We present a study on InAs/InGaAs QDs nanostructures grown by molecular beam epitaxy on InGaAs metamorphic buffers, that are designed so as to determine the strain of QD and, then, to shift the luminescence emission t...We present a study on InAs/InGaAs QDs nanostructures grown by molecular beam epitaxy on InGaAs metamorphic buffers, that are designed so as to determine the strain of QD and, then, to shift the luminescence emission towards the 1.5 μm region （QD strain engineering）. Moreover, we embed the QDs in InAIAs or GaAs barriers in addition to the InGaAs confining layers, in order to increase the activation energy for confined carrier thermal escape; thus, we reduce the thermal quenching of the photoluminescence, which prevents room temperature emission in the long wavelength range. We study the dependence of QD properties, such as emission energy and activation energy, on barrier thickness and height and we discuss how it is possible to compensate for the barrier-induced QD emission blue-shift taking advantage of QD strain engineering. Furthermore, the combination of enhanced barriers and QD strain engineering in such metamorphic QD nanostmctures allowed us to obtain room temperature emission up to 1.46μm, thus proving how this is a valuable approach in the auest for 1.55 um room temperature emission from ODs grown on GaAs substrates.展开更多
WT8.BZ]The effects of postgrowth rapid thermal annealing have been studied on the optical properties of 3-nm-height InAs/GaAs quantum dots covered by 3-nm-thick In xGa 1-x As (x=0,0 1 and 0 2) overgrowth layer...WT8.BZ]The effects of postgrowth rapid thermal annealing have been studied on the optical properties of 3-nm-height InAs/GaAs quantum dots covered by 3-nm-thick In xGa 1-x As (x=0,0 1 and 0 2) overgrowth layer.At a higher annealing temperature (T≥750℃),the photoluminescence peak of InGaAs layer has been observed at the lower-energy side of InAs quantum-dot peak.In addition,a similar blueshift in photoluminescence (PL) emission energy is observed for all samples when the annealing temperature increases from 650 to 850℃.However,the trend of photoluminescence linewidth towards narrowing is totally different for InAs quantum dots with different In mole fraction in InGaAs overgrowth layer.The results suggest that the intermixing in the lateral direction plays an important role in obtaining a better understanding of the modification of optical properties induced by the rapid thermal annealing.展开更多
The effcts of various InGaAs layers on the structural and optical properties of InAs self-assembled quantum dots（ QDs ） grown by molecular-beam epitaxy （MBE） were investigated. The emission wavelength of 1317 nm ...The effcts of various InGaAs layers on the structural and optical properties of InAs self-assembled quantum dots（ QDs ） grown by molecular-beam epitaxy （MBE） were investigated. The emission wavelength of 1317 nm was obtained by embedding InAs QDs in InGaAs / GaAs quantum well. The temperature-dependent and time-resolved photoluminescence （ TDPL and TRPL ） were used to study the dynomic characteristics of carriers. InGaAs cap layer may improve the quality of quantum dots for the strain relaxation around QDs, which results in a stronger PL inteasity and an increase of PL peak lifetime up to 170 K. We found that InGaAs buffer layer may reduce the PL peak lifetime of InAs QDs, which is due to the buffer layer accelerating the carrier migration. The results also show that InGaAs cap layer can increase the temperature point when the thermal reemission and nonradiative recombination contribute significantly to the carrier dynamics.展开更多
用 PL谱测试研究了 Ga As和不同 In组份 Inx Ga1 - x As(x=0 .1,0 .2 ,0 .3)覆盖层对分子束外延生长的 In As/Ga As自组织量子点发光特性的影响 .用 Inx Ga1 - x As外延层覆盖 In As/ Ga As量子点 ,比用 Ga As做覆盖层其发光峰能量向低...用 PL谱测试研究了 Ga As和不同 In组份 Inx Ga1 - x As(x=0 .1,0 .2 ,0 .3)覆盖层对分子束外延生长的 In As/Ga As自组织量子点发光特性的影响 .用 Inx Ga1 - x As外延层覆盖 In As/ Ga As量子点 ,比用 Ga As做覆盖层其发光峰能量向低能端移动 ,发光峰半高宽变窄 ,量子点发光峰能量随温度的红移幅度变小 .理论计算证实这是由于覆盖层 Inx Ga1 - x As减小了 In As表面应力导致发光峰红移 ,而 In元素有效抑制了 In As/ Ga As界面组份的混杂 ,量子点的均匀性得到改善 ,PL 谱半高宽变窄 .用 In Ga As覆盖的 In0 .5 Ga0 .5 As/ Ga As自组织量子点实现了 1.3μm发光 ,室温下 PL谱半高宽为 19.2 me V。展开更多
For enhancement-mode InGaP/A1GaAs/InGaAs PHEMTs,gate annealing is conducted between gate structures of Ti/Pt/Au and Pt/Ti/Pt/Au. Comparison is made after thermal annealing and an optimum annealing process is ob- taine...For enhancement-mode InGaP/A1GaAs/InGaAs PHEMTs,gate annealing is conducted between gate structures of Ti/Pt/Au and Pt/Ti/Pt/Au. Comparison is made after thermal annealing and an optimum annealing process is ob- tained. Using the structure of Ti/Pt/Au, about a 200mV positive shift of threshold voltage is achieved by thermal annea- ling at 320℃ for 40min in N2 ambient. Finally, a stable and consistent enhancement-mode PHEMT is produced successfully with higher threshold voltage.展开更多
