the system , as shown in fig1 for producing semiconductor layer structures by way of epitaxial growth consists of the following principal sections : a loading area 1 , an epitaxial - growth region 2 and an unloading area 3 . a reaction space 4 is enclosed by an envelope of quartz glass 5 and by housing members of high - grade steel 6 and 7 which , on both end sides and at several connecting points , are connected among each other and to further parts of the system by means of sealing flanges as denoted in the drawing , such as by the flanges 8 . within the epitaxial - growth region 2 , the reaction space 4 is surrounded by a diffusion furnace 10 comprising three separately heatable temperature zones , of which in particular the temperature of the center zone 11 must be very exactly kept constant . within the section including this center temperature zone 11 , an upper crucible part 12 , also known as an epitaxial boat , is disposed within the reaction space . this upper part 12 comprises several , e . g ., five chambers 13 for taking up the coating or deposition substance solutions . below the upper crucible part 12 , cassette - shaped lower crucible parts l4a are pushed i . e ., ( in the representation of fig1 ) from right to left through the reaction space 4 . they each contain a thin semiconductor slice or wafer 15 which successively comes to lie below the individual chambers 13 where it remains for the necessary crystallization period . following each of these lower parts l4a , a container - like lower crucible part l4b by which the used - up solution is removed , and a lower crucible part 14c serving as a spacer , are moved through the reaction space 4 . details of the multi - chamber upper crucible part 12 and of the various lower crucible parts 14a , l4b and 14c are explained in greater detail hereinafter with reference to fig2 to 4 of the drawings . with the aid of a photosensor assembly consisting of a phototransmitter 16 , of optical fibers 17 extending to the chambers 13 of the upper part 12 , of the optical fibers 18 extending from the lower parts 14 disposed below the upper part 12 , and of a photoreceiver 19 , the individual lower parts l4a , l4b , l4c are each positioned exactly below the associated chamber 13 . since the epitaxial process has to be carried out under a protective - gas atmosphere , the quartz tube 5 surrounding the reaction space , and the spaces of the loading area 1 and of the unloading area 3 as connected thereto , are provided with air - vent pipes 20 via which , within the reaction space 4 , it is possible to produce an ultra - high vacuum . via supply pipes 21 , a protective gas , such as hydrogen , can be introduced into the loading area or the loading station 1 and into the unloading area or the unloading station 3 . the loading area 1 comprises a storage space or storage container 22 which is filled with a stack of lower crucible parts 14 which each contain an uncoated semiconductor wafer 15 . the unloading area 3 is provided with a corresponding storage space 23 for taking up the lower parts 14 together with the semiconductor wafer 15 after the latter has been coated . in order to prevent the reaction space 4 from coming into contact with surrounding atmosphere either during the filling of the storage space 22 or the emptying of the storage space 23 -- with all the disadvantageous interactions resulting therefrom -- one airlock device 25 , 25 &# 39 ; each is inserted between the connections of the storage spaces 22 and 23 at the housing members 6 , 7 , with these airlock devices , for example , consisting of a high - grade steel pendulum slider or gate valve provided with an electropneumatic drive 26 , 26 &# 39 ;. before the storage space 22 or 23 is opened or separated for the respective purposes of filling or emptying , the reaction space 4 is hermetically sealed with respect to the surrounding atmosphere by either the airlock device 25 or 25 &# 39 ;. from the storage space 22 the lower crucible parts 14 are pushed , with the aid of a piston 28 , successively into the reaction space 4 . for this purpose , the piston 28 is actuated by a drive 29 which , appropriately , is designed as a stepper motor . a high - grade steel bellows 30 seals the grommet through which the piston rod 31 passes through the housing 32 of the drive , against the surrounding atmosphere , so that the vacuum inside the reaction space 4 is maintained also when the airlock device 25 and the connected storage space 22 are opened . the unloading area 3 likewise comprises a piston 28 &# 39 ; with a drive 29 &# 39 ;, with the aid of which the individual lower parts 14 are removed from the reaction space 4 and introduced into the storage space 23 . here , too , a bellows 30 &# 39 ; effects the necessary sealing with respect to the surroundings . a push rod 34 which is capable of being moved to and fro , and an associated drive 35 in the form of a stepper motor , form a conveying device for pushing the lower crucible parts 14 through the reaction space 4 . this push rod 34 is likewise sealed against the atmosphere by means of a high - grade steel bellows 36 . the lower parts 14 rest on a glideway or rail 38 extending from the loading area 1 up to the unloading area 3 through the reaction space 4 . after the semiconductor wafers respectively placed below the upper crucible part 12 have been coated , the push rod 34 pushes the lower parts 14 by the length of one lower part to the left and then returns to its initial position . the piston 28 in the loading area is then moved in the upward direction and transfers a further lower part 14 up to the level of the slideway 38 . the piston 28 &# 39 ; of the unloading area 3 is moved in the downward direction , lowering the top one of the lower parts 14 lying on the stack , and thus making room for the next lower part 14 arriving on the slideway 38 . this process is repeated until the storage space 22 within the loading area is empty , or until the storage space 23 is filled . after that , as already mentioned hereinbefore , the airlock devices 25 and 25 &# 39 ; are closed , the storage space 22 is refilled with new semiconductor wafers 15 , and the lower parts 14 with the readily coated semiconductor wafers 15 are removed from the storage space 23 . the vacuum or the protective gas atmosphere within the reaction space remains unaffected by the surrounding atmosphere during the loading and unloading of the storage spaces 22 and 23 . above all , however , there is no need for the diffusion furnace 10 to be cooled and reheated thereafter . a drive 41 is connected to a slider in the upper crucible part 12 ( cf . fig4 ). with