JP2010027936A - Optical semiconductor element and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily form Ru doping semi-insulating semiconductor layer having higher insulation with high reproducibility even under a growth environment in which a large amount of hydrogen exists in order to practically use a buried type optical semiconductor element using the Ru doping semi-insulating semiconductor layer. <P>SOLUTION: During the growth of the Ru doping semi-insulating semiconductor layer, gas containing halogen atoms is added simultaneously with hydrogen independently of raw material gas of a compound semiconductor and carrier gas so as to suppress bonding between Ru and hydrogen. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical semiconductor device having a structure in which a compound semiconductor layer is embedded with a semi-insulating semiconductor layer doped with Ru, and a method for manufacturing the same.

  With the explosive growth of the Internet population in recent years, there has been a demand for rapid increase in information transmission and capacity, and optical communication will continue to play an important role in the future. A semiconductor laser element is mainly used as a light source used for optical communication. Therefore, the optical semiconductor element will be required to have particularly high characteristics in the future. As a semiconductor laser for optical communication for short-distance applications up to a transmission distance of about 10 km, a direct modulation method is used in which the semiconductor laser is directly driven by an electric signal. Since this direct modulation method can realize a module with a simple configuration, the power consumption is low and the number of components can be reduced, so that the cost can be reduced. On the other hand, for optical communication over long distances exceeding 10 km, it is not possible to deal with by directly modulating a semiconductor laser, so an electro-absorption (EA) modulator integrated with an optical modulator is integrated. Type semiconductor lasers are used. Further, a Mach Zehnder (MZ) modulator with small chirping is used at a distance exceeding 80 km.

  The basic structure of such a semiconductor laser is broadly divided into two types: a ridge waveguide (RWG) structure and a buried hetero (BH) structure.

  FIG. 1 is a sectional view of an edge emitting semiconductor laser. The RWG type shown in FIG. 1A has a structure in which an active layer 102, an upper cladding layer 103, and a p + -InGaAs contact layer 104 are stacked on an n-InP substrate 101, and the upper cladding layer 103 has a width. The adjacent region of the mesa stripe is dug by etching so that a mesa stripe of several μm is formed. However, in this digging, the upper cladding layer is etched to a region close to the active layer 102, but the etching is stopped at a depth at which the active layer 102 is not exposed.

  On the other hand, the BH type shown in FIG. 1B has a structure in which an active layer 107, a semi-insulating semiconductor layer 106, a p + -InGaAs contact layer 108, and an upper cladding layer 109 are stacked on a lower cladding layer and a substrate 105. The mesa stripe is formed by etching not only the upper clad layer 109 but also the active layer 107, the lower clad layer, and the substrate 105, and the grooves on both sides of the mesa stripe are formed as semi-insulating semiconductor layers. Embed with 106. In this BH structure, a semiconductor layer having high insulation can efficiently inject current only into the active layer, so that in principle, laser operation can be performed with a threshold current lower than that of the RWG type.

  The semi-insulating semiconductor layer 106 of a conventional BH type semiconductor laser is composed of InP doped with Fe as a semi-insulating dopant, and this semi-insulating semiconductor layer 106 is a metal organic vapor phase capable of high quality buried regrowth. The growth method (MOVPE: Metal-orgnic vapor phase epitaxy) has been mainly used as a growth method.

  However, Fe doped in the semi-insulating semiconductor layer 106 has a property of interdiffusion with Zn, which is usually used as a p-type dopant, so that when an n-type substrate is used, the semi-insulating semiconductor from the p-type upper cladding layer 109 is used. There is a problem that Zn is diffused into the layer 106 and the insulation is impaired, or conversely, Fe is diffused from the buried layer to the p-type cladding layer, resulting in a decrease in conductivity.

  Conventionally, in order to suppress interdiffusion of Fe—Zn, the doping concentration of Fe was reduced as much as possible, but the current blocking effect was insufficient. Therefore, due to the generation of a leakage current component that is not injected into the active layer 107, the expected effect of the BH type semiconductor laser has not been sufficiently obtained so far.

  Therefore, the present inventors examined the introduction of Ru as an alternative dopant in place of Fe.

  Non-Patent Documents 1 to 3 and Patent Document 1 disclose the semi-insulating semiconductor layer using Ru as a dopant.

  First, Dadgar et al. Proposed Ru as a semi-insulating dopant to replace Fe at the 8th MOVPE International Conference (Non-patent Document 1).

  Kondo et al. Reported an optical modulator having a Ru embedded structure (Non-patent Document 2).

  Iga et al. Have proposed a buried semiconductor laser having a semi-insulating semiconductor layer doped with Ru in an InGaAsP laser on a p-InP substrate (Non-patent Document 3).

