D.C. Tsui

Far infrared emission from plasma oscillations of Si inversion layers

Abstract We observed narrow-band far infrared emission from Si-MOSFETs with metallic gratings fabricated on the optically semitransparent gate. The gate voltage dependence of the emission frequency, analyzed by a magnetic field tuned detector, shows that it results from radiative decay of the two-dimensional metallic grating.

Observation of oscillatory linewidth in the cyclotron-resonance of GaAs-AlxGa1-xAs heterostructures

Abstract The linewidth of the far infrared cyclotron resonance in the 2-D electron gas in GaAs-AlxGa1−xAs heterojunctions show oscillations between 0.070 and 0.32 T as a function of the resonance magnetic field at 5 K. With increasing temperature the maximum linewidth decreases, whereas the minimum increases. This oscillatory behavior is shown to be correlated with the filling factor of the Landau levels.

High frequency conductivity in silicon inversion layers: Drude relaxation, 2D plasmons and minigaps in a surface superlattice

Abstract We review experiments that measure the inversion layer conductivity as a function of frequency in the far infrared. Drude relaxation is considered prototypic. 2D plasmons excited by a spatially modulated infrared field are discussed, and the direct observation of a minigap produced by a surface superlattice is presented.

High field magnetoconductivity of Si inversion layers

Abstract The transverse magnetoconductivity (σχχ) of electron inversion layers on (100) Si is measured in magnetic fields up to 220 kG at temperatures from 4.2 to 1.6 K. The dependence of σχχ on T, H, and the electric field along the inversion layer suggests that immobile electrons between two Landau subbands are to a large extent localized out of the top of the lower subband. Fine structure, which may be indicative of inhomogeneities of electronic origin, is observed in σχχ vs electron density.

Transport properties of GaAs‐AlxGa1−x As heterojunction field‐effect transistors

We report low field transport properties of n‐channel GaAs‐AlxGa1−x As heterojunction field‐effect transistors. Studies of the Shubnikov‐de Haas effect confirm that the devices are insulated‐gate field‐effect transistors, with AlxGa1−x As as the gate insulator. The channel mobility increases with density following μ2∼ nγ, with γ varying from 0.45 to 1.4. μ = 1.2×105 cm2/V sec at 78 K and 3.6×105 cm2/V sec at 4.2 K are observed at n∼4×1011/cm2.

Far infrared resonant magnetoabsorption in low density Si inversion layers

The density and temperature dependences of high frequency/resonant field (61.3 cm-1, 11T) resonant magnetoabsorption data in (100) Si inversion layers at low densities are strikingly different from those observed at lower frequencies/fields. The results, which include a dramatic resonant line narrowing at high fields, are discussed in light of single-electron localization and the possibility of a cooperative electronic transition assisted by the large magnetic field.

Valley degeneracy of electrons in accumulation and inversion layers on Si (111) surface

Abstract We report three experiments exploring the valley degeneracy of electrons in n-channel MOSFETs on the Si (111) surface. The results suggest that the reduction of the valley degeneracy from 6 to 2 can be explained by the existence of highly stressed domains at the Si-SiO2 interface. The stress, being much too large for those known from thermal mismatch between Si-SiO2, is attributed to mismatch between the Si-Si bonds in Si and the Si-O-Si bonds in SiO2.

Zero resistance state and origin of the quantized Hall effect in two-dimensional electron systems

We investigate 2D electron systems in high magnetic fields in the region where the Permi energy is pinned between Landau levels. In GaAs (AlGaAs heterojunctions we find vanishing resistanceρxx along the current path and determine an upper limit of ρxx⩽5×10−7Ω□at 1.23 K In MOSFETs we observe a correlation between sample mobility and stability of the quantized Hall resistance ρxy. For high mobility specimens the plateau width of ρxyincreases with decreasing mobility. If the Fermi energy is kept between the same Landau levels a linear dependence between magnetic field and plateau width is found. These results are discussed in terms of theoretical considerations based on the existence of magnetic field induced localized states.

Effect of a parallel magnetic field on surface quantization

Abstract Using electron tunneling techniques, we have observed the effect of a parallel magnetic field on surface quantization, as predicted by Stern and Howard. This observation allows for the first time a direct determination of ( 2 > − 2 ) 1 2 , which is a measure of the spread of the quantized state wave function.

Far infrared emission from 2D electrons at the GaAsAlxGa1-xAs interface

Abstract We report the first observation of far infrared emission resulting from radiative decay of intersubband excitations and cyclotron excitations of the two-dimensional electrons in GaAs Al x Ga 1-x As heterostructures.