WO2023013374A1 - 紫外発光ダイオードおよびそれを備える電気機器 - Google Patents
紫外発光ダイオードおよびそれを備える電気機器 Download PDFInfo
- Publication number
- WO2023013374A1 WO2023013374A1 PCT/JP2022/027508 JP2022027508W WO2023013374A1 WO 2023013374 A1 WO2023013374 A1 WO 2023013374A1 JP 2022027508 W JP2022027508 W JP 2022027508W WO 2023013374 A1 WO2023013374 A1 WO 2023013374A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- layer
- light emitting
- ultraviolet light
- emission
- emitting diode
- Prior art date
Links
- 239000000203 mixture Substances 0.000 claims abstract description 162
- 230000004888 barrier function Effects 0.000 claims abstract description 98
- 125000006850 spacer group Chemical group 0.000 claims abstract description 70
- 230000000903 blocking effect Effects 0.000 claims abstract description 42
- 229910002704 AlGaN Inorganic materials 0.000 claims abstract description 34
- 239000013078 crystal Substances 0.000 claims abstract description 27
- 230000007423 decrease Effects 0.000 claims description 22
- 238000009826 distribution Methods 0.000 claims description 11
- 238000011144 upstream manufacturing Methods 0.000 claims description 4
- 238000003475 lamination Methods 0.000 claims description 2
- 239000010410 layer Substances 0.000 description 303
- 230000001965 increasing effect Effects 0.000 description 32
- 230000000694 effects Effects 0.000 description 20
- 239000000758 substrate Substances 0.000 description 20
- 238000002347 injection Methods 0.000 description 19
- 239000007924 injection Substances 0.000 description 19
- 239000000463 material Substances 0.000 description 19
- 238000004364 calculation method Methods 0.000 description 18
- 238000010586 diagram Methods 0.000 description 17
- 230000003287 optical effect Effects 0.000 description 14
- 230000007704 transition Effects 0.000 description 11
- 230000003247 decreasing effect Effects 0.000 description 10
- 239000004065 semiconductor Substances 0.000 description 10
- 239000000969 carrier Substances 0.000 description 8
- 238000000295 emission spectrum Methods 0.000 description 8
- 150000004767 nitrides Chemical class 0.000 description 8
- 230000006870 function Effects 0.000 description 7
- 230000005855 radiation Effects 0.000 description 7
- 230000005428 wave function Effects 0.000 description 7
- 230000006872 improvement Effects 0.000 description 6
- 230000007246 mechanism Effects 0.000 description 6
- 230000010287 polarization Effects 0.000 description 6
- 230000006798 recombination Effects 0.000 description 6
- 238000005215 recombination Methods 0.000 description 6
- 230000008859 change Effects 0.000 description 5
- 238000005401 electroluminescence Methods 0.000 description 5
- 238000002474 experimental method Methods 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 5
- 238000000034 method Methods 0.000 description 5
- 230000009467 reduction Effects 0.000 description 5
- 238000004088 simulation Methods 0.000 description 5
- 230000009471 action Effects 0.000 description 4
- 238000000605 extraction Methods 0.000 description 4
- 239000002356 single layer Substances 0.000 description 4
- 238000007796 conventional method Methods 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 230000004048 modification Effects 0.000 description 3
- 238000012986 modification Methods 0.000 description 3
- 230000001629 suppression Effects 0.000 description 3
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 2
- 229910005191 Ga 2 O 3 Inorganic materials 0.000 description 2
- 230000002411 adverse Effects 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- 238000013459 approach Methods 0.000 description 2
- 238000005452 bending Methods 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 230000005684 electric field Effects 0.000 description 2
- 238000001194 electroluminescence spectrum Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 238000003780 insertion Methods 0.000 description 2
- 230000037431 insertion Effects 0.000 description 2
- 238000011835 investigation Methods 0.000 description 2
- 238000001451 molecular beam epitaxy Methods 0.000 description 2
- 238000005457 optimization Methods 0.000 description 2
- 229910052594 sapphire Inorganic materials 0.000 description 2
- 239000010980 sapphire Substances 0.000 description 2
- 238000001228 spectrum Methods 0.000 description 2
- 230000001954 sterilising effect Effects 0.000 description 2
- XCZXGTMEAKBVPV-UHFFFAOYSA-N trimethylgallium Chemical compound C[Ga](C)C XCZXGTMEAKBVPV-UHFFFAOYSA-N 0.000 description 2
- 241000700605 Viruses Species 0.000 description 1
- 230000002238 attenuated effect Effects 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 229910052733 gallium Inorganic materials 0.000 description 1
- 230000000415 inactivating effect Effects 0.000 description 1
- 238000004020 luminiscence type Methods 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 230000001902 propagating effect Effects 0.000 description 1
- 238000002310 reflectometry Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 229910052703 rhodium Inorganic materials 0.000 description 1
- 238000004659 sterilization and disinfection Methods 0.000 description 1
- 235000013619 trace mineral Nutrition 0.000 description 1
- 239000011573 trace mineral Substances 0.000 description 1
- 238000002834 transmittance Methods 0.000 description 1
- JLTRXTDYQLMHGR-UHFFFAOYSA-N trimethylaluminium Chemical compound C[Al](C)C JLTRXTDYQLMHGR-UHFFFAOYSA-N 0.000 description 1
- 238000000927 vapour-phase epitaxy Methods 0.000 description 1
Images
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
- H01L33/14—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a carrier transport control structure, e.g. highly-doped semiconductor layer or current-blocking structure
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
- H01L33/26—Materials of the light emitting region
- H01L33/30—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table
- H01L33/32—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table containing nitrogen
Definitions
- the present disclosure relates to ultraviolet light emitting diodes and electrical equipment including the same. More particularly, the present disclosure relates to ultraviolet light emitting diodes that emit deep ultraviolet rays and electrical equipment comprising the same.
- UVLEDs ultraviolet light emitting diodes
- a wavelength region of 350 nm or less in the ultraviolet region is also called a deep ultraviolet region (DUV), of which about 200 nm to 280 nm is also called a UVC wavelength band.
- a wavelength range of about 260 to 280 nm, which is a part thereof, is called a sterilization wavelength, and technical development of UVLEDs for this wavelength range is vigorously carried out.
- Far-UVC far-ultraviolet
- DUVLEDs deep ultraviolet LEDs
- AlGaN nitride semiconductor AlGaN crystals.
- AlN 210 nm
- GaN 340 nm
- LQB last quantum barrier
- Non-Patent Document 3 A similar attempt has been made with an ultraviolet LED that emits near-ultraviolet rays with a wavelength of about 360 nm (Non-Patent Document 3), and a theoretical investigation has also been conducted with a wavelength of about 290 nm in the DUV region (Non-Patent Document 4). . The role played by the thickness of the LQB in the DUV region has also been investigated (Non-Patent Document 5).
- Non-Patent Document 6 a device that introduces a superlattice into the LQB of an LED device that emits light at 285 nm
- Non-Patent Document 7 a configuration that places a high barrier layer in addition to the EBL in an LED device that emits light at 270 nm
- a GaN/AlGaN/InGaN-based nitride semiconductor light-emitting device by adopting a multiple quantum well structure, the overlapping of the distribution of electrons and holes due to wave function confinement is increased. A method of increasing the internal quantum efficiency by generating a large number of pairs of is adopted.
- the luminous efficiency of light emitting devices in the actual UVC wavelength range decreases exponentially as the luminous wavelength becomes shorter.
- Far-UVC (210 to 230 nm) light-emitting diodes referred to as "Far-UVC LEDs"
- Far-UVC LEDs have extremely low external quantum efficiencies of 0.03% or less.
- technical ideas that have been adopted to improve efficiency on the longer wavelength side than Far-UVC can be applied. Good results are not obtained.
