纳米电子器件及其集成

对基于Top-Down加工技术的纳米电子器件如：单电子器件、共振器件、分子电子器件等的研究现状、面临的主要挑战等进行了讨论. 采用CMOS兼容的工艺成功地研制出单电子器件，观察到明显的库仑阻塞效应；在半绝缘GaAs衬底上制作了AlAs/GaAs/In0.1Ga0.9As/GaAs/AlAs双势垒共振隧穿二极管,采用环型集电极和薄势垒结构研制的共振隧穿器件，在室温下测得其峰谷电流比高达13.98，峰电流密度大于89kA/cm2；概述了交叉阵列的分子存储器的研究进展.     

STM probe-assisted site-control of self-organized InAs quantum dots on GaAs surfaces

A site-control technique for individual InAs quantum dots (QDs) has been developed by using scanning tunneling microscope (STM) probe-assisted nanolithography and self-organizing molecular-beam epitaxy. We find that nano-scale deposits can be created on a GaAs surface by applying voltage and current pulses between the surface and a tungsten tip of the STM, and that they act as “nano-masks” on which GaAs does not grow directly. Accordingly, subsequent thin GaAs growth produces GaAs nano-holes above the deposits. When InAs is supplied on this surface, QDs are self-organized at the hole sites, while hardly any undesirable Stranski-Krastanov QDs are formed in the flat surface region. Using this technique with nanometer precision, a QD pair with 45-nm pitch is successfully fabricated. An erratum to this article is available at .     

Well-defined electrical properties of high-strain resonant interband tunneling structure

The GaAs/InAs high-strain resonant interband tunneling diodes (HSRITDs) have been implemented by metal organic chemical vapor deposition (MOCVD). The current-voltage characteristics of variable quantum well and barrier thickness grown on (1 1 1) GaAs substrates are investigated. Experimental results reveal that the quantum barrier and well layer will influence current-voltage properties such as the peak current density, valley current density, and peak-to-valley current ratio (PVCR). Both peak current and valley current density decrease with increasing layers width. This result also exhibits the variation of PVCR with layers width.     

Light emission by semiconductor structure with quantum well and array of quantum dots

A new type of composite active region of a laser, which contains an In_0.2Ga_0.8As quantum well (QW) and an array of InAs quantum dots (QDs) embedded in GaAs is studied. The QW acts as accumulator of injected carriers, and the QD array is the emitting system located in tunneling proximity to the QW. A theory for the calculation of electron and hole energy levels in the QD is developed. Occupation of the QDs due to the resonance tunneling of electrons and holes from the QW to the QD is considered; the conclusions are compared with the results obtained in studying an experimental laser with a combined active region.     

Tuning the energy spectrum of InAs/GaAs quantum dots by varying the thickness and composition of the thin double GaAs/InGaAs cladding layer

It is shown that the ground state transition energy in quantum dots in heterostructures grown by atmospheric-pressure MOCVD can be tuned in the range covering both transparence windows of the optical fiber at wavelengths of 1.3 and 1.55 μm by varying the thickness and composition of the thin GaAs/In_xGa_1−x As double cladding layer. These structures also exhibit a red shift of the ground state transition energy of the In_xGa_1−x As quantum well (QW) as a result of the formation of a hybrid QW In_xGa_1−x As/InAs (wetting layer) between the quantum dots (QDs). The Schottky diodes based on these structures are characterized by an increased reverse current, which is attributed to thermally activated tunneling of electrons from the metal contact to QD levels. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 38, No. 4, 2004, pp. 448–454. Original Russian Text Copyright ? 2004 by Karpovich, Zvonkov, Levichev, Baidus, Tikhov, Filatov, Gorshkov, Ermakov.     

