Influence of strain on two-dimensional electron gas in pseudomorphic HEMT structures

Strain effect on two-dimensional electron gas (2DEG) was investigated systematically in pseudomorphic In_0.52Al_0.48As/In_xGa_1-xAs/InP high electron mobility transistor (HEMT) by self-consistence of Schrodinger and Poisson equations. The indium content in channel layer was varied from the lattice match to high strained composition (0.53>x>0.8). In order to fully incorporate the strain effect the 14-band k.p Hamiltonian was employed to calculate 2DEG states including the non-parabolic band near Γ point, interaction between bands and strain-induced band mixing. The eigen-function was expanded by Fourier series to avoid discontinuity of the wave function at heterojunction interfaces especially when the 2DEG states modify the Hartee potential. Fermi energy level is determined when the iterative calculations satisfy the charge neutrality condition. Average distance of 2DEG distribution and the Fermi energy as a function of carrier concentration were fitted to the empirical formulas, which were used to evaluate the small signal parameters circuits analysis. Transconductance as a function of the drain current was determined for the pseudomorphic HEMT at various indium contents in the channel layer and then associated the influence of the composition variation with the strain modification on the device performance.