Topography of (202¯1) AlGaN, GaN and InGaN layers grown by metal-organic vapor phase epitaxy

The growth of AlGaN, GaN and InGaN layers on (202¯1) GaN substrates was investigated by metal-organic vapor phase epitaxy. All layers exhibit undulations along [101¯4] with a period length between 20nm and 45nm. Under certain growth conditions, GaN exhibits bunching of the undulations leading to an increase of the undulation period and amplitude. This is also observed in the ternary alloys InGaN and AlGaN. Strong impact of the growth temperature and reactor pressure on the surface roughness and photoluminescence properties is found for GaN layers, with the smoothest layers obtained at low growth temperatures and low reactor pressures. Atomic scale interpretation suggests that the undulations originate from (101¯0) and (101¯1) microfacets. ► Semipolar (202¯1) AlGaN, GaN and InGaN layers were grown on (202¯1) GaN substrates by MOVPE. ► Undulations along [101¯4] were observed in all layers. ► A model to explain the undulations was developed and exhibits (101¯1) and (101¯0) microfacets to be the origin. ► TEM images confirm that 50nm long (101¯1) and (101¯0) microfacets to be very stable. ► Growth condition for smooth (202¯1) GaN layers with rms roughness