WO2008007522A1 - Semiconductor element, optical switching element and quantum cascade laser element - Google Patents
Semiconductor element, optical switching element and quantum cascade laser element Download PDFInfo
- Publication number
- WO2008007522A1 WO2008007522A1 PCT/JP2007/062237 JP2007062237W WO2008007522A1 WO 2008007522 A1 WO2008007522 A1 WO 2008007522A1 JP 2007062237 W JP2007062237 W JP 2007062237W WO 2008007522 A1 WO2008007522 A1 WO 2008007522A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- layer
- well
- well layer
- inn
- superlattice
- Prior art date
Links
- 239000004065 semiconductor Substances 0.000 title claims abstract description 62
- 230000003287 optical effect Effects 0.000 title claims abstract description 43
- 230000004888 barrier function Effects 0.000 claims abstract description 44
- 229910002704 AlGaN Inorganic materials 0.000 claims abstract description 43
- 230000007704 transition Effects 0.000 claims abstract description 30
- 230000005428 wave function Effects 0.000 claims abstract description 8
- 238000005215 recombination Methods 0.000 claims abstract 2
- 230000006798 recombination Effects 0.000 claims abstract 2
- 238000000034 method Methods 0.000 claims description 32
- 239000000758 substrate Substances 0.000 claims description 22
- 238000005253 cladding Methods 0.000 claims description 15
- 125000006850 spacer group Chemical group 0.000 claims description 11
- 230000008569 process Effects 0.000 claims description 7
- 238000002347 injection Methods 0.000 claims description 4
- 239000007924 injection Substances 0.000 claims description 4
- 230000031700 light absorption Effects 0.000 claims description 3
- 230000003993 interaction Effects 0.000 claims description 2
- 102100021711 Ileal sodium/bile acid cotransporter Human genes 0.000 description 44
- 101710156096 Ileal sodium/bile acid cotransporter Proteins 0.000 description 44
- 239000013078 crystal Substances 0.000 description 29
- 238000001451 molecular beam epitaxy Methods 0.000 description 20
- 238000010521 absorption reaction Methods 0.000 description 12
- 238000010586 diagram Methods 0.000 description 10
- 230000000694 effects Effects 0.000 description 10
- 230000015572 biosynthetic process Effects 0.000 description 9
- 150000004767 nitrides Chemical class 0.000 description 9
- 239000000463 material Substances 0.000 description 8
- 229910052751 metal Inorganic materials 0.000 description 8
- 239000002184 metal Substances 0.000 description 8
- 238000004519 manufacturing process Methods 0.000 description 7
- 238000000927 vapour-phase epitaxy Methods 0.000 description 7
- 238000003917 TEM image Methods 0.000 description 6
- 239000010408 film Substances 0.000 description 6
- 238000000151 deposition Methods 0.000 description 5
- 230000010355 oscillation Effects 0.000 description 5
- 238000004904 shortening Methods 0.000 description 5
- 241000652704 Balta Species 0.000 description 4
- 238000002441 X-ray diffraction Methods 0.000 description 4
- 238000000862 absorption spectrum Methods 0.000 description 4
- 238000004364 calculation method Methods 0.000 description 4
- 238000013461 design Methods 0.000 description 4
- 238000009825 accumulation Methods 0.000 description 3
- 230000007547 defect Effects 0.000 description 3
- 238000009826 distribution Methods 0.000 description 3
- 238000002474 experimental method Methods 0.000 description 3
- 239000012535 impurity Substances 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 229910052594 sapphire Inorganic materials 0.000 description 3
- 239000010980 sapphire Substances 0.000 description 3
- 239000010409 thin film Substances 0.000 description 3
- 230000008901 benefit Effects 0.000 description 2
- 230000001427 coherent effect Effects 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 230000005684 electric field Effects 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 239000010931 gold Substances 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 229910052738 indium Inorganic materials 0.000 description 2
- 230000000737 periodic effect Effects 0.000 description 2
- 238000004549 pulsed laser deposition Methods 0.000 description 2
- 238000005979 thermal decomposition reaction Methods 0.000 description 2
- 239000010936 titanium Substances 0.000 description 2
- 238000001947 vapour-phase growth Methods 0.000 description 2
- JMASRVWKEDWRBT-UHFFFAOYSA-N Gallium nitride Chemical class [Ga]#N JMASRVWKEDWRBT-UHFFFAOYSA-N 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 125000004429 atom Chemical group 0.000 description 1
- 229910052788 barium Inorganic materials 0.000 description 1
- DSAJWYNOEDNPEQ-UHFFFAOYSA-N barium atom Chemical compound [Ba] DSAJWYNOEDNPEQ-UHFFFAOYSA-N 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000005229 chemical vapour deposition Methods 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 238000003795 desorption Methods 0.000 description 1
- 238000010494 dissociation reaction Methods 0.000 description 1
- 230000005593 dissociations Effects 0.000 description 1
- 239000007772 electrode material Substances 0.000 description 1
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
- 238000002248 hydride vapour-phase epitaxy Methods 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- 238000003475 lamination Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000005121 nitriding Methods 0.000 description 1
- 125000004433 nitrogen atom Chemical group N* 0.000 description 1
- 230000010287 polarization Effects 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 230000002269 spontaneous effect Effects 0.000 description 1
- 238000004381 surface treatment Methods 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/30—Structure or shape of the active region; Materials used for the active region
- H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
- H01S5/343—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser
- H01S5/34333—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser with a well layer based on Ga(In)N or Ga(In)P, e.g. blue laser
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/015—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction
- G02F1/017—Structures with periodic or quasi periodic potential variation, e.g. superlattices, quantum wells
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/015—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction
- G02F1/017—Structures with periodic or quasi periodic potential variation, e.g. superlattices, quantum wells
- G02F1/01725—Non-rectangular quantum well structures, e.g. graded or stepped quantum wells
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/30—Structure or shape of the active region; Materials used for the active region
- H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
- H01S5/3401—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers having no PN junction, e.g. unipolar lasers, intersubband lasers, quantum cascade lasers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/30—Structure or shape of the active region; Materials used for the active region
- H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
- H01S5/3403—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers having a strained layer structure in which the strain performs a special function, e.g. general strain effects, strain versus polarisation
- H01S5/3406—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers having a strained layer structure in which the strain performs a special function, e.g. general strain effects, strain versus polarisation including strain compensation
Definitions
- the present invention relates to a semiconductor device, an optical switching device, and a quantum cascade laser, and more particularly to a device utilizing intersubband transition.
- Discrete energy levels exist in well layers such as quantum well structures and superlattice structures formed in semiconductor devices, and light absorption and electron transition occur between these levels. This is generally called intersubband transition.
- ISBT Transition between subbands
- the relaxation rate is about nsec order.
- the relaxation rate of ISBT is ⁇ psec to fsec order, and it can be applied to future terabit-class ultrafast optical switches. Expected.
- GaNZAIN which is a nitride-based ISBT structure
- CdSZBeTe CdSZBeTe
- InGaAsZAlAs the GaNZAIN superlattice
- the GaNZAIN superlattice which is a nitride-based ISBT structure
- fsec order See, for example, Patent Documents 1 and 2 and Non-patent Document 1).
- Non-Patent Document 1 the shortest ISBT wavelength has been reported to date.
- 100 periods of GaNlnmZAlN4nm superlattice were grown using molecular beam epitaxy (hereinafter referred to as “MBE” t) method, and an ISBT wavelength of 1.08 m was observed.
- MBE molecular beam epitaxy
- the ISBT can easily control the transition wavelength only by changing the quantum well width or the periodic structure of the superlattice.
- An example of such a device that utilizes light emission between subbands is a quantum cascade laser.
- Ordinary semiconductor lasers have conduction bands and valence charges. Laser oscillation occurs due to the inversion distribution between the subbands, but the cascade laser forms an inversion distribution between discrete levels in the conduction band of the quantum well and causes laser oscillation.
- the quantum cascade laser can control the lasing wavelength simply by changing the quantum well structure. The range is limited by the band offset of the quantum well. In other words, it is impossible to obtain laser oscillation with energy larger than the band offset amount.
- the GaNZAIN superlattice currently has the fastest electron relaxation rate and is considered to be able to achieve the largest conduction band offset, so the basic structure of ultrafast optical switches and quantum cascade laser devices This is a very promising structure with the possibility of further shortening the intersubband transition wavelength.
- Patent Document 1 Japanese Patent Laid-Open No. 8-179387
- Patent Document 2 JP 2001-108950 A
- Non-Patent Document 1 K. Kishino et al., APL., Vol. 81, 1234-1236 (2002) Disclosure of the Invention
- the GaNZAIN superlattice structure has a very large conduction band offset, and is suitable for shortening the ISBT T wavelength.
- the degree of lattice mismatch between GaNZAIN is as large as 2.4%. Lamination is difficult.
- the A1N barrier layer is subject to tensile strain. This tensile strain causes cracks in the A1N layer, making it difficult to maintain crystal quality.
- the short wavelength of the I SBT wavelength is also very important.
- the GaNZAIN superlattice has observed 1.08 m ISBT absorption, but the GaN well layer thickness needs to be further reduced to make the wavelength shorter than this. However, in this case, the ratio of the A1N layer of the entire superlattice increases, so that cracks are more likely to occur and it becomes difficult to maintain the crystal quality.
- the GaN well layer thickness is also less than lnm, making it difficult to control. In other words: Shortening the wavelength below L m is difficult with the current GaNZAIN superlattice structure.
- an ultrafast optical switch or a quantum cascade laser structure is a quantum well structure.
- an ISBT ultrafast optical switch has a quantum well structure of about 100 cycles to minimize the optical energy required for switching and increase the amount of light absorbed in the ISBT region.
- the GaNZAIN superlattice structure has a very large conduction band offset and is suitable for shortening the wavelength of ISBT.
- the lattice mismatch between GaNZAIN is as large as 2.4%. Many stacks are difficult.
- the A1N barrier layer is subject to tensile strain. When the number of periods in the superlattice is increased, cracks easily occur, the crystal quality deteriorates rapidly, and ISBT absorption cannot be observed.
- an object of the present invention is to provide a novel semiconductor device, an optical switching device using the same, and a quantum cascade laser.
- the inventors of the present invention have made extensive studies on the above-mentioned problems.
- the AlGa N barrier layer is introduced into the well layer by introducing a layer that generates a compressive strain that eliminates the tensile strain applied to the AlGaN barrier layer. It was possible to prevent the generation of cracks, and when a layer having an InN force was used for this layer, the inventors realized that the ISBT wavelength could be shortened, and the present invention was completed.
- a semiconductor device includes a well layer having a GaN well layer and an InN well layer, and a superlattice layer having a pair of AlGaN barrier layers sandwiching the well layer.
- AlGaN layer the generation of cracks due to the tensile stress of the A1N layer (AlGaN layer) is a problem, and it is difficult to increase the number of cycles. Can do.
- tensile stress is applied to the AlGaN barrier layer, but compressive stress is applied to the InN layer by providing the InN layer (the lattice mismatch between InNZGaN is about + 11%).
- the InN well layer has the smallest bandgap energy (approximately 0.63 eV) among nitride semiconductors, and the conduction band offset amount from GaN is approximately 1.7 eV, which is the difference from A1N. Can be estimated to be about 3.5 eV.
- this semiconductor device can achieve a value about twice the conduction band offset of the GaNZAIN superlattice, and can further shorten the intersubband transition wavelength (less than 1 ⁇ m). .
- Such a large band offset can be realized by using a nitride semiconductor, particularly InN.
- the thickness of the InN well layer in the well layer is at least one of a thickness of 2 molecules or less and a thickness of 0.6 nm or less. It is more preferable that the thickness is not more than 1 molecule or not more than 0.3 nm in that the effect of the invention can be ensured.
- “single molecule thickness” refers to the length of one half of one side of the crystal unit cell in the growth direction. Although not limited, for example, in the growth of a nitride semiconductor crystal in the C-axis direction, the length becomes 1Z2 of the C-axis length. In other words, it corresponds to 2.9A for InN and 2.6A for GaN.
- the critical thickness of InN is 1 to 2 molecules in InNZGaN heterostructures.
- an InN2 molecular thickness is grown in the GaN well layer, more preferably one molecular thickness, the lattice relaxation due to the lattice mismatch between InNZGaN is prevented and the InN ultrathin film layer becomes coherent.
- Grows in the GaN well layer if this single-molecule-thick InNZGaN well layer has a compressive strain due to In N, and becomes a strain opposite to that of the A1N barrier layer, so that a strain compensation structure can be formed. Accumulation and cracking can be prevented, and poor crystal quality can be prevented.
- A1N has a lattice mismatch degree of 2.4% (tensile strain) with respect to GaN.
- InN is + 11% (compressive strain) with respect to GaN. Since A1N has an even greater degree of lattice mismatch of 13% or more, it is practically difficult to produce a high-quality superlattice structure.
- InN is thermally unstable compared to other nitride semiconductors. However, there is also a problem that the optimum growth temperature differs greatly compared to GaN and A1N.
- the critical growth temperature on the high-temperature side of InN single crystals is about 500 ° C
- GaN and A1N usually grow at a high temperature of 650 ° C to 1000 ° C or higher.
- These heterostructures, quantum well structures and superlattice structures are also difficult to form.
- the thermal properties of ultra-thin InN layer growth are different from Balta InN. Normally, when the growth temperature is 500 ° C or higher (in this case, it is assumed that the growth is on the group III polar surface), the crystal growth hardly occurs due to the thermal instability 'dissociation of InN.
- the InN layer is less than 2 molecules thick, so unlike the case of Balta, the InN ultra-thin film can be formed without thermal decomposition even at higher temperatures. It is done.
- the results of our studies to date have shown that it is possible to form an ultra-thin InZ thin-film layer with pseudo-lattice matching up to 650 ° C and the formation of a ZGaN multiple quantum well structure. It is predicted that formation is possible by controlling the feed ratio of VZIII group raw materials. In other words, according to this, it is possible to produce a GaNZAIN superlattice ISBT structure in which InN having a thickness of less than two molecules is introduced at a high temperature of 650 to 700 ° C.
- one form of the thickness of the In N well layer is preferably 2 molecular thickness or less, but may be a fractional molecular thickness.
- “Fractional molecular thickness” refers to a state in which InN layers are not uniformly present in a planar shape, but InN having a thickness of about 1 molecule is dispersed in an island shape. Even in such an InN fractional molecular thickness ZGaN well layer ZAIGaN barrier layer, the above-described intersubband transition wavelength can be shortened and a strain compensation structure can be formed.
- the well layer has a plurality of GaN well layers, and the InN well layer is sandwiched between the plurality of GaN well layers. .
- the GaN well layer is arranged between the AlGaN barrier layer and the InN well layer, and the above tensile stress and compressive stress can be surely offset.
- the well layers may have the same number of GaN well layers and In N well layers.
- the well layer and the pair of AlGaN barrier layers sandwiching the well layer have a one-cycle quantum well structure, and the AlGa in this quantum well structure
- a plurality of quantum well structures are stacked in common with the N barrier layer. By doing so, it is possible to reduce the number of steps for manufacturing a semiconductor element and to have an advantage that the design becomes easy.
- the well layer and the pair of AlGaN barrier layers sandwiching the well layer may have a single-period quantum well structure, and a plurality of quantum well structures may be stacked via a spacer layer. preferable. By doing so, accumulation of strain energy in the AlGaN barrier layer can be prevented, and cracks can be more easily suppressed.
- the well layer has subbands, and the optical wavelength corresponding to the energy in the subband interval can be controlled to 2 m or less.
- this means is not limited, but has a subband in the well layer, and utilizes a light absorption transition in the subband interval and a fast relaxation process via an electron-phonon interaction. Thus, it is also preferable to function as an ultrafast optical switch.
- the superlattice layer is electrically controlled by adjusting the period of the well layer and the AlGaN barrier layer of the superlattice layer, which has subbands in the well layer. It is also preferable to provide a child injection layer and a light emitting layer to function as a quantum cascade laser.
- an optical switching element comprises a substrate, a nother layer, a cladding layer, a superlattice layer, and a cap layer, which are laminated in order, and the superlattice layer comprises: A well layer having a GaN well layer and an InN well layer and a pair of AlGaN barrier layers sandwiching the well layer are provided.
- the generation of cracks due to the tensile stress of the A1N layer is a problem, and it is difficult to increase the number of cycles. be able to. In other words, the tensile force is applied to the AlGaN barrier layer.
- the InN layer By providing the InN layer, compressive stress is applied to the InN layer (the lattice mismatch between InNZGaN is approximately + 11%). By providing it in the GaN layer, it is possible to form a strain compensation structure that cancels the tensile strain in the A1N layer. Even if the period is increased, the generation of cracks can be suppressed.