the aid of this slider , the portion of growth solution respectively required for one epitaxial coating can be separated from the contents of the chambers 13 and , moreover , the used - up portion of growth solution can be emptied into containerlike lower crucible part l4b . also the passage through which the push rod 40 extends through the housing 42 of a drive is sealed against the atmosphere with the aid of a bellows 43 . the controllers of the individual aforementioned drives will be explained hereinafter . the lower crucible part l4a as shown in fig2 consists of a cassette - like housing 45 which is provided with a displaceable cover ( lid ) 46 . one recess of the housing 45 takes up the semiconductor wafer 15 to be coated , and is covered by a slice 47 of e . g ., indium phosphide ( inp ). by means of the cover 46 the protective gas may be prevented , during its entire stay within the reaction space 4 , from acting upon the semiconductor wafer 15 or the inp slice 47 , and from causing possible changes . the cover 46 is pushed aside as soon as the lower part 14 reaches the upper part 13 . it is then received in a recess 48 as is indicated by the long arrow in the drawing . the containerlike lower crucible part 14b as shown in fig3 consists of a body 44 and of a recess 49 which respectively receives one portion of used - up growth solution and is moved out of the reaction space 4 . the lower crucible parts 14c which are not shown in greater detail and which serve as spacers , merely consist of a body 44 without a recess . below the upper crucible part 12 ( fig4 ) there is positioned a cassette - shaped lower crucible part 14a containing a semiconductor wafer 15 to be coated . by means of a slider 70 which is actuated via the push rod 40 , one portion 72 of the growth solution contained in the chambers 13 of the upper part 12 , is respectively separated and used for applying an epitaxial growth layer onto the semiconductor wafer 15 lying therebeneath . after that , the portion of growth solution 72 is used up and , after the lower crucible parts have been shifted toward the left , is taken up in the recess 49 of the containerlike lower crucible part 14b and can thus , without having to interrupt the epitaxial process , be removed from the reaction space 4 . while the semiconductor wafer 15 is conveyed from the loading area to the crucible 12 it is , as is already mentioned hereinbefore , protected by the cover 46 ( cf . right - hand side of fig4 ). no sooner than after the lower part 14a with the wafer 15 has reached the upper part 12 , the cover 46 is stripped and drops into the recess 48 . fig5 in a schematic representation , shows the most important constituent parts of the system according to the invention which have already been described hereinbefore with reference to fig1 . identical parts are indicated by the same reference numerals and will not be explained again in greater detail . the system is provided with a modular type of controller which offers the advantage that the individual control modules can be more easily adapted to their respective tasks and can also be replaced in a more simple way . a process computer 50 coordinates the functions of the individual control modules and monitors the entire system . via control and signal lines 51 , computer 50 is connected to a valve spindle ( leadscrew ) 52 which controls the flow of the protective gas through the supply pipe 21 , and to a positioning controller 53 which controls the drive 41 designed as a stepper motor . by the action of this drive , and via the push rod 40 , the slider 70 is displaced which separates the portions of growth melt from the remaining contents of the chambers 13 . after several stacks of lower crucible parts 14a , 14b , 14c have passed through the reaction space , and the semiconductor wafers 15 as contained therein have been coated , the content of the chambers 13 is exhausted . at that point , the sealing flange 8 has to be opened and the upper crucible part has to be moved out and a new or newly filled upper crucible part 12 has to be moved into the reaction space . the necessary exact positional control is supervised with the aid of the photosensor assembly 16 to 19 ( fig1 ). an air - lock controller 54 controls the electro - pneumatic drive 26 &# 39 ; of the pendulum gate valve 25 &# 39 ; within the unloading area 3 . a second positioning controller 55 controls the stepper motor of the drive 29 &# 39 ; associated with the piston 28 &# 39 ; of the unloading area or station 3 . within the loading area 1 , the drive 35 is controlled by a positioning controller 56 , while the drive 26 is controlled by an airlock controller 57 , and the drive 29 is controlled by a further positioning controller 58 . further control and signal lines 61 connect the process computer 50 to the just - mentioned control modules 56 , 57 and 58 as well as to a valve spindle or lead screw 62 which controls the gas flow through the one or more vent pipes 20 . a sensor 64 of the photosensor assembly 17 , 18 , 19 , which is connected via a signal line 63 to the process computer 50 , reports the respective positions of the lower crucible parts 14 to the process computer 50 . a regulating circuit , only schematically denoted in the drawing , consists of three temperature - detector circuits 65 ( one for each temperature zone of the diffusion furnace 10 ), of three pid ( proportional , integral and derivative controller type ) regulators 66 which are provided with a common time - program controller , and of three heater current setting circuits 67 . it represents a very exactly controlling regulating circuit for regulating the temperature of the diffusion furnace 10 , in the three zones of which the temperature is each time controlled independently . within the reaction range of the diffusion furnace , the temperature must be kept constant with an admissible tolerance at the most of ± 0 . 5 °. the described controller permits a quasi - continuous process execution resulting in a high throughput rate and an exact reproducibility of the epitaxial layers . moreover , the system results in a high productivity rate owing to the fact that it is capable of treating the undivided semiconductor wafers in the state as supplied by the manufacture , in their original sizes with e . g ., two inch diameters . there is no longer any need for the wafers to be previously cut through . while we have described above the principles of our invention in connection with specific apparatus , it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of our invention as set forth in the objects thereof and in the accompanying claims .