Pub Date : 2017-07-12DOI: 10.1117/2.1201702.006743
H. Ohadi, P. Savvidis, J. Baumberg
Light travels fast, which is why nowadays all of our communications involve optical fibers. But our computations are based on matter, specifically, electrons that move inside wires and transistors. The problem is that electrons interact with matter, thus causing heat. To minimize heat and to squeeze more transistors onto chips, we have made them smaller and smaller to keep up with Moore’s law (the observation that the number of transistors in CPUs—central processing units—doubles every two years). It seems, however, that that we are about to hit a hard wall. When we make the wires very thin and our transistors very small, quantum mechanical interference ruins the signals. Consequently, large technology companies like Intel and IBM are trying new ways of using optical interconnects between separate chips or even integrated inside chips. The idea here is that light does not produce as much heat as electronics do, and it can be 100 times faster. The bottleneck is the conversion between electronics and optics. The Holy Grail for optical computing is a switch that can convert electrical signals to optical signals quickly and efficiently and can be integrated inside chips. Our group has recently demonstrated an ultra-low-energy spin switch based on a ‘liquid-light’ exciton-polariton condensate.1 These condensates are half-matter, half-light. Using their matter properties, we can electronically control them and take advantage of their fast dynamics (because they are half-light). It turns out that, similar to field-effect transistors (FETs), we can switch the polarization of liquid lights with minuscule amounts of energy and, because they are micrometer size, they can be integrated into chips as well. Exciton-polaritons (polaritons) are a superposition of photons in a Fabry-Pérot microcavity and confined excitons (typically in 2D quantum wells).2 They are very light (100,000 times lighter than electrons) and very fast (>100GHz) thanks to their photonic component, but they can also strongly interact with each Figure 1. (a) Electrically controlled polariton spin switch. (b) Trapped condensate of polaritons (yellow emission) forms by nonresonant excitation (with blue lasers) of the microcavity. V ̇: Voltage.
{"title":"A sub-femtojoule electrical spin switch based on liquid light","authors":"H. Ohadi, P. Savvidis, J. Baumberg","doi":"10.1117/2.1201702.006743","DOIUrl":"https://doi.org/10.1117/2.1201702.006743","url":null,"abstract":"Light travels fast, which is why nowadays all of our communications involve optical fibers. But our computations are based on matter, specifically, electrons that move inside wires and transistors. The problem is that electrons interact with matter, thus causing heat. To minimize heat and to squeeze more transistors onto chips, we have made them smaller and smaller to keep up with Moore’s law (the observation that the number of transistors in CPUs—central processing units—doubles every two years). It seems, however, that that we are about to hit a hard wall. When we make the wires very thin and our transistors very small, quantum mechanical interference ruins the signals. Consequently, large technology companies like Intel and IBM are trying new ways of using optical interconnects between separate chips or even integrated inside chips. The idea here is that light does not produce as much heat as electronics do, and it can be 100 times faster. The bottleneck is the conversion between electronics and optics. The Holy Grail for optical computing is a switch that can convert electrical signals to optical signals quickly and efficiently and can be integrated inside chips. Our group has recently demonstrated an ultra-low-energy spin switch based on a ‘liquid-light’ exciton-polariton condensate.1 These condensates are half-matter, half-light. Using their matter properties, we can electronically control them and take advantage of their fast dynamics (because they are half-light). It turns out that, similar to field-effect transistors (FETs), we can switch the polarization of liquid lights with minuscule amounts of energy and, because they are micrometer size, they can be integrated into chips as well. Exciton-polaritons (polaritons) are a superposition of photons in a Fabry-Pérot microcavity and confined excitons (typically in 2D quantum wells).2 They are very light (100,000 times lighter than electrons) and very fast (>100GHz) thanks to their photonic component, but they can also strongly interact with each Figure 1. (a) Electrically controlled polariton spin switch. (b) Trapped condensate of polaritons (yellow emission) forms by nonresonant excitation (with blue lasers) of the microcavity. V ̇: Voltage.","PeriodicalId":22075,"journal":{"name":"Spie Newsroom","volume":"60 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-07-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84957826","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-07-10DOI: 10.1117/2.1201704.006844