CaN-based heterostructures with an InAlCaN/AlCaN composite barrier on sapphire （0001） substrates are grown by a low-pressure metal organic chemical vapor deposition system. Compositions of the InAiGaN layer are dete...CaN-based heterostructures with an InAlCaN/AlCaN composite barrier on sapphire （0001） substrates are grown by a low-pressure metal organic chemical vapor deposition system. Compositions of the InAiGaN layer are determined by x-ray photoelectron spectroscopy, structure and crystal quality of the heterostruetures are identified by high resolution x-ray diffraction, surface morphology of the samples are examined by an atomic force microscope, and Hall effect and capacitance-voltage measurements are performed at room temperature to evaluate the electrical properties of heterostructures. The Al/In ratio of the InAlGaN layer is 4.43, which indicates that the InAlCaN quaternary layer is nearly lattice-matched to the CaN channel. Capacitance-voltage results show that there is no parasitic channel formed between the InAIGaN layer and the AlCaN layer. Compared with the InAl- CaN/CaN heterostructure, the electrical properties of the InAlCaN/AlGaN/GaN heterostructure are improved obviously. Influences of the thickness of the AlGaN layer on the electrical properties of the heterostructures are studied. With the optimal thickness of the AlGaN layer to be 5 nm, the 2DEG mobility, sheet density and the sheet resistance of the sample is 1889.61 cm2/V.s, 1.44 × 10^13 cm-2 and as low as 201.1 Ω/sq, respectively.展开更多
Lattice-matched In0.5 Ga0.47 As/In0.52 Al 0.48 As high electron mobility transistors （HEMTs） with a cutoff frequency （ft） as high as 218GHz are reported. This fT is the highest value ever reported for HEMTs in Chi...Lattice-matched In0.5 Ga0.47 As/In0.52 Al 0.48 As high electron mobility transistors （HEMTs） with a cutoff frequency （ft） as high as 218GHz are reported. This fT is the highest value ever reported for HEMTs in China. These devices also demonstrate excellent DC characteristics：the extrinsic transconductance is 980mS/mm and the maximum current density is 870mA/mm. The material structure and all the device fabrication technology in this work were developed by our group.展开更多
基金The work has been partially supported by the "SANDiE" Networkof Excellence of EU(contract no. NMP4-CT-2004-500101).
文摘We present a study on InAs/InGaAs QDs nanostructures grown by molecular beam epitaxy on InGaAs metamorphic buffers, that are designed so as to determine the strain of QD and, then, to shift the luminescence emission towards the 1.5 μm region （QD strain engineering）. Moreover, we embed the QDs in InAIAs or GaAs barriers in addition to the InGaAs confining layers, in order to increase the activation energy for confined carrier thermal escape; thus, we reduce the thermal quenching of the photoluminescence, which prevents room temperature emission in the long wavelength range. We study the dependence of QD properties, such as emission energy and activation energy, on barrier thickness and height and we discuss how it is possible to compensate for the barrier-induced QD emission blue-shift taking advantage of QD strain engineering. Furthermore, the combination of enhanced barriers and QD strain engineering in such metamorphic QD nanostmctures allowed us to obtain room temperature emission up to 1.46μm, thus proving how this is a valuable approach in the auest for 1.55 um room temperature emission from ODs grown on GaAs substrates.
文摘WT8.BZ]The effects of postgrowth rapid thermal annealing have been studied on the optical properties of 3-nm-height InAs/GaAs quantum dots covered by 3-nm-thick In xGa 1-x As (x=0,0 1 and 0 2) overgrowth layer.At a higher annealing temperature (T≥750℃),the photoluminescence peak of InGaAs layer has been observed at the lower-energy side of InAs quantum-dot peak.In addition,a similar blueshift in photoluminescence (PL) emission energy is observed for all samples when the annealing temperature increases from 650 to 850℃.However,the trend of photoluminescence linewidth towards narrowing is totally different for InAs quantum dots with different In mole fraction in InGaAs overgrowth layer.The results suggest that the intermixing in the lateral direction plays an important role in obtaining a better understanding of the modification of optical properties induced by the rapid thermal annealing.
