlGaAs layer 11 includes a layer whose carrier concentration is monotonously increasing or monotonically decreasing from the back surface 11b toward the main surface 11a” means that at least a part of the AlGaAs layer 11 is on the back surface 11b side. Means that the carrier concentration is monotonously increased or monotonously decreased from the main surface 11a toward the main surface 11a, and the carrier concentration on the main surface 11a and the back surface 11b is not particularly limited.

  Thus, in the AlGaAs layer 11, when the carrier concentration changes from the back surface 11b side to the main surface 11a side, the reliability of an infrared LED manufactured using the AlGaAs layer 11 can be improved. . The reason will be described below. When the carrier concentration is high, the conductivity is increased, but the transmittance is deteriorated. When the transmittance deteriorates, heat is generated due to light absorption. For this reason, reliability falls. On the other hand, when the carrier concentration is low, the transmittance is improved, but the conductivity is deteriorated. When the conductivity is deteriorated, heat is generated due to high resistance. For this reason, reliability falls. In the present embodiment, since the carrier concentration changes from the back surface 11b side to the main surface 11a side, the carrier concentration is controlled in the entire AlGaAs layer 11 in order to improve the balance between conductivity and transmittance. can do. Thereby, reliability can be improved when infrared LED is formed by suppressing the heat_generation | fever by reducing the influence by electrical conductivity and the transmittance | permeability. In particular, the AlGaAs layer 11 includes a layer whose carrier concentration monotonously increases or monotonously decreases from the back surface 11b side to the main surface 11a side, so that the balance between conductivity and transmittance is improved. Since the carrier concentration can be controlled in the entire AlGaAs layer 11, an increase in cost can be suppressed and the epitaxial wafer 20a can be realized.

The absolute value of the carrier concentration gradient of the AlGaAs layer 11 is preferably 3 × 10 ¹⁵ cm ⁻³ / μm to 5 × 10 ¹⁷ cm ⁻³ / μm. That is, the absolute value of the carrier concentration gradient in at least a part of the AlGaAs layer 11 is preferably 3 × 10 ¹⁵ cm ⁻³ / μm or more and 5 × 10 ¹⁷ cm ⁻³ / μm or less. The carrier concentration gradient is a value obtained by measuring Δcc / Δd by measuring a carrier concentration difference Δcc at an arbitrary thickness Δd of the AlGaAs layer 11. In this case, since it is possible to simultaneously reduce the influence of the conductivity and transmittance of the AlGaAs layer 11, the reliability can be further improved.

The range of the carrier concentration of the AlGaAs layer 11 is preferably 1 × 10 ¹⁷ cm ⁻³ or more and 3 × 10 ¹⁸ cm ⁻³ or less. In this case, in the AlGaAs layer 11, both the reduction of the influence due to the conductivity and the reduction of the influence due to the transmittance can be achieved, so that the reliability can be improved.

  The dopant of the AlGaAs layer 11 is not particularly limited, but for example, p-type dopants such as Zn (zinc), Mg (magnesium), and C (carbon), and n such as Se (selenium), S (sulfur), and Te (tellurium). A type dopant can be used. The dopant of the AlGaAs layer 11 is preferably at least one substance selected from the group consisting of silicon, zinc, selenium, and tellurium. However, when the AlGaAs layer 11 has a plurality of layers, it may be changed for each layer.

  Epitaxial layer 21 includes an active layer. The active layer desirably has a smaller band gap than the AlGaAs layer 11. However, since the Al composition ratio has a gradient, the magnitude relationship may be partially reversed.

  The active layer preferably has a multiple quantum well structure (MQW structure) in which well layers and barrier layers having a larger band gap than the well layers are alternately stacked. In the case where the active layer has a multiple quantum well structure, the active layer preferably has 3 to 20 well layers. In this case, when an infrared LED is manufactured, the rise time and fall time in pulse application can be shortened.

  The material of the well layer is not particularly limited as long as the band gap is smaller than that of the barrier layer. be able to. These materials are materials that emit infrared light that are compatible with the degree of lattice matching with the AlGaAs layer 11. However, even if the lattice matching is deviated, it is sufficient that the distortion is not relaxed completely or partially.

  The material of the barrier layer is not particularly limited as long as the band gap is larger than that of the well layer. For example, AlGaAs, GaAsP (gallium arsenide phosphorus), AlGaAsP (aluminum gallium arsenide phosphorus), InGaP, AlInGaP, InGaAsP, or the like can be used. These materials are materials that are compatible with the degree of lattice matching with the AlGaAs layer 11. Further, as in the case of the well layer, even if the lattice matching is deviated, it is sufficient that the strain is not relaxed completely or partially.

  The active layer preferably has a thickness of 1.5 μm or less, and more preferably has a thickness of 300 nm to 1300 nm. In this case, when an infrared LED is manufactured, the rise time and fall time in pulse application can be shortened.

  The active layer is not particularly limited to a multiple quantum well structure, and may be composed of one layer or may have a double hetero structure.

  Moreover, although the case where the epitaxial layer 21 contained the active layer was demonstrated in this Embodiment, the epitaxial layer 21 may contain another layer. The epitaxial layer 21 including other layers includes, for example, an n-type buffer layer, an n-type cladding layer formed on the n-type buffer layer, an active layer formed on the n-type cladding layer, and an active layer. A p-type cladding layer formed, a p-type window layer formed on the p-type cladding layer, and a p-type contact layer formed on the p-type window layer are included. In the above configuration, at least one of the other layers may be omitted, and the p-type and n-type may be reversed.