P. Xi
The physical phenomenon of fluorescence has a number of fundamental dimensions, e.g., intensity, wavelength, time, and polarization. In particular, the fluorescence polarization effect— first discovered in 19261—arises from the transverse nature of light waves (i.e., from dipole orientations). Various fluorescence anistropy techniques have previously been developed to study the dipole orientation of fluorophores. For example, fluorescence polarization microscopy (FPM) is used extensively for biological imaging applications. In this technique, the angle of a fluorophore is measured so that the orientation and structural details of a targeted protein can be resolved. Conventional FPM methods, however, are limited because of the presence of many molecules within the diffraction-limited volume. This means that the fluorescence polarization information is collected from dipoles with many different orientations. The idea of using super-resolution to improve imaging resolving power was first proposed in 1995.2 This idea has since been realized, i.e., with a photobleaching-photoactivation process used to separate molecules (with a resolution of about 20nm) in the time domain.3 Previously developed super-resolution microscopy approaches, which extend vision beyond the diffraction limit, are mostly based on the intensity, wavelength, and temporal dimensions of fluorescence. Although the fourth dimension of fluorescence, i.e., polarization, can also be used to modulate fluorescence (without restriction to specific fluorophores), this mode of super-resolution microscopy has only recently been investigated. Indeed, a new technique—sparse deconvolution of polarization-modulated fluorescent images (SPoD)—was first developed in 2014 (with which a resolution of 5nm was demonstrated at 1 frame/second).4 Although super-resolution can be achieved with this technique, the dipole orientation information is lost during the SPoD reconstruction and an interesting debate—whether or not fluorescent Figure 1. Illustration of the super-resolution dipole orientation mapping (SDOM) technique. (a) Two fluorophores, 100nm apart, with different dipole orientations are shown in red and green. When excited by rotating polarized light they emit periodic signals. The emission ratio between the two molecules can be modulated accordingly and used to separate them in the polarization domain. The SDOM procedure provides a super-resolution image of the effective dipole intensities (compared with an unresolved wide-field image). Arrows indicate the different dipole orientations. Scale bar denotes 200nm. (b) SDOM result for two fluorophores, superimposed on top of a super-resolution image, where the two molecules cannot be separated. (c) The same data shown in a 3D coordinate system (XY is the plane of the super-resolved intensity image and is the dipole orientation). In this perspective, the two molecules can be completely resolved.7
{"title":"Polarization as a new dimension in super-resolution microscopy","authors":"P. Xi","doi":"10.1117/2.1201704.006844","DOIUrl":"https://doi.org/10.1117/2.1201704.006844","url":null,"abstract":"The physical phenomenon of fluorescence has a number of fundamental dimensions, e.g., intensity, wavelength, time, and polarization. In particular, the fluorescence polarization effect— first discovered in 19261—arises from the transverse nature of light waves (i.e., from dipole orientations). Various fluorescence anistropy techniques have previously been developed to study the dipole orientation of fluorophores. For example, fluorescence polarization microscopy (FPM) is used extensively for biological imaging applications. In this technique, the angle of a fluorophore is measured so that the orientation and structural details of a targeted protein can be resolved. Conventional FPM methods, however, are limited because of the presence of many molecules within the diffraction-limited volume. This means that the fluorescence polarization information is collected from dipoles with many different orientations. The idea of using super-resolution to improve imaging resolving power was first