Molecular beam epitaxial regrowth of InAs/AiSb/GaSb heterostructures on patterned substrates

The molecular beam epitaxial growth of InAs/AISb/GaSb heterostructures on GaSb epilayers patterned by dry etching is investigated. Faceted growth occurs at pattern edges, depending on the adatom species, crystallographic planes and growth parameters. The morphology of the overgrown structure is determined by (111), (110), and (100) Planes near the edges of the patterned stripes, oriented in the [011], [001 ], or [0 11] direction. During the regrowth of InAs, additional (311)A planes are formed at the edges for stripe orientations in the [0 11] direction. Utilizing the faceted growth behavior at pattern edges, resonant interband tunneling diodes with a room temperature peak-to-valley current ratio of 13 have been fabricated on patterned substrates. The results indicate that this approach has the potential of realizing advanced devices with higher complexity.     

InAs/InGaSb photodetectors grown on GaAs bonded substrates

The results of wafer fusion between GaAs and InP followed by transfer of an InGaAs film from the InP to GaAs substrate are presented in this paper. This technique of film transfer allowed the subsequent growth of epitaxial materials with approximately 7% lattice mismatch. Type-II InAs/GaInSb superlattices photodetectors of different designs have been grown by molecular beam epitaxy (MBE) on the alternative InGaAs/GaAs substrate and on standard GaSb substrates. Comparison between photodetectors grown on the two different substrates with nearly identical superlattice periods showed a shift in the cut-off wavelength. The superlattices grown on the alternative substrates were found to have uniform layers, with broader x-ray linewidths than superlattices grown on GaSb substrates.     

GaSb基的InAs/GaSbⅡ类超晶格背景载流子浓度的测量

高质量的InAs/GaSbⅡ类超晶格(SLs)材料生长在晶格匹配的GaSb衬底上,由于GaSb衬底具有良好的导电性,传统的霍尔测量难以直接得到外延超晶格材料的载流子浓度等电学参数,所以,如何准确地获得InAs/GaSb超晶格外延材料中的载流子浓度成为了研究人员关注的焦点之一。主要介绍了InAs/GaSbⅡ类超晶格背景载流子浓度测量的四种典型的方法:低温霍尔技术;变磁场霍尔技术以及迁移率谱拟合;衬底去除技术;电容-电压技术。并给出了各种方法的基本原理,评价了每种方法的优缺点。     

GaSb衬底上分子束外延生长的低温GaSb薄膜的低缺陷表面

本论文系统的研究了,随着GaSb薄膜生长温度的降低,V/III比的变化对薄膜低缺陷表面质量的影响。为了获得良好表面形貌的GaSb外延层,生长温度与V/III比均需要同时降低。当Sb源裂解温度为900℃时,生长得到低缺陷表面的低温GaSb薄膜的最佳生长条件是生长温度为在再构温度的基础上加60℃且V/III比为7.1。     

Molecular beam epitaxy growth of InAs-AlSb-GaSb interband tunneling diodes

This paper presents our studies of the growth of InAs/GaAs and GaSb/GaAs heterojunctions by molecular beam epitaxy and their applications in fabricating the InAs-AlSb-GaSb interband tunneling devices. The Hall effect and x-ray diffraction were used to determine the optimum growth conditions for the layers. In addition, the qualities of the InAs and GaSb epilayers, grown under their optimum conditions, were compared. The full width at half maximum (FWHM) from the x-ray diffraction for a GaSb epilayer is about 50 arcsec narrower than an InAs epilayer of the same thickness. The narrower FWHM and excellent surface morphology of the GaSb layer have led us to grow the polytype heterostructure on a p⁺-GaAs substrate using a p⁺-GaSb as the buffer layer. The polytype tunneling structures grown on GaAs substrates under these conditions show good negative differential resistance properties. Five different interband tunneling structures are compared and discussed in terms of their peak-current densities and peak-to-valley current ratios.     

(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。     

Study of Short- and Long-Term Effectiveness of Ammonium Sulfide as Surface Passivation for InAs/GaSb Superlattices Using X-Ray Photoelectron Spectroscopy

The surface quality of as-etched and ammonium sulfide [(NH₄)₂S]-treated samples of an indium arsenide/gallium antimonide (InAs/GaSb) superlattice structure were compared using x-ray photoelectron spectroscopy (XPS). After short exposure to the atmosphere following passivation, treated samples displayed a complete absence or significant reduction of native oxides compared with untreated samples, confirming better quality of surface passivation. However, extensive sulfidization was not observed, and after extended exposure, the native oxides reappeared on the treated surface, establishing the need for a capping layer for long-term passivation stability. The surface study provides definitive confirmation of previous results on electrical properties of photodetectors fabricated on InAs/GaSb superlattices.     

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.     

