Self-consistent analysis of double-delta-doped InAlAs/InGaAs/InP HEMTs

We have carried out a theoretical study of double-delta-doped InAlAs/InGaAs/InP high electron mobility transistor (HEMT) by means of the finite differential method. The electronic states in the quantum well of the HEMT are calculated self-consistently. Instead of boundary conditions, initial conditions are used to solve the Poisson equation. The concentration of two-dimensional electron gas (2DEG) and its distribution in the HEMT have been obtained. By changing the doping density of upper and lower impurity layers we find that the 2DEG concentration confined in the channel is greatly affected by these two doping layers. But the electrons depleted by the Schottky contact are hardly affected by the lower impurity layer. It is only related to the doping density of upper impurity layer. This means that we can deal with the doping concentrations of the two impurity layers and optimize them separately. Considering the sheet concentration and the mobility of the electrons in the channel, the optimized doping densities are found to be 5 x 10(12) and 3 x 10(12) cm(-2) for the upper and lower impurity layers, respectively, in the double-delta-doped InAlAs/InGaAs/InP HEMTs.

The keys to get high transconductance of AlGaAs/InGaAs/GaAs pseudomorphic HEMTs devices

There are two key points to get high transconductance of pseudomorphic HEMTS (pHEMTs) devices. From the point view of materials, the transfer efficiency of the electrons from the delta -doped AlGaAs layer to the InGaAs channel must be high. From the point view of device processing, the gate recess depth must be carefully controlled. In the present work, AlGaAs/InGaAs/GaAs pHEMTs structures were grown by molecular beam epitaxy. Layer structures of the pHEMTs were optimized to get high transfer efficiency of the electrons. Gate recess depth was also optimized. A 0.2 mum pHEMT was fabricated on the materials with optimized layer structure using the optimized gate recess depth. The maximum transconductance of 650 mS/mm and the cut-off frequency of 81 GHz were achieved. (C) 2001 published by Elsevier Science Ltd.