- a quantum cascade laser device includes a substrate, a buffer layer, a first contact layer, a first cladding layer, a superlattice layer, a second cladding layer, a second cladding layer, The contact layers are sequentially stacked, and the superlattice layer has a well layer having a GaN well layer and an InN well layer, and a pair of AlGaN barrier layers sandwiching the well layer.
- the present invention can provide a novel semiconductor device, an optical switching device using the same, and a quantum force scaled laser.
- FIG. 1 is a schematic diagram of a semiconductor element (ISBT optical switch) according to the present embodiment.
- the semiconductor optical device 1 according to the present embodiment is configured by sequentially stacking a buffer layer 3, a cladding layer 4, a superlattice layer 5, and a cap layer 6 on a substrate 2.
- the semiconductor element according to this embodiment can be used as an optical switching element.
- the substrate 2 serves as a basis for growing the noffer layer 3, the clad layer 4, the superlattice layer 5 and the like, and is not limited to, for example, a sapphire substrate, a SiC substrate, a GaN barrier, A1 N-balta substrates can be used, and other substrates with GaN and A1N crystal layers deposited by hydride vapor phase epitaxy (HV PE), metal organic chemical vapor deposition (MOCVD), etc. be able to.
- HV PE hydride vapor phase epitaxy
- MOCVD metal organic chemical vapor deposition
- the polarity of the surface of the substrate 2 and the polarity of the layer laminated on it by the surface treatment (nitriding treatment) are determined.
- the surface polarity can be either a group III polar surface or a group V polar surface.
- Substrate 2 is formed using an R-plane sapphire substrate, GaN grown in the A-plane or M-plane direction, or a selective growth technique to reduce the effect of the internal electric field (11-22) or (1-101) Surface GaN film can be used.
- the noffer layer 3 is for growing the superlattice layer 5 with good crystal quality, and various types can be adopted without being limited as long as it exhibits the above functions.
- a GaN crystal, A1N crystal, AlGaN mixed crystal, or the like can be suitably used.
- the clad layer 4 is for confining electrons efficiently in the superlattice layer 5 and minimizing the optical power required for optical switching, and various types can be adopted without limitation.
- AlGaN mixed crystal, GaN crystal, A1N crystal, etc. can be used preferably.
- the superlattice layer 5 includes a pair of GaN well layers 51 la and b, and a well layer 51 having an InN well layer 512 sandwiched between the pair of GaN well layers and a pair of AlGaN sandwiching the well layer 51.
- the barrier layers 52a and 52b and the quantum well structure 53, which is also a force, are formed as one cycle, and this is repeated a plurality of times through the spacer layer 54.
- FIG. 2 shows a schematic cross-sectional view of the superlattice layer 5 according to the present embodiment.
- the pair of GaN well layers 51la and b are layers including a GaN crystal doped with an impurity such as Si.
- the composition of the GaN well layers 511a, b may include other group III elements such as In or A1 even if the composition is only a GaN layer.
- the ratio of elements other than Ga is preferably less than 0.5 with respect to the total amount of Group III elements.
- the thickness of the GaN well layers 511a and b is not limited, but is preferably 0.5 nm or more and 5 nm or less, for example, more preferably 0.5 nm or more and 2 nm or less.
- the total thickness of the pair of GaN well layers 51 la and b and the InN well layer 512 (the distance between the pair of AlGaN barrier layers 52 a and b) is changed. It is possible to control the energy between subbands, and it is not limited, but it is preferable that the total is within the range of 1 nm or more and 2 Onm or less. It is more preferable that the energy is 1 nm or more and 5 nm or less. Yes. Note that in the transition between subbands, absorption occurs due to the transition of electrons to the first level force of the subband and the second level. Therefore, by using an n-type semiconductor layer, a large number of electrons exist in the first level. Allows intersubband absorption. Therefore, impurities such as Si are doped to control the n-type semiconductor.
- the InN well layer 512 is a layer that can obtain a strain compensation effect due to an increase in the conduction band offset amount and a compressive strain opposite to that of the AlGaN barrier layer 511.
- the thread of the InN well layer 512 may be a layer composed only of InN, or may contain other group elements such as Ga. However, in this case, the percentage of elements other than In is 0 Preferably less than 1.
- the thickness of the InN well layer is not limited, but is preferably 2 molecular thickness or less, more preferably 1 molecular thickness or less. This is because InN crystals and GaN crystals usually have a lattice mismatch of about 11%! / Although they can grow without causing lattice relaxation by making the InN well layer 53 sufficiently thin.
- Molecular thickness here means the length of the molecule formed by In and N atoms. Although not limited, for example, in the case of a crystal growing in the c-axis direction, it means half the length of the c-axis in the crystal lattice. As described above, the maximum thickness (hereinafter referred to as “critical film thickness”) of In N grown on GaN that does not cause lattice relaxation is 1 to 2 molecular thickness. If this can be realized, defects due to lattice relaxation can be prevented and a superlattice layer with high crystal quality can be realized.
- the thickness of the InN well layer may be a fractional molecular thickness.
- Fractional molecular thickness refers to a state in which InN with a thickness of about 1 molecule is dispersed and formed in islands, in which the InN layer does not exist evenly. Even in such an InN fractional molecular thickness ZGaN well layer ZAIGaN barrier layer, the above-described intersubband transition wavelength can be shortened and a strain compensation structure can be formed.
- the pair of AlGaN barrier layers 511a and 51 lb are mixed crystal layers of A1N crystal and GaN crystal.
- the composition of the A1 GaN barrier layer can be expressed as AlGaN, and x is a force that is larger than 0 and takes a value of 1 or less, preferably 0.5 or more and 1 or less.
- the thickness of the pair of AlGaN barrier layers 51 la and 51 lb is not limited, but is preferably 1 nm or more and 50 nm or less, more preferably 1 nm or more and 5 nm or less.
- Spacer layer 54 is a layer having a function of preventing the occurrence of cracks accompanying an increase in the number of superlattice periods, and is not limited, but is preferably composed of, for example, GaN. Further, the thickness is not limited as long as it exhibits the above function, but it is preferably lOnm or more and 50 nm or less. In this way, strain accumulation is prevented, cracks are less likely to occur as the number of superlattice periods increases, and an ISBT structure with a high absorption amount can be realized, and an ISBT wavelength of 1 ⁇ m or less can be realized more easily. Become.
- the number of layers stacked via the spacer layer 56 is not limited, but is preferably 10 cycles or more. Number of cycles As the layer thickness increases, the amount of absorption is expected to increase due to the increase in the total layer thickness. However, it should be considered that there is concern about the generation of cracks as the layer thickness increases.
- the cap layer 6 is a layer having a function of efficiently confining electrons in the superlattice layer 5 and maintaining the crystal quality, and various types can be adopted without limitation.
- AlGaN, GaN, A1N, etc. can be suitably used.
- FIG. 3 shows a schematic diagram of energy bands in the semiconductor optical functional device.
- FIG. 3 (a) is a band diagram of the ISBT structure in the GaNZAIN superlattice not including the InN layer
- FIG. 3 (b) is a band diagram of the ISBT structure in the InNZGaNZAIN superlattice according to the present embodiment.
- the slope of the band in the figure is the result of considering the influence of the internal electric field due to the piezo effect and spontaneous polarization when assuming growth in the C-axis direction.
- the GaNZAIN structure has a band offset of about 1.8 eV
- the InNZGaNZAIN structure with the InN layer inserted has a larger conduction band.
- An offset amount ( ⁇ 3.5eV) can be obtained.
- the InN well layer is a very thin film, it greatly affects the intersubband level energy.
- the first level can be greatly shifted downward, and the ISBT wavelength can be further shortened. Conceivable. In particular, it is possible to cause ISBT absorption up to the near infrared range.
- the layer thickness control of the ISBT superlattice can be performed according to the semiconductor optical functional device according to the present embodiment. Can be easily.
- the nitride ISBT structure fabricated by metalorganic vapor phase epitaxy cannot cover the 1.55 / zm band, which is more difficult to control strictly than the MBE method, and the shortest wavelength is currently 2 m.
- the GaN well layer has a thickness of ⁇ 3 nm and a 1.55 m band. Compared to the case where no InN layer is inserted (2 nm or less), the strictness of layer thickness control is relaxed, and the metal-organic vapor phase epitaxy can realize a nitride-based ISBT structure that covers the 1.55 m band. There is an advantage
- the dependence of the ISBT wavelength on the GaN well layer thickness of the GaNZAIN superlattice and InNZGaNZAIN superlattice was determined by theoretical calculation. The results are shown in Fig. 4. In the figure, The horizontal axis shows the thickness of the GaN well layer, and the vertical axis shows the intersubband transition energy. In this calculation, the thickness of the InN well layer is assumed to be one molecular thickness and is calculated at the center of the GaN well layer.
- the GaNZAIN superlattice, InNZGaNZAIN superlattice! / the GaNZAIN superlattice, InNZGaNZAIN superlattice! /
- the ISBT wavelength becomes shorter as the GaN well layer thickness decreases, but the same GaN well layer.
- the InNZGaNZAIN superlattice has a shorter wavelength than the transition energy between subbands.
- the ISBT wavelength is about 1.2 ⁇ ⁇ (1.05 eV)
- the ISBT is about 650 nm (l. Wavelength can be obtained.
- the semiconductor optical device can reduce the wavelength to the ISBT wavelength in the visible light region.
- the structure proposed in the present invention has further shortened the operating wavelength of quantum cascade lasers that have been actively studied mainly on the long wavelength side of 3 m or more (to 1.55 m band and visible light source). It is very promising for expansion.
- the ISBT wavelength when the stacked structure according to the present embodiment, that is, the InN well layer 512 is located between the GaN well layers 511a and b, more specifically at the center thereof, is calculated.
- the wave function of the electrons in the subband changes depending on the position of the InN well layer 512 in the GaN well layers 511a and b, and the ISBT wavelength and transition probability can be controlled.
- the InN well layer 512 can be placed at positions other than the centers of the GaN well layers 51 la and b, and further transition wavelength control and wave function control can be performed depending on the position.
- a structure in which the InN well layer 512 is not sandwiched between GaN well layers is also possible.
- a plurality of InN well layers may be arranged between a pair of AlGaN layers.
- FIG. 6 shows a theoretical prediction of the change of the wave function depending on the position of the InN well layer 512 in the InNZGaNZAIN superlattice.
- the figure shows the calculation result of the wave function (I ⁇ 2 I) generated in the conduction band and valence band potentials.
- the GaN well layer 511 has a thickness of 8 molecules
- the A1 N layer has a thickness of 4 nm. It can be seen that the wave function in the subband in the conduction band and the wave function in the valence band vary greatly depending on the position of the InN well layer.
- the inter-subband transition wavelength changes depending on the position of the InN well layer, and the transition probability of one electron hole also changes.InN well layers are inserted and shifted from the center position compared to the superlattice. Insert It can be seen that the transition probability is greatly improved in the structure. In other words, it is predicted that the InNZGaNZAIN superlattice is also effective in dramatically improving the transition probability between the conduction band and the valence band.
- the semiconductor element according to the present embodiment can shorten the ISBT wavelength, and can be manufactured easily by forming a distortion compensation structure.
- the manufacturing process of the semiconductor optical functional device according to this embodiment includes at least the step of forming the buffer layer 3 on the substrate 2, the step of forming the cladding layer 4, the step of forming the superlattice layer 5, and the cap layer 6. Forming the process.
- the step of forming the noffer layer 3 is not limited, but, for example, an organic metal growth method.
- MBE or pulsed laser deposition can be used. Note that this step can be omitted when the substrate 1 is a GaN buttery or A1N buttery substrate or a substrate on which a GaN or A1N layer is formed.
- the step of forming the clad layer 4 is not limited, and a metal organic vapor phase growth method, an MBE method, or a laser beam deposition method can be used.
- the substrate temperature varies depending on the material of the layer to be formed and can be adjusted as appropriate.For example, when GaN is used as the cladding layer 4, it may be 600 ° C or higher and 800 ° C or lower. I like it.
- the step of forming the superlattice layer 5 further includes the step of forming the AlGaN barrier layer 511, the step of forming the GaN well layer 512, the step of forming the InN well layer 513, and the spacer layer 52. The process of carrying out.
- the step of forming the AlGaN barrier layers 52a and 52b is not limited, but a metal organic vapor phase epitaxy method, an MBE method, or a laser beam deposition method can be used.
- the conditions can be appropriately adjusted depending on the material and the like, but are not limited, but it is preferably 600 ° C or higher and 900 ° C or lower, but 600 ° C or higher and 700 ° C or lower. It is more preferable.
- the step of forming the GaN well layers 511a and b is not limited, and a metal organic vapor phase epitaxy method, an MBE method, and a laser beam deposition method can be used.
- the conditions can be appropriately adjusted depending on the material, etc., and are not limited, but it is preferably 600 ° C or higher and 900 ° C or lower, but 600 ° C or higher and 700 ° C or lower. Is more preferred.
- the process of forming the InN well layer 512 is not limited, but an MBE method or a pulsed laser deposition method can be used.
- the conditions can be appropriately adjusted depending on the material and the like, but are not limited, but it is preferably 600 ° C or more and 700 ° C or less.
- the growth temperature of the InN well layer 512 according to this embodiment is 150 ° C. or more higher than the growth limit temperature of the In-polar InN single film.
- the InN layer is very thin, with a thickness of less than 2 molecules, unlike Balta InN, it can be grown at higher temperatures.
- the process of forming the InN well layer 512 remains a problem in controlling the ultrathin film at the atomic and molecular level, but can also be performed by metal organic vapor phase epitaxy, which is generally used for the growth of nitride semiconductor devices.
- the step of forming the spacer layer 54 is not limited, and a metal organic vapor phase growth method, an MBE method, and a laser laser deposition method can be used.
- the substrate temperature varies depending on the material of the layer to be formed and can be adjusted as appropriate.For example, when GaN is used as the cladding layer 4, it may be 600 ° C or higher and 800 ° C or lower. I like it.
- the step of forming the cap layer 6 is not limited, but metal organic vapor phase epitaxy, MBE, and laser laser deposition can be used.
- the conditions can be adjusted as appropriate depending on the material, etc., and are not limited, but it is preferably 600 ° C or higher and 900 ° C or lower, and 600 ° C or higher and 700 ° C or lower. More preferably.
- the semiconductor device according to the present embodiment can be manufactured through the above steps.
- FIG. 7 shows a schematic cross-sectional view of the superlattice layer 5 of the semiconductor optical functional device according to the present embodiment.
- the superlattice layer 5 according to the present embodiment includes a well layer 51 having a GaN well layer 511a, b and an InN well layer, and a pair of AlGaN barrier layers 52a, b sandwiching the well layer 51. Force common to the point that the quantum well structure 53 has one period Unlike the first embodiment, the AlGaN barrier layer in the adjacent quantum well structure is formed in common without using the spacer layer 52. .
- the semiconductor optical functional device in the present embodiment can be manufactured by omitting the step of forming the spacer layer.
- the present embodiment is an embodiment of a quantum cascade laser element, and has the same configuration as that of the first embodiment except that means for injecting electrons into the superlattice layer 5 is provided.
- Figure 8 shows a schematic cross-sectional view of the quantum cascade laser device according to this embodiment. Here, only different configurations will be described, and the other configurations are the same configurations, and thus description thereof will be omitted.
- the quantum cascade laser device 11 includes a buffer layer 3, a contact layer 7a, a cladding layer 4a, a superlattice layer 5, a cladding layer 4b, and a contact layer 7b on a substrate 2. Are sequentially laminated.
- the contact layers 7a and 7b are connected to the first electrode 8a and the second electrode 8b, respectively.
- the contact layers 7a and 7b are layers that can ensure electrical connection with the first and second electrodes 8a and 8b, and are not limited to, but, for example, GaN, InGaN, or AlGaN.
- a layer in which Si or the like is implanted as an impurity can be preferably used.
- the first and second electrodes 8a and b are not limited as long as they have electrical conductivity, but are composed of, for example, aluminum (A1), titanium (Ti), gold (Au), or the like. You can use electrode materials!
- the electron injection layer and the light emitting layer are provided by changing the superlattice period and controlling the subband level position in the conduction band in the above configuration.
- laser emission can be performed by forming an inversion distribution between the subband levels.
- the electrons that contributed to the light emission can contribute to the light emission again, which is suitable for high external quantum efficiency and high output. It is easy to control by changing the period of the laser, and it is possible to design the laser oscillation wavelength longer to a longer wavelength range (for example, terahertz range) without any material restrictions.