Self-organized anisotropic strain engineering: a new concept for quantum dot ordering

We have established a new concept for creating ordered arrays of quantum dots by self-organized epitaxy. The concept is based on self-organized anisotropic strain engineering of strained layer templates and is demonstrated for (In,Ga)As/GaAs superlattice structures on GaAs (100) and strain-induced (In,Ga)As growth instability on GaAs (311)B. The well-defined one- and two-dimensional networks of InAs quantum dots grown on top of these templates are of excellent structural and optical quality. This breakthrough, thus, allows for novel fundamental studies and device operation principles based on single and multiple carrier- and photon-, and coherent quantum interference effects.     

X-Ray Photoelectron Spectroscopy Study of Oxide Removal Using Atomic Hydrogen for Large-Area II–VI Material Growth

This study investigates using atomic hydrogen to clean GaSb (211)B and (111)B substrates as an alternative to thermal desorption under an Sb overpressure. X-ray photoelectron spectroscopy measurement verified the oxide removal on the atomic hydrogen-cleaned GaSb. Atomic force microscopy was used to characterize the surface morphologies of GaSb after atomic hydrogen cleaning with various conditions. All substrates investigated contained a high density of pits that became larger as higher deoxidation temperatures were used, with or without atomic hydrogen. Growth of homoepitaxial GaSb (100) and (211)B was used to compare stoichiometry changes with various oxide removal conditions, and growth effects on sequential epilayers.     

Novel InAs/(Al,Ga)Sb FET with direct gate-to-channel contact

A new type of FET has been fabricated in which the gate is in direct contact with the channel. There is no intervening charge separating layer. Instead, the separation of gate and channel carriers is achieved by using the staggered band alignment of InAs/(Al,Ga)Sb such that a p⁺ (Al,Ga)Sb gate layer is placed in direct contact with the n-type InAs channel. At 77 K the measured devices show both current gain and voltage gain, and a maximum transconductance of 500 mS/mm has been observed     

In-situ monitoring, structural, and optical properties of ultrathin GaSb/GaAs quantum wells grown by OMVPE

We present a study of the growth of strained ultrathin GaSb quantum well (QW) layers in a GaAs host crystal by organometallic vapor phase epitaxy (OMVPE). We report surface anisotropy features observed by reflectance difference spectroscopy (RDS) during exposure of the GaAs (001) surface to trimethylantimony (TMSb) and during subsequent growth interruption. We demonstrate the formation of a floating layer of Sb during growth of GaAs over GaSb quantum well layers. The periodic nature of the RDS signal during growth of multiple quantum well (MQW) structures allows us to construct time-resolved RDS spectra, detailing the evolution of the surface anisotropy. We show how x-ray diffraction (XRD) data may be used to determine the graded compositional profile resulting from Sb segregation at the GaAs/GaSb interface. Photoluminescence (PL) spectra at 2 K from MQW structures exhibit two peaks below the GaAs bandgap. The lower-energy peak, which we attribute to a type-II transition at the GaSb/GaAs interface, shifts logarithmically with excitation power density. The higher energy peak shows no shift with excitation power, and is attributed to a transition occurring within the graded barrier layers.     

Arrays of strained InAs quantum dots in an (In Ga)As matrix, grown on InP substrates by molecular-beam epitaxy

Arrays of strained InAs islands in an (In, Ga)As matrix on an InP(100) substrate are synthesized by molecular-beam epitaxy, and their structural and optical properties are investigated. According to transmission electron microscope and high-energy electron diffraction data, the critical thickness corresponding to the onset of island growth is 3 monolayers. The resulting InAs islands are coherently strained, and their base diameter varies from 20 nm to 90 nm. The formation of islands produces in the photoluminescence spectra a dominant long-wavelength line, which shifts toward lower energies as the effective thickness of the InAs increases. The radiation emitted by the InAs islands spans a wavelength range of 1.65–2 μm. Fiz. Tekh. Poluprovodn. 31, 1256–1260 (October 1997)     

Structural Characterization of Integrated II–VI and III–V Heterostructures for Solar Cell Applications

We report on the microstructural characterization of monolithically integrated II–VI and III–V heterostructures that are being developed for possible solar cell applications. Observations by transmission electron microscopy have shown that the growth of lattice-matched ZnTe layers on GaSb(100) substrates resulted in very high quality interfaces and very few structural defects. We then investigated short-period superlattices (SSLs) of CdSe and CdTe digital alloys grown using ZnTe buffer layers on GaSb substrates. The effect of rapid thermal annealing was also studied. High-resolution electron micrographs showed that the CdSe-CdTe SSL had very high quality for approximately 25–50 periods closest to the substrate but that considerable stacking faults and microtwins were visible in layers near the top surface of the sample. For comparison purposes, CdSe layers grown on InAs(100) substrates, again using ZnTe as a buffer layer, were also characterized. The quality of the CdSe layer was not as good as that observed in the SSL sample, possibly because of the larger lattice mismatch between the materials.     

