Growth-temperature optimization for low-carrier-density In0.75Ga0.25As-based high electron mobility transistors on InP

Two-dimensional electron gases (2DEGs) were formed in undoped In0.75Al0.25As∕In0.75Ga0.25As∕In0.75Al0.25As quantum wells. The optimal growth temperature for this structure is 410°C, with peak 2DEG electron mobility and density values of μ=221000cm2∕Vs and n=1.36×1011cm−2 at 1.5K. This electron mobility is equal to the highest previously published for these undoped structures but with a factor of 2 reduction in n. This has been achieved through the use of a significantly thinner InAlAs graded buffer, which supports the theory that this is the source of the 2DEG electrons. For n>1.6×1011cm−2, μ is shown to be 10% higher for transport parallel to the [011] crystal axis. This is a direct result of anisotropic surface morphology.