- One of the essential reasons is that there is little room for increasing the Al composition ratio in Far-UVCLEDs, considering AlGaN with an Al composition ratio as high as 0.8 or more.
- AlGaN having an Al composition ratio of about 0.6 to 0.7 has been adopted.
- the Al composition ratio of AlGaN must be 0.8 or more.
- the difference from the upper limit of the Al composition ratio of 1.0 that is, AlN
- the approach of increasing the Al composition ratio that has been employed in light-emitting diodes that emit light at longer wavelengths is insufficient for the electron block's function as a means of suppressing severe electron overflow.
- AlGaN with a high Al composition ratio greatly changes the electronic structure compared to those with a small Al composition ratio.
- AlGaN has an Al composition ratio of about 0.5 as a boundary, and the properties of AlGaN change completely at higher Al composition ratios.
- TM emission is dominant over TE emission in ultraviolet light emitting diodes in which AlGaN has an Al composition ratio exceeding 0.5.
- TM emission is more difficult to extract than TE emission.
- the emission wavelength is 240 nm or longer, it is effective to provide a quantum well in the light emitting layer to increase the ratio of TE emission due to the quantum confinement effect.
- the ratio of TE emission cannot be sufficiently increased.
- An object of the present disclosure is to solve at least one of the above problems.
- a new design concept suitable for the material properties of AlGaN with high Al composition is essential.
- the present disclosure contributes to the development of various applications that employ Far-UVCLEDs as light sources by providing a new design concept that can also adapt to the properties of AlGaN with a high Al composition used in Far-UVCLEDs.
- the present inventors premised on the intrinsic limitations of AlGaN with a high Al composition and its material properties, have improved the efficiency of Far-UVC LEDs by making full use of precise control of the electronic band structure (band engineering). We have found that it is possible, and have completed the invention according to the present application.
- an ultraviolet light emitting diode including an AlGaN-based crystal or an InAlGaN-based crystal, wherein the light emitting layer, the spacer layer, and the electron blocking layer are arranged from upstream to downstream of the electron flow.
- An ultraviolet light emitting diode is provided in which the layers are stacked in order, and the Al composition ratio in the spacer layer varies according to the position in the thickness direction of the stack.
- an ultraviolet light emitting diode containing an AlGaN-based crystal or an InAlGaN-based crystal comprising a light-emitting layer including at least one barrier layer and at least two quantum well layers sandwiching the barrier layer. and wherein the barrier layer is thinned.
- the composition distribution of the spacer layer is preferably inclined so that the Al composition ratio decreases from the light emitting layer toward the electron blocking layer. It is also preferable that the Al composition ratio is inclined so as to increase from the light emitting layer toward the electron blocking layer.
- the barrier layer preferably has a thickness of 0.2 nm or more and 4 nm or less, and more preferably has a thickness of 1 nm or more and 3 nm or less.
- the thickness of the barrier layer in these ultraviolet light emitting diodes is preferably a thickness that makes the TE emission stronger than the TM emission in the emission layer, and may be equal to or less than the thickness of the quantum well layer. preferable.
- These ultraviolet light emitting diodes preferably emit ultraviolet light having a major wavelength of 210 to 230 nm.
- an embodiment of the present disclosure also provides an electrical device comprising the above-described ultraviolet light emitting diode as an ultraviolet emission source.
- ultraviolet rays in the Far-UVC region refer to ultraviolet rays in the wavelength range of approximately 210 to 230 nm.
- a "dominant wavelength of emitted ultraviolet light” is generally a wavelength that characterizes the emission spectrum of a light emitting diode, not necessarily a single wavelength, and typically includes the peak wavelength of a single-peak chevron emission spectrum.
- the stated wavelength range for a dominant wavelength does not imply that the wavelength range stated for that dominant wavelength should encompass all of the emission spectrum.
- the device structures and functions are described using technical terms that are transferred or borrowed from the fields of electronic devices and physics that target visible light and ultraviolet light.
- the light emitting layer includes quantum well layers and barrier layers.
- a quantum well layer is a layer that provides electrons with a conduction band edge potential that forms a quantum well
- a barrier layer is a layer that provides a relatively high conduction band edge potential in association with the quantum well layer.
- the electron blocking layer is a layer with a high conduction band edge potential provided for the purpose of preventing electron leakage, and the spacer layer is between the quantum well layer and the electron blocking layer, which are the most downstream in the flow of electrons in the light emitting layer. , and has a conduction band edge potential height between them.
- the ultraviolet light emitting diode provided in any aspect of the present disclosure realizes light emitting operation with higher efficiency than conventional.
- FIG. 1 is a perspective view showing a schematic configuration common to both a conventional LED and an LED according to embodiments of the present disclosure.
- FIG. 2 is an explanatory diagram for explaining the problem to be solved by the present embodiment of the present disclosure, and shows electron conduction band edge profiles of the n-type layer, the light emitting layer, the spacer layer, and the electron blocking layer.
- FIG. 3 shows the relationship between the position in the thickness direction of the stack and the Al composition ratio (vertical direction) in the barrier layer, quantum well layer, spacer layer, and electron blocking layer in the conventional LED and the LED of the embodiment of the present disclosure. It is a schematic diagram showing.
- FIG. 4A-C are explanatory diagrams showing the distribution of the Al composition ratio in the thickness direction of the structure adopted for the calculation for the LED of the embodiment of the present disclosure (FIG. 4A), the current obtained by the calculation - the internal quantum efficiency 4B is a graph (FIG. 4B) and a graph of injection efficiency obtained with varying compositional gradients (FIG. 4C).
- 5A-C are exemplary band diagrams for explaining calculations for block heights of LEDs of embodiments of the present disclosure, including an operating band diagram (FIG. 5A) and electron and hole block heights.
- FIG. 5B and 5C are enlarged views of the band diagram of the portion that gives the height.
- 6A-B show the calculated block heights for electrons (FIG. 6A) and holes (FIG.
- FIG. 7 is a graph of the radiative recombination rate calculated at each position in the thickness direction of the LED according to the embodiment of the present disclosure.
- 8A-B are electroluminescence (EL) spectra (FIG. 8A) and current-light output characteristics (FIG. 8B) observed for LED samples of conventional and embodiments of the present disclosure.
- FIG. 9 is the EL spectra obtained from each of the samples with varying starting Al composition ratios for LEDs of embodiments of the present disclosure.
- FIG. 10A and 10B are band diagrams to illustrate polarization of UV emitted in conventional LEDs and LEDs of embodiments of the present disclosure, respectively.
- FIG. 11 is a graph showing measured emission spectra of samples of conventional LEDs and LEDs of embodiments of the present disclosure.
- FIG. 12 is a graph showing the relationship between the thickness of the barrier layer and the intensity of TE emission, which was obtained in a simulation for confirming the technical idea of the embodiment of the present disclosure.
- 13A-B are graphs of emission spectra (FIG. 13A) and current light output characteristics (FIG. 13B) for LED samples in embodiments of the present disclosure.
- Far-UVC LEDs also referred to as LEDs
- LEDs Far-UVC light-emitting diodes
- Embodiment in the LED 100A of the present embodiment electron overflow is suppressed by adopting the spacer layer 136A having a composition gradient.
- the band structure advantageous for the emission of TE light is achieved by thinning the barrier layers 13B located between the plurality of quantum well layers 13W, either in combination with or without combination thereof.
- the structure of an LED that employs both the compositionally graded spacer layer 136A and the thinned barrier layer 13B will be described (1-1), and further the compositionally graded spacer layer will be described in detail (1-2). , the details of the thinned barrier layer (1-3), their combination (1-4), and finally the modification (1-5).
- FIG. 1 is a perspective view showing a schematic structure common to both a conventional LED 100 and an LED 100A of this embodiment.
