Si/SiC heterostructural impact avalanche transit time (IMPATT) diode indicates of important applications in Terahertz (THz) power source, integrated circuit etc. In this paper, the (n)Si/(p)4H-SiC, (n)Si/(p)6H-SiC, (n)Si/(p)3C-SiC heterostructural double drift region IMPATT diodes operating at the atmospheric window frequency of 0.85 THz are designed by the drift-diffusion model while their static state, large signal and noise properties are numerically simulated. The performance parameters of the studied devices such as breakdown voltage, peak electric field strength, optimal negative conductance, output power, power conversion efficiency, admittance-frequency relation, quality factor, noise electric field, mean-square noise voltage per band-width and noise measure were calculated and compared. This method can guide for optimizing the Si/SiC heterostructural IMPATT device in the future.

Short circuit current density (Jsc) and photoelectric conversion efficiency (η) of the different material quantum dot intermediate band solar cells (QD-IBSCs) under full concentrated sunlight were compared in this work. The QD-IBSCs were designed with QDs formed from different excitonic Bohr radius semiconductors embedding in the different wide band gap materials. Modulation doping was used to realize partially filling the IB with electrons in QD, the influence of localized states from doping on IB was also considered. The performance of these SCs was numerically simulated based on the detailed balance principle. TheJscandηin QD-IBSCs can be adjusted via tuning the position and density of states of IB due to varying the mean size (d) and doping level of QDs in absorption region. Under the same doping level in an identical host gap material withΔEG=2.0 eV, theJscandηof the Si QD-IBSCs can be optimized with 4.3 nm-QDs, however, those of CdTe devices raises while those of Ge cells drops with increasing the sizes of QD from 2 nm to 8 nm. With changing the host gapΔEG, variation of the IB energy levelEHwith respect to valence band corresponding to the maximumηmwas explored, dependence ofηon the operation voltage was analyzed, and the impurity effect on theηwas taken into account. Present work indicates that an appropriate band gap material should be adopted to fabricate QDs to embed in suitable doped host gap one to obtain the high performance QD-IBSC.

Performance of micro-/poly-crystalline SiGe alloy solar cell of TCO/(n)a-Si:H/(i)a-Si/(p) c(pc)-SiGe/(p+)μc-Si/Al structure was analyzed via the AFORS-HET software. Cell structures can be designed to reach up to the optimal performance. Employment of back surface electric field layer of (p+)μc-Si could improve cell properties. The maximum photoelectric conversion efficiency η=21.48% occurs in a cell with average Ge percent content x0.1 and 250 m-thick Si1-xGex alloy light absorption layer, which is higher than the experimental result of the same absorption layer thickness crystalline Si HIT cell [Progress in Photovoltaics: Research and Applications, 8 (2000) 503.]. Temperature dependence of the cell performance parameters (open circuit voltage Voc, circuit current density Jsc, fill factor FF and efficiency η) indicates that Si0.9Ge0.1 cell shows weaker temperature sensitivity than that of pure Si cell. Numerical calculation illustrates that Voc decreases while Jsc, FF and η heighten with raising mean grain sizes and crystalline volume fractions, these variations with the later are more remarkable. Present optimized technique will be benefit to designing and fabricating the high performance solar cell.

Hetero-structure of AlxGa1-xN/GaN exhibits important applications in high frequency and large power devices. In this paper, AlN/GaN is adopted to optimal design the large power impact avalanche transit time (IMPATT) and mixed tunneling avalanche transit time (MITATT) diodes operating at the atmospheric low loss window frequency of 0.85 THz. The static state and large signal characteristics of the devices are numerically simulated. The values of peak electric field strength, break-down voltage, avalanche voltage, the maximum generation rates of avalanche and tunneling, admittance-frequency relation, output power, conversion efficiency, quality factor of the proposed hetero-structural IMPATT and MITATT diodes are calculated, respectively. Via comparing the obtained results of (n)AlN/(p)GaN and (n)GaN/(p)AlN IMPATT diodes to those of the MITATT counterparts, there exists little performance difference between IMPATT and MITATT devices while implies significant difference between the (n)AlN/(p)GaN and (n)GaN/(p)AlN diodes.