proposed in 1995.2 This idea has since been realized, i.e., with a photobleaching-photoactivation process used to separate molecules (with a resolution of about 20nm) in the time domain.3 Previously developed super-resolution microscopy approaches, which extend vision beyond the diffraction limit, are mostly based on the intensity, wavelength, and temporal dimensions of fluorescence. Although the fourth dimension of fluorescence, i.e., polarization, can also be used to modulate fluorescence (without restriction to specific fluorophores), this mode of super-resolution microscopy has only recently been investigated. Indeed, a new technique—sparse deconvolution of polarization-modulated fluorescent images (SPoD)—was first developed in 2014 (with which a resolution of 5nm was demonstrated at 1 frame/second).4 Although super-resolution can be achieved with this technique, the dipole orientation information is lost during the SPoD reconstruction and an interesting debate—whether or not fluorescent Figure 1. Illustration of the super-resolution dipole orientation mapping (SDOM) technique. (a) Two fluorophores, 100nm apart, with different dipole orientations are shown in red and green. When excited by rotating polarized light they emit periodic signals. The emission ratio between the two molecules can be modulated accordingly and used to separate them in the polarization domain. The SDOM procedure provides a super-resolution image of the effective dipole intensities (compared with an unresolved wide-field image). Arrows indicate the different dipole orientations. Scale bar denotes 200nm. (b) SDOM result for two fluorophores, superimposed on top of a super-resolution image, where the two molecules cannot be separated. (c) The same data shown in a 3D coordinate system (XY is the plane of the super-resolved intensity image and is the dipole orientation). In this perspective, the two molecules can be completely resolved.7","PeriodicalId":22075,"journal":{"name":"Spie Newsroom","volume":"162 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86370177","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-07-06DOI: 10.1117/2.1201703.006829
Shau-Yu Lan, Pei-Chen Kuan, Chang Huang
A velocity sensor (or velocimeter) is a device used to measure the rate of change of a moving object’s position. Such devices (which have important applications in, e.g., navigation and manufacturing) are typically based on measuring the first-order Doppler shift of electromagnetic waves that are reflecting or scattering off of a moving object. In the quantum regime, the velocity measurements of particles are important for studying fundamental physics. As an example, when a photon is absorbed by an atom, the atom will gain a recoil energy, or recoil velocity. By measuring this recoil velocity from the spectral shift of the atomic resonance, the fine-structure constant can be determined and the theory of quantum electrodynamics tested.1 Another example of its usefulness is in the measurement of the local gravitational acceleration of two different species of free-falling atoms (to test Einstein’s equivalence principle).1 All atom-based sensors rely on measuring the first-order Doppler shift of the atomic transition. By using Dopplersensitive methods to detect the population of atomic states, the velocity can be measured precisely. However, due to the thermal distribution of an atomic ensemble, the uncertainty of the measurement is limited by the Doppler width of the ensemble. Thus, to determine its center-of-mass motion, one usually needs to map or truncate the velocity distribution of the ensemble. This approach complicates the process and lowers the data rate.1 In our experiment, we demonstrate the light-dragging effect (i.e., the deviation of the phase velocity of an electromagnetic wave from the speed of light in a moving medium) and use it to directly sense the center-of-mass motion of an atomic ensemble. The light-dragging effect was first observed by Fizeau in a flowing-water experiment for the study of ether, before the era of Einstein’s special theory of relativity. It was later explained by the Lorentz addition to the first order of velocity in the equation related to Einstein’s theory.2 The effect (illustrated in Figure 1) Figure 1. Illustration of the light-dragging effect in a moving medium. The phase velocity (Vp) of light is modified by an additional term, Fd V (where Fd is the dragging coefficient and V is the velocity of the moving medium). The dragged light has a phase shift of ̊ compared to a reference light. c: The speed of light in a vacuum.
