High Doping Regime Research Articles

Combination of Counterion Size and Doping Concentration Determines the Electronic and Thermoelectric Properties of Semiconducting Polymers.

In both chemical and electrochemical doping of organic semiconductors (OSCs), a counterion, either from the electrolyte or ionized dopant, balances the charge introduced to the OSC. Despite the large influence of this counterion on OSC optical and electronic response, there remains substantial debate on how a fundamental parameter, ion size, impacts these properties. This work resolves much of this debateby accounting for two doping regimes. In the low-doping regime, the Coulomb binding energies between charge carrierson the OSC and the counterions are significant, and larger counterions lead to decreased Coulomb interactions, more delocalized charge carriers, and higher electrical conductivities. In the high-doping regime, the Coulomb binding energies become negligible due to the increased dielectric constant of the films and a smoothing of the energy landscape; thereby, the electrical conductivities depend primarily on the extent of morphological disorder in the OSC. Moreover, in regioregular poly(3-hexylthiophene), rr-P3HT, smaller counterions lead to greater bipolaron concentrations in the low-doping regime due to the increased Coulomb interactions. Emphasizing the impact of the counterion size, it is shown that larger counterions can lead to increased thermoelectric power factors for rr-P3HT.

Electronic and phononic absorption contributions to near-infrared reflectance of Mg1−xCoxAl2O4, Zn1−xCoxFe2O4 and CrxSbxTi1–2xO2 pigments

Mg1−xCoxAl2O4, Zn1−xCoxFe2O4 and CrxSbxTi1–2xO2 pigment series with varying chemical constitution were prepared and structurally confirmed. Valence band maximum extracted from photoemission spectrum and Raman signal area obtained from Raman spectrum were used as representative of electronic and phononic absorption, respectively. Mg1−xCoxAl2O4, Zn1−xCoxFe2O4 exhibit a trivial cooperative behavior of electronic and phononic absorption to the near-infrared reflectance. Nevertheless, CrxSbxTi1–2xO2 established a nontrivial phononic absorption behavior. At low doping regime in CrxSbxTi1–2xO2, electronic absorption dominates the controlling of near-infrared reflectance. Conversely, at high doping regime, the shrinking of phononic absorption play a dominance role to the reflectance. The nontrivial scenario could lead to the understanding of underlying reflective mechanism associated with effects from electronic structure and lattice properties. The results would pave the way for the improvement of solar reflective pigment with compromise of color tuning.

Heavy-fermion metallic state and Mott transition induced by Li-ion intercalation in LiV2O4 epitaxial films

The spinel-type ${\mathrm{LiV}}_{2}{\mathrm{O}}_{4}$ exhibits heavy-fermion metallic behaviors at low temperatures, but the effect of composition modulation on them is unknown. We realized the epitaxial growth of highly crystalline ${\mathrm{LiV}}_{2}{\mathrm{O}}_{4}$ films and conducted the electrochemical Li-ion intercalation (electron doping) to investigate systematic variation of transport properties in ${\mathrm{Li}}_{1+x}{\mathrm{V}}_{2}{\mathrm{O}}_{4}$. We found that adjustment of Li content during pulsed-laser deposition was important to obtain films exhibiting the heavy-fermion metallic behavior comparable to that of a bulk single crystal. At low doping regime $(x\ensuremath{\le}0.5)$, resistivity increased with increasing electron filling. The slope of their linear ${T}^{2}$ dependence also increased in accordance of a Fermi-liquid model. At high doping regime $(x>0.5)$, a Mott transition was observed over a range of Li content where a new spinel phase and the original one coexisted. The results revealed that the electron doping induced enhancement of the electron correlation and the resultant Mott transition.

Self-compensation in heavily Ge doped AlGaN: A comparison to Si doping

Self-compensation in Ge- and Si-doped Al0.3Ga0.7N has been investigated in terms of the formation of III vacancy and donor-vacancy complexes. Both Ge- and Si-doped AlGaN layers showed a compensation knee behavior with impurity compensation (low doping regime), compensation plateau (medium doping regime), and self-compensation (high doping regime). A maximum free carrier concentration of 4–5 × 1019 cm−3 was obtained by Ge doping, whereas Si doping resulted in only half of that value, ∼2 × 1019 cm−3. A DFT calculation with the grand canonical thermodynamics model was developed to support the hypothesis that the difference in self-compensation arises from the difference in the formation energies of the VIII-n•donor complexes relative to their onsite configurations. The model suggested that the VIII-2•donor and VIII-3•donor complexes were responsible for self-compensation for both Ge- and Si-doped AlGaN. However, a lower free carrier concentration in Si-doped samples was due to a high VIII-3•Si concentration, resulting from a lower energy of formation of VIII-3•Si.