  In addition, A. Dadgar et al. Show that a film formation method with little presence of hydrogen atoms is used in forming a semi-insulating semiconductor layer doped with Ru (Patent Document 1). They use Group V source gases (tertiary butylphosphine, ditertiary butylphosphine, etc.) with less than 3 hydrogen atoms directly bonded to group V elements as a method of manufacturing a high resistance Ru-doped semiconductor layer. And the use of an inert gas other than hydrogen as the carrier gas. It is said that a Ru-doped semi-insulating semiconductor layer manufactured under such an environment with few hydrogen atoms can increase the impurity concentration of deep levels induced by Ru and improve its insulating characteristics.

  Non-Patent Document 4 describes the production of a semi-insulating semiconductor layer doped with Ru by the HVPE (Hydride vapor-phase epitaxy) method. Since the HVPE method is used, HCl, which is a kind of halogen gas, is added to the furnace. This HCl gas is used to generate InCl, which is a group III chloride, and is an essential gas in the HVPE method. In the present application, the halogen-containing gas in the HPVE method is distinguished from the present invention. Treat as source gas. In the HVPE method, the entire reaction furnace is heated, and the growth is not rate-limited only by heating on the substrate as in the MOVPE method. Therefore, a semiconductor layer with high shape reproducibility cannot be realized.

Dadgar et al., 8th MOVPE International Conference, Abstract PDSP.7, 1996 Kondo et al., Journal of Applied Physics, Vol. 41, p. 1171, 2002 Iga et al., 52nd Joint Conference on Applied Physics Lecture Proceedings 1307 p. 31p-ZH-10 2004 Journal of Electrochemical Society 148 G375 2001 WO 99/21216

  The inventors decided to study an optical semiconductor element using a semi-insulating semiconductor layer doped with Ru as described in the above-mentioned documents 1 to 3.

  First, an InP buried layer doped with Ru was prototyped under the same conditions as the InP buried layer doped with Fe of a conventional semiconductor laser. This is a prototype in an environment where there is a very large amount of hydrogen using phosphine (PH3) with 3 hydrogen atoms as the carrier gas, and V group source gas as the number of bonds directly bonded to group V elements. . As a result of the trial production, only insufficient insulation characteristics could be obtained. As described in Patent Document 1, it is considered that the insulating characteristics of the semi-insulating semiconductor layer doped with Ru are deteriorated by hydrogen atoms.

  Then, the process of patent document 1 was examined. However, the method of Patent Document 1 cannot be expected to greatly improve the device characteristics, and the use of tertiary butyl phosphine and ditertiary butyl phosphine is problematic in terms of the safe operation of the apparatus, and carriers other than H2 gas. It has been found that the use of gas has problems in terms of its purity and gas flow control during growth.

  Further, although the method of Patent Document 4 was also examined, a semi-insulating semiconductor layer having high shape reproducibility could not be realized for the above-described reason. Moreover, high mass productivity and sufficient insulation characteristics could not be secured.

  An object of the present invention is to improve the insulating characteristics of an optical semiconductor device in which a semi-insulating semiconductor layer doped with Ru is safely and easily embedded.

  In order to solve the above-mentioned problems, when embedding a III-V compound semiconductor layer with a semi-insulating semiconductor layer doped with Ru, we can either use the HVPE method of Patent Document 4 or another growth method. investigated. A growth method (metal organic vapor phase epitaxy (MOVPE) method, molecule, in which the reaction is rate-determined by thermal decomposition of the substrate surface, represented by the metal organic vapor phase epitaxy (MOVPE) method, which makes it easy to control the shape of the semi-insulating semiconductor layer. It was decided to employ a molecular beam epitaxy (MBE) method, a chemical beam epitaxy (CBE) method, a metal-organic molecular beam epitaxy (MOMBE), and the like. At that time, in addition to the supply of the group III source gas, the group V source gas, and the Ru doping source gas, a gas containing a halogen atom having an atomic weight of iodine or less was added to the growth method.

Hereinafter, preferable manufacturing conditions and structures are described when the above growth method is used.
(1) Hydrogen is included in the carrier gas used in the metal organic chemical vapor deposition (MOVPE) method.
(2) The semi-insulating semiconductor layer is a layer doped with Ru with respect to (AlxGa1-x) yIn1-yAszP1-z (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1). .
(3) In the case of (2), phosphine (PH3), arsine (AsH3), or both are used as the group V source gas.
(4) As a gas containing a halogen atom, hydrogen chloride, methyl chloride, carbon tetrachloride, hydrogen bromide, methyl bromide, carbon tetrabromide, carbon trichlorobromide or tertiary butyl chloride is used.
(5) The substrate temperature for growing the semi-insulating semiconductor layer is set to 540 ° C. or higher and 580 ° C. or lower.
(6) The supply ratio of the Group V source gas and the Group III source gas when growing the semi-insulating semiconductor layer is 1: 1 or more and 100: 1 or less.
(7) As the Ru source gas, at least one kind of organometallic source material of Chemical Formula 1 is used.

