InAs/GaSb超晶格和M结构超晶格能带结构研究

本文通过k·p方法研究了传统InAs/GaSb超晶格和M结构超晶格的能带结构。首先,计算了不同周期厚度的InAs/GaSb超晶格的能带结构,得到用于长波超晶格探测器吸收层的周期结构。然后,计算了用于超晶格长波探测器结构的M结构超晶格的能带结构,并给出长波InAs/GaSb超晶格与M结构超晶格之间的带阶。最后,基于能带结构,计算出长波超晶格与M结构超晶格的态密度,进而得出的载流子浓度（掺杂浓度）与费米能级的关系。这些材料参数可以为超晶格探测器结构设计提供基础。     

Investigation of negative differential resistance phenomena inGaSb/AlSb/InAs/GaSb/AlSb/InAs structures

The negative differential resistance (NDR) phenomena were observed in GaSb/AlSb/InAs/-GaSb/AlSb/InAs resonant interband tunnel structures. Electrons have resonantly achieved interband tunneling through the InAs/GaSb broken-gap quantum well. The InAs well width causes significant variations of the peak current density and NDR behaviors. The peak current density varies exponentially with the AlSb barrier thickness. The multiple NDR behavior was observed with appropriate InAs well and AlSb barrier thicknesses, e.g., 30 Å thick AlSb barrier and 240 Å wide InAs well. Only single negative resistance has, otherwise, been seen. The three-band model was used to interpret the effect of the InAs well and AlSb barrier on the current-voltage characteristics of GaSb/AlSb/InAs/GaSb/AlSb/InAs structures     

Persistent photoconductivity in InAs/AlSb heterostructures with double quantum wells

Effects of persistent photoconductivity in InAs/AlSb heterostructures with the cap GaSb layer and two-dimensional electron gas in the InAs double quantum wells at T = 4.2 K are studied. From Fourier analysis of the Shubnikov-de Haas oscillations, electron concentrations in each quantum well are determined at various wavelengths of illumination and pronounced asymmetry of the structure caused by the built-in electric field is demonstrated explicitly. The self-consistent calculations of the energy profile of the double quantum well are performed and the concentrations of ionized donors on both sides of the well are determined, which provided concretization of the previously suggested mechanism of bipolar persistent photoconductivity in such structures.     

A complementary heterostructure field effect transistor technologybased on InAs/AlSb/GaSb

A complementary heterojunction field effect transistor technology based on the InAs/AlSb/GaSb system is proposed. The structure is formed by the vertical integration of InAs n-channel and GaSb p-channel HFET devices. The superior transport properties of electrons in InAs and holes in GaSb and their band offsets to AlSb or AlSbAs yield devices with transconductances much greater than AlGaAs/GaAs n- and p-channel HFETs. It is shown that a complementary circuit fabricated from these devices could provide room-temperature performance up to six times greater than that predicted for AlGaAs/GaAs complementary circuits     

Negative differential resistance in InAs/GaSb single-barrier heterostructures

The authors report the first observation of negative differential resistance (NDR) at room temperature in InAs/GaSb barrier heterostructures, where the conduction band in InAs lies below the GaSb valence band.<>     

Intersubband optical transitions in InAs/GaSb quantum wells

The effects of electron-hole hybridization, structural asymmetry with respect to spatial inversion, bulk asymmetry, and the interface Hamiltonian upon the optical absorption of linearly polarized light in broken-gap heterostructures are treated with the use of the eight-band Burt-Foreman envelope function theory and the self-consistent solution of the Schrödinger equation and the Poisson equation. The broken-gap heterostructures, specifically, the AlSb/InAs/GaSb/AlSb quantum wells, grown along the [001] direction offer promise for the fabrication of various devices. The anisotropy induced by the above-listed effects in the dispersion relations of size-quantization subbands and in optical matrix elements is established. The bulk asymmetry and the interface Hamiltonian modify the selection rules for intersubband transitions on the exposure of the structures to linearly polarized light. As a result, the initially forbidden spin-flip transitions are allowed. This brings about a large number of peaks in the dependence of the absorption coefficient on the photon energy, if the light polarization vector is directed along the axis of growth of the structure. If the light polarization vector is in the plane of the structure, the bulk asymmetry and the interface Hamiltonian induce strong longitudinal anisotropy of the absorption due to the hybridization of states with oppositely oriented spins. These effects are comprehensively studied for optical transitions involving hybridized electron-hole states in quantum wells grown on InAs.     

