Volume 32, Issue 10, 01 October 1961
Index of content:
- 3–5 COMPOUNDS: BAND STRUCTURE, ELECTRICAL AND OPTICAL PROPERTIES
32(1961); http://dx.doi.org/10.1063/1.1777026View Description Hide Description
Magnetoreflection experiments involving both intraband and interband transitions can provide valuable information about the electronic band structure of semiconductors. In the intraband experiments, performed near the plasma reflection edge, the application of a magnetic field splits the edge and results in the formation of two minima separated by the cyclotron frequency. It is thus possible to determine the cyclotron frequency directly, at room temperature, and for high carrier concentrations. When scattering losses are taken into account in the theory, it becomes possible to determine the carrier concentration,scattering time, and effective mass from the optical measurements alone. The theory of the effect is discussed for applied magnetic field transverse and parallel to the direction of propagation, and experimental results are presented for InSb,InAs, and HgSe. A consistent fit to Kane's theory for the variation of mass with concentration in InSb is obtained when previously published data have been corrected for reststrahl dispersion.
Interband magnetoreflection experiments can be useful in cases where high absorption coefficients or difficulty of preparing thin samples make transmission experiments unfavorable. This type of experiment yields information on energy band gaps, effective masses, and g factors. Experimental data for the direct transition in InSb are presented.
32(1961); http://dx.doi.org/10.1063/1.1777027View Description Hide Description
Polarized oscillatory magnetoabsorption spectra of exciton formation transitions in InSb have been measured under high resolution at liquid helium temperature. An unstrained high‐mobility sample 5 μ thick and magnetic fields up to 39.1 kgauss were used. Diffraction gratingdispersion for the region 3.7<λ<6.0 μ made possible a resolution of 1−7×10−4 ev and the determination of absorption maxima to ±5×10−5 ev. Sixteen minima were resolved with E⊥B for a field of only 5.0 kgauss. The initial interpretation of the detailed spectra obtained involved fitting theoreticalspectra calculated from the theories of Kane, Luttinger, and Elliott‐Loudon in order to account for band nonparabolicities, valence band degeneracy effects, and exciton binding energies, respectively. The results experimentally established the light‐hole nonparabolicity, the valence band degeneracy effects for low magnetic quantum numbers, and the existence of high‐field excitons in InSb.
32(1961); http://dx.doi.org/10.1063/1.1777028View Description Hide Description
A new method in making single crystals of GaP and the preparation of diodes is described. The p‐nluminescence and photoluminescence of undoped and Zn‐doped GaP are investigated and the light output of the p‐nluminescence as a function of temperature and excitation density is discussed. The spectral sensitivity of the p‐nphotovoltaic effect is recorded.
32(1961); http://dx.doi.org/10.1063/1.1777029View Description Hide Description
Experimental investigation of Faraday rotation in III–V compounds has exhibited a striking singularity at photon frequencies just below the energy gap. A quantum theoretical result associated with the direct transition has been developed to explain the phenomenon. The treatment has been extended to include forbidden transitions which are readily applicable to such materials as InAs,GaAs, and GaSb where interband transitions between the split‐off valence bands have been observed. The treatment for observing Faraday rotation by reflection has also been considered and experimental results in InSb at optical frequencies will be presented. The calculations have also been performed for degenerate semiconductors at low temperature.
Free Carrier Cyclotron Resonance, Faraday Rotation, and Voigt Double Refraction in Compound Semiconductors32(1961); http://dx.doi.org/10.1063/1.1777030View Description Hide Description
Measurements of cyclotron resonance absorption have been made in the far infrared spectral region from 25−150 μ on several III–V compounds at room and liquid‐nitrogen temperatures using steady magnetic fields as high as 75 kgauss. For n‐type InSb,InAs,InP, and GaAs, the data yield information concerning the conduction electron effective mass at the bottom of the band and its variation with magnetic field. Experiments have also been carried out on p‐type InSb and corresponding information has been obtained for light holes. The dependence of the effective masses on both temperature and magnetic field can be satisfactorily interpreted in terms of Kane's theory for the band structure of these materials.
Measurements of Faraday rotation and Voigt double refraction have been made in the spectral region between 15 and 25 μ on a number of compound semiconductors at liquid‐nitrogen temperatures. Either experiment gives the effective mass of the free carriers if their concentration is known. If both experiments can be performed, the results can be combined to give both the effective mass and carrier concentration directly without recourse to electrical measurements.
32(1961); http://dx.doi.org/10.1063/1.1777031View Description Hide Description
Values of absorption constant covering the range 1 cm−1 to 104 cm−1 have been derived from transmission measurements made on single‐crystal gallium arsenide. The absorption edge is very steep up to ∼4000 cm−1, where there is a knee beyond which the absorption increases relatively slowly with photon energy. The energy bands have been calculated using Kane's theory. From these a theoretical absorption curve has been obtained which shows very good agreement with the experimental data.
Using semi‐insulating material, it has been possible to measure the shift of the edge with applied electric field. The effect is small (∼200‐μ ev shift for 5000‐v/cm field) but is in good agreement with theory.
32(1961); http://dx.doi.org/10.1063/1.1777032View Description Hide Description
Conductivity in impurity bands is observed in gallium arsenide at low temperatures. The impurity banding phenomena observed in n‐ and p‐type crystals are markedly different due to the wide divergence in their effective masses. In the temperature interval where the crystal conductivity is determined by conduction in the impurity band, resistivity of n‐type material decreases with increasing magnetic field.
The temperature dependences of carrier mobility indicate that at low temperature the impurity ions play the dominant role of the scattering centers. In order to investigate scattering processes more thoroughly, studies were made of the thermomagnetic Nernst‐Ettingshausen effects which are very sensitive to the scattering mechanism. It was found that, in the case of nondegenerate specimens at low temperatures,scattering by impurity ions dominates, and at high temperatures by acoustical lattice vibrations;scattering by acoustical lattice vibrations becomes dominant even at low temperature in specimens of high degeneracy. Scattering was also investigated in indium arsenide and indium antimonide.