- a novel quantum cascade laser device can also be provided by this embodiment.
- Figure 9 shows a cross-sectional TEM image of a single-molecule InNZGaN superlattice structure grown at 600 ° C. According to this cross-sectional TEM image, it was found that a single-molecule-thick InN layer with steep interface roughness at the atomic layer level could be realized, and a 14-nm GaN layer could be realized. Also, no new defects were found here, and it was confirmed that a very high quality superlattice structure was formed.
- FIG. 10 shows a cross-sectional TEM image of a single-molecule InNZGaN superlattice structure grown at 650 ° C. It can be seen that in the sample of this example, the InN layer does not exist uniformly in a planar shape, but an InN layer in which InN having a thickness of about one molecule is dispersed in an island shape is formed. In other words, formation of fractional molecular InN was confirmed.
- a Ga-polar GaN film grown on C-plane sapphire by metalorganic vapor phase epitaxy was used as the substrate.
- This GaN substrate is organically cleaned, then introduced into an MBE device, heat-treated at 820 ° C, and a superlattice structure of InN (single molecule) ZGaN (lnm) / A1N (3nm) at 650 ° C.
- A1N layer 100 periods of growth were made common, and a Ga-polar GaN layer of 20 nm was formed as a cap layer thereon.
- Figure 11 shows a schematic diagram of this superlattice structure.
- Fig. 12 shows the X-ray diffraction measurement results of sample 3, grown at 650 ° C, InN (single molecule thickness) / GaN (lnm) / A1N (3 nm) superlattice structure.
- InN single molecule thickness
- GaN (lnm) / Al N (3 nm) superlattice structure formed under the same conditions as in sample 3 except that InN (one molecular thickness) is inserted for comparison are also shown. I will show you.
- a satellite peak indicating the formation of a periodic structure can be clearly seen.
- the introduced sample Compared to the sample that had been introduced with InN (single molecule thickness), the introduced sample had a stronger satellite peak. This is thought to be due to the improved interface flatness and crystallinity due to the strain compensation effect of introducing the InN well layer (single molecule thickness).
- FIG. 13 is a diagram showing an absorption spectrum of p-polarized light incident on the surface of Sample 3 at an angle of 60 degrees.
- two Clear ISBT absorption could be observed from the structure.
- the ISBT absorption wavelength is observed at 1. 48 m.
- the InN (single molecule thickness) ZGaNZAIN superlattice structure is sufficiently applicable to ultrafast optical switches and quantum cascade lasers using the ISBT process.
- the wavelength is shorter than that of the GaN (lnm) ZAlN (3 nm) superlattice, and the actual thickness of each superlattice is thicker than the design value.
- layer control position of single molecule InN, etc.
- the present invention can be industrially used as a semiconductor optical functional device, an ultrafast semiconductor optical switch, and a quantum cascade laser.
- FIG. 1 is a schematic sectional view of a semiconductor device according to a first embodiment.
- FIG. 2 is a schematic cross-sectional view of a superlattice layer in a semiconductor device according to Embodiment 1.
- FIG. 2 is a schematic cross-sectional view of a superlattice layer in a semiconductor device according to Embodiment 1.
- FIG. 3 is an energy band diagram of the semiconductor element according to the first embodiment.
- FIG. 4 is a graph showing the dependence of inter-subband transition energy on the well layer thickness of the semiconductor optical functional device according to Embodiment 1 obtained by theoretical calculation.
- FIG. 5 is a schematic cross-sectional view of another example superlattice structure in the semiconductor element according to Embodiment 1.
- FIG. 6 is a schematic cross-sectional view of a superlattice layer in a semiconductor element according to Embodiment 2.
- FIG. 7 is a schematic cross-sectional view of a superlattice layer in a quantum cascade laser device according to a third embodiment.
- FIG. 8 Cross-sectional TEM image of sample 1 superlattice structure (600 ° C) in the example (drawing) Substitute).
- FIG. 9 is a cross-sectional TEM image (drawing substitute) of the superlattice structure (650 ° C.) in the semiconductor optical functional device of Sample 2 in the example.
- FIG. 10 is a schematic sectional view of a semiconductor optical functional device of Sample 3 in an example.
- FIG. 11 is a diagram showing an X-ray diffraction measurement result of the superlattice structure in the semiconductor optical functional device of Sample 3.
- FIG. 12 is a diagram showing a result of an X-ray diffraction measurement of a comparative example for sample 3.
- FIG. 13 is a diagram showing an absorption spectrum by p-polarized light incident at an angle of 60 degrees with respect to the surface of the semiconductor element of sample 3.
- SYMBOLS 1 Semiconductor device, 2 ... Board
Landscapes
- Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Engineering & Computer Science (AREA)
- General Physics & Mathematics (AREA)
- Chemical & Material Sciences (AREA)
- Nonlinear Science (AREA)
- Nanotechnology (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- Electromagnetism (AREA)
- Life Sciences & Earth Sciences (AREA)
- Biophysics (AREA)
- Crystallography & Structural Chemistry (AREA)
- Semiconductor Lasers (AREA)
Abstract
Provided are novel semiconductor element, optical switching element and quantum cascade laser. The semiconductor element includes a well layer having a GaN well layer and an InN well layer, and a superlattice layer having a pair of AlGaN barrier layers sandwiching the well layer. In the semiconductor element, increase of an electron-hole recombination probability (transition probability) between a conduction band and a valence band by wave function control, and an emission wavelength control are performed. The semiconductor element has, as an active layer, a stacked structure composed of the well layer, which has the GaN well layer and the InN well layer, and the pair of AlGaN barrier layers sandwiching the well layer.
Description
明 細 書 Specification
半導体素子、光スイッチング素子及び量子カスケードレーザ素子 技術分野 Semiconductor device, optical switching device and quantum cascade laser device
[0001] 本発明は、半導体素子、光スイッチング素子及び量子カスケードレーザに関し、特 にサブバンド間遷移を利用したものに関する。 [0001] The present invention relates to a semiconductor device, an optical switching device, and a quantum cascade laser, and more particularly to a device utilizing intersubband transition.
背景技術 Background art
[0002] 半導体素子にお!、て形成される量子井戸構造や超格子構造などの井戸層内には 離散化したエネルギー準位が存在し、この準位間でも光吸収'電子遷移が起こる。こ れを一般にサブバンド間遷移と呼ぶ。 [0002] Discrete energy levels exist in well layers such as quantum well structures and superlattice structures formed in semiconductor devices, and light absorption and electron transition occur between these levels. This is generally called intersubband transition.
[0003] サブバンド間遷移 (以下「ISBT」という。)は、伝導帯—価電子帯間のバンド遷移と は異なるいくつかの特徴を有している。一つは量子井戸や超格子構造によって ISB Tの遷移エネルギーが可変であること。もう一つは遷移した電子の緩和速度がバンド 間遷移の場合に比べて非常に速いことである。 [0003] Transition between subbands (hereinafter referred to as "ISBT") has several characteristics different from band transition between conduction band and valence band. One is that the transition energy of ISBT is variable depending on the quantum well and superlattice structure. The other is that the transition rate of the transitioned electrons is much faster than in the case of interband transitions.
[0004] 通常のバンド間遷移の場合、緩和速度は〜 nsecオーダーである力 ISBTの緩和 速度は〜 psecから fsecオーダーと非常に速ぐ将来的なテラビット級の超高速光スィ ツチへの応用が期待されて 、る。 [0004] In the case of normal interband transition, the relaxation rate is about nsec order. The relaxation rate of ISBT is ~ psec to fsec order, and it can be applied to future terabit-class ultrafast optical switches. Expected.
[0005] ISBTを用いた超高速光スィッチの基本構造としては現在まで代表的なものとして 3 つ上げられる。 GaNZAIN系、 CdSZBeTe系、 InGaAsZAlAs系である。中でも 窒化物系の ISBT構造である GaNZAIN系超格子はこの 3つの中でも最も大きい伝 導帯バンドオフセットを有し (〜2eV)、かつ最も速 、緩和速度 (f secオーダー)を有 することが報告されており(例えば特許文献 1及び 2、非特許文献 1参照)、特に下記 非特許文献 1では、現在まででもっとも短い ISBT波長が報告されている。この論文 では GaNlnmZAlN4nm超格子 100周期を分子線エピタキシー(以後「MBE」 t ヽ う。)法を用いて成長し、 1. 08 mの ISBT波長を観測している。 [0005] There are three typical basic structures of ultrafast optical switches using ISBT. GaNZAIN, CdSZBeTe, and InGaAsZAlAs. Among them, the GaNZAIN superlattice, which is a nitride-based ISBT structure, has the largest conduction band offset (-3 eV) among these three, and is reported to have the fastest and relaxation rate (fsec order). (See, for example, Patent Documents 1 and 2 and Non-patent Document 1). Particularly, in Non-Patent Document 1 below, the shortest ISBT wavelength has been reported to date. In this paper, 100 periods of GaNlnmZAlN4nm superlattice were grown using molecular beam epitaxy (hereinafter referred to as “MBE” t) method, and an ISBT wavelength of 1.08 m was observed.
[0006] 一方、 ISBTは上述したように量子井戸幅や超格子の周期構造を変化させるだけで 容易に遷移波長を制御できる。このようなサブバンド間の発光を利用したデバイスと しては、例えば量子カスケードレーザがある。通常の半導体レーザは伝導帯と価電
子帯間の反転分布によりレーザ発振を起こすが、カスケードレーザは量子井戸の伝 導帯中の離散化された準位間に反転分布を形成してレーザ発振を起こす。前述した ように量子カスケードレーザは量子井戸構造を変化させるだけで、レーザ発振波長 が制御可能である力 その範囲は量子井戸のバンドオフセット量で制限される。つま り、バンドオフセット量よりも大きいエネルギーのレーザ発振を得るのは不可能である[0006] On the other hand, as described above, the ISBT can easily control the transition wavelength only by changing the quantum well width or the periodic structure of the superlattice. An example of such a device that utilizes light emission between subbands is a quantum cascade laser. Ordinary semiconductor lasers have conduction bands and valence charges. Laser oscillation occurs due to the inversion distribution between the subbands, but the cascade laser forms an inversion distribution between discrete levels in the conduction band of the quantum well and causes laser oscillation. As described above, the quantum cascade laser can control the lasing wavelength simply by changing the quantum well structure. The range is limited by the band offset of the quantum well. In other words, it is impossible to obtain laser oscillation with energy larger than the band offset amount.
。ちなみに、現在までに 3. 4〜24 mの発振波長が得られている。 . Incidentally, an oscillation wavelength of 3.4 to 24 m has been obtained so far.
[0007] つまり、 GaNZAIN超格子は現在もっとも高速な電子緩和速度を有し、最も大きな 伝導帯バンドオフセット量が実現可能であると考えられるため、超高速光スィッチやま た量子カスケードレーザデバイスの基本構造、サブバンド間遷移波長の更なる短波 長化の可能性を有する非常に有望な構造であるといえる。 In other words, the GaNZAIN superlattice currently has the fastest electron relaxation rate and is considered to be able to achieve the largest conduction band offset, so the basic structure of ultrafast optical switches and quantum cascade laser devices This is a very promising structure with the possibility of further shortening the intersubband transition wavelength.
[0008] 特許文献 1 :特開平 8— 179387号公報 Patent Document 1: Japanese Patent Laid-Open No. 8-179387
特許文献 2:特開 2001— 108950号公報 Patent Document 2: JP 2001-108950 A
非特許文献 1 :K. Kishino et al.、 APL.、 vol. 81、 1234- 1236 (2002) 発明の開示 Non-Patent Document 1: K. Kishino et al., APL., Vol. 81, 1234-1236 (2002) Disclosure of the Invention
発明が解決しょうとする課題 Problems to be solved by the invention
[0009] GaNZAIN超格子構造は非常に大きな伝導帯バンドオフセット量を有しており ISB Tの短波長化には適している力 GaNZAIN間の格子不整合度が 2. 4%と大きく 多数層の積層は困難である。 GaNにコヒーレントに成長すると仮定した場合、 A1N障 壁層は引っ張り歪を受ける。この引っ張り歪は A1N層におけるクラックの発生をもたら し、結晶品質の維持を困難とさせる。 [0009] The GaNZAIN superlattice structure has a very large conduction band offset, and is suitable for shortening the ISBT T wavelength. The degree of lattice mismatch between GaNZAIN is as large as 2.4%. Lamination is difficult. Assuming coherent growth on GaN, the A1N barrier layer is subject to tensile strain. This tensile strain causes cracks in the A1N layer, making it difficult to maintain crystal quality.
[0010] また、 ISBTを用いた量子カスケードレーザなどの光素子への応用を考えた場合、 I SBT波長の短波長ィヒも非常に重要な意味をもつ。 GaNZAIN超格子では 1. 08 mの ISBT吸収を観測しているがこれより更に短波長させるには GaN井戸層厚をさら に小さくする必要がある。しかし、この場合超格子全体の A1N層比率が増加するため 、よりクラックが発生しやすい状態となり、結晶品質を維持するのが困難となる。また G aN井戸層厚も lnm以下となり、制御が難しくなる。つまり: L m以下の短波長化は現 状の GaNZAIN超格子構造のままでは困難である。 [0010] When considering application to optical devices such as quantum cascade lasers using ISBT, the short wavelength of the I SBT wavelength is also very important. The GaNZAIN superlattice has observed 1.08 m ISBT absorption, but the GaN well layer thickness needs to be further reduced to make the wavelength shorter than this. However, in this case, the ratio of the A1N layer of the entire superlattice increases, so that cracks are more likely to occur and it becomes difficult to maintain the crystal quality. The GaN well layer thickness is also less than lnm, making it difficult to control. In other words: Shortening the wavelength below L m is difficult with the current GaNZAIN superlattice structure.
[0011] ところで、一般に、超高速光スィッチや量子カスケードレーザ構造は量子井戸構造
を多数積層した光素子構造となっている。例えば ISBT超高速光スィッチは、スィッチ ングに必要な光エネルギーを最小限に抑え、 ISBT領域の光吸収量を高めるため 10 0周期程度の量子井戸構造を積層する。 GaNZAIN超格子構造は非常に大きな伝 導帯バンドオフセット量を有しており ISBTの短波長化には適して 、るが、上記の通り GaNZAIN間の格子不整合度が 2. 4%と大きぐ多数の積層は困難である。そし て GaNにコヒーレントに成長すると仮定した場合、 A1N障壁層は引っ張り歪を受ける 。超格子における周期数を増やすと容易にクラックが発生し、結晶品質が急激に悪 化し、 ISBT吸収が観測できなくなると 、つた課題がある。 By the way, in general, an ultrafast optical switch or a quantum cascade laser structure is a quantum well structure. An optical element structure in which a large number of layers are stacked. For example, an ISBT ultrafast optical switch has a quantum well structure of about 100 cycles to minimize the optical energy required for switching and increase the amount of light absorbed in the ISBT region. The GaNZAIN superlattice structure has a very large conduction band offset and is suitable for shortening the wavelength of ISBT. However, as described above, the lattice mismatch between GaNZAIN is as large as 2.4%. Many stacks are difficult. And assuming that it grows coherently on GaN, the A1N barrier layer is subject to tensile strain. When the number of periods in the superlattice is increased, cracks easily occur, the crystal quality deteriorates rapidly, and ISBT absorption cannot be observed.
[0012] なお、周期数を減らせば、クラック発生を抑制し結晶品質を保つことは可能である 力 吸収量が減少してしまうため光スイッチングに必要な ONZOFF比を得ることが 困難となるため好ましくない。また量子カスケードレーザ構造を作製 'デザインする場 合、多段の発光層及び電子注入層を設ける必要があるため同様な問題が起こり、超 格子の周期数の制限は構造設計上大きなデメリットである。 [0012] It should be noted that if the number of cycles is reduced, it is possible to suppress the generation of cracks and maintain the crystal quality. This is preferable because the amount of force absorption decreases, making it difficult to obtain the ONZOFF ratio necessary for optical switching. Absent. When manufacturing and designing a quantum cascade laser structure, it is necessary to provide a multi-stage light emitting layer and an electron injection layer, and the same problem arises. Limiting the number of periods of the superlattice is a major demerit in the structural design.
[0013] そこで、本発明は、上記課題を鑑み、新規な半導体素子、これを用いた光スィッチ ング素子、量子カスケードレーザを提供することを目的とする。 In view of the above problems, an object of the present invention is to provide a novel semiconductor device, an optical switching device using the same, and a quantum cascade laser.
