Mn Acceptor In GaAs Research Articles

Exchange interaction for Mn acceptors in GaAs: Revealing its strong deformation dependence

In this paper we calculate exchange interaction constant between manganese ion inner electronic $d$-shell and GaAs valence band bounded hole using their microscopic multiparticle wave functions. We reveal its parametric dependence on crystal lattice deformations and find out that it could be about and even more than dozens percent when the strain tensor reaches values of $10^{-3} \div 10^{-2}$. This fact is in accordance with the previous hypothesis of deformation dependence of Mn acceptors in GaAs fine energy structure obtained from Raman spectroscopy, and we show that this dependence has the same magnitude. Also, we resolve here the problem of a substantial high temperature mismatch between well-developed theory and experimental data for the static magnetic susceptibility of Mn ions in GaAs. We show by numerical estimates and calculations that quite a strong parametric dependence of the exchange coupling value on GaAs lattice expansion determines the high temperature (above $50~$K) magnetic susceptibility reduction as well.

Energy Structure of an Individual Mn Acceptor in GaAs : Mn

The energy structure of the Mn acceptor, which is a complex of Mn2+ ion plus valence band hole, is investigated in the external magnetic field and under presence of an uniaxial stress has been studied. The spin-flip Raman spectra are studied under resonant excitation of exciton bound to the Mn acceptor. The gfactors of the ground F = 1 and the first excited F = 2 states are determined and selection rules for the optical transitions between the acceptor states are described. The value of the random field (stress or electric field) acting on manganese acceptor and the deformation potential for the exchange interaction constant of the Mn2+ + hole complex are obtained. A theoretical model is developed that takes into account the influence of random internal and uniaxial external stress and magnetic field. The proposed model describes well the lines of spin-flip Raman scattering of Mn acceptor.

Fine structure of the Mn acceptor in GaAs

We reveal the electronic level structure of the Mn acceptor, which consists of a valence-band hole bound to an ${\mathrm{Mn}}^{2+}$ ion, in presence of applied uniaxial stress and an external magnetic field in bulk GaAs. Resonant spin-flip Raman scattering is used to measure the $g$ factor of the ${\mathrm{A}}_{\text{Mn}}^{0}$ center in the ground and excited states with the total angular momenta $F=1$ and $F=2$ and characterize the optical selection rules of the spin-flip transitions between these Mn-acceptor states. We determine the random stress fields near the Mn acceptor, the constant of the antiferromagnetic exchange interaction between the valence-band holes and the electrons of the inner ${\mathrm{Mn}}^{2+}$ shell as well as the deformation potential for the exchange energy. The $p\text{\ensuremath{-}}d$ exchange energy, in particular, decreases significantly with increasing compressive stress. By combining the experimental Raman study with the developed theoretical model on the scattering efficiency, in which also the random local and external uniaxial stresses and magnetic field are considered, the fine structure of the Mn acceptor is determined in full detail.

Influence of the local environment on Mn acceptors in GaAs

As transistors continue to shrink toward nanoscale dimensions, their characteristics are increasingly dependent on the statistical variations of impurities in the semiconductor material. The scanning tunneling microscope (STM) can be used to not only study prototype devices with atomically precise placement of impurity atoms, but can also probe how the properties of these impurities depend on the local environment. Tunneling spectroscopy of Mn acceptors in GaAs indicates that surface-layer Mn act as a deep acceptor, with a hole binding energy that can be tuned by positioning charged defects nearby. Band bending induced by the tip or by these defects can also tune the ionization state of the acceptor complex, evident as a ring-like contrast in STM images. The interplay of these effects is explored over a wide range of defect distances, and understood using iterative simulations of tip-induced band bending.

