Heavy-hole Effective Mass Research Articles

Investigation of Aluminum Arsenide Honeycomb Monolayer via Density Functional Theory

First principle calculations are performed to theoretically predict the physical properties of hexagonal aluminium arsenide planar and buckled monolayers. The structural characteristics showed that the buckled parameter is about 0.32 A°. Cohesive energies have favourable values and it indicates the fabrication possibility. Phonon dispersion properties indicated that the planar aluminium arsenic monolayers are dynamically unstable, while the buckled is less dynamically unstable. The elastic constant parameters achieved the required characteristics of stable hexagonal monolayer structures. The study of electronic band structure prefers to indirect semiconductor band gaps, and the density of states showed strong orbital hybridization in the conduction band. Planar structure has isotropic light electron effective mass and anisotropic heavy hole effective mass. The buckled structure has isotropic light electron effective mass and isotropic heavy hole effective mass. The absorption spectra have high absorption coefficient in various visible and ultraviolet wavelength. The absorption coefficient levels off at about direct and indirect band gaps.

Enhanced Light Emission from Type-II Red InGaN/GaNSb/GaN Quantum-Well Structures

Electronic and optical properties of type-II InGaN/GaNSb/GaN quantum-well (QW) structures are investigated by using the multiband effective mass theory for potential applications in red light-emitting diodes. The heavy-hole effective mass around the topmost valence band is not affected much by the insertion of the GaNSb layer, and the optical matrix elements are greatly increased by the inclusion of the GaNSb layer in the InGaN/GaN QW structure. As a result, the type-II InGaN/GaNSb/GaN QW structure shows a much larger emission peak than the conventional type-I QW structure owing to the decrease in spatial separation between electron and hole wavefunctions, in addition to the reduction of the effective well width. It is also observed that the In content in InGaN well can be significantly reduced for the type-II QW structure with a large Sb content, compared to that for the type-I QW structure.

Anisotropic g -tensors in hole quantum dots: Role of transverse confinement direction

Qubits encoded in the spin state of heavy holes confined in Si- and Ge-based semiconductor quantum dots are currently leading the efforts toward spin-based quantum information processing. The virtual absence of spinful nuclei in purified samples yields long qubit coherence times and the intricate coupling between spin and momentum in the valence band can provide very fast spin-orbit-based qubit control, e.g., via electrically induced modulations of the heavy-hole $g$-tensor. A thorough understanding of all aspects of the interplay between spin-orbit coupling, the confining potentials, and applied magnetic fields is thus essential for the development of the optimal hole-spin-based qubit platform. Here we theoretically investigate the manifestation of the effective $g$-tensor and effective mass of heavy holes in two-dimensional hole gases as well as in lateral quantum dots. We include the effects of the anisotropy of the effective Luttinger Hamiltonian (particularly relevant for Si-based systems) and we focus on the detailed role of the orientation of the transverse confining potential. We derive general analytic expressions for the anisotropic $g$-tensor and we present a general and straightforward way to calculate corrections to this $g$-tensor for localized holes due to various types of spin-orbit interaction, exemplifying the approach by including a simple linear Rashba-like term. Our results thus contribute to the understanding needed to find optimal points in parameter space for hole-spin qubits, where confinement is effective and spin-orbit-mediated electric control over the spin states is efficient.

Influence of the spin-orbit split-off valence band on the hole g factor in semiconductor nanocrystals