Role of substrate strain to tune energy bands–Seebeck relationship in semiconductor heterostructures

In doped semiconductors and metals, the Seebeck coefficient or thermopower decreases monotonically with increasing carrier concentration in agreement with the Pisarenko relation. Here, we establish a fundamental mechanism to modulate and increase the thermopower of silicon (Si)/germanium (Ge) heterostructures beyond this relation, induced by the substrate strain. We illustrate the complex relationship between the lattice strain and the modulated thermopower by investigating the electronic structure and cross-plane transport properties of substrate strained [001] Si/Ge superlattices (SLs) with two independent theoretical modeling approaches: first-principles density functional theory and the analytical Krönig–Penny model in combination with the semi-classical Boltzmann transport equation. Our analysis shows that the SL bands, formed due to the cubic structural symmetry, combined with the potential perturbation and the intervalley mixing effects, are highly tunable with epitaxial substrate strain. The strain tuned energy band shifts lead to modulated thermopowers, with a peak approximately fivefold Seebeck enhancement in strained [001] Si/Ge SLs in the high-doping regime. As a consequence, the power factor of a 2.8% substrate strained SL shows a ≈1.8-fold improvement over bulk Si at high carrier concentrations, ≈12×1020cm−3. It is expected that the fundamental understanding discussed here, regarding the complex effect of lattice strain to control energy bands of heterostructures, will help to exploit strain engineering strategies on a class of future technology-enabling materials, such as novel Si/Ge heterostructures as well as layered materials, including van der Waals heterostructures.

Theoretical Prediction of Enhanced Thermopower in n-Doped Si/Ge Superlattices Using Effective Mass Approximation

We analyze the cross-plane miniband transport in n-doped [001] silicon (Si)/germanium (Ge) superlattices using an effective mass approximation (EMA) approach that correctly accounts for the indirect nature of the Si and Ge band gaps. Direct-gap based EMA has been employed so far to investigate the electronic properties of these superlattices, that does not accurately predict transport properties. We use the Boltzmann transport equation framework in combination with the EMA band analysis, and predict that significant improvement of the thermopower of n-doped Si/Ge superlattices can be achieved by controlling the lattice strain environment in these heterostructured materials. We illustrate that a remarkable degree of tunability in the Seebeck coefficient can be attained by growing the superlattices on various substrates, and varying the periods, and the compositions. Our calculations show up to ~3.2-fold Seebeck enhancement in Si/Ge [001] superlattices over bulk silicon, in the high-doping regime, breaking the Pisarenko relation. The thermopower modulations lead to an increase of power factor by up to 20%. Our approach is generically applicable to other superlattice systems, e.g., to investigate dimensional effects on electronic transport in two-dimensional nanowire and three dimensional nanodot superlattices. A material with high S potentially improves the energy conversion efficiency of thermoelectric applications and additionally, is highly valuable in various Seebeck metrology techniques including thermal, flow, radiation, and chemical sensing applications. We anticipate that the ideas presented here will have a strong impact in controlling electronic transport in various thermoelectric, opto-electronic, and quantum-enhanced materials applications.

The Doping Mechanism of Halide Perovskite Unveiled by Alkaline Earth Metals.

Halide perovskites are a strong candidate for the next generation of photovoltaics. Chemical doping of halide perovskites is an established strategy to preparethe highest efficiency andmost stable perovskite-based solar cells. In this study, we unveil the doping mechanism of halide perovskites using a series of alkaline earth metals. We find that low doping levels enable the incorporation of the dopant within the perovskite lattice, whereas high doping concentrations induce surface segregation. The threshold from low to high doping regime correlates to the size of the doping element. We show that the low doping regime results in a more n-typematerial, while the high doping regime induces a less n-type doping character. Our work provides a comprehensive picture of the unique doping mechanism of halide perovskites, which differs fromclassical semiconductors. We proved the effectiveness of the low doping regime for the first time, demonstrating highly efficient methylammonium lead iodide based solar cells in both n-i-p and p-i-n architectures.

