In this paper, an efficient thermal analysis method is presented for large scale compound semiconductor integrated circuits based on a heterojunction bipolar transistor with considering the change of thermal conductiv...In this paper, an efficient thermal analysis method is presented for large scale compound semiconductor integrated circuits based on a heterojunction bipolar transistor with considering the change of thermal conductivity with temperature.The influence caused by the thermal conductivity can be equivalent to the increment of the local temperature surrounding the individual device. The junction temperature for each device can be efficiently calculated by the combination of the semianalytic temperature distribution function and the iteration of local temperature with high accuracy, providing a temperature distribution for a full chip. Applying this method to the InP frequency divider chip and the GaAs analog to digital converter chip, the computational results well agree with the results from the simulator COMSOL and the infrared thermal imager respectively. The proposed method can also be applied to thermal analysis in various kinds of semiconductor integrated circuits.展开更多
Preparation method of photocatalyst, using TiCl4 and SnCl2 as raw material and photocatalytic activity of nano-scaled core-shell Sn^2＋ -doped titania photocatalyst was studied in this paper. The as-prepared samples w...Preparation method of photocatalyst, using TiCl4 and SnCl2 as raw material and photocatalytic activity of nano-scaled core-shell Sn^2＋ -doped titania photocatalyst was studied in this paper. The as-prepared samples were studied by UV-Vis, XRD, XPS, TEM. The particles of Sn^2＋-doped TiO2 photocatalyst, calcined from 150 to 600 ℃ for 5 h, possesses narrow particle size distribution and the sample was composed of anatase phase. Its photocatalytic efficiency was investigated by UV irradiation.展开更多
For the detached growth and crystal perfection investigation,Thallium doped Indium-antimonide(InSb:TI)ingots have been grown using vertical directional solidification(VDS)technique.Tiny melt(molecular incorporation)fr...For the detached growth and crystal perfection investigation,Thallium doped Indium-antimonide(InSb:TI)ingots have been grown using vertical directional solidification(VDS)technique.Tiny melt(molecular incorporation)freezes in conical geometry ampoule at one end at the beginning and it acts as seed.The small meniscus shape under the capillarity effect setup,then gap could be build up by the melt free surface(meniscus).It depends on the ampoule geometry and melt dissolved gases enter into the gap.It is attributed to the gap to compensate the thermal differential dilatation of the ingot that has grown with reduced diameter than the diameter of ampoule.Besides optimum conditions and parameters,freezing rate,growth velocity,cooling down time and the pressure differences across the meniscus are essential.Physical properties of InSb:T1 bulk crystals grown under the detached growths showed highest mobility.This reveals the nucleus and composition restrain by the influence of detached growth.In chemical etching,the dislocation density from first freeze front is decreases in the direction of growth.展开更多
We optimize the room-temperature etching of InP using Cl2/CH4/H2 and Cl2/N2 inductively coupled plasma reactive ions. A design of experiment is used in the optimization. The results, in terms of etch rate, surface rou...We optimize the room-temperature etching of InP using Cl2/CH4/H2 and Cl2/N2 inductively coupled plasma reactive ions. A design of experiment is used in the optimization. The results, in terms of etch rate, surface roughness and etched profile, are presented. These Cl2-based recipes do not require substrate heating and thus can be more cost effectively and widely applied. The Cl2/CH4/H2 process is able to give a higher etch rate （about 850 nm/min） and cleaner surface with less polymer formation compared to the conventional CH4/H2 process. The Cl2/N2 process produces even higher etch rate （as high as 2μm/rain）, but rougher surface with slight sidewall undercut. The Cl2/N2 process also has no polymer formation due to the absence of methane gas. Both the processes give very good selectivity to the silicon dioxide （SiO2） etch mask. The selectivity of InP to the oxide mask （up to 55：1） for the Cl2/N2 process is one of the highest reported so far. The etched structures possess reasonably good sidewall verticality and surface quality comparable to that obtained under elevated temperature condition （〉 200℃）.展开更多