We present results of $\mathbit{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbit{p}$ calculations of the effective $g$ factor of holes confined in spherical, cube, and planar semiconductor nanocrystals (NCs). We use the six-band Luttinger model for semiconductors with the zinc-blende crystal structure and study the size dependence of the ${\mathrm{\ensuremath{\Gamma}}}_{8}$ top valence subband hole $g$ factor caused by the admixture of the spin-orbit split-off valence subband ${\mathrm{\ensuremath{\Gamma}}}_{7}$. We present semianalytical expressions for the hole $g$ factor which depends on the light- to heavy-hole effective mass ratio $\ensuremath{\beta}$ and on the ratio between spin-orbit energy splitting of valence band ${\mathrm{\ensuremath{\Delta}}}_{\text{SO}}$ and the hole quantization energy ${E}_{h}$. The admixture of ${\mathrm{\ensuremath{\Gamma}}}_{7}$ states is significant for small ${\mathrm{\ensuremath{\Delta}}}_{\text{SO}}/{E}_{h}$ and, in spherical and cube NCs, leads to a strong size dependence of the hole $g$ factor. In thin planar nanoplatelets (NPLs) with infinite or large lateral sizes, the dependence of the heavy-hole $g$ factor on NPL thickness is relatively weak. It is drastically enhanced and may become nonmonotonic in NPLs with finite in-plane sizes due to the additional hole states mixing. We discuss our results in comparison with published experimental data for CdSe- and InP-based spherical NCs and NPLs and point out the specificity of extracting hole $g$ factor from the data measured on excitons.

Recombination Rate and Internal Field Efficiency of Staggered InGaN/GaN Light-Emitting Diodes with Left and Right Steps

In this study, the recombination rate and internal field efficiency of staggered InGaN/GaN quantum well lightemitting diodes with left and right steps were investigated using the multiband effective mass theory. The left step quantum well structure shows a larger optical matrix element than that of the right step quantum well structure. In addition, the heavy-hole effective mass around the uppermost valence band for the left step quantum well structure is slightly larger than that for the right step quantum well structure. Consequently, the staggered left step quantum well structure shows a much larger radiative recombination rate and internal quantum efficiency than that of the right step structure.

Electron and hole mobilities of GaN with bulk, quantum well, and HEMT structures

Electron and hole mobilities of GaN are calculated for three-dimensional (3D, bulk) and two-dimensional [2D, quantum well (QW), and HEMT] structures, including scattering processes of acoustic deformation potential, polar optical phonon, piezoelectric, ionized impurity, and so on. The calculated mobilities for 2D structures are strongly dependent on quantum well structures and impurity densities, although the temperature dependence of the mobilities behaves in a similar way to bulk values. In the present analysis, energy band structures of GaN are calculated by the empirical pseudopotential method including spin–orbit interaction, and then the electron effective mass of the conduction band and the hole effective masses of the valence bands are evaluated, which are used for the calculations of electron and hole mobilities. The calculated valence band structure of the heavy, light, and crystal field splitted valence bands reveal complicated dispersion due to the spin–orbit interaction. The obtained electron effective mass mc=0.145m is isotropic, and the heavy hole effective mass in the c∥ plane is mhh∥=1.20m, while in the c⊥ plane, the band edge effective mass is mhh0⊥=0.55m and the over all fitted heavy hole effective mass is mhh⊥=1.20m. The light hole effective masses are mlh∥=1.35m and mlh⊥=0.165m. Both of the electron and hole mobilities are limited by ionized impurity scattering at low temperatures and by polar optical phonon scattering at high temperatures. Calculated electron mobilities are 7100 cm2/Vs for bulk, 4600 cm2/Vs for high electron mobility transistor (HEMT), and 3600 cm2/Vs for QW at room temperature and calculated hole mobilities are 450 cm2/Vs for bulk, 450 cm2/Vs for HEMT, and 500 cm2/Vs for QW at room temperature. All the expressions for scattering rates and respective mobilities are derived for 3D and 2D (QW and HEMT) structures and enable readers to calculate electron and hole mobilities in different structures with parameters given in the table or modified ones.

Electronic Structure and Quantum Transport Properties of 2D SiP: A First-Principles Study