Optimization of Seebeck coefficients of strain-symmetrized semiconductor heterostructures

A nonmonotonic thermopower (S) as a function of the carrier concentration (ne) has been reported for III–V semiconductor superlattices (SLs), deviating from the Pisarenko relation. However, |S| has been shown to decrease with increasing ne in n-type Si/Ge heterostructures, the widely used systems for numerous applications. Here, we illustrate that S of a SinGem SL, with n Si and m Ge monolayers, can deviate from the Pisarenko relation depending on the period and the composition; for example, oscillations of S of a Si12Ge12 SL reach a peak |S|=540 μV/K at ne=1.3×1020 cm−3, 5.4 times higher than that of bulk Si at the same doping level. Additionally, S shows an interesting sign-change nature at certain carrier concentrations. We demonstrate the direct relationship between the electronic structure and S of strain-symmetrized Si/Ge SLs using two independent modeling approaches. We anticipate that this relationship will provide insight into fully exploiting S as a tool to control electronic properties of Si/Ge heterostructures as well as future technology-enabling materials. Furthermore, we expect that this analysis will encourage future investigations to enhance thermoelectric properties of a broad class of semiconductor SLs in the high-doping regime.

Donor–acceptor pair emission via defects with strong electron–phonon coupling in heavily doped AlxGa1−xN:Si layers with Al content x > 0.5

We report the results of time-resolved and temperature-dependent stationary photoluminescence investigations of the defects responsible for emission in the visible spectral range in heavily silicon-doped AlxGa1–xN layers grown by molecular beam epitaxy on sapphire substrates. The emission band was attributed to donor–acceptor transitions. The transitions were described using the one-dimensional configuration coordinate model taking into account the high-doping regime. An increase in Al content from 0.56 to 1 leads to an increase in the acceptor ionization energy from 1.4 to 1.87 eV. The value of the Franck–Condon shift is about 1 eV at x = 0.56–0.74 and decreases to 0.8 eV at x > 0.74. The changes in the donor–acceptor transition energy parameters with increasing silicon concentration are discussed.

Microscopic origin of the bolometric effect in graphene

While the thermoelectric and photoconduction effects are crucial in pristine and low-doped graphene, the bolometric effect is known to dominate the photoresponse in biased graphene. Here, we present a detailed microscopic investigation of the photoresponse due to the bolometric effect in graphene. Based on the semiconductor Bloch equations, we investigate the time- and momentumresolved carrier dynamics in graphene in the presence of a constant electric field under optical excitation. The magnitude of the bolometric effect is determined by the optically induced increase of temperature times the conductivity change. Investigating both factors independently, we reveal that the importance of the bolometric effect in the high-doping regime can be mostly ascribed to the latter showing a parabolic dependence on the doping.

(Invited) Probing the Intrinsic Limitations of the Contact Resistance of Metal/Semiconductor Interfaces through Atomistic Simulations

