Subband electron properties of highly doped InAlAs/InGaAs metamorphic high-electron-mobility transistors on GaAs substrates

A Shubnikov-de Haas (SdH) oscillation measurement was performed on highly doped InAlAs/ InGaAs metamorphic high-electron-mobility transistors on GaAs substrates at a temperature of 1.4 K. By analyzing the experimental data using fast Fourier transform, the electron densities and mobilities of more than one subband are obtained, and an obvious double-peak structure appears at high magnetic field in the Fourier spectrum. In comparing the results of SdH measurements, Hall measurements, and theoretical calculation, we found that this double-peak structure arises from spin splitting of the first-excited subband (i = 1). Very close mobilities of 5859 and 5827cm²/V s are deduced from this double-peak structure. The sum of the carrier concentration of all the subbands in the quantum well is only 3.95 × 10¹² cm^-2 due to incomplete transfer of the electrons from the Si δ-doped layer to the well.