Molecular-beam epitaxial growth and characterization of strained GaInAs/AlInAs and InAs/GaAs quantum well two-dimensional electron gas field-effect transistors

Abstract

Defect free strained layer epitaxy opens possibilities for further improvement on the quantum well two-dimensional electron gas (TEG) structures grown using the GaInAs/AlInAs on InP materials system. Increased freedom with composition allows for optimizing certain properties of the structure, such as, the conduction edge discontinuity which controls the maximum sheet concentration (ns); and the electron effective mass which influences the speed of the structure. These enhancements can be made, respectively, by increasing the Al concentration in the AlInAs and/or by decreasing the Ga concentration in the GaInAs. The maximum amount of strain which can be incorporated into the unrelaxed material sets an upper limit on the compositional tolerances. The tolerances will be shown to be large for the AlInAs and the active TEG GaInAs region. The compositions are obtained using the intensity oscillations observed in the reflective high-energy electron diffraction (RHEED) specular beam during growth of GaAs, AlAs, and subsequently GaInAs and AlInAs on GaAs. X-ray rocking curves and photoluminescence (PL) are used to verify the calibrations for growths on InP. The dependency of the mobility on strain is shown. The maximum 300 K mobility obtained was 12 360 cm2/V s, with ns of 1.25×1012/cm2. The well thickness was 84 nm. The AlInAs and GaInAs were estimated to be +0.04 and +0.17 In mole fraction from lattice match, respectively. A mobility of 11 550 cm2/V s was obtained using a 34-nm well. InAs/GaAs superlattice quantum well TEG structures were grown and characterized. TEG field-effect transistors performance comparable to standard structures were obtained in preliminary layers. Exceptionally high Si doping levels roughly 20 times the maximum obtained with Al0.25Ga0.75As have been achieved with lattice matched AlInAs.