Impact of buffer layer design on the performance of AlInAs-GaInAs HEMTs

Abstract

The authors report a study of the impact of buffer layer design on the characteristics of Al/sub 0.48/In/sub 0.52/As-Ga/sub 0.47/In/sub 0.53/As HEMTs (high-electron-mobility transistors). The aim of the study is to understand and correct the problem of high output conductance observed in devices with a high transconductance. Devices with 1.0- mu m gate lengths were fabricated using modulation-doped Al/sub 0.48/In/sub 0.52/As-Ga/sub 0.47/In/sub 0.53/As epitaxial layers which had sheet charge densities between 3*10/sup 12/ and 3.5*10/sup 12/ cm/sup -2/ and mobilities at 300 K between 9000 and 10000 cm V/sup -1/ S/sup -1/. The different buffer layer designs used were: (1) a standard undoped Al/sub 0.48/In/sub 0.52/As buffer 250-nm-thick; (2) an Al/sub 0.48/In/sub 0.52/As buffer with a 20-AA thick highly doped p-type region 50 AA below the channel; (3) a Ga/sub 0.47/In/sub 0.53/As buffer with a 20-AA-thick highly doped p-type region below the channel; and (4) a low-temperature AlInAs buffer layer. The device with the low-temperature AlInAs had the best output characteristics, signifying that it was the best mode of confining electrons in the channel.