(Where A and B are cycloheptane, cycloheptene, cycloheptadiene, heptane, heptene, heptadiene, heptadiyne, cyclohexane, cyclohexene, cyclohexadiene, hexane, hexene, hexadiene, hexadiyne, phenyl, Selected from cyclopentane, cyclopentene, cyclopentadiene, pentane, pentene, pentadiene, pentadiyne, butane, butene, butadiene, butyne, propane, propene, propyne, ethane, ethene residues, or methane residues, C1, C2, D1, D2 is H, CO-RX, CN-RX, N = RX, CnH2n + 1, or CnH2n-1 (n = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10) (Chosen from the inside)
(8) The leakage current can be suppressed and lattice matching can be achieved by growing a layer having a material composition different from that of the aforementioned semi-insulating semiconductor layer before, after, or before and after forming the semi-insulating semiconductor layer.

  According to the present invention, it is possible to improve the insulating characteristics of an optical semiconductor element in which a Ru-doped semi-insulating semiconductor layer is embedded safely and easily.

  First, the outline and principle of the present invention will be described.

  As described in the section on the means for solving the problems, when embedding a III-V compound semiconductor layer with a semi-insulating semiconductor layer doped with Ru, we can either use an HVPE method or other gas phase. We examined whether to use the growth method. We decided to adopt a vapor phase growth method, which is easy to control the shape of the semi-insulating semiconductor layer, which is controlled by thermal decomposition of the substrate surface, represented by metal organic vapor phase epitaxy (MOVPE). At that time, separately from the supply of the group III source gas, the group V source gas, and the Ru doping source gas, by adding a gas containing a halogen atom having an atomic weight equal to or less than iodine, the halogen is a source gas as in the HVPE method. Insulation characteristics are improved by functioning as a dehydrogenating agent or a hydrogen bond preventing film.

  This principle will be described in detail below using an example of forming a Ru-doped InP semi-insulating semiconductor layer using methyl chloride (CH3Cl) as a gas containing a halogen atom having an atomic weight of iodine or less. To do.

  FIG. 3 is a diagram for explaining the principle of the present invention. SUB indicates a substrate, pentagon indicates a compound, and circle indicates an atom. As shown in FIG. 3 (a), when the organometallic raw material containing Ru and methyl chloride supplied into the growth furnace reach the substrate, Ru and Cl atoms and other hydrogen and hydrocarbons are decomposed by thermal decomposition. Breaks down into groups. In the conventional method where halogen atoms do not exist in the growth atmosphere, the ruthenium-free bonds of the decomposed Ru atoms are easily combined with a large amount of hydrogen atoms present as a carrier gas in the atmosphere and incorporated into the film. Binds to hydrogen and is susceptible to this. On the other hand, in the method of the present invention, halogen atoms (Cl atoms) are present in the growth atmosphere. Cl atoms form temporary bonds with Ru atoms as shown in FIG. Thereafter, Cl atoms themselves bind to hydrogen atoms and leave as HCl, while broken Ru atoms bind to Group III atoms or Group V atoms and are taken into the film. In this way, it is possible to suppress the bond with hydrogen and increase the proportion of Ru atoms that are not affected by the bond. Furthermore, even when a Ru atom and a hydrogen atom form a bond, the Cl atom becomes HCl and desorbs, so that there is an effect of removing the hydrogen atom from the Ru atom. As a result, as shown in FIG. 3 (c), it is possible to increase the proportion of Ru atoms that do not bond with hydrogen and are not affected by this, and as a result, increase the insulating properties of the semiconductor layer doped with Ru. Can do. The gas acting in this way can be obtained similarly by supplying a gas containing Cl other than methyl chloride or a gas containing a halogen atom (fluorine, bromine, iodine) other than Cl.

  In addition, from the prototype results of the above principle confirmation, it was found that the above reaction is most effective under the following growth conditions that can suppress excessive generation of Ru—P bonds.

  The supply ratio of the Group V source gas and the Group III source gas in normal MOVPE growth is several hundreds. However, since such a supply ratio makes a P-rich environment, there are excessive Ru-P bonds. Will occur. Therefore, it is most preferable that the supply amount ratio of the group V source gas and the group III source gas (group V source gas / group III source gas) be in the range of 1 to 100.

  In order to suppress the increase in resistance due to the diffusion of Ru into the III-V compound semiconductor layer and to increase the impurity concentration of deep levels induced by Ru, Ru doping at a substrate temperature of 580 ° C. or lower InP layer formation is important.

  In addition, when the mesa stripe is embedded using the method of the present invention, an optical semiconductor element with high reproducibility and stable characteristics can be realized if the (111) surface is formed favorably. This temperature condition is also important because the (111) surface can be formed with good controllability when the substrate temperature is 540 ° C. or higher.

