We report on the photoresponse of mid-wavelength infrared radiation (MWIR) type-II superlattices (T2SLs) InAs/InAsSb high operating temperature (HOT) photoresistor grown on GaAs substrate. The device consists of a 200 periods of active layer grown on GaSb buffer layer. The photoresistor reached a 50% cut-off wavelength of 5 µm and 6 µm at 200 K and 300 K respectively. The time constant of 30 ns is observed at 200 K under 1 V bias. This is the first observation of the photoresponse in MWIR T2SLs InAs/InAsSb above 200 K.
The main work of this paper focuses on the simulation of binary alloy solidification using the phase field model and adaptive octree grids. Ni-Cu binary alloy is used as an example in this paper to do research on the numerical simulation of isothermal solidification of binary alloy. Firstly, the WBM model, numerical issues and adaptive octree grids have been explained. Secondary, the numerical simulation results of three dimensional morphology of the equiaxed grain and concentration variations are given, taking the efficiency advantage of the adaptive octree grids. The microsegregation of binary alloy has been analysed emphatically. Then, numerical simulation results of the influence of thermo-physical parameters on the growth of the equiaxed grain are also given. At last, a simulation experiment of large scale and long-time has been carried out. It is found that increases of initial temperature and initial concentration will make grain grow along certain directions and adaptive octree grids can effectively be used in simulations of microstructure.