Magnetic anisotropy of single Mn acceptors in GaAs in an external magnetic field

We investigate the effect of an external magnetic field on the physical properties of the acceptor hole states associated with single Mn acceptors placed near the (110) surface of GaAs. Cross-sectional scanning tunneling microscopy images of the acceptor local density of states (LDOS) show that the strongly anisotropic hole wave function is not significantly affected by a magnetic field up to 6 T. These experimental results are supported by theoretical calculations based on a tight-binding model of Mn acceptors in GaAs. For Mn acceptors on the (110) surface and the subsurfaces immediately underneath, we find that an applied magnetic field modifies significantly the magnetic anisotropy landscape. However, the acceptor hole wave function is strongly localized around the Mn and the LDOS is quite independent of the direction of the Mn magnetic moment. On the other hand, for Mn acceptors placed on deeper layers below the surface, the acceptor hole wave function is more delocalized and the corresponding LDOS is much more sensitive on the direction of the Mn magnetic moment. However, the magnetic anisotropy energy for these magnetic impurities is large (up to 15 meV), and a magnetic field of 10 T can hardly change the landscape and rotate the direction of the Mn magnetic moment away from its easy axis. We predict that substantially larger magnetic fields are required to observe a significant field dependence of the tunneling current for impurities located several layers below the GaAs surface.

Tunable Control over the Ionization State of Single Mn Acceptors in GaAs with Defect-Induced Band Bending

A scanning tunneling microscope was used to study the ionization of single Mn acceptors in GaAs(110). The ionization state switches when the GaAs valence band is bent across a Mn acceptor level. This produces a ringlike feature in STM images, whose diameter depends on the tunneling conditions and distance to charged arsenic vacancies. By varying the latter, we could tune the ionization switching, as well as quantify the contributions from tip- and vacancy-induced band bending.

Enhanced magnetization by modulated Mn delta doping in GaAs

The magnetic property of GaMnAs can be enhanced by increasing the Mn concentration as well as hole concentration. The interstitial Mn is inevitably formed when Mn concentration is very high even if the growth condition is carefully controlled. They act as a double donor and compensates for Mn acceptors in GaAs. The interstitial Mn atoms also tend to be bound by those occupying the substitutional Ga site. The combination of interstitial and substitial Mn atom produces antiferromagnetic pairs. In order to reduce the interstitial Mn and increase hole concentration, we introduce Mn delta-doped layers separated by undoped GaAs layers. The magnetic properties are investigated as a function the spacing between Mn delta-doped layers. It is found that magnetization characteristics such as the magnetic susceptibility, coercive force and Curie temperature are enhanced when the spacing between Mn delta-doped layers is optimized.

Mn Impurity in Bulk GaAs Crystals

Magnetic and electron transport properties of GaAs:Mn crystals grown by Czochralski method were studied. Electron spin resonance showed the presence of Mn acceptor A in two charge states: singly ionized A i in the form of Mn 2+ (d 5 ), and neutral A 0 in the form of Mn 2+ (d 5 ) plus a bound hole (h). It was possible to determine the relative concentration of both types of centers from intensity of the corresponding electron spin resonance lines. Magnetization measured as a function of magnetic fleld (up to 6 T) in the temperature range of 2{300 K revealed overall paramagnetic behavior of the samples. Efiective spin was found to be about 1.5 value, which was consistent with the presence of two types of Mn conflgurations. In most of the studied samples the dominance of Mn 2+ (d 5 ) + h conflguration was established and it increased after annealing of native donors. The total value of Mn content was obtained from fltting of magnetization curves with the use of parameters obtained from electron spin resonance. In electron transport, two mechanisms of conductivity were observed: valence band transport dominated above 70 K, and hopping conductivity within Mn impurity band at lower temperatures. From the analysis of the hopping conductivity and using the obtained values of the total Mn content, the efiective radius of Mn acceptor in GaAs was estimated as a = 11 § 3 ”

Spatial structure of an individual Mn acceptor in GaAs.

The wave function of a hole bound to an individual Mn acceptor in GaAs is spatially mapped by scanning tunneling microscopy at room temperature and an anisotropic, crosslike shape is observed. The spatial structure is compared with that from an envelope-function, effective mass model and from a tight-binding model. This demonstrates that anisotropy arising from the cubic symmetry of the GaAs crystal produces the crosslike shape for the hole wave function. Thus the coupling between Mn dopants in GaMnAs mediated by such holes will be highly anisotropic.