The hydrogen concentration in the Ru-doped p-InP film when the present invention is applied is 1 × 10 ¹⁸ cm ⁻³ or less.

  In order to enhance the effect of removing hydrogen by halogen atoms, it is important to increase the efficiency of the thermal decomposition of the halogen material and the Ru material only on the substrate, as described with reference to FIG. Therefore, it is effective to use a raw material that has high stability and is difficult to decompose in a gas as the Ru raw material. As a result of intensive studies, we have found that at least one organometallic raw material of the following form is suitable as the Ru raw material gas. The form of such Ru source gas is represented by Chemical Formula 1.

(Where A and B are cycloheptane, cycloheptene, cycloheptadiene, heptane, heptene, heptadiene, heptadiyne, cyclohexane, cyclohexene, cyclohexadiene, hexane, hexene, hexadiene, hexadiyne, phenyl, Selected from cyclopentane, cyclopentene, cyclopentadiene, pentane, pentene, pentadiene, pentadiyne, butane, butene, butadiene, butyne, propane, propene, propyne, ethane, ethene residues, or methane residues, C1, C2, D1, D2 is H, CO-RX, CN-RX, N = RX, CnH2n + 1, or CnH2n-1 (n = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10) (Chosen from the inside)
Of these types of raw materials, bisethylcyclopentadienyl ruthenium is a preferable raw material because it can be handled in a liquid state. For example, in this raw material, the Ru atom has two bonds and is bonded to the cyclopentane group. Although there are two main bonds of Ru atoms, since each bond is equivalent to all C atoms belonging to the cyclopentane group, the bond strength is high. Therefore, since the stability of the raw material is high and it is difficult to decompose in gas, the efficiency of decomposition only by heat on the substrate can be increased.

FIG. 4 shows a comparison of IV characteristics of a semi-insulating semiconductor layer doped with Ru compared with and without addition of a halogen gas. Ru layer_A shows the measurement result of voltage (V) -current characteristics (I) of Ru-doped InP single layer film with Cl gas added during growth, Ru layer_B shows Ru-doped InP single layer with no Cl gas added during growth The measurement result of the voltage (V) -current characteristic (I) of the film is shown. As the Ru organometallic raw material, bisethylcyclopentadienyl ruthenium, which is a kind of raw material in the form already described, was used. The film thickness of the Ru-doped InP single layer film is 1 μm. In the low voltage region, the current values of both films are as low as 10 ⁻¹¹ to 10 ⁻¹⁰ (A), indicating high resistivity. On the other hand, when the applied voltage is increased, the current value increases rapidly in the film without Cl because the insulating properties of the film are insufficient. On the other hand, the film with Cl does not show a sudden increase in current value up to a high voltage, and exhibits good insulation characteristics. This result clearly shows that the manufacturing method of adding Cl improves the insulating properties of the semi-insulating semiconductor layer doped with Ru.

  FIG. 2 shows a bird's-eye view of an edge-emitting laser with a part cut away and a cross section exposed. A mesa comprising an n-InP buffer layer 203 formed on an n-InP substrate 202, a multiple quantum well (MQW) 206, an upper p-InP cladding layer 207, and a p + -InGaAs contact layer 208. The structure is embedded with a Ru-doped InP layer 204, which is a semi-insulating semiconductor layer doped with Ru according to the technique of the present invention. In the present invention, when a mesa stripe is formed in the [011] direction, a terrace composed of a (100) system surface is formed over several μm after a (111) system surface appears on the side of the mask. It becomes such a characteristic shape.

  FIG. 5 shows a comparison diagram of IL characteristics of the semiconductor laser element when the present invention is applied and when it is not applied. Comparison was made between a semiconductor laser embedded with InP doped with Ru under growth conditions with and without Cl gas, and a semiconductor laser embedded with InP doped with Fe when driven continuously at 85 ° C. The figure is shown. In the figure, RuBH_A is the characteristic of the semiconductor laser embedded with Ru doped with Cl gas addition, RuBH_B is the characteristic of the semiconductor laser embedded with InP doped with Ru without Cl addition, FeBH is The characteristics of a semiconductor laser buried with InP doped with Fe are shown. In the case of laser embedded with InP doped with Ru without Cl addition, the light output was saturated at around 180 mA. This characteristic was comparable to that of a semiconductor laser embedded with InP doped with Fe. On the other hand, in the case of a semiconductor laser embedded with InP doped with Ru grown by adding Cl gas, the optical output did not saturate up to 250 mA and showed better characteristics than others. As a result, the insulation characteristics were improved by forming a semi-insulating semiconductor layer embedded with InP doped with Ru by adding Cl, and it was possible to suppress an increase in leakage current components in the high voltage region during driving. Is due to. As described above, in a laser on an n-InP substrate, a semiconductor laser embedded with InP doped with Ru can realize a remarkable improvement in insulation characteristics as compared with a semiconductor laser embedded with InP doped with Fe.

