Self-assembled In 0.35Ga 0.65As/GaAs quantum dots with low indium content are grown under different growth temperature and investigated using contact atomic force microscopy(AFM).In order to obtain high density ...Self-assembled In 0.35Ga 0.65As/GaAs quantum dots with low indium content are grown under different growth temperature and investigated using contact atomic force microscopy(AFM).In order to obtain high density and high uniformity of quantum dots,optimized conditions are concluded for MBE growth.Optimized growth conditions also compared with these of InAs/GaAs quantum dots.This will be very useful for InGaAs/GaAs QDs optoelectronic applications,such as quantum dots lasers and quantum dots infrared photodetectors.展开更多
Contacting mode atomic force microscopy (AFM) is used to measure the In 0.35 Ga 0.65 As/GaAs epilayer grown at low temperature (460℃).Unlike the normal layer by layer growth (FvdM mode) or self organized i...Contacting mode atomic force microscopy (AFM) is used to measure the In 0.35 Ga 0.65 As/GaAs epilayer grown at low temperature (460℃).Unlike the normal layer by layer growth (FvdM mode) or self organized islands growth (SK mode),samples grown under 460℃ are found to be large islands with atomic thick terraces.AFM measurements reveale near one monolayer high steps.This kind of growth is good between FvdM and SK growth modes and can be used to understand the evolution of strained epitaxy from FvdM to SK mode.展开更多
研究了用分子束外延(MBE)方法,在SI-GaAs衬底上不同低温生长的台阶式组分渐变InAlAs缓冲层结构.用原子力显微镜(AFM)观测表面形貌,生长温度为340℃时,外延层表面粗糙度为1.79nm.用Van der Pauw方法研究了材料的电学特性,室温电阻率ρ:2....研究了用分子束外延(MBE)方法,在SI-GaAs衬底上不同低温生长的台阶式组分渐变InAlAs缓冲层结构.用原子力显微镜(AFM)观测表面形貌,生长温度为340℃时,外延层表面粗糙度为1.79nm.用Van der Pauw方法研究了材料的电学特性,室温电阻率ρ:2.6× 10Ω·cm.(电学性能测试表明200V电压间距1mm时,漏电流仅为0.3μA).高分辨X射线测试样品显示为良好的层状结构,晶体质量随生长逐渐变好.首次用变温Hall测试研究多层InAlAs缓冲层材料内部的载流子传输机制,并用热激电流谱(TSC)分析了其高阻机制.展开更多
Thick GaN films were grown on GaN/sapphire template in a vertical HVPE reactor. Various material characterization techniques,including AFM, SEM, XRD, RBS/Channeling, CL, PL, and XPS, were used to characterize these Ga...Thick GaN films were grown on GaN/sapphire template in a vertical HVPE reactor. Various material characterization techniques,including AFM, SEM, XRD, RBS/Channeling, CL, PL, and XPS, were used to characterize these GaN epitaxial films. It was found that stepped/terraced structures appeared on the film surface,which were indicative of a nearly step-flow mode of growth for the HVPE GaN despite the high growth rate. A few hexagonal pits appeared on the surface, which have strong light emission. After being etched in molten KOH, the wavy steps disappeared and hexagonal pits with {1010} facets appeared on the surface. An EPD of only 8 ×10^6cm^-2 shows that the GaN film has few dislocations. Both XRD and RBS channeling indicate the high quality of the GaN thick films. Sharp band-edge emission with a full width at half maximum（FWHM）of 67meV was observed, while the yellow and infrared emissions were also found. These emissions are likely caused by native defects and C and O impurities.展开更多
高质量AlN薄膜对制造高性能深紫外器件非常重要,但是目前还很难使用大型工业MOCVD生长出高质量的AlN薄膜。采用磁控溅射制备了不同厚度的用作成核层的AlN薄膜,使用大型工业MOCVD直接在成核层上高温生长AlN外延层,研究了不同成核层对AlN...高质量AlN薄膜对制造高性能深紫外器件非常重要,但是目前还很难使用大型工业MOCVD生长出高质量的AlN薄膜。采用磁控溅射制备了不同厚度的用作成核层的AlN薄膜,使用大型工业MOCVD直接在成核层上高温生长AlN外延层,研究了不同成核层对AlN外延层质量的影响。通过扫描电子显微镜和原子力显微镜对成核层AlN薄膜的表面形貌进行表征;使用高分辨X射线衍射仪对AlN外延层晶体质量进行表征,结果表明:在溅射成核层上生长的AlN外延层的晶体质量有显著提高。使用大型工业MOCVD在蓝宝石衬底上成功制备出中心波长为282 nm的可商用深紫外LED,在注入电流为20 m A时,单颗深紫外LED芯片的光输出功率达到了1.65 m W,对应的外量子效率为1.87%,饱和光输出功率达到4.31 mW。展开更多
High-resolution X-ray diffraction has been employed to investigate the diffuse scattering in a （0001） oriented GaN epitaxial film grown on sapphire substrate. The analysis reveals that defect clusters are present in...High-resolution X-ray diffraction has been employed to investigate the diffuse scattering in a （0001） oriented GaN epitaxial film grown on sapphire substrate. The analysis reveals that defect clusters are present in GaN films and their concentration increases as the density of threading dislocations increases. Meanwhile, the mean radius of these defect clus- ters shows a reverse tendency. This result is explained by the effect of clusters preferentially forming around dislocations, which act as effective sinks for the segregation of point defects. The electric mobility is found to decrease as the cluster concentration increases.展开更多
