Highly transparent aluminum nitride single crystalline layers and devices made therefrom

A method for growing highly transparent single crystalline AlN layers, comprising:

• supplying an aluminum chloride gas from a supply nozzle and a nitrogen precursor gas from a supply nozzle to a reactor having walls, wherein a portion of the walls of the reactor form a flow channel segment defined as the walls of the reactor from 200 mm upstream to 200 mm downstream of the location of a tip of the aluminum chloride gas supply nozzle;
• and
• reacting the aluminum chloride gas with the nitrogen precursor gas on a substrate in the reactor in order to grow an AlN single crystalline layer on the substrate;
• and
• supplying a carrier gas to the flow channel of the reactor and directing the carrier gas toward the substrate, the carrier gas being supplied around the supply nozzles for the aluminum chloride gas and the nitrogen precursor gas, wherein the carrier gas passes through a baffle plate comprising a plurality of holes;
• wherein, during the reacting step, the amount of aluminum contained in wall deposits formed in the flow channel segment is maintained at a level lower than or equal to 30% of the total amount of aluminum fed into the reactor, and wherein the wall temperature in the flow channel is maintained at less than or equal to 1200° C.