{"title":"An atomic velocity sensor based on the light-dragging effect","authors":"Shau-Yu Lan, Pei-Chen Kuan, Chang Huang","doi":"10.1117/2.1201703.006829","DOIUrl":"https://doi.org/10.1117/2.1201703.006829","url":null,"abstract":"A velocity sensor (or velocimeter) is a device used to measure the rate of change of a moving object’s position. Such devices (which have important applications in, e.g., navigation and manufacturing) are typically based on measuring the first-order Doppler shift of electromagnetic waves that are reflecting or scattering off of a moving object. In the quantum regime, the velocity measurements of particles are important for studying fundamental physics. As an example, when a photon is absorbed by an atom, the atom will gain a recoil energy, or recoil velocity. By measuring this recoil velocity from the spectral shift of the atomic resonance, the fine-structure constant can be determined and the theory of quantum electrodynamics tested.1 Another example of its usefulness is in the measurement of the local gravitational acceleration of two different species of free-falling atoms (to test Einstein’s equivalence principle).1 All atom-based sensors rely on measuring the first-order Doppler shift of the atomic transition. By using Dopplersensitive methods to detect the population of atomic states, the velocity can be measured precisely. However, due to the thermal distribution of an atomic ensemble, the uncertainty of the measurement is limited by the Doppler width of the ensemble. Thus, to determine its center-of-mass motion, one usually needs to map or truncate the velocity distribution of the ensemble. This approach complicates the process and lowers the data rate.1 In our experiment, we demonstrate the light-dragging effect (i.e., the deviation of the phase velocity of an electromagnetic wave from the speed of light in a moving medium) and use it to directly sense the center-of-mass motion of an atomic ensemble. The light-dragging effect was first observed by Fizeau in a flowing-water experiment for the study of ether, before the era of Einstein’s special theory of relativity. It was later explained by the Lorentz addition to the first order of velocity in the equation related to Einstein’s theory.2 The effect (illustrated in Figure 1) Figure 1. Illustration of the light-dragging effect in a moving medium. The phase velocity (Vp) of light is modified by an additional term, Fd V (where Fd is the dragging coefficient and V is the velocity of the moving medium). The dragged light has a phase shift of ̊ compared to a reference light. c: The speed of light in a vacuum.","PeriodicalId":22075,"journal":{"name":"Spie Newsroom","volume":"35 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-07-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79632592","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-07-03DOI: 10.1117/2.1201704.006840
A. Gragossian, M. Ghasemkhani, Junwei Meng, A. Albrecht, M. Tonelli, M. Sheik-Bahae
Superconductivity, longand mid-wave IR detectors, and ultrastable laser cavities that operate in the 77–150K temperature range can all benefit from vibration-free cooling.1 Currently, such low temperatures can only be achieved using cryogenic gases or liquids, solid cryogens, or mechanical refrigerators. Unfortunately, these coolers require regular attention, introduce vibrational noise, and are subject to mechanical wear over time. Many space-based applications (particularly ultra-stable laser cavities) cannot tolerate these drawbacks. All-solid-state cryocoolers are therefore desirable because of their inherent vibration-free operation and potentially long lifetime. Optical refrigeration (i.e., anti-Stokes fluorescence cooling) is the only solid-state cooling technology capable of reaching cryogenic temperatures. Anti-Stokes cooling—in which a doped crystal is excited by a laser with a wavelength that is longer than the average wavelength of the resulting fluorescence, thus leading to cooling of the crystal—was first suggested by Peter Pringsheim almost 90 years ago.2 It was not actually observed, however, until years after the invention of lasers and the availability of high-purity host materials. The first demonstration of optical refrigeration, reported in 1995, used a fluorozirconate glass doped with ytterbium (Yb). The resulting material is known as Yb3C: ZBLANP.3 Cooling occurs when low-entropy laser light (tuned to a slightly lower energy than the mean fluorescence of a material) is absorbed, thus giving rise to efficient fluorescence generation and escape. On average, each pump photon removes vibrational energy (i.e., phonons) from the cooling sample after being absorbed and re-emitted. Figure 1. Schematic of our astigmatic Herriott cell. The geometry of the cell enables laser light (red) to be trapped inside of the crystal, ensuring more than 95% absorption. R1x;y D 50cm, R2x D 1, and R2y D 50cm, where R1 and R2 are the radii of curvature of the spherical and cylindrical mirrors, respectively. x;y : Launching angle. W : Crystal length, width, and height (Wx D Wy D W ).