The uppermost layer of the epitaxial layer 21 (the layer in contact with the transparent conductive film 26) is preferably p-type. In this case, the epitaxial layer 21 includes a p-type cladding layer formed on the active layer, and the p-type cladding layer has a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or more and 2 × 10 ¹⁸ cm ⁻³ or less. Is preferred. The epitaxial layer 21 includes a p-type cladding layer formed on the active layer and a p-type window layer formed on the p-type cladding layer, and at least one of the p-type cladding layer and the p-type window layer is More preferably, it has a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or more and 2 × 10 ¹⁸ cm ⁻³ or less.

  The transparent conductive film 26 has an effect of spreading the current over the entire surface (lateral direction in FIG. 1) on the top surface of the chip when an infrared LED is manufactured using the epitaxial wafer 20a. As a result, current is injected into the active layer over the entire surface of the chip, light emission occurs, and high output can be achieved. Further, when there is no transparent conductive film 26, the series resistance on the upper surface of the chip becomes high, which causes the high-speed response to deteriorate.

  The transparent conductive film 26 has high permeability and low resistivity. Such a transparent conductive film 26 has a transmittance of 85% or more at a wavelength of 850 nm or more and 1000 nm or less, for example, and a resistivity of 5 mΩcm or less at a thickness of 300 nm, for example.

As the transparent conductive film, for example, ITO which is indium oxide (In ₂ O ₃ ) doped with tin (Sn), indium oxide (In ₂ O ₃ ), IFO which is In ₂ O ₃ doped with fluorine (F) , Tin oxide (SnO ₂ ), antimony (Sb) -doped SnO ₂ ATO, F-doped SnO ₂ FTO, cadmium (Cd) -doped SnO ₂ CTO, aluminum (Al ) Doped with zinc oxide (ZnO), IZO as Zn doped with In, GZO as ZnO doped with Ga, and the like. In particular, it is preferable that the transparent conductive film 26 is ITO because transparency and conductivity can be maintained in a well-balanced manner.

  The transparent conductive film 26 is not particularly limited to the above materials, and for example, a metal film having a thickness of 50 nm or less so that light can be transmitted may be used. As such a metal film, for example, gold (Au) or Al having a thickness of 15 nm or less can be used.

  The thickness of the epitaxial layer 21 is preferably 50 μm or more and 300 μm or less. In the case of 50 μm or more, handling can be improved. In the case of 300 μm or less, the output can be improved and the cost can be reduced.

  Then, the manufacturing method of the epitaxial wafer 20a in this Embodiment is demonstrated.

  First, a GaAs substrate 13 is prepared. Next, the AlGaAs layer 11 having the main surface 11a is grown on the GaAs substrate 13 by, for example, an LPE (Liquid Phase Epitaxy) method. In the step of growing the AlGaAs layer 11, the AlGaAs layer 11 is grown such that the Al composition ratio x at the interface (back surface 11b) with the GaAs substrate 13 is higher than the Al composition ratio x of the main surface 11a.

  The LPE method is not particularly limited, and a slow cooling method, a temperature difference method, or the like can be used. The LPE method is a method for growing an AlGaAs crystal from a liquid phase. The slow cooling method is a method of growing AlGaAs crystals by gradually lowering the temperature of the raw material solution. The temperature difference method is a method in which a temperature gradient is created in a raw material solution to grow an AlGaAs crystal.

  When growing a layer having a constant Al composition ratio x in the AlGaAs layer 11, a temperature difference method and a slow cooling method are used to grow a layer in which the Al composition ratio x decreases upward (growth direction). It is preferable to use a slow cooling method. It is particularly preferable to use the slow cooling method because of its excellent mass productivity and low cost. Moreover, you may combine them.

In this step, it is preferable to grow an AlGaAs layer including a layer in which the carrier concentration monotonously increases or monotonously decreases from the back surface 11b toward the main surface 11a. In this case, it is preferable to grow the AlGaAs layer 11 so that the absolute value of the gradient of the carrier concentration is 3 × 10 ¹⁵ cm ⁻³ / μm to 5 × 10 ¹⁷ cm ⁻³ / μm. Further, it is preferable to grow the AlGaAs layer 11 so that the carrier concentration is 1 × 10 ¹⁷ cm ⁻³ or more and 3 × 10 ¹⁸ cm ⁻³ or less.

  Next, the main surface 11a of the AlGaAs layer 11 is polished. When the AlGaAs layer 11 is grown by the LPE method, the main surface 11a is uneven, but the main surface 11a can be flattened by this process.

  Thereby, the AlGaAs substrate 10 including the AlGaAs layer 11 and the GaAs substrate 13 can be manufactured.

  Next, an active layer is included on the main surface 11a of the AlGaAs layer 11 of the AlGaAs substrate 10 by an OMVPE (Organo Metallic Vapor Phase Epitaxy) method or an MBE (Molecular Beam Epitaxy) method. Epitaxial layer 21 is formed. In this step, an epitaxial layer including the active layer as described above is grown on the AlGaAs layer 11.