With the rapid evolution of microelectronics, the field of integrated circuits is facing unprecedented challenges. Traditional silicon-based transistors cannot maintain the advantages of high performance during the process of further ultra-scaling due to severe short-channel effects. Two-dimensional (2D) materials are potential channel materials that can replace silicon. Herein, 2D SiP is predicted to have a band gap of 1.49 eV with anisotropic electronic properties by means of first-principles calculations, which is suitable as a channel candidate of transistors. Hence, we investigate the ballistic transport properties of 2D SiP double-gate metal oxide semiconductor field-effect transistors (MOSFETs) by using ab initio quantum transport simulations. Despite anisotropic electronic properties of 2D SiP, the performances of monolayer SiP MOSFETs have weak directional dependence due to high valley degeneracy. The n-MOSFETs with 10-nm gate length can fulfill the high-performance requirements of the International Roadmap for Devices and Systems 2020 Edition (IRDS 2020). However, the p-MOSFETs cannot fulfill the demands of IRDS 2020 because of heavy hole effective masses. Considering the appropriate on-current of 1292 μA/μm for SiP n-MOSFETs, 2D SiP could be utilized as a potential channel material in the next-generation FETs.Graphic abstract

Effects of composition modulation on the type of band alignments for Pd2Se3/CsSnBr3 van der waals heterostructure: A transition from type I to type II

Constructing perovskite-based van der Waals heterostructures (vdWHs) have rapidly advanced the field of optoelectronics and solar cells due to their unprecedented property to integrate excellent characteristics of different materials. In general, the perovskite-based vdWHs have various functional properties due to their different band alignments for Type I, Type II and Type III. However, it is challenging to realize the flexible switch of band alignments in heterostructure for diverse applications. In this paper, we systematically investigate the electronic and optical properties of novel heterostructure system composed of emerging two-dimensional material Pd2Se3 and all-inorganic halide perovskite CsSnBr3 for the first time. A Type I–Type II transition of band alignments in Pd2Se3/CsSnBr3 vdWH is achieved by partly replacing the Pd atom in Pd2Se3 monolayer with Ni atom, facilitating the highly efficient separation of photo-generated carriers. Meanwhile, the heavy hole effective mass along [1 0 0] direction is greatly reduced due to the transition of band alignment, which will improve the photoelectric conversion efficiency. Our works indicate that such a controllable band alignment of Pd2Se3/CsSnBr3 heterostructure holds a significant potential for future photoelectric applications.

TCAD Simulation of a 3D NAND Memory Utilizing In-Ga-Zn-Oxide: "3D OS NAND" with 4 V Drive, High Endurance and Density

Memory-centric computing has been actively researched for AI application. To achieve this, there are growing demands on memories for high density and high endurance. To demonstrate the application, a variety of emerging memory technologies have been proposed; however, they still have difficulties in achieving a density comparable to NAND flash and in improving endurance.CAAC-IGZO, with a wide bandgap and a heavy hole effective mass, can be applied to a field-effect transistor that is characterized by its extremely-low off-leakage current. Use of CAAC-IGZO FET in non-display fields has been reported in recent years, and 3D NAND utilizing CAAC-IGZO FET has been researched. However, the reported memory cell architecture involves through-dielectric charge trapping in MONOS structures, and has low endurance in the same way as conventional Si-based NAND flash.In view of the above, we propose a 3D OS NAND memory, a vertically-stackable 2Tr-1C memory having CAAC-IGZO FETs. Potentially, this memory not only enjoys main features of NAND flash such as high density and non-volatility, but also achieves a DRAM-like endurance. In this study, we evaluated our novel memory architecture with TCAD Sentaurus produced by Synopsys.The cross section, circuit diagram, and 3D overall structure of the memory cell are shown in Fig. 1(a), Fig. 1(b), and Fig. 1(c), respectively. The 3D OS NAND has a memory cell architecture in which a pair of vertically-positioned transistors on the A-A' plane is connected in series to another pair in the Z-axis direction. Taking advantage of extremely-low off-leakage current of CAAC-IGZO FET, the memory cell is composed of only a switching CAAC-IGZO FET and a MIM capacitor. The timing chart of a string of four memory cells connected in the Z-axis direction is shown in Fig. 1(d). Write operation is performed by sequentially lowering the voltage of WG from the bottom with respect to the Z-axis direction, and read operation is performed by lowering the voltage of CG of the memory cell being read. The retention properties of memory cells to which a checker pattern is written are shown in Fig. 1(e). The device simulation indicates a possibility that a memory cell composed of only an CAAC-IGZO FET and a MIM capacitor achieves a retention time of 109 sec or longer. In this paper, we propose a novel memory architecture with CAAC-IGZO FET by discussing the overview of 3D OS NAND and its write and read performance. Fig. 1(a) Cross section of 3D OS NAND memory cell, (b) circuit diagram of 3D OS NAND memory cell, (c) 3D structure of 3D OS NAND, (d) timing chart of 3D OS NAND, and (d) retention properties of 3D OS NAND Figure 1