Thick GaN films of high quality are directly grown on wet-etching patterned sapphire in a vertical hydride vapour phase epitaxy reactor. The optical and structural properties of GaN films are studied using scanning el...Thick GaN films of high quality are directly grown on wet-etching patterned sapphire in a vertical hydride vapour phase epitaxy reactor. The optical and structural properties of GaN films are studied using scanning electronic microscopy and cathodoluminescence. Test results show that initial growth of hydride vapour phase epitaxy GaN occurs not only on the mesas but also on the two asymmetric sidewalls of the V-shaped grooves without selectivity. After the two-step coalescence near the interface, the GaN films near the surface keep on growing along the direction perpendicular to the long sidewall. Based on Raman results, GaN of the coalescence region in the grooves has the maximum residual stress and poor crystalline quality over the whole GaN film, and the coalescence process can release the stress. Therefore, stress-free thick GaN films are prepared with smooth and crack-free surfaces by this particular growth mode on wet-etching patterned sapphire substrates.展开更多
Graphene on gallium nitride （GaN） will be quite useful when the graphene is used as transparent electrodes to improve the performance of gallium nitride devices. In this work, we report the direct synthesis of graph...Graphene on gallium nitride （GaN） will be quite useful when the graphene is used as transparent electrodes to improve the performance of gallium nitride devices. In this work, we report the direct synthesis of graphene on GaN without an extra catalyst by chemical vapor deposition. Raman spectra indicate that the graphene films are uniform and about 5-6 layers in thickness. Meanwhile, the effects of growth temperatures on the growth of graphene films are systematically studied, of which 950 ℃ is found to be the optimum growth temperature. The sheet resistance of the grown graphene is 41.1 Ω/square, which is close to the lowest sheet resistance of transferred graphene reported. The mechanism of graphene growth on GaN is proposed and discussed in detail. XRD spectra and photoluminescence spectra indicate that the quality of GaN epi-layers will not be affected after the growth of graphene.展开更多
Thick GaN films with high quality are directly grown on sapphire in a home-built vertical hydride vapour phase epitaxy （HVPE） reactor. The optical and structural properties of large scale columnar domains near the i...Thick GaN films with high quality are directly grown on sapphire in a home-built vertical hydride vapour phase epitaxy （HVPE） reactor. The optical and structural properties of large scale columnar domains near the interface are studied using cathodoluminescence and micro-Raman scattering. These columnar domains show a strong emission intensity due to extremely high free carrier concentration up to 2 × 10^19 cm^-3, which are related with impurities trapped in structural defects. The compressive stress in GaN film clearly decreases with increasing distance from interface. The quasi-continuous columnar domains play an important role in the stress relaxation for the upper high quality layer.展开更多
119Sn Mossbauer research is carried out on (La1-xSrx)2Cu1-xSnxO4( x = 0.075 and 0.110) superconductors which are designed under a new concept. The Mossbauer spectra results show that Sn occupies Cu position in Sn4+ st...119Sn Mossbauer research is carried out on (La1-xSrx)2Cu1-xSnxO4( x = 0.075 and 0.110) superconductors which are designed under a new concept. The Mossbauer spectra results show that Sn occupies Cu position in Sn4+ state, and there is no Sn2+ ion occupying La position. The local lattice deformation near Sn4+ site is small, but displays an increasing tendency with Sn doping. For La2CuO4 matrix, the simultaneous dopings of Sr/Sn induce holes and electrons on CuO2 layer in a new mechanism which influences superconductivity. Under a new mechanism of extra oxygen, the ex-tra oxygen effect of Sn-doping on superconductivity is discussed.展开更多
文摘Self-assembled In 0.35Ga 0.65As/GaAs quantum dots with low indium content are grown under different growth temperature and investigated using contact atomic force microscopy(AFM).In order to obtain high density and high uniformity of quantum dots,optimized conditions are concluded for MBE growth.Optimized growth conditions also compared with these of InAs/GaAs quantum dots.This will be very useful for InGaAs/GaAs QDs optoelectronic applications,such as quantum dots lasers and quantum dots infrared photodetectors.
