Optimization of AlN spacer layer in MOVPE grown AlGaN/AlN/InGaN/GaN high electron mobility heterostructure

Abstract

High electron mobility heterostructure AlGaN/AlN/InGaN/GaN, employing InGaN as the channel were grown using metal organic vapor phase epitaxy (MOVPE). In different samples, the AlN spacer layers were grown differently but at the temperature that were used for growth of InGaN channel i.e. at low temperature (LT) ~ 720°C. The grown samples were characterized using photoluminescence (PL), atomic force microscope (AFM) and Van der Pauw Hall measurement. As a result of optimization of AlN spacer, a significant improvement in rms surface roughness from Rq ~ 3.87 nm to Rq ~ 0.82 nm was obtained. The corresponding improvement in mobility of 2DEG was from µ ~ 39 cm2/V·s to µ ~ 201 cm2/V·s. The results show that optimum growth condition of LT AlN in such InGaN channel heterostructures should be decided on the basis of a reasonable trade-off between surface roughness and the transport properties of 2DEG.