CVD systems, and in particular MOCVD systems, are used to produce light-emitting diodes, in particular green, blue and also white light-emitting diodes.  Compound nitrides are deposited on a semiconductor surface in order to deposit white light-emitting diodes.  In the production processes used hitherto, first and second process gases, for example in the form of TMG or NH3, have been passed into the process chamber, where the process gases decompose or react with one another, and the reaction or decomposition products are deposited on the surface of a substrate so as to form a layer or layers.  The processes used hitherto are expensive, since the outlay on materials, in particular with regard to the nitrogen hydride, is considerably higher than the outlay on materials for the metal alkyl, for example TMG.  NH3, PH3 or ASH3 have to be introduced into the process chamber in a concentration which is higher by an order of magnitude than the metal alkyls.  Although the hydrides are relatively inexpensive compared to the alkyls, the consumption costs are approximately the same, on account of the high consumption.  The high consumption is a result of the high thermal activation energy of the hydrides compared to the activation energies of the metal alkyls. 
To promote decomposition of the reaction gases, U.S. Pat.  No.  4,539,068 proposes that a plasma be ignited between the gas inlet member and the substrate holder. 
U.S. Pat.  No.  3,757,733 also proposes a plasma in the process chamber for this purpose. 
U.S. Pat.  No.  6,289,842 B1 deals with the deposition of semiconductor layers in the MOCVD system, in which the process gases are introduced into the process chamber through a showerhead. 
A plasma pre-treatment of a reaction gas is also known from JP 08-167596. 
WO 01/46498 describes introducing the alkyls separately from the hydrides.