- a buffer layer 120 is epitaxially grown on one surface 104 of a substrate 110 made of flat ⁇ -Al 2 O 3 single crystal (sapphire) using a material such as AlN crystal.
- An n-type conductive layer 132 is laminated in this order from the buffer layer 120 side.
- n-type conductive layer 132 following the n-type conductive layer 132, a light-emitting layer 134, a spacer layer 136, an electron blocking layer 138, a p-type contact layer 150, and an electrode 160 acting as a second electrode are laminated in this order.
- the direction of electron flow from upstream to downstream during operation is also the same as this stacking order.
- the material of the n-type conductive layer 132 to the spacer layer 136 is typically AlGaN or InAlGaN, or either of them is doped with trace elements (Si for n-type, Mg for p-type, etc.) as necessary.
- the electron block layer 138 is a single layer for providing a high barrier against electrons, and its material is AlGaN with an increased Al composition ratio or AlN.
- a first electrode 140 is electrically connected to the n-type conductive layer 132 .
- Electrode 160 establishes electrical connection with electron blocking layer 138 through p-type contact layer 150 .
- a light output L which is radiation UV, is emitted through the substrate 110 from the other surface, the light extraction surface 102 .
- the substrate 110 is a growth substrate on which the n-type conductive layer 132 to the p-type contact layer 150 can be epitaxially grown, and is selected from any material that satisfies conditions such as crystal orientation and heat resistance for growth. If the substrate 110 is left in the end, the substrate 110 is also required to be transparent to radiation UV.
- Typical materials for the substrate 110 include the above-mentioned ⁇ -Al 2 O 3 single crystal (sapphire), AlN single crystal substrate, and Ga 2 O 3 substrate in the case of UV radiation with a wavelength of 300 nm or more, A material having an appropriate crystal orientation and off-angle is appropriately selected according to each material.
- the buffer layer 120 is formed in a single layer or multiple layers as necessary in order to meet the crystal growth requirement of forming a good quality AlGaN layer (AlN layer) or InAlGaN layer on the substrate 110 and increasing the internal luminous efficiency ⁇ IQE .
- AlN layer AlGaN layer
- InAlGaN layer InAlGaN layer
- ⁇ IQE internal luminous efficiency
- n-type conductive layer 132 is, for example, an Al 0.85 Ga 0.15 N layer doped with Si so as to be n-type. Al 0.85 Ga 0.15 N; Si layer.
- the barrier layers 13B and the quantum well layers 13W are alternately laminated. From the n-type conductive layer 132 side, the barrier layers 13B, the quantum well layers 13W, the barrier layers 13B, It has a structure of an MQW (multiple quantum well) stack.
- At least two quantum well layers 13W are included in the light emitting layer 134, and some barrier layers 13B are sandwiched between at least two quantum well layers 13W.
- the material of the light emitting layer 134 has a composition of Al 0.94 Ga 0.06 N for the barrier layers 13B and Al 0.82 Ga 0.18 N for the quantum well layers 13W.
- a typical number of quantum wells is, for example, on the order of three.
- the spacer layer 136 is an undoped AlGaN layer. Also when adopting an InAlGaN layer for the ultraviolet light emitting layer 130, a configuration according to this can be adopted.
- the p-type contact layer 150 is p-type AlGaN or p-type InAlGaN obtained by doping Mg into AlGaN or InAlGaN material. If the Al composition ratio is appropriately selected, the p-type contact layer 150 can have a high transmittance for UV radiation.
- the first electrode 140 is a metal electrode having a laminated structure of Ni/Au from the base side. This Ni is a layer with a thickness of, for example, 25 nm inserted between the Au and the underlying semiconductor layer in order to realize an ohmic contact.
- the reflective electrode 160 employs a UV reflective film 164 that exhibits high reflectivity to emitted UV.
- This UV reflection film 164 is a film made of a material containing, for example, Al, Mg, and Rh as main components.
- Ni is inserted on the underlayer side of the reflective electrode 160 as well to form an insertion metal layer 162 which is a part of the reflective electrode.
- the LED 100A of this embodiment is the same as the conventional LED 100 except for the internal configuration of the light emitting layer 134 and the specific configuration of the spacer layer 136A.
- an LED that employs a quantum well in a nitride semiconductor electrons pass through the conduction band from the n-type conductive layer 132 and valence from the p-type contact layer 150 in the quantum confinement state of the quantum well layer 13W formed in the light-emitting layer 134. Holes are injected through the electron bands, respectively. Electrons and holes recombine in the quantum well by band-to-band transitions to emit ultraviolet light.
- the present inventors have focused on the problems for LEDs in the Far-UVC region, firstly, the overflow of electrons, and secondly, the polarization state of the emitted light.
- FIG. 2 is an explanatory diagram for explaining the problem to be solved by this embodiment.
- the electron conduction band edge profile of each layer of layer 138 is shown.
- Overflow is a phenomenon in which a portion of carriers pass through the light-emitting layer 134 and current is wasted without causing intended recombination, and electrons exhibiting high mobility in nitride semiconductor carriers pose a problem.
- a nitride semiconductor LED is generally provided with a high barrier layer called an electron blocking layer 138 at a position downstream of the electron flow when viewed from the light emitting layer 134 .
- the Al composition ratio can only be increased to the upper limit (100%, ie, AlN). is.
- the conduction band edge of the electron blocking layer 138 is not sufficiently high in view of the light emitting layer 134 made of AlGaN with a high Al composition, and it is difficult to exhibit the function of blocking electrons.
- the luminous efficiency of the LED is reduced due to reactive current that does not contribute to light emission.
- the polarization state of light emission is whether the emitted ultraviolet light is TM (transverse magnetic) mode light or TE (transverse electric) mode light.
- TM mode The case where the electric field oscillates in the thickness direction of the light-emitting layer 134 is called TM mode, and the case where the electric field oscillates in the plane of the light-emitting layer 134 is called TE mode.
- the emitted radiative action is also called TE light and TE emission, respectively, and the same applies to TM.
- the optical transition emitting TM light has a profile in which the light is emitted in the in-plane direction of the laminated structure of the quantum well layer 13W, the barrier layer 13B, and the like.
- the light is scattered or absorbed while propagating inside the LED having a size of about mm, and tends to be attenuated before being emitted to the outside.
- the optical transition that emits TE light has a profile in which the radial direction is oriented in the thickness direction of the laminated structure. Therefore, the TE light can be easily extracted from the LED by being directly emitted to the outside, or being emitted with the propagation direction reversed with the help of the reflective electrode 160, for example.
- Increasing the ratio of TE light is particularly advantageous for improving the light extraction efficiency.
- the Al composition ratio is increased to 0.8 or more for the Far-UVC region in AlGaN, TM emission becomes dominant due to the influence of the band structure, especially the influence of the electronic state that becomes holes, and the light extraction efficiency decreases. .
- FIG. 3 is a schematic diagram showing the relationship between the position in the stack thickness direction and the Al composition ratio in the barrier layer 13B, the quantum well layer 13W, the spacer layers 136 and 136A, and the electron block layer 138. As shown in FIG. The horizontal direction and vertical direction of the drawing are the positions in the stacking direction and the AlN composition ratio at each position in the LEDs 100 and 100A, respectively.
- the spacer layers 136 and 136A are sandwiched between the electron blocking layer 138 and the most downstream one of the plurality of quantum well layers 13W in the direction of electron flow (rightward in the drawing).
- the Al composition ratio is small in the quantum well layer 13W and large in the electron blocking layer 138, and the spacer layers 136, 136A are configured to have a value between the quantum well layer 13W and the electron blocking layer 138.
- the spacer layer 136 of the conventional LED 100 is manufactured so as to have an Al composition ratio (dashed line 136F in the figure) that is evenly distributed regardless of the position in the thickness direction.