  In the OMVPE method, the active gas is grown by the thermal decomposition reaction of the source gas on the AlGaAs layer 11, and in the MBE method, the active layer is grown by a method that does not involve a chemical reaction process in a non-equilibrium system. Can easily control the thickness of the active layer. Therefore, an active layer having a plurality of well layers of two or more layers can be easily grown.

  Further, since the main surface 11a of the AlGaAs layer 11 of the AlGaAs substrate 10 is flat, the abnormal growth of the epitaxial layer 21 can be suppressed when the epitaxial layer 21 including the active layer is formed on the main surface 11a of the AlGaAs layer 11. it can.

  Next, a transparent conductive film 26 is formed on the epitaxial layer 21. A method for forming the transparent conductive film 26 is not particularly limited, and for example, an electron beam evaporation method, a sputtering method, or the like can be employed.

  By performing the above steps, the epitaxial wafer 20a shown in FIG. 1 can be manufactured. A step of removing a part of the GaAs substrate 13 may be further performed. In this case, an epitaxial wafer 20a having a GaAs substrate having a smaller thickness than the prepared GaAs substrate is manufactured.

  As described above, epitaxial wafer 20a in the present embodiment is formed of GaAs substrate 13, AlGaAs layer 11 formed on GaAs substrate 13 and having main surface 11a and back surface 11b opposite to main surface 11a. In the AlGaAs layer 11, an AlGaAs substrate 10 including: an epitaxial layer 21 formed on the main surface 11 a of the AlGaAs layer 11 and including an active layer; and a transparent conductive film 26 formed on the epitaxial layer 21. The Al composition ratio x of the back surface 11b is higher than the Al composition ratio x of the main surface 11a.

  According to epitaxial wafer 20a in the present embodiment, Al composition ratio x of back surface 11b is higher than Al composition ratio x of main surface 11a. For this reason, it can suppress that Al which has the property which is easy to be oxidized exists in the main surface 11a. Thus, it is possible to suppress the formation of an insulating oxide layer on the surface of the AlGaAs substrate 10 (in this embodiment, the main surface 11a of the AlGaAs layer 11). For this reason, it is possible to suppress the introduction of defects into the epitaxial layer formed on the AlGaAs substrate 10.

  The Al composition ratio x of the main surface 11a is lower than the Al composition ratio x of the back surface 11b. As a result of diligent research, the present inventor has found that the higher the Al composition ratio x, the better the transmission characteristics of the AlGaAs substrate 10. Even if a large amount of Al is contained on the back surface 11b side, since the time exposed on the surface is short, the formation of an oxide layer on the main surface 11a can be reduced. For this reason, the transmission characteristics can be improved by growing an AlGaAs crystal having a high Al composition ratio x in a portion where the formation of the oxide layer can be suppressed.

  In this way, in the AlGaAs layer 11, the Al composition ratio x is lowered so as to suppress the introduction of defects on the main surface 11a side, and the Al composition ratio x is improved so as to improve the transmission characteristics on the back surface 11b side. Is high.

  Further, a transparent conductive film 26 is formed on the epitaxial layer. The transparent conductive film 26 can promote current diffusion even when the epitaxial layer 21 is thin.

  Therefore, when an infrared LED is manufactured using the epitaxial wafer 20a in the present embodiment, a decrease in light emission characteristics due to defects can be suppressed, light absorption can be reduced by improving transmission characteristics, and the current of the transparent conductive film 26 can be reduced. By spreading the light, the light can be spread over the entire surface of the chip. Therefore, the output of the infrared LED manufactured using this epitaxial wafer 20a can be improved.

  Further, the lateral resistance can be reduced by the transparent conductive film 26. For this reason, the high-speed responsiveness of infrared LED produced using this epitaxial wafer 20a is realizable.

  In the epitaxial wafer 20a of the present embodiment, the AlGaAs substrate 10 includes a GaAs substrate 13 that is in contact with the back surface 11b of the AlGaAs layer 11.

  When the AlGaAs substrate 10 includes the GaAs substrate 13, not only the AlGaAs layer 11 but also the entire epitaxial wafer 20a can be designed with the GaAs substrate 13 to suppress the occurrence of wafer cracking in the chip manufacturing process. be able to.

  In addition, since it is not necessary to remove the GaAs substrate 13 in the present embodiment, it is possible to shorten the time for the process of removing the GaAs substrate 13 as compared with the second embodiment in which the GaAs substrate 13 described later is removed. For this reason, cost can be reduced.

  Further, when an electrode is formed on the GaAs substrate 13 in order to fabricate an infrared LED using the epitaxial wafer 20a in the present embodiment, a contact electrode having a lower resistance than the case where an electrode is formed on the AlGaAs layer 11. Can be produced. For this reason, an infrared LED having higher reliability and lower operating temperature can be manufactured.

  In the epitaxial wafer 20a, the transparent conductive film 26 is preferably ITO. ITO achieves both high permeability and high conductivity. The output can be further improved by the high permeability. Resistance can be reduced due to high conductivity.

  In epitaxial wafer 20a, the layer in contact with transparent conductive film 26 in epitaxial layer 21 is preferably p-type.

  The contact resistance between the p-type layer and the transparent conductive film 26 can be reduced as compared with the contact resistance between the n-type layer and the transparent conductive film 26. For this reason, when an infrared LED is produced, the speed of the infrared LED can be increased.

