Temperature-dependent optical properties of wurtzite InN

Optical properties and carrier recombination dynamics of a series of InN epilayers, with varying free electron concentrations, grown by molecular beam epitaxy were studied by steady-state photoluminescence (PL) and time-resolved differential transmission spectroscopy. At room temperature strong PL around 0.7 eV was observed. Temperature-dependent PL measurements show a redshift of the peak energy and a linear increase of the emission linewidth with temperature. Furthermore, our results demonstrate that room temperature carrier lifetimes are inversely proportional to the free electron concentrations for theses samples. Carrier lifetime as long as 1.3 ns was observed in the best quality sample, indicating a highly improved crystalline quality.     

Ab-initio study of electronic and optical properties of InN in wurtzite and cubic phases

We have performed systematic first principle calculations for the electronic and optical properties of a narrow band gap semiconductor InN in cubic and wurtzite phases by ‘state-of-the-art’ DFT calculations within generalized gradient approximation (GGA) and Engel-Vosko's corrected generalized gradient approximation (EVGGA) using full potential linear augmented plane wave (FPLAPW) method as implemented in WIEN2k code. The total energy for the wurtzite phase of InN was found to be smaller by 0.0184 Ry/molecule by cubic phase which confirms the greater stability of the wurtzite structure than the cubic one. Band structure, effective masses, density of states, valence charge densities, and dielectric functions are computed and presented in detail. The critical points are extracted out of calculated dielectric function, compared with available measured data and are explained in terms of transitions occurred in the band structure along different symmetry and antisymmetry lines. The valence band maxima and conduction band minima are strongly dominated by N-2p states and located at the Γ-symmetrical line which predicts its direct band gap nature in both phases.     

Anisotropy of the dielectric function for wurtzite InN

A -plane InN film grown by molecular beam epitaxy on -plane sapphire substrate with an AlN nucleation layer and a GaN buffer was studied by spectroscopic ellipsometry. The data analysis yields both the ordinary and the extraordinary dielectric tensor components perpendicular and parallel to the optical axis, respectively. Strong optical anisotropy is demonstrated over the whole energy range from 0.72 up to 9.5 eV. The line shapes of the tensor components and the polarisation behaviour are in very good agreement with the results of recently published band structure and dielectric function calculations. Above the band gap, five van Hove singularities are evidenced from the ordinary component, while three are resolved from the extraordinary part. The polarisation dependence below 1 eV can be interpreted in terms of optical selection rules for three energetically split valence bands around the Γ-point of the Brillouin zone, similar to the well known behaviour of wurtzite GaN. This emphasises a band gap of hexagonal InN of about 0.7 eV.     

Nonlinear dynamics in wurtzite InN diodes under terahertz radiation

We carry out a theoretical study of nonlinear dynamics in terahertz-driven n⁺nn⁺ wurtzite InN diodes by using time-dependent drift diffusion equations. A cooperative nonlinear oscillatory mode appears due to the negative differential mobility effect, which is the unique feature of wurtzite InN aroused by its strong nonparabolicity of the Γ₁ valley. The appearance of different nonlinear oscillatory modes, including periodic and chaotic states, is attributed to the competition between the self-sustained oscillation and the external driving oscillation. The transitions between the periodic and chaotic states are carefully investigated using chaos-detecting methods, such as the bifurcation diagram, the Fourier spectrum and the first return map. The resulting bifurcation diagram displays an interesting and complex transition picture with the driving amplitude as the control parameter.     

Nonlinear dynamics in wurtzite InN diodes under terahertz radiation

We carry out a theoretical study of nonlinear dynamics in terahertz-driven n+ nn+ wurtzite InN diodes by using time-dependent drift diffusion equations.A cooperative nonlinear oscillatory mode appears due to the negative differential mobility effect,which is the unique feature of wurtzite InN aroused by its strong nonparabolicity of the Γ 1 valley.The appearance of different nonlinear oscillatory modes,including periodic and chaotic states,is attributed to the competition between the self-sustained oscillation and the external driving oscillation.The transitions between the periodic and chaotic states are carefully investigated using chaos-detecting methods,such as the bifurcation diagram,the Fourier spectrum and the first return map.The resulting bifurcation diagram displays an interesting and complex transition picture with the driving amplitude as the control parameter.     

Electronic,optical, and mechanical properties of BN,AlN, and InN with zinc-blende structure under pressure

In this work, the electronic, optical, and mechanical properties of BN, AlN, and InN under the action of pressure are calculated. For each of these compounds, the energy band structure, band gaps(E~L_g, E~Γ_g, E~X_g), refractive index(n),dielectric constants(ε_∞, ε_0), elastic constants(C_11, C_12, C_44), and relevant parameters such as bulk(B_u), shear(S_h), and Young's(Y_0) moduli are studied, and other important parameters such as bond-stretching(α), bond-bending(β) force constant, internal-strain parameter(ζ), effective charges(e~*_T, Z~*), anisotropy factor(I_s), Poisson's ratio(P_o), Cauchy ratio(C_a), the ductility index(μ_D), and linear compressibility(C0_) are also calculated. The effects of pressure on all studied properties are investigated. Our results are in good agreement with the available experimental and theoretical data for BN,AlN, and InN.     