超导，长波和中波红外探测器，以及在77-150K温度范围内工作的超稳定激光腔都可以从无振动冷却中受益目前，这种低温只能通过使用低温气体或液体、固体低温剂或机械冰箱来实现。不幸的是，这些冷却器需要定期注意，引入振动噪声，并且随着时间的推移会受到机械磨损。许多天基应用(特别是超稳定激光腔)不能容忍这些缺点。因此，由于其固有的无振动操作和潜在的长寿命，全固态制冷机是可取的。光学制冷(即反斯托克斯荧光冷却)是唯一能够达到低温的固态冷却技术。反斯托克斯冷却——用波长比荧光平均波长长得多的激光激发掺杂晶体，从而导致晶体冷却——是由彼得·普林斯海姆在大约90年前首次提出的然而，直到激光发明和高纯度宿主材料问世多年之后，人们才真正观察到这种现象。1995年报道的第一次光学制冷示范使用了掺有镱的氟锆酸盐玻璃。所得材料称为Yb3C: ZBLANP.3当低熵激光(调谐到比材料的平均荧光能量略低的能量)被吸收时，就会发生冷却，从而产生有效的荧光并逸出。平均而言，每个泵浦光子在被吸收和重新发射后从冷却样品中去除振动能量(即声子)。图1所示。散光Herriott细胞示意图。电池的几何形状使激光(红色)被困在晶体内部，确保95%以上的吸收率。R1x;y D 50cm, R2x d1，和R2y D 50cm，其中R1和R2分别为球面和圆柱形反射镜的曲率半径。x;y:发射角度。W:晶体长度、宽度和高度(Wx D Wy D W)。
{"title":"Optical refrigeration inches toward liquid-nitrogen temperatures","authors":"A. Gragossian, M. Ghasemkhani, Junwei Meng, A. Albrecht, M. Tonelli, M. Sheik-Bahae","doi":"10.1117/2.1201704.006840","DOIUrl":"https://doi.org/10.1117/2.1201704.006840","url":null,"abstract":"Superconductivity, longand mid-wave IR detectors, and ultrastable laser cavities that operate in the 77–150K temperature range can all benefit from vibration-free cooling.1 Currently, such low temperatures can only be achieved using cryogenic gases or liquids, solid cryogens, or mechanical refrigerators. Unfortunately, these coolers require regular attention, introduce vibrational noise, and are subject to mechanical wear over time. Many space-based applications (particularly ultra-stable laser cavities) cannot tolerate these drawbacks. All-solid-state cryocoolers are therefore desirable because of their inherent vibration-free operation and potentially long lifetime. Optical refrigeration (i.e., anti-Stokes fluorescence cooling) is the only solid-state cooling technology capable of reaching cryogenic temperatures. Anti-Stokes cooling—in which a doped crystal is excited by a laser with a wavelength that is longer than the average wavelength of the resulting fluorescence, thus leading to cooling of the crystal—was first suggested by Peter Pringsheim almost 90 years ago.2 It was not actually observed, however, until years after the invention of lasers and the availability of high-purity host materials. The first demonstration of optical refrigeration, reported in 1995, used a fluorozirconate glass doped with ytterbium (Yb). The resulting material is known as Yb3C: ZBLANP.3 Cooling occurs when low-entropy laser light (tuned to a slightly lower energy than the mean fluorescence of a material) is absorbed, thus giving rise to efficient fluorescence generation and escape. On average, each pump photon removes vibrational energy (i.e., phonons) from the cooling sample after being absorbed and re-emitted. Figure 1. Schematic of our astigmatic Herriott cell. The geometry of the cell enables laser light (red) to be trapped inside of the crystal, ensuring more than 95% absorption. R1x;y D 50cm, R2x D 1, and R2y D 50cm, where R1 and R2 are the radii of curvature of the spherical and cylindrical mirrors, respectively. x;y : Launching angle. W : Crystal length, width, and height (Wx D Wy D W ).","PeriodicalId":22075,"journal":{"name":"Spie Newsroom","volume":"102 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87859447","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-06-27DOI: 10.1117/2.1201704.006858