  In addition, in semiconductor lasers embedded with Fe-doped InP, there is also known a process in which Fe-doped InP is vapor-phase grown by a MOVPE method using a halogen gas. There is no report that this halogen gas contributes to the improvement of the insulation characteristics. Therefore, as in the present invention, in a semi-insulating semiconductor layer doped with Ru, it has not been conventionally known to be used as a manufacturing method for suppressing the influence of hydrogen atoms and improving insulating characteristics. Compared with a p-InP buried laser doped with Fe, it can be said that it has a different and remarkable effect.

  The technique of the present invention can be applied not only to a light emitting semiconductor element typified by a laser, but also to a buried layer of a light receiving semiconductor element. Needless to say, the present invention can also be applied to electronic devices and the like.

  Hereinafter, a more detailed embodiment of the present invention will be described with reference to FIGS. 2, 6, 7, and 8. FIG. In the following example, only the optical semiconductor element on the InP substrate that is currently used has been described, but it goes without saying that it can also be applied to a III-V group compound semiconductor element using a GaAs substrate or the like. There is no. Further, in the following example, only the case where an InP film doped with Ru is used for the buried layer is described, but not only the semiconductor layer having P atoms in the V group but also the semiconductor layer having As in the V group or Needless to say, the present invention can also be applied to a semiconductor layer having both P and As. In this case, AsH3 or the like can be used as the source gas for As, similarly to PH3. Needless to say, the present invention can be applied not only to a group III atom but also to a film containing atoms such as Al and Ga. That is, if a compound semiconductor suitable as a semi-insulating semiconductor layer doped with Ru is described, (AlxGa1-x) yIn1-yAszP1-z (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1).

In the first embodiment, the present invention is applied to an edge-emitting laser. The MOVPE method was used as the growth method. Hydrogen was used as the carrier gas. Triethylgallium (TEG) and trimethylindium (TMI) were used as the Group III element raw material. Arsine (AsH3) and phosphine (PH3) were used as raw materials for group V elements. In addition, as an n-type dopant, disilane (Si2H6)
And dimethyl zinc (DMZ) was used as the p-type dopant. As the halogen atom-containing gas to be added, methyl chloride (CH 3 Cl) was used, and as the organometallic raw material for Ru, bisethylcyclopentadienyl ruthenium was used. The growth method is not limited to MOVPE alone, but includes molecular beam epitaxy (MBE) method, chemical beam epitaxy (CBE) method, metal organic molecular beam epitaxy (MOMBE: Metal). The effects of the present invention can be obtained by a technique in which growth is rate-limited mainly by thermal decomposition on a substrate, such as the -organic molecular beam epitaxy method.

  FIG. 2 is a bird's-eye view of an edge-emitting laser to which the present invention is applied, with a part cut away and a cross-section exposed. An n-InP buffer layer 203 is formed on the n-InP substrate 202, and then a laser part MQW layer 206 and a diffraction grating layer 209 made of InGaAsP are grown. Usually, a p-InP cap layer is usually formed on top for protection. After forming the diffraction grating by a normal process, the upper p-InP cladding layer 207 fills the diffraction grating 209 and continuously forms the p + -InGaAs contact layer 208. After forming a mesa stripe mask in such a multilayer structure and removing portions other than the mesa structure by etching, an appropriate pretreatment is performed, and the InP doped with Ru using a halogen gas according to the method of the present invention. Perform buried growth of layer 204. At that time, methyl chloride was added simultaneously. According to this method, although hydrogen was used as the carrier gas and PH3 was used as the V group source gas, the InP layer 204 doped with Ru having high insulating properties could be formed. Thereafter, the passivation film 210, the upper electrode 205, the lower electrode 201, and the like were formed using a normal element manufacturing method, and the element was completed.

  The device thus fabricated had a threshold current of 15 mA at 85 ° C., and exhibited high light output characteristics exceeding 20 mW. Also, the modulation characteristics were good. Furthermore, the device characteristics did not deteriorate even during long-time operation, and high device reliability was shown. In addition, the device manufacturing yield was high.

  In the second embodiment, the present invention is applied to a modulator integrated light source. FIG. 6 is an explanatory diagram of a modulator integrated semiconductor laser to which the present invention is applied. Note that, in order to easily understand the layer structure, a part is cut out and the cross section is exposed, but originally there is no such cutout. In this element, a modulator part EAR, a waveguide part WGR, and a laser part LDR are formed. As a growth method, the MOVPE method was used in the same manner as in Example 1. The group III element source gas used trimethylaluminum (TMA) as the Al source in addition to the source gas of Example 1. Hydrogen chloride (HCl) was used as the halogen atom-containing gas to be added, and bismethylcyclopentadienyl ruthenium was used as the organometallic raw material of Ru.