Over the last technology nodes, the continuous reduction of the CMOS dimensions has been pushing the physical limits of the transistor into numerous ends. Consequently, a straightforward linear scaling of device dimensions does not apply anymore to all the aspects of the CMOS transistor. For instance, the aggressive scaling of the transistor gate pitch requires that both the gate length and the S/D contact dimensions are reduced in size; constraining the gate, the sidewall spacers and the S/D contacts to compete continuously for space. On the other hand, the transistor gate length has also to follow a different scaling law and is kept as large as possible to ensure a proper electrostatic control. A direct consequence of this approach is the need to keep on decreasing the S/D contact resistance, which currently constitutes a new bottleneck in the scaling of modern CMOS. Aside from being able to reduce the physical dimensions of the contact, it is paramount to minimize the metal/semiconductor intrinsic resistivity which has now become a major roadblock to be conquered. Recently, the cumulated efforts of the scientific and engineering communities have substantially extended the physical limits of the S/D contact resistance thanks to the increase in the concentration of activated dopants in the semiconductors and to the engineering of their Schottky barrier. The latter is achieved by integrating metals with a weak Fermi level pinning at the interface with the semiconductor. As a result, contact resistivities as low as 2x10-9 Ω.cm2 [1] and 8.4x10-10 Ω.cm2 [2] have been reported for n-Si-TiSi(amorphous) and p-Si30Ge70-TiSi(amorphous) with dopant concentrations as high as 6x1020cm-3 and 1x1021cm-3[1,2]. Although these accomplishments are very impressive, little is known on the intrinsic limits that will ultimately determine the contact resistivity and it remains unclear whether even higher doping concentrations would be desirable or not. In this contribution, we will report a fundamental study of the factors that set the contact resistivity between metals and highly doped semiconductors. We will investigate the case of n-type doped Si contacted with amorphous TiSi combining first-principles calculations with Non-Equilibrium Green functions transport simulations [4][5]. We will show that, whereas the metal/semiconductor intrinsic contact resistivity initially scales with the doping concentration, it is found to saturate at ~2x10-10 Wcm2, as of a doping concentration of ~5x1021 cm-3. From this concentration on, electron injection is governed by Ohm’s law. It turns out that, in such high doping regimes, the electron injection does no longer depend on the barrier height set by the interface potential to be crossed. In turn, it becomes less sensitive to the chemical composition of the interface/degree of disorder and is limited by the intrinsic transmission probability of electrons being injected from the metal into the semiconductor. The latter depends on both the effective masses of the metal and of the semiconductor [3] and imposes an intrinsic physical limit to the contact resistance. We will show that, in this regime, contacting metals with a heavy electron effective mass are favorable to increase the transmission probability and, hence, to reduce of the semiconductor-metal intrinsic contact resistivity. Acknowledgements: The authors thank the imec industrial affiliation core CMOS program and quantumwise for financial and technical supports, respectively.

Electron effective mass and mobility limits in degenerate perovskite stannateBaSnO3

The high room temperature mobility and the electron effective mass in BaSnO$_3$ are investigated in depth by evaluation of the free carrier absorption observed in infrared spectra for epitaxial films with free electron concentrations from $8.3 \times 10^{18}$ to $7.3 \times 10^{20}$~cm$^{-3}$. Both the optical band gap widening by conduction band filling and the carrier scattering mechanisms in the low and high doping regimes are consistently described employing parameters solely based on the intrinsic physical properties of BaSnO$_3$. The results explain the current mobility limits in epitaxial films and demonstrate the potential of BaSnO$_3$ to outperform established wide band gap semiconductors also in the moderate doping regime.

Alkali doping of graphene: The crucial role of high-temperature annealing

The doping efficiency of lithium deposited at cryogenic temperatures on epitaxial and CVD monolayer graphene has been investigated under ultra-high vacuum conditions. Change of charge carrier density was monitored by gate voltage shift of the Dirac point and by Hall measurements, in low and high doping regimes. It was found that pre-annealing the graphene greatly enhanced the maximum levels of doping that could be achieved: doping saturated at $\Delta n = 2\times 10^{13}$ e$^-$/cm$^2$ without annealing, independent of sample type or previous processing; after a 900 K anneal, the saturated doping rose one order of magnitude to $\Delta n = 2\times 10^{14}$ e$^-$/cm$^2$.

Reversible phase modulation and hydrogen storage in multivalent VO2 epitaxial thin films.

Hydrogen, the smallest and the lightest atomic element, is reversibly incorporated into interstitial sites in vanadium dioxide (VO2), a correlated oxide with a 3d(1) electronic configuration, and induces electronic phase modulation. It is widely reported that low hydrogen concentrations stabilize the metallic phase, but the understanding of hydrogen in the high doping regime is limited. Here, we demonstrate that as many as two hydrogen atoms can be incorporated into each VO2 unit cell, and that hydrogen is reversibly absorbed into, and released from, VO2 without destroying its lattice framework. This hydrogenation process allows us to elucidate electronic phase modulation of vanadium oxyhydride, demonstrating two-step insulator (VO2)-metal (HxVO2)-insulator (HVO2) phase modulation during inter-integer d-band filling. Our finding suggests the possibility of reversible and dynamic control of topotactic phase modulation in VO2 and opens up the potential application in proton-based Mottronics and novel hydrogen storage.

