Field-effect transistors fabricated from diluted magnetic semiconductor colloidal nanowires

Field-effect transistors (FETs) fabricated from undoped and Co2+-doped CdSe colloidal nanowires show typical n-channel transistor behaviour with gate effect. Exposed to microscope light, a 10 times current enhancement is observed in the doped nanowire-based devices due to the significant modification of the electronic structure of CdSe nanowires induced by Co2+-doping, which is revealed by theoretical calculations from spin-polarized plane-wave density functional theory.

Electrical and mechanical properties of diluted magnetic semiconductor Zn1-xMnxS nanocrystalline films

Nanostructured Zn1-xMnxS films (0 less-than-or-equals, slant x less-than-or-equals, slant 0.25) were deposited on glass substrates by simple resistive thermal evaporation technique. All the films were deposited at 300 K in a vacuum of 2*10-6 m bar. All the films temperature dependence of resistivity revealed semiconducting behaviour of the samples. Hot probe test revealed that all the samples exhibited n-type conductivity. The nanohardness of the films ranges from 4.7 to 9.9 GPa, Young's modulus value ranging 69.7-94.2 GPa.

Magneto-transport and optical properties of diluted magnetic semiconductor Ga1-xMnxSb

We have studied magneto-transport and optical properties of Ga1-xMnxSb crystals (x = 0.01, 0.02, 0.03 and 0.04) grown by horizontal Bridgman method. Negative magnetoresistance and anomalous Hall effect have been observed below 10K. Temperature dependence of magnetization measurement shows a magnetic ordering below 10K which could arise from Ga1-xMnxSb alloy formation. Also, saturation in magnetization observed even at room temperature suggests the existence of ferromagnetic MnSb clusters. Reduction in band gap is observed with increasing Mn concentration in the crystals. Temperature dependence of band gap follows Bose-Einstein's model.

Temperature dependence of effective g factor in diluted magnetic semiconductor (Ga,Mn)As

Time resolved magneto-optic Kerr rotation measurements of optically induced spin quantum beats are performed on heavily doped bulk (Ga,Mn)As diluted magnetic semiconductors (DMS). An effective g-factor of about 0.2-0.3 over a wide range of temperature for both as-grown and annealed (Ga,Mn)As samples is obtained. A larger effective g-factor at lower temperature and an increase of the spin relaxation with increasing in-plane magnetic field are observed and attributed to the stronger p-d exchange interaction between holes and the localized magnetic ion spins, leading to a larger Zeeman splitting and heavy-hole-light-hole mixing. An abnormal dip structure of the g-factor in the vicinity of the Curie temperature suggests that the mean-field model is insufficient to describe the interactions and dynamics of spins in DMS because it neglects the short-range spin correlation effect. (c) 2008 American Institute of Physics.

Mn-AlInN: a new diluted magnetic semiconductor

Mn ions have been incorporated into MOCVD grown Al1-x In (x) N/GaN thin films by ion implantation to achieve the room temperature ferromagnetism in the samples. Magnetic characterizations revealed the presence of two ferromagnetic transitions one has Curie points at similar to 260 K and the other above room temperature. In-diffusion of indium caused by the Mn implantation leads to the partition of AlInN epilayer into two diluted magnetic semiconductor sub-layers depending on the Mn concentration. The Curie temperature of 260 K is assigned to the layer having lower concentration, whereas T (c) above room temperature is assumed to be associated to the layer having higher Mn concentration.

Growth Parameter Dependence of Structural Characterizations of Diluted Magnetic Semiconductor (Ga, Cr)As

We report the influence of growth parameters and post-growth annealing on the structural characterizations and magnetic properties of (Ga, Cr)As films. The crystalline quality and magnetic properties are sensitive to the growth conditions. The single-phase (Ga, Cr)As film with the Curie temperature of 10 K is synthesized at growth temperature T-s = 250 degrees C and with nominal Cr content x = 0.016. However, for the films with x > 0.02, the aggregation of Cr atoms is strongly enhanced as both T. and x increase, which not only brings strong compressive strain in the epilayer, but also roughens the surface. The origin of room-temperature ferromagnetism in (Ga, Cr)As films with nanoclusters is also discussed.

Electron and hole states in diluted magnetic semiconductor quantum dots

The electronic structure of a diluted magnetic semiconductor (DMS) quantum dot (QD) is studied within the framework of the effective-mass theory. We find that the energies of the electron with different spin orientation exhibit different behavior as a function of magnetic field at small magnetic fields. The energies of the hole decreases rapidly at low magnetic fields and saturate at higher magnetic field due to the sp-d exchange interaction between the carriers and the magnetic ions. The mixing effect of the hole states in the DMS QD can be tuned by changing the external magnetic field. An interesting crossing behavior of the hole ground state between the heavy-hole state and the light-hole state is found with variation of the QD radius. The strength of the interband optical transition for different circular polarization exhibts quite different behavior with increasing magnetic field and QD radius.

