Ferromagnetic Ga1-xMnxAs produced by ion implantation and pulsed-laser melting

Journal ArticleWe demonstrate the formation of ferromagnetic Ga1-xMnxAs films by Mn ion implantation into GaAs followed by pulsed-laser melting. Irradiation with a single excimer laser pulse results in the epitaxial regrowth of the implanted layer with Mn substitutional fraction up to 80% and effective Curie temperature up to 29 K for samples with a maximum Mn concentration of x ≈0.03. A remanent magnetization persisting above 85 K has been observed for samples with x≈0.10, in which 40% of the Mn resides on substitutional lattice sites. We find that the ferromagnetism in Ga1-xMnxAs is rather robust to the presence of structural defects

Carrier Concentration Dependencies of Magnetization & Transport in Ga1-xMnxAs1-yTey

We have investigated the transport and magnetization characteristics of Ga1-xMnxAs intentionally compensated with shallow Te donors. Using ion implantation followed by pulsed-laser melting, we vary the Te compensation and drive the system through a metal-insulator transition (MIT). This MIT is associated with enhanced low-temperature magnetization and an evolution from concave to convex temperature-dependent magnetization.Comment: 2 pages, 2 figures. To appear in the proceedings of the 27th International Conference on the Physics of Semiconductors (ICPS-27, Flagstaff, AZ, July 26-30, 2004

Electrical transport and ferromagnetism in Ga1-xMnxAs synthesized by ion implantation and pulsed-laser melting

We present a detailed investigation of the magnetic and magnetotransport properties of thin films of ferromagnetic Ga1-xMnxAs synthesized using ion implantation and pulsed-laser melting (II-PLM). The field and temperature-dependent magnetization, magnetic anisotropy, temperature-dependent resistivity, magnetoresistance, and Hall effect of II-PLM Ga1-xMnxAs films have all of the characteristic signatures of the strong p-d interaction of holes and Mn ions observed in the dilute hole-mediated ferromagnetic phase. The ferromagnetic and electrical transport properties of II-PLM films correspond to the peak substitutional Mn concentration meaning that the non-uniform Mn depth distribution is unimportant in determining the film properties. Good quantitative agreement is found with films grown by low temperature molecular beam epitaxy (LT-MBE) and having the similar substitutional Mn_Ga composition. Additionally, we demonstrate that II-PLM Ga1-xMnxAs films are free from interstitial Mn_I because of the high temperature processing. At high Mn implantation doses the kinetics of solute redistribution during solidification alone determine the maximum resulting Mn_Ga concentration. Uniaxial anisotropy between in-plane [-110]and [110] directions is present in II-PLM Ga1-xMnxAs giving evidence for this being an intrinsic property of the carrier-mediated ferromagnetic phase

Electronic structure of ferromagnetic semiconductor Ga1-xMnxAs probed by sub-gap magneto-optical spectroscopy

We employ Faraday and Kerr effect spectroscopy in the infrared range to investigate the electronic structure of Ga1-xMnxAs near the Fermi energy. The band structure of this archetypical dilute-moment ferromagnetic semiconductor has been a matter of controversy, fueled partly by previous measurements of the unpolarized infrared absorption and their phenomenological impurity-band interpretation. The infrared magneto-optical effects we study arise directly from the spin-splitting of the carrier bands and their chiral asymmetry due to spin-orbit coupling. Unlike the unpolarized absorption, they are intimately related to ferromagnetism and their interpretation is much more microscopically constrained in terms of the orbital character of the relevant band states. We show that the conventional theory of the disordered valence band with dominant As p-orbital character and coupled by kinetic-exchange to Mn local moments accounts semi-quantitatively for the overall characteristics of the measured infrared magneto-optical spectra.Comment: 4 pages 3 figure

Compensation-dependent in-plane magnetization reversal processes in Ga1-xMnxP1-ySy

We report the effect of dilute alloying of the anion sublattice with S on the in-plane uniaxial magnetic anisotropy and magnetization reversal process in Ga1-xMnxP as measured by both ferromagnetic resonance (FMR) and superconducting quantum interference device (SQUID) magnetometry. At T=5K, raising the S concentration increases the uniaxial magnetic anisotropy between in-plane directions while decreasing the magnitude of the (negative) cubic anisotropy field. Simulation of the SQUID magnetometry indicates that the energy required for the nucleation and growth of domain walls decreases with increasing y. These combined effects have a marked influence on the shape of the field-dependent magnetization curves; while the direction remains the easy axis in the plane of the film, the field dependence of the magnetization develops double hysteresis loops in the [011] direction as the S concentration increases similar to those observed for perpendicular magnetization reversal in lightly doped Ga1-xMnxAs. The incidence of double hysteresis loops is explained with a simple model whereby magnetization reversal occurs by a combination of coherent spin rotation and noncoherent spin switching, which is consistent with both FMR and magnetometry experiments. The evolution of magnetic properties with S concentration is attributed to compensation of Mn acceptors by S donors, which results in a lowering of the concentration of holes that mediate ferromagnetism.Comment: 37 pages, 9 figures, 3 table

Fabrication of GaNxAs1-x Quantum Structures by Focused Ion Beam Patterning

A novel approach to the fabrication of GaNxAs1-x quantum dots and wires via ion beam patterning is presented. Photomodulated reflectance spectra confirm that N can be released from the As sublattice of an MBE-grown GaNxAs1-x film by amorphization through ion implantation followed by regrowth upon rapid thermal annealing (RTA). Amorphization may be achieved with a focused ion beam (FIB), which is used to implant Ga ions in patterned lines such that annealing produces GaAs regions within a GaNxAs1-x film. The profiles of these amorphized lines are dependent upon the dose implanted, and the film reaches a damage threshold during RTA due to excess Ga. By altering the FIB implantation pattern, quantum dots or wires may be fabricated.Comment: To appear in the proceedings of the 27th International Conference on the Physics of Semiconductors (ICPS-27, Flagstaff, AZ, July 26-30, 2004