Some characteristics of mobility enhancement in pseudomorphic In xGa1-xAs/In0.52Al0.48As/InP high electron mobility transistor structures

Pseudomorphic In_xGa_1-xAs/In_0.52Al _0.48As modulation-doped field-effect transistor (MODFET) structures were grown by molecular beam epitaxy (MBE) on InP(100) substrates over a range of indium compositions from x=0.53 to 0.75. Low temperature photoluminescence (PL) measurements show a prominent reduction in the InGaAs linewidth due to the quantum-size effect as the indium composition is increased from its lattice-match value of 0.53. The lowest linewidth of 6.8 meV was achieved at an indium composition of 0.65, above which an increase in the linewidth was observed due to the overwhelming effects of interfacial strain. The Hall mobilities at 300 K and 77 K increase in correspondence to the PL linewidth reduction as the indium composition is increased. Although initial signs of mobility saturation can be seen at an indium composition of 0.65, the peak mobility at 77 K of 8.9×10⁴ cm²/Vs was achieved at an indium composition of 0.70. There is experimental evidence to indicate that the mobility enhancement at increasing indium composition is due to an effect of a reduction in the alloy scattering and in the effective mass of the carriers. It was found that the insertion of an additional In_0.53Ga_0.47As interface-smoothing layer between the strained InGaAs channel and the In _0.52A1_0.48As spacer layer did not have a significant effect on the mobility enhancement in the heterostructures