Thermal characteristics of InP, InAlAs, and AlGaAsSb metamorphic buffer layers used in In0.52Al0.48As/In0.53Ga0.47As heterojunction bipolar transistors grown on GaAs substrates

In_0.52Al_0.48As/In_0.53Ga_0.47As heterojunction bipolar transistors (HBTs) were grown metamorphically on GaAs substrates by molecular beam epitaxy. In these growths, InAlAs, AlGaAsSb, and InP metamorphic buffer layers were investigated. The InAlAs and AlGaAsSb buffer layers had linear compositional grading while the InP buffer layer used direct binary deposition. The transistors grown on these three layers showed similar characteristics. Bulk thermal conductivities of 10.5, 8.4, and 16.1 W/m K were measured for the InAlAs, AlGaAsSb, and InP buffer layers, as compared to the 69 W/m K bulk thermal conductivity of bulk InP. Calculations of the resulting HBT junction temperature strongly suggest that InP metamorphic buffer layers should be employed for metamorphic HBTs operating at high power densities.     

InP衬底上InAlAs异变缓冲层和高铟组分InGaAs的生长温度优化

利用气态源分子束外延技术在InP衬底上生长了包含InAlAs异变缓冲层的In0.83Ga0.17As外延层.使用不同生长温度方案生长的高铟InGaAs和InAlAs异变缓冲层的特性分别通过高分辨X射线衍射倒易空间图、原子力显微镜、光致发光和霍尔等测量手段进行了表征.结果表明, InAlAs异变缓冲层的生长温度越低, X射线衍射倒易空间图 (004) 反射面沿Qx方向的衍射峰半峰宽就越宽, 外延层和衬底之间的倾角就越大, 同时样品表面粗糙度越高.这意味着材料的缺陷增加, 弛豫不充分.对于生长在具有相同生长温度的InAlAs异变缓冲层上的In0.83Ga0.17As外延层, 采用较高的生长温度时, X射线衍射倒易空间图 (004) 反射面沿Qx方向的衍射峰半峰宽较小, 77K下有更强的光致发光, 但是表面粗糙度会有所增加.这说明生长温度提高后, 材料中的缺陷得到抑制.     

Interrelation of the construction of the metamorphic InAlAs/InGaAs nanoheterostructures with the InAs content in the active layer of 76–100% with their surface morphology and electrical properties

The influence of the construction of a metamorphic buffer on the surface morphology and electrical properties of InAlAs/InGaAs/InAlAs nanoheterostructures with InAs content in the active layer from 76 to 100% with the use of the GaAs and InP substrates is studied. It is shown that such parameters as the electron mobility and the concentration, as well as the root-mean-square surface roughness, substantially depend on the construction of the metamorphic buffer. It is established experimentally that these parameters largely depend on the maximal local gradient of the lattice constant of the metamorphic buffer in the growth direction of the layers rather than on its average value. It is shown that, with selection of the construction of the metamorphic buffer, it is possible to form nanostructured surfaces with a large-periodic profile.     

Thermal resistance of metamorphic InP-based HBTs on GaAs substrates using a linearly graded In/sub x/Ga/sub 1-x/P metamorphic buffer

Thermal properties of metamorphic InP-InGaAs heterojunction bipolar transistors (HBTs) on GaAs substrates using a linearly graded InGaP buffer have been investigated. Compared to the widely used InAlAs metamorphic buffer, InGaP offers better thermal properties resulting in a much smaller thermal resistance for the metamorphic HBTs (MHBTs). Theoretical calculations of the thermal resistance of devices have been made based on a simple constant heat-spreading model, and the results are shown to be consistent with experimental results. It has been made clear that the smaller thermal resistance measured from the MHBTs using a linearly graded InGaP buffer is due to the small bowing parameters and high thermal conductivity of the binary endpoints. Although the use of InGaP as a buffer may slightly degrade the devices thermal properties compared to one using InP directly on GaAs substrate, it gives more freedom to the growth optimization of metamorphic buffer by using compositional grading. With regards to the thermal conductivity and flexible growth optimization, InGaP metamorphic buffer could be considered as an important alternative to the existing InAlAs and InP schemes.     