- the spacer layer 136A of the LED element 100A of the present embodiment has a slope 136U that increases the Al composition ratio or a slope 136D that decreases the Al composition ratio depending on the position in the thickness direction from the light emitting layer 134 toward the electron blocking layer 138. It has become.
- structures having a gradient in which the Al composition ratio increases and decreases in the direction from the light emitting layer 134 toward the electron blocking layer 138 are also referred to as increasing composition and decreasing composition, respectively.
- the conduction band edge profile of the spacer layer 136 shown in FIG. 2 due to the polarity of the crystal, piezoelectric polarization or the like may occur at positions where the composition changes.
- the conduction band edge profile of the spacer layer 136 with a flat Al composition ratio also generally accompanies a slope or bending.
- the inventor investigated the electron injection efficiency by theoretical calculation, and then confirmed the actual light emitting operation by experiment.
- Theoretical calculations were performed with the simulation software Silense (Semiconductor Technology Research (STR), St. Moscow, Russia). The calculation is performed using a realistic configuration.
- Typical conditions for both the conventional LED 100 and the LED 100A of the present embodiment are that the quantum well layer 13W has a thickness of 3 nm, the Al composition ratio is 0.82, and the The number is four.
- the electron block layer 138 has a thickness of 9 nm and an Al composition ratio of 1.0 (that is, AlN).
- the Al composition ratio is constant at 0.94, and in the composition-graded spacer layer 136A for the LED 100A of the present embodiment, the Al composition ratio is changed from the quantum well layer to the electron block layer. , according to the position in the thickness direction, and a configuration for linearly decreasing from 0.94 to 0.82. In these calculations, the effect of band tilting and bending due to polarization when a polar substrate is employed is reflected. The effect of electron leakage was evaluated by calculating the electron injection efficiency.
- FIGS. 4A to 4C are explanatory diagrams (FIG. 4A) showing the thickness direction distribution of the Al composition ratio of the structure adopted for the calculation for the LED element of this embodiment, and the graph of the current obtained by the calculation versus the internal quantum efficiency.
- FIG. 4B and a graph of the injection efficiency obtained with varying compositional gradients (FIG. 4C).
- "Flat (-)”, “Graded (-)”, and “Graded (+)” in FIGS. 4A and 4B are flat (that is, the spacer layer 136) and the Al composition ratio x is from 0.94 to 0.82, respectively.
- a decreasing composition reduction configuration and an increasing composition increase configuration from 0.94 to 1.0 are attached.
- the Al composition ratio x is a numerical value of a fraction expressed also as Al x Ga 1-x N or (AlN) x (GaN) 1-x .
- the characteristics showed an upward sloping characteristic in which the internal quantum efficiency increased as the current increased.
- the internal quantum efficiency is higher in the composition gradient than in the flat composition distribution, regardless of whether the gradient is increased or decreased. That is, in the compositionally graded spacer layer 136A, recombination is realized as designed, more than in the flat compositional spacer layer 136.
- FIG. FIG. 4C is a more detailed investigation of how much gradient should be given to the composition distribution.
- the Al composition ratio of the spacer layer 136A is fixed to 0.94 at the position in contact with the quantum well layer 13W (referred to as the “starting Al composition ratio”), and the electron block layer 138 is reached.
- the injection efficiency was calculated with respect to x.
- the final Al composition ratio x 0.94 results in a flat spacer layer 136 configuration. As can be seen, the injection efficiency was the lowest for the flat spacer layer 136, and the injection efficiency increased for compositional grading, whether the grading was increased or decreased.
- FIG. 5A-C are exemplary band diagrams for explaining calculations for determining the block height of the LEDs of the present embodiment, the band diagram at 100 mA operation (FIG. 5A), and the electron and hole block heights
- FIG. 5B and 5C are enlarged views of the band diagram of the portion giving .
- 6A-B also show the calculated block heights for electrons (FIG. 6A) and holes (FIG. 6B) for the conventional and inventive Far-UVC LEDs compared to flat, reduced composition, and It is shown for the case of increasing composition.
- the block height indicates the energy difference between the quasi-Fermi level and the maximum potential value of the block layer 138 in units of eV (or meV).
- the quasi-Fermi level is indicated by dashed lines, and the potentials for electrons and holes are indicated by solid lines.
- the quasi-Fermi levels are denoted by E Fn (electrons) and E Fp (holes), and the potentials are denoted by the conduction band edge E C and the valence band edge E V . are attached respectively.
- the block height is preferably a large value for the function of the electron blocking layer for electrons, but a small value for the hole injection operation. From FIG. 6A and FIG. 6B, in comparison with the flat composition, the electron block height increases and the hole block height decreases with the decrease in composition. In other words, the decrease in composition achieves the effect of improving the efficiency of both electron and hole carriers, the electron blocking functions as intended, and the hole injection also becomes smooth. On the other hand, with increasing composition, the electron block height decreases and the hole block height decreases even more. In other words, compared to the flat structure, electron blocking is insufficient due to the increase in composition, but the injection efficiency is further improved by simultaneously improving hole injection.
- FIG. 7 is a graph of the radiative recombination rate calculated at each position in the thickness direction of the LED 100A of this embodiment.
- the symbols QW1 to QW4 are identifiers assigned to the quantum well layers 13W in the stacking order toward the electron blocking layer 138, and IQW is the interface quantum well substantially occurring at the interface between the spacer layer 136A and the electron blocking layer 138. means well.
- the signs of “Flat (-)”, “Graded (-)”, and “Graded (+)” are the same as in FIGS.
- the Al composition ratio is 0.94 for flat, and the starting Al composition The ratio was 0.94, the final Al composition ratio was 0.82, and the composition increase was set at the starting Al composition ratio of 0.94 and the final Al composition ratio of 1.0.
- FIG. 7 the luminescence rate in each well increases from flat for both the decrease in composition and the increase in composition.
- the emission component of the interfacial quantum well (IQW) is also large when the composition is decreased.
- the composition reduction exhibited superior properties to the flat structure for all mechanisms A, B, and C.
- the emission peak wavelength of IQW depends on the Al composition ratio x reached when the composition is reduced. If the ultimate Al composition ratio x is less than 80% and the emission peak wavelength of the IQW is separated from the wavelengths of the other quantum wells, the characteristics may be unsuitable for an LED. Whether or not to incorporate IQWs into the light-emitting region and whether the emission peak wavelength of the IQWs is appropriate are each determined according to the applied application. The optimum value and range of the target Al composition ratio x can be determined from the viewpoint of necessity and appropriateness of IQW light emission.
- determining the ultimate Al composition ratio x so as to achieve an IQW emission peak wavelength that matches the emission wavelength of the light emitting layer 134 is a typical example of this optimization.
- Another typical example of this optimization is adjusting the emission peak wavelength of the IQW so that the suppression of adverse effects on the human body, which is one of the characteristics of Far-UVC, for example, is maintained.
- the electron injection efficiency is about 1.7 times that of the flat spacer layer 136 in the compositionally graded spacer layer 136A that increases the Al composition ratio.
- the spacer layer 136 with a flat composition and the spacer layer 136A with a composition gradient of increasing and decreasing Al composition ratios were used for the conventional and LEDs 100 and 100A of the present embodiment. were fabricated and the electroluminescence was measured.
- the LED samples were fabricated by the MOVPE (metal-organic vapor phase epitaxy) method in the same manner as conventional nitride semiconductor ultraviolet LEDs. tri-methyl-aluminum) and TMGa (tri-methyl-gallium), which is the material gas for Ga, was changed according to whether the spacer layer had a flat Al composition or a composition gradient. were made different, and the fabrication conditions for the other structures were the same.
- the electrode size is 0.4 mm square, and constant current operation is performed.
- 8A-B are electroluminescence (EL) spectra (FIG. 8A) and current-light output characteristics (FIG. 8B) measured for conventional and LED samples of the present embodiment.