課題を解決するための手段 Means for solving the problem
[0014] 本発明者らは、上記課題について鋭意検討を行ったところ、井戸層に、 AlGaN障 壁層が受ける引っ張り歪を解消する圧縮歪を発生させる層を導入することで、 AlGa N障壁層のクラック発生を防止することができ、し力もこの層に InN力もなる層を採用 すると、 ISBT波長の短波長化ができる点に想到し、本発明を完成させるに至った。 [0014] The inventors of the present invention have made extensive studies on the above-mentioned problems. As a result, the AlGa N barrier layer is introduced into the well layer by introducing a layer that generates a compressive strain that eliminates the tensile strain applied to the AlGaN barrier layer. It was possible to prevent the generation of cracks, and when a layer having an InN force was used for this layer, the inventors realized that the ISBT wavelength could be shortened, and the present invention was completed.
[0015] 即ち、本発明の一手段に係る半導体素子は、 GaN井戸層及び InN井戸層を有す る井戸層と、この井戸層を挟む一対の AlGaN障壁層を有する超格子層を含む。従 来の GaNZAIN超格子 ISBT構造では、 A1N層(AlGaN層)の引っ張り応力に起因 したクラックの発生が問題となり、周期数の増加が困難である力 上記手段によるとこ の問題を根本力も解決することができる。つまり、 AlGaN障壁層には引っ張り応力が かかるが、 InN層を設けることで InN層には圧縮応力が力かるため(InNZGaN間の 格子不整合度は約 + 11%である)、 InN層を GaN層中に設けることで A1N層におけ る引っ張り歪を相殺する歪補償構造を形成することが可能であり、周期を多くしてもク
ラック発生を抑 ff¾することができるのである。 That is, a semiconductor device according to one means of the present invention includes a well layer having a GaN well layer and an InN well layer, and a superlattice layer having a pair of AlGaN barrier layers sandwiching the well layer. In the conventional GaNZAIN superlattice ISBT structure, the generation of cracks due to the tensile stress of the A1N layer (AlGaN layer) is a problem, and it is difficult to increase the number of cycles. Can do. In other words, tensile stress is applied to the AlGaN barrier layer, but compressive stress is applied to the InN layer by providing the InN layer (the lattice mismatch between InNZGaN is about + 11%). It is possible to form a strain compensation structure that cancels the tensile strain in the A1N layer by providing it in the layer. Rack generation can be suppressed.
[0016] さらに InN井戸層は、窒化物半導体の中で最も小さいバンドギャップエネルギー( 約 0. 63eV)を有しており、 GaNとの伝導帯バンドオフセット量は約 1. 7eV、 A1Nと の差は約 3. 5eVであると見積もることができる。つまり、 GaNZAIN超格子の伝導帯 バンドオフセット量に比べて倍程度の値を本半導体素子では実現することができ、サ ブバンド間遷移波長の更なる短波長化(1 μ m以下)が可能となる。このような大きな バンドオフセット量を実現できるのは窒化物半導体、特に InNを用いることで実現可 能である。 [0016] Furthermore, the InN well layer has the smallest bandgap energy (approximately 0.63 eV) among nitride semiconductors, and the conduction band offset amount from GaN is approximately 1.7 eV, which is the difference from A1N. Can be estimated to be about 3.5 eV. In other words, this semiconductor device can achieve a value about twice the conduction band offset of the GaNZAIN superlattice, and can further shorten the intersubband transition wavelength (less than 1 μm). . Such a large band offset can be realized by using a nitride semiconductor, particularly InN.
[0017] また、この手段において、限定されるわけではないが、井戸層における InN井戸層 の厚さは、 2分子厚以下であること、 0. 6nm以下であることの少なくともいずれかであ ることが好ましぐ 1分子厚以下又は 0. 3nm以下であることが発明の効果を確実にす ることができる点においてより好ましい。ここで「1分子厚」とは、成長方向の結晶単位 格子 1辺の半分の長さを指す。限定されるわけではないが、例えば C軸方向の窒化 物半導体結晶の成長においては C軸長の 1Z2の長さとなる。つまり InNの場合は 2. 9A、 GaNの場合 2. 6Aに相当する。 InNZGaNヘテロ構造において InNの臨界膜 厚は 1〜2分子厚であることが我々の実験によりわかっている。つまり GaNZAIN超 格子層を成長する際、 GaN井戸層中に InN2分子厚以下、より望ましくは 1分子厚を 成長すれば、 InNZGaN間の格子不整合度による格子緩和を防ぎ InN超薄膜層が コヒーレントに GaN井戸層内に成長する。さらにこの 1分子厚 InNZGaN井戸層は In Nにより圧縮歪を有し、 A1N障壁層とは逆の歪となるため歪補償構造を形成すること が可能となり、上述の問題である層数増加による歪の蓄積、クラックの発生を防ぎ、結 晶品質の悪ィ匕を防ぐことができる。なお、例えば簡単な見積りによると、 GaNの格子 を基準に考えた 1分子厚 InNZGaNZAIN超格子の場合、 A1N層厚を約 1. 3nmと することで歪補償構造を形成することが可能である。 [0017] In this means, although not limited, the thickness of the InN well layer in the well layer is at least one of a thickness of 2 molecules or less and a thickness of 0.6 nm or less. It is more preferable that the thickness is not more than 1 molecule or not more than 0.3 nm in that the effect of the invention can be ensured. Here, “single molecule thickness” refers to the length of one half of one side of the crystal unit cell in the growth direction. Although not limited, for example, in the growth of a nitride semiconductor crystal in the C-axis direction, the length becomes 1Z2 of the C-axis length. In other words, it corresponds to 2.9A for InN and 2.6A for GaN. Our experiments show that the critical thickness of InN is 1 to 2 molecules in InNZGaN heterostructures. In other words, when growing a GaNZAIN superlattice layer, if an InN2 molecular thickness is grown in the GaN well layer, more preferably one molecular thickness, the lattice relaxation due to the lattice mismatch between InNZGaN is prevented and the InN ultrathin film layer becomes coherent. Grows in the GaN well layer. In addition, this single-molecule-thick InNZGaN well layer has a compressive strain due to In N, and becomes a strain opposite to that of the A1N barrier layer, so that a strain compensation structure can be formed. Accumulation and cracking can be prevented, and poor crystal quality can be prevented. For example, according to a simple estimate, in the case of a single molecular thickness InNZGaNZAIN superlattice based on the GaN lattice, it is possible to form a strain compensation structure by setting the A1N layer thickness to about 1.3 nm.
[0018] なお一方で、一般的には、 GaNに対して A1Nは 2. 4% (引っ張り歪)の格子不整 合度を有している力 InNは GaNに対して + 11% (圧縮歪)、 A1Nに対しては 13% 以上とさらに大きい格子不整合度を有するため、現実的には良質な超格子構造の作 製が困難と考えられる。そして更に、 InNは他の窒化物半導体に比べ熱的に不安定
であり、最適成長温度が GaNや A1Nに比べて大きく異なるといった課題もある。具体 的には InN単結晶の高温側臨界成長温度は約 500°Cであるのに対し、 GaN、 A1N は通常 650°Cから 1000°C以上という高温で結晶成長が行われるため、一般的にこ れらのへテロ構造や量子井戸構造、超格子構造の形成は困難といった課題もある。 しかしながら、我々は、超薄膜 InN層成長ではその熱的性質がバルタ InNと異なるこ とを実験的に確認している。通常、ノ レク InN結晶成長では成長温度が 500°C以上 の場合 (この場合 III族極性面上成長を仮定)、 InNの熱的不安定性'解離が要因と なり結晶成長が殆ど起きない。しかし、超薄膜 InN層の場合、 InN層は 2分子厚以下 であるため、熱的安定性がバルタの場合と異なり、より高温でも InN超薄膜の熱分解 が起きず形成が可能であると考えられる。現在までの我々の検討結果では 650°Cま で擬似格子整合性を有する InN超薄膜層 ZGaN多重量子井戸構造の形成が実現 可能であることがわかっており、 700°Cまでであれば成長速度や VZIII族原料供給 比を制御することにより形成が可能であると予測している。つまり、これによれば、 650 〜700°Cといった高温での 2分子厚以下の InNを導入した GaNZAIN超格子 ISBT 構造が作製可能であり、この構造ではクラック発生が抑制され、 1 m以下の短波長 域でのサブバンド間遷移を実現することが可能である。なお、この手段において、 In N井戸層の厚さの一つの形態としては 2分子厚以下であることが好ましいが、分数分 子厚とすることもできる。「分数分子厚」とは InN層が面状均一に存在するのではなく 、厚さ 1分子厚程度の InNが島状に分散して形成されている状態を指す。このような I nN分数分子厚 ZGaN井戸層 ZAIGaN障壁層にお 、ても、上述したサブバンド間 遷移波長の短波長化や歪補償構造の形成が可能である。 [0018] On the other hand, in general, A1N has a lattice mismatch degree of 2.4% (tensile strain) with respect to GaN. InN is + 11% (compressive strain) with respect to GaN. Since A1N has an even greater degree of lattice mismatch of 13% or more, it is practically difficult to produce a high-quality superlattice structure. In addition, InN is thermally unstable compared to other nitride semiconductors. However, there is also a problem that the optimum growth temperature differs greatly compared to GaN and A1N. Specifically, the critical growth temperature on the high-temperature side of InN single crystals is about 500 ° C, whereas GaN and A1N usually grow at a high temperature of 650 ° C to 1000 ° C or higher. These heterostructures, quantum well structures and superlattice structures are also difficult to form. However, we have experimentally confirmed that the thermal properties of ultra-thin InN layer growth are different from Balta InN. Normally, when the growth temperature is 500 ° C or higher (in this case, it is assumed that the growth is on the group III polar surface), the crystal growth hardly occurs due to the thermal instability 'dissociation of InN. However, in the case of an ultra-thin InN layer, the InN layer is less than 2 molecules thick, so unlike the case of Balta, the InN ultra-thin film can be formed without thermal decomposition even at higher temperatures. It is done. The results of our studies to date have shown that it is possible to form an ultra-thin InZ thin-film layer with pseudo-lattice matching up to 650 ° C and the formation of a ZGaN multiple quantum well structure. It is predicted that formation is possible by controlling the feed ratio of VZIII group raw materials. In other words, according to this, it is possible to produce a GaNZAIN superlattice ISBT structure in which InN having a thickness of less than two molecules is introduced at a high temperature of 650 to 700 ° C. It is possible to realize intersubband transition in the wavelength region. In this means, one form of the thickness of the In N well layer is preferably 2 molecular thickness or less, but may be a fractional molecular thickness. “Fractional molecular thickness” refers to a state in which InN layers are not uniformly present in a planar shape, but InN having a thickness of about 1 molecule is dispersed in an island shape. Even in such an InN fractional molecular thickness ZGaN well layer ZAIGaN barrier layer, the above-described intersubband transition wavelength can be shortened and a strain compensation structure can be formed.
[0019] また、この手段において、限定されるわけではないが、井戸層は、複数の GaN井戸 層を有し、 InN井戸層は、複数の GaN井戸層の間に挟まれていることが好ましい。こ のようにすることで AlGaN障壁層と InN井戸層との間に GaN井戸層を配置した状態 となり、上記の引っ張り応力と圧縮応力とを相殺することが確実にできるようになる。 [0019] In this means, although not limited, it is preferable that the well layer has a plurality of GaN well layers, and the InN well layer is sandwiched between the plurality of GaN well layers. . By doing so, the GaN well layer is arranged between the AlGaN barrier layer and the InN well layer, and the above tensile stress and compressive stress can be surely offset.
[0020] また、この手段において、限定されるわけではないが、井戸層は、 GaN井戸層と In N井戸層を同数有することも可能である。この場合、 AlGaN障壁層と InN井戸層とが 隣接して積層されることとなる力 他方の AlGaN障壁層と InN井戸層との間には Ga
Nが存在することができ、本手段における効果を達成できる。 [0020] Further, although not limited in this means, the well layers may have the same number of GaN well layers and In N well layers. In this case, the force that the AlGaN barrier layer and the InN well layer are stacked adjacent to each other. Ga between the other AlGaN barrier layer and the InN well layer N can be present and the effect in this means can be achieved.
[0021] また、この手段において、限定されるわけではないが、井戸層と、井戸層を挟む一 対の AlGaN障壁層を一周期の量子井戸構造とし、この量子井戸構造における AlGa[0021] Further, although not limited to this means, the well layer and the pair of AlGaN barrier layers sandwiching the well layer have a one-cycle quantum well structure, and the AlGa in this quantum well structure
N障壁層を共通して複数の量子井戸構造が積層されて 、ることも好ま 、。このよう にすることで、半導体素子製造の工程数を減少させることができるとともに、設計が容 易となるという利点を有する。 It is also preferable that a plurality of quantum well structures are stacked in common with the N barrier layer. By doing so, it is possible to reduce the number of steps for manufacturing a semiconductor element and to have an advantage that the design becomes easy.
[0022] また、この手段において、井戸層と、井戸層を挟む一対の AlGaN障壁層を一周期 の量子井戸構造とし、スぺーサ一層を介して複数の量子井戸構造が積層されている ことも好ましい。このようにすることで AlGaN障壁層における歪エネルギーの蓄積を 防ぎ、クラック発生をより容易に抑制することができる。 [0022] In this means, the well layer and the pair of AlGaN barrier layers sandwiching the well layer may have a single-period quantum well structure, and a plurality of quantum well structures may be stacked via a spacer layer. preferable. By doing so, accumulation of strain energy in the AlGaN barrier layer can be prevented, and cracks can be more easily suppressed.
[0023] また、この手段において、限定されるわけではないが、井戸層中にサブバンドを有 し、このサブバンド間隔におけるエネルギーに相当する光波長を 2 m以下に制御 できる。 [0023] Further, although not limited to this means, the well layer has subbands, and the optical wavelength corresponding to the energy in the subband interval can be controlled to 2 m or less.
[0024] また、この手段において、限定されるわけではないが、井戸層中にサブバンドを有 し、サブバンド間隔における光吸収遷移と電子―フオノン相互作用を介した高速緩 和過程を利用することで超高速光スィッチとして機能させることも好ましい。 [0024] Further, this means is not limited, but has a subband in the well layer, and utilizes a light absorption transition in the subband interval and a fast relaxation process via an electron-phonon interaction. Thus, it is also preferable to function as an ultrafast optical switch.
[0025] また、この手段において、限定されるわけではないが、井戸層中にサブバンドを有 し、超格子層の井戸層及び AlGaN障壁層の周期を調整することで、超格子層を電 子注入層及び発光層を設け量子カスケードレーザとして機能させることも好ましい。 [0025] Further, although not limited in this means, the superlattice layer is electrically controlled by adjusting the period of the well layer and the AlGaN barrier layer of the superlattice layer, which has subbands in the well layer. It is also preferable to provide a child injection layer and a light emitting layer to function as a quantum cascade laser.
[0026] また、本発明の他の一手段に係る光スイッチング素子は、基板、ノ ッファ層、クラッド 層、超格子層、キャップ層と、を順に積層してなり、かつ、超格子層は、 GaN井戸層 及び InN井戸層を有する井戸層と、井戸層を挟む一対の AlGaN障壁層と、を有する こととする。従来の GaNZAIN超格子 ISBT構造では、 A1N層(AlGaN層)の引っ張 り応力に起因したクラックの発生が問題となり、周期数の増加が困難であるが、上記 手段によるとこの問題を根本力も解決することができる。つまり、 AlGaN障壁層には 引っ張り応力が力かる力 InN層を設けることで InN層には圧縮応力が力かるため(I nNZGaN間の格子不整合度は約 + 11%である)、 InN層を GaN層中に設けること で A1N層における引っ張り歪を相殺する歪補償構造を形成することが可能であり、周
期を多くしてもクラック発生を抑制することができる。 [0026] Further, an optical switching element according to another means of the present invention comprises a substrate, a nother layer, a cladding layer, a superlattice layer, and a cap layer, which are laminated in order, and the superlattice layer comprises: A well layer having a GaN well layer and an InN well layer and a pair of AlGaN barrier layers sandwiching the well layer are provided. In the conventional GaNZAIN superlattice ISBT structure, the generation of cracks due to the tensile stress of the A1N layer (AlGaN layer) is a problem, and it is difficult to increase the number of cycles. be able to. In other words, the tensile force is applied to the AlGaN barrier layer. By providing the InN layer, compressive stress is applied to the InN layer (the lattice mismatch between InNZGaN is approximately + 11%). By providing it in the GaN layer, it is possible to form a strain compensation structure that cancels the tensile strain in the A1N layer. Even if the period is increased, the generation of cracks can be suppressed.