M. Meitl, C. Bower
{"title":"Power to the pixel","authors":"M. Meitl, C. Bower","doi":"10.1117/2.1201704.006858","DOIUrl":"https://doi.org/10.1117/2.1201704.006858","url":null,"abstract":"","PeriodicalId":22075,"journal":{"name":"Spie Newsroom","volume":"4 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74997704","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-06-26DOI: 10.1117/2.1201704.006869
Tae Geun Kim, T. Lee
Nitride-based UV LEDs are promising replacements for conventional UV lamps1 because of their higher energy efficiency, longer lifetime, and greater reliability. However, the external quantum efficiency of UV LEDs is currently much lower than that of visible LEDs. This difference is mainly due to the light absorption that occurs in the p-type gallium nitride (p-GaN) contact layer and the metal electrode layers. In deep-UV LEDs, absorption becomes an even greater problem.2 One possible solution to this fundamental issue is to obtain a direct ohmic contact to p-type aluminum gallium nitride (p-AlGaN). This can be achieved using UV-transparent conductive electrodes (TCEs), thus avoiding absorption and increasing device efficiency. Prior to our work, no solution had been found to overcoming the trade-off between high electrical conductivity and high optical transmittance. Indeed, these properties have generally been considered mutually exclusive. In recent years, some groups have reported the use of metal nanowires, metal nanomeshes, graphene, carbon nanotubes, metal oxides, and conductive polymers as replacements for conventional indium tin oxide (ITO),3, 4 but these efforts are still under way. We have proposed a universal method for producing TCEs using wide bandgap (WB) materials such as silicon oxides and nitrides.5 Glass-based TCEs (G-TCEs) enable effective current injection from a metal to a WB semiconductor (e.g., p-type AlGaN under bias) via conducting filaments (CFs) that are formed by the electrical breakdown (EBD) that occurs in the G-TCE. In these devices, high transmittance is maintained even in the deep-UV region (i.e., more than 95% at a wavelength of 280nm). To achieve this, we developed a G-TCE using aluminum nitride (AlN) as a unique solution and implemented the resultant Figure 1. (a) Schematic view of a lateral-type aluminum gallium nitride—(Al)GaN—based LED with aluminum nitride (AlN)-based glass transparent conducting electrodes (G-TCEs), after electrical breakdown (EBD). This magnified image shows that current can be injected via conductive filaments (CFs), which are formed in the AlN layer after EBD, and can subsequently spread through the device via thin indium-tin-oxide (ITO) buffer layers. (b) Current-voltage characteristics measured for the AlN-based G-TCE, before (red) and after (blue) EBD. The inset shows conductive atomic force microscopy images taken for the AlN top layer before (left) and after (right) EBD at 1V with a compliance current of 10nA.