Preferably, in the epitaxial wafer 20a, the epitaxial layer 21 includes a p-type cladding layer formed on the active layer and a p-type window layer formed on the p-type cladding layer, and the p-type cladding layer and the p-type cladding layer are formed. At least one of the window layers has a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or more and 2 × 10 ¹⁸ cm ⁻³ or less.

In the case of 1 × 10 ¹⁷ cm ⁻³ or more, since the resistance can be lowered, the high-speed response can be improved. In the case of 2 × 10 ¹⁸ cm ⁻³ or less, high output can be maintained by suppressing light absorption, and high reliability can be maintained.

  In the epitaxial wafer 20a, the active layer preferably has a thickness of 1.5 μm or less.

  Thereby, the depletion layer capacity of the pn junction can be reduced, and when an infrared LED is manufactured, the rise time and the fall time in pulse application can be shortened. For this reason, high-speed response can be improved.

  In the epitaxial wafer 20a, preferably, the active layer has three or more and 20 or less well layers.

  Thereby, when an infrared LED is manufactured, the rise time and fall time in pulse application can be shortened. For this reason, high-speed response can be improved.

(Embodiment 2)
With reference to FIG. 8, infrared LED epitaxial wafer 20b in the present embodiment will be described.

  Referring to FIG. 8, epitaxial wafer 20b in the present embodiment basically has the same configuration as epitaxial wafer 20a in the first embodiment, but differs in that GaAs substrate 13 is not provided.

  The thickness of the AlGaAs layer 11 in the present embodiment is preferably so thick that the AlGaAs substrate 10 becomes a free-standing substrate. Such a thickness is, for example, 70 μm or more.

  Then, the manufacturing method of the epitaxial wafer 20b in this Embodiment is demonstrated. The method for manufacturing epitaxial wafer 20b in the present embodiment has basically the same configuration as the method for manufacturing epitaxial wafer 20a in the first embodiment, but further includes a step of removing GaAs substrate 13. It is different in point.

  The method for removing the GaAs substrate 13 is not particularly limited, and for example, a method such as polishing or etching can be used. Polishing refers to mechanically scraping off the GaAs substrate 13 using a polishing agent such as alumina, colloidal silica, diamond, or the like in a grinding facility having a diamond grindstone. Etching means that the GaAs substrate 13 is removed using a selective etching solution having a slow etching rate with AlGaAs and a fast etching rate with GaAs by optimally preparing ammonia, hydrogen peroxide, or the like.

  As described above, epitaxial wafer 20b in the present embodiment includes AlGaAs substrate 10 including AlGaAs layer 11 having main surface 11a and back surface 11b opposite to main surface 11a, and main surface 11a of AlGaAs layer 11. The AlGaAs layer 11 includes an epitaxial layer 21 including an active layer formed thereon and a transparent conductive film 26 formed on the epitaxial layer 21. In the AlGaAs layer 11, the Al composition ratio x of the back surface 11b is equal to that of the main surface 11a. It is higher than the Al composition ratio x.

  The epitaxial wafer 20b in the present embodiment includes the AlGaAs substrate 10 that includes only the AlGaAs layer 11 without including the GaAs substrate 13. Since the GaAs substrate 13 absorbs light having a wavelength of 870 nm or less, if an infrared LED is manufactured using the epitaxial wafer 20b including the AlGaAs substrate 10 from which the GaAs substrate 13 has been removed, the transmittance can be further improved. For this reason, the output of infrared LED produced using this epitaxial wafer 20b can be improved more.

(Embodiment 3)
With reference to FIG. 9, the infrared LED 30a in the present embodiment will be described. As shown in FIG. 9, infrared LED 30a in the present embodiment is formed on epitaxial wafer 20a for infrared LED shown in FIG. 1 in the first embodiment, and on the main surface and the back surface of this epitaxial wafer 20a. Electrodes 31 and 32. In order to extract light, the electrode 31 covers only a part of the surface of the epitaxial wafer 20a and exposes the remaining part. The electrode 32 covers the back surface of the epitaxial wafer 20a. The electrode 32 may cover the entire back surface of the epitaxial wafer 20a or a part thereof. When a part is covered, it can be formed in a dot shape or a lattice shape, for example.

  When the layer in contact with the transparent conductive film 26 in the epitaxial layer 21 is p-type, the electrode 31 is a p-type electrode made of, for example, an alloy of Au (gold) and Zn (zinc), and is formed under the AlGaAs substrate 10. The electrode 32 is an n-type electrode made of, for example, an alloy of Au and Ge (germanium).

  The emission wavelength of the infrared LED 30a is, for example, not less than 850 nm and not more than 1 μm. In the infrared LED 30a, the light emission output when an operating current of 20 mA is passed is, for example, 3 mW or more and 6 mW or less.

  In the infrared LED 30a, the rise time and the fall time in pulse application are, for example, 5 nsec to 100 nsec, and preferably 5 nsec to 27 nsec. In this case, an infrared LED 30a having high-speed response can be realized.

  Note that the “rise time and fall time in pulse application” refers to the output waveform from 10% based on the transient change time of the output voltage when the pulse generator generates a rectangular pulse and the output is turned on / off. The time required to reach 90% is defined as the rise time, and the time required for the output waveform to reach 90% to 10% is defined as the fall time.

