Metamorphic InGaAs/InAlAs quantum well structures grown on GaAs substrates for high electron mobility transistor applications

Abstract

Modulation-doped In0.5Ga0.5As/In0.5Al0.5As quantum well structures grown by molecular beam epitaxy on GaAs substrates using a relaxed AlGaAsSb buffer showed carrier mobilities of 8500 cm2/V s for a sheet concentration of 3.5×1012 cm−2 at room temperature. The crystallinity of the quaternary buffer layer was verified by x-ray diffractometry. Transistors with 0.25×100 μm2 gates demonstrated transconductance values as high as 800 mS/mm. S-parameter measurements revealed a cutoff frequency fT of 87 GHz and a maximum oscillation frequency fMAX of 140 GHz (both extrinsic values).

Strain relaxation and surface morphology of high indium content InAlAs metamorphic buffers with reverse step

“…The surface of sample performed on 5 mm  5 mm area is rough with typical patterns resulting from tensile strain during the growth of the inverse step [16]. It is a pattern characterized by a high density of lines almost exclusively aligned along the [1][2][3][4][5][6][7][8][9][10] direction, especially in sample B. And the surface morphology also confirms the two-dimensional growth mode of step layers grown at low temperature on step-graded buffer layer (except sample D).…”

“…The values of the residual strain in [1 1 0] and [1][2][3][4][5][6][7][8][9][10] are À0.44 and À0.59%, respectively. And hence the strain relaxation is anisotropy.…”

“…The residual strain e for samples B was measured both in [1 1 0] and [1][2][3][4][5][6][7][8][9][10] directions. The values of the residual strain in [1 1 0] and [1][2][3][4][5][6][7][8][9][10] are À0.44 and À0.59%, respectively.…”

“…It provides much better performance than the conventional InGaAs/GaAs heterostructures for device applications such as high electron mobility transistors (HEMTs) [1], heterojunction bipolar transistors (HBTs) [2], and resonant tunneling diodes (RTDs) [3]. Therefore the so-called metamorphic InGaAs or InAlAs materials grown on GaAs substrate have been investigated intensively recently.…”

Comparison of different pathways in metamorphic graded buffers on GaAs substrate: Indium incorporation with surface roughness

“…Compositionally graded metamorphic buffers have been widely utilized to accommodate the lattice mismatch and to produce a template for further growth of active layers having low defect densities [6]. Different buffer routes have been studied previously employing compositionally graded ternary alloys such as InGaAs [7], InAlAs [8] and quaternary alloys such as InAlGaAs [9], InGaAsP [10] and AlGaAsSb [11]. Among them, In(Ga,Al)As buffer have been rigorously studied as substitutes for InP substrates [12,13] because of their equivalent performance in devices and the freedom of choice for the indium content in the field of the band gap engineering [4,14].…”