四层结构模型下的InAs/GaSb超晶格材料能带计算

在包络函数近似下采用K.P理论计算了InAs/Ga(In) Sb Ⅱ类超晶格材料的能带结构.同时,计算了超晶格材料的电子有效质量和空穴有效质量,以及不同的结构对应的吸收系数.在此基础上使用了考虑包括界面在内的四层超晶格模型进行能带计算,并与实验结果进行比较,超晶格材料响应截止波长的结果更为接近实验值.不同的界面也会引起能带结构的变化,带来截止波长的变化.对于应变补偿的InAs/GaSb超晶格材料,非对称InSb界面相比对称界面有更大的截止波长.     

四层结构模型下的InAs/GaSb超晶格材料能带计算

在包络函数近似下采用K.P理论计算了InAs/Ga(In)Sb II类超晶格材料的能带结构.同时, 计算了超晶格材料的电子有效质量和空穴有效质量, 以及不同的结构对应的吸收系数.在此基础上使用了考虑包括界面在内的四层超晶格模型进行能带计算, 并与实验结果进行比较, 超晶格材料响应截止波长的结果更为接近实验值.不同的界面也会引起能带结构的变化, 带来截止波长的变化.对于应变补偿的InAs/GaSb超晶格材料, 非对称InSb界面相比对称界面有更大的截止波长.     

InAs/GaSb II型超晶格红外探测器的研究进展

InAs/GaSb Ⅱ型超晶格材料理论上性能优于HgCdTe、InSb等红外探测材料,基于成熟的Ⅲ-V族化合物材料与器件工艺,使得Ⅱ型超晶格材料容易满足均匀大面阵、双色或多色集成等红外探测器的要求,因而InAs/GaSb Ⅱ型超晶格材料将逐步替代HgCdTe、InSb等材料成为第三代红外探测器的首选材料。本文阐述了InAs/GaSb超晶格红外探测器的基本原理、以及材料生长和器件结构,并对其研究进展进行了综述性介绍。     

(111)方向的InAs/GaSb超晶格材料电子结构的杂化泛函计算

采用电子密度泛函理论方法计算了一系列（111）方向的InAs/GaSb超晶格的电子结构和能带结构。将杂化泛函的计算结果与普通密度泛函方法的计算结果进行了比较。Heyd-Scuseria-Ernzerhof (HSE)杂化与对固体修正的Perdew-Burke-Ernzerhof (PBE)近似结合的杂化泛函显示了较传统PBE方法和若干其他杂化泛函更符合实验数据的结果。采用该方法研究了InAs/GaSb超晶格的带隙随超晶格周期厚度以及InAs/GaSb比例变化的规律。其结果与以往实验结果符合很好。这些结果表明HSE-PBEsol方法对于估计InAs/GaSb超晶格的电子性质适用。     

Intersubband Raman scattering in InAs/AlSb quantum wells

Raman spectroscopy has been used to study intersubband transitions in InAs/AlSb single quantum wells grown by molecular-beam epitaxy on (100) GaAs substrates using strain-relaxed AlSb or GaSb buffer layers. From the measured energies of the coupled longitudinal optical phonon-intersubband plasmon modes the single particle transition energies between the first and second confined electron subbands were deduced as a function of the width of the pseudomorphically strained InAs well. Subband spacings calculated including the effects of strain and nonparabolicity were found to be in agreement with the experimental transition energies. For a given well width, the two-dimensional electron concentration deduced from the Raman measurements was found to be lower than the concentration measured in the dark by Hall effect, but showed a significant increase with increasing optical excitation intensity.     

