Electronic transport properties of very thin undoped GaInP/GaAs quantum wells have been measured by temperature dependent low field Hall effect and by Shubnikov–de Haas effect. Strong Shubnikov–de Haas oscillations were observed after increasing the electron concentration via the persistent photocurrent effect. Low temperature mobilities of up to 70 000 cm2/V s at carrier concentrations of 6.5×1011 cm−2 were observed in a 20 Å quantum well. The results are compared with the theory of interface roughness scattering which indicates extremely smooth interfaces; however, discrepancies between experiment and theory are observed.
Persistent photoconductivity has been observed at low temperatures in thin, unintentionally doped GaInP/GaAs/GaInP quantum wells. The two-dimensional electron gas was studied by low field Hall and Shubnikov–de Haas effects. After illumination with red light, the electron concentration increased from low 1011 cm−2 to more than 7×1011 cm−2 resulting in an enhancement of both the carrier mobility and the quantum lifetime. The persistent photocarriers cannot be produced by DX-like defects since the shallow dopant concentration in the GaInP layers is too low to produce the observed concentration. We suggest that the persistent carriers are produced by photoionization of deep intrinsic donors in the GaInP barrier layer. We also report observation of a parallel conduction path in GaInP induced by extended illumination.
Magnetic resonance spectra at 12–36 GHz are reported for Fe2+(3d6, S=2) in the 1D Ising ferromagnet [(CH3)3NH]FeCl3⋅2H2O, known as FeTAC, between 2.5 and 13 K. The main signal was identified as a spin-cluster resonance (SCR) because of its characteristic temperature dependence below 6 K and the linear dependence of the resonance field on the microwave frequency for H parallel to the easy axis at 4.2 K. The temperature dependence of the line intensity was fitted to the function exp[−(2J+hν)/kBT], with 2J/kB=(41±1) K, and the linear field dependence was explained by the value gz=8.26±0.05 in the S=1/2 representation and a demagnetization field of several hundred gauss, which depended on the sample shape. A frequency-dependent satellite structure observed on the low field side of the main line, which appeared as a broad line below 15 GHz, is tentatively associated with energy shifts of the lower-lying spin-cluster states produced by the magnetic dipole interaction and other terms in the Hamiltonian.
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