Metamorphic modulation-doped InAlAs/InGaAs/InAlAs heterostructures with high electron mobility grown on gaas substrates

Metamorphic modulation-doped InGaAs/InAlAs heterostructures have been MBE-grown on GaAs substrates. The optimization of low-temperature growth conditions for a graded-composition buffer layer made it possible to reduce the amount of structural defects in the active layers of the structure. The electron mobility in the 2D channel of metamorphic structures grown under optimum conditions (8100 cm²/V s at 300 K) noticeably exceeds the values achievable in strained InGaAs/AlGaAs heterostructures on GaAs substrates.     

Ultrahigh-Speed 0.5 V Supply Voltage In0.7 Ga0.3As Quantum-Well Transistors on Silicon Substrate

The direct epitaxial growth of ultrahigh-mobility InGaAs/InAlAs quantum-well (QW) device layers onto silicon substrates using metamorphic buffer layers is demonstrated for the first time. In this letter, 80 nm physical gate length depletion-mode InGaAs QW transistors with saturated transconductance gm of 930 muS / mum and fT of 260 GHz at V_DS = 0.5 V are achieved on 3.2 mum thick buffers. We expect that compound semiconductor-based advanced QW transistors could become available in the future as very high-speed and ultralow-power device technology for heterogeneous integration with the mainstream silicon CMOS.     

（英）组分过冲对InP基InAlAs递变缓冲层的影响

通过在InP基InxAl1-xAs 递变缓冲层上生长In0.78Ga0.22As/In0.78Al0.22As量子阱和In0.84Ga0.16As探测器结构,研究了缓冲层中组分过冲对材料特性的影响。原子力显微镜结果表明,在InAlAs缓冲层中采用组分过冲可以使量子阱及探测器样品表面粗糙度都得到降低。对于相对较薄的量子阱结构,X射线衍射倒易空间扫描图和光致发光谱的测量表明,使用组分过冲可以增加弛豫度、减小剩余应力并改善光学性质。而对于较厚的探测器结构,X射线衍射和光致发光谱测试发现使用组分过冲后的材料性质没有明显的变化。量子阱和探测器结构的这些不同特性需要在器件设计应用中加以考虑。     

Improvement of Impact Ionization Effect and Subthreshold Current in InAlAs/InGaAs Metal–Oxide–Semiconductor Metamorphic HEMT With a Liquid-Phase Oxidized InAlAs as Gate Insulator

The oxidation of InAlAs and its application to InAlAs/InGaAs metal-oxide-semiconductor metamorphic high-electron mobility transistors (MOS-MHEMTs) are demonstrated in this study. After the highly selective gate recessing of InGaAs/InAlAs using citric buffer etchant, the gate dielectric is obtained directly by oxidizing the InAlAs layer in a liquid-phase solution at near room temperature. As compared to its counterpart MHEMT, the fabricated InAlAs/InGaAs MOS-MHEMT exhibits a larger tolerance to gate bias, higher breakdown voltage, lower subthreshold current, improved gate leakage current with the effectively suppressed impact ionization effect, and improved radio-frequency performance. Consequently, the liquid-phase oxidation may also be used to produce gate oxides and as an effective passivation on III-V compound semiconductor devices     

Photoluminescence studies of In0.7Al0.3As/In0.75Ga0.25As/In0.7Al0.3As metamorphic heterostructures on GaAs substrates

The influence of the design of the metamorphic buffer of In_0.7Al_0.3As/In_0.75Ga_0.25As metamorphic nanoheterostructures for high-electron-mobility transistors (HEMTs) on their electrical parameters and photoluminescence properties is studied experimentally. The heterostructures are grown by molecular-beam epitaxy on GaAs (100) substrates with linear or step-graded In _x Al_{1 ? x} As metamorphic buffers. For the samples with a linear metamorphic buffer, strain-compensated superlattices or inverse steps are incorporated into the buffer. At photon energies ?ω in the range 0.6–0.8 eV, the photoluminescence spectra of all of the samples are identical and correspond to transitions from the first and second electron subbands to the heavy-hole band in the In_0.75Ga_0.25As/In_0.7Al_0.3As quantum well. It is found that the full width at half-maximum of the corresponding peak is proportional to the two-dimensional electron concentration and the luminescence intensity increases with increasing Hall mobility in the heterostructures. At photon energies ?ω in the range 0.8–1.3 eV corresponding to the recombination of charge carriers in the InAlAs barrier region, some features are observed in the photoluminescence spectra. These features are due to the difference between the indium profiles in the smoothing and lower barrier layers of the samples. In turn, the difference arises from the different designs of the metamorphic buffer.     

