Charge carrier parameters in the conductive channels of HEMTs

Summary In summary, four different InGaAs/InAlAs/InP structures were fabricated, each having a single QW-channel to make a HEMT. Structures #1088, #1607 and #1093 have sharp interfaces, while the structure #1093 has a channel with changing composition. Structures with sharp interfaces have a different content of InAs in the QW-channel: 53% for #1088, 65% for #1607, and 75% for #1093. The maximum mobility of the 2DEG in the InGaAs QW-channel of HEMT was obtained in structure #1607, which has a special buffer on the InP-substrate. The lowest electron mobility was determined in structure #1093 having the maximum difference of InAs contents in the barrier and QW, which are 53% and 75%, respectively, though the effective mass of electrons in the QW is the smallest. This means, that the scattering on interface dislocations is significant. Structure #1098 owing a smooth barrier–QW transition, that allows to decrease the mismatch as well as to form a rectangular QW, is an interesting case. Calculations confirm, that the rectangular QW model used to determine the Landau level energy provides a better fitting to the experimental positions of the SdH peaks than the three-angular QW model. Thus, the InGaAs channel in structure #1098 forms a quasi-rectangular QW. The 2D electron density and electron mobility in this channel reach the highest values of 2.6