文摘The effcts of various InGaAs layers on the structural and optical properties of InAs self-assembled quantum dots（ QDs ） grown by molecular-beam epitaxy （MBE） were investigated. The emission wavelength of 1317 nm was obtained by embedding InAs QDs in InGaAs / GaAs quantum well. The temperature-dependent and time-resolved photoluminescence （ TDPL and TRPL ） were used to study the dynomic characteristics of carriers. InGaAs cap layer may improve the quality of quantum dots for the strain relaxation around QDs, which results in a stronger PL inteasity and an increase of PL peak lifetime up to 170 K. We found that InGaAs buffer layer may reduce the PL peak lifetime of InAs QDs, which is due to the buffer layer accelerating the carrier migration. The results also show that InGaAs cap layer can increase the temperature point when the thermal reemission and nonradiative recombination contribute significantly to the carrier dynamics.
文摘用 PL谱测试研究了 Ga As和不同 In组份 Inx Ga1 - x As(x=0 .1,0 .2 ,0 .3)覆盖层对分子束外延生长的 In As/Ga As自组织量子点发光特性的影响 .用 Inx Ga1 - x As外延层覆盖 In As/ Ga As量子点 ,比用 Ga As做覆盖层其发光峰能量向低能端移动 ,发光峰半高宽变窄 ,量子点发光峰能量随温度的红移幅度变小 .理论计算证实这是由于覆盖层 Inx Ga1 - x As减小了 In As表面应力导致发光峰红移 ,而 In元素有效抑制了 In As/ Ga As界面组份的混杂 ,量子点的均匀性得到改善 ,PL 谱半高宽变窄 .用 In Ga As覆盖的 In0 .5 Ga0 .5 As/ Ga As自组织量子点实现了 1.3μm发光 ,室温下 PL谱半高宽为 19.2 me V。
文摘For enhancement-mode InGaP/A1GaAs/InGaAs PHEMTs,gate annealing is conducted between gate structures of Ti/Pt/Au and Pt/Ti/Pt/Au. Comparison is made after thermal annealing and an optimum annealing process is ob- tained. Using the structure of Ti/Pt/Au, about a 200mV positive shift of threshold voltage is achieved by thermal annea- ling at 320℃ for 40min in N2 ambient. Finally, a stable and consistent enhancement-mode PHEMT is produced successfully with higher threshold voltage.
基金Supported by the National Science and Technology Major Project under Grant No 2013ZX02308-002the National Natural Science Foundation of China under Grant Nos 11435010,61474086 and 61334002
文摘CaN-based heterostructures with an InAlCaN/AlCaN composite barrier on sapphire （0001） substrates are grown by a low-pressure metal organic chemical vapor deposition system. Compositions of the InAiGaN layer are determined by x-ray photoelectron spectroscopy, structure and crystal quality of the heterostruetures are identified by high resolution x-ray diffraction, surface morphology of the samples are examined by an atomic force microscope, and Hall effect and capacitance-voltage measurements are performed at room temperature to evaluate the electrical properties of heterostructures. The Al/In ratio of the InAlGaN layer is 4.43, which indicates that the InAlCaN quaternary layer is nearly lattice-matched to the CaN channel. Capacitance-voltage results show that there is no parasitic channel formed between the InAIGaN layer and the AlCaN layer. Compared with the InAl- CaN/CaN heterostructure, the electrical properties of the InAlCaN/AlGaN/GaN heterostructure are improved obviously. Influences of the thickness of the AlGaN layer on the electrical properties of the heterostructures are studied. With the optimal thickness of the AlGaN layer to be 5 nm, the 2DEG mobility, sheet density and the sheet resistance of the sample is 1889.61 cm2/V.s, 1.44 × 10^13 cm-2 and as low as 201.1 Ω/sq, respectively.
文摘Lattice-matched In0.5 Ga0.47 As/In0.52 Al 0.48 As high electron mobility transistors （HEMTs） with a cutoff frequency （ft） as high as 218GHz are reported. This fT is the highest value ever reported for HEMTs in China. These devices also demonstrate excellent DC characteristics：the extrinsic transconductance is 980mS/mm and the maximum current density is 870mA/mm. The material structure and all the device fabrication technology in this work were developed by our group.