Special features of the formation of Ge(Si) islands on the relaxed Si1−xGex/Si(001) buffer layers

The results of studying the growth of self-assembled Ge(Si) islands on relaxed Si_1?xGe_x/Si(001) buffer layers (x≈25%), with a low surface roughness are reported. It is shown that the growth of self-assembled islands on the buffer SiGe layers is qualitatively similar to the growth of islands on the Si (001) surface. It is found that a variation in the surface morphology (the transition from dome-to hut-shaped islands) in the case of island growth on the relaxed SiGe buffer layers occurs at a higher temperature than for the Ge(Si)/Si(001) islands. This effect can be caused by both a lesser mismatch between the crystal lattices of an island and the buffer layer and a somewhat higher surface density of islands, when they are grown on an SiGe buffer layer.     

采用Ga(In,As)P异变缓冲层的GaP/Si衬底上InAs量子阱

本工作在GaP/Si衬底上基于In0.83Al0.17As异变缓冲层实现了InAs/In0.83Al0.17As量子阱的生长.研究了GaxIn1-xP和GaAsyP1-y递变缓冲层对量子阱结构材料性能的影响.采用GaxIn1-xP组分渐变缓冲层的样品X射线衍射倒易空间衍射峰展宽更小,表明样品中的失配位错更少.两个样品均...     

Study of new designs for the InAlAs metamorphic buffer on GaAs substrates with distributed compensation of elastic deformations

Two new designs for a metamorphic buffer, which are modifications of the In _x Al_{1 ? x} As metamorphic buffer due to groups of layers with differing lattice parameters, are proposed and implemented. This makes it possible to affect the relaxation of the metamorphic buffer. The structural and electrical characteristics of the obtained metamorphic HEMT nanoheterostructures are also studied.     

失配异质结构InGaAs/InP的MOCVD生长

基于延展波长(截止波长2.2μm)InGaAs-PIN光电探测器进行了失配异质结构InxGa1-xAs(x=0.72)/InP的MOCVD外延生长研究。采用宽带隙组分梯度渐变的InAlAs作为缓冲层和顶层,通过生长优化,获得了满足器件要求的外延材料。     

Metamorphic Heterostructure InP/GaAsSb/InP HBTs on GaAs Substrates by MOCVD

Good-quality metamorphic InP buffer layers have been successfully grown on GaAs substrates by metal-organic chemical vapor deposition. Characterization by atomic force microscope, transmission electron microscopy, high-resolution X-ray diffraction, and Hall measurements indicated that the layers are of high crystalline quality, good mobility, and excellent surface morphology. On this buffer, we demonstrated the first metamorphic InP/GaAsSb/InP double heterojunction bipolar transistors (DHBTs) with good material quality and device performance. Metamorphic DHBTs showed direct-current and radio-frequency characteristics that are comparable to those grown on lattice-matched InP substrates.     

Quantum dot structures: Fabrication technology and control of parameters

Quantum dot (QD) semiconductor heterostructures for device applications are currently synthesized using the effect of spontaneous transformation of the growth surface at the initial stage of heteroepitaxy of lattice-mismatched layers. When a certain critical layer thickness is reached, the planar growth surface is transformed into an array of nanoscale islands, as was first demonstrated for an InAs/GaAs system. For various device applications, it is desirable to control the shape and size of individual QDs. This is achieved by variation of the effective thickness of the deposited InAs layer, deposition of several QD layers, the use of various matrix materials and a metamorphic buffer layer, and the addition of a small amount of nitrogen into QDs and the matrix material.     

Heterostructures of metamorphic GaInAs photovoltaic converters fabricated by MOCVD on GaAs substrates

Heterostructures of metamorphic GaInAs photovoltaic converters (PVCs) are on GaAs substrates by the metal-organic chemical vapor deposition (MOCVD) method. It is shown that using a multilayer metamorphic buffer with a step of 2.5% in indium content and layer thicknesses of 120 nm provides the high quality of bulk layers subsequently grown on the buffer up to an indium content of 24%. PVCs with a long-wavelength photosensitivity edge up to 1300 nm and a quantum efficiency of ~80% in the spectral range 1050–1100 nm are fabricated. Analysis of the open-circuit voltage of the PVCs and diffusion lengths of minority carriers in the layers demonstrates that the density of misfit dislocations penetrating into the bulk layers increases at an indium content exceeding 10%.     

