We report the observation of the spin-doublet splitting of cyclotron resonance (CR) in a twodimensional electron gas (2DEG). Two discernible CR peaks, originating from spin-conserved transitions between adjacent sets of spin-split Landau states, are observed at a magnetic field as low as 4.4 T.The observed doublet features in the vicinity of even and odd integer filling factors are attributed to the linear dependence of the g factor and effective mass on the electron energy, respectively. In addition, our data show that the g factor of a 2DEG has a smaller energy dependence than that of bulk electrons.Cyclotron resonance (CR) has been used to study the effective mass and the dynamic transport properties of a two-dimensional electron gas (2DEG) for two decades. ' However, up to now, the spin-doublet splitting (also called bg splitting) in a 2DEG has not been observed in GaAs/AI"Ga, As heterojunctions, where numbers of low-dimensional properties have been extensively studied. This is partially because the criterion of observing the spin-doublet CR is much more stringent than, e.g. , the spin-resolved Shubnikovde Haas (SdH) oscillations. In dc transport, when spin Zeeman splitting is larger than a few kT, and there are sufhcient localized states between two spin-split extend states, a minimum in SdH oscillations would occur when the Fermi level lies at the middle of N+ and N levels (N is the Landau level index, and + andrepresent spin up and down). In contrast, in order to obtain spin-resolved CR, it is not the total energy of the Zeeman splitting which matters. Instead, it is the energy difference of two adjacent Zeeman splittings which should be larger than the broadening of Landau levels.The Zeeman splitting is determined by g *p&B, where g*, pz, and 8 are the effective g factor, Bohr magneton, and magnetic field, respectively.The g * values at the conduction-band edge in III-V semiconductors are smaller than the free-electron value, +2, due to the spin-orbit interaction between the s-like (the lowest conduction band) and p-like (both the valence bands and the next higher conduction bands) states. When the electron energy is increased, the g factor approaches the free-electron value. As a result, if the band-edge g factor is negative (positive), the Zeeman splitting is smaller (larger) for Landau levels with a higher index. Within a small energy range, it has been found that the g factor can be approximated by g*=go+PE from experiments performed in three-dimensional (3D) systems. ' ' Here P and E are in units of eV and eV, respectively. It is this energy dependence of the g factor which makes the spin-doublet CR observable, regardless of how large the absolute go is.However, on the other hand, the more the go deviates from the free-electron value, the stronger the energy dependence will be (a larger P), which can be seen in Table I.To observe this Ag splitting, a high-mobility sample is required due to the small difference between adjacent TABLE I. The energy-dependent g factor g* =go+PE of the conduction electro...
The InAs/GaSb materials system, with different species for both cations and anions, allows one to envision the construction of heterojunctions with either InSb- or GaAs-like interfaces. As a result, this system provides a unique opportunity to explore the limits of interfacial control that can be achieved at the monolayer level by vapor phase growth techniques. Using migration-enhanced epitaxial techniques, we have prepared a series of InAs/GaSb superlattices with both types of interfaces. The large differences in bond lengths and vibrational properties of InSb and GaAs interfaces allow x-ray diffraction and Raman spectroscopy to be sensitive probes of interfacial structure. The x-ray and Raman measurements reveal that it is possible to grow superlattices with almost pure InSb-like or GaAs-like interfaces.
We have performed optical transmission measurements on radiatively heated GaAs substrates as a function of molecular beam epitaxial growth of InAs, GaSb, AlSb, and GaAs films. The energy gap of the GaAs substrate is observed to decrease strongly in energy when materials with band gaps smaller than GaAs are deposited. This decrease in energy gap is a consequence of a substantial increase in growth temperature induced by the deposition of the film. We have observed increases in temperature of over 150 °C from the temperature measured before film growth. Because the thermocouple is weakly coupled to the radiatively heated substrate, conventional temperature controllers are ineffective at measuring or accounting for this change in temperature.
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