Optoelectronic properties of coexisting InGaZnO4 structures

Indium gallium zinc oxides (IGZO) have been developed for thin-film transistor technologies. In this work, we analyze the fundamental properties of crystalline InGaZnO4, considering all possible Ga/Zn atomic distribution patterns. Using the hybrid Hartree-Fock density functional approach, the most stable configurations are identified. The simulations reveal that the considered configurations are indirect band-gap semiconductors with highly dispersive conduction bands (CB) and very flat valence bands (VB). Thereby, the electron effective masses are light, contrary to the heavy hole effective masses. This implies a good electron mobility and suppressed hole mobility, and consequently a low off-state current that minimizes the power consumption in future InGaZnO4-based transistors. Coexistence of different configurations is not an issue for InGaZnO4 since they all present very similar optoelectronic properties.

Electronic and optical properties of InSb quantum dots from pseudopotential calculation

The electronic and optical features of InSb spherical quantum dots have been investigated by a pseudopotential approach as a function of their radius taken in the range 1-10 nm. The direct- and indirect band gaps along with the electron and heavy hole effective masses are all found to be diminished as the quantum dot radius is increased. However, the refractive index, the static- and high frequency dielectric constant as well as the transverse effective charge are shown to be augmented by increasing the quantum dot radius. It is noted that the quantum confinement is of great impact on all the studied quantities for quantum dot radius below 6 nm. This could result in more opportunities to obtain desired optoelectronic properties that cannot be obtained in the bulk InSb materials.

Phonon and Polaron properties in InSb spherical quantum dots

The size-dependent energy gaps, electron and heavy hole effective masses, phonon frequencies and polaron related parameters in InSb spherical quantum dots are investigated. The calculations are performed using a pseudopotential approach. Good agreement is obtained between our results and those of the literature for bulk InSb. When proceeding from bulk to nano-scale, all studied properties are found to be changed significantly. This is attributed to the quantum confinement effect.

Two-Dimensional 111-TypeIn-Based Halide PerovskiteCs3In2X9(X=Cl,Br,I)with Optimal Band Gap for Photovoltaics and Defect-Insensitive Blue Emission

Despite rapid progress in the power-conversion efficiency of $\mathrm{Pb}$-based perovskite solar cells, both the long-term instability and $\mathrm{Pb}$ toxicity are still the main challenges for their commercial applications. Here, by first-principles $GW$ calculations, we find three kinds of two-dimensional (2D) 111-type $\mathrm{Pb}$-free $\mathrm{In}$-based halide perovskites of the form ${\mathrm{Cs}}_{3}{\mathrm{In}}_{2}{X}_{9}\phantom{\rule{0.2em}{0ex}}(X=\mathrm{Cl},\mathrm{Br},\mathrm{I})$ as promising alternatives to the star material ${{\mathrm{CH}}_{3}{\mathrm{NH}}_{3}\mathrm{Pb}\mathrm{I}}_{3}$ (${\mathrm{MA}\mathrm{Pb}\mathrm{I}}_{3}$) because of the following excellent electronic, optical, and transport properties: (i) The 2D $\mathrm{In}$-based halide perovskites are environmentally friendly lead-free materials. (ii) Compared with $\mathrm{MA}\mathrm{Pb}{X}_{3}$, they have greater structural stability. (iii) As energetic photovoltaic materials, 2D ${\mathrm{Cs}}_{3}{\mathrm{In}}_{2}{\mathrm{I}}_{9}$ perovskites are direct-band-gap semiconductors with optimal band gaps from 1.25 eV (trilayer) to 1.47 eV (monolayer). (iv) The 2D ${\mathrm{Cs}}_{3}{\mathrm{In}}_{2}{X}_{9}$ perovskites have ideal band structures for solid-state lighting with a wide direct-optical-band-gap range (approximately 0.94--3.54 eV), covering the whole visible-light region, and light electron (heavy hole) effective mass, which will directly enhance the defect-insensitive emission efficiency due to the localization of holes. Particularly, ${\mathrm{Cs}}_{3}{\mathrm{In}}_{2}{\mathrm{Br}}_{x}{\mathrm{Cl}}_{9\ensuremath{-}x}$ has a suitable direct optical band gap for highly desired blue emission. (v) The absorption coefficient of ${\mathrm{Cs}}_{3}{\mathrm{In}}_{2}{X}_{9}$ is up to $7\ifmmode\times\else\texttimes\fi{}{10}^{4}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, which is between that of $\mathrm{Ga}\mathrm{As}$ (${10}^{4}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$) and that of ${\mathrm{MA}\mathrm{Pb}\mathrm{I}}_{3}$ (${10}^{5}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$). (vi) The estimated power-conversion efficiency in ${\mathrm{Cs}}_{3}{\mathrm{In}}_{2}{\mathrm{I}}_{9}$ reaches 28%, which is close to that of ${\mathrm{MA}\mathrm{Pb}\mathrm{I}}_{3}$ (30%). These findings pave a way for designing nontoxic, stable, and high-performance photovoltaic and light-emitting devices.

