Chhi-Chong Wu

Effects of energy band model on magnetoresistance in bismuth

Using the quantum statistical method, a study is made of the effect of a dc magnetic field on the longitudinal and transverse magnetoresistance in the very low-temperature limit, and numerical results are presented for the MNENP, NENP, ENP, and EP models. The results show that the larger the magnetic field, the greater is the amplitude of the oscillations. The amplitude of oscillations in the transverse magnetoresistance is much larger than that in the longitudinal magnetoresistance. There are spikelike discontinuities in the transverse magnetoresistance. The quantum oscillations of both magnetoresistances for the MNENP model show up much more clearly than those for the NENP, ENP, and EP models.

Magnetoacoustic effects of nonparabolic band structure in nondegenerate piezoelectric semiconductors

Effects of ultrasonic waves propagating at an angle ϑ relative to the direction of a dc magnetic field in nondegenerate piezoelectric semiconductors such as n‐type InSb have been studied by using a quantum treatment which is valid at high frequencies and in strong magnetic fields. The interaction of conduction electrons with waves is via deformation‐potential and piezoelectric couplings. Results show that variation of the direction of the magnetic field with respect to the direction of propagation of ultrasonic waves will affect the ultrasonic absorption coefficient and change in sound velocity. Therefore the absorption coefficient and change in sound velocity depend strongly on the dc magnetic field, the sound frequency, the temperature, and the direction of the propagation of ultrasonic waves relative to that of the field.

Hall effect in bismuth in quantizing magnetic fields

The Hall effect has been investigated in the very low-temperature limit in bismuth, when the lattice scattering is dominant in solids. The energy band structure of bismuth carriers is assumed to follow the modified nonellipsoidal, nonparabolic (MNENP) model. Results show that the Hall coefficient and Hall angle oscillate with the dc magnetic field, and the period and amplitude of the oscillations increase with the dc magnetic field. We also compare our numerical results with those found using other types of energy bands.

Free‐carrier absorption in n‐type gallium arsenide films for polar optical phonon scattering

The free‐carrier absorption in n‐type GaAs films has been investigated for quantum well structures fabricated from III–V semiconducting materials where polar optical phonon scattering is predominant. Attention is given mainly to the case where the electromagnetic radiation is polarized in the layer plane, and the processes involving both emission and absorption of polar optical phonons. The energy band of electrons in semiconductors is assumed to be nonparabolic. Results are shown that the free‐carrier absorption coefficient in n‐type GaAs films depends upon the photon frequency, the width of the quantum wells, and temperature. However, in the small quantum well region such as the width of quantum wells d<30 A, the free‐carrier absorption coefficient will be independent of temperature. Moreover, the free‐carrier absorption coefficient oscillates with the width of quantum wells for larger quantum wells.

Free-carrier absorption in n-type piezoelectric semiconductor films

Free-carrier absorption in n-type GaAs films has been investigated for the case where the free carriers are confined in a quasi-two-dimensional semiconducting structure with a non-parabolic energy band of electrons. It is assumed that the carriers in semiconductors are scattered by acoustic phonons via firstly the deformation-potential coupling and secondly the piezoelectric coupling. Results show that the free-carrier absorption coefficient depends upon the polarization of the electromagnetic radiation relative to the direction normal to the quasi-two-dimensional structure, the film thickness, the photon frequency and the temperature of the semiconductors. The free-carrier absorption coefficient could be complex owing to the interaction of photons, phonons and conduction electrons in piezoelectric semiconductors. Firstly, when the deformation-potential coupling is dominant, the absorption coefficient increases with decreasing photon frequency and increasing temperature for the radiation field polarized parallel and perpendicular to the layer plane. It is also shown that the absorption coefficient increases with decreasing film thickness. Secondly, when the piezoelectric scattering is dominant, the absorption coefficient increases with decreasing photon frequency and decreasing film thickness for the radiation field polarized parallel and perpendicular to the layer plane. However, the absorption coefficient increases with increasing temperature for the radiation field polarized parallel to the layer plane while, for the radiation field polarized perpendicular to the layer plane, the absorption coefficient increases with decreasing temperature.

