Enhancement of terahertz coupling efficiency by improved antenna design in GaN/AlGaN high electron mobility transistor detectors

An optimized micro-gated terahertz detector with novel triple resonant antenna is presented.The novel resonant antenna operates at room temperature and shows more than a 700% increase in photocurrent response compared to the conventional bowtie antenna.In finite-difference-time-domain simulations,we found the performance of the self-mixing GaN/AlGaN high electron mobility transistor detector is mainly dependent on the parameters L gs(the gap between the gate and the source/drain antenna) and L w(the gap between the source and drain antenna).With the improved triple resonant antenna,an optimized micrometer-sized AlGaN/GaN high electron mobility transistor detector can achieve a high responsivity of 9.45×102 V/W at a frequency of 903 GHz at room temperature.     

Enhancement of Magnetoresistance in Granular CrO2／Polystyrene Composites

We present a study of magnetotransport in CrO2/polystyrene (PS) composites over a range of polystyrene concentration (0-30 wt. %). In the experiment, an obvious enhancement in magnetoresistance (MR) is observed at 77K and at room temperature as the hadf-metadlic Cr02 particles are encapsulated with a thin layer of insulating polystyrene. The enhanced MR can be interpreted in terms of spin-dependent intergranular tunnelling with 4-nm-thick PS barrier. Moreover, it is found that the novel PS barrier contributes to room-temperature MR more significantly than that at 77K. Temperature dependence of resistance is good agreement with -T^-1/4 in the temperature range from 77 to 298K.     

磁性颗粒复合体磁渗流区矫顽力异常的研究

制备了MnZn铁氧体/SiO₂颗粒复合体.研究了磁性颗粒复合体的有效磁导率μ、 比磁化强度σ以及矫顽力H_c随磁性颗粒含量的变化.研究发现，在MnZn铁氧体体积百分含 量为90%—98%的区域，复合体的有效磁导率μ的变化速率发生突变，出现磁渗流现象，从实验得到的体系磁渗流阈值V_c=97.9%.在磁渗流区，矫顽力表现出异常行为.结果表明 ，这种异常行为与复合体微观结构有着密切关系.在磁渗流前，矫顽力H_c的变化主要来 源于磁 关键词： 颗粒复合体 磁渗流 矫顽力     

Electric field driven plasmon dispersion in AlGaN/GaN high electron mobility transistors

We present a theoretical study on the electric field driven plasmon dispersion of the two-dimensional electron gas(2DEG)in AlGaN/GaN high electron mobility transistors(HEMTs).By introducing a drifted Fermi–Dirac distribution,we calculate the transport properties of the 2DEG in the AlGaN/GaN interface by employing the balance-equation approach based on the Boltzmann equation.Then,the nonequilibrium Fermi–Dirac function is obtained by applying the calculated electron drift velocity and electron temperature.Under random phase approximation(RPA),the electric field driven plasmon dispersion is investigated.The calculated results indicate that the plasmon frequency is dominated by both the electric field and the angle between wavevector and electric field.Importantly,the plasmon frequency could be tuned by the applied source–drain bias voltage besides the gate voltage(change of the electron density).