[0027] また、本発明の他の一手段に係る量子カスケードレーザ素子は、基板、バッファ層 、第一のコンタクト層、第一のクラッド層、超格子層、第二のクラッド層、第二のコンタ タト層、順に積層してなり、かつ、超格子層は、 GaN井戸層及び InN井戸層を有する 井戸層と、井戸層を挟む一対の AlGaN障壁層と、を有することとする。 In addition, a quantum cascade laser device according to another means of the present invention includes a substrate, a buffer layer, a first contact layer, a first cladding layer, a superlattice layer, a second cladding layer, a second cladding layer, The contact layers are sequentially stacked, and the superlattice layer has a well layer having a GaN well layer and an InN well layer, and a pair of AlGaN barrier layers sandwiching the well layer.
発明の効果 The invention's effect
[0028] 以上本発明により、新規な半導体素子、これを用いた光スイッチング素子、量子力 スケードレーザを提供することができる。 As described above, the present invention can provide a novel semiconductor device, an optical switching device using the same, and a quantum force scaled laser.
発明を実施するための最良の形態 BEST MODE FOR CARRYING OUT THE INVENTION
[0029] 以下、本発明の実施の形態について図面を用いて詳細に説明する。但し、本発明 は多くの異なる実施の形態、実施例として表すことができ、本実施形態、実施例に狭 く限定されることはない。 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention can be expressed as many different embodiments and examples, and is not limited to the present embodiments and examples.
[0030] 図 1は、本実施形態に係る半導体素子 (ISBT光スィッチ)の概略図である。本実施 形態に係る半導体光素子 1は、図 1に示すとおり、基板 2上にバッファ層 3、クラッド層 4、超格子層 5、キャップ層 6を順次積層して構成されている。なお、本実施形態に係 る半導体素子は、光スイッチング素子として利用可能である。 FIG. 1 is a schematic diagram of a semiconductor element (ISBT optical switch) according to the present embodiment. As shown in FIG. 1, the semiconductor optical device 1 according to the present embodiment is configured by sequentially stacking a buffer layer 3, a cladding layer 4, a superlattice layer 5, and a cap layer 6 on a substrate 2. The semiconductor element according to this embodiment can be used as an optical switching element.
[0031] 基板 2は、ノ ッファ層 3、クラッド層 4、超格子層 5等を成長させる基礎となるものであ つて、限定されるわけではないが例えばサファイア基板や SiC基板、 GaNバルタ、 A1 Nバルタ基板を用いることができ、また、その他の基板にハイドライド気相成長法 (HV PE)、有機金属気相成長法 (MOCVD)などにより GaN、 A1N結晶からなる層を積層 させたものも用いることができる。なお、基板 2の表面の極性や表面処理 (窒化処理) によりこの上に積層されていく層の極性が決定されていく力 表面の極性としては III 族極性面、 V族極性面のいずれであってもよぐ限定されない。また基板 2は、内部 電場の影響を小さくするために R面サファイア基板や A面や M面方向に成長した Ga N、選択成長手法などにより形成した(11— 22)面や(1— 101)面 GaN膜を用いるこ とがでさる。 [0031] The substrate 2 serves as a basis for growing the noffer layer 3, the clad layer 4, the superlattice layer 5 and the like, and is not limited to, for example, a sapphire substrate, a SiC substrate, a GaN barrier, A1 N-balta substrates can be used, and other substrates with GaN and A1N crystal layers deposited by hydride vapor phase epitaxy (HV PE), metal organic chemical vapor deposition (MOCVD), etc. be able to. Note that the polarity of the surface of the substrate 2 and the polarity of the layer laminated on it by the surface treatment (nitriding treatment) are determined. The surface polarity can be either a group III polar surface or a group V polar surface. It is not limited. Substrate 2 is formed using an R-plane sapphire substrate, GaN grown in the A-plane or M-plane direction, or a selective growth technique to reduce the effect of the internal electric field (11-22) or (1-101) Surface GaN film can be used.
[0032] ノ ッファ層 3は、結晶品質の良い超格子層 5を成長させるためのものであって、上記 機能を奏する限りにおいて限定されることなく種々のものを採用することができるが、
例えば GaN結晶や A1N結晶、 AlGaN混晶などを好適に用いることができる。 [0032] The noffer layer 3 is for growing the superlattice layer 5 with good crystal quality, and various types can be adopted without being limited as long as it exhibits the above functions. For example, a GaN crystal, A1N crystal, AlGaN mixed crystal, or the like can be suitably used.
[0033] クラッド層 4は、電子を効率よく超格子層 5に閉じ込め、光スイッチングに必要な光 パワーを最低限に抑えるものであって、限定されることなく種々のものを採用すること ができる力 例えば AlGaN混晶ゃ GaN結晶、 A1N結晶などを好適に用いることがで きる。 [0033] The clad layer 4 is for confining electrons efficiently in the superlattice layer 5 and minimizing the optical power required for optical switching, and various types can be adopted without limitation. For example, AlGaN mixed crystal, GaN crystal, A1N crystal, etc. can be used preferably.
[0034] 超格子層 5は、一対の GaN井戸層 51 la、 b及びこの一対の GaN井戸層の間に挟 まれた InN井戸層 512を有する井戸層 51と、井戸層 51を挟む一対の AlGaN障壁層 52a、 bと、力もなる量子井戸構造 53を一周期とし、これをスぺーサ一層 54を介して 複数繰り返して構成されている。図 2に本実施形態に係る超格子層 5の断面概略図 を示す。 The superlattice layer 5 includes a pair of GaN well layers 51 la and b, and a well layer 51 having an InN well layer 512 sandwiched between the pair of GaN well layers and a pair of AlGaN sandwiching the well layer 51. The barrier layers 52a and 52b and the quantum well structure 53, which is also a force, are formed as one cycle, and this is repeated a plurality of times through the spacer layer 54. FIG. 2 shows a schematic cross-sectional view of the superlattice layer 5 according to the present embodiment.
[0035] 一対の GaN井戸層 51 la、 bは、 Si等の不純物がドープされた GaN結晶を含む層 である。 GaN井戸層 511a、 bの組成は GaNのみからなる層であってもよぐ他の III 族元素、例えば Inや A1を含んでもよい。ただし、この場合 Ga以外に含まれる元素の 割合としては III族元素全量に対し、 0. 5より少ないことが好ましい。 GaN井戸層 511 a、 bの厚さは、限定されるわけではないが、例えば 0. 5nm以上 5nm以下であること が好ましぐ 0. 5nm以上 2nm以下であることがより好ましい。なお、本実施形態に係 る半導体素子においては、一対の GaN井戸層 51 la、 b及び InN井戸層 512の厚さ の合計 (一対の AlGaN障壁層 52a、 bの間の距離)を変えることでサブバンド間のェ ネルギーを制御することが可能であり、限定されるわけではないが、合計 lnm以上 2 Onm以下の範囲内にあることが好ましぐ lnm以上 5nm以下であることがより好まし い。なお、サブバンド間遷移ではサブバンドの第 1準位力 第 2準位へと電子が遷移 することで吸収が起こるため、 n型半導体層とすることで第 1準位に多数の電子を存 在させサブバンド間吸収を可能とする。よって Si等の不純物を n型半導体制御のため にドープする。 [0035] The pair of GaN well layers 51la and b are layers including a GaN crystal doped with an impurity such as Si. The composition of the GaN well layers 511a, b may include other group III elements such as In or A1 even if the composition is only a GaN layer. However, in this case, the ratio of elements other than Ga is preferably less than 0.5 with respect to the total amount of Group III elements. The thickness of the GaN well layers 511a and b is not limited, but is preferably 0.5 nm or more and 5 nm or less, for example, more preferably 0.5 nm or more and 2 nm or less. In the semiconductor device according to the present embodiment, the total thickness of the pair of GaN well layers 51 la and b and the InN well layer 512 (the distance between the pair of AlGaN barrier layers 52 a and b) is changed. It is possible to control the energy between subbands, and it is not limited, but it is preferable that the total is within the range of 1 nm or more and 2 Onm or less. It is more preferable that the energy is 1 nm or more and 5 nm or less. Yes. Note that in the transition between subbands, absorption occurs due to the transition of electrons to the first level force of the subband and the second level. Therefore, by using an n-type semiconductor layer, a large number of electrons exist in the first level. Allows intersubband absorption. Therefore, impurities such as Si are doped to control the n-type semiconductor.
[0036] InN井戸層 512は、伝導帯バンドオフセット量の増大と AlGaN障壁層 511とは逆の 圧縮歪を有することによる歪補償効果を得ることができる層である。 InN井戸層 512 の糸且成は InNのみからなる層であってもよぐ他の ΠΙ族元素、例えば Gaを含んでもよ い。ただし、この場合 In以外に含まれる元素の割合としては ΠΙ族元素全量に対し、 0
. 1より少ないことが好ましい。 InN井戸層の厚さとしては、限定されるわけではないが 2分子厚以下であることが好ましぐ 1分子厚以下であることがより好ましい。これは、 通常 InN結晶と GaN結晶は約 11 %の格子不整合度を有して!/ヽるものの、 InN井戸 層 53の厚さを十分に薄くすることで格子緩和を起こさず成長させることが可能となる と考えられるためである。ここで「分子厚」とは、 In原子と N原子とで形成する分子の長 さを意味する。限定されるわけではないが、例えば c軸方向に成長する結晶の場合は 結晶格子における c軸の長さの半分を意味する。上述したように GaN上に成長した In Nの格子緩和を起こさない最大厚さ(以下「臨界膜厚」という。)は 1〜2分子厚であり 、このような厚さ以下の膜厚制御が実現できれば格子緩和による欠陥発生を防ぎ、 結晶品質の高い超格子層の実現が可能となる。逆に言えば、これ以上の厚さで InN 層成長を行うと結晶中にはミスフィット転位が発生し、結晶品質の大幅な悪ィ匕が懸念 される。なお、ここにおいて、 InN井戸層の厚さを分数分子厚とすることもできる。「分 数分子厚」とは InN層が面状均一に存在するのではなぐ厚さ 1分子厚程度の InNが 島状に分散して形成されて ヽる状態を指す。このような InN分数分子厚 ZGaN井戸 層 ZAIGaN障壁層にお 、ても、上述したサブバンド間遷移波長の短波長化や歪補 償構造の形成が可能である。 The InN well layer 512 is a layer that can obtain a strain compensation effect due to an increase in the conduction band offset amount and a compressive strain opposite to that of the AlGaN barrier layer 511. The thread of the InN well layer 512 may be a layer composed only of InN, or may contain other group elements such as Ga. However, in this case, the percentage of elements other than In is 0 Preferably less than 1. The thickness of the InN well layer is not limited, but is preferably 2 molecular thickness or less, more preferably 1 molecular thickness or less. This is because InN crystals and GaN crystals usually have a lattice mismatch of about 11%! / Although they can grow without causing lattice relaxation by making the InN well layer 53 sufficiently thin. This is because it is considered possible. “Molecular thickness” here means the length of the molecule formed by In and N atoms. Although not limited, for example, in the case of a crystal growing in the c-axis direction, it means half the length of the c-axis in the crystal lattice. As described above, the maximum thickness (hereinafter referred to as “critical film thickness”) of In N grown on GaN that does not cause lattice relaxation is 1 to 2 molecular thickness. If this can be realized, defects due to lattice relaxation can be prevented and a superlattice layer with high crystal quality can be realized. Conversely, if an InN layer is grown at a thickness greater than this, misfit dislocations will occur in the crystal, and there is a concern that the crystal quality will be greatly degraded. Here, the thickness of the InN well layer may be a fractional molecular thickness. “Fractional molecular thickness” refers to a state in which InN with a thickness of about 1 molecule is dispersed and formed in islands, in which the InN layer does not exist evenly. Even in such an InN fractional molecular thickness ZGaN well layer ZAIGaN barrier layer, the above-described intersubband transition wavelength can be shortened and a strain compensation structure can be formed.
[0037] 一対の AlGaN障壁層 511a、 51 lbは、 A1N結晶と GaN結晶との混晶層である。 A1 GaN障壁層の組成は具体的には Al Ga Nと表すことができ、 xは 0より大きく 1以 下の値をとる力 好ましくは 0. 5以上 1以下である。一対の AlGaN障壁層 51 la、 51 lbの厚さとしては、限定されるわけではないが、 lnm以上 50nm以下であることが好 ましぐ lnm以上 5nm以下であることがより好ましい。 [0037] The pair of AlGaN barrier layers 511a and 51 lb are mixed crystal layers of A1N crystal and GaN crystal. Specifically, the composition of the A1 GaN barrier layer can be expressed as AlGaN, and x is a force that is larger than 0 and takes a value of 1 or less, preferably 0.5 or more and 1 or less. The thickness of the pair of AlGaN barrier layers 51 la and 51 lb is not limited, but is preferably 1 nm or more and 50 nm or less, more preferably 1 nm or more and 5 nm or less.
[0038] スぺーサ一層 54は、超格子周期数増加に伴うクラック発生を防止する機能を有す る層であって、限定されるわけではないが、例えば GaNで構成されることが好ましい 。またこの厚さとしては、上記機能を奏する限り限定されるわけではないが、 lOnm以 上 50nm以下であることが好ましい。このようにすることで、歪の蓄積を防ぎ、超格子 周期数増加に伴うクラック発生が起きにくくなり、吸収量の高い ISBT構造の実現、 1 μ m以下の ISBT波長がより容易に実現可能となる。なおスぺーサ一層 56を介して 積層される数は、限定されるわけではないが 10周期以上あることが好ましい。周期数
が増加することにより総層厚増加による吸収量増加が期待されるが、層厚増加に伴 いクラックの発生が懸念される点は考慮すべきである。 [0038] Spacer layer 54 is a layer having a function of preventing the occurrence of cracks accompanying an increase in the number of superlattice periods, and is not limited, but is preferably composed of, for example, GaN. Further, the thickness is not limited as long as it exhibits the above function, but it is preferably lOnm or more and 50 nm or less. In this way, strain accumulation is prevented, cracks are less likely to occur as the number of superlattice periods increases, and an ISBT structure with a high absorption amount can be realized, and an ISBT wavelength of 1 μm or less can be realized more easily. Become. The number of layers stacked via the spacer layer 56 is not limited, but is preferably 10 cycles or more. Number of cycles As the layer thickness increases, the amount of absorption is expected to increase due to the increase in the total layer thickness. However, it should be considered that there is concern about the generation of cracks as the layer thickness increases.
[0039] キャップ層 6は超格子層 5内に電子を効率よく閉じ込め、結晶品質を保持させる機 能を有する層であって、限定されることなく種々のものを採用することができるが、例 えば AlGaNや GaN、 A1Nなどを好適に用いることができる。 [0039] The cap layer 6 is a layer having a function of efficiently confining electrons in the superlattice layer 5 and maintaining the crystal quality, and various types can be adopted without limitation. For example, AlGaN, GaN, A1N, etc. can be suitably used.
[0040] ここで半導体光機能素子におけるエネルギーバンドの模式図を図 3に示す。図 3 (a )は、 InN層を含まない GaNZAIN超格子における ISBT構造のバンド図であり、図 3 (b)は本実施形態に係る InNZGaNZAIN超格子における ISBT構造のバンド図で ある。なお図中におけるバンドの傾きは、 C軸方向の成長を仮定した際のピエゾ効果 や自発分極による内部電場の影響を考慮した結果である。 Here, FIG. 3 shows a schematic diagram of energy bands in the semiconductor optical functional device. FIG. 3 (a) is a band diagram of the ISBT structure in the GaNZAIN superlattice not including the InN layer, and FIG. 3 (b) is a band diagram of the ISBT structure in the InNZGaNZAIN superlattice according to the present embodiment. The slope of the band in the figure is the result of considering the influence of the internal electric field due to the piezo effect and spontaneous polarization when assuming growth in the C-axis direction.
[0041] 図 3 (a)、(b)から明らかなように、 GaNZAIN構造では 1. 8eV程度のバンドオフセ ット量であるのに対し、 InN層を挿入した InNZGaNZAIN構造ではより大きな伝導 帯バンドオフセット量 (〜3. 5eV)を得ることができる。 InN井戸層は非常に薄膜では あるが、サブバンド間準位エネルギーに大きく影響し、特に第 1準位を大きく下側に シフトさせることができ、 ISBT波長をより短波長化させることができると考えられる。特 に、可視光域力 近赤外域まで ISBT吸収を起こさせることまでも可能となる。 [0041] As can be seen from Figs. 3 (a) and (b), the GaNZAIN structure has a band offset of about 1.8 eV, whereas the InNZGaNZAIN structure with the InN layer inserted has a larger conduction band. An offset amount (~ 3.5eV) can be obtained. Although the InN well layer is a very thin film, it greatly affects the intersubband level energy. In particular, the first level can be greatly shifted downward, and the ISBT wavelength can be further shortened. Conceivable. In particular, it is possible to cause ISBT absorption up to the near infrared range.