Metamorphic graded bandgap InGaAs-InGaAlAs-InAlAs doubleheterojunction p-i-I-n photodiodes

High-speed metamorphic double heterojunction photodiodes were fabricated on GaAs substrates for long-wavelength optical fiber communications. The high quality linearly graded quaternary InGaAlAs metamorphic buffer layer made possible the growth of excellent InGaAs-InGaAlAs-InAlAs heterostructures on GaAs substrates. The use of a novel double heterostructure employing an InGaAlAs optical impedance matching layer, a chirped InGaAs-InAlAs superlattice graded bandgap layer (SL-GBL), and a large bandgap i-InAlAs drift region enabled photodiodes to achieve a low dark current of 500 pA, a responsivity of 0.6 A/W, and a -3 dB bandwidth of 38 GHz at -5 V reverse bias for 1.55 μm light. The effect of accumulated charges at the InGaAs-InAlAs heterointerface was examined through a comparison of the dark currents of InGaAs-InAlAs and InGaAs-InP abrupt single heterojunction photodiodes; to photodiodes with chirped InGaAs-InAlAs SL-GBLs. The charge accumulation effects observed in abrupt heterojunction devices were suppressed by including a chirped InGaAs-InAlAs SL-GBL between the InGaAs absorption layer and InAlAs drift layer. The effect of passivation techniques was evaluated by comparing dark currents of unpassivated photodiodes and photodiodes passivated with either polyimide or SiN_x. The enhancement of photodiode bandwidth through the inclusion of a transparent large bandgap I-InAlAs drift region was verified by comparing the bandwidths of the P-i-I-N photodiodes that have I-InAlAs between i-InGaAs photoabsorption layer and N⁺ InAlAs cathode to conventional P-i-N photodiodes without a drift region     

Effect of growth temperature on photoluminescence of self-assembled Ge(Si) islands confined between strained Si layers

The effect of growth temperature on photoluminescence is studied for structures with Ge(Si) islands grown on relaxed SiGe/Si(001) buffer layers and confined between strained Si layers. It is shown that, with decreasing growth temperature in the range from 700 to 630°C, the photoluminescence peak associated with the islands shifts to lower energies, which is due to the increase in Ge content in the islands and to suppression of degradation of the strained Si layers. The experimentally observed shift of the photoluminescence peak to higher energies with decreasing temperature from 630 to 600°C is attributed to the change in the type of the islands from domelike to hutlike in this temperature range. This change is accompanied by an abrupt decrease in the average height of the islands. The larger width of the photoluminescence peak produced by the hut islands in comparison with the width of the peak produced by the domelike islands is interpreted as a result of a wider size dispersion of the hutlike islands.     

Effects of Doping of Bragg Reflector Layers on the Electrical Characteristics of InGaAs/GaAs Metamorphic Photovoltaic Converters

Semiconductors - The current–voltage characteristics of InxGa1 –xAs/GaAs metamorphic photovoltaic converters with built-in n-InGaAs/InAlAs Bragg reflectors are studied at an indium...     

Low frequency noise sources in InAlAs/InGaAs MODFETs

Detailed analysis of the 1/f low-frequency noise (LFN) in In/sub 0.52/Al/sub 0.48/As/InGaAs MODFET structures is performed, for low drain bias (below pinch-off voltage), in order to identify the physical origin and the location of the noise sources responsible for drain current fluctuations in the frequency range 0.1 Hz-10/sup 5/ Hz. Experimental data were analyzed with the support of a general modeling of the 1/f LFN induced by traps distributed within the different layers and interfaces which constitute the heterostructures. Comparative noise measurements are performed on a variety of structures with different barrier (InAIAs, InP) and different channel (InGaAs lattice matched to InP, strained InGaAs, InP) materials. It is concluded that the dominant low frequency noise sources of InAlAs/InGaAs MODFET transistors in the ON state are generated by deep traps distributed within the "bulk" InAlAs barrier and buffer layers. For reverse gate bias, the gate current appears to be the dominant contribution to the channel LFN, whereas both the gate current and the drain and source ohmic contacts are the dominant sources of noise when the device is biased strongly in the ON state. Heterojunction FET's on InP substrate with InP barrier and buffer layers show significantly lower LFN and appear to be more suitable for applications such as nonlinear circuits that have noise upconversion.