Browsing by Author "Nilsson, K"

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Effects of lattice mismatch and bulk anisotropy on interband tunneling in broken-gap heterostructures
(2005-03-15)
Zakharova, A
;
Yen, ST
;
Nilsson, K
;
Chao, KA
;
電子工程學系及電子研究所
We have studied the effects of bulk anisotropy and the strain induced by lattice mismatch on the interband tunneling in broken-gap single-barrier InAs/AlSb/GaSb heterostructures and double-barrier InAs/AlSb/GaSb/InAs/AlSb/GaSb heterostructures. We have used the eight-band k.p model and the scattering matrix method, combined with the Burt envelope function theory, to calculate the interband transmission coefficients through the broken-gap heterostructures. We have found a noticeable anisotropy of the transmission coefficients when the magnitude of the in-plane wave vector increases to around 0.25 nm(-1). We have also found that the strain and the bulk anisotropy of quasiparticle dispersion produce additional peaks in the tunneling probability. For the double-barrier resonant-tunneling structures we discover a large spin splitting of the resonant-tunneling peaks caused by the lack of inversion symmetry. A strong influence of the strain induced by lattice mismatch appears in the current-voltage characteristics of the studied broken-gap heterostructures. In InAs/AlSb/GaSb structures the interband tunneling processes into the heavy-hole states contribute mainly to the peak current density if the sample is grown on InAs, but if the sample is grown on GaSb the interband tunneling processes into the light-hole states become the main contribution to the peak current density. As a result, the structure grown on GaSb has a much larger peak current density. This phenomenon was observed experimentally. (C) 2005 American Institute of Physics.
Six-band k center dot p calculation of spin-dependent interband tunneling in strained broken-gap heterostructures under a quantizing magnetic field
(2005-09-01)
Zakharova, A
;
Nilsson, K
;
Chao, KA
;
Yen, ST
;
電子工程學系及電子研究所
We investigate spin-dependent interband magnetotunneling processes in strained broken-gap resonant tunneling structures made from InAs, AlSb, and GaSb, which are promising materials for quantum devices. InAs/AlSb/GaSb/InAs/AlSb/GaSb double-barrier structures grown on both InAs and GaSb are considered. Transmission coefficients for interband tunneling processes from individual eigenstates in the InAs emitter as well as current-voltage characteristics were calculated using a six-band k center dot p model and the scattering matrix method. We predict that due to lattice-mismatch induced strain, the interband tunneling current density for the structure grown on InAs can be one or two orders of magnitude less than that for the structure grown on GaSb. Furthermore, as a consequence of interband magnetotunneling, structures grown on different substrates yield different spin polarization of the tunneling current. It is obtained that the current spin polarization can be greater than 90%. These resonant tunneling structures can be used as spin filters in the rapidly growing field of spintronics.
Spin polarization of an electron-hole gas in InAs/GaSb quantum wells under a dc current
(2006-03-01)
Zakharova, A
;
Lapushkin, I
;
Nilsson, K
;
Yen, ST
;
Chao, KA
We have investigated the spin polarization of electrons and holes in InAs/GaSb broken-gap quantum wells under nonequilibrium conditions when a dc electric field is applied parallel to interfaces. The existence of a nonzero asymmetric part of the quasiparticle distribution function caused by the dc current and the spin-split of the electron-hole hybridized states generates a finite spin polarization in both the InAs layer and the GaSb layer. With a very weak asymmetry of the distribution function, our self-consistent calculation yields about 1% spin polarization for electrons in the InAs layer and holes in the GaSb layer. The signs of these spin polarizations depend on the widths of the layers, changing the widths drives a phase transition in the electron-hole gas between the hybridized semiconducting phase and the normal semiconducting phase. In the hybridized semiconducting phase, the spin polarizations in both the InAs layer and the GaSb layer have the same sign. Crossing the phase boundary, the electron spin polarization and the total spin polarization in the InAs/GaSb quantum well can change their signs.