  First, an n-InP buffer layer 603 is formed on an n-InP substrate 602, and then a modulator MQW layer 604 made of InGaAlAs is grown. Usually, a p-InP cap layer is usually formed on top for protection. Next, a mask pattern is formed at a desired location on the wafer. Using this as an etching mask, the p-InP cap layer and the modulator part MQW layer 604 are removed. Next, the wafer is introduced into a growth furnace, and the MQW layer 606, the diffraction grating layer 607, and the p-InP cap layer of the laser part made of InGaAlAs are regrown by butt joint (BJ: Butt-joint). Next, after removing the previous mask, a BJ mask is formed again at desired locations in the modulator section MQW604 and the laser section MQW606, and the MQW and p-InP cap layers are removed by etching. Further, the waveguide layer 605 made of InGaAsP and the p-InP cap layer are regrown BJ. Here, BJ connection was simultaneously performed at two locations of the modulator section and the laser section. After removing the wafer from the growth furnace, the mask is removed, and a diffraction grating 607 is formed on the laser unit MQW layer 606. Thereafter, the wafer is introduced into the furnace body, a p-InP cladding layer 610 and a p + -InGaAs contact layer are grown on the front surface of the wafer, and the crystal growth process is completed. A mesa stripe mask is formed in such a multilayer structure, and portions other than the mesa structure are removed by etching, and then appropriate pretreatment is performed, and a buried growth is performed with the Ru-doped InP layer 608 according to the method of the present invention. At that time, HCl gas was added simultaneously. In the method of the present invention, hydrogen is used as a carrier gas and PH3 is used as a group V source gas. However, a semi-insulating semiconductor layer doped with Ru having high insulating properties could be formed. In order to prevent return light due to reflection of the emitted light, the light emission end on the modulator side is embedded with a Ru-doped InP layer 608, which has a so-called window structure. After removing the p + -InGaAs contact layer on the top of the waveguide and isolating the p + -InGaAs contact layer 612 in the modulator part and the p-InGaAs contact layer 611 in the laser part, the passivation film is formed using a normal element fabrication method. Formation of 613, formation of the upper electrode 614 in the modulator part, formation of the upper electrode 609 and lower electrode 601 in the laser part, and the like were completed.

  The threshold current of the device fabricated in this way is 15mA at 85 ° C, 10GHz without a cooler in the range of -5 ° C to 85 ° C, and the device characteristics deteriorate even after long-term operation. High device reliability was demonstrated. In addition, the device manufacturing yield was high. As the MQW of the laser or the modulator, not only an InGaAlAs material but also an InGaAsP material or a material added with Sb or N can be used.

  In the third embodiment, the present invention is applied to a back emission laser. FIG. 7 is an explanatory diagram of a horizontal cavity surface emitting laser to which the present invention is applied. Note that, in order to easily understand the layer structure, a part is cut out and the cross section is exposed, but originally there is no such cutout. The element structure is called a planar BH structure. As a growth method, the MOVPE method is used here, but the method is not limited to this, and other methods may be used as long as the same effect can be obtained. The raw materials used were the same as in Examples 1 and 2, but carbon tetrachloride (CCl4) was used as the halogen atom-containing gas to be added, and bisdimethylpentadienyl ruthenium was used as the organometallic raw material for Ru. Although the present Ru raw material is not an organometallic raw material having the most effective form in the present invention, the effect can be obtained because a halogen atom-containing gas is added.

  In this embodiment, a p-InP substrate 702 is used. Thereafter, a p-InP buffer layer 703, an InGaAlAs-based laser part MQW layer 708, and a diffraction grating layer 709 are formed. At this time, an n-InP cap layer is mostly formed for surface protection. After forming the diffraction grating 709 by a normal process, it is filled with a thin n-InP cladding layer 705 and an InGaAsP cap layer. After forming a mesa stripe mask in such a multilayer structure and removing portions other than the mesa structure by etching, an appropriate pretreatment was performed, and buried growth was performed with the Ru-doped InP layer 704 according to the technique of the present invention. At that time, CCl4 was added simultaneously. In the method of the present invention, hydrogen is used as a carrier gas and PH3 is used as a group V source gas. However, a semi-insulating semiconductor layer doped with Ru having high insulating properties could be formed. A p-InP layer 712 was continuously grown to prevent current leakage from the upper n-InP cladding layer. As described above, by forming not only the Ru-doped InP layer as the buried layer but also the Ru-doped InP layer (before or before and after is also within the scope of the present invention), a plurality of layers having different material compositions are provided. The technique of the present invention is also effective when embedding.