Imaging of the (Mn 2+3d 5 + hole) complex in GaAs by cross-sectional scanning tunneling microscopy

We present results on the direct spatial mapping of the wave function of a hole bound to a Mn acceptor in GaAs. To investigate individual Mn dopants at the atomic scale in both ionized and neutral configurations, we used a room temperature cross-sectional scanning tunneling microscope. We found that in the neutral configuration manganese manifests itself as an anisotropic cross-like feature. We attribute this feature to a hole, weakly bound to the Mn ion forming the (Mn 2+3d 5 + hole) complex.

Charge manipulation and imaging of the Mn acceptor state in GaAs by cross-sectional scanning tunneling microscopy

An individual Mn acceptor in GaAs is mapped by cross-sectional scanning tunneling microscopy (X-STM) at room temperature and a strongly anisotropic shape of the acceptor state is observed. An acceptor state manifests itself as a cross-like feature which we attribute to a valence hole weakly bound to the Mn ion forming the (Mn 2+3d 5+hole) complex. We propose that the observed anisotropy of the Mn acceptor wavefunction is due to the d-wave present in the acceptor ground state.

Model for the Mn acceptor in GaAs

We present a model based on the Baldereschi–Lipari effective mass theory and the sp–d exchange interaction between the valence band and the Mn d electrons (3 d 5). It fits in with the available experimental data and yields a relationship between the exchange-induced splitting of the 1S 3/2 impurity ground state and the valence band exchange constant N 0 β. By using the recently reported value of the splitting, deduced from infrared spectroscopy, and fitting the known ground state binding energy, we obtain N 0β≃−0.9 eV. We also study the two-hole bound state in the Hartree self-consistent approximation and account for the absence of Mn-associated bound exciton and discuss the sign anomalies in the magneto-optical data in dilute Ga 1− x Mn x As.

Electronic structure of the GaAs:MnGascenter

The excitation spectrum of the 0.11-eV Mn acceptor in GaAs has been thoroughly investigated by uniaxial stress and Zeeman fourier transform infrared spectroscopy. The results give strong evidence for the ${3\mathrm{d}}^{5}$ +shallow hole model for the ${\mathrm{Mn}}^{0}$ center. The deformation potentials as well as the g values determined for the hole are in close agreement with those previously reported for the ${1\mathrm{S}}_{3\mathrm{/}2}$(${\mathrm{\ensuremath{\Gamma}}}_{8}$) state for shallow acceptors in GaAs. All experimental results are in accordance with a J=1 ground-state level derived from exchange coupling of the shallow ${1\mathrm{S}}_{3\mathrm{/}2}$(${\mathrm{\ensuremath{\Gamma}}}_{8}$) hole and the S=5/2 ${\mathrm{Mn}}^{\mathrm{\ensuremath{-}}}$ core. A splitting between J=2 and J=1 levels in the range from 9 to 12 meV is inferred and is considerably larger than the 2--3 meV splitting previously suggested

Strongly quenched deformation potentials of the Mn acceptor in GaAs

We have measured the luminescence spectrum of Mn-doped GaAs at liquid-He temperatures with and without an applied uniaxial stress. At zero stress we found clearly resolved donor-acceptor (DA) and band-acceptor recombination bands involving Mn. From these measurements we get a precise acceptor binding energy of 113 \ifmmode\pm\else\textpm\fi{} 0.5 meV. The stress dependence of the peak energy and of the polarization of the DA recombination spectrum was used to derive the following deformation potentials of the acceptor: ${a}^{\ensuremath{'}}=\ensuremath{-}9.1$ eV, ${b}^{\ensuremath{'}}=\ensuremath{-}0.35$ eV, and ${d}^{\ensuremath{'}}=\ensuremath{-}0.8$ eV. The potentials ${b}^{\ensuremath{'}}$ and ${d}^{\ensuremath{'}}$ are only 18% and 15%, respectively, of the corresponding shear-strain-deformation potentials of the valence band. We attribute this reduction principally to the localization of the bound hole with an additional contribution from a dynamic Jahn-Teller effect.

Thermal activation energy of manganese acceptors in gallium arsenide as a function of impurity spacing

The thermal ionization energy for Mn acceptors in GaAs decreases with increasing density of either Mn atoms or compensators. Measurements of the correlation of Ea with Na or Nd are complicated by impurity inhomogeneity. Envelope functions fitted to the data show the same energy (0.11 eV) for the infinite dilution asymptotic value as is found for the optical activation threshold.