Transport properties of $n$-type metalorganic chemical-vapor-deposited ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As} (0\mathrm{}\le x\le 0.6)$

Temperature-dependent measurements in the range $20\le T\le 600$ K have been made on undoped and Si-doped metalorganic chemical-vapor-deposition—grown ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As} (0\mathrm{}\le x\le 0.6)$ on GaAs. Data obtained from Hall and high-field measurements with the use of the probe technique have been analyzed. The transport parameters in the samples have been obtained from analysis of data and the relative importance of the various scattering mechanisms in different composition ranges have been elucidated. It is found that space-charge scattering plays an important role in limiting electron mobility at 300 K for $0<x\le 0.3$, and intervalley scattering plays the dominant role in the composition range $0.3\le x\le 0.5$. Donor levels, with their activation energy $E_D$ increasing with $x$ up to 0.133 eV at $x=0.35\mathrm{}$, are present in the undoped samples. The dominant donor level in the Sidoped samples also exhibits a similar trend, with $E_D=0.095\mathrm{}$ eV for $x=0.35\mathrm{}$. High values of drift velocity in samples with $x\ge 0.4$ at 300 K and similar features observed in some samples with $x<\mathrm{}0.4\mathrm{}$ at high temperatures have been attributed to electron transfer from the substrate to the epitaxial layers.