High-rate deposition of a-Si 1- x Ge x : H alloys was performed in order to both improve quality and to lower the fabrication cost of narrow-gap materials for use in amorphous solar cells. This paper presents the characteristics of a-Si 1- x Ge x : H alloys prepared by glow discharge decomposition of a Si 2H 6 and GeH 4 gas mixture. An excellent quality alloy with E g=1.55 eV, a photoconductivity of σ p=3X10 -5 Ω -1 cm -1 and a dark conductivity of σ d=4X10 -9 Ω -1 cm -1 is obtained under the high deposition rate of 4 Å/s. In addition, it is proposed that at least two types of heterostructure, which deviate from a randomly mixed homogeneous structure, exist. Therefore, reduction of these heterostructure are necessary to improve alloy quality.