Dislocation-mediated plasticity in inorganic semiconductors and oxides has attracted increasing research interest because of the promising mechanical and functional properties tuned by dislocations.In this study,we in...Dislocation-mediated plasticity in inorganic semiconductors and oxides has attracted increasing research interest because of the promising mechanical and functional properties tuned by dislocations.In this study,we investigated the effects of light illumination on the dislocation-mediated plasticity in hexagonal wurtzite ZnO,a representative third-generation semiconductor material.A(0001)45o off sample was specially designed to preferentially activate the basal slip on(0001)plane.Three types of nanoindentation tests were performed under four different light conditions(550 nm,334 nm,405 nm,and darkness),including low-load(60μN)pop-in tests,high-load(500μN)nanoindentation tests,and nanoindentation creep tests.The maximum shear stresses at pop-in were found to approximate the theoretical shear strength regardless of the light conditions.The activation volume at pop-ins was calculated to be larger in light than in darkness.Cross-sectional transmission electron microscope images taken from beneath the indentation imprints showed that all indentation-induced dislocations were located beneath the indentation imprint in a thin-plate shape along one basal slip plane.These indentation-induced dislocations could spread much deeper in darkness than in light,revealing the suppressive effect of light on dislocation behavior.An analytical model was adopted to estimate the elastoplastic stress field beneath the indenter.It was found that dislocation glide ceased at a higher stress level in light,indicating the increase in the Peierls barrier under light illumination.Furthermore,nanoindentation creep tests showed the suppression of both indentation depth and creep rate by light.Nanoindentation creep also yielded a larger activation volume in light than in darkness.展开更多
By means of scanning electron microscopope and X-ray diffraction, microstructural evolution of well-aligned ZnO nanorod array films was studied. The films were prepared on a glass using direct deposition method in an ...By means of scanning electron microscopope and X-ray diffraction, microstructural evolution of well-aligned ZnO nanorod array films was studied. The films were prepared on a glass using direct deposition method in an aqueous solution. The experimental results show that the highly oriented rods grew from the randomly oriented crystals. Those rod-like randomly oriented crystals began to impinge on other neighboring crystals and their growth became physically limited; only the rods perpendicular to the substrate were allowed to grow freely. This kinetically controlled nucleation and growth would be responsible for producing the uniformly oriented nanorods. During the ZnO rods＇ growth, the topology of their top faces changed from flat, prismatic to finally flat.展开更多
The minority carrier diffusion length of n-type GaN fdms grown by metalorganic chemical vapor deposition （MOCVD） has been studied by measuring the surface photovoltaic （PV） spectra. It was found that the minority ...The minority carrier diffusion length of n-type GaN fdms grown by metalorganic chemical vapor deposition （MOCVD） has been studied by measuring the surface photovoltaic （PV） spectra. It was found that the minority carrier diffusion length of undoped n-type GaN is considerably larger than that in lightly Si-doped GaN. However, the data suggested that the dislocation and electron concentration appear not to be responsible for the minority cartier diffusion length. It is suggested that Si doping plays an important role in decreasing the minority carrier diffusion length.展开更多
The effects of Bi flux and pressure of AsH3 on Bi incorporation,surface morphology and optical properties of InGa As Bi grown by gas source molecular beam epitaxy are studied.It is found that using relatively low pres...The effects of Bi flux and pressure of AsH3 on Bi incorporation,surface morphology and optical properties of InGa As Bi grown by gas source molecular beam epitaxy are studied.It is found that using relatively low pressure of AsH3 and high Bi flux can strengthen the effect on the incorporation of Bi and increase its content linearly with Bi flux until it nearly reaches a saturation value.The result from Rutherford backscattering spectroscopy（RBS） confirms that the Bi incorporation can increase up to 1.13%.By adjusting Bi and As flux,we could improve the surface morphology of In Ga As Bi sample.Room temperature photoluminescence shows strong and broad light emission at energy levels much smaller than the In Ga As bandgap.展开更多