High-speed tunneling-barrier GaAs light emitters

High-speed GaAs light-emitting diodes are described that contain a single-AlAs tunneling barrier for localization of the carriers. These devices are identical to double-barrier resonant tunneling light emitters in speed and efficiency, but are not dependent on resonant tunneling of charge carriers. An external quantum efficiency of 0.18% and a 3-dB modulation bandwidth of 1.3 GHz are reported. These devices are less affected by nonradiative recombination compared to the conventional heavy-doping approach, in which a high-modulation bandwidth is obtained at the expense of a more than proportional reduction in quantum efficiency     

The power density giving rise to optical degradation of mirrors in InGaAs/AlGaAs/GaAs-based laser diodes

The InGaAs/AlGaAs/GaAs double laser heterostructures of separate confinement with a quantum well were formed by molecular-beam epitaxy. The study of characteristics of laser diodes with a wide contact (100 μm) showed that the power corresponding to the catastrophic degradation of mirrors may attain nearly the highest values ever achieved (20 MW/cm²) that were previously obtained for laser diodes based on InGaAsP/GaAs heterostructures alone. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 34, No. 11, 2000, pp. 1394–1395. Original Russian Text Copyright ? 2000 by Kotel’nikov, Katsnel’son, Kudryashov, Rastegaeva, Richter, Evtikhiev, Tarasov, Alferov.     

Efficient Near‐Infrared Light‐Emitting Diodes based on In(Zn)As–In(Zn)P–GaP–ZnS Quantum Dots

Near‐infrared (NIR) lighting plays an increasingly important role in new facial recognition technologies and eye‐tracking devices, where covert and nonvisible illumination is needed. In particular, mobile or wearable gadgets that employ these technologies require electronic lighting components with ultrathin and flexible form factors that are currently unfulfilled by conventional GaAs‐based diodes. Colloidal quantum dots (QDs) and emerging perovskite light‐emitting diodes (LEDs) may fill this gap, but generally employ restricted heavy metals such as cadmium or lead. Here, a new NIR‐emitting diode based on heavy‐metal‐free In(Zn)As–In(Zn)P–GaP–ZnS quantum dots is reported. The quantum dots are prepared with a giant shell structure, enabled by a continuous injection synthesis approach, and display intense photoluminescence at 850 nm with a high quantum efficiency of 75%. A postsynthetic ligand exchange to a shorter‐chain 1‐mercapto‐6‐hexanol (MCH) affords the QDs with processability in polar solvents as well as an enhanced charge‐transport performance in electronic devices. Using solution‐processing methods, an ITO/ZnO/PEIE/QD/Poly‐TPD/MoO₃/Al electroluminescent device is fabricated and a high external quantum efficiency of 4.6% and a maximum radiance of 8.2 W sr^?1 m^?2 are achieved. This represents a significant leap in performance for NIR devices employing a colloidal III–V semiconductor QD system, and may find significant applications in emerging consumer electronic products.     

Tunnel injection and power efficiency of InGaN/GaN light-emitting diodes

The results of studying the influence of the finite tunneling transparency of injection barriers in light-emitting diodes with InGaN/GaN quantum wells on the dependences of the current, capacitance, and quantum efficiency on the p-n junction voltage and temperature are presented. It is shown that defectassisted hopping tunneling is the main transport mechanism through the space charge region (SCR) and makes it possible to lower the injection barrier. It is shown that, in the case of high hopping conductivity through the injection barrier, the tunnel-injection current into InGaN band-tail states is limited only by carrier diffusion from neutral regions and is characterized by a close-to-unity ideality factor, which provides the highest quantum and power efficiencies. An increase in the hopping conductivity through the space charge region with increasing frequency, forward bias, or temperature has a decisive effect on the capacitance-voltage characteristics and temperature dependences of the high-frequency capacitance and quantum efficiency. An increase in the density of InGaN/GaN band-tail states and in the hopping conductivity of injection barriers is necessary to provide the high-level tunnel injection and close-to-unity power efficiency of high-power light-emitting diodes.     

OMVPE of InAs quantum dots on an InGaP surface

The organometallic vapor phase epitaxy of InAs quantum dots has been investigated by comparing the effect the underlying surface has on the quantum dot physical characteristics. Atomic force microscopy measurements were used to identify the InAs QDs coalesce to significantly larger size when deposited on an InGaP surface compared to a GaAs surface. Quantitative assessment of the total QD volume on different surfaces such as GaAs, InGaP, and GaAsP implicates the role of indium in the underlying surface for the increase in QD size on InGaP surfaces.     

Revisiting Hole Injection in Quantum Dot Light-Emitting Diodes

Injecting holes from the hole transport layer (HTL) into the quantum dot (QD) emitting layer in quantum dot light-emitting diodes (QLEDs) is considered challenging due to the presence of a relatively high hole injection barