Surface passivation of III-V semiconductors for future CMOS devices—Past research, present status and key issues for future

Currently, III-V metal-insulator-semiconductor field effect transistors (MISFETs) are considered to be promising device candidates for the so-called “More Moore Approach” to continue scaling CMOS transistors on the silicon platform. Strong interest also exists in III-V nanowire MISFETs as a possible candidate for a “Beyond CMOS”-type device. III-V sensors using insulator-semiconductor interfaces are good candidates for “More Moore”-type of devices on the Si platform. The success of these new approaches for future electronics depends on the availability of a surface passivation technology which can realize pinning-free, high-quality interfaces between insulator and III-V semiconductors.This paper reviews the past history, present status and key issues of the research on the surface passivation technology for III-V semiconductors. First, a brief survey of previous research on surface passivation and MISFETs is made, and Fermi level pinning at insulator-semiconductor interface is discussed. Then, a brief review is made on recent approaches of interface control for high-k III-V MIS structures. Subsequently, as an actual example of interface control, latest results on the authors’ surface passivation approach using a silicon interface control layer (Si ICL) are discussed. Finally, a photoluminescence (PL) method to characterize the interface quality is presented as an efficient contactless and non-destructive method which can be applied at each step of interface formation process without fabrication of MIS capacitors and MISFETs.     

硅基混合集成技术的研究进展

硅基光电子集成技术(PICs)为高速宽带光互连和光通信的发展提供了一种低成本的有效方案,受到人们的高度重视.目前将III-V族和锗等半导体化合物集成到硅衬底的方法主要分为两类:异质结外延生长和异质材料的键合.低温下晶片键合的方法克服了异质结外延生长中的生长温度高、晶格失配和材料热膨胀系数非共容性的缺点,为大规模的异质(不同半导体材料)集成提供了可能.文章综述了近几年来一些常用的键合方法,并对低温键合方法的发展动向做了展望.     

Fast emission dynamics in droplet epitaxy GaAs ring-disk nanostructures integrated on Si

The emission dynamics in GaAs/AlGaAs coupled ring-disk (CRD) quantum structures fabricated on silicon substrates is presented. The CRD structures are self-assembled via droplet epitaxy, a growth technique which, due to its low thermal budget, is compatible with the monolithic integration of III-V devices on Si based electronic circuits. Continuous wave, time resolved photoluminescence and theoretical calculations in the effective mass approximations are presented for the assessment of the electronic and carrier properties of the CRDs. The CRDs show a fast carrier dynamics which is expected to be suitable for ultrafast optical switching applications integrated on silicon.     

硅基III-V族量子点激光器的发展现状和前景

本文简要综述了硅基III-V族量子点激光器的研究进展. 在介绍了量子点激光器的优势和发展后, 重点介绍了近年来硅基、锗基III-V族量子点材料生长上的突破性进展及所带来的器件性能的大幅提高, 如实现了锗基和硅基1.3 μm InAs/GaAs量子点激光器的室温激射, 锗基量子点激光器的阈值电流低至55.2 A/cm²并可达60 ℃以上的连续激射, 通过锗硅虚拟衬底, 在硅基上实现了30 ℃下以16.6 mW的输出功率达到4600 h的激光寿命, 这些突破性的进展为硅基光电子集成打开了新的大门.     

室内光伏的应用前景与挑战

社会的发展离不开能源的发现与创造,光伏能源的多形式运用在能源领域大放异彩,室 内光伏器件逐渐成为大家所关注的热点。室内光伏IPV (Indoor photovoltaics) 作为低照度条件 下的电源,可以满足低功率电子器件的工作要求。本文主要比较了基于硅、染料、III-V 族半导 体、有机化合物和卤化物钙钛矿这些不同类型的IPV 器件。得益于卤化物钙钛矿活性层具有优 异的光物理特性,钙钛矿光伏具有成为高性能室内光伏器件的潜力。与此同时也讨论了室内光伏 的局限性。最后,提出了制备生产高效率、无毒、稳定的钙钛矿室内光伏器件的解决方案以及未 来应用展望。     

