InAs-inserted-channel InAlAs/InGaAs inverted HEMTs with direct ohmic contacts

We have investigated the device characteristics of InAs-inserted-channel In0.52Al0.48As/In0.53Ga0.47As inverted high electron mobility transistors (HEMTs) with a novel ohmic structure. The ohmic contact between the ohmic electrodes and the two-dimensional electron gas (2DEG) formed in the InAs layer is obtained by direct contact with the ohmic electrodes-InAs, instead of an alloyed normal-metal and semiconductor as in a conventional inverted HEMT, The contact resistance of 0.11 Omega mm between the ohmic electrodes and the channel is smaller by a factor of 4, than that obtained using a conventional AuGeNi alloyed ohmic contact. For a 0.5 mu m-gate device, a maximum extrinsic transconductance of 1.2 S/mm was obtained at 4.2 K, even at a very low drain voltage of 0.2 V. These results show that this ohmic contact formation allows us to obtain the improved HEMT characteristics. (C) 1998 Elsevier Science B.V. All rights reserved.