(DE4333416-C2)      Prodn. of microcrystalline layers made of gp.IVa elements, esp. Si, Ge, Sn or their alloys, e.g. SiC or SiGe, using cyclic CVD or related methods is claimed. The 1st step comprises mfr. of an amorphous layer of the element in which a suitable process gas, e.g. the element-hydrogen cpds. and hydrogen, is fed under the usual CVD conditions into the reactor above the substrate. The 2nd step comprises treating with hydrogen. During the 2nd step, the feeding of the process gas stream, the hydrogen supply and connection of the CVD reactor to the pump are closed so that hydrogen treatment takes place in a closed CVD process with the amt. of hydrogen or element-hydrogen cpds. in the reactor.    Prodn. of luminescent element structures on substrates is also claimed.    The luminescent element structures are produced by: (a) forming a microcrystalline layer as above; (b) producing an active layer under CVD conditions by passivating an oxidising gas or nitriding gas; and (c) contacting the active layer so that a voltage can be applied.     The hydrogen supply is interrupted when the pressure in the reactor increases to 1 atmosphere. The hydrogen treatment is carried out depending on the desired crystal amt. in the region 20-95%. 2-2000 cycles are carried out. The element is Si. The process gases are SiH4 and H2.    USE -   In prodn. of solar cells and transistors.    (EP721656-A1)      Prodn. of microcrystalline layers made of gp.IVa elements, esp. Si, Ge, Sn or their alloys, e.g. SiC or SiGe, using cyclic CVD or related methods is claimed. The 1st step comprises mfr. of an amorphous layer of the element in which a suitable process gas, e.g. the element-hydrogen cpds. and hydrogen, is fed under the usual CVD conditions into the reactor above the substrate. The 2nd step comprises treating with hydrogen. During the 2nd step, the feeding of the process gas stream, the hydrogen supply and connection of the CVD reactor to the pump are closed so that hydrogen treatment takes place in a closed CVD process with the amt. of hydrogen or element-hydrogen cpds. in the reactor.    Prodn. of luminescent element structures on substrates is also claimed.    The luminescent element structures are produced by: (a) forming a microcrystalline layer as above; (b) producing an active layer under CVD conditions by passivating an oxidising gas or nitriding gas; and (c) contacting the active layer so that a voltage can be applied.     The hydrogen supply is interrupted when the pressure in the reactor increases to 1 atmosphere. The hydrogen treatment is carried out depending on the desired crystal amt. in the region 20-95%. 2-2000 cycles are carried out. The element is Si. The process gases are SiH4 and H2.    USE -   In prodn. of solar cells and transistors.