Asymmetry in dislocation density and strain relaxation has a significant impact on device performance since it leads to anisotropic electron transport in metamorphic materials. So it is preferred to obtain metamorphic...Asymmetry in dislocation density and strain relaxation has a significant impact on device performance since it leads to anisotropic electron transport in metamorphic materials. So it is preferred to obtain metamorphic materials with symmetric properties. In this paper, we grew metamorphic Ino.27Gao.73As epilayers with symmetric low threading dislocation density and symmetric strain relaxation in two (110) directions using InA1GaAs buffer layers on 7° misoriented GaAs (001) substrates. To understand the control mechanism of symmetric properties of Ino.27Gao.73As layers by the substrate miscut angles, Ino.27Gao.73As grown on 2° and 15° misoriented substrates were also characterized as reference by atomic force microscopy, transmission electron microscopy, and high resolution triple axis x-ray diffraction. The phase separation and interaction of 60° misfit dislocations were found to be the reasons for asymmetry properties of Ino.27Gao33As grown on 2° and 15° substrates, respectively. Photoluminescence results proved that the Ino.27G°ao.73As with symmetric properties has better optical properties than the Ino.27Gao.73As with asymmetric properties at room temperature. These results imply that high quality metamorphic Ino.27Gao.73As can be achieved with controllable isotropic electron transport property.展开更多
Compositionally undulating step-graded Al(Ga)InxAs (x = 0.05-0.52) buffers with the following InP layer were grown by metal-organic chemical vapor deposition (MOCVD) on (001) GaAs with a 15° miscut. The d...Compositionally undulating step-graded Al(Ga)InxAs (x = 0.05-0.52) buffers with the following InP layer were grown by metal-organic chemical vapor deposition (MOCVD) on (001) GaAs with a 15° miscut. The dislocation dis- tribution and tilts of the epilayers were examined using x-ray rocking curve and (004) reciprocal space maps (RSM) along two orthogonal (110) directions. The results suggested that such reverse-graded layers have different effects on a and 13 dislocations. A higher dislocation density was observed along the [ 110] direction and an epilayer tilt of - 1.43° was attained in the [1-10] direction when a reverse-graded layer strategy was employed. However, for conventional step-graded samples, the dislocation density is normally higher along the [1-10] direction.展开更多
Low metal-graphene contact resistance is important in making high-performance graphene devices.In this work,we demonstrate a lower specific contact resistivity of Au0.88Ge0.12/Ni/Au-graphene contact compared with Ti/A...Low metal-graphene contact resistance is important in making high-performance graphene devices.In this work,we demonstrate a lower specific contact resistivity of Au0.88Ge0.12/Ni/Au-graphene contact compared with Ti/Au and Ti/Pt/Au contacts.The rapid thermal annealing process was optimized to improve AuGe/Ni/Au contact resistance.Results reveal that both pre- and post-annealing processes are effective for reducing the contact resistance.The specific contact resistivity decreases from 2.5 × 10^-4 to 7.8 × 10^-5 Ω·cm^2 by pre-annealing at 300 ℃ for one hour,and continues to decrease to 9.5 × 10^-7 H·cm2 after post-annealing at 490 ℃ for 60 seconds.These approaches provide reliable means of lowering contact resistance.展开更多
Lattice-matched lnGaAs(P) photovoltaic devices were grown on lnP substrates by metal-organic chem- ical vapor deposition. InGaAsP/InGaAs ( 1.07/0.74 eV) dual-junction (D J) solar cells were fabricated and charac...Lattice-matched lnGaAs(P) photovoltaic devices were grown on lnP substrates by metal-organic chem- ical vapor deposition. InGaAsP/InGaAs ( 1.07/0.74 eV) dual-junction (D J) solar cells were fabricated and charac- terized by quantum efficiency and I-V measurements. The open circuit voltage, short circuit current density, fill factor, and efficiency of lnGaAsP/lnGaAs DJ solar cell are 0.977 V, 10.2 mA/cm2, 80.8%, and 8.94%, respectively, under one sun illumination of the AM 1.5D spectrum. For the lnGaAsP/lnGaAs DJ solar cell, with increasing con- centration, the conversion efficiency first increases steadily and reaches 13% around 280 suns, and finally decreases due to the drop in fill factor at higher concentration ratios. These experimental results demonstrate the promising prospect of GaInP/GaAs/lnGaAsP/lnGaAs four-junction solar cells.展开更多