Silicon Porosification: State of the Art

This review is devoted to the analysis of the problems related to fabrication of the Si porous layers. The review was motivated by a great interest to Si-based porous materials from nano- to macro-scale for various applications in electronics, optoelectronics, photonics, chemical sensors, biosensors, etc. The peculiarities of the silicon porosification and the principles of preparing porous layers are considered in the present article. Various methods used for Si porosification such as chemical stain etching, chemical vapor etching, laser-induced etching, metal-assisted etching, spark processing and reactive ion (plasma) etching were analyzed. However, the main attention was focused on electrochemical porosification of Si. The review discusses in detail the influence of parameters such as electrolyte composition and pH, current density, etching time, temperature, wafer doping and orientation, lighting, magnetic field, and ultrasonic agitation on the process of Si porosification. It was shown that the structure of porous silicon strongly depends on both technological parameters of electrochemical etching and the parameters of the semiconductor subject to treatment. This review also addresses the main properties of porous silicon, porous multilayer and 3D structure formation, oxidation of porous Si, release of the porous layer, drying, storage, etching, filling and surface functionalizing of porous Si. Features of III-V compound porosification are also briefly analyzed.     

Calculation of distribution coefficients of donors in III-V semiconductors

The techniques recently developed for the calculation of III-V ternary phase diagrams have been extended to the calculation of distribution coefficients of impurities in III-V semiconductors. The distribution coefficients are calculated with no adjustable parameters, the calculation requiring only the temperatures and entropies of fusion, binary phase diagrams and lattice parameters of the relevant III-V compounds, and the tetrahedral covalent radii, electronegativities, molar volumes and atomization energies of the donor impurities and group III and V elements concerned.The calculation is carried out for common donors S, Se, Te and Sn at the melting points of the III-V compounds GaP, GaAs, GaSb, InP, InAs and InSb, and the results compared with experimental results where available. In GaAs and GaP, the distribution coefficients are calculated vs temperature for solidification from the group III rich melt.     

Fabrication of sol-gel-derived optical waveguide on InP for hybridized photonics applications

In this paper, we report on the first successful fabrication, using spin-coating and low-temperature (200 °C) annealing, of organically modified sol-gel planar optical waveguides on InP substrates. Considering the fact that the sol-gel technique is simple and cheap, and III-V compound semiconductors are the essential substrate materials for manufacturing data communication devices, we believe that our demonstration of optical waveguiding in sol-gel-derived waveguides on III-V compound semoconductors is interesting. It opens the possibility of hybridizating traditional glass or optical-crystal-based integrated optics with III-V compound semiconductor-based optoelectronics. Received: 4 August1999 / Accepted: 6 August 1999 / Published online: 16 September 1999     

The path to stoichiometric composition of III-V binary quantum dots through plasma/ion-assisted self-assembly

Semiconductor III-V quantum dots (QDs) are particularly enticing components for the integration of optically promising III-V materials with the silicon technology prevalent in the microelectronics industry. However, defects due to deviations from a stoichiometric composition [group III: group V = 1] may lead to impaired device performance. This paper investigates the initial stages of formation of InSb and GaAs QDs on Si(1 0 0) through hybrid numerical simulations. Three situations are considered: a neutral gas environment (NG), and two ionized gas environments, namely a localized ion source (LIS) and a background plasma (BP) case. It is shown that when the growth is conducted in an ionized gas environment, a stoichiometric composition may be obtained earlier in the QD as compared to a NG. Moreover, the stoichiometrization time, t_st, is shorter for the BP case compared to the LIS scenario. A discussion of the effect of ion/plasma-based tools as well as a range of process conditions on the final island size distribution is also included. Our results suggest a way to obtain a deterministic level of control over nanostructure properties (in particular, elemental composition and size) during the initial stages of growth which is a crucial step towards achieving highly tailored QDs suitable for implementation in advanced technological devices.     