- EL electroluminescence
- FIG. 8B a large improvement in output was observed with the reduced composition compared to the flat.
- increasing the composition resulted in a slight decrease in output compared to flat.
- the difference from simulation can be attributed to a wide range of factors such as differences in physical parameters and structures.
- composition ratio of the spacer layer has the minimum efficiency when it is flat, and the efficiency improves as the amount of change in composition (composition gradient) increases from there. can be read as follows.
- the present inventor has confirmed that the present structure is almost optimal in terms of changes in the thickness of the spacer layer and the ultimate Al composition ratio in the experimental results. This was confirmed by changing the parameters more comprehensively through the experiments described below.
- the dependence of the thickness of the spacer layer 136 (spacer layer film thickness) when the composition reduction was employed was investigated.
- the light output was 0.15 mW in the range where the starting Al composition ratio was fixed at 0.94 and the final Al composition ratio was fixed at 0.82, and the thickness of the spacer layer 136 was changed to 3, 6, and 9 nm. , 0.48 mW and 0.33 mW.
- the optical output was 0.20 mW, 0.48 mW and 0.10 mW in order in the range where the ultimate Al composition ratio x was changed to 0.78, 0.82 and 0.86.
- FIG. 9 shows EL spectra obtained from samples of the LED of this embodiment with different starting Al composition ratios of 0.90 and 0.94.
- the spacer layer 136A with a spacer layer thickness of 6 nm, a starting Al composition ratio of 0.94, and a final Al composition ratio of 0.82 can achieve good characteristics.
- Non-Patent Documents 1 to 7 compositionally graded LQB layers have been investigated for LEDs with emission wavelengths longer than 240 nm.
- Non-Patent Document 4 theoretically investigates the composition gradient of the spacer layer.
- the disclosures in any of the documents are limited to devices with long wavelengths in view of Far-UVC (210 nm to 230 nm) in the present application. Since the limit of the Al composition ratio is not a problem in the wavelength region as in the present application, the limitation caused by the Al composition ratio is not taken into consideration in the conventional method. In particular, it is necessary to pay particular attention to the fact that the effect of the compositional gradient varies greatly depending on the employed emission wavelength and material composition.
- the Al composition ratio toward the electron blocking layer it cannot be determined which of the increase in composition and the decrease in composition increases the emission intensity without considering the emission wavelength. For example, at an emission wavelength of 280 nm, there is sufficient room for increasing the Al composition ratio in the composition of the electron blocking layer, so the Al composition ratio of the electron blocking layer can be adjusted over a wide range.
- the contributions of the LQB layer and the spacer layer themselves to electron leakage are relatively limited. Therefore, findings at emission wavelengths longer than 240 nm are not applicable to Far-UVC. Indeed, in the present embodiment, which typically involves operation in the 210-230 nm wavelength range, the experimental results of FIG. has been confirmed for the first time.
- the compositional gradient may increase the barrier height of the electron blocking layer 138 when viewed from the quasi-Fermi level of electrons, thereby suppressing the overflow.
- the inventors speculate.
- the effect of increasing the barrier height of the electron blocking layer 138 with reference to the quasi-Fermi level is produced both in the Al composition ratio decreasing slope 136D and increasing composition slope 136U (both of which are shown in FIG. 3). sell.
- FIG. 10A and 10B compare the conventional LED (FIG. 10A) and the LED of the present embodiment (FIG. 10B), focusing on the polarization of the emitted UV. It is a band diagram for explaining the technical idea of the embodiment.
- the simulation software nextnano (nextnano GmbH, Kunststoff, Germany) was used for calculation of the band diagram, and the Al compositions of the barrier layer and well layer used for the calculation were 0.94 and 0.82, respectively.
- These figures are enlarged portions of a portion of the quantum well layer 13W, showing two band profiles near the conduction band edge (E C ) and the valence band edge (E V ) and the amplitude at each position of the wave function. The envelope with the magnitude of is shown.
- FIG. 10A shows a configuration in which the quantum well layer 13W is 2 nm thick and the barrier layer 13B is 6 nm thick
- FIG. 10B is a configuration in which the quantum well layer 13W is 2 nm thick and the barrier layer 13B is 1 nm thick. are the conditions for crystal growth.
- the horizontal direction of the drawing is the position in the thickness direction, but as shown in the scale, the scale in the thickness direction is enlarged in FIG. 10B as compared to FIG. 10A.
- the ranges of the quantum well layer 13W and barrier layer 13B are shown above the graphs of FIGS. 10A and 10B.
- the origin (0 nm) to 6 nm and 8 nm to 14 nm are the barrier layers 13B, and -2 nm to 0 nm, 6 nm to 8 nm, and 14 nm to 16 nm are the quantum well layers 13W.
- the origin (0 nm) to 1 nm and 3 nm to 4 nm are the barrier layers 13B, and 1 nm to 3 nm and 4 nm to 6 nm are the quantum well layers 13W.
- the thickness of the barrier layer has been generally adopted in the configuration of conventional LEDs with an emission wavelength of about 280 nm. Also, as described above, TE emission is emitted in the thickness direction of the laminated structure of the LED in FIG. .
- a plurality of quantum well layers 13W are provided, and adjacent quantum well layers 13W are partitioned by barrier layers 13B.
- the quantum well layer 13W and the barrier layer 13B are drawn at the low-energy and high-energy positions of the conduction band edges E C , respectively.
- the two profiles near the valence band edge E V are the opposite. This figure is obtained by simultaneous calculation of Schrödinger's equation and Poisson's equation for a structure in which well layers and barrier layers are periodically repeated.
- Two band profiles near the conduction band edge and the valence band edge each have a slope corresponding to a crystal formed on a polar substrate.
- the low-energy position of the conduction band edge of the quantum well layer 13W is located below the high-energy position of the conduction band edge of the adjacent barrier layer 13B. acts as a quantum well. Electrons that contribute to light emission undergo an optical transition from the state formed in the quantum well.
- An optical transition of an electron is a pairwise recombination with a valence band edge state (hole state) that satisfies a selection rule due to spatial symmetry. At that time, in addition to the selection rule based on spatial symmetry, the optical transition with holes, which has the smallest energy difference, becomes dominant, and photons with that energy difference are emitted.
- the radiation pattern depends on the direction of the electric dipole moment of the optical transition, and the orientation of the optical transition with the electric dipole moment depends on the initial and final states allowed by the selection rule reflecting the spatial symmetry. is determined by the pair of wavefunctions that yield the pair of In FIGS. 10A and 10B, the two states near the valence band edge include TE and , and those in which TM emission is dominant are labeled with TM.
- one wave function envelope curve is shown at the conduction band edge and two wave function envelope curves are shown at the valence band edge, roughly matching the quantum well layer 13W. .
- the number of these envelopes corresponds to the number of conduction band edge and valence band edge profiles, respectively.
- the vertical position of the straight line drawn for the envelope amplitude reference corresponds to the energy value on the scale for the band profile shown on the left axis of each figure, except for the enlarged figures. It is drawn to match.
- TM emission dominates if the barrier layer 13B has a conventional thickness of 6 nm. target. This has been clarified as one of the factors for the low luminous efficiency. Note that TE emission is realized in LEDs designed by a conventional method that employs a material in which the Al composition ratio of GaN-based materials (including InGaN-based materials) is 0, such as blue light-emitting diodes.
- the relative ratio of TM emission increases as the Al composition ratio increases to shorten the wavelength by adopting AlGaN-based crystals, and the Al composition ratio is about 0.5.
- TE emission and TM emission are at odds with each other. If the Al composition ratio is increased as it is, eventually almost 100% of the light will be TM light emission.
- conventional deep ultraviolet LEDs that operate at 260 to 280 nm, for example, that employ an Al composition ratio exceeding about 0.5, a thin quantum well layer of about 2 nm is adopted to solve this problem, and the confinement of the quantum effect results in TE Approaches have been taken to increase the relative ratio of emissions.