文摘Contacting mode atomic force microscopy (AFM) is used to measure the In 0.35 Ga 0.65 As/GaAs epilayer grown at low temperature (460℃).Unlike the normal layer by layer growth (FvdM mode) or self organized islands growth (SK mode),samples grown under 460℃ are found to be large islands with atomic thick terraces.AFM measurements reveale near one monolayer high steps.This kind of growth is good between FvdM and SK growth modes and can be used to understand the evolution of strained epitaxy from FvdM to SK mode.
文摘研究了用分子束外延(MBE)方法,在SI-GaAs衬底上不同低温生长的台阶式组分渐变InAlAs缓冲层结构.用原子力显微镜(AFM)观测表面形貌,生长温度为340℃时,外延层表面粗糙度为1.79nm.用Van der Pauw方法研究了材料的电学特性,室温电阻率ρ:2.6× 10Ω·cm.(电学性能测试表明200V电压间距1mm时,漏电流仅为0.3μA).高分辨X射线测试样品显示为良好的层状结构,晶体质量随生长逐渐变好.首次用变温Hall测试研究多层InAlAs缓冲层材料内部的载流子传输机制,并用热激电流谱(TSC)分析了其高阻机制.
文摘Thick GaN films were grown on GaN/sapphire template in a vertical HVPE reactor. Various material characterization techniques,including AFM, SEM, XRD, RBS/Channeling, CL, PL, and XPS, were used to characterize these GaN epitaxial films. It was found that stepped/terraced structures appeared on the film surface,which were indicative of a nearly step-flow mode of growth for the HVPE GaN despite the high growth rate. A few hexagonal pits appeared on the surface, which have strong light emission. After being etched in molten KOH, the wavy steps disappeared and hexagonal pits with {1010} facets appeared on the surface. An EPD of only 8 ×10^6cm^-2 shows that the GaN film has few dislocations. Both XRD and RBS channeling indicate the high quality of the GaN thick films. Sharp band-edge emission with a full width at half maximum（FWHM）of 67meV was observed, while the yellow and infrared emissions were also found. These emissions are likely caused by native defects and C and O impurities.
文摘高质量AlN薄膜对制造高性能深紫外器件非常重要,但是目前还很难使用大型工业MOCVD生长出高质量的AlN薄膜。采用磁控溅射制备了不同厚度的用作成核层的AlN薄膜,使用大型工业MOCVD直接在成核层上高温生长AlN外延层,研究了不同成核层对AlN外延层质量的影响。通过扫描电子显微镜和原子力显微镜对成核层AlN薄膜的表面形貌进行表征;使用高分辨X射线衍射仪对AlN外延层晶体质量进行表征,结果表明:在溅射成核层上生长的AlN外延层的晶体质量有显著提高。使用大型工业MOCVD在蓝宝石衬底上成功制备出中心波长为282 nm的可商用深紫外LED,在注入电流为20 m A时,单颗深紫外LED芯片的光输出功率达到了1.65 m W,对应的外量子效率为1.87%,饱和光输出功率达到4.31 mW。
文摘High-resolution X-ray diffraction has been employed to investigate the diffuse scattering in a （0001） oriented GaN epitaxial film grown on sapphire substrate. The analysis reveals that defect clusters are present in GaN films and their concentration increases as the density of threading dislocations increases. Meanwhile, the mean radius of these defect clus- ters shows a reverse tendency. This result is explained by the effect of clusters preferentially forming around dislocations, which act as effective sinks for the segregation of point defects. The electric mobility is found to decrease as the cluster concentration increases.