Anisotropic density fluctuations, plasmons, and Friedel oscillations in nodal line semimetal

Motivated by recent experimental efforts on three-dimensional semimetals, we investigate the static and dynamic density response of the nodal line semimetal by computing the polarizability for both undoped and doped cases. The nodal line semimetal in the absence of doping is characterized by a ring-shape zero energy contour in momentum space, which may be considered as a collection of Dirac points. In the doped case, the Fermi surface has a torus shape and two independent processes of the momentum transfer contribute to the singular features of the polarizability even though we only have a single Fermi surface. In the static limit, there exist two independent singularities in the second derivative of the static polarizability. This results in the highly anisotropic Friedel oscillations which show the angle-dependent algebraic power law and the beat phenomena in the oscillatory electron density near a charged impurity. Furthermore, the dynamical polarizability has two singular lines along and , where η is the angle between the external momentum and the plane where the nodal ring lies. From the dynamical polarizability, we obtain the plasmon modes in the doped case, which show anisotropic dispersions and angle-dependent plasma frequencies. Qualitative differences between the low and high doping regimes are discussed in light of future experiments.

On the Origin of the 4.7 eV Absorption and 2.8 eV Emission Bands in Bulk AlN Substrates

AlGaN alloys are the building blocks for deep UV optoelectronics and high-power devices. It has been demonstrated that the highest crystalline quality AlGaN films with high Al content are obtained on AlN single crystal substrates. The resulting mismatch between AlGaN and AlN causes a compressive strain within the AlGaN layers, which varies with composition. Nevertheless, pseudomorphic AlGaN films with Al content higher than 50%, and dislocation densities lower than 104 cm-2 have been achieved, sustaining compressive stresses with thicknesses exceeding 3 µm. Such results demonstrate the advantages of using AlN substrates for this technology, and at such some have been realized on several deep-UV optoelectronics applications. Kinoshita et al. have demonstrated UV LEDs emitting at 265 nm with output powers exceeding 80 mW. UV LEDs grown on these native substrates have higher reliabilities and higher output powers. In addition, optically pumped lasers emitting at wavelengths between 230 nm and 280 nm that display cavity modes and single polarized-state emission with low lasing thresholds have been developed. Nevertheless, there are several limitations related to the performance and further improvement of the active regions as related to their quantum efficiencies and the polarization of their emission is desired. These limitations will be classified in two main categories: (1) identification and control of point defects, and (2) efficient doping. One of the main limitations based on point defects is the one related to the UV absorption band present at 265 nm in AlN. This relatively broad absorption band limits the use of the substrate within the deep UV range and several complicated fabrication procedures were devised to overcome this limitation. In this work, the origin of this absorption band will be discussed, along with other related optical features and the use of co-doping as a way of removing this undesired absorption. Experimental and theoretical results that explore the optical properties of native and impurity point defects as well as point-defect complexes in AlN with respect to the 265 nm absorption band will be presented. Theoretical results, based on DFT, are compared to photoluminescence and absorption measurements of AlN samples grown by physical vapor transport, metal-organic chemical vapor deposition, and hydride vapor-phase epitaxy . Our results demonstrate that there are multiple sources of a deep-UV absorption between 4.5 and 5.0 eV. The presence of the isolated carbon substitutional CN - produces an absorption band centered at 4.7 eV and emission at 3.9 eV, thus its reduction leads to the reduction of the absorption band. In addition, one mechanism that contributes to the apparent UV transparency when the material is co-doped with Si is discussed. These schemes produced transparent AlN wafers suitable for deep UV LED production. The other limitation relates to obtaining technologically useful n-type conductivities in high Al-content AlGaN within the low and high doping regimes. Besides dislocation density reduction, identification and elimination of compensating defects are necessary to achieve this goal. AlGaN films with high Al mole fractions (0.65<x<1) were grown by MOCVD on single crystalline AlN and sapphire. It is found that with an increase in Al content, there was both a decrease in the free carrier concentration and mobility. The reduction in free carrier concentration for x>0.8 was primarily caused by an increase in activation energy. This is due to the formation of a Si DX-center, thus inspiring the search for alternative dopants. Preliminary data on Ge doping of AlGaN will be presented to assess its effectiveness as a donor throughout the whole composition regime. In addition, for samples grown with different Si doping levels it is observed that up to a critical Si concentration, the carrier concentration was always proportional to the Si source flow. Any further increase led to a free carrier concentration reduction. PL spectra exhibited deep defect-related peaks corresponding to transitions between Si and deep acceptor states. For Si concentrations less than an Al-content dependent critical concentration, a higher energy peak dominates the spectra. This peak was related to a (VAl-complex)2- based on DFT calculations. For Si concentrations greater than the critical concentration, a (VAl)3- related lower energy peak dominates the spectra. The energy levels associated with these defects increased with Al composition where the energy increase was the same as the increase in band gap. Acknowledgement: Partial financial support from NSF (DMR-1312582 and ECCS-1508854), DARPA (W911QX-10-C-0027), ARPA-E (DE-AR0000299), ARO (W911NF14C0008) is greatly appreciated. All PVT AlN wafers used for homoepitaxial growth were supplied by HexaTech, Inc., Morrisville, NC.