We investigate a novel Ga As-based laser power converters(LPCs) grown by metal-organic chemical vapor deposition(MOCVD),which uses a single monolithic structure with six junctions connected by tunnel junctions to obta...We investigate a novel Ga As-based laser power converters(LPCs) grown by metal-organic chemical vapor deposition(MOCVD),which uses a single monolithic structure with six junctions connected by tunnel junctions to obtain a high output voltage. The LPCs with diameters of active aperture of 2 mm and 4 mm were fabricated and tested. The test results show that under an 808 nm laser,two LPCs both show an open circuit voltage of above 6.5 V. A maximum power conversion efficiency of 50.2% is obtained by 2 mm sample with laser power of 0.256 W,and an output electric power of 1.9 W with laser power of 4.85 W is obtained by 4 mm sample. The performances of the LPCs are deteriorated under illumination of high flux,and the 4 mm sample shows a higher laser power tolerance.展开更多
Optically stimulated luminescence (OSL) is the luminescence emitted from a semiconductor during its exposure to light. The OSL intensity is a function of the total dose absorbed by the sample. The dose-rate dependen...Optically stimulated luminescence (OSL) is the luminescence emitted from a semiconductor during its exposure to light. The OSL intensity is a function of the total dose absorbed by the sample. The dose-rate dependence of the OSL signal of the semiconductor CaS doped Ce and Sm was studied by numerical simulation and experiments. Based on a one-trap/one-center model, the whole OSL process was represented by a series of differential equations. The dose-rate properties of the materials were acquired theoretically by solving the equations. Good coherence was achieved between numerical simulation and experiments, both of which showed that the OSL signal was independent of dose rate. This result validates that when using OSL as a dosimetry technique, the dose-rate effect can be neglected.展开更多
CuPt-type ordering with undesirable properties always occurs in GaInP at growth conditions that are very close to those leading to the highest quality material in metal organic chemical vapor deposition. In this work,...CuPt-type ordering with undesirable properties always occurs in GaInP at growth conditions that are very close to those leading to the highest quality material in metal organic chemical vapor deposition. In this work, highly disordered GaInP with high crystalline quality was obtained by optimizing growth conditions. Room- temperature and low-temperature photoluminescence (PL) spectra of A1GalnP/GaInP/A1GaInP double heterostruc- tures (DHs) reveal that the band edge emission intensity is enhanced by optimizing growth temperature, V/III ratio, and reactor pressure at the expense of low energy peak originating from spatially indirect recombination due to the ordering-related defects. The DH sample with less ordering-related defects demonstrates a longer effective minority carrier lifetime, consequently, the GaInP solar cell shows a significant improvement in the performance.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.61376065)the Suzhou Science and Technology Project,China(Grant No.ZXG2013044)
文摘Asymmetry in dislocation density and strain relaxation has a significant impact on device performance since it leads to anisotropic electron transport in metamorphic materials. So it is preferred to obtain metamorphic materials with symmetric properties. In this paper, we grew metamorphic Ino.27Gao.73As epilayers with symmetric low threading dislocation density and symmetric strain relaxation in two (110) directions using InA1GaAs buffer layers on 7° misoriented GaAs (001) substrates. To understand the control mechanism of symmetric properties of Ino.27Gao.73As layers by the substrate miscut angles, Ino.27Gao.73As grown on 2° and 15° misoriented substrates were also characterized as reference by atomic force microscopy, transmission electron microscopy, and high resolution triple axis x-ray diffraction. The phase separation and interaction of 60° misfit dislocations were found to be the reasons for asymmetry properties of Ino.27Gao33As grown on 2° and 15° substrates, respectively. Photoluminescence results proved that the Ino.27G°ao.73As with symmetric properties has better optical properties than the Ino.27Gao.73As with asymmetric properties at room temperature. These results imply that high quality metamorphic Ino.27Gao.73As can be achieved with controllable isotropic electron transport property.
基金Project supported by the National Natural Science Foundation of China(Grant No.61376065)
文摘Compositionally undulating step-graded Al(Ga)InxAs (x = 0.05-0.52) buffers with the following InP layer were grown by metal-organic chemical vapor deposition (MOCVD) on (001) GaAs with a 15° miscut. The dislocation dis- tribution and tilts of the epilayers were examined using x-ray rocking curve and (004) reciprocal space maps (RSM) along two orthogonal (110) directions. The results suggested that such reverse-graded layers have different effects on a and 13 dislocations. A higher dislocation density was observed along the [ 110] direction and an epilayer tilt of - 1.43° was attained in the [1-10] direction when a reverse-graded layer strategy was employed. However, for conventional step-graded samples, the dislocation density is normally higher along the [1-10] direction.