Hall effect of nonparabolicity in a nondegenerate indium antimonide

The Hall effect and transverse magnetoresistance in an intrinsic nondegenerate InSb have been investigated when the acoustic phonon scattering is the dominant scattering process. The energy‐band structure is assumed to be nonparabolic. Results show that Hall angle, Hall coefficient, and transverse magnetoresistance depend strongly on the dc magnetic field because of the energy‐dependent relaxation time. We have also studied the temperature dependence of the Hall effect and transverse magnetoresistance in an intrinsic nondegenerate InSb. The results show that the Hall coefficient is greatly enhanced in low temperatures, whereas the Hall angle changes very slowly with temperature.

Effect of velocity operator on acoustic‐harmonic generation in n‐type piezoelectric semiconductors

Using the velocity operator derived from the Heisenberg equation of motion, we have investigated second‐harmonic generation of acoustic waves propagating in nondegenerate piezoelectric semiconductors with a uniform dc magnetic field B directed along the waves. Since we are interested in both high‐and low‐frequency regions, an electron relaxation time due to the scatterings in solids is taken into account. Results show that the second‐harmonic generation due to the piezoelectric polarization is insignificant in the very low‐frequency region. However, when the frequency is coming into the microwave region, the second‐harmonic generation increases quite rapidly with the sound frequency up to some maximum points at the range of frequency ω=1011–2×1011 rad/s, and then decreases. There are two maximum points in this range of frequency at very low temperatures. When the temperature increases, these two maximum points will be reduced to only a single maximum point. It is also found that the second‐harmonic genera...

Amplification of total‐reflection‐mode acoustic surface waves in n‐type GaAs films

The effect of nonparabolicty on the amplification of total‐reflection‐mode acoustic surface waves in n‐type GaAs films has been investigated quantum mechanically in the GHz frequency region. Numerical results are obtained for an n‐type GaAs epitaxial layer on a semi‐insulating GaAs substrate at 77 K. Results show that the amplification coefficient oscillates with the frequency in the high‐frequency region due to the inter‐sub‐band transitions.

Effect of nonparabolicity on transverse magnetoresistance in nondegenerate semiconductors

The effect of nonparabolicity on transverse magnetoresistance in nondegenerate semiconductors has been investigated taking into account the inelasticities in the electron‐phonon scattering due to the finite energy of he phonons involved. Our numerical results are shown to be in qualitative agreement with experimental results in the quantum limit. It is found that the nonparabolicity causes the nature of its temperature dependence to change as computed for the case of parabolicity.

Effect of phonon scattering on free-carrier absorption in n-type indium antimonide films

The free-carrier absorption in n-type InSb films has been investigated for carriers confined in quasi-two-dimensional (2D) semiconductors with the nonparabolic energy band of electrons. We discuss the effect of phonon scattering on the free-carrier absorption coefficient (~) for both deformation-potential coupling and piezoelectric coupling. ~ is found to depend on the photon polarization relative to the direction normal to the quasi-2D structure, the photon frequency, the film thickness, and the temperature. ~ could be complex due to the interaction between photons, phonons, and electrons. (i) When the acoustic phonon scattering is dominant, ~ increases with decreasing the film thickness for phonons polarized parallel or perpendicular to the layer plane. It is also shown that ~t increases with decreasing photon frequency and increasing temperature for photons polarized parallel to the layer plane, while for photons polarized perpendicular to the layer plane the ct temperature-dependence is more complicated. (ii) If the piezoelectric scattering is dominant, ~ is also decreasing with increasing the film thickness for photons polarized parallel or perpendicular to the layer plane. But ct decreases with increasing temperature for photons polarized perpendicular to the layer plane. Moreover, numerical results for the parallel polarization are much smaller than those for the perpendicular polarization.