- the quantum confinement effect by thinning the quantum well layer cannot cause the reversal of the energy value of the hole state.
- the ratio of TM emission becomes high as shown in FIG. This is unavoidable, and efficiency improvement cannot be expected.
- FIG. 11 is a graph showing the measured values of emission spectra of LED samples actually produced with barrier layers having a thickness of 6 nm (curve C1) and 1 nm (curve C2) in order to confirm the technical concept of the present embodiment. be.
- the operating conditions were room temperature (300 K) and 50 mA (device size 0.16 mm 2 ).
- the composition-graded spacer layer 136A was employed, the thickness of the quantum well layer 13W was fixed to 2 nm, and the barrier layer 13B was set to 6 nm and 1 nm for comparison. Both emission wavelengths are 227 nm, and the number of quantum well layers 13W is four.
- FIG. 12 shows the relationship between the thickness of the barrier layer 13B and the intensity of TE emission with the thickness of the quantum well layers fixed to 3 nm and the number of quantum well layers fixed to 4, which was obtained in a simulation for confirming the technical idea of the present embodiment. It is a graph showing the relationship. As shown in FIG. 11, by changing the thickness of the barrier layer 13B from the conventional 6 nm to 1 nm, the emission intensity is substantially doubled.
- the emission intensity begins to significantly increase when the thickness of the barrier layer 13B is 4 nm or less.
- the thickness of the barrier layer 13B is preferably 4 nm or less, more preferably 3 nm or less, even more preferably 2 nm or less, and even more preferably 1 nm or less. If the thickness of the barrier layer 13B is thicker than 0.25 nm, which is the thickness of the monolayer, there is no particular problem in manufacturing. Also, the thickness of the barrier layer 13B can be determined based on the thickness of the quantum well layer.
- the thickness of the barrier layer 13B it is preferable to set the thickness of the barrier layer 13B so as to be equal to or less than the thickness of the quantum well layer. Furthermore, it is also useful to determine by the relative ratio of TE emission and TM emission. When the thickness of the barrier layer 13B is set to 3 nm to 4 nm or less, the intensity of the TE emission becomes about 50% of the intensity of the total emission (TE emission+TM emission) and exceeds the TM emission. Therefore, it is also preferable to determine the thickness of the barrier layer 13B so that the TE emission is stronger than the TM emission. However, the ratio of TE emission exceeds 90% by setting the thickness of the barrier layer 13B to about 1 nm.
- the thickness of the barrier layer 13B is less than 0.25 nm, for example, about 0.2 nm. There can be situations.
- the preferable thickness of the barrier layer 13B suitable for a monolayer is 0.2 nm or more. Reducing the thickness of the barrier layer 13B in addition to the quantum well layer 13W not only makes it possible to generate TE light emission, but also maintains carrier trapping, so there is no fear of a decrease in efficiency due to carrier detachment. Furthermore, although there is generally a concern that the carrier mobility will decrease at a high Al composition ratio, thinning the barrier layer 13B also has the advantage of making the carrier distribution uniform among the plurality of quantum well layers 13W. becomes. If the thickness of the barrier layer 13B is 6 nm, the ratio of TE emission is about 20%.
- TM emission or TE emission is determined by the direction of the electric dipole moment realized by the large value of the dipole matrix element between the initial state and the final state.
- TM emission or TE emission is determined by the direction of the electric dipole moment realized by the large value of the dipole matrix element between the initial state and the final state.
- the state that contributes to light emission in the quantum well must have energy smaller than the maximum energy of the barrier layer, and generally this state is the bound state.
- States above the maximum energy are unbound states.
- the number of bound states depends on the size of the effective mass and the size of the confinement potential (energy difference between the barrier layer and the well layer), and the smaller the effective mass and the smaller the confinement potential, the smaller the number.
- the confinement potential cannot be made too large in order to achieve a short wavelength. Therefore, there is only one bound state for electrons in this calculation. This is in contrast to the possibility of more than one bound state for an electron in an LED emitting at 280 nm.
- the number of bound states of holes is quite large, about 10 under the calculation conditions of this time. However, how much carriers are distributed in the bound state is important in determining whether or not a carrier contributes to light emission. Because the number of carriers decreases exponentially with deeper bound states (lower in the band diagram), emission properties are mostly determined by comparing the shallowest and second shallowest bound states. be done. 10A and 10B show only two levels in that sense. Although the TE/TM emission intensity ratio in FIG. 12 is calculated considering up to the fourth bound state, the number of carriers in the fourth is actually 1% or less of that in the first. This is shown in FIGS. 10A and 10B.
- the quantum confinement effect causes the valence band edge state to widen in energy difference from the conduction band edge state, that is, to the low energy side (Fig. 10A, B).
- This amount of shift is due to quantum confinement, and is more fundamentally a manifestation of the uncertainty principle. Since electrons have a smaller effective mass in the two states of interest at the valence band edge in the one responsible for TM emission than in the one responsible for TE emission, the state responsible for TM emission in which the electron has a lower effective mass is There is a large downward shift, whereas the states responsible for TE emission with large effective masses shift relatively small.
- the state responsible for TM emission with a small effective mass is largely shifted downward, and the state responsible for TE emission can be passed over. This would be the cause of the change from TM emission to TE emission between FIGS. 10A and 10B.
- the quantum confinement effect was considered by thinning the quantum well layer 13W.
- the shift is also effective for optical transitions at wavelengths.
- the barrier layer 13B contributes to the quantum confinement effect may be related to the valence band edge profile in which the quantum wells and barriers are inclined and bent in a sawtooth shape.
- a valence band edge profile reflects that the crystal has a polar orientation.
- the quantum well layer 13W and the thinned barrier layer 13B collectively affect the valence band edge profile, resulting in the shift described above.
- the effect brought about by thinning in one layer is not limited to the case where the crystal has a polar orientation, and the substrate for epitaxial growth may be a semipolar substrate or a nonpolar substrate instead of a polar substrate. Even in such a case, thinning the barrier layer 13B can be effective.
- FIG. 13A is a graph of the characteristics (FIG. 13B); As shown in FIG. 13A, a narrow single-peak emission with an emission wavelength of 227 nm and a full width at half maximum of 10 nm was observed in the Far-UVC region in continuous operation at room temperature. It was confirmed that a practical level Far-UVC LED with 0.2% and an optical output of 1.2 mW can be realized.
- the composition-graded spacer layer and the reduction in the thickness of the barrier layer for enhancing TE emission are not limited to AlGaN-based crystals. It is also applicable to structures made of InAlGaN-based crystals. These technical ideas are also applicable to LEDs emitting light in a wavelength range outside the range of 210 to 230 nm.
- the manufacturing method of the LED that can be employed in this embodiment is not particularly limited, and for example, in addition to the MOVPE method, the MBE (Molecular Beam Epitaxy) method can be employed.
- the Far-UVC LED with improved luminous efficiency of the present disclosure can be used in any device that has it as a source of ultraviolet radiation.