基金Project supported by the National Natural Science Foundation of China(Grant No.61376065)the Science and Technology Project of Suzhou,China(Grant No.ZXG2013044)
文摘Low metal-graphene contact resistance is important in making high-performance graphene devices.In this work,we demonstrate a lower specific contact resistivity of Au0.88Ge0.12/Ni/Au-graphene contact compared with Ti/Au and Ti/Pt/Au contacts.The rapid thermal annealing process was optimized to improve AuGe/Ni/Au contact resistance.Results reveal that both pre- and post-annealing processes are effective for reducing the contact resistance.The specific contact resistivity decreases from 2.5 × 10^-4 to 7.8 × 10^-5 Ω·cm^2 by pre-annealing at 300 ℃ for one hour,and continues to decrease to 9.5 × 10^-7 H·cm2 after post-annealing at 490 ℃ for 60 seconds.These approaches provide reliable means of lowering contact resistance.
基金supported by the National Natural Science Foundation of China(No.61376065)
文摘Lattice-matched lnGaAs(P) photovoltaic devices were grown on lnP substrates by metal-organic chem- ical vapor deposition. InGaAsP/InGaAs ( 1.07/0.74 eV) dual-junction (D J) solar cells were fabricated and charac- terized by quantum efficiency and I-V measurements. The open circuit voltage, short circuit current density, fill factor, and efficiency of lnGaAsP/lnGaAs DJ solar cell are 0.977 V, 10.2 mA/cm2, 80.8%, and 8.94%, respectively, under one sun illumination of the AM 1.5D spectrum. For the lnGaAsP/lnGaAs DJ solar cell, with increasing con- centration, the conversion efficiency first increases steadily and reaches 13% around 280 suns, and finally decreases due to the drop in fill factor at higher concentration ratios. These experimental results demonstrate the promising prospect of GaInP/GaAs/lnGaAsP/lnGaAs four-junction solar cells.
基金supported by the National Natural Science Foundation of China(Nos.61376065 and 61604171)Zhongtian Technology Group Co.Ltd
文摘We investigate a novel Ga As-based laser power converters(LPCs) grown by metal-organic chemical vapor deposition(MOCVD),which uses a single monolithic structure with six junctions connected by tunnel junctions to obtain a high output voltage. The LPCs with diameters of active aperture of 2 mm and 4 mm were fabricated and tested. The test results show that under an 808 nm laser,two LPCs both show an open circuit voltage of above 6.5 V. A maximum power conversion efficiency of 50.2% is obtained by 2 mm sample with laser power of 0.256 W,and an output electric power of 1.9 W with laser power of 4.85 W is obtained by 4 mm sample. The performances of the LPCs are deteriorated under illumination of high flux,and the 4 mm sample shows a higher laser power tolerance.
基金Project supported by the National Natural Science Foundation of China(Nos.10875168,10475112)
文摘Optically stimulated luminescence (OSL) is the luminescence emitted from a semiconductor during its exposure to light. The OSL intensity is a function of the total dose absorbed by the sample. The dose-rate dependence of the OSL signal of the semiconductor CaS doped Ce and Sm was studied by numerical simulation and experiments. Based on a one-trap/one-center model, the whole OSL process was represented by a series of differential equations. The dose-rate properties of the materials were acquired theoretically by solving the equations. Good coherence was achieved between numerical simulation and experiments, both of which showed that the OSL signal was independent of dose rate. This result validates that when using OSL as a dosimetry technique, the dose-rate effect can be neglected.
基金Project supported by the National Natural Science Foundation of China(No.61376065)the Suzhou Science and Technology Project(No.ZXG2013044)
文摘CuPt-type ordering with undesirable properties always occurs in GaInP at growth conditions that are very close to those leading to the highest quality material in metal organic chemical vapor deposition. In this work, highly disordered GaInP with high crystalline quality was obtained by optimizing growth conditions. Room- temperature and low-temperature photoluminescence (PL) spectra of A1GalnP/GaInP/A1GaInP double heterostruc- tures (DHs) reveal that the band edge emission intensity is enhanced by optimizing growth temperature, V/III ratio, and reactor pressure at the expense of low energy peak originating from spatially indirect recombination due to the ordering-related defects. The DH sample with less ordering-related defects demonstrates a longer effective minority carrier lifetime, consequently, the GaInP solar cell shows a significant improvement in the performance.