{"title":"UV-transparent glass electrodes for high-efficiency nitride-based LEDs","authors":"Tae Geun Kim, T. Lee","doi":"10.1117/2.1201704.006869","DOIUrl":"https://doi.org/10.1117/2.1201704.006869","url":null,"abstract":"Nitride-based UV LEDs are promising replacements for conventional UV lamps1 because of their higher energy efficiency, longer lifetime, and greater reliability. However, the external quantum efficiency of UV LEDs is currently much lower than that of visible LEDs. This difference is mainly due to the light absorption that occurs in the p-type gallium nitride (p-GaN) contact layer and the metal electrode layers. In deep-UV LEDs, absorption becomes an even greater problem.2 One possible solution to this fundamental issue is to obtain a direct ohmic contact to p-type aluminum gallium nitride (p-AlGaN). This can be achieved using UV-transparent conductive electrodes (TCEs), thus avoiding absorption and increasing device efficiency. Prior to our work, no solution had been found to overcoming the trade-off between high electrical conductivity and high optical transmittance. Indeed, these properties have generally been considered mutually exclusive. In recent years, some groups have reported the use of metal nanowires, metal nanomeshes, graphene, carbon nanotubes, metal oxides, and conductive polymers as replacements for conventional indium tin oxide (ITO),3, 4 but these efforts are still under way. We have proposed a universal method for producing TCEs using wide bandgap (WB) materials such as silicon oxides and nitrides.5 Glass-based TCEs (G-TCEs) enable effective current injection from a metal to a WB semiconductor (e.g., p-type AlGaN under bias) via conducting filaments (CFs) that are formed by the electrical breakdown (EBD) that occurs in the G-TCE. In these devices, high transmittance is maintained even in the deep-UV region (i.e., more than 95% at a wavelength of 280nm). To achieve this, we developed a G-TCE using aluminum nitride (AlN) as a unique solution and implemented the resultant Figure 1. (a) Schematic view of a lateral-type aluminum gallium nitride—(Al)GaN—based LED with aluminum nitride (AlN)-based glass transparent conducting electrodes (G-TCEs), after electrical breakdown (EBD). This magnified image shows that current can be injected via conductive filaments (CFs), which are formed in the AlN layer after EBD, and can subsequently spread through the device via thin indium-tin-oxide (ITO) buffer layers. (b) Current-voltage characteristics measured for the AlN-based G-TCE, before (red) and after (blue) EBD. The inset shows conductive atomic force microscopy images taken for the AlN top layer before (left) and after (right) EBD at 1V with a compliance current of 10nA.","PeriodicalId":22075,"journal":{"name":"Spie Newsroom","volume":"158 7","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91499825","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-06-23DOI: 10.1117/2.1201703.006827
J. Wun, Jin-Wei Shi
Driven primarily by the use of wireless mobile data and Internet videos, global network data traffic is continuing to increase. The information and communication technology sector thus takes up an ever-larger portion of global electricity consumption (now at about 10%).1 To minimize the demands of this growth, it is therefore necessary to increase the energy efficiency of high-speed network data processing. To date, a number of processing techniques have been adapted to increase the energy efficiency of high-speed networks. For instance, optical interconnect (OI) techniques2 provide a revolutionary way to reduce the carbon footprint of data centers and their wired networks. The DC component of the high-speed optical data signal at the receiving end of an OI system, however, still produces waste heat energy. This energy is proportional to the product of the DC reverse bias of the photodiodes (PDs) and the output photocurrent,3 and this heating effect could thus be a serious issue for the next generation of OI systems. Such systems have densely packaged integrated circuits, with millions of optoelectronic components and optical channels for high-speed linking (i.e., at >50Gb/s). PDs that could sustain high-speed performance, even under zero (forward)-bias operation, would thus be a potentially effective solution for minimizing the OI thermal issue. In this work, we describe our recently developed unitraveling carrier photodiodes (UTC-PDs).4, 5 We include type-II (i.e., staggered-jump) p-n absorption/collector (A/C) interfaces in these devices to further improve their speed under zero-bias operation.6, 7 In addition, we have designed and demonstrated7 our UTC-PD—with a gallium arsenide/indium gallium phosphide (GaAs/In0:5Ga0:5P) A/C junction—for application at 850nm because this is the most popular optical wavelength for very short reach linking (i.e., <300m) in modern data centers.2 To minimize the increase in the junction capacitance of our Figure 1. (a) Conceptual cross section of the proposed gallium arsenide/indium gallium phosphide (GaAs/In0:5Ga0:5P) unitraveling carrier photodiode (UTC-PD), which includes an undercut mesa structure. S. I.: Semi-insulating. (b) The DC optical–electrical (O–E) power conversion efficiency of the device at different biases.