Electronic properties of monoclinic (InxGa1-x)2O3 alloys by first-principle

We report on the electronic properties of β-(InxGa1-x)2O3 alloys with different In-content up to 18.75% using density functional theory (DFT) calculations. The effect of In-content on the band structures as well as the crystal structures of β-(InxGa1-x)2O3 alloys is presented and discussed. Our analysis shows that β-(InxGa1-x)2O3 alloys exhibits indirect gap property, with the band gap reducing from 4.817 eV to 4.422 eV when the In-content increases up to 18.75%. The bandgap energy corresponds to the wavelength region extending from 255 to 280 nm, which implies the possibility for β-(InxGa1-x)2O3 alloys to be applied in the deep UV photodetectors. The electron and heavy hole effective masses are also obtained for the first time based on the band edge dispersions of the β-(InxGa1-x)2O3 materials. Additionally, the effect of band parameters on the impact ionization processes using β-(InxGa1-x)2O3 materials are analyzed. Our new insight regarding the electronic properties indicate the potential of β-(InxGa1-x)2O3 alloys in deep ultraviolet photodetector applications.

Electron states, effective masses and transverse effective charge of InAs quantum dots

The electron energy levels, direct energy band gaps, electron and hole effective masses as well as the transverse effective charge of InAs spherically shaped quantum dots have been studied as a function of the quantum dot radius considered as varying from 1 to 10 nm. The direct energy band-gap as well as the electron and heavy hole effective masses decrease non-linearly with increasing the quantum dot radius. Nevertheless, the transverse effective charge is found to increase with increasing the quantum dot radius. It is concluded that the quantum confinement has a strong influence on all the studied physical quantities for quantum dot radius below 6 nm. The results of the present contribution show that more opportunities can be offered to tailor desired optoelectronic properties surpassing those presented by bulk InAs materials.

Energy gaps, effective masses and ionicity of AlxGa1−xSb ternary semiconductor alloys

A pseudopotential calculation of the electronic structure of Al[Formula: see text]Ga[Formula: see text]Sb ternary alloys in the zinc-blende structure has been performed. The compositional dependence of energy gaps, electron and heavy hole effective masses and ionicity of the material system of interest have been examined and discussed. Special attention has been given to the effect of the alloy disorder on the direct ([Formula: see text]–[Formula: see text]) bandgap energy. It is found that all features of interest vary monotonically with increasing the Al concentration [Formula: see text]. Besides, bandgap bowing parameters and extent of the direct-to-indirect bandgap transition have been determined. Our findings agree generally well with the data reported in the literature. Trends in ionicity are found to be consistent with the Phillips ionicity scale.