[0042] また、 InN井戸層を挿入することで伝導帯バンドオフセット量を十分大きくとれる(〜3 . 5eV)ため、本実施形態に係る半導体光機能素子によると ISBT超格子の層厚制 御を容易にすることができる。例えば有機金属気相成長法で作製した窒化物系 ISB T構造では MBE法に比べ、厳密な膜厚制御が難しぐ 1. 55 /z m帯をカバーするこ とができず、最短波長は現在 2 m程度である。よって、 1. 55 /z m帯をカバーする窒 化物系 ISBT t造はすべて MBE法によって形成せざるを得ないが、本実施形態に 係る構造によると GaN井戸層は〜 3nmで 1. 55 m帯をカバーでき、 InN層を挿入 しない場合 (2nm以下)に比べて層厚制御の厳密性が緩和され、有機金属気相成長 法でも 1. 55 m帯をカバーする窒化物系 ISBT構造を実現できるという利点がある [0042] In addition, since the conduction band offset amount can be sufficiently increased by inserting an InN well layer (-3.5 eV), the layer thickness control of the ISBT superlattice can be performed according to the semiconductor optical functional device according to the present embodiment. Can be easily. For example, the nitride ISBT structure fabricated by metalorganic vapor phase epitaxy cannot cover the 1.55 / zm band, which is more difficult to control strictly than the MBE method, and the shortest wavelength is currently 2 m. Therefore, all of the nitride-based ISBT t structures covering the 1.55 / zm band must be formed by the MBE method, but according to the structure according to this embodiment, the GaN well layer has a thickness of ~ 3 nm and a 1.55 m band. Compared to the case where no InN layer is inserted (2 nm or less), the strictness of layer thickness control is relaxed, and the metal-organic vapor phase epitaxy can realize a nitride-based ISBT structure that covers the 1.55 m band. There is an advantage
[0043] またここで GaNZAIN超格子、 InNZGaNZAIN超格子それぞれの ISBT波長の GaN井戸層厚依存性を理論計算により求めた。この結果を図 4に示す。なお図中、
横軸は GaN井戸層の厚さを、縦軸はサブバンド間遷移エネルギーをそれぞれ示して いる。また本計算においては InN井戸層の厚さは 1分子厚とし、かつ GaN井戸層の 中心にあると仮定して計算して 、る。 [0043] Here, the dependence of the ISBT wavelength on the GaN well layer thickness of the GaNZAIN superlattice and InNZGaNZAIN superlattice was determined by theoretical calculation. The results are shown in Fig. 4. In the figure, The horizontal axis shows the thickness of the GaN well layer, and the vertical axis shows the intersubband transition energy. In this calculation, the thickness of the InN well layer is assumed to be one molecular thickness and is calculated at the center of the GaN well layer.
[0044] 図 4で示すとおり、 GaNZAIN超格子、 InNZGaNZAIN超格子!/、ずれにお 、て も GaN井戸層厚が減少するに伴い ISBT波長は短波長となっていくが、同じ GaN井 戸層厚の場合、 InNZGaNZAIN超格子の方がサブバンド間遷移エネルギーが大 きぐより短波長となっている。特に、 GaNZAIN超格子では GaN井戸層厚が 1. 5n mである場合約 1. 2 ^ πι (1. 05eV)程度の ISBT波長となるが InNZGaNZAlGa N超格子では 650nm(l. 9eV)程度の ISBT波長を得ることができる。即ち、本実施 形態に係る半導体光素子によると、可視光領域での ISBT波長まで短波長化ができ ることがゎカゝる。これは本発明で提案する構造が、現在まで主に 3 m以上の長波長 側で研究が盛んであった量子カスケードレーザの動作波長を更に短波長化(1. 55 m帯や可視光城まで拡張)する上で非常に有望であることを示している。 [0044] As shown in Fig. 4, the GaNZAIN superlattice, InNZGaNZAIN superlattice! /, And the deviation, the ISBT wavelength becomes shorter as the GaN well layer thickness decreases, but the same GaN well layer. In the case of thickness, the InNZGaNZAIN superlattice has a shorter wavelength than the transition energy between subbands. In particular, when the GaN well layer thickness is 1.5 nm for the GaNZAIN superlattice, the ISBT wavelength is about 1.2 ^ πι (1.05 eV), whereas for the InNZGaNZAlGa N superlattice, the ISBT is about 650 nm (l. Wavelength can be obtained. That is, the semiconductor optical device according to the present embodiment can reduce the wavelength to the ISBT wavelength in the visible light region. This is because the structure proposed in the present invention has further shortened the operating wavelength of quantum cascade lasers that have been actively studied mainly on the long wavelength side of 3 m or more (to 1.55 m band and visible light source). It is very promising for expansion.
[0045] なお図 4では本実施形態に係る積層構造すなわち InN井戸層 512が GaN井戸層 511a, bの間、より具体的にはその中心においた場合の ISBT波長を計算したもので あるが、 GaN井戸層 511a、 b中の InN井戸層 512の位置によってサブバンド内の電 子の波動関数は変化し、 ISBT波長、遷移確率の制御が可能である。つまり、 InN井 戸層 512の位置は GaN井戸層 51 la、 bの中心以外でも配置することが可能であり、 その位置によりさらなる遷移波長制御、波動関数制御が可能となる。例えば図 5で示 すように、 InN井戸層 512が GaN井戸層に挟まれていない構造も可能ではある。ま た、 InN井戸層も一対の AlGaN層の間に複数配置された構成も可能である。 In FIG. 4, the ISBT wavelength when the stacked structure according to the present embodiment, that is, the InN well layer 512 is located between the GaN well layers 511a and b, more specifically at the center thereof, is calculated. The wave function of the electrons in the subband changes depending on the position of the InN well layer 512 in the GaN well layers 511a and b, and the ISBT wavelength and transition probability can be controlled. In other words, the InN well layer 512 can be placed at positions other than the centers of the GaN well layers 51 la and b, and further transition wavelength control and wave function control can be performed depending on the position. For example, as shown in FIG. 5, a structure in which the InN well layer 512 is not sandwiched between GaN well layers is also possible. In addition, a plurality of InN well layers may be arranged between a pair of AlGaN layers.
[0046] 図 6は InNZGaNZAIN超格子における InN井戸層 512の位置による波動関数の 変化の理論的予測を示す。図では伝導帯、価電子帯のポテンシャル中にできる波動 関数( I Ψ2 I )の計算結果を示す。ここで GaN井戸層 511の厚さは 8分子厚とし、 A1 N層厚は 4nmとした。 InN井戸層の位置により伝導帯中のサブバンド内の波動関数 および価電子帯中の波動関数が大きく変化することがわかる。 InN井戸層の位置に よりサブバンド間遷移波長が変化し、さらに電子一ホールの遷移確率も変化し、 InN 井戸層を挿入して ヽな 、超格子に比べ、中心位置よりずらして InN井戸層を挿入し
た構造では遷移確率が大きく改善することがわかる。つまりこれは伝導帯と価電子帯 間の遷移確率の飛躍的改善においても InNZGaNZAIN超格子が効果的であるこ とが予測される。 [0046] FIG. 6 shows a theoretical prediction of the change of the wave function depending on the position of the InN well layer 512 in the InNZGaNZAIN superlattice. The figure shows the calculation result of the wave function (I Ψ 2 I) generated in the conduction band and valence band potentials. Here, the GaN well layer 511 has a thickness of 8 molecules, and the A1 N layer has a thickness of 4 nm. It can be seen that the wave function in the subband in the conduction band and the wave function in the valence band vary greatly depending on the position of the InN well layer. The inter-subband transition wavelength changes depending on the position of the InN well layer, and the transition probability of one electron hole also changes.InN well layers are inserted and shifted from the center position compared to the superlattice. Insert It can be seen that the transition probability is greatly improved in the structure. In other words, it is predicted that the InNZGaNZAIN superlattice is also effective in dramatically improving the transition probability between the conduction band and the valence band.
[0047] 以上、本実施形態に係る半導体素子は、 ISBT波長をより短波長化でき、歪補償構 造を形成することにより製造しやす!ゝと ゝぅ効果を奏する。 As described above, the semiconductor element according to the present embodiment can shorten the ISBT wavelength, and can be manufactured easily by forming a distortion compensation structure.
[0048] 次に、本実施形態に係る半導体光機能素子の製造工程について説明する。本実 施形態に係る半導体光機能素子の製造工程は、少なくとも、基板 2上にバッファ層 3 を形成する工程、クラッド層 4を形成する工程、超格子層 5を形成する工程、キャップ 層 6を形成する工程、を有して構成されている。 Next, a manufacturing process of the semiconductor optical functional device according to the present embodiment will be described. The manufacturing process of the semiconductor optical functional device according to this embodiment includes at least the step of forming the buffer layer 3 on the substrate 2, the step of forming the cladding layer 4, the step of forming the superlattice layer 5, and the cap layer 6. Forming the process.
[0049] ノ ッファ層 3を形成する工程は、限定されるわけではないが例えば有機金属成長法[0049] The step of forming the noffer layer 3 is not limited, but, for example, an organic metal growth method.
、 MBE法又はパルスレーザー堆積法を用いることができる。なお、基板 1として GaN バルタ、 A1Nバルタ基板や GaN、 A1N層を形成した基板を用いる場合、本工程は省 略可能である。 MBE or pulsed laser deposition can be used. Note that this step can be omitted when the substrate 1 is a GaN buttery or A1N buttery substrate or a substrate on which a GaN or A1N layer is formed.
[0050] クラッド層 4を形成する工程としては、限定されるわけではないが、有機金属気相成 長法、 MBE法、ノ ルスレーザー堆積法を用いることができる。 MBE法で形成する場 合、基板温度は形成する層の材料によって異なるため適宜調整が可能であるが、例 えばクラッド層 4として GaNを用いる場合、 600°C以上 800°C以下であることが好まし い。また MBE法で形成する場合、クラッド層形成の前に有機洗浄、熱処理を行って おくことも好ましい。この熱処理の温度も形成する層の材料によって異なるが、 GaN 層を形成する場合は 800°C以上 1000°C以下が好ましい範囲である。 [0050] The step of forming the clad layer 4 is not limited, and a metal organic vapor phase growth method, an MBE method, or a laser beam deposition method can be used. When formed by the MBE method, the substrate temperature varies depending on the material of the layer to be formed and can be adjusted as appropriate.For example, when GaN is used as the cladding layer 4, it may be 600 ° C or higher and 800 ° C or lower. I like it. In the case of forming by the MBE method, it is also preferable to perform organic cleaning and heat treatment before forming the cladding layer. The temperature of this heat treatment also varies depending on the material of the layer to be formed, but when a GaN layer is formed, a preferable range is 800 ° C. or higher and 1000 ° C. or lower.
[0051] 超格子層 5を形成する工程は、更に AlGaN障壁層 511を形成する工程、 GaN井 戸層 512を形成する工程、 InN井戸層 513を形成する工程、スぺーサ一層 52を形 成する工程、を有している。 [0051] The step of forming the superlattice layer 5 further includes the step of forming the AlGaN barrier layer 511, the step of forming the GaN well layer 512, the step of forming the InN well layer 513, and the spacer layer 52. The process of carrying out.
[0052] AlGaN障壁層 52a、 bを形成する工程としては、限定されるわけではないが、有機 金属気相成長法、 MBE法、ノ ルスレーザー堆積法を用いることができる。 MBE法で 形成する場合、材料等により条件は適宜調整可能であり限定されるわけではないが 、 600°C以上 900°C以下であることが好ましぐ 600°C以上 700°C以下であることがよ り好ましい。
[0053] GaN井戸層 511a、 bを形成する工程は、限定されるわけではないが有機金属気相 成長法、 MBE法、ノ ルスレーザー堆積法を用いることができる。 MBE法で形成する 場合、材料等により条件は適宜調整可能であり限定されるわけではないが、 600°C 以上 900°C以下であることが好ましぐ 600°C以上 700°C以下であることがより好まし い。 [0052] The step of forming the AlGaN barrier layers 52a and 52b is not limited, but a metal organic vapor phase epitaxy method, an MBE method, or a laser beam deposition method can be used. When forming by the MBE method, the conditions can be appropriately adjusted depending on the material and the like, but are not limited, but it is preferably 600 ° C or higher and 900 ° C or lower, but 600 ° C or higher and 700 ° C or lower. It is more preferable. [0053] The step of forming the GaN well layers 511a and b is not limited, and a metal organic vapor phase epitaxy method, an MBE method, and a laser beam deposition method can be used. When forming by the MBE method, the conditions can be appropriately adjusted depending on the material, etc., and are not limited, but it is preferably 600 ° C or higher and 900 ° C or lower, but 600 ° C or higher and 700 ° C or lower. Is more preferred.
[0054] InN井戸層 512を形成する工程は、限定されるわけではないが、 MBE法、パルス レーザー堆積法を用いることができる。 MBE法で形成する場合、材料等により条件 は適宜調整可能であり限定されるわけではないが、 600°C以上 700°C以下であるこ とが好ま ヽ。本実施形態に係る InN井戸層 512の成長温度は In極性 InN単膜の成 長限界温度よりも 150°C以上高い。 InN層厚が 2分子厚以下と非常に薄膜の場合、 バルタ InNと違ってより高温でも成長が可能である。なお InN井戸層 512を形成する 工程は、原子 ·分子レベルの超薄膜制御において課題を残すが窒化物半導体素子 の成長に一般的に使われて 、る有機金属気相成長法でも可能である。 [0054] The process of forming the InN well layer 512 is not limited, but an MBE method or a pulsed laser deposition method can be used. When forming by the MBE method, the conditions can be appropriately adjusted depending on the material and the like, but are not limited, but it is preferably 600 ° C or more and 700 ° C or less. The growth temperature of the InN well layer 512 according to this embodiment is 150 ° C. or more higher than the growth limit temperature of the In-polar InN single film. When the InN layer is very thin, with a thickness of less than 2 molecules, unlike Balta InN, it can be grown at higher temperatures. The process of forming the InN well layer 512 remains a problem in controlling the ultrathin film at the atomic and molecular level, but can also be performed by metal organic vapor phase epitaxy, which is generally used for the growth of nitride semiconductor devices.
[0055] スぺーサ一層 54を形成する工程は、限定されるわけではないが、有機金属気相成 長法、 MBE法、ノ ルスレーザー堆積法を用いることができる。 MBE法で形成する場 合、基板温度は形成する層の材料によって異なるため適宜調整が可能であるが、例 えばクラッド層 4として GaNを用いる場合、 600°C以上 800°C以下であることが好まし い。 [0055] The step of forming the spacer layer 54 is not limited, and a metal organic vapor phase growth method, an MBE method, and a laser laser deposition method can be used. When formed by the MBE method, the substrate temperature varies depending on the material of the layer to be formed and can be adjusted as appropriate.For example, when GaN is used as the cladding layer 4, it may be 600 ° C or higher and 800 ° C or lower. I like it.
[0056] キャップ層 6を形成する工程は、限定されるわけではないが、有機金属気相成長法 、 MBE法、ノ ルスレーザー堆積法を用いることができる。 MBE法で形成する場合、 材料等により条件は適宜調整可能であり限定されるわけではないが、 600°C以上 90 0°C以下であることが好ましぐ 600°C以上 700°C以下であることがより好ましい。 [0056] The step of forming the cap layer 6 is not limited, but metal organic vapor phase epitaxy, MBE, and laser laser deposition can be used. When forming by the MBE method, the conditions can be adjusted as appropriate depending on the material, etc., and are not limited, but it is preferably 600 ° C or higher and 900 ° C or lower, and 600 ° C or higher and 700 ° C or lower. More preferably.
[0057] 以上の工程により、本実施形態に係る半導体素子を製造することができる。 [0057] The semiconductor device according to the present embodiment can be manufactured through the above steps.
