GaAs Nanomembranes in the High Electron Mobility Transistor Technology

A 100 nm MOCVD-grown HEMT AlGaAs/InGaAs/GaAs heterostructure nanomembrane was released from the growth GaAs substrate by ELO using a 300 nm AlAs layer and transferred to sapphire. The heterostructure contained a strained 10 nm 2DEG In0.23Ga0.77As channel with a sheet electron concentration of 3.4 × 1012 cm−2 and Hall mobility of 4590 cm2V−1s−1, which was grown close to the center of the heterostructure to suppress a significant bowing of the nanomembrane both during and after separation from the growth substrate. The as-grown heterostructure and transferred nanomembranes were characterized by HRXRD, PL, SEM, and transport measurements using HEMTs. The InGaAs and AlAs layers were laterally strained: ~−1.5% and ~−0.15%. The HRXRD analysis showed the as-grown heterostructure had very good quality and smooth interfaces, and the nanomembrane had its crystalline structure and quality preserved. The PL measurement showed the nanomembrane peak was shifted by 19 meV towards higher energies with respect to that of the as-grown heterostructure. The HEMTs on the nanomembrane exhibited no degradation of the output characteristics, and the input two-terminal measurement confirmed a slightly decreased leakage current.

SCANNING ELECTRON MICROSCOPY OBSERVATION OF IN-DEVICE InAs/AlAs QUANTUM DOTS BY SELECTIVE ETCHING OF CAPPING LAYERS

Self-assembled InAs/AlAs quantum dots embedded in a resonant tunneling diode device structure are grown by molecular beam epitaxy. Through the selective etching in a C 6 H 8 O 7 · H 2 O-K 3 C 6 H 5 O 7 · H 2 O-H 2 O 2 buffer solution, 310 nm GaAs capping layers are removed and the InAs/AlAs quantum dots are observed by field-emission scanning electron microscopy. It is shown that as-fabricated quantum dots have a diameter of several tens of nanometers and a density of 1010 cm-2 order. The images taken by this means are comparable or slightly better than those of transmission electron microscopy. The undercut of the InAs/AlAs layer near the edges of mesas is detected and that verifies the reliability of the quantum dot images. The inhomogeneous oxidation of the upper AlAs barrier in H 2 O 2 is also observed. By comparing the morphologies of the mesa edge adjacent regions and the rest areas of the sample, it is concluded that the physicochemical reaction introduced in this letter is diffusion limited.

Wet oxidation kinetics of AlAs at elevated temperatures

Wet oxidation in the AlAs layer sandwiched between two GaAs plates was investigated for the temperature range of 400 to 480 °C. The oxidation rate increased with increasing thickness of the AlAs layer. Theoretical analysis based on the boundary layer diffusion was performed to account for the thickness effect. The theory is in excellent agreement with the experimental measurement.