Influence of strain compensation on structural and electrical properties of InAlAs/InGaAs HEMT structures grown on InP

In this work, in order to improve mechanical stability of pseudomorphic HEMTs (PMHEMTs), we propose a pseudomorphic InAlAs/InGaAs/InP structure where the channel and the spacer are strain compensated: as in the conventional structure, the InGaAs channel is compressively strained, but the InAlAs spacer is now tensilely strained. Such a configuration stabilises the whole structure because any strain relaxation in the channel (resp. spacer) should induce an increase of strain in the spacer (resp. channel). In other words, the mechanical state remains metastable but the structure must overcome a higher energy barrier to reach the actual stable state (fully relaxed). Strain compensation has been successfully used previously, in InAsP/lnGaP multi quantum well (MQW) structures for optoelectronic devices. These authors show that a higher number of strained quantum wells can be grown before the appearance of plastic relaxation. In HEMTs, where no MQW is used, an increase of the critical thickness of the channel is expected. In our study, we demonstrate that the use of strain compensation can stabilise PMHEMT structures without spoiling their electrical properties.