[0058] (実施形態 2) [Embodiment 2]
本実施形態は、超格子層 5において実施形態 1と異なるものの、それ以外は実施形 態 1と同様の構成である。図 7に本実施形態に係る半導体光機能素子の超格子層 5 の断面概略図を示す。本実施形態では異なる超格子層 5の構成について説明し、そ の他の構成については同様の構成であるため、説明を省略する。
[0059] 本実施形態に係る超格子層 5は、 GaN井戸層 511a、 b及び InN井戸層を有する井 戸層 51と、この井戸層 51を挟む一対の AlGaN障壁層 52a、 bと、を有する量子井戸 構造 53を一周期としている点において共通している力 実施形態 1とは異なりスぺー サ一層 52を介さず、隣り合う量子井戸構造における AlGaN障壁層を共通のものとし て形成されている。 Although the present embodiment is different from the first embodiment in the superlattice layer 5, the configuration other than that is the same as that of the first embodiment. FIG. 7 shows a schematic cross-sectional view of the superlattice layer 5 of the semiconductor optical functional device according to the present embodiment. In the present embodiment, the configuration of the different superlattice layer 5 will be described, and the other configurations are the same, and thus the description thereof will be omitted. The superlattice layer 5 according to the present embodiment includes a well layer 51 having a GaN well layer 511a, b and an InN well layer, and a pair of AlGaN barrier layers 52a, b sandwiching the well layer 51. Force common to the point that the quantum well structure 53 has one period Unlike the first embodiment, the AlGaN barrier layer in the adjacent quantum well structure is formed in common without using the spacer layer 52. .
[0060] 本実施形態によると、スぺーサ一層を用いないため成長時間の大幅な短縮という 効果を奏することができる。なお、本実施形態における半導体光機能素子は、スぺー サ一層を形成する工程を省略することで製造することができる。 [0060] According to this embodiment, since one spacer is not used, the effect of greatly shortening the growth time can be achieved. Note that the semiconductor optical functional device in the present embodiment can be manufactured by omitting the step of forming the spacer layer.
[0061] 以上により、本実施形態によっても新規な半導体光機能素子を提供することができ る。 As described above, a novel semiconductor optical functional device can also be provided by this embodiment.
[0062] (実施形態 3) [0062] (Embodiment 3)
本実施形態は、量子カスケードレーザ素子についての実施形態であり、超格子層 5 に電子を注入するための手段を設けた以外は実施形態 1と同様の構成である。図 8 に本実施形態に係る量子カスケードレーザ素子の断面概略図を示す。なお、ここで は異なる構成についてのみ説明し、その他の構成については同様の構成であるため 、説明を省略する。 The present embodiment is an embodiment of a quantum cascade laser element, and has the same configuration as that of the first embodiment except that means for injecting electrons into the superlattice layer 5 is provided. Figure 8 shows a schematic cross-sectional view of the quantum cascade laser device according to this embodiment. Here, only different configurations will be described, and the other configurations are the same configurations, and thus description thereof will be omitted.
[0063] 本実施形態に係る量子カスケードレーザ素子 11は、図 8に示すとおり、基板 2上に バッファ層 3、コンタクト層 7a、クラッド層 4a、超格子層 5、クラッド層 4b、コンタクト層 7 bを順次積層して構成されている。また、コンタクト層 7a、 7bのそれぞれは第一の電 極 8a、第二の電極 8bにそれぞれ接続されている。 As shown in FIG. 8, the quantum cascade laser device 11 according to this embodiment includes a buffer layer 3, a contact layer 7a, a cladding layer 4a, a superlattice layer 5, a cladding layer 4b, and a contact layer 7b on a substrate 2. Are sequentially laminated. The contact layers 7a and 7b are connected to the first electrode 8a and the second electrode 8b, respectively.
[0064] コンタクト層 7a及び 7bは、第一および二の電極 8a、 bとの電気的な接続を確保する ことができる層であり、限定されるわけではないが、例えば GaN、 InGaN又は AlGaN に Si等を不純物として注入した層を好適に用いることができる。 [0064] The contact layers 7a and 7b are layers that can ensure electrical connection with the first and second electrodes 8a and 8b, and are not limited to, but, for example, GaN, InGaN, or AlGaN. A layer in which Si or the like is implanted as an impurity can be preferably used.
[0065] 第一、二の電極 8aおよび bは、導電性を有する限りにおいて限定されるわけではな V、が、例えばアルミニウム (A1)やチタン (Ti)、金 (Au)等から構成される電極材料を 用!/、ることができる。 [0065] The first and second electrodes 8a and b are not limited as long as they have electrical conductivity, but are composed of, for example, aluminum (A1), titanium (Ti), gold (Au), or the like. You can use electrode materials!
[0066] 本実施形態に係る量子カスケードレーザ素子は、以上の構成において、超格子周 期を変化させ伝導帯内のサブバンド準位位置を制御し電子注入層と発光層を設ける
ことにより、サブバンド準位間に反転分布を形成することでレーザ発光することができ る。し力も、本実施形態に係る量子カスケードレーザ素子によると、発光に寄与した電 子は再度発光に寄与することができるので高外部量子効率、高出力化に適しており 、レーザ発振波長は超格子の周期を変化させるだけで容易に制御でき、長波長域( 例えばテラへルツ域)などへのレーザ発振波長の長波長化は材料的な制約はなく設 計が可能である。 [0066] In the quantum cascade laser device according to the present embodiment, the electron injection layer and the light emitting layer are provided by changing the superlattice period and controlling the subband level position in the conduction band in the above configuration. Thus, laser emission can be performed by forming an inversion distribution between the subband levels. In addition, according to the quantum cascade laser element according to the present embodiment, the electrons that contributed to the light emission can contribute to the light emission again, which is suitable for high external quantum efficiency and high output. It is easy to control by changing the period of the laser, and it is possible to design the laser oscillation wavelength longer to a longer wavelength range (for example, terahertz range) without any material restrictions.
[0067] 以上により、本実施形態によっても新規な量子カスケードレーザ素子を提供するこ とがでさる。 [0067] As described above, a novel quantum cascade laser device can also be provided by this embodiment.
実施例 Example
[0068] 以上の実施形態に係る半導体素子の効果を確認すベぐ実際に InNZGaNZAl N超格子構造を作成し、 ISBT吸収を確認した。以下に説明する。 [0068] InNZGaNZAl N superlattice structures were actually created to confirm the effects of the semiconductor elements according to the above embodiments, and ISBT absorption was confirmed. This will be described below.
[0069] (サンプル 1の製造) [0069] (Production of sample 1)
まず、 GaN井戸層中の InN井戸層の形成について構造を MBE法により作製し評 価した。本サンプルでは InN層形成の確認のための実験であって AlGaN障壁層形 成は省略した。図 9に 600°Cで成長した 1分子厚 InNZGaN超格子構造の断面 TE M像を示す。本断面 TEM像によると、原子層レベルで急峻な界面粗さを持つ 1分子 厚 InN層が実現できていること、 14nmの GaN層が実現できていることがわかった。 またここでは新たな欠陥の発生などは見られず、非常に高品質な超格子構造が形成 されていることが確認できた。このような超平坦'超薄膜 InN層厚制御は厳密な膜厚' 供給速度制御により実現されており、これらの技術を用いることで 1分子厚 InNZGa NZAlGaN超格子構造の作製ができる可能性を確認した。 First, the structure of the InN well layer in the GaN well layer was fabricated and evaluated by the MBE method. In this sample, it was an experiment to confirm the formation of the InN layer, and the formation of the AlGaN barrier layer was omitted. Figure 9 shows a cross-sectional TEM image of a single-molecule InNZGaN superlattice structure grown at 600 ° C. According to this cross-sectional TEM image, it was found that a single-molecule-thick InN layer with steep interface roughness at the atomic layer level could be realized, and a 14-nm GaN layer could be realized. Also, no new defects were found here, and it was confirmed that a very high quality superlattice structure was formed. Such ultra-flat 'ultra-thin InN layer thickness control is realized by strict film-thickness' supply rate control. Using these technologies, we confirmed the possibility of producing a single-molecule-thick InNZGa NZAlGaN superlattice structure. did.
[0070] (サンプル 2の製造) [0070] (Production of sample 2)
次に成長温度を 600°Cから 650°Cに昇温した構造の GaN井戸層中の InN井戸層 の形成にっ 、て評価した。なおこのサンプルでは InN層形成の確認のための実験と し AlGaN障壁層は形成しなかった。図 10に 650°Cで成長した 1分子厚 InNZGaN 超格子構造の断面 TEM像を示す。本実施例のサンプルでは InN層が面状均一に 存在するのではなく、厚さ 1分子厚程度の InNが島状に分散した InN層が形成され ていることがわかる。つまり分数分子厚の InNの形成が確認された。 600°Cで成長し
たサンプル 1の場合と比べて InN井戸層の形成が大きく異なるのは成長温度の差に 起因すると考えられる。 ΠΙ族極性 InNバルタの高温側臨界成長温度が 500°Cである ことを考慮すると、 650°Cの高温では成長とともに In原子や InNの熱的分解'熱的脱 離も起こっていると考えられる。本断面 TEM像によると、図 9の場合と同様、超格子 領域での新たな欠陥の発生などは見られず、非常に高品質な超格子構造が形成さ れて 、ることが確認できた。以上の結果から 650°Cと!、う比較的高温成長条件下でも 超薄膜の InN井戸層の導入が可能であり、これらの技術を用いることでサンプル 3の ように InNZGaNZAIN超格子の作製ができる可能性が確認できた。 Next, we evaluated the formation of an InN well layer in a GaN well layer with a structure in which the growth temperature was raised from 600 ° C to 650 ° C. In this sample, the AlGaN barrier layer was not formed as an experiment to confirm the formation of the InN layer. Figure 10 shows a cross-sectional TEM image of a single-molecule InNZGaN superlattice structure grown at 650 ° C. It can be seen that in the sample of this example, the InN layer does not exist uniformly in a planar shape, but an InN layer in which InN having a thickness of about one molecule is dispersed in an island shape is formed. In other words, formation of fractional molecular InN was confirmed. Grows at 600 ° C Compared to the case of Sample 1, the formation of the InN well layer is thought to be due to the difference in growth temperature. Considering that the high temperature critical growth temperature of barium polar InN Balta is 500 ° C, it is considered that thermal decomposition of the In atom and InN and thermal desorption occur at high temperature of 650 ° C. . According to this cross-sectional TEM image, as in the case of FIG. 9, the generation of new defects in the superlattice region was not observed, and it was confirmed that a very high quality superlattice structure was formed. . From the above results, it is possible to introduce an ultra-thin InN well layer even under relatively high temperature growth conditions at 650 ° C! By using these techniques, an InNZGaNZAIN superlattice can be fabricated as in Sample 3. The possibility was confirmed.
[0071] (サンプル 3の製造) [0071] (Production of Sample 3)
本サンプルでは有機金属気相成長法により C面サファイア上に成長した Ga極性 Ga N膜を基板として用いた。この GaN基板を有機洗浄した後、 MBE装置に導入し、 82 0°Cで熱処理後、 650°Cで InN (1分子厚) ZGaN (lnm) /A1N (3nm)の超格子構 造を A1N層を共通させつつ 100周期成長し、その上部にキャップ層として Ga極性 Ga N層を 20nm形成した。この超格子構造の模式図を図 11に示す。 In this sample, a Ga-polar GaN film grown on C-plane sapphire by metalorganic vapor phase epitaxy was used as the substrate. This GaN substrate is organically cleaned, then introduced into an MBE device, heat-treated at 820 ° C, and a superlattice structure of InN (single molecule) ZGaN (lnm) / A1N (3nm) at 650 ° C. A1N layer 100 periods of growth were made common, and a Ga-polar GaN layer of 20 nm was formed as a cap layer thereon. Figure 11 shows a schematic diagram of this superlattice structure.
[0072] (サンプル 3の X線回折測定結果) [0072] (X-ray diffraction measurement result of sample 3)
ここで図 12に 650°Cで成長したサンプル 3、 InN (1分子厚) /GaN (lnm) /A1N ( 3nm)超格子構造の X線回折測定結果を示す。なお、図 11に比較のため InN (1分 子厚)を挿入して 、な 、以外はサンプル 3と同様の条件で形成した GaN (lnm) /Al N (3nm)超格子構造の結果も同時に示しておく。二つの構造を比べると、周期構造 の形成を示すサテライトピークが明瞭に確認できる。またここではサテライトピークの 半値幅が非常に狭いことから急峻な界面が形成されていることがわかる。 InN (1分子 厚)を導入して ヽな 、サンプルに比べて、導入したサンプルにお 、てはより強!ヽサテ ライトピークが得られている。これは、 InN井戸層(1分子厚)を導入したことによる歪 補償効果により界面平坦性、結晶性が向上したことに起因していると考えられる。 Here, Fig. 12 shows the X-ray diffraction measurement results of sample 3, grown at 650 ° C, InN (single molecule thickness) / GaN (lnm) / A1N (3 nm) superlattice structure. For comparison, the results of the GaN (lnm) / Al N (3 nm) superlattice structure formed under the same conditions as in sample 3 except that InN (one molecular thickness) is inserted for comparison are also shown. I will show you. When the two structures are compared, a satellite peak indicating the formation of a periodic structure can be clearly seen. Here, it can be seen that since the full width at half maximum of the satellite peak is very narrow, a steep interface is formed. Compared to the sample that had been introduced with InN (single molecule thickness), the introduced sample had a stronger satellite peak. This is thought to be due to the improved interface flatness and crystallinity due to the strain compensation effect of introducing the InN well layer (single molecule thickness).
[0073] (吸収スペクトル測定結果) [0073] (Absorption spectrum measurement result)
図 13は、サンプル 3の表面に対し 60度の角度をもって入射させた p偏光による吸収 スペクトルを示す図である。なおここでも比較のため InN (1分子厚)を挿入して!/、な!/ヽ GaN (lnm) /A1N (3nm)超格子構造の吸収スペクトルも同時に示しておく。二つ
の構造から明瞭な ISBT吸収を観測することができた。具体的には、 GaNZAIN超 格子構造では ISBT吸収波長は 1. 48 mに観測された力 InNを挿入した InN ( 1 分子厚) ZGaN (lnm) ZAlN (3nm)超格子では 1. 49 μ m付近で ISBT吸収を確 認することができた。この結果は InN (1分子厚) ZGaNZAIN超格子構造が ISBT 過程を利用した超高速光スィッチ、量子カスケードレーザなどへの応用が十分可能 であることを示している。なおこの場合において、 GaN (lnm) ZAlN (3nm)超格子 に比べて短波長化されて 、な 、のは設計値に比べて実際の超格子の各層厚が厚 、 ことや、 1分子厚 InN層制御(1分子厚 InNの位置など)に問題があるものと考えられ る。 InN層の供給速度などの成長条件を最適化し、 1分子厚 InN制御手法技術を向 上させることにより短波長化が実現可能であると考えられる。 FIG. 13 is a diagram showing an absorption spectrum of p-polarized light incident on the surface of Sample 3 at an angle of 60 degrees. For comparison, here is also shown the absorption spectrum of the superlattice structure with InN (one molecular thickness) inserted! /, N! / ヽ GaN (lnm) / A1N (3 nm). two Clear ISBT absorption could be observed from the structure. Specifically, in the GaNZAIN superlattice structure, the ISBT absorption wavelength is observed at 1. 48 m. InN (single molecule thickness) ZGaN (lnm) ZAlN (3 nm) superlattice with an InN insertion of around 1.49 μm Successfully confirmed ISBT absorption. This result shows that the InN (single molecule thickness) ZGaNZAIN superlattice structure is sufficiently applicable to ultrafast optical switches and quantum cascade lasers using the ISBT process. In this case, the wavelength is shorter than that of the GaN (lnm) ZAlN (3 nm) superlattice, and the actual thickness of each superlattice is thicker than the design value. There seems to be a problem with layer control (position of single molecule InN, etc.). By optimizing the growth conditions such as the supply rate of the InN layer and improving the single-molecule-thickness InN control technique technology, it is considered possible to reduce the wavelength.
[0074] 以上の通り、本実施例により、上記実施形態に係る半導体光機能デバイスの効果 を達成することができるのを確認することができ、 1分子厚 InN層を導入した GaNZA IN超格子 ISBT構造を実現することができる。 [0074] As described above, according to this example, it can be confirmed that the effect of the semiconductor optical functional device according to the above embodiment can be achieved, and a GaNZA IN superlattice ISBT in which a single-molecule-thick InN layer is introduced. A structure can be realized.
産業上の利用可能性 Industrial applicability
[0075] 以上の通り、本発明は半導体光機能素子、超高速半導体光スィッチ、量子カスケ 一ドレーザとして産業上利用可能である。 As described above, the present invention can be industrially used as a semiconductor optical functional device, an ultrafast semiconductor optical switch, and a quantum cascade laser.
図面の簡単な説明 Brief Description of Drawings
[0076] [図 1]実施形態 1に係る半導体素子の断面概略図である。 FIG. 1 is a schematic sectional view of a semiconductor device according to a first embodiment.
[図 2]実施形態 1に係る半導体素子における超格子層の断面概略図である。 2 is a schematic cross-sectional view of a superlattice layer in a semiconductor device according to Embodiment 1. FIG.
