Agnieszka Wolos

Properties of arsenic antisite defects in Ga1−xMnxAs

We report the results of optical absorption measurements on Ga1−xMnxAs layers grown by low-temperature molecular beam epitaxy. In the paramagnetic layers grown at very low temperatures (below 250 °C) the experiments reveal an absorption band at 1.2 eV arising from the presence of neutral arsenic antisites, AsGa. From the magnitude of the absorption we determine the concentration of AsGa to be between 4×1019 and 8×1019 cm−3 in these paramagnetic samples. These values are typical for GaAs specimens grown below 250 °C. Extrapolating the AsGa concentration from low-temperature-grown GaAs to Ga1−xMnxAs, we determine the concentration of this defect in ferromagnetic Ga1−xMnxAs layers grown at temperatures above 250 °C as 1×1019 down to 1×1018 cm−3. We conclude that the compensating role of arsenic antisites in Ga1−xMnxAs becomes gradually less important with increasing growth temperature.

Properties of metal-insulator transition and electron spin relaxation in GaN:Si

We investigate properties of doping-induced metal-insulator transition in GaN:Si by means of electron spin resonance and Hall effect. While increasing the doping concentration, Si-related bands are formed below the bottom of the GaN conduction band. The D0 band of single-occupied Si donor sites is centered 27 meV below the bottom of the GaN conduction band, the D- band of double-occupied Si states at 2.7 meV below the bottom of the GaN conduction band. Strong damping of the magnetic moment occurs due to filling of the D- states at Si concentrations approaching the metal-insulator transition. Simultaneously, shortening of electron spin relaxation time due to limited electron lifetime in the single-occupied D0 band is observed. The metal-insulator transition occurs at the critical concentration of uncompensated donors equal to about 1.6 * 10^18 cm^-3. Electronic states in metallic samples beyond the metal-insulator transition demonstrate non-magnetic character of double-occupied states.

Electron spin resonance of erbium in gallium nitride

Abstract We performed electron spin resonance (ESR) measurements on Er-doped single GaN crystals synthesized from the solution of nitrogen in liquid gallium under high pressure of N2. The axial Er3+ spectrum was observed with g∥=2.861±0.003, g⊥=7.645±0.003, A∥=(110±5)×10−4cm−1, and A ⊥ =(290±5)×10 −4 cm −1 . The magnitude of an average g-factor gav=1/3(g∥+2g⊥) was nearly equal to the g(Γ7) ground state, as expected for Er3+ ions substituting for Ga in the GaN structure.

S-d exchange interaction in GaN:Mn studied by electron paramagnetic resonance

We present the electron paramagnetic resonance investigations of GaN:Mn bulk crystals. The performed measurements revealed the Korringa scattering as the dominant spin relaxation mechanism in the investigated highly n-type GaN:Mn samples. The temperature dependence of the spin relaxation time determines the effective s–d exchange constant for such crystals {N0α}=14 meV. Weak exchange interaction between Mn2+ and GaN band electrons excludes carrier mediation as an origin of high-temperature ferromagnetism in n-type GaMnN.

Chapter 8 Magnetic Impurities in Wide Band‐gap III–V Semiconductors

Publisher Summary This chapter discusses the magnetic impurities in wide band-gap III–V semiconductors. The chapter describes the general properties of diluted magnetic semiconductors (DMSs) that result because of the presence of magnetic ions along with the nature of Mn impurity in III–V semiconductors. The focus is on GaN:Mn as it has been, in recent years, the most extensively studied DMS material for possible spintronic application. The electron configuration of a free Mn atom is [Ar]3d 5 4s 2 . In III–V semiconductors, Mn substitutes the cation site, thus giving three electrons to crystal bonds. Depending on the compensation ratio, Mn can exist in different charge states and electron configurations. Most common are the ionized Mn 2+ (d 5 ) and neutral Mn 3+ acceptors, often denoted as A¯and A 0 , respectively. The latter center corresponds to Mn 2+ (d 5 )+ hole configuration, and the localization of the hole varies depending on a compound. The magnetic interactions in III–V DMSs with Mn are discussed.

Diluted Magnetic III‐V Semiconductors With Mn For Possible Spintronic Applications

In this paper we present results of comprehensive studies performed on GaN, GaP, InP and GaAs semiconductors containing Mn ions. Electron Paramagnetic Resonance, optical absorption, magnetization and hopping transport measurements performed on the samples with different Mn concentration allowed to determine the nature of neutral Mn acceptor center in the studied crystals. It occurred that for neutral Mn acceptor, configuration of Mn2+(d5) plus a bound hole was realized. The localization radius of a bound hole changed from 1.1nm for GaAs though 0.7nm for InP to 0.4nm for GaP. The highest localization was reached for Mn doped GaN, in which configuration Mn3+(d4) was observed.

Neutral Mn Acceptor in GaN Studied in High Magnetic Fields

In this paper we present optical studies of neutral Mn intracenter absorption band in bulk GaN performed in magnetic field up to 22 T in both Faraday and Voigt configurations. The experiment revealed very weak influence of magnetic field on the absorption spectrum. In particular no splitting of the zero‐phonon line was observed. The only characteristic feature in magnetic field was step‐like behavior of the spectral position of the zero‐phonon line, recorded in Faraday configuration. The step appeared at magnetic field of about 7 T with shift in energy of 1.3 meV. The results were interpreted basing on a crystal‐field model for Mn3+(d4) ion in trigonal crystal field, with Jahn‐Teller distortion and spin‐orbit coupling. The model explains reasonably experimental results supporting localized character of neutral Mn acceptor in GaN.