Characterization of Selectively Doped InAs-Quantum-Dot GaAs-Based Multilayer Heterostructures by High-Resolution X-ray Diffraction

GaAs-based heterostructures with one, two, or three InAs quantum-dot layers are examined by high-resolution x-ray diffraction. The quality and structure of the specimens are characterized from rocking curves. In the case of three quantum-dot layers, two different superlattices alternating in the lateral direction are discovered in the specimen. The superlattices differ in the InAs content of the GaAs matrix. It is shown that the existence of two superlattices is due to the vertical correlated growth of quantum dots and is related to an InAs wetting layer.     

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。     

利用GaAs基上InGaAs应变层制备有序排列的InAs量子点

在GaAs基InxGa1-xAs(x=0.15)应变层上生长了InAs量子点(QD)层,通过分析各层之间的应力状况和位错的演变过程,配合生长过程中对反射式高能电子衍射仪(RHEED)实时监测,并观察生长后的表面形貌,发现可以通过控制应变层厚度来控制应变层表面布纹结构的宽度,而且在应变层厚度低于位错增殖的临界厚度时布纹宽度较窄.如果同时控制QD层在刚刚出点,则QD主要沿着较窄的布纹结构排列,从而得到有序排列的QD     

Determination of Critical Thickness for Epitaxial ZnTe Layers Grown by Molecular Beam Epitaxy on (211)B and (100) GaSb Substrates

Cross-section electron micrographs, cathodoluminescence images, and confocal photoluminescence (cPL) images have been acquired for ZnTe layers deposited to various thicknesses on GaSb substrates with (211)B and (100) orientations. The critical thickness of ZnTe on GaSb is predicted to range between 115 nm and 329 nm, depending on the theoretical approach chosen. For ZnTe layers grown on (211)B GaSb with thickness exceeding 150 nm, dark spots and lines are present in all images. We associate these with dislocations generated at the ZnTe/GaSb interface. The discrepancy between this thickness value and a critical thickness value (350 nm to 375 nm) obtained for the (211)B orientation in a previous study is related to the distinction between the onset of misfit dislocations and the onset of significant plastic deformation. The former requires a direct imaging technique, as strain-related measurements such as x-ray diffraction do not have the resolution to detect the effects of small numbers of dislocations. For ZnTe layers on (100) GaSb, x-ray diffraction measurements indicate an abrupt change characteristic of dislocation multiplication at a thickness value in the range from 250 nm to 275 nm. High-resolution electron micrographs of the ZnTe/GaSb interface indicate that deoxidation using atomic hydrogen produces GaSb surfaces suitable for ZnTe epitaxy. cPL images of a 1.2-μm-thick lattice-matched ZnTe_0.99Se _0.01 layer grown on a 150-nm-thick ZnTe buffer layer on a (211)B GaSb substrate yield a threading dislocation density of ～7 × 10⁴ cm^?2.     

Piezoelectric field measurements by photoreflectance in strained InGaAs/GaAs structures grown on polar substrates

Photoreflectance (PR) measurements were performed on specific structures grown by molecular-beam epitaxy on different substrate orientations: 111B, 111B 2° off, 111A and 100. A strained In_0.2Ga_0.8As quantum well was grown in the space charge layer of an undoped GaAs layer. On a polar substrate orientation 111, the strain-induced piezoelectric field in the quantum well modifies the field in the space charge layer. PR spectra recorded in such structures exhibit Franz Keldysh oscillations from which we can measure the internal electric field. The piezoelectric field is then deduced from a comparison between two structures differing only by the presence of the strained quantum well. Experimental values ranged between 110 kV/cm and 150 kV/cm, and were used to determine experimentally the piezoelectric constant e₁₄ in In_0.2Ga_0.8As.     

LP-MOCVD grown (lnAs)m(GaAs)m short period superlattices on InP

(InAs)_m(GaAs)_m (1 ≤ m ≤ 12) short period superlattices (SPSs) have been grown on semi-insulated InP substrates with a 200 nm InP cap layer using low pressure metalorganic chemical vapor deposition (MOCVD). According to double crystal x-ray diffraction and transmission electron microscopy results, the critical layer thickness of (InAs)_m(GaAs)_m SPS was observed to be ～30Å (m = 5). For the SPS below the critical layer thickness, mirror-like surface morphology was found without defects, and strong intensity Fourier transformed photoluminescence (FT-PL) spectra were also obtained at room temperature. The SPS with m = 4 showed a drastic improvement in photoluminescence intensity of order of two compared to an InGaAs ternary layer. However, the SPS with a large value of m (m ≥ 6), rough surface was observed with defects, with broad and weak FT-PL spectra. The surface morphology of SPS was greatly affected by the substrate orientation. The SPS with m = 5 was grown on two degree tilted substrate from (100) direction and showed poor surface morphology as compared to the one grown on (100) exact substrate Moreover, the SPS grown on a (111)B substrate showed a rough triangular pattern with Nomarski optical microscopy. In-situ thermal annealed SPS with m = 4 showed a 18 meV increase in PL peak energy compared to the as-grown sample due to phase separation resulting from thermal interdiffusion.