InAlAs/InGaAs/InP sub-micron HEMTs grown by CBE

Abstract

The InAlAs/InGaAs/InP high electron mobility transistor (HEMT) lattice matched to InP offers excellent high frequency, low noise operation for MMICs and low-noise amplifiers. The InP channel in the InP/InAlAs HEMT offers the advantages of improved high field velocity and higher breakdown voltages (the potential for higher power applications) over InGaAs channel HEMTs. InAlAs has been grown for the first time by CBE using TMAA producing InGaAs/InAlAs and InP/InAlAs HEMTs. Sub-micron InGaAs/InAlAs HEMTs with planar Si doping have been fabricated with ft values of 150 GHz and fmax values of 160 GHz. This device showed excellent pinch-off charateristics, with a maximum transconductance of 890 mS/mm. The planar doped InGaAs channel HEMT had a higher ft than a similar uniformly doped device. However, the non-optimized structure of the planar doped device resulted in a large output conductance of 120 mS/mm, limiting fmax for that device. A sub-micron InP channel device was grown with a quantum well channel and double-sided planar Si doping. A sheet charge density of 4.4 x 1012 cm-2 and associated room temperature mobility of 2800 cm2/V[middle dot]s were achieved; however, the saturation current was low. The most likely causes for this are diffusion of the planar doping beneath the channel and the poor quality of the InP on InAlAs interface at the bottom of the quantum well channel.