High-transconductance delta-doped InAs/AlSb HFETs with ultrathinsilicon-doped InAs quantum well donor layer

Modulation-doping of InAs/AlSb quantum wells generally requires the use of chalcogenide donor impurities because silicon, the usual donor of choice in MBE, displays an amphoteric behavior in antimonide compounds. In this letter, we demonstrate the use of an ultrathin 9 Å silicon doped InAs well to delta-dope the current-carrying InAs channel of an InAs/AlSb heterostructure field-effect transistor (HFET). Using this new approach, we have fabricated delta-doped 0.6-μm gate InAs/AlSb HFETs with a measured extrinsic transconductance of 800 mS/mm at V_DS=0.8 V, a cutoff frequency f_T=60 GHz (F_MAX=87 GHz), and well-behaved I-V curves. HFET's with a 2-μm gatelength also feature very high transconductances in the 700-800 mS/mm range at V_DS=1.5 V. The present work eliminates the requirement for chalcogenide compound donor sources to delta-dope InAs/AlSb quantum wells by allowing the use of silicon in the fabrication of high-performance InAs/AlSb HFET's     

Exchange-induced band hybridization in InAs/GaSb based type II and broken-gap quantum well systems

We demonstrate theoretically that the many-body effect such as exchange interaction can cause the hybridization of the electron and hole dispersion relations in InAs/GaSb based type II and broken-gap quantum well (QW) systems. As a result, a terahertz mini-gap at the anti-crossing points of the conduction and valence bands can be induced by the inter-layer electron–hole coupling via the Coulomb interaction. It is shown that the many-body effect is another important source of the hybridization of the dispersion relations in InAs/GaSb QW systems.     

分子束外延InAs/GaSb II类超晶格材料

InAs/GaSb II类超晶格由于具有独特的能带结构和良好的材料性能被认为是第三代红外探测器的首选,近年来被广泛研究,并取得快速发展。分子束外延能够精确控制材料界面与周期厚度,是超晶格材料生长的主流手段。利用分子束外延技术在GaSb衬底上分别生长了中波、长波超晶格材料,并对所生长的超晶格材料的性能进行了全面表征,最后用制备的面阵器件验证了该材料的性能。}     

Unintentional As incorporation in molecular beam epitaxially grown InAs/AlSb/GaSb heterostructures

We investigate unintentional arsenic incorporation during the molecular-beam epitaxial growth of AlSb/InAs/GaSb heterostructures, using both a standard As₄ evaporation cell and a valved arsenic cracker. When a standard As₄ cell is used, unintentional arsenic concentrations as large as 10–20% can be incorporated into the AlSb and GaSb layers from the background As ambient in the growth chamber, both during growth and on stationary surfaces. This incorporation can be controlled and suppressed with the use of a valved As cracker. Suppression of the As background substantially improves the electrical transport properties of AlSb/InAs/AlSb quantum well structures.     

Modeling InAs/GaSb and InAs/InAsSb Superlattice Infrared Detectors

InAs/GaSb and InAs/InAsSb type II superlattices have been proposed as promising alternatives to HgCdTe for the photon-absorbing layer of an infrared detector. When combined with a barrier layer based on an InAs/AlSb superlattice or an AlSbAs alloy, respectively, they can be used to make diffusion-limited “barrier” detectors with very low dark currents. In this work we compare theoretical simulations with experimental bandgap and photoabsorption data for such superlattices, spanning from the mid to the long-wave infra-red (2.3–12 μm). The spectral response of detectors based on these materials is also simulated. The simulations are based on a version of the k · p model developed by one of the authors, which takes interface contributions and bandgap bowing into account. Our results provide a way of assessing the relative merits of InAs/GaSb and InAs/InAsSb superlattices as potential detector materials.     