[図 3]実施形態 1に係る半導体素子のエネルギーバンド図である。 FIG. 3 is an energy band diagram of the semiconductor element according to the first embodiment.
[図 4]理論計算により求めた実施形態 1に係る半導体光機能素子のサブバンド間遷 移エネルギーの井戸層厚依存性を示す図である。 FIG. 4 is a graph showing the dependence of inter-subband transition energy on the well layer thickness of the semiconductor optical functional device according to Embodiment 1 obtained by theoretical calculation.
[図 5]実施形態 1に係る半導体素子における他の例の超格子構造の断面概略図であ る。 FIG. 5 is a schematic cross-sectional view of another example superlattice structure in the semiconductor element according to Embodiment 1.
[図 6]実施形態 2に係る半導体素子における超格子層の断面概略図である。 FIG. 6 is a schematic cross-sectional view of a superlattice layer in a semiconductor element according to Embodiment 2.
[図 7]実施形態 3に係る量子カスケードレーザ素子における超格子層の断面概略図 である。 FIG. 7 is a schematic cross-sectional view of a superlattice layer in a quantum cascade laser device according to a third embodiment.
[図 8]実施例におけるサンプル 1の超格子構造 (600°C)における断面 TEM像(図面
代用)である。 [Fig. 8] Cross-sectional TEM image of sample 1 superlattice structure (600 ° C) in the example (drawing) Substitute).
[図 9]実施例におけるサンプル 2の半導体光機能素子における超格子構造 (650°C) の断面 TEM像 (図面代用)である。 FIG. 9 is a cross-sectional TEM image (drawing substitute) of the superlattice structure (650 ° C.) in the semiconductor optical functional device of Sample 2 in the example.
[図 10]実施例におけるサンプル 3の半導体光機能素子の断概略図である。 FIG. 10 is a schematic sectional view of a semiconductor optical functional device of Sample 3 in an example.
[図 11]サンプル 3の半導体光機能素子における超格子構造の X線回折測定結果を 示す図である。 FIG. 11 is a diagram showing an X-ray diffraction measurement result of the superlattice structure in the semiconductor optical functional device of Sample 3.
[図 12]サンプル 3に対する比較例の X線回折測定結果を示す図である。 FIG. 12 is a diagram showing a result of an X-ray diffraction measurement of a comparative example for sample 3.
[図 13]サンプル 3の半導体素子の表面に対し 60度の角度をもって入射した p偏光に よる吸収スペクトルを示す図である。 FIG. 13 is a diagram showing an absorption spectrum by p-polarized light incident at an angle of 60 degrees with respect to the surface of the semiconductor element of sample 3.
符号の説明 Explanation of symbols
1…半導体素子、 2…基板、 3· ··バッファ層、 4、 4a、 4b…クラッド層、 5…超格子層、 6…キャップ層、 7、 7a、 7b…コンタクト層、 8· ··電極、 8a…第一の電極、 8b…第二の 電極、 51· ··井戸層、 52、 52a, 52b- "AlGaN障壁層、 53· ··量子井戸構造、 54· ··ス ぺ一サ一層、 511、 511a, 511b- "GaN井戸層、 512· ··ΙηΝ井戸層
DESCRIPTION OF SYMBOLS 1 ... Semiconductor device, 2 ... Board | substrate, 3 ... Buffer layer, 4, 4a, 4b ... Cladding layer, 5 ... Superlattice layer, 6 ... Cap layer, 7 , 7a , 7b ... Contact layer, 8 ... Electrode 8a ... first electrode, 8b ... second electrode, 51 ... well layer, 52, 52a, 52b- "AlGaN barrier layer, 53 ... quantum well structure, 54 ... spacer layer 511, 511a, 511b- "GaN well layer, 512 ... 512ηΝ well layer
Claims
請求の範囲 The scope of the claims
[I] GaN井戸層及び InN井戸層を有する井戸層と、 [I] a well layer having a GaN well layer and an InN well layer;
前記井戸層を挟む一対の AlGaN障壁層を有する超格子層を含む半導体素子。 A semiconductor device comprising a superlattice layer having a pair of AlGaN barrier layers sandwiching the well layer.
[2] 前記井戸層における前記 InN井戸層の厚さは、 2分子厚以下である請求項 1記載 の半導体素子。 [2] The semiconductor device according to [1], wherein the InN well layer in the well layer has a thickness of 2 molecules or less.
[3] 前記井戸層における前記 InN井戸層の厚さは、 0. 6nm以下である請求項 1記載 の半導体素子。 [3] The semiconductor device according to [1], wherein the thickness of the InN well layer in the well layer is 0.6 nm or less.
[4] 前記井戸層は、複数の GaN井戸層を有し、前記 InN井戸層は、前記複数の GaN 井戸層の間に挟まれている請求項 1記載の半導体素子。 4. The semiconductor device according to claim 1, wherein the well layer has a plurality of GaN well layers, and the InN well layer is sandwiched between the plurality of GaN well layers.
[5] 前記井戸層は、 GaN井戸層と前記 InN井戸層を同数有する請求項 1記載の半導 体素子。 5. The semiconductor element according to claim 1, wherein the number of well layers includes the same number of GaN well layers and InN well layers.
[6] 前記井戸層と、前記井戸層を挟む一対の AlGaN障壁層を一周期の量子井戸構造 とし、該量子井戸構造における前記 AlGaN障壁層を共通して複数の前記量子井戸 構造が積層されている請求項 1記載の半導体素子。 [6] The well layer and the pair of AlGaN barrier layers sandwiching the well layer have a single-period quantum well structure, and the plurality of quantum well structures are stacked in common with the AlGaN barrier layer in the quantum well structure. The semiconductor device according to claim 1.
[7] 前記井戸層と、前記井戸層を挟む一対の AlGaN障壁層を一周期の量子井戸構造 とし、スぺーサ一層を介して複数の前記量子井戸構造が積層されている請求項 1記 載の半導体素子。 7. The semiconductor device according to claim 1, wherein the well layer and a pair of AlGaN barrier layers sandwiching the well layer have a one-period quantum well structure, and a plurality of the quantum well structures are stacked via a spacer layer. Semiconductor element.
[8] 波動関数制御による伝導帯 価電子帯間の電子 ホールの再結合確率 (遷移確 率)の増大及び発光波長制御を目的とし、 GaN井戸層及び InN井戸層を有する井 戸層と、前記井戸層を挟む一対の AlGaN障壁層から形成される積層構造を活性層 として有する半導体素子。 [8] Conduction band by wave function control For the purpose of increasing the recombination probability (transition probability) of electron holes between valence bands and controlling the emission wavelength, the well layer having a GaN well layer and an InN well layer, A semiconductor element having a stacked structure formed of a pair of AlGaN barrier layers sandwiching a well layer as an active layer.
[9] 基板、ノ ッファ層、クラッド層、超格子層、キャップ層と、を順に積層してなる光スイツ チング素子であって、 [9] An optical switching element in which a substrate, a nofer layer, a cladding layer, a superlattice layer, and a cap layer are laminated in order,
前記超格子層は、 GaN井戸層及び InN井戸層を有する井戸層と、前記井戸層を 挟む一対の AlGaN障壁層と、を有する光スイッチング素子。 The superlattice layer is an optical switching element having a well layer having a GaN well layer and an InN well layer, and a pair of AlGaN barrier layers sandwiching the well layer.
[10] 前記井戸層中にサブバンドを有し、前記サブバンド間隔におけるエネルギーに相 当する光波長が 2 m以下である請求項 1記載の半導体素子。 10. The semiconductor device according to claim 1, wherein the well layer has subbands, and an optical wavelength corresponding to energy in the subband interval is 2 m or less.
[II] 前記井戸層中にサブバンドを有し、前記サブバンド間隔における光吸収遷移と電
子 フオノン相互作用を介した高速緩和過程を利用した請求項 1記載の光半導体素 子。 [II] The well layer has a subband, and the light absorption transition and the electric current in the subband interval 2. The optical semiconductor device according to claim 1, wherein a fast relaxation process via a phonon interaction is utilized.
[12] 基板、ノ ッファ層、第一のコンタクト層、第一のクラッド層、超格子層、第二のクラッド 層、第二のコンタクト層、を有する量子カスケードレーザ素子であって、 [12] A quantum cascade laser device having a substrate, a nofer layer, a first contact layer, a first cladding layer, a superlattice layer, a second cladding layer, and a second contact layer,
前記超格子層は、 GaN井戸層及び InN井戸層を有する井戸層と、前記井戸層を 挟む一対の AlGaN障壁層と、を有する量子カスケードレーザ素子。 The quantum lattice laser element, wherein the superlattice layer has a well layer having a GaN well layer and an InN well layer, and a pair of AlGaN barrier layers sandwiching the well layer.
[13] 前記井戸層中にサブバンドを有し、前記超格子層の前記井戸層及び前記 AlGaN 障壁層の周期を調整することで、前記超格子層は電子注入層及び発光層として機 能する請求項 1記載の半導体素子。
[13] The well layer has subbands, and the superlattice layer functions as an electron injection layer and a light emitting layer by adjusting the period of the well layer and the AlGaN barrier layer of the superlattice layer. The semiconductor device according to claim 1.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2008524744A JP5388274B2 (en) | 2006-06-19 | 2007-06-18 | Semiconductor device, optical switching device, and quantum cascade laser device |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2006-169182 | 2006-06-19 | ||
JP2006169182 | 2006-06-19 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO2008007522A1 true WO2008007522A1 (en) | 2008-01-17 |
Family
ID=38923087
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/JP2007/062237 WO2008007522A1 (en) | 2006-06-19 | 2007-06-18 | Semiconductor element, optical switching element and quantum cascade laser element |
Country Status (2)
Country | Link |
---|---|
JP (1) | JP5388274B2 (en) |
WO (1) | WO2008007522A1 (en) |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2010177552A (en) * | 2009-01-30 | 2010-08-12 | Samsung Electro-Mechanics Co Ltd | Nitride semiconductor growth substrate having polar plane |
JP2013171842A (en) * | 2012-02-17 | 2013-09-02 | National Institute Of Information & Communication Technology | Quantum cascade laser |
CN104300051A (en) * | 2014-09-16 | 2015-01-21 | 天津三安光电有限公司 | Nitride-based light emitting diode |
EP3154140A4 (en) * | 2014-06-04 | 2017-06-07 | Sharp Kabushiki Kaisha | Quantum cascade laser |
CN113764549A (en) * | 2021-09-07 | 2021-12-07 | 圆融光电科技股份有限公司 | Preparation method of light-emitting diode |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH10289877A (en) * | 1997-04-15 | 1998-10-27 | Hitachi Ltd | Forming method of compound semiconductor and semiconductor device |
JP2004133437A (en) * | 2002-09-17 | 2004-04-30 | Nippon Telegr & Teleph Corp <Ntt> | Semiconductor optical modulator and laser with optical modulator |
JP2004140339A (en) * | 2002-09-25 | 2004-05-13 | Univ Chiba | Device having nitride-based heterostructure and its manufacturing method |
Family Cites Families (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6593589B1 (en) * | 1998-01-30 | 2003-07-15 | The University Of New Mexico | Semiconductor nitride structures |
JP5257967B2 (en) * | 2006-05-17 | 2013-08-07 | 国立大学法人 千葉大学 | Semiconductor optical device |
-
2007
- 2007-06-18 JP JP2008524744A patent/JP5388274B2/en not_active Expired - Fee Related
- 2007-06-18 WO PCT/JP2007/062237 patent/WO2008007522A1/en active Application Filing
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH10289877A (en) * | 1997-04-15 | 1998-10-27 | Hitachi Ltd | Forming method of compound semiconductor and semiconductor device |
JP2004133437A (en) * | 2002-09-17 | 2004-04-30 | Nippon Telegr & Teleph Corp <Ntt> | Semiconductor optical modulator and laser with optical modulator |
JP2004140339A (en) * | 2002-09-25 | 2004-05-13 | Univ Chiba | Device having nitride-based heterostructure and its manufacturing method |
Non-Patent Citations (2)
Title |
---|
CHO H.K. ET AL.: "Nanostructure formation and emission characterization of blue emission InN/GaN quantum well with thin InN well layers", JOURNAL OF CRYSTAL GROWTH, vol. 281, no. 2-4, 1 August 2005 (2005-08-01), pages 349 - 354, XP003024652 * |
YAMAGUCHI W. ET AL.: "1 Bunshiso InN Idoso o Mochiita InN/GaN Taju Ryoshi Ido Kozo no Sakusei to Hyoka", DAI 53 KAI EXTENDED ABSTRACTS, JAPAN SOCIETY OF APPLIED PHYSICS AND RELATED SOCIETIES, no. 1, 22 March 2006 (2006-03-22), pages 353, XP003024653 * |
Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2010177552A (en) * | 2009-01-30 | 2010-08-12 | Samsung Electro-Mechanics Co Ltd | Nitride semiconductor growth substrate having polar plane |
JP2013171842A (en) * | 2012-02-17 | 2013-09-02 | National Institute Of Information & Communication Technology | Quantum cascade laser |
EP3154140A4 (en) * | 2014-06-04 | 2017-06-07 | Sharp Kabushiki Kaisha | Quantum cascade laser |
US10340662B2 (en) | 2014-06-04 | 2019-07-02 | Sharp Kabushiki Kaisha | Quantum cascade laser |
CN104300051A (en) * | 2014-09-16 | 2015-01-21 | 天津三安光电有限公司 | Nitride-based light emitting diode |
CN113764549A (en) * | 2021-09-07 | 2021-12-07 | 圆融光电科技股份有限公司 | Preparation method of light-emitting diode |
CN113764549B (en) * | 2021-09-07 | 2024-05-24 | 圆融光电科技股份有限公司 | Preparation method of light-emitting diode |
Also Published As
Publication number | Publication date |
---|---|
JP5388274B2 (en) | 2014-01-15 |
JPWO2008007522A1 (en) | 2009-12-10 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
CN110249491B (en) | Laser or LED based on nanowires grown on graphene-type substrates | |
EP1672757B1 (en) | Blue and green laser diodes with gallium nitride or indium gallium nitride cladding laser structure | |
WO1997011518A1 (en) | Semiconductor material, method of producing the semiconductor material, and semiconductor device | |
WO2013002389A1 (en) | Group iii nitride semiconductor element and method for manufacturing group iii nitride semiconductor element | |
WO2008029915A1 (en) | Semiconductor light emitting device and process for producing the same | |
US11862750B2 (en) | Optoelectronic device | |
JP5388274B2 (en) | Semiconductor device, optical switching device, and quantum cascade laser device | |
JP2000332362A (en) | Semiconductor device and semiconductor light emitting element | |
JP3589301B2 (en) | Structure of quantum layer | |
Che et al. | Fabrication of asymmetric GaN/InN/InGaN/GaN quantum-well light emitting diodes for reducing the quantum-confined stark effect in the blue-green region | |
JP5366279B1 (en) | Multiple quantum well solar cell and method of manufacturing multiple quantum well solar cell | |
JP5257967B2 (en) | Semiconductor optical device | |
JP5561629B2 (en) | Semiconductor optical device | |
JP5158834B2 (en) | Semiconductor light emitting device and method for manufacturing semiconductor light emitting device | |
US8879595B2 (en) | Quantum cascade structures on metamorphic buffer layer structures | |
JP4786481B2 (en) | Semiconductor device and manufacturing method of semiconductor device | |
JP2003224071A (en) | Manufacturing method for nitride based semiconductor and nitride semiconductor element using the same | |
JP2005203411A (en) | Nitride semiconductor light-emitting element | |
US9099843B1 (en) | High operating temperature laser diodes | |
Kuwabara et al. | Laser operation of nitride laser diodes with GaN well layer in 340 nm band | |
JP4491610B2 (en) | Semiconductor functional element | |
JP2009212343A (en) | Nitride semiconductor element, and method of manufacturing the same | |
Nagamatsu et al. | Growth and conductivity control of high quality AlGaN and its application to high-performance ultraviolet laser diodes | |
CN113611595B (en) | Semiconductor structure and preparation method thereof | |
WO2003075365A1 (en) | Photoelectric conversion function device |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
121 | Ep: the epo has been informed by wipo that ep was designated in this application |
Ref document number: 07745479 Country of ref document: EP Kind code of ref document: A1 |
|
WWE | Wipo information: entry into national phase |
Ref document number: 2008524744 Country of ref document: JP |
|
NENP | Non-entry into the national phase |
Ref country code: DE |
|
NENP | Non-entry into the national phase |
Ref country code: RU |
|
122 | Ep: pct application non-entry in european phase |
Ref document number: 07745479 Country of ref document: EP Kind code of ref document: A1 |