研究目的
To propose a new heterostructure PbTe/ZnTe by capping the p-type PbTe epilayer with insulating ZnTe layer, and to develop a high-performance room-temperature lateral-photovoltaic MIR photodetector based on this novel heterostructure.
研究成果
A novel heterostructure PbTe/ZnTe was fabricated and the origin of the high conductive interface inversion layer has been revealed by determination of band o?set with XPS. Based on the novel heterostructure, a mid-infrared (MIR) lateral photovoltaic e?ect (LPE) with very fast response speed bene?ting from the high conductive inversion layer was demonstrated. By innovatively designing an asymmetric light-blocking photomask on the surface of PbTe/ZnTe, a room-temperature high-performance MIR photodetector based on the LPE has been realized for the ?rst time, covering the wavelength range from 1.2 μm to 4.8 μm.
研究不足
The responsivity of the PbTe/ZnTe LPE photodetector is approximately one order of magnitude smaller than that of a typical PbTe diode, but it still can be optimized to higher level by adjusting the dimension and position of photomask gap.
The PbTe/ZnTe heterostructures were grown by a telluride MBE system with the base pressure better than 2 × 10?10 torr. First, a 1 μm thick PbTe ?lm was grown on a freshly cleaved BaF2 (111) substrate. Then, a layer of 50 nm thick ZnTe ?lm was epitaxially deposited on the PbTe ?lm at a rate of 10 nm/min using a ZnTe compound e?usion cell. Post-growth XRD measurements demonstrated that both PbTe and ZnTe epilayers were (111) oriented. The conventional ultraviolet photolithography was utilized to de?ne the device geometry and the mesa structure was obtained by etching. Then, electrodes made of Cr (5 nm)/Cu (50 nm)/Au (50 nm) multilayers were fabricated with a thermal evaporation deposition method and a lift-o? technique. Following the electrodes, an insulating Ta2O5 layer was deposited on the active area of the mesa by magnetron sputtering in order to isolate the light-blocking photomask from other parts of the device electrically. At last, the light-blocking photomask composed of Cr (5 nm)/Au (100 nm) multilayers was deposited on top of the insulating layer using the similar procedures for making electrodes.
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