  In the infrared LED 30a, the cutoff frequency in applying the pulse is, for example, 10 MHz or more, and preferably 16 MHz or more and 43 MH or less. In this case, the performance of the infrared LED 30a can be improved.

The “cutoff frequency” is a frequency that is _{½ in} the ratio of output power (P _out ) / input power (P _in ). For example, in the actual measurement shown in FIG. 13, the ratio of the output power (P _out ) / input power (P _in ) is the value at the point where the attenuation is −3 dB.

  Then, the manufacturing method of infrared LED30a in this Embodiment is demonstrated. First, the epitaxial wafer 20a is manufactured by the manufacturing method of the infrared LED epitaxial wafer 20a in the first embodiment.

  Next, the electrodes 31 and 32 are formed on the main surface and the back surface of the infrared-LED epitaxial wafer 20a. Specifically, for example, by vapor deposition, Au and Zn are vapor-deposited on the main surface, and Au and Ge are vapor-deposited on the back surface, and then alloyed to form the electrodes 31 and 32. .

  By performing the above steps, the infrared LED 30a shown in FIG. 9 can be manufactured.

  As described above, the infrared LED 30 a in the present embodiment includes the epitaxial wafer 20 a in the first embodiment and the electrodes 31 and 32 formed on the epitaxial layer 21.

  According to the infrared LED 30a in the present embodiment, since the AlGaAs substrate 10 in which the Al composition ratio x of the AlGaAs layer 11 is controlled and the current is diffused by the transparent conductive film 26, the infrared light with improved output is provided. The LED 30a can be realized.

  In the infrared LED 30a, the rise time and the fall time in the pulse application are preferably 5 nsec or more and 100 nsec or less. By using the epitaxial wafer 20a of the first embodiment, the infrared LED 30a having a short rise time and short fall time can be realized. Thereby, the response speed can be improved.

  In the infrared LED 30a, the cut-off frequency in pulse application is preferably 10 MHz or more. By using the epitaxial wafer 20a of the first embodiment, the infrared LED 30a having a large cutoff frequency can be realized. Thereby, the response speed can be improved. Thereby, the performance of the infrared LED 30a can be improved.

(Embodiment 4)
With reference to FIG. 10, infrared LED 30b in the present embodiment will be described. As shown in FIG. 10, the infrared LED 30 b in the present embodiment basically has the same configuration as the infrared LED 30 a in the third embodiment, but differs in that the GaAs substrate 13 is not provided.

  Specifically, the infrared LED 30b of the present embodiment includes the epitaxial wafer 20b of the second embodiment. The electrode 31 is provided in contact with the surface of the epitaxial wafer 20b, and the electrode 32 is provided in contact with the back surface (in this embodiment, the back surface 11b of the AlGaAs layer 11).

  The emission wavelength of the infrared LED 30b is, for example, not less than 850 nm and not more than 1 μm. In the infrared LED 30b, the light emission output when an operating current of 20 mA is passed is, for example, not less than 4.5 mW and not more than 6 mW.

  The manufacturing method of the infrared LED 30b in the present embodiment basically has the same configuration as the manufacturing method of the infrared LED 30a in the third embodiment, but is implemented instead of the epitaxial wafer 20a in the first embodiment. This is different in that the epitaxial wafer 20b of the form is manufactured.

  As described above, the infrared LED 30 b in the present embodiment includes the epitaxial wafer 20 b in the second embodiment and the electrodes 31 and 32 formed on the epitaxial layer 21.

  According to the infrared LED 30b in the present embodiment, the AlGaAs substrate 10 including only the AlGaAs layer 11 without including the GaAs substrate 13 is provided. Since the GaAs substrate 13 absorbs light having a wavelength of 870 nm or less, the infrared LED 30b including the AlGaAs substrate 10 from which the GaAs substrate 13 has been removed can further improve the transmittance. For this reason, the output of infrared LED30b can be improved more.

  In this example, the effect of including the AlGaAs layer 11 having a higher Al composition ratio x of the back surface 11b than the Al composition ratio x of the main surface 11a and the transparent conductive film was examined.

(Invention Example 1)
Invention Example 1 followed the manufacturing method of the infrared LED 30b in the fourth embodiment. Specifically, first, a GaAs substrate 13 manufactured by the VB method and having a diameter of 2 inches and a thickness of 270 μm was prepared.

Next, the AlGaAs layer 11 was grown on the GaAs substrate 13 by a slow cooling method under a temperature condition between 920 ° C. and room temperature. In this step, the AlGaAs layer was grown so as to include three monotonically decreasing layers having an Al composition ratio of 0.3 on the back surface 11b side and an Al composition ratio of 0.1 on the main surface 11a side. The thickness of each layer was 50 μm, and the thickness of the AlGaAs layer was 150 μm. Further, tellurium was doped as a dopant, and an AlGaAs layer was grown so that the carrier concentration of the back surface 11b was 2 × 10 ¹⁸ cm ⁻³ and the carrier concentration of the main surface 11a was 1 × 10 ¹⁷ cm ⁻³ .