Surface passivation technology for III-V semiconductor nanoelectronics

The present status and key issues of surface passivation technology for III-V surfaces are discussed in view of applications to emerging novel III-V nanoelectronics. First, necessities of passivation and currently available surface passivation technologies for GaAs, InGaAs and AlGaAs are reviewed. Then, the principle of the Si interface control layer (ICL)-based passivation scheme by the authors’ group is introduced and its basic characterization is presented. Ths Si ICL is a molecular beam epitaxy (MBE)-grown ultrathin Si layer inserted between III-V semiconductor and passivation dielectric. Finally, applications of the Si ICL method to passivation of GaAs nanowires and GaAs nanowire transistors and to realization of pinning-free high-k dielectric/GaAs MOS gate stacks are presented.     

Molecular beam epitaxy of III–V semiconductors

Molecular beam epitaxy (MBE) has been instrumental in the advancement of the physics and technology of semiconductors that has occurred over the last few decades. The III-V material system has led the way in these new developments. This article discusses the technology of III-V MBE, highlights selected topics in its development, discusses growth mechanisms, and mentions possible future directions.     

Compositional contrast in AlxGa1−xN/GaN heterostructures using scanning spreading resistance microscopy

Scanning spreading resistance microscopy has found extensive use as a dopant-profiling technique for silicon-based devices, and to a lesser extent for some III-V materials. Here we demonstrate its efficacy for wide bandgap nitrides and, in particular, show that it may be used to differentiate between layers of different Al-content in an Al_xGa_1−xN/GaN heterostructure. A monotonic increase in resistance signal with increasing Al-content is demonstrated, under optimal imaging conditions. The variation in measured resistance with applied bias is shown to be dependent on the aluminium content, and this is discussed, along with other issues, in the context of potential quantification of unknown samples. The procedure for forming an optimal image is different from that for silicon, in terms of contact forces and applied biases.     

III-V compounds for solar cell applications

Research activities in the field of III-V solar cells are reviewed. III-V compound semiconductors are used for space solar cells, concentrator solar cells, and in thermophotovoltaic generators. The epitaxial growth of ternary and quaternary material by MOVPE and LPE allows us to realize various band gaps. Multi-junction solar cells with different band gaps are necessary to obtain efficiencies larger than 30%. Recent results of the III-V solar cell research at the Fraunhofer ISE are presented. A mechanically stacked GaAs/GaSb tandem concentrator solar cell achieved an efficiency of 31.1% under 100×AM1.5d. An efficiency of 23% for a two-terminal concentrator module (486 cm²) with Fresnel lenses has been measured under realistic outdoor conditions. Received: 1 March 1999 / Accepted: 28 March 1999 / Published online: 24 June 1999     

Evolution of III-V nitride alloy electronic structure: the localized to delocalized transition

Addition of nitrogen to III-V semiconductor alloys radically changes their electronic properties. We report large-scale electronic structure calculations of GaAsN and GaPN using an approach that allows arbitrary states to emerge, couple, and evolve with composition. We find a novel mechanism of alloy formation where localized cluster states within the gap are gradually overtaken by a downwards moving conduction band edge, composed of both localized and delocalized states. This localized to delocalized transition explains many of the hitherto puzzling experimentally observed anomalies in III-V nitride alloys.     

Statistical mechanical models for liquid and amorphous structure in covalently bonded systems

Summary Considerable effort has been given for some years to developing models of interatomic forces aimed at accounting for bond directionality in liquid and amorphous state calculations. Models involving three-body potentials have been especially useful for computer simulation studies of liquid and amorphous states in elemental semiconductors and binary chalcogenides of group-IV elements, starting with the work of Stillinger and Weber on silicon. However, pair potential models that may still account for the main effects of angular dependences of the effective interatomic forces, though at a primitive level, are desirable from the viewpoint of liquid structure theory. Developments in this direction are briefly reviewed, with particular emphasis on bond particle models for the structure of liquid and amorphous germanium. We also discuss the relation between liquid structure in a bond-particle model and crystallization accompanied by electron localization and volume expansion, as observed in elemental and III-V polar semiconductors. Paper presented at the workshop ?Highlights on Simple Liquids?, held in Turin at ISI on 1–3 May, 1989.     

