Space-charge-limited current investigation of the density of states in a-SiGe:H alloys

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Abstract
Space‐charge‐limited current measurements have been carried out on undoped amorphous silicon‐germanium alloys as a function of the Ge content in the range 0%–36%. The scaling law is checked for different series of samples with varying thickness, and the J‐V data consequently analyzed by using the Weisfield method. The position of the Fermi levelE F is obtained from the activation energy of the ohmic conductivity E a . The deduced value of the density of states (DOS) near E F increases as a function of the Ge content in the range 1016 to 4×1017 cm−3 eV−1. A factor of 7 improvement of the Si0.74Ge0.26:H alloy DOS is clearly evidenced when the material is prepared using high H2 dilution of GeH4–SiH4 mixtures, leading to a DOS value of 1×1016 cm−3 eV−1.