  Next, after removing the mask and performing appropriate pretreatment to remove the InGaAsP cap layer, an upper n-InP cladding layer 705 and an n-InGaAsP contact layer 706 were successively formed. At that time, regrowth was performed under the condition of flattening the unevenness due to the crystal plane formed by Ru embedded growth. Thereafter, a reflecting mirror 710 having an angle of 135 degrees on the front surface, a back lens 711 for converging outgoing light on the back surface, and an upper electrode 707 and a lower electrode 701 were formed to complete the device.

  The device thus fabricated had a low device resistance of 3 ohms and oscillated with a low threshold current of 10 mA even at 85 ° C. In addition, it showed good modulation characteristics at 10 GHz without a cooler, and showed high element reliability without deterioration of element characteristics even after long-term operation. In addition, the device manufacturing yield was high.

  The fourth embodiment is an example in which the present invention is applied to a 2 × 2 type InP-based MQW type MZ modulator. FIG. 8 shows a bird's-eye view of an MZ modulator to which the present invention is applied. In this element, an input light separation unit MMI_DIV, an MZ modulator unit MZ_EAR, and an output light multiplexing unit MMI_MP are formed. As a growth method, the MOVPE method is used here, but the method is not limited to this, and other methods may be used as long as the same effect can be obtained. The raw materials used are the same as those in Examples 1 to 3, but as the halogen atom-containing gas to be added, tertiary butyl chloride (TBCl), and as the organometallic raw material of Ru, the most advantageous effect described above can be obtained. The form of biscyclopentadienyl ruthenium was used.

  First, an n-InP buffer layer 803, an MQW layer 804 made of InGaAsP, a p-InP cladding layer 805, and a p + -InGaAs contact layer are continuously grown on the n-InP substrate 802. After forming the insulating film, the element shape was patterned, and this was used as an etching mask to remove unnecessary portions. Subsequently, after appropriate pretreatment, buried growth was performed with a Ru-doped InP layer 806 according to the technique of the present invention. At that time, TBCl was added simultaneously. In the method of the present invention, hydrogen is used as a carrier gas and PH3 is used as a group V source gas. However, a semi-insulating semiconductor layer doped with Ru having high insulating properties could be formed. Thereafter, unnecessary contact layers were removed, and an upper electrode 807 and a lower electrode 801 were formed to complete the device.

  The device thus fabricated showed high modulation characteristics exceeding 10 GHz over the entire C band. The drive voltage was 3V or less. The device characteristics did not deteriorate even after long-term operation, and high device reliability was shown. In addition, the device manufacturing yield was high.

  As in these examples, when producing a semi-insulating semiconductor layer buried type optical semiconductor element doped with Ru by the MOVPE method, if growth is performed simultaneously with a gas containing halogen atoms, hydrogen is absorbed by the effect of the halogen atoms. Even in a growth environment where a large amount exists, the insulating characteristics of the semi-insulating semiconductor layer doped with Ru can be improved, and an optical semiconductor element in which the semi-insulating semiconductor layer doped with high-performance Ru is embedded can be obtained.

It is sectional drawing of an edge-emitting type semiconductor laser. 1 is a bird's-eye view of an edge emitting laser to which the present invention is applied, with a part cut away and a cross section exposed. It is a principle explanatory view of the present invention. It is a IV characteristic comparison figure of the semi-insulating semiconductor layer which doped Ru compared with the presence or absence of addition of halogen gas. It is an IL characteristic comparison figure of the semiconductor laser element when not applying with the case where the present invention is applied. It is explanatory drawing of the modulator integrated type semiconductor laser to which this invention is applied. It is explanatory drawing of the horizontal resonance type | mold surface emitting laser to which this invention is applied. It is a bird's-eye view of the MZ modulator to which the present invention is applied.

Explanation of symbols

101 ・ ・ ・ n-InP substrate,
102 ... active layer,
103 ... upper clad layer,
104 ・ ・ ・ p + -InGaAs contact layer,
105 ... lower clad layer and substrate,
106 ・ ・ ・ Semi-insulating semiconductor layer,
107 ... active layer,
108 ・ ・ ・ p + -InGaAs contact layer,
109 ... upper clad layer,
201 ... lower electrode,
202 ・ ・ ・ n-InP substrate,
203 ... n-InP buffer layer,
204 ... Ru-doped InP layer,
205 ... upper electrode,
206 ... Laser part MQW layer,
207 ... Upper p-InP cladding layer,
208 ・ ・ ・ p + -InGaAs contact layer,
209 ... Diffraction grating,
210 ・ ・ ・ Passivation film,
601 ... Lower electrode,
602 ... n-InP substrate,
603 ... n-InP buffer layer,
604 ・ ・ ・ Modulator part MQW layer,
605 ... Waveguide layer,
606 ... MQW layer of laser part,
607 ... Diffraction grating,
608 ... Ru-doped InP layer,
609... Upper electrode of laser part,
610 ... p-InP cladding layer,
611 ... p + -InGaAs contact layer of laser part,
612 ... p + -InGaAs contact layer of the modulator section,
613 ・ ・ ・ Passivation film,
614 ... Upper electrode of the modulator section,
701 ... Lower electrode,
702 ... p-InP substrate,
703 ... p-InP buffer layer,
704 ... Ru doped InP layer,
705 ... Upper n-InP cladding layer,
706 ... n-InGaAsP contact layer,
707 ... Upper electrode,
708 ... Laser part MQW layer,
709 ... Diffraction grating,
710 ... 135 degree reflector,
711 ・ ・ ・ Back lens,
712 ... p-InP layer,
801 ... lower electrode,
802 ... n-InP substrate,
803 ... n-InP buffer layer,
804 ... MQW layer,
805 ・ ・ ・ p-InP cladding layer,
806 ... Ru doped InP layer,
807 ... Upper electrode