Magnetic circular dichroism from the impurity band in III-V diluted magnetic semiconductors

The magnetic circular dichroism of III-V diluted magnetic semiconductors, calculated within a theoretical framework suitable for highly disordered materials, is shown to be dominated by optical transitions between the bulk bands and an impurity band formed from magnetic dopant states. The real-space Green's functions incorporate spatial correlations in the disordered conduction band and valence-band electronic structure, and include extended and localized states on an equal basis. Our findings reconcile unusual trends in the experimental magnetic circular dichroism in III-V diluted magnetic semiconductors with the antiferromagnetic p-d exchange interaction between a magnetic dopant spin and its host.     

Dopant patterning in three dimensions during molecular beam epitaxial growth using anin-situfocused ion gun

Conventional molecular beam epitaxial (MBE) growth of III-V semiconductor material systems use a thermal silicon effusion cell as the n-type dopant source. In the technique described here, the thermal source is replaced with a scanning Si focused ion gun. It is therefore possible to directly write dopant patterns into the semiconductor waferit as it is being grown. The precise control over the elemental composition in the growth (z) direction permitted by MBE, combined with high spatial resolution of the focused dopant ion beam in the lateral (xy) plane, allows direct registration of fully integrated, three-dimensional semiconductor structures and devices otherwise unobtainable via conventional lithographic techniques. In this paper, we present electrical measurements of high mobility GaAs/AlGaAs modulation doped heterostructures fabricated using this technique.Fabrication of novel undoped channel FET structures is also discussed, where the dopant beam is used to form extended contacts to the induced electron gas. FET action is demonstrated for the first time using this technique, eliminating the constraint for self-alignment in undoped structures.     

LO-phonon effect on the exciton binding energy in polar rectangular quantum wires

Longitudinal optical phonon effect on Wannier excitons in polar rectangular quantum wires is studied by a variational approach. The binding energy is calculated and the numerical results for several II-VI and III-V compound semiconductor rectangular quantum wires are given. The results show that the phonon effect reduces the binding energy and cannot be neglected. The phonon contribution to the binding energy is sensitive to the size of the rectangular quantum wire section, and increases with decreasing section area. The results for the GaAs rectangular quantum wires coincide with the experimental results. The calculated binding energy and the phonon effect in II-VI QWWs are both stronger than those in III-V compound systems, and the results for ZnSe QWW are qualitatively in agreement with the experiments.     

“Antisite” incorporation of Sb dopant in GaN

Radioactive ¹¹⁹Sb was implanted in an undoped GaN single crystal and Mössbauer spectra were taken of the 23.8 keV gamma rays of ¹¹⁹Sn emitted in its decay. A comparison with Mössbauer spectra of ¹¹⁹Sb implantated in other III-V compounds leads to the conclusion that Sb in GaN lands in the Ga site in contrast to all common III-V compounds, where Sb occupies the anion site. Calculations of electronegativity differences for Sb incorporation in either Ga or N site support our interpretation of the experimental data.     

Transparent conducting indium-tin-oxide (ITO) film as full front electrode in III-V compound solar cell

The application of transparent conducting indium-tin-oxide (ITO) film as full front electrode replacing the conventional bus-bar metal electrode in III-V compound GaInP solar cell was proposed. A high-quality, non-rectifying contact between ITO and 10 nm N⁺-GaAs contact layer was formed, which is benefiting from a high carrier concentration of the terrilium-doped N⁺-GaAs layer, up to 2×10¹⁹ cm^-3. A good device performance of the GaInP solar cell with the ITO electrode was observed. This result indicates a great potential of transparent conducting films in the future fabrication of larger area flexible III-V solar cell.