Charge dynamics in doped Mott insulators on a honeycomb lattice

Within the framework of the fermion-spin theory, the charge transport in the doped Mott insulators on a honeycomb lattice is studied by taking into account the pseudogap effect. It is shown that the conductivity spectrum in the low-doped regime is separated by the pseudogap into a low-energy non-Drude peak followed by a broad mid-infrared band. However, the decrease of the pseudogap with the increase of doping leads to a shift of the position of the mid-infrared band towards the low-energy non-Drude peak, and then the low-energy Drude behavior recovers in the high-doped regime. The combined results of both the doped honeycomb-lattice and square-lattice Mott insulators indicate that the two-component conductivity induced by the pseudogap is a universal feature in the doped Mott insulators.

Magnetic and nonmagnetic phases in dopedAB2 t−JHubbard chains

We discuss the rich phase diagram of doped AB2 $t-J$ chains by using data from density matrix renormalization group and exact diagonalization techniques. The $J$ vs $\delta$ (hole doping) phase diagram exhibits regions of itinerant ferrimagnetism, incommensurate, resonating valence bond and Nagaoka states, phase separation, and Luttinger liquid (LL) physics. Several features are highlighted, such as the modulated ferrimagnetic structure, the occurrence of Nagaoka spin polarons in the underdoped regime and small values of $J=4t^2/U$, where $t$ is the first-neighbor hopping amplitude and $U$ is the on-site repulsive Coulomb interaction, incommensurate structures with nonzero magnetization, and strong-coupling LL physics in the high-doped regime. We also verify that relevant findings are in agreement with the corresponding findings in square and n-leg ladder lattices. In particular, we mention the instability of Nagaoka ferromagnetism against $J$ and $\delta$.

The effect of impurity and the suppression of superconductivity in Na(Fe0.97−xCo0.03Tx)As (T = Cu, Mn)

We report the successful growth of and the effect of impurity scattering in single crystals of Na()As (T = Cu, Mn). The temperature dependence of the DC magnetization at high magnetic fields is measured for different concentrations of Cu and Mn. Detailed analysis based on the Curie–Weiss law indicates that Cu doping weakens the average magnetic moments, while doping with Mn enhances the local magnetic moments greatly, suggesting that the former may produce nonmagnetic or very weak magnetic impurities, and that the latter may give rise to magnetic impurities. However, it is found that both doping with Cu and doping with Mn will enhance the residual resistivity and suppress the superconductivity, at similar rates, in the low doping region, which is consistent with the prediction of the S model. For the Cu-doped system, the superconductivity is suppressed completely at a residual resistivity of mΩ cm, for which a strong localization effect is observed. However, in the case of Mn doping, the suppression of becomes much weaker beyond x = 0.03 and superconductivity is maintained even up to a residual resistivity of 2.86 mΩ cm. Clearly the magnetic Mn impurities may even be not as detrimental as the nonmagnetic or very weak magnetic Cu impurities to the superconductivity in the high doping regime.

Quantum Corrections Crossover and Ferromagnetism in Magnetic Topological Insulators

Revelation of emerging exotic states of topological insulators (TIs) for future quantum computing applications relies on breaking time-reversal symmetry and opening a surface energy gap. Here, we report on the transport response of Bi2Te3 TI thin films in the presence of varying Cr dopants. By tracking the magnetoconductance (MC) in a low doping regime we observed a progressive crossover from weak antilocalization (WAL) to weak localization (WL) as the Cr concentration increases. In a high doping regime, however, increasing Cr concentration yields a monotonically enhanced anomalous Hall effect (AHE) accompanied by an increasing carrier density. Our results demonstrate a possibility of manipulating bulk ferromagnetism and quantum transport in magnetic TI, thus providing an alternative way for experimentally realizing exotic quantum states required by spintronic applications.