主要受无线移动数据和互联网视频使用的推动，全球网络数据流量正在继续增加。因此，信息和通信技术部门在全球电力消耗中所占的比例越来越大(目前约为10%)为了最大限度地减少这种增长的需求，因此有必要提高高速网络数据处理的能源效率。迄今为止，许多处理技术已被用于提高高速网络的能源效率。例如，光互连(OI)技术为减少数据中心及其有线网络的碳足迹提供了一种革命性的方法。然而，在OI系统的接收端，高速光数据信号的直流分量仍然会产生废热。这种能量与光电二极管(pd)的直流反向偏置和输出光电流的乘积成正比，因此这种热效应可能成为下一代OI系统的一个严重问题。这种系统具有密集封装的集成电路，具有数百万个光电元件和用于高速连接(即>50Gb/s)的光通道。即使在零(正向)偏置操作下，pd也可以保持高速性能，因此可能是最小化OI热问题的有效解决方案。在这项工作中，我们描述了我们最近开发的单位行载流子光电二极管(utc - pd)。4,5我们在这些器件中包括ii型(即交错跳变)p-n吸收/集热器(A/C)接口，以进一步提高零偏操作下的速度。6,7此外，我们还设计并演示了我们的utc - pd -含砷化镓/磷化铟镓(GaAs/In0:5Ga0:5P) a /C结，用于850nm的应用，因为这是现代数据中心中最流行的用于极短距离连接(即<300m)的光学波长为了最小化图1中结电容的增加。(a)提议的砷化镓/磷化铟镓(GaAs/In0:5Ga0:5P)单行程载流子光电二极管(UTC-PD)的概念截面，其中包括一个凹边台面结构。半绝缘。(b)不同偏置下器件的直流光电(O-E)功率转换效率。
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Pub Date : 2017-06-21DOI: 10.1117/2.1201703.006832
J. Bauer
In the search for materials that are both light and strong, classic material design—such as optimizing the chemistry and/or microstructure of bulk materials—has been systematically exploited over centuries, leaving limited room for further improvements.1 Although major advancements have been made with respect to mechanical strength and density, light materials generally remain weak and heavy materials strong; hence, the two properties have historically been considered to be connected. However, in recent years, the field of so-called ‘metamaterials’ (materials engineered to possess properties not usually found in nature) has made considerable advances in the development of materials that are both light and strong. Metamaterials usually consist of assemblies of multiple repeating elements, and their special properties are primarily determined by their topology rather than their composition. Initially, these materials were designed to display unique optical, electromagnetic, or acoustic characteristics. Recently, mechanical metamaterials have also emerged, with principally opposing mechanical properties, such as both high stiffness and high damping (mechanical energy dissipation) capability2 or a negative Poisson’s ratio (i.e., a material that expands laterally when stretched).3 In addition, a class of lightweight mechanical metamaterials has been developed, inspired by natural hierarchical cellular materials and triggered by the recent evolution of high-resolution 3D printing technologies that enable the miniaturization of lattice structures. The properties of these lightweight metamaterials depend on the microscopic length scales of their patterns as well as their topologies.5–9 Because of their specifically designed architectures, these lattice materials reach remarkable strengths at low densities that might never be achieved using classic material Figure 1. Scanning electron microscopy images of a glassy carbon nanolattice. (a,b) A polymer microlattice fabricated by 3D printing. (c,d) Vacuum pyrolysis transforms the polymer to glassy carbon and isotropically shrinks the lattice by 80%, producing a nanolattice. Lattice distortion during pyrolysis is eliminated by including pedestals and coiled spring supports, distancing the lattice from the substrate. Scale bars: (a,c) 5 m, (b,d) 1 m. Reproduced with permission.4
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Pub Date : 2017-06-19DOI: 10.1117/2.1201704.006786
D. Kessel
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