Claims (12)

A method for manufacturing an optical semiconductor element in which a group III-V compound semiconductor layer formed on a substrate is embedded using a semi-insulating semiconductor layer doped with Ru,
Forming the III-V compound semiconductor layer;
Burying the Ru-doped semi-insulating semiconductor layer in the III-V compound semiconductor layer,
In the growth of the semi-insulating semiconductor layer, an optical semiconductor characterized in that a gas containing a halogen atom having an atomic weight of iodine or less is supplied separately from the supply of a group III source gas, a group V source gas, and a Ru source gas Device manufacturing method. In claim 1,
The semi-insulating semiconductor layer is grown by metal organic vapor phase epitaxy (MOVPE), molecular beam epitaxy (MBE), chemical beam epitaxy (CBE), metal organic molecular beam epitaxy (MOMBE: Metal- An organic molecular beam epitaxy) method. In claim 2,
A method for producing an optical semiconductor element, wherein a carrier gas used in the metal organic chemical vapor deposition (MOVPE) method contains hydrogen. In claim 1,
The semi-insulating semiconductor layer is a layer doped with Ru with respect to (AlxGa1-x) yIn1-yAszP1-z (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1). A method for manufacturing an optical semiconductor device. In claim 4,
A method for manufacturing an optical semiconductor element, wherein phosphine (PH3), arsine (AsH3), or both are used as the group V source gas. In claim 1,
Light characterized by using hydrogen chloride, methyl chloride, carbon tetrachloride, hydrogen bromide, methyl bromide, carbon tetrabromide, carbon trichlorobromide or tertiary butyl chloride as the gas containing a halogen atom. A method for manufacturing a semiconductor device. In claim 1,
The method of manufacturing an optical semiconductor element, wherein the temperature of the substrate when growing the semi-insulating semiconductor layer is 540 ° C. or higher and 580 ° C. or lower. In claim 1,
A method for manufacturing an optical semiconductor device, wherein a supply ratio of the group V source gas and the group III source gas when growing the semi-insulating semiconductor layer is 1: 1 or more and 100: 1 or less. In claim 1,
A method for producing an optical semiconductor element, wherein at least one kind of organometallic raw material of Chemical Formula 1 is used as the Ru raw material gas.

(Where A and B are cycloheptane, cycloheptene, cycloheptadiene, heptane, heptene, heptadiene, heptadiyne, cyclohexane, cyclohexene, cyclohexadiene, hexane, hexene, hexadiene, hexadiyne, phenyl, Selected from cyclopentane, cyclopentene, cyclopentadiene, pentane, pentene, pentadiene, pentadiyne, butane, butene, butadiene, butyne, propane, propene, propyne, ethane, ethene residues, or methane residues, C1, C2, D1, D2 is H, CO-RX, CN-RX, N = RX, CnH2n + 1, or CnH2n-1 (n = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10) (Chosen from the inside) In claim 1,
A method of manufacturing an optical semiconductor element, comprising growing a layer having a material composition different from that of the semi-insulating semiconductor layer before, after or before and after forming the semi-insulating semiconductor layer. A substrate,
A III-V compound semiconductor layer formed on the substrate;
In an optical semiconductor device comprising a Ru-doped semi-insulating semiconductor layer that embeds the III-V compound semiconductor layer,
An optical semiconductor element, wherein a hydrogen concentration in the semi-insulating semiconductor film is 1 × 10 ¹⁸ cm ⁻³ or less. A substrate,
On the substrate, a III-V group compound semiconductor layer formed in a mesa stripe shape,
In an optical semiconductor device comprising a Ru-doped semi-insulating semiconductor layer that embeds the III-V compound semiconductor layer,
The semi-insulating semiconductor layer includes an (111) system surface adjacent to both sides of the mesa stripe, and a (100) system surface adjacent to the (111) system surface. element.

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