Giant growth-plane optical anisotropy in wurtzite InN/GaN disk-in-wire structures

Using a combination of valence force-field molecular mechanics, 20-band sp³d⁵s^∗ atomistic tight-binding approach, and appropriate post-processing tools, we have studied the origin and nature of optical polarization anisotropy in semiconducting GaN/InN/GaN disk-in-wire structures having wurtzite crystal symmetry and varying InN disk thicknesses. True atomistic symmetry due to the presence of strong internal fields, coupled with quantum mechanical size quantization effects, results in unconventional characteristics in the electronic structure related to non-degeneracy in the excited P states and rotation (symmetry lowering) in the wavefunctions. The optical polarization ratio projected on the XY (growth) plane and, in particular, the transition rates have been shown to be strongly dependent on the crystal internal fields and the thickness of the InN disk.     

不同价态Mn掺杂InN电子结构、磁学和光学性质的第一性原理研究

采用密度泛函理论体系下的广义梯度近似GGA+U平面波超软赝势方法,在构建了纤锌矿结构的InN超胞及三种不同有序占位Mn~(2+),Mn~(3+)价态分别掺杂InN超胞模型,并进行几何优化的基础上,计算了掺杂前后体系的电子结构、能量以及光学性质.计算结果表明:Mn掺杂后体系总能量和形成能降低,稳定性增加,并在费米能级附近引入自旋极化杂质带,体系具有明显的自旋极化现象.掺杂不同价态的Mn元素对体系电子结构和磁学性质产生了不同的影响.电子结构和磁性分析表明掺杂体系的磁性来源于p-d交换机制和双交换机制的共同作用,Mn~(3+)价态掺杂有利于掺杂体系的居里温度达到室温以上.与未掺杂InN相比,不同价态Mn元素掺杂后体系的静态介电函数显著增大,掺杂体系介电函数虚部和吸收光谱在低能区域出现了较强的新峰,分析认为这些新峰主要来自与费米能级附近自旋极化杂质带相关的跃迁.     

厚度对MOCVD生长InN薄膜位错特性与光电性质的影响

研究了金属有机物化学气相沉积法制备的不同厚度InN薄膜的位错特性与光电性质.基于马赛克微晶模型,通过X射线衍射非对称面摇摆曲线测量,拟合出样品刃型位错密度分别为4.2×10¹⁰cm^-2和6.3×10¹⁰cm^-2,并发现样品的微晶扭转角与位错密度随薄膜厚度增加而减小.通过室温霍尔效应测量得到样品载流子浓度分别为9×10¹⁸cm^-3和1.2×10¹⁸cm关键词： 氮化铟 位错 载流子起源 局域态     

The structural, elastic and thermodynamical properties of zinc-blend structure InN from first principles

A theoretical study of the structural, elastic and thermodynamic properties of the cubic zinc-blende (ZB) structure InN are presented in this paper by performing first principles calculations within local density approximation. The values of lattice constant, bulk modulus and its pressure derivatives and elastic constants are in excellent agreement with the available experimental data and other theoretical results. It is found that the ZB structure InN should be unstable above 20 GPa mechanically. The pressure and temperature dependencies of the bulk modulus, the heat capacity and the thermal expansion coefficient and the entropy S, as well as the Grüneisen parameter are obtained by the quasi-harmonic Debye model in the ranges of 0-1500 K and 0-25 GPa.     

InN的光致发光特性研究

研究了利用金属有机化学气相淀积生长的氮化铟薄膜的光致发光特性. 由于氮化铟本身具有很高的背景载流子浓度, 费米能级在导带之上, 通过能带关系图以及相关公式拟合光致发光图谱可以得到生长的氮化铟的带隙为0.67 eV, 并且可以计算出相应的载流子浓度为n=5.4×10¹⁸ cm^-3, 从而找到了一种联系光致发光谱与载流子浓度两者的方法. 另外通过测量变温条件下氮化铟的发光特性, 研究了发光峰位以及发光强度随温度的变化关系, 发现光致发光强度随温度的升高逐渐降低, 发光峰位随温度的升高只是红移, 并没有出现"S"形的非单调变化, 这种差异可能是由于光致发光谱的半高宽过高导致, 同时也可能与载流子浓度以及内建电场强度有关. 关键词： 氮化铟 金属有机化学气相淀积 光致发光 载流子浓度     

Effect of Pressure on Electronic Structures and Optical Properties of Rocksalt InN

用基于密度泛函理论的第一性原理结合广义梯度近似研究了高压下盐岩相InN的电子结构和光学性质. 计算得到的晶格常数与实验值非常吻合,并发现Γ和X的带隙随压力增加而增大,而带隙在L点却并不明显. 计算出Γ点的带隙的压力系数是44 meV/GPa. 讨论计算得到的InN的光学性质,结合能带结构和电子态密度.     