Mid-infrared absorption by short-period InAs/GaSb type II superlattices

We present a theoretical study on optical properties of short-period InAs/GaSb type-II superlattices (SLs) which can serve for mid-infrared (MIR) detection. The miniband structure of such SLs is calculated using the Kronig–Penney model. On the basis of the energy-balance equation derived from the Boltzmann equation we calculate the optical absorption coefficient. The obtained results agree with recent experimental findings. Moreover, the dependence of the MIR absorption in InAs/GaSb type-II SLs on temperature and well-widths are examined.     

Spectra of persistent photoconductivity in InAs/AlSb quantum-well heterostructures

Persistent photoconductivity at T = 4.2 K in AlSb/InAs/AlSb heterostructures with two-dimensional (2D) electron gas in InAs quantum wells is studied. Under illumination by IR radiation (?ω = 0.6–1.2 eV), positive persistent photoconductivity related to the photoionization of deep-level donors is observed. At shorter wavelengths, negative persistent photoconductivity is observed that originates from band-to-band generation of electron-hole pairs with subsequent separation of electrons and holes by the built-in electric field, capture of electrons by ionized donors, and recombination of holes with 2D electrons in InAs. It is found that a sharp drop in the negative photoconductivity takes place at ?ω > 3.1 eV, which can be attributed to the appearance of a new channel for photoionization of deep-level donors in AlSb via electron transitions to the next energy band above the conduction band.     

Vertical transport in type-II heterojunctions with InAs/GaSb/AlSb composite quantum wells in a high magnetic field

Vertical transport in type-II heterojunctions with a two-barrier AlSb/InAs/GaSb/AlSb quantum well (QW) grown by MOVPE on an n-InAs (100) substrate is investigated in quantizing magnetic fields up to B = 14 T at low temperatures T = 1.5 and 4.2 K. The width of the QWs is selected from the formation condition of the inverted band structure. Shubnikov–de Haas oscillations are measured at two orientations of the magnetic field (perpendicular and parallel) relative to the structure plane. It is established that conduction in the structure under study is occurs via both three-dimensional (3D) substrate electrons and two-dimensional 2D QW electrons under quantum limit conditions for bulk electrons (B > 5 T). The electron concentrations in the substrate and InAs QW are determined. The g-factor for 3D carriers is determined by spin splitting of the zero Landau level. It is shown that the conductance maxima in a magnetic field perpendicular to the structure plane and parallel to the current across the structure in fields B > 9 T correspond to the resonant tunneling of 3D electrons from the emitter substrate into the InAs QW through the 2D electron states of the Landau levels.     

256×256 focal plane array midwavelength infrared camera based on InAs/GaSb short-period superlattices

An infrared camera based on a 256×256 focal plane array (FPA) for the second atmospheric window (3–5 μm) has been realized for the first time with InAs/GaSb short period superlattices (SLs). The SL detector structure with a broken gap type-II band alignment was grown by molecular beam epitaxy on GaSb substrates. Effective bandgap and strain in the superlattice were adjusted by varying the thickness of the InAs and GaSb layers and the controlled formation of InSb-like bonds at the interfaces. The FPAs were processed in a full wafer process using optical lithography, chemical-assisted ion beam etching, and conventional metallization technology. The FPAs were flip-chip bonded using indium solder bumps with a read-out integrated circuit and mounted into an integrated detector cooler assembly. The FPAs with a cut-off wavelength of 5.4 μm exhibit quantum efficiencies of 30% and detectivity values exceeding 10¹³ Jones at T=77 K. A noise equivalent temperature difference (NETD) of 11.1 mK was measured for an integration time of 5 ms using f/2 optics. The NETD scales inversely proportional to the square root of the integration time between 5 ms and 1 ms, revealing background limited performance. Excellent thermal images with low NETD values and a very good modulation transfer function demonstrate the high potential of this material system for the fabrication of future thermal imaging systems.