▁l iner , ▁a ▁sus ceptor , ▁gas ▁injection ▁units , ▁and ▁temperature ▁control ▁units . ▁Usually , ▁the ▁re actor ▁walls ▁are ▁made ▁from ▁st ain less ▁steel ▁or ▁quart z . ▁Cer am ic ▁or ▁special ▁glass es , ▁such ▁as ▁quart z , ▁are ▁often ▁used ▁as ▁the ▁l iner ▁in ▁the ▁re actor ▁chamber ▁between ▁the ▁re actor ▁wall ▁and ▁the ▁sus ceptor . ▁To ▁prevent ▁over he ating , ▁cool ing ▁water ▁must ▁be ▁flow ing ▁through ▁the ▁channels ▁within ▁the ▁re actor ▁walls . ▁ ▁A ▁substr ate ▁s its ▁on ▁a ▁sus ceptor ▁which ▁is ▁at ▁a ▁controlled ▁temperature . ▁The ▁sus ceptor ▁is ▁made ▁from ▁a ▁material ▁resist ant ▁to ▁the ▁metal organ ic ▁comp ounds ▁used ; ▁graph ite ▁is ▁sometimes ▁used . ▁For ▁growing ▁nit rides ▁and ▁ ▁related ▁materials , ▁a ▁special ▁co ating , ▁typically ▁of ▁sil icon ▁nit ride , ▁on ▁the ▁graph ite ▁sus ceptor ▁is ▁necessary ▁to ▁prevent ▁cor ros ion ▁by ▁am mon ia ▁( N H 3 ) ▁gas . ▁ ▁One ▁type ▁of ▁re actor ▁used ▁to ▁carry ▁out ▁MO C VD ▁is ▁a ▁cold - wall ▁re actor . ▁In ▁a ▁cold - wall ▁re actor , ▁the ▁substr ate ▁is ▁supported ▁by ▁a ▁ped est al , ▁which ▁also ▁acts ▁as ▁a ▁sus ceptor . ▁The ▁ped est al / s us ceptor ▁is ▁the ▁primary ▁origin ▁of ▁heat ▁energy ▁in ▁the ▁reaction ▁chamber . ▁Only ▁the ▁sus ceptor ▁is ▁he ated ,