Development of novel class of the far IR detectors based on heavily doped A~(Ⅳ)B~(Ⅵ) epitaxial films

摘要

A~(Ⅳ)B~(Ⅵ) (chalcogenides of Ⅵ-group elements) semiconductors are well-known materials having applications in infrared optoelectronics. Major efforts in the field of physics of the condensed matter are aimed at elucidating the influence of defects and impurities on the properties of semiconductor materials. In many cases, impurities can dramatically change the properties of semiconductor materials. Pb_(1-x-y) Sn_x Ge_y Te is a well-known narrow-band-gap semiconductor with usually high (n ≥ 10~16 cm~-) intrinsic defects. The introduction of indium into these solid solutions establishes an impurity level that is a function of the Sn and Ge concentration and of temperature. For x > 0.22, the In impurity level lies within the forbidden band (dielectric state) and exhibits the attendant sharp drop in the electron density. In the dielectric state (temperatures below 25 K) the In-doped alloys are unique in that they are photosensitive with a decrease in the electrical resistivity and an increase of carrier lifetime by several orders of magnitude (10~(-3)-10~4 s) depending on the temperature. The long relaxation time of the non-equilibrium concentration of electrons, manifested as persistent photoconductivity (PPC) effect. One of the advantages of PPC effect is the possibility of increasing the signaloise ratio by an increase of the charge integration time. Therefore one of the major challengos in developing array photodetectors operating in the television standard with a frame time ～ carrier lifetime is to ensure signal accumulation in each element of the array. As it is seen we have unequal possibility to realize novel type of array photodetectors over a wide range of the IR spectrum (up to 30 μm), in which each element provides radiation detection and its accumulation.