Nonmagnetic GaAs Research Articles

Theoretical study of the magnetoresistance under electric field in III–V diluted magnetic semiconductor

In this paper we study the magnetoresistance and the coupling energy in heterostructures formed by two magnetic layers Ga 1− x Mn x As separated by a nonmagnetic spacer GaAs under an electric field and develop a mean-field theory of carrier in diluted magnetic semiconductor. Our main result indicates that magnetoresistance can be dramatically suppressed by an external electric field.

Luminescence spectra in metallic and ferromagnetic GaMnAs/GaAs multilayers: a self-consistent super-cell Kane k.p calculation

We present a self-consistent Kane k.p calculation for obtaining the luminescence spectra of GaMnAs/GaAs multilayers. Our model consists of substitutional Mn ions uniformly distributed in GaMnAs layers of width d1 at a concentration of 5%. The high Mn concentration allows to approximating the density of the magnetic moments by a continuous distribution when treating the magnetic interaction between holes and the localized moment on the Mn++ sites. These DMS layers are assumed to be ferromagnetic, at T = 0 K, metallic, and with a hole concentration equivalent, in bulk, to 1 × 1020 cm–3. The DMS layers are separated by non-magnetic GaAs layers. The magnetization is kept perpendicular-to-the-plane (parallel to the growth direction) by the application of a weak magnetic field, which does not affect the electronic structure directly. The luminescence spectrum is obtained for several numbers of DMS layers in the structure. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Theoretical study of diluted magnetic semiconductor trilayers

We focus on transport of electron spins for which spin currents can be controlled and manipulated via the electron energy and momentum. In our work we analyze the properties of the hole gas formed in Ga ( 1 - x ) Mn x As/GaAs/ Ga ( 1 - x ) Mn x As heterostructure: the electronic structures, polarization and coupling energy E C are obtained using an efficient self-consistent procedure to solve simultaneously the Schrodinger and Poisson equations tacking account the interaction with Mn magnetic moments and for different parameters of the magnetic Ga ( 1 - x ) Mn x As layer and the nonmagnetic GaAs spacer.

Ferromagnetism and interlayer exchange coupling in short-period (Ga,Mn)As/GaAs superlattices

Magnetic properties of (Ga,Mn)As/GaAs superlattices are investigated. The structures contain magnetic (Ga,Mn)As layers, separated by thin layers of nonmagnetic GaAs spacer. The short-period Ga0.93Mn0.07As/GaAs superlattices exhibit a paramagnetic-to-ferromagnetic phase transition close to 60 K, for thicknesses of (Ga,Mn)As down to 23 Å. For Ga0.96Mn0.04As/GaAs superlattices of similar dimensions, the Curie temperature associated with the ferromagnetic transition is found to oscillate with the thickness of nonmagnetic spacer. The observed oscillations are related to an interlayer exchange interaction mediated by the polarized holes of the (Ga,Mn)As layers.

Ferromagnetic GaMnAs/GaAs superlattices—MBE growth and magnetic properties

We have studied the magnetic properties of (GaMnAs) m (GaAs) n superlattices with magnetic GaMnAs layers of thickness between eight and 16 molecular layers (ML) (23–45 Å), and with non-magnetic GaAs spacers from 4 to 10 ML (11–28 Å). While previous reports state that GaMnAs layers thinner than 50 Å are paramagnetic in the whole Mn composition range achievable using MBE growth (up to 8% Mn), we have found that short period superlattices exhibit a paramagnetic-to-ferromagnetic phase transition with a transition temperature which depends on both the thickness of the magnetic GaMnAs layer and the non-magnetic GaAs spacer. The neutron scattering experiments have shown that the magnetic layers in superlattices are ferromagnetically coupled for both thin (below 50 Å) and thick (above 50 Å) GaMnAs layers.