Landscapes
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Computer Hardware Design (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Power Engineering (AREA)
- Led Devices (AREA)
Abstract
Description
本実施形態のLED100Aでは、組成傾斜のスペーサー層136Aを採用することにより電子のオーバーフローを抑制する。本実施形態のLED100Aではさらにそれと組合わせて、または組合わせることなく単独で、複数の量子井戸層13Wの間に位置する障壁層13Bを薄層化することによりTE光の発光に有利なバンド構造を実現する。以下、組成傾斜のスペーサー層136Aと薄層化した障壁層13Bとを両方採用するLEDの構造を説明し(1-1)、さらに、組成傾斜のスペーサー層の詳細を説明し(1-2)、薄層化した障壁層の詳細を説明し(1-3)、これらの組み合わせについて説明し(1-4)、最後に変形例について説明する(1-5)。
図1は、従来のLED100および本実施形態のLED100Aの両者に共通する概略構成を示す斜視図である。LED100および100Aの典型的な構成では、平板状のα-Al2O3単結晶(サファイア)である基板110の一方の面104にバッファー層120がAlN結晶等の材質によりエピタキシャル成長される。そのバッファー層120の側から、n型導電層132がこの順に積層し形成されている。
本実施形態のLED100Aでは、スペーサー層136AのAl組成比を厚み方向の位置に応じて連続的に変化させる。この連続的変化は、位置に応じて増加したり減少したりするよう傾斜させるものが典型であるため、本実施形態において「組成傾斜」と呼ぶ。図3は、障壁層13B、量子井戸層13W、スペーサー層136、136A、電子ブロック層138における積層の厚み方向の位置とAl組成比との間の関係を示す模式図である。図面横方向および縦方向は、それぞれ、LED100、100Aにおける積層方向の位置および各位置でのAlN組成比である。スペーサー層136、136Aは、複数ある量子井戸層13Wのうち電子の流れの向き(図面における右向き)における最下流のものと電子ブロック層138との間に挟まれている。Al組成比は、量子井戸層13Wでは小さく、電子ブロック層138では大きく、スペーサー層136、136Aは、量子井戸層13Wと電子ブロック層138との間の値になるよう構成されている。従来のLED100のスペーサー層136は厚み方向の位置によらず平坦(フラット)に分布するAl組成比(図の鎖線136F)を持つように作製される。これに対し、本実施形態のLED素100Aのスペーサー層136Aは、発光層134から電子ブロック層138に向かう厚み方向の位置に応じてAl組成比を増加する傾斜136Uまたは減少する傾斜136Dを持つようになっている。本出願書面において、Al組成比を発光層134から電子ブロック層138に向かう向きにおいて増加および減少する傾斜を持つような構成を、それぞれ、組成増加および組成減少とも呼ぶ。なお、図2に示していたスペーサー層136の伝導帯端プロファイルは、結晶がもつ極性のために、組成が変化する位置においてピエゾ分極などが生じうる。結果、フラットなAl組成比のスペーサー層136の伝導帯端プロファイルも、一般に傾斜やベンディングを伴っている。
A)組成傾斜ではフラットなものに比べ、電子ブロック高さが実質的に増加しており、電子のオーバーフローが抑制されている。
B)組成傾斜ではフラットなものに比べ、正孔ブロック高さが減少する作用が生まれ、正孔の注入効率が増加している。
C)組成傾斜ではフラットなものに比べ、スペーサ層と電子ブロック層との界面に蓄積したキャリアが発光に寄与する。これは、実質的に量子井戸が1個追加されるかのような作用をもつ。この実質的な量子井戸を「界面量子井戸(Interface Quantum Well:IQW)」と呼ぶ。
なお、現実には、これらの物理的メカニズムのうち、少なくともいずれかが作用しており、いずれか複数が同時に作用していることもあり得るものと予測している。
図10A、図10Bは、従来のLED(図10A)と本実施形態のLED(図10B)とを対比させて、放出されるUVの偏光に着目して本実施形態の技術思想を説明するためのバンドダイアグラムである。バンドダイアグラムの計算にはシミュレーションソフトウエアnextnano(nextnano GmbH、ミュンヘン、ドイツ)を採用し、計算に用いた障壁層および井戸層のAl組成はそれぞれ0.94、0.82とした。これらの図は、一部の量子井戸層13Wの部分を拡大するものであり、伝導帯端(EC)および価電子帯端(EV)付近2つのバンドプロファイルと波動関数の各位置の振幅の大きさによる包絡線とが示されている。各図の円内に一対の価電子帯端付近の2つの波動関数包絡線の拡大図も示している。図10Aは量子井戸層13Wを2nm厚、障壁層13Bを6nm厚とした構成、図10Bは、量子井戸層13Wを2nm厚、障壁層13Bを1nmとした構成のものであり、ともに極性基板での結晶成長の条件のものである。図面左右方向は厚み方向の位置であるが、目盛に示されるように図10Bは図10Aよりも厚み方向のスケールが拡大されている。量子井戸層13W、障壁層13Bの範囲は、図10A、図10Bのグラフの上方に示している。具体的には、厚み方向の位置で、従来のLEDでは原点(0nm)~6nmおよび8nm~14nmが障壁層13B、-2nm~0nm、6nm~8nm、14nm~16nmが量子井戸層13Wである。これに対し、障壁層を1nm厚とした本実施形態のものでは、原点(0nm)~1nmおよび3nm~4nmが障壁層13B、1nm~3nm、4nm~6nmが量子井戸層13Wである。
図11に曲線C2で示される発光スペクトルを示したLEDサンプルでは、組成傾斜のスペーサー層136Aを採用した上で障壁層13Bの厚みの違いを検証していた。また、組成傾斜のスペーサー層136Aにおいて電子の注入効率が改善されることは図8Aに関連して上述した通りである。つまり、いずれも発光に関連している組成傾斜のスペーサー層136Aと薄層化した障壁層13は、組合わせることについて技術的障害を生じない。このため、これらの技術思想を重複して採用することは実用性の観点で有利である。図13A、図13Bは、図8Aと同様に組成傾斜のスペーサー層と薄層化した障壁層とを重複して適用した本実施形態のFar-UVCLEDサンプルにおける発光スペクトル(図13A)と電流光出力特性(図13B)のグラフである。図13Aに示すように、室温の連続動作においてFar-UVC領域で発光波長227nm、半値全幅10nmの狭い単一ピークの発光が観察され、さらに図13Bに示すように、パルス動作において外部量子効率0.2%、光出力1.2mWという実用レベルのFar-UVCLEDが実現できることが確認された。
本実施形態の技術思想である組成傾斜のスペーサー層や、TE発光増強のための障壁層の薄膜化は、AlGaN系結晶だけではなく、例えばInもいずれかの層の組成の一部に含むInAlGaN系結晶による構造においても同様に適用可能である。これらの技術思想は、また、210~230nmの範囲を外れる波長域を発光波長とするLEDについても適用可能である。さらに、本実施形態として採用可能なLEDの製法は特段限定されるものではなく、例えばMOVPE法に加え、MBE(Molecular Beam Epitaxy)法を採用することができる。スペーサー層136におけるAl組成比の組成分布は直線的に増加させたり、直線的に減少させたりする構成について説明したが、積層の厚み方向の位置に応じて種々の変化を与えることも本実施形態の変形として採用しうる。
102 光取出し面
104 基板の一方の面
110 基板
120 バッファー層
132 n型導電層
134 発光層
13W 量子井戸層
13B 障壁層
136 スペーサー層
136A スペーサー層(組成傾斜)
138 電子ブロック層
140 第1電極
150 p型コンタクト層
160 反射電極
162 挿入金属層
164 UV反射膜
Claims (12)
- AlGaN系結晶またはInAlGaN系結晶を含む紫外発光ダイオードであって、
発光層と、
スペーサー層と、
電子ブロック層と
を電子の流れの上流から下流に向かってこの順に積層して備えており、
前記スペーサー層におけるAl組成比が積層の厚み方向の位置に応じて変化している
紫外発光ダイオード。 - AlGaN系結晶またはInAlGaN系結晶を含む紫外発光ダイオードであって、
少なくとも1つの障壁層および該障壁層を挟む少なくとも2つの量子井戸層を含む発光層を備えており、
該障壁層が薄層化されている
紫外発光ダイオード。 - 前記発光層が、少なくとも1つの障壁層および該障壁層を挟む少なくとも2つの量子井戸層を含むものであり、
該障壁層が薄層化されている
請求項1に記載の紫外発光ダイオード。 - 前記スペーサー層の組成分布が、前記発光層から前記電子ブロック層に向かって前記Al組成比が減少するよう傾斜しているものである
請求項1または請求項3に記載の紫外発光ダイオード。 - 前記スペーサー層と前記電子ブロック層との界面が形成する界面量子井戸による発光ピーク波長に応じて、前記電子ブロック層に到達する位置の前記スペーサー層のAl組成比である前記到達Al組成比の値が決定される
請求項4に記載の紫外発光ダイオード。 - 前記スペーサー層の組成分布が、前記発光層から前記電子ブロック層に向かって前記Al組成比が増加するよう傾斜しているものである
請求項1または請求項3に記載の紫外発光ダイオード。 - 前記障壁層の厚みが0.2nm以上4nm以下である
請求項2または請求項3に記載の紫外発光ダイオード。 - 前記障壁層の厚みが1nm以上3nm以下である
請求項7に記載の紫外発光ダイオード。 - 前記障壁層の厚みは、前記発光層での発光を、TE発光がTM発光よりも強くなるようにする厚みである
請求項2または請求項3に記載の紫外発光ダイオード。 - 前記障壁層の厚みが、前記量子井戸層の厚み以下である
請求項2または請求項3に記載の紫外発光ダイオード。 - 発光する紫外線の主要波長が210~230nmである
請求項1~請求項3のいずれか1項に記載の紫外発光ダイオード。 - 請求項1~請求項3のいずれか1項に記載の紫外発光ダイオードを紫外線の放出源として備える電気機器。