We report the synthesis and characterization of a Si-based ternary semiconductor Mg_(3)Si_(2)Te_(6),which exhibits a quasitwo-dimensional structure,where the trigonal Mg_(3)Si_(2)Te_(6)layers are separated by Mg ions....We report the synthesis and characterization of a Si-based ternary semiconductor Mg_(3)Si_(2)Te_(6),which exhibits a quasitwo-dimensional structure,where the trigonal Mg_(3)Si_(2)Te_(6)layers are separated by Mg ions.Ultraviolet-visible absorption spectroscopy and density functional theory calculations were performed to investigate the electronic structure.The experimentally determined direct band gap is 1.39 eV,consistent with the value of the density function theory calculations.Our results reveal that Mg_(3)Si_(2)Te_(6)is a direct gap semiconductor,which is a potential candidate for near-infrared optoelectronic devices.展开更多
The intrinsic defect of cadmium vacancy （Vcd） in cadmium telluride （CdTe） has been studied by first-principles cal- culations using potentials with both the screened hybrid functional of Heyd, Scuseria, and Ernzer...The intrinsic defect of cadmium vacancy （Vcd） in cadmium telluride （CdTe） has been studied by first-principles cal- culations using potentials with both the screened hybrid functional of Heyd, Scuseria, and Ernzerhof （HSE） approximation and the generalized gradient approximation of the Perdew-Burke-Ernzerhof form （PBE-GGA）. Both results show that the Ta structure of the Vctl defect for different charges is the most stable structure as compared with the distorted C3v structure with one hole localized at one of the four nearest Te atoms. This indicates that the John-Teller distortion （C3v） structure may be unstable in bulk CdTe crystal. The reason likely lies in the delocalized resonance nature of the t2 state of the Vcd defect. Moreover, the formation energy obtained by the HSE method is about 0.6-0.8 eV larger than that obtained by the PBE method. The transition levels calculated by the PBE method and the HSE method are similar and well consistent with the experimental results.展开更多
Since 1994, the vertical directional solidification （VDS） technique is employed for the growths of bulk crystals-without the seed, without contact to the ampoule wall, without coating and without external pressure, ...Since 1994, the vertical directional solidification （VDS） technique is employed for the growths of bulk crystals-without the seed, without contact to the ampoule wall, without coating and without external pressure, which leads to the detached growth. Growth velocities ranged from 3 mm/h to 10 mm/h, and rotation rates 10-20 rpm have been used. Ingots, 10-20 mm diameter and 60-65 mm length, have been grown with the conical ampoule geometry and these ingots have shown symmetric detachment. Crystals grown under such conditions showed the relatively low dislocation density and the highest carrier mobility,/tn = 5.9 x 104 cm2＂Vl-sl than the crystal grown ever. For the detached crystals, the dislocation density is 104 cm＂2 in conical region, and reached less than 103 cm-2 in the direction of the growth, when the ingots are not in contact with the ampoule wall. Experiments for indium-antimonide （InSb） growth have shown that the 80% growth environments have detachment, 15% entrapped in conical region and 5% attached.展开更多
A complete and accurate surface potential based large-signal model for compound semiconductor HEMTs is presented. A surface potential equation resembling the one used in conventional MOSFET models is achieved. The ana...A complete and accurate surface potential based large-signal model for compound semiconductor HEMTs is presented. A surface potential equation resembling the one used in conventional MOSFET models is achieved. The analytic solutions from the traditional surface potential theory that developed in MOSFET models are inherited. For core model derivation, a novel method is used to realize a direct application of the standard surfacepotentialmodelofMOSFETsforHEMTmodeling,withoutbreakingthemathematicstructure.Thehigh-order derivatives of I–V /C–V remain continuous, making the model suitable for RF large-signal applications. Furthermore, the self-heating effects and the transconductance dispersion are also modelled. The model has been verified through comparison with measured DC IV, Gummel symmetry test, CV, minimum noise figure, small-signal Sparameters up to 66 GHz and single-tone input power sweep at 29 GHz for a 475 m0.1 m InGaAs/GaAs power pHEMT, fabricated at a commercial foundry.展开更多