基金Supported by the National High-Technology Research and Development Program of China under Grant Nos 2006AA03A143, the National Natural Science Foundation of China under Grant No 60806001, and the Knowledge Innovation Project of Chinese Academy of Sciences under Grant No ISCAS2008T03.
文摘Thick GaN films of high quality are directly grown on wet-etching patterned sapphire in a vertical hydride vapour phase epitaxy reactor. The optical and structural properties of GaN films are studied using scanning electronic microscopy and cathodoluminescence. Test results show that initial growth of hydride vapour phase epitaxy GaN occurs not only on the mesas but also on the two asymmetric sidewalls of the V-shaped grooves without selectivity. After the two-step coalescence near the interface, the GaN films near the surface keep on growing along the direction perpendicular to the long sidewall. Based on Raman results, GaN of the coalescence region in the grooves has the maximum residual stress and poor crystalline quality over the whole GaN film, and the coalescence process can release the stress. Therefore, stress-free thick GaN films are prepared with smooth and crack-free surfaces by this particular growth mode on wet-etching patterned sapphire substrates.
基金supported by the National Natural Science Foundation of China(Grant Nos.61274040 and 51102226)the National Basic Research Program of China(Grant No.2011CB301904)+2 种基金the National High Technology Program of China(Grant Nos.2011AA03A103 and 2011AA03A105)the National Science Foundation of China(Grant Nos.10774032 and 90921001)the Key Knowledge Innovation Project of the Chinese Academy of Sciences on Water Science Research,Instrument Developing Project of the Chinese Academy of Sciences(Grant No.Y2010031)
文摘Graphene on gallium nitride （GaN） will be quite useful when the graphene is used as transparent electrodes to improve the performance of gallium nitride devices. In this work, we report the direct synthesis of graphene on GaN without an extra catalyst by chemical vapor deposition. Raman spectra indicate that the graphene films are uniform and about 5-6 layers in thickness. Meanwhile, the effects of growth temperatures on the growth of graphene films are systematically studied, of which 950 ℃ is found to be the optimum growth temperature. The sheet resistance of the grown graphene is 41.1 Ω/square, which is close to the lowest sheet resistance of transferred graphene reported. The mechanism of graphene growth on GaN is proposed and discussed in detail. XRD spectra and photoluminescence spectra indicate that the quality of GaN epi-layers will not be affected after the growth of graphene.
文摘Thick GaN films with high quality are directly grown on sapphire in a home-built vertical hydride vapour phase epitaxy （HVPE） reactor. The optical and structural properties of large scale columnar domains near the interface are studied using cathodoluminescence and micro-Raman scattering. These columnar domains show a strong emission intensity due to extremely high free carrier concentration up to 2 × 10^19 cm^-3, which are related with impurities trapped in structural defects. The compressive stress in GaN film clearly decreases with increasing distance from interface. The quasi-continuous columnar domains play an important role in the stress relaxation for the upper high quality layer.
文摘119Sn Mossbauer research is carried out on (La1-xSrx)2Cu1-xSnxO4( x = 0.075 and 0.110) superconductors which are designed under a new concept. The Mossbauer spectra results show that Sn occupies Cu position in Sn4+ state, and there is no Sn2+ ion occupying La position. The local lattice deformation near Sn4+ site is small, but displays an increasing tendency with Sn doping. For La2CuO4 matrix, the simultaneous dopings of Sr/Sn induce holes and electrons on CuO2 layer in a new mechanism which influences superconductivity. Under a new mechanism of extra oxygen, the ex-tra oxygen effect of Sn-doping on superconductivity is discussed.