Next, an epitaxial layer including an active layer was formed by OMVPE. Specifically, an n-type buffer layer, an n-type cladding layer, an active layer, a p-type cladding layer, a p-type window layer, and a p-type contact layer were grown in this order on the main surface 11a of the AlGaAs layer 11. The growth temperature of each layer was 760 ° C. The n-type buffer layer had a thickness of 0.5 μm, was made of Al _0.15 Ga _0.85 As doped with Si, and had a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ . The n-type cladding layer had a thickness of 1.0 μm, and was made of Al _0.35 Ga _0.65 As doped with Si, and had a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ . The p-type cladding layer had a thickness of 1.0 μm, was made of Zn-doped Al _0.35 Ga _0.65 As, and had a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ . The p-type window layer had a thickness of 3.5 μm, was made of Zn-doped Al _0.20 Ga _0.80 As, and had a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ . The p-type contact layer had a thickness of 0.2 μm, was made of Zn-doped GaAs, and had a carrier concentration of 4 × 10 ¹⁹ cm ⁻³ . The active layer has an emission wavelength of 940 nm, a thickness of 5 nm, a well layer made of In _0.25 Ga _0.75 As, and a barrier layer made of Al _0.30 Ga _0.70 As, each having a thickness of 15 nm. The layer had a multiple quantum well structure (MQW). The thickness of the active layer was 897 nm.

  Next, a transparent conductive film was formed on the surface of the epitaxial layer opposite to the surface in contact with the AlGaAs substrate by electron beam evaporation at a temperature of 300 ° C. in an oxygen atmosphere in a vacuum furnace. The transparent conductive film was ITO having a thickness of 300 nm.

  Next, a p-type electrode was formed as the electrode 31 on the transparent conductive film 26. The pad diameter of the electrode 31 was 120 μm, the electrode material was Au, and the total thickness was 1 μm.

  Next, the GaAs substrate 13 was removed, and an n-type electrode was formed as the electrode 32 on the back surface 11 b of the AlGaAs layer 11. The electrode 32 was in the form of dots, the material was an AuGe alloy, and the thickness was 1 μm.

By carrying out the above steps, an infrared LED 30b of Example 1 of the present invention was manufactured.
(Invention Example 2)
Infrared LED 30b of Invention Example 2 was basically manufactured in the same manner as Infrared LED 30b of Invention Example 1, except that an active layer in which 20 well layers and 20 barrier layers were alternately laminated was formed. Only was different. However, strains in opposite directions are introduced into the well layer and the barrier layer, respectively, and strain compensation is performed for the entire epitaxial layer.

(Invention Example 3)
Infrared LED 30a of Invention Example 3 followed the manufacturing method of infrared LED 30a of Embodiment 3. Specifically, the infrared LED 30a of Example 3 of the present invention is basically manufactured in the same manner as the infrared LED of Example 1 of the present invention, but after the epitaxial layer 21 is grown on the GaAs substrate 13, GaAs is polished. The substrate 13 was partially removed from the rear surface side, and the difference was that the thickness of the GaAs substrate 13 was 140 μm and the thickness of the AlGaAs layer was 80 μm. The emission wavelength of the infrared LED of Invention Example 3 was 936 nm.

(Invention Example 4)
Infrared LED 30b of Invention Example 4 was basically manufactured in the same manner as Infrared LED 30b of Invention Example 3, except that an active layer in which 20 well layers and 20 barrier layers were alternately laminated was formed. Only was different. However, strains in opposite directions are introduced into the well layer and the barrier layer, respectively, and strain compensation is performed for the entire epitaxial layer.

(Comparative Example 1)
The infrared LED of Comparative Example 1 was basically manufactured in the same manner as Example 1 of the present invention, but differed in that a transparent conductive film was not formed.

(Evaluation methods)
The infrared LEDs of Invention Examples 1 to 4 and Comparative Example 1 were mounted on a TO can with Ag paste, and a gold wire with a diameter of 30 μm was bonded to the electrode 31 which is a p-side electrode. And the output when the operating current IF was 20 mA was measured. The result is shown in FIG.

  In addition, a rectangular pulse was generated by a pulse generator, and the response speed of light output was measured. The rise time Tr and fall time Tf were defined on the basis of the transient change time of the output voltage when the output was turned on / off when a forward current (IF) was passed through the light emission side as a pulse. That is, the rise time Tr is a time from the output waveform reaching 10% to 90%. The fall time Tf was the time from 90% to 10% of the output waveform. The result is shown in FIG.

(Evaluation results)
As shown in FIG. 11, the inventive examples 1 to 4 including the AlGaAs layer having the Al composition ratio x of the back surface 11 b higher than the Al composition ratio x of the main surface 11 a and the transparent conductive film are transparent. It was found that the output can be improved as compared with Comparative Example 1 in which no conductive film was provided. In particular, the inventive examples 1 and 2 from which the GaAs substrate was removed were able to improve the output further than the inventive examples 3 and 4 having the GaAs substrate.

  Here, in Comparative Example 1, since the Al composition ratio x of the back surface 11b in the AlGaAs layer 11 was higher than the Al composition ratio x of the main surface 11a, the output of the infrared LED of Comparative Example 1 was Al The inventor has obtained the knowledge that the composition of the above is higher than the output of a conventional infrared LED having a uniform AlGaAs layer.