A silicon solar cell with a power conversion efficiency (PCE)of 4% was born in Bell Lab in 1954, seven decades ago. Today,silicon solar cells have reached an efficiency above 25% andachieved pervasive commercial succe...A silicon solar cell with a power conversion efficiency (PCE)of 4% was born in Bell Lab in 1954, seven decades ago. Today,silicon solar cells have reached an efficiency above 25% andachieved pervasive commercial success [1]. In spite of the steadyimprovement in efficiency, the interest and enthusiasm in searchfor new materials and innovative device architectures for newgenerationsolar cells have never diminished or subsided;ratheropposite, such efforts have led to significant and rapid ascendance,particularly in recent decades, showing promise to circumventthe limitations of silicon solar cells, which suffer fromhigh manufacturing cost and long energy payback time.The second generation of solar cells is thin-film solar cells,made from compound semiconductors like copper indium galliumselenide (CIGS), cadmium telluride (CdTe), and amorphoussilicon (a-Si). These cells featuring a thin film structurerequire less material, are more flexible and lightweight, andexhibit a higher tolerance to temperature changes, with anefficiency range of 10%–15% [2]. The third generation includesdye-sensitized solar cells, organic solar cells (OSCs), and perovskitesolar cells, utilizing materials that are cheaper than thoseused in the first- and second-generation solar cells [3,4].OSCs, also known as organic photovoltaics (OPVs), started inthe mid-1980s [5] and picked up the speed in the 90s.展开更多
We report a new nBn photodetector(nBn-PD)design based on the InAlSb/AlSb/InAlSb/InAsSb material systems for midwavelength infrared(MWIR)applications.In this structure,delta-doped compositionally graded barrier(δ-DCGB...We report a new nBn photodetector(nBn-PD)design based on the InAlSb/AlSb/InAlSb/InAsSb material systems for midwavelength infrared(MWIR)applications.In this structure,delta-doped compositionally graded barrier(δ-DCGB)layers are suggested,the advantage of which is creation of a near zero valence band ofset in nBn photodetectors.The design of theδ-DCGB nBn-PD device includes a 3µm absorber layer(n-InAs0.81Sb0.19),a unipolar barrier layer(AlSb),and 0.2μm contact layer(n-InAs0.81Sb0.19)as well as a 0.116µm linear grading region(InAlSb)from the contact to the barrier layer and also from the barrier to the absorber layer.The analysis includes various dark current contributions,such as the Shockley-Read-Hall(SRH),trap-assisted tunneling(TAT),Auger,and Radiative recombination mechanisms,to acquire more precise results.Consequently,we show that the method used in the nBn device design leads to difusion-limited dark current so that the dark current density is 2.596×10^(−8)A/cm^(2)at 150 K and a bias voltage of−0.2 V.The proposed nBn detector exhibits a 50%cutof wavelength of more than 5µm,the peak current responsivity is 1.6 A/W at a wavelength of 4.5µm and a−0.2 V bias with 0.05 W/cm2 backside illumination without anti-refective coating.The maximum quantum efciency at 4.5µm is about 48.6%,and peak specifc detectivity(D*)is of 3.37×10^(10)cm⋅Hz1/2/W.Next,to solve the refection concern in this nBn devices,we use a BaF_(2)anti-refection coating layer due to its high transmittance in the MWIR window.It leads to an increase of almost 100%in the optical response metrics,such as the current responsivity,quantum efciency,and detectivity,compared to the optical response without an anti-refection coating layer.展开更多
Highly faceted geometries such as nanowires are prone toform self-formed features,especially those that are driven by segregation.Understanding these features is important in preventing their formation,understanding t...Highly faceted geometries such as nanowires are prone toform self-formed features,especially those that are driven by segregation.Understanding these features is important in preventing their formation,understanding their effects on nanowire properties,or engineering them for applications.Single elemental segregation lines that run along the radii of the hexagonal cross-section have been a common observation in alloy semiconductor nanowires.Here,in GaAsP nanowires,two additional P rich bands are formed on either side of the primary band,resulting in a total of three segregation bands in the vicinity of three of the alternating radii.These bands are less intense than the primary band and their formation can be attributed to the inclined nanofacets that form in the vicinity of the vertices.The formation of the secondary bands requires a higher composition of P in the shell,and to be grown under conditions that increase the diffusivity difference between As and P.Furthermore,it is observed that the primary band can split into two narrow and parallel bands.This can take place in all six radii,making the cross sections to have up to a maximum of 18 radial segregation bands.With controlled growth,these features could be exploited to assemble multiple different quantum structures in a new dimension(circumferential direction)within nanowires.展开更多