Photoluminescence properties of selectively grown InN microcrystals

We investigated the photoluminescence (PL) properties of regularly arranged N‐polar InN microcrystals with m ‐plane sidewall facets. We observed narrow PL emission at 0.678 eV with a linewidth of ～14 meV at 4 K and a clear band‐filling effect with increasing excitation power. We also observed a normal red shift of the PL peak energy as large as 51 meV (～150 nm) with increasing temperature from 4 to 300 K, similar to that observed for non‐degenerated semiconductors. The integrated PL intensity ratio I_300K/I_4K was measured to be 6.1%. These results indicate that InN microcrystals have a low residual carrier density and excellent optical properties without being adversely affected by surface electron accumulation, despite their relatively high surface area. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

单轴应变对氮化铟电子结构及光学性质的影响

采用密度泛函理论框架下的第一性原理平面波赝势方法,计算单轴应变下闪锌矿氮化铟的电子结构及光学性质.结果表明：施加应变会使带隙变窄.对于拉应变,随着应变增大带隙减小程度增大;对于压应变,随应变增大带隙减小程度减弱;且拉、压应变对带隙调控都是线性的.在能量区间4 eV~12 eV范围内施加应变时,氮化铟的吸收光谱发生红移,随拉应变程度增加,吸收光谱的红移进一步加大;随压应变增加,吸收光谱红移减弱;在该范围内,氮化铟的折射率、反射率随拉应变的增大而增加,随压应变增加减小;施加拉应变时能量损失函数峰值增大,施加压应变后能量损失函数峰值减小.通过施加单轴应变能有效调节氮化铟材料的电结构及光学性质.     

Exciton effects on the refractive index and optical absorption in wurtzite quantum wells via a fractional-dimensional space approach

The optical refractive index changes and absorption coefficients of quantum wells (QWs) are theoretically investigated with considering exciton effects within the framework of the fractional-dimensional space approach. The exciton wave functions and bound energies are obtained as a function of spatial dimensionality, and the dimension increases with the well width increasing. Then optical properties are obtained by using the compact-density matrix approach and an iterative method. Numerical results are presented for wurtzite ZnO/Mg_xZn_1−xO QWs. The calculated results show that the changes of refractive index and absorption coefficients are greatly enhanced due to the quantum confinement of exciton. And the smaller the QW width (dimension) is, the larger influence of exciton on the optical properties will be. Furthermore, the exciton effects make the resonant peaks move to a lower energy. In addition, the optical properties are related to the QW width, the incident optical intensity and carrier density.     

纤锌矿InGaN staggered量子阱中的激子态和光学性质

本文将基于有效质量近似下的变分法,理论研究了纤锌矿InGaN/GaN staggered量子阱中的激子态和光学性质.数值结果显示了InGaN量子阱中的量子尺寸和staggered受限垒对束缚于量子阱中的激子态和光学性质有着明显的影响.当阱宽增加时,量子受限效应减弱,激子结合能降低,带间发光波长增加.另一方面,当量子阱中staggered受限势增加时,量子受限效应增强,激子结合能升高,带间发光波长降低.本文的理论结果证明了可以通过调节staggered垒高和量子尺寸来调控纤锌矿InGaN staggered量子阱中的激子态和光学性质.     

纤锌矿InGaN staggered量子阱中的激子态和光学性质

本文将基于有效质量近似下的变分法,理论研究了纤锌矿InGaN/GaN staggered 量子阱中的激子态和光学性质。数值结果显示了InGaN量子阱中的量子尺寸和staggered受限垒对束缚于量子阱中的激子态和光学性质有着明显地影响。当阱宽增加时,量子受限效应减弱,激子结合能降低, 带间发光波长增加。另一方面,当量子阱中staggered受限势增加时,量子受限效应增强,激子结合能升高,带间发光波长降低。本文的理论结果证明了可以通过调节staggered垒高和量子尺寸来调控纤锌矿InGaN staggered 量子阱中的激子态和光学性质。     

Elastic properties and phonon dispersions of rhenium in hexagonal-close-packed structure under pressure from first principles

The elastic properties of the hexagonal-close-packed (hcp) structure rhenium (Re) and their behavior under pressure are investigated using the local density approximation (LDA) and the generalized gradient approximation (GGA). The obtained high pressure elastic constants are well consistent with previous theoretical date, while large discrepancies are found between theory and the high pressure experiments. The calculated isothermal bulk modulus B₀ (376 GPa for GGA and 389 GPa for LDA) and its initial pressure derivative (4.52 for LDA and 4.58 for GGA) compare favorably with the experimental values. Moreover, it is found that the value of c/a, B/G, Poisson's ratio, and B_c/B_a are virtually independent of pressure. We also performed calculation for phonon dispersions at high pressure. GGA in our calculation exhibits a same trend as the high pressure experimental curve.