High Gm MBE-grown InP based HEMTs with a very low contact resistance triple capping layer

A highly-doped triple capping layer consisting of n/sup +/-In/sub 0.53/Ga/sub 0.47/As, n/sup +/-In/sub 0.52/Al/sub 0.48/As, and n/sup +/-In/sub 0.53/Ga/sub 0.47/As was investigated with the goal of reducing parasitic source resistance in InAlAs/InGaAs HEMTs. Analysis of the source resistance revealed that the contribution of the resistance element at n/sup +/-In/sub 0.53/Ga/sub 0.47/As/un-In/sub 0.52/Al/sub 0.48/As/un-In/sub 0.53/Ga/sub 0.47/As channel hetero-interfaces is as large as 70% of the total source resistance when non-alloyed ohmic electrodes are used. The highly-doped triple capping layer reduces the resistance element of vertical conduction between the capping layer and the 2DEG channel. Thus, source resistance was reduced to 0.57 /spl Omega/ mm and contact resistance to 3/spl times/10/sup -5/ /spl Omega/ cm/sup 2/ in the HEMTs with a highly-doped triple capping layer. This source resistance is 60% that of HEMTs with a conventional single capping layer, and the contact resistance is one order of magnitude smaller. The low source resistance results in peak extrinsic transconductance as high as 1 S/mm for a device with a 0.4-/spl mu/m-long gate, which is 42% higher than that of previously reported HEMTs with the same gate length.