Ferromagnetic Resonant Tunneling Diode

We have studied theoretically the magnetotransport in a ferromagnetic resonant tunneling diode (FRTD), where alternating magnetic Ga1-xMnxAs and non-magnetic GaAs and AlAs layers give rise to strongly spin-polarization dependent electronic transport. We have studied a FRDT structure having a non-magnetic quantum well between magnetic emitter and collector layers. The infinite order correction to the energy of the band edge due to the exchange interaction between the charge carrier spin and the magnetic moments of the Mn ions is calculated by using Zubarev's double time Green's functions. Then the current-voltage characteristics of the FRTD is calculated as a function of temperature and magnetic field by using a modified Tsu-Esaki formula. In a FRTD the transport depends strongly on the spin- polarization of the magnetic lattice, and in a certain bias voltage range near the negative resistance region the model predicts colossal magnetoresistance at temperatures close to the Curie temperature.

Magnetotransport in ferromagnetic resonant tunnelling diodes

We have studied theoretically the magnetotransport in ferromagnetic resonant tunnelling diodes (FRTDs), where alternating magnetic Ga1-xMnxAs and non-magnetic GaAs and AlAs layers give rise to strongly spin-polarization-dependent electronic transport. We have studied two cases: (1) an FRTD structure with a non-magnetic quantum well between magnetic emitter and collector layers, and equation (2) an FRTD structure with a ferromagnetic quantum well between non-magnetic emitter and collector layers. First a correction to the energy of the band edge due to the exchange interaction between the charge carrier spin and the magnetic moments of the Mn ions is estimated. Then the current-voltage characteristics of the FRTD are calculated as a function of temperature and magnetic field using a modified Tsu-Esaki formula. In the FRTD the transport depends strongly on the spin polarization of the magnetic lattice, and in a certain bias voltage range near the negative resistance region the model predicts colossal magnetoresistance at temperatures close to the Curie temperature.

Spin Manipulation Using Magnetic II–VI Semiconductors

Recently, efficient spin injection, being the first step towards semiconductor spin electronics, by using BeMnZnSe as a spin filter was accomplished. Such a spin filter made it possible to align the spin orientation of conduction electrons and subsequently inject them into GaAs. However, controlling spin orientation of conduction electrons by an external voltage would be very desirable for semiconductor-based magnetoelectronics. This can be accomplished by using spin switch structures, based on resonant tunneling through magnetic quantum wells, with two separate spin-up and spin-down resonances. Here we summarize both our recent results on spin injection as well as on spin aligner and magnetic resonant tunneling structures. For accomplishing the latter, we have developed magnetic resonant tunneling diodes based on BeTe–ZnMnSe–BeTe structures. Resonant tunneling diode is meant to serve as a spin switch because of the existence of two separate spin-up and spin-down resonances. The tunneling carriers have subsequently been injected into a nonmagnetic GaAs p–i–n light emitting diode. Circular polarization of the emitted light is an indicator of the spin polarization of injected electrons. At constant magnetic field and current, degree of spin polarization could be changed from 81% to 38% by only varying the voltage across the magnetic resonant tunneling device.

III-V Based Ferromagnetic Semiconductors

Current status of III-V based ferromagnetic semiconductors, especially (Ga, Mn)As, a GaAs based diluted magnetic semiconductor, is reviewed. Low solubility of magnetic elements was overcome by low temperature nonequilibrium molecular beam epitaxial growth to realize successfully (Ga, Mn)As as well as (In, Mn)As. Magnetization measurements showed that GaAs based (Ga, Mn) As is ferromagnetic with Curie temperature TC as high as 110 K. Magnetotransport measurements of (Ga, Mn) As epitaxial films revealed that the p-d exchange N0β is 3 eV. This strong interaction was shown to be large enough to explain the high TC by the RKKY interaction. Multilayer heterosturctures including superlattices and resonant tunneling diodes (RTD's) were also successfully fabricated. The magnetic coupling between two ferromagnetic (Ga, Mn)As films separated by a nonmagnetic GaAs (or AlGaAs) layer was found to be a function of thickness and composition of the intermediary layer, indicating the critical role of the holes on the magnetic coupling. This observation of magnetic coupling in all semiconductor ferromagnetic/nonmagnetic layered structures, together with the possibility of spin dependent tunneling in RTD's, showed the potential of the present material system for exploring new physics and for developing new functionality toward future electronics.