To provide a method for producing a polycrystalline thin film and a method for producing a composite nanocrystal layer, with which variation in size of a great number of columnar crystals grown in a direction perpendicular to one surface of a substrate and variation in formation positions can be suppressed, and a field-emission electron source enhancing electron emission efficiency and a luminescent device enhancing luminous efficiency.

A microcrystalline silicon thin film forming step (nucleus forming step) is carried out (figure (a)), wherein a microcrystalline silicon thin film 21 containing a great number of microcrystalline silicon grains in an amorphous silicon film is formed on one surface of a substrate 11, and then a polycrystalline silicon thin film forming step (crystal growing step) is carried out (figure (b)), wherein a polycrystalline silicon thin film (polycrystalline thin film) 31 comprising aggregates of a great number of columnar silicon crystals 31a is formed by growing the columnar silicon crystals (columnar crystals) 31a using the microcrystalline silicon grains in the microcrystalline silicon thin film 21 as nuclei.