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2023539734A JPWO2023013374A1 (ja) | 2021-08-03 | 2022-07-13 |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2021127756 | 2021-08-03 | ||
JP2021-127756 | 2021-08-03 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO2023013374A1 true WO2023013374A1 (ja) | 2023-02-09 |
Family
ID=85155975
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/JP2022/027508 WO2023013374A1 (ja) | 2021-08-03 | 2022-07-13 | 紫外発光ダイオードおよびそれを備える電気機器 |
Country Status (2)
Country | Link |
---|---|
JP (1) | JPWO2023013374A1 (ja) |
WO (1) | WO2023013374A1 (ja) |
Citations (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2009054780A (ja) * | 2007-08-27 | 2009-03-12 | Institute Of Physical & Chemical Research | 光半導体素子及びその製造方法 |
US8451877B1 (en) * | 2010-03-23 | 2013-05-28 | Sandia Corporation | High efficiency III-nitride light-emitting diodes |
US20170358705A1 (en) * | 2014-12-22 | 2017-12-14 | Lg Innotek Co., Ltd. | Light emitting device and light emitting device package having same |
JP2018049949A (ja) * | 2016-09-21 | 2018-03-29 | シャープ株式会社 | 窒化アルミニウム系半導体深紫外発光素子 |
JP2019029536A (ja) * | 2017-07-31 | 2019-02-21 | Dowaホールディングス株式会社 | Iii族窒化物エピタキシャル基板、電子線励起型発光エピタキシャル基板及びそれらの製造方法、並びに電子線励起型発光装置 |
US20190148584A1 (en) * | 2017-11-15 | 2019-05-16 | Cornell University | Light emitting diodes using ultra-thin quantum heterostructures |
JP2019530228A (ja) * | 2016-09-13 | 2019-10-17 | エルジー イノテック カンパニー リミテッド | 半導体素子およびこれを含む半導体素子パッケージ |
JP2020098908A (ja) * | 2018-12-14 | 2020-06-25 | Dowaエレクトロニクス株式会社 | Iii族窒化物半導体発光素子及びその製造方法 |
-
2022
- 2022-07-13 WO PCT/JP2022/027508 patent/WO2023013374A1/ja active Application Filing
- 2022-07-13 JP JP2023539734A patent/JPWO2023013374A1/ja active Pending
Patent Citations (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2009054780A (ja) * | 2007-08-27 | 2009-03-12 | Institute Of Physical & Chemical Research | 光半導体素子及びその製造方法 |
US8451877B1 (en) * | 2010-03-23 | 2013-05-28 | Sandia Corporation | High efficiency III-nitride light-emitting diodes |
US20170358705A1 (en) * | 2014-12-22 | 2017-12-14 | Lg Innotek Co., Ltd. | Light emitting device and light emitting device package having same |
JP2019530228A (ja) * | 2016-09-13 | 2019-10-17 | エルジー イノテック カンパニー リミテッド | 半導体素子およびこれを含む半導体素子パッケージ |
JP2018049949A (ja) * | 2016-09-21 | 2018-03-29 | シャープ株式会社 | 窒化アルミニウム系半導体深紫外発光素子 |
JP2019029536A (ja) * | 2017-07-31 | 2019-02-21 | Dowaホールディングス株式会社 | Iii族窒化物エピタキシャル基板、電子線励起型発光エピタキシャル基板及びそれらの製造方法、並びに電子線励起型発光装置 |
US20190148584A1 (en) * | 2017-11-15 | 2019-05-16 | Cornell University | Light emitting diodes using ultra-thin quantum heterostructures |
JP2020098908A (ja) * | 2018-12-14 | 2020-06-25 | Dowaエレクトロニクス株式会社 | Iii族窒化物半導体発光素子及びその製造方法 |
Non-Patent Citations (7)
Also Published As
Publication number | Publication date |
---|---|
JPWO2023013374A1 (ja) | 2023-02-09 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
Ren et al. | Band engineering of III-nitride-based deep-ultraviolet light-emitting diodes: a review | |
JP5843238B2 (ja) | 窒化物半導体多重量子障壁を有する発光素子及びその製造方法 | |
JP5238865B2 (ja) | 半導体発光素子 | |
KR100689782B1 (ko) | 반도체 발광 소자 및 그 제조 방법 | |
JP5963004B2 (ja) | 窒化物半導体発光素子 | |
TWI403002B (zh) | 半導體發光元件 | |
KR101199677B1 (ko) | 반도체 발광 소자 및 그 제조 방법 | |
US8519411B2 (en) | Semiconductor light emitting device | |
TW200303105A (en) | Nitride semiconductor device | |
CN107809057B (zh) | GaN基复合DBR谐振腔激光器外延片、激光器及制备方法 | |
Ahmad et al. | Performance enhancement of UV quantum well light emitting diode through structure optimization | |
Usman et al. | Quantum efficiency enhancement by employing specially designed AlGaN electron blocking layer | |
US9673352B2 (en) | Semiconductor light emitting device | |
JP6754918B2 (ja) | 半導体発光素子 | |
JP2007251092A (ja) | 半導体レーザ | |
WO2023013374A1 (ja) | 紫外発光ダイオードおよびそれを備える電気機器 | |
JP6183060B2 (ja) | 半導体発光素子 | |
JP2012069901A (ja) | 半導体発光素子 | |
CN111446621B (zh) | 半导体激光元件及其制造方法 | |
JP2012060170A (ja) | 半導体発光素子及びその製造方法 | |
WO2023162839A1 (ja) | 紫外発光素子およびそれを備える電気機器 | |
Saranya et al. | Parameter Analysis Review on Multiple Quantum Well based InGaN/GaN Light Emitting Diode | |
JP5865827B2 (ja) | 半導体発光素子 | |
CN108574004B (zh) | 具有内场防护有源区的半导体器件 | |
JP2012186410A (ja) | 半導体素子 |
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: 22852800 Country of ref document: EP Kind code of ref document: A1 |
|
WWE | Wipo information: entry into national phase |
Ref document number: 2023539734 Country of ref document: JP |
|
WWE | Wipo information: entry into national phase |
Ref document number: 2022852800 Country of ref document: EP |
|
NENP | Non-entry into the national phase |
Ref country code: DE |
|
ENP | Entry into the national phase |
Ref document number: 2022852800 Country of ref document: EP Effective date: 20240304 |