基金Project supported by the Advance Research Foundation of China(Grant No.9140Axxx501)the National Defense Advance Research Project,China(Grant No.3151xxxx301)+1 种基金the Frontier Innovation Program,China(Grant No.48xx4)the 111 Project,China(Grant No.B12026)
文摘In this paper, an efficient thermal analysis method is presented for large scale compound semiconductor integrated circuits based on a heterojunction bipolar transistor with considering the change of thermal conductivity with temperature.The influence caused by the thermal conductivity can be equivalent to the increment of the local temperature surrounding the individual device. The junction temperature for each device can be efficiently calculated by the combination of the semianalytic temperature distribution function and the iteration of local temperature with high accuracy, providing a temperature distribution for a full chip. Applying this method to the InP frequency divider chip and the GaAs analog to digital converter chip, the computational results well agree with the results from the simulator COMSOL and the infrared thermal imager respectively. The proposed method can also be applied to thermal analysis in various kinds of semiconductor integrated circuits.
基金The National Natural Science Foundation of China(No.20271007 and 20331010)Specialized Research Fund for the Doctoral Program of Higher Education(No.20030007014)are acknowledged for financial support.
文摘Preparation method of photocatalyst, using TiCl4 and SnCl2 as raw material and photocatalytic activity of nano-scaled core-shell Sn^2＋ -doped titania photocatalyst was studied in this paper. The as-prepared samples were studied by UV-Vis, XRD, XPS, TEM. The particles of Sn^2＋-doped TiO2 photocatalyst, calcined from 150 to 600 ℃ for 5 h, possesses narrow particle size distribution and the sample was composed of anatase phase. Its photocatalytic efficiency was investigated by UV irradiation.
文摘For the detached growth and crystal perfection investigation,Thallium doped Indium-antimonide(InSb:TI)ingots have been grown using vertical directional solidification(VDS)technique.Tiny melt(molecular incorporation)freezes in conical geometry ampoule at one end at the beginning and it acts as seed.The small meniscus shape under the capillarity effect setup,then gap could be build up by the melt free surface(meniscus).It depends on the ampoule geometry and melt dissolved gases enter into the gap.It is attributed to the gap to compensate the thermal differential dilatation of the ingot that has grown with reduced diameter than the diameter of ampoule.Besides optimum conditions and parameters,freezing rate,growth velocity,cooling down time and the pressure differences across the meniscus are essential.Physical properties of InSb:T1 bulk crystals grown under the detached growths showed highest mobility.This reveals the nucleus and composition restrain by the influence of detached growth.In chemical etching,the dislocation density from first freeze front is decreases in the direction of growth.
文摘We optimize the room-temperature etching of InP using Cl2/CH4/H2 and Cl2/N2 inductively coupled plasma reactive ions. A design of experiment is used in the optimization. The results, in terms of etch rate, surface roughness and etched profile, are presented. These Cl2-based recipes do not require substrate heating and thus can be more cost effectively and widely applied. The Cl2/CH4/H2 process is able to give a higher etch rate （about 850 nm/min） and cleaner surface with less polymer formation compared to the conventional CH4/H2 process. The Cl2/N2 process produces even higher etch rate （as high as 2μm/rain）, but rougher surface with slight sidewall undercut. The Cl2/N2 process also has no polymer formation due to the absence of methane gas. Both the processes give very good selectivity to the silicon dioxide （SiO2） etch mask. The selectivity of InP to the oxide mask （up to 55：1） for the Cl2/N2 process is one of the highest reported so far. The etched structures possess reasonably good sidewall verticality and surface quality comparable to that obtained under elevated temperature condition （〉 200℃）.