Spin-dependent transport through Cd1-xMnxTe diluted magnetic semiconductor quantum dots

We theoretically investigate the spin-dependent transport through Cd1-xMnxTe diluted magnetic semiconductor (DMS) quantum dots (QD's) under the influence of both the external electric field and magnetic field using the recursion method. Our results show that (1) it can get a 100% polarized electric current by using suitable structure parameters; (2) for a fixed Cd1-xMnxTe DMS QD, the wider the system is, the more quickly the transmission coefficient increases; (3) for a fixed system length, the transmission peaks of the spin-up electrons move to lower Fermi energy with increasing Cd1-xMnxTe DMS QD radius, while the transmission of the spin-down electrons is almost unchanged; (4) the spin-polarized effect is slightly increased for larger magnetic fields; (5) the external static electric field moves the transmission peaks to higher or lower Fermi energy depending on the direction of the applied field; and (6) the spin-polarized effect decreases as the band offset increases. Our calculated results may be useful for the application of Cd1-xMnxTe DMS QD's to the spin-dependent microelectronic and optoelectronic devices.

Spin-polarized ballistic transport in diluted magnetic semiconductor quantum wire systems

The energy dispersion of an electron in a double quantum wire with a diluted magnetic semiconductor barrier in between is calculated. An external magnetic field modifies significantly the energy dispersion of the electron which is different for the two spin states. The conductance exhibits many interesting peaks and dips which are directly related to the energy dispersions of the different electron spin states. These phenomena are attributed to the interwell coupling which can be tuned by the magnetic field due to the s-d exchange interaction.

Spin relaxation in diluted magnetic semiconductor quantum dots

Electron spin relaxation induced by phonon-mediated s-d exchange interaction in a II-VI diluted magnetic semiconductor quantum dot is investigated theoretically. The electron-acoustic phonon interaction due to piezoelectric coupling and deformation potential is included. The resulting spin lifetime is typically on the order of microseconds. The effectiveness of the phonon-mediated spin-flip mechanism increases with increasing Mn concentration, electron spin splitting, vertical confining strength, and lateral diameter, while it shows nonmonotonic dependence on the magnetic field and temperature. An interesting finding is that the spin relaxation in a small quantum dot is suppressed for strong magnetic field and low Mn concentration at low temperature.

Spin-polarized transport of two-dimensional electron gas embedded in a diluted magnetic semiconductor

The spin-polarized transport property of a diluted magnetic semiconductor two-dimensional electron gas is investigated theoretically at low temperature. A large current polarization can be found in this system even at small magnetic fields and oscillates with increasing magnetic field while the carrier polarization is vanishingly small. The magnitude as well as the sign of the current polarization can be tuned by varying magnetic field, the electron density and the Mn concentration. (c) 2005 American Institute of Physics.

Spin-polarized tunneling through a diluted magnetic semiconductor quantum dot

Spin-polarized tunneling through a diluted magnetic semiconductor quantum dot embedded in a tunneling barrier is investigated using the Bardeen transfer Hamiltonian. The tunneling current oscillates with an increasing magnetic field for a fixed bias. Many peaks are observed with an increasing external bias under a fixed magnetic field. Spin polarization of the tunneling current is tuned by changing the external bias under a weak magnetic field.

High and electric field tunable Curie temperature in diluted magnetic semiconductor nanowires and nanoslabs

The Curie temperature of diluted magnetic semiconductor (DMS) nanowires and nanoslabs is investigated using the mean-field model. The Curie temperature in DMS nanowires can be much larger than that in corresponding bulk material due to the density of states of one-dimensional quantum wires, and when only one conduction subband is filled, the Curie temperature is inversely proportional to the carrier density. The T-C in DMS nanoslabs is dependent on the carrier density through the number of the occupied subbands. A transverse electric field can change the DMS nanowires from the paramagnet to ferromagnet, or vice versae. (c) 2007 American Institute of Physics.

Electronic noise of diluted magnetic semiconductor (Ga,Mn)As around Curie point

National Natural Science Foundation of China 10674129

Spin-polarized transport in a lateral two-dimensional diluted magnetic semiconductor electron gas

The transport property of a lateral two-dimensional paramagnetic diluted magnetic semiconductor electron gas under a spatially periodic magnetic field is investigated theoretically. We find that the electron Fermi velocity along the modulation direction is highly spin dependent even if the spin polarization of the carrier population is negligibly small. It turns out that this spin-polarized Fermi velocity alone can lead to a strong spin polarization of the current, which is still robust against the energy broadening effect induced by the impurity scattering. (c) 2006 American Institute of Physics.