  Further, as shown in FIG. 12, the infrared LEDs of Invention Examples 1 to 4 having well layers of 3 to 20 layers had rise times and fall times of 5 nsec to 100 nsec in pulse application. In particular, the infrared LEDs of Invention Examples 1 and 3 having three well layers were able to improve the response speed further than the infrared LEDs of Invention Examples 2 and 4 having 20 well layers.

  As described above, according to the present embodiment, in the AlGaAs layer 11, the Al composition ratio x of the back surface 11b is higher than the Al composition ratio x of the main surface 11a, and the output can be improved by providing the transparent conductive film. Was confirmed.

  In this example, the Al composition ratio x of the back surface 11b in the AlGaAs layer 11 was higher than the Al composition ratio x of the main surface 11a, and the effect of providing a transparent conductive film was further investigated.

(Invention Example 5)
Invention Example 5 was basically produced in the same manner as Invention Example 2, but differed in that the thickness of the AlGaAs layer was 80 μm. The emission wavelength of the infrared LED of Invention Example 5 was 945 nm.

(Invention Example 6)
Invention Example 6 was basically manufactured in the same manner as Invention Example 1, but differed in that the thickness of the AlGaAs layer was 180 μm. The emission wavelength of the infrared LED of Invention Example 6 was 940 nm.

(Evaluation methods)
For the infrared LEDs of Invention Examples 3, 5, 6 and Comparative Example 1, the output was measured in the same manner as in Example 1. The results are shown in Table 1 below.

The cut-off frequency fc was measured for the infrared LEDs of Invention Examples 5 and 6 and Comparative Example 1. The result is shown in FIG. The cut-off frequency fc was a point attenuated by −3 dB _in the ratio of output power (P _out ) / input power (P _in ). The results are shown in Table 1 below.

  As shown in Table 1, Examples 3, 5, and 6 of the present invention were provided with an AlGaAs layer in which the Al composition ratio x of the back surface 11b was higher than the Al composition ratio x of the main surface 11a and a transparent conductive film. Compared with the comparative example 1 which was not equipped with the transparent conductive film, it turned out that an output can be improved. In particular, the inventive examples 5 and 6 from which the GaAs substrate was removed were able to improve the output further than the inventive example 3 provided with the GaAs substrate.

  Further, as shown in Table 1 and FIG. 13, the Al composition ratio x of the back surface 11b is higher than the Al composition ratio x of the main surface 11a, the transparent conductive film is provided, and the GaAs substrate is removed. Thus, the invention example 6 having three active layers was able to improve the cut-off frequency as compared with the invention example 5 and the comparative example 1.

In the present embodiment, a p-type cladding layer formed on the active layer and a p-type window layer formed on the p-type cladding layer, and at least one of the p-type cladding layer and the p-type window layer is 1 The effect of having a carrier concentration of × 10 ¹⁷ cm ⁻³ or more and 2 × 10 ¹⁸ cm ⁻³ or less was examined.

Specifically, in Example 1 of the present invention, the carrier concentration of the p-type cladding layer and the p-type window layer was set to 5 × 10 ¹⁷ cm ⁻³ , but in this example, the p-type cladding layer and the p-type window layer Five types of infrared LEDs that differ in the carrier concentration described in Table 2 below were further manufactured.

  For each infrared LED, the output, rise time, and fall time were measured in the same manner as in Example 1. The results are shown in Table 2 below. In Table 2, ○ of output means 2.5 mW or more, and Δ means 1 mW or more and less than 2.5 mW. In addition, “◯” in the high-speed response means that the rise time and the fall time are 100 nsec or less, and “x” means that the rise time and the fall time are over 100 nsec.

As shown in Table 2, the infrared LED in which the p-type cladding layer and the p-type window layer have a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or more and 2 × 10 ¹⁸ cm ⁻³ or less has high output and response. It was found that the performance can be improved.

In the infrared LED in which the p-type cladding layer and the p-type window layer had a carrier concentration of 7 × 10 ¹⁶ cm ⁻³ , the rise time and fall time were increased. In the infrared LED having a carrier concentration of 2.5 × 10 ¹⁸ cm ⁻³ , the rise time and fall time were increased, and the output was slightly reduced.

As described above, according to the present embodiment, the p-type cladding layer formed on the active layer and the p-type window layer formed on the p-type cladding layer are used. It has been confirmed that at least one of the carriers has a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or more and 2 × 10 ¹⁸ cm ⁻³ or less, thereby improving output and maintaining high-speed response. In addition, even if it is a case where a p-type window layer is abbreviate | omitted, this inventor has acquired that it can improve an output similarly and can maintain high-speed responsiveness.

  In this example, the effect of the thickness of the AlGaAs substrate being 50 μm or more and 300 μm or less was examined.

  More specifically, in this example, basically, it was manufactured in the same manner as Example 1 of the present invention, but six types of infrared LEDs that differ in the thickness of the AlGaAs substrate described in Table 3 below were further manufactured. did.

  For each infrared LED, the output, rise time, and fall time were measured in the same manner as in Example 1. The results are shown in Table 3 below. In Table 3, Δ of output and ○ and × and ○ of high-speed answer were evaluated in the same manner as in Example 3.

  As shown in Table 3, it was found that an infrared LED having an AlGaAs substrate with a thickness of 50 μm or more and 300 μm or less has high output and can improve responsiveness.