基金supported by Japan Society for the Promotion of Science KAKENHI(Grant Nos.JP19H05786,JP21H04532,JP21H04618,JP21K20484,JP20H02421,JP22K14143,JP17H01238,and JP17H06094)A.Nakamura and E.Tochigi acknowledge the financial support of JST PRESTO(Grant Nos.JPMJPR199A and JPMJPR1999)X.Fang acknowledges the financial support by the Athene Young Investigator Programme at TU Darmstadt.
文摘Dislocation-mediated plasticity in inorganic semiconductors and oxides has attracted increasing research interest because of the promising mechanical and functional properties tuned by dislocations.In this study,we investigated the effects of light illumination on the dislocation-mediated plasticity in hexagonal wurtzite ZnO,a representative third-generation semiconductor material.A(0001)45o off sample was specially designed to preferentially activate the basal slip on(0001)plane.Three types of nanoindentation tests were performed under four different light conditions(550 nm,334 nm,405 nm,and darkness),including low-load(60μN)pop-in tests,high-load(500μN)nanoindentation tests,and nanoindentation creep tests.The maximum shear stresses at pop-in were found to approximate the theoretical shear strength regardless of the light conditions.The activation volume at pop-ins was calculated to be larger in light than in darkness.Cross-sectional transmission electron microscope images taken from beneath the indentation imprints showed that all indentation-induced dislocations were located beneath the indentation imprint in a thin-plate shape along one basal slip plane.These indentation-induced dislocations could spread much deeper in darkness than in light,revealing the suppressive effect of light on dislocation behavior.An analytical model was adopted to estimate the elastoplastic stress field beneath the indenter.It was found that dislocation glide ceased at a higher stress level in light,indicating the increase in the Peierls barrier under light illumination.Furthermore,nanoindentation creep tests showed the suppression of both indentation depth and creep rate by light.Nanoindentation creep also yielded a larger activation volume in light than in darkness.
基金Shandong Provincial Education Department(No.JO5D08)Qingdao Science and Technology Office(No.05-1-JC-89)the Scientific Research Foundation for the Returned Overseas Chinese Scholars,State Education Ministry
文摘By means of scanning electron microscopope and X-ray diffraction, microstructural evolution of well-aligned ZnO nanorod array films was studied. The films were prepared on a glass using direct deposition method in an aqueous solution. The experimental results show that the highly oriented rods grew from the randomly oriented crystals. Those rod-like randomly oriented crystals began to impinge on other neighboring crystals and their growth became physically limited; only the rods perpendicular to the substrate were allowed to grow freely. This kinetically controlled nucleation and growth would be responsible for producing the uniformly oriented nanorods. During the ZnO rods＇ growth, the topology of their top faces changed from flat, prismatic to finally flat.
文摘The minority carrier diffusion length of n-type GaN fdms grown by metalorganic chemical vapor deposition （MOCVD） has been studied by measuring the surface photovoltaic （PV） spectra. It was found that the minority carrier diffusion length of undoped n-type GaN is considerably larger than that in lightly Si-doped GaN. However, the data suggested that the dislocation and electron concentration appear not to be responsible for the minority cartier diffusion length. It is suggested that Si doping plays an important role in decreasing the minority carrier diffusion length.
基金Project supported by the National Natural Science Foundation of China(Grant No.61434006)the National Basic Research Program of China(Grant No.2014CB643902)
文摘The effects of Bi flux and pressure of AsH3 on Bi incorporation,surface morphology and optical properties of InGa As Bi grown by gas source molecular beam epitaxy are studied.It is found that using relatively low pressure of AsH3 and high Bi flux can strengthen the effect on the incorporation of Bi and increase its content linearly with Bi flux until it nearly reaches a saturation value.The result from Rutherford backscattering spectroscopy（RBS） confirms that the Bi incorporation can increase up to 1.13%.By adjusting Bi and As flux,we could improve the surface morphology of In Ga As Bi sample.Room temperature photoluminescence shows strong and broad light emission at energy levels much smaller than the In Ga As bandgap.