Ordered and Disordered Phases in Mo1\u2212xWxS2 Monolayer

With special quasirandom structure approach and cluster expansion method combined with first-principle calculations, we explore the structure and electronic properties of monolayer Mo1−xWxS2 alloy with disordered phase and ordered phase. The phase transition from ordered phase to disordered phase is found to happen at 41 K and 43 K for x = 1/3 and x = 2/3, respectively. The band edge of VBM is just related with the composition x, while the band edge of CBM is sensitive to the degree of order, besides the concentration of W. Near the CBM band edge, there are two bands with the Mo-character and W-character, respectively. It is found that in disordered phase the Mo-character band is mixed with the W-character band, while the opposite happens in ordered phase. This result leads to that the splitting of two bands near CBM in ordered phase is larger than in disordered phase and gives rise to the smaller band gap in ordered phase compared to the disordered phase. The electron effective mass in ordered phase is smaller than in disordered phase, while the heavy hole effective mass in ordered phase is larger than that in disordered phase.

Pseudopotential calculations of AlSb under pressure

The dependence on hydrostatic pressure of the electronic and optical properties of zinc-blende AlSb semiconducting material in the pressure range of 0–20kbar has been reported using a pseudopotential approach. At zero pressure, our findings showed that the electron and heavy hole effective masses are 0.11 and 0.38m0, respectively. Moreover, our results yielded values of 3.3289 and 11.08 for refractive index and high frequency dielectric constant, respectively. These results are found to be in good accord with experiment. Upon compression, all physical parameters of interest showed a monotonic behavior. The pressure-induced energy shifts for the optical transition related to band-gaps indicated that AlSb remains an indirect (Г-X) band-gap semiconductor at pressures from 0 to 20kbar. The trend in all features of interest versus pressure has been presented and discussed. It is found that the lattice parameter is reduced from 0.61355 to 0.60705nm when pressure is raised from 0 to 20kbar. The present investigation may be useful for mid-infrared lasers applications, detectors and communication devices.

Structural and electronic properties of wurtzite BxAl1–xN from first‐principles calculations

The structural and electronic properties of wurtzite BxAl1−xN (0 ≤ x ≤ 1) are studied using density functional theory. The change of lattice parameters with increased B composition shows small bowing parameters and thus slightly nonlinearity. The bandgap exhibits strong dependence on the B composition, where transition from direct to indirect bandgap occurs at a relatively low B composition (x ∼ 0.12) is observed, above which the bandgap of BxAl1−xN maintained indirect, thus desirable for low‐absorption optical structures. The Γv‐Ac and Γv‐Kc indirect bandgaps are dominant at lower and higher B compositions, respectively. Density of states (DOS) of the valence band is susceptible to the B incorporation. Strong hybridization of Al, B, and N in p‐states leads to high DOS near the valence band maximum. The hybridization of Al and B in s‐states at lower B compositions and p‐states of B at higher B compositions give rise to high DOS near lower end of the upper valence band. Charge density analysis reveals the B‐N chemical bond is more covalent than the Al‐N bond. This will lead to more covalent crystal with increasing B composition. Dramatic change of the heavy hole effective mass is found due to significant curvature increase of the band by minor B incorporation.

Theoretical study of the carrier effective mass in diluted III-N-V semiconductor alloys by using 10-band k.p model

The dependence of carrier effective mass of GaNxAs1−x, InNx P1−x, InNxAs1−x, and InNxSb1−x alloys on nitrogen content is investigated using a 10-band k.p model. The electron effective mass me⁎ at the bottom of conduction band in GaNxAs1−x and InNxP1−x exhibits a gradual increase as a function of N concentration in the range 0−1% and a decrease of x value between 1 and 5%. However, the behavior of me⁎ in InNxAs1−x and InNxSb1−x shows a strong decrease in all studied x-range. Our results are compared to the available data reported in the literature. On the other hand, contrary to heavy-hole effective mass mhh⁎, the light-hole effective mass mlh⁎ in all studied alloys is significantly affected by nitrogen states, which modify the non-parabolicity of the LH band. The modification of the carrier effective mass affects the transport properties of the III-N-V alloys.