  Infrared LEDs with an AlGaAs substrate thickness of 30 μm are difficult to handle due to their thin thickness, the output is slightly reduced, and high-speed response is reduced. Infrared LEDs having an AlGaAs substrate thickness of 500 μm have a rough surface and a slightly reduced output. In addition, since the series resistance increased, the high-speed response decreased.

  As described above, according to this example, it was confirmed that the output can be improved and the high-speed response can be maintained when the thickness of the AlGaAs substrate is 50 μm or more and 300 μm or less.

In this example, the effect of having three to twenty well layers was examined.
Specifically, an infrared LED having an MQW in which three well layers and barrier layers similar to Example 1 of the present invention were alternately laminated was manufactured.

  Moreover, one kind of infrared LED having MQW in which 20 well layers and barrier layers similar to Example 2 of the present invention were alternately laminated was manufactured.

  For these infrared LEDs, the rise time Tr and the fall time Tf were measured in the same manner as in Example 1. The results are shown in FIGS. 14 and 15, respectively.

  As shown in FIGS. 14 and 15, it was confirmed that the infrared LED including the active layer having the well layer of 3 layers or more and 20 layers or less can maintain high-speed response.

In this example, the effect of the active layer having a thickness of 1.5 μm or less was examined.
Specifically, in Example 1 of the present invention, the thickness of the active layer was 897 nm, but in this example, the thickness of the active layer was set to 7 in FIGS. 16 and 17 in the same manufacturing method as Example 1 of the present invention. Further types of infrared LEDs were manufactured.

  Note that the thickness of the active layer is the thickness of an undoped layer that is not intentionally doped with impurities, or a layer sandwiched between clad layers with different band gaps and refractive indexes in order to improve the confinement of injected electrons. did.

  For these infrared LEDs, the rise time Tr and the fall time Tf were measured in the same manner as in Example 1. The results are shown in FIGS. 16 and 17, respectively.

  As shown in FIGS. 16 and 17, it was confirmed that the infrared LED having an active layer thickness of 1.5 μm can maintain high-speed response.

  In the present embodiment, in the AlGaAs layer 11, the Al composition ratio x of the back surface 11b is higher than the Al composition ratio x of the main surface 11a and the transparent conductive film is provided. We investigated whether it was feasible.

  In this example, it was basically manufactured in the same manner as Example 1 of the present invention. However, the thickness of the active layer, the number of well layers are shown in Table 4 below, and the width of the well layer of the active layer and Infrared LEDs having different In composition ratios of InGaAs were further manufactured.

  For each infrared LED, the rise time and fall time were measured in the same manner as in Example 1, the cut-off frequency was measured in the same manner as in Example 2, and the emission wavelength was also measured. The results are shown in Table 4 below.

  As shown in Table 4, it was found that an infrared LED capable of emitting light having a wavelength of 850 nm to 1000 nm could be realized.

  Although the embodiments and examples of the present invention have been described above, it is also planned from the beginning to appropriately combine the features of the embodiments and examples. The embodiments and examples disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the embodiments and examples described above but by the scope of claims for patent, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims for patent.

  10 AlGaAs substrate, 11 AlGaAs layer, 11a main surface, 11b back surface, 13 GaAs substrate, 20a, 20b epitaxial wafer, 21 epitaxial layer, 26 transparent conductive film, 30a, 30b LED, 31, 32 electrodes.

Claims (10)

An Al _y Ga _(1-y) As substrate (0 ≦ y ≦ 1) including an Al _x Ga _(1-x) As layer (0 ≦ x ≦ 1) having a main surface and a back surface opposite to the main surface. )When,
An epitaxial layer formed on the main surface of the Al _x Ga _(1-x) As layer and including an active layer;
A transparent conductive film formed on the epitaxial layer,
In the Al _x Ga _(1-x) As layer, an infrared LED epitaxial wafer in which the Al composition ratio x on the back surface is higher than the Al composition ratio x on the main surface.   The epitaxial wafer for infrared LEDs according to claim 1, wherein the transparent conductive film is ITO.   3. The infrared-LED epitaxial wafer according to claim 1, wherein the layer in contact with the transparent conductive film in the epitaxial layer is p-type. The epitaxial layer includes another layer formed on the active layer,
The other layer has a layer having a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or more and 2 × 10 ¹⁸ cm ⁻³ or less,
The layer is a p-type cladding layer formed on the active layer, or a p-type cladding layer formed on the active layer and a p-type window layer formed on the p-type cladding layer. The epitaxial wafer for infrared LEDs according to claim 3.   The infrared wafer for infrared LEDs according to claim 1, wherein the active layer has a thickness of 1.5 μm or less.   The said active layer is an epitaxial wafer for infrared LEDs of any one of Claims 1-5 which has a well layer of 3 layers or more and 20 layers or less. The infrared LED according to claim 1, wherein the Al _y Ga _(1-y) As substrate includes a GaAs substrate in contact with the back surface of the Al _x Ga _(1-x) As layer. Epitaxial wafer. An epitaxial wafer for infrared LEDs according to any one of claims 1 to 7,
An infrared LED comprising an electrode formed on the epitaxial wafer.   The infrared LED according to claim 8, wherein a rise time and a fall time in pulse application are 5 nsec or more and 100 nsec or less.   The infrared LED according to claim 8 or 9, wherein a cutoff frequency in applying a pulse is 10 MHz or more.

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