基金the National Natural Science Foundation of China(Grant Nos.12174454,11904414,11904416,and 12104427)the Guangdong Basic and Applied Basic Research Foundation,China(Grant No.2021B1515120015)+1 种基金the Guangzhou Basic and Applied Basic Research Foundation(Grant No.202201011123)the National Key Research and Development Program of China(Grant No.2019YFA0705702).
文摘We report the synthesis and characterization of a Si-based ternary semiconductor Mg_(3)Si_(2)Te_(6),which exhibits a quasitwo-dimensional structure,where the trigonal Mg_(3)Si_(2)Te_(6)layers are separated by Mg ions.Ultraviolet-visible absorption spectroscopy and density functional theory calculations were performed to investigate the electronic structure.The experimentally determined direct band gap is 1.39 eV,consistent with the value of the density function theory calculations.Our results reveal that Mg_(3)Si_(2)Te_(6)is a direct gap semiconductor,which is a potential candidate for near-infrared optoelectronic devices.
基金supported by the National Natural Science Foundation of China(Grant No.A050506)the Innovation Program of Shanghai Municipal Education Commission,China(Grant No.12ZZ096)+1 种基金the Shanghai Leading Academic Disciplines,China(Grant No.S30107)the Science and Technology Commissionof Shanghai,China(Grant No.11530500200)
文摘The intrinsic defect of cadmium vacancy （Vcd） in cadmium telluride （CdTe） has been studied by first-principles cal- culations using potentials with both the screened hybrid functional of Heyd, Scuseria, and Ernzerhof （HSE） approximation and the generalized gradient approximation of the Perdew-Burke-Ernzerhof form （PBE-GGA）. Both results show that the Ta structure of the Vctl defect for different charges is the most stable structure as compared with the distorted C3v structure with one hole localized at one of the four nearest Te atoms. This indicates that the John-Teller distortion （C3v） structure may be unstable in bulk CdTe crystal. The reason likely lies in the delocalized resonance nature of the t2 state of the Vcd defect. Moreover, the formation energy obtained by the HSE method is about 0.6-0.8 eV larger than that obtained by the PBE method. The transition levels calculated by the PBE method and the HSE method are similar and well consistent with the experimental results.
文摘Since 1994, the vertical directional solidification （VDS） technique is employed for the growths of bulk crystals-without the seed, without contact to the ampoule wall, without coating and without external pressure, which leads to the detached growth. Growth velocities ranged from 3 mm/h to 10 mm/h, and rotation rates 10-20 rpm have been used. Ingots, 10-20 mm diameter and 60-65 mm length, have been grown with the conical ampoule geometry and these ingots have shown symmetric detachment. Crystals grown under such conditions showed the relatively low dislocation density and the highest carrier mobility,/tn = 5.9 x 104 cm2＂Vl-sl than the crystal grown ever. For the detached crystals, the dislocation density is 104 cm＂2 in conical region, and reached less than 103 cm-2 in the direction of the growth, when the ingots are not in contact with the ampoule wall. Experiments for indium-antimonide （InSb） growth have shown that the 80% growth environments have detachment, 15% entrapped in conical region and 5% attached.
文摘A complete and accurate surface potential based large-signal model for compound semiconductor HEMTs is presented. A surface potential equation resembling the one used in conventional MOSFET models is achieved. The analytic solutions from the traditional surface potential theory that developed in MOSFET models are inherited. For core model derivation, a novel method is used to realize a direct application of the standard surfacepotentialmodelofMOSFETsforHEMTmodeling,withoutbreakingthemathematicstructure.Thehigh-order derivatives of I–V /C–V remain continuous, making the model suitable for RF large-signal applications. Furthermore, the self-heating effects and the transconductance dispersion are also modelled. The model has been verified through comparison with measured DC IV, Gummel symmetry test, CV, minimum noise figure, small-signal Sparameters up to 66 GHz and single-tone input power sweep at 29 GHz for a 475 m0.1 m InGaAs/GaAs power pHEMT, fabricated at a commercial foundry.
文摘A silicon solar cell with a power conversion efficiency (PCE)of 4% was born in Bell Lab in 1954, seven decades ago. Today,silicon solar cells have reached an efficiency above 25% andachieved pervasive commercial success [1]. In spite of the steadyimprovement in efficiency, the interest and enthusiasm in searchfor new materials and innovative device architectures for newgenerationsolar cells have never diminished or subsided;ratheropposite, such efforts have led to significant and rapid ascendance,particularly in recent decades, showing promise to circumventthe limitations of silicon solar cells, which suffer fromhigh manufacturing cost and long energy payback time.The second generation of solar cells is thin-film solar cells,made from compound semiconductors like copper indium galliumselenide (CIGS), cadmium telluride (CdTe), and amorphoussilicon (a-Si). These cells featuring a thin film structurerequire less material, are more flexible and lightweight, andexhibit a higher tolerance to temperature changes, with anefficiency range of 10%–15% [2]. The third generation includesdye-sensitized solar cells, organic solar cells (OSCs), and perovskitesolar cells, utilizing materials that are cheaper than thoseused in the first- and second-generation solar cells [3,4].OSCs, also known as organic photovoltaics (OPVs), started inthe mid-1980s [5] and picked up the speed in the 90s.
文摘We report a new nBn photodetector(nBn-PD)design based on the InAlSb/AlSb/InAlSb/InAsSb material systems for midwavelength infrared(MWIR)applications.In this structure,delta-doped compositionally graded barrier(δ-DCGB)layers are suggested,the advantage of which is creation of a near zero valence band ofset in nBn photodetectors.The design of theδ-DCGB nBn-PD device includes a 3µm absorber layer(n-InAs0.81Sb0.19),a unipolar barrier layer(AlSb),and 0.2μm contact layer(n-InAs0.81Sb0.19)as well as a 0.116µm linear grading region(InAlSb)from the contact to the barrier layer and also from the barrier to the absorber layer.The analysis includes various dark current contributions,such as the Shockley-Read-Hall(SRH),trap-assisted tunneling(TAT),Auger,and Radiative recombination mechanisms,to acquire more precise results.Consequently,we show that the method used in the nBn device design leads to difusion-limited dark current so that the dark current density is 2.596×10^(−8)A/cm^(2)at 150 K and a bias voltage of−0.2 V.The proposed nBn detector exhibits a 50%cutof wavelength of more than 5µm,the peak current responsivity is 1.6 A/W at a wavelength of 4.5µm and a−0.2 V bias with 0.05 W/cm2 backside illumination without anti-refective coating.The maximum quantum efciency at 4.5µm is about 48.6%,and peak specifc detectivity(D*)is of 3.37×10^(10)cm⋅Hz1/2/W.Next,to solve the refection concern in this nBn devices,we use a BaF_(2)anti-refection coating layer due to its high transmittance in the MWIR window.It leads to an increase of almost 100%in the optical response metrics,such as the current responsivity,quantum efciency,and detectivity,compared to the optical response without an anti-refection coating layer.
基金the EPSRC grants Nos.EP/P000916/1 and E P/P000886/1.The University of Warwick Electron Microscopy Research Technology Platform and the EPSRC National Epitaxy Facility are acknowledged for providing access to the equipment used.Dr.Anton Velichko is thanked for the careful reading of the manuscript.
文摘Highly faceted geometries such as nanowires are prone toform self-formed features,especially those that are driven by segregation.Understanding these features is important in preventing their formation,understanding their effects on nanowire properties,or engineering them for applications.Single elemental segregation lines that run along the radii of the hexagonal cross-section have been a common observation in alloy semiconductor nanowires.Here,in GaAsP nanowires,two additional P rich bands are formed on either side of the primary band,resulting in a total of three segregation bands in the vicinity of three of the alternating radii.These bands are less intense than the primary band and their formation can be attributed to the inclined nanofacets that form in the vicinity of the vertices.The formation of the secondary bands requires a higher composition of P in the shell,and to be grown under conditions that increase the diffusivity difference between As and P.Furthermore,it is observed that the primary band can split into two narrow and parallel bands.This can take place in all six radii,making the cross sections to have up to a maximum of 18 radial segregation bands.With controlled growth,these features could be exploited to assemble multiple different quantum structures in a new dimension(circumferential direction)within nanowires.
