R. J. Wagner

Electron cyclotron resonance in cubic SiC

Abstract Electron cyclotron resonance has been studied in films of β-SiC grown on Si(100) surfaces previously reacted with carbon. The effective mass values m ∗ t = (0.247 ± 0.011)m 0 , m ∗ l = (0.677 ± 0.015)m 0 were determined. Resonance line width in the range 40–100 K followed a T - 3 2 dependence, consistent with scattering by intraband acoustic phonons, and yielded the deformation potential Ξ = 22 eV. The extrapolated mobility at 300 K was 670 cm2/V-s.

Disorder-induced far infrared absorption in amorphous materials

Abstract In a variety of amorphous materials, the far infrared and microwave absorption (3–3000 GHz or 0.1–100 cm−1) is orders of magnitude greater than that observed in corresponding crystalline materials. This absorption is temperature independent and rises with frequency as νβ (β ≲ 2). The magnitude of the absorption correlates with the density of states inferred from the T3 term in specific heat, and is interpreted as due to a disorder-induced coupling of the far infrared radiation to a density of low frequency Debye modes in the amorphous solids.

Control of interface stoichiometry in InAs/GaSb superlattices grown by molecular beam epitaxy

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.

Identification of AsGa antisite defects in liquid encapsulated Czochralski GaAs

We have identified the electron paramagnetic resonance (EPR) spectrum of the As on a Ga site (AsGa) defect in bulk undoped liquid encapsulated Czochralski grown GaAs. The intensity of the EPR signal can be correlated with the concentration of compensating carbon acceptors in the GaAs crystals. These results indicate that AsGa are responsible for the compensation of the undoped semi‐insulating material, and thus can be identified with the deep donor EL2 in such material.

Large temperature changes induced by molecular beam epitaxial growth on radiatively heated substrates

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.

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.

Infrared pulsed gas laser studies of combined resonance and cyclotron-phonon resonance in Hg1−xCdxTe

Abstract Combined resonance and cyclotron-phonon resonance have been observed for the first time in Hg1−xCdxTe (x = 0.203) using a far infrared pulsed gas laser. The results are in good agreement with the transition energies calculated from the theory of Bowers and Yafet with the following band parameters: EG = 0.064 ± 0.003 eV, Ep = 18.5 ± 1 eV, and the zero field g-value is −172.

Determination of band gap and effective masses in InAs/Ga1−xInxSb superlattices

InAs/Ga1−xInxSb superlattices have been investigated by magneto‐optical and magnetotransport techniques. Band gaps, determined from interband magneto‐optical measurements and from the temperature dependence of the intrinsic carrier concentration, are in the long wavelength infrared region (8.3–12.4 μm) and are in good agreement with gaps calculated from a two‐band model. Both electron and hole effective masses were measured by cyclotron resonance and the electron effective mass is found to be a factor of 4–5 larger than in HgCdTe (the industry standard IR material). This is necessary for reduced dark currents and good optical absorption coefficients in this material.

Pulsed far-infrared spectroscopy of GaAs:Cr at high magnetic fields in the field-modulation mode

Abstract A magnetic field-modulation technique has been developed for sensitive far infrared electron paramagnetic resonance (EPR) spectroscopy on Cr2+ centers in GaAs. A hundred-fold improvement in signal-to-noise ratio relative to non-modulation techniques was obtained. The results of this experiment have been analyzed and agree well with a spin Hamiltonian and parameters obtained from microwave EPR studies of Cr2+ in GaAs. No evidence could be found to support the view that this ground state is the terminal level of the finely structured 0.839 eV luminescence line reported in earlier high resolution absorption and luminescence studies.

Lineshape distortions in fir cyclotron resonance of MOS structures

Abstract Cyclotron resonance lineshape distortions which include appreciable shifts in the peak position have been observed in far infrared laser transmission measurements of MOS structures. Experimental studies and a complete theoretical treatment show that these distortions arise from multiple interference effects in plane parallel sample substrates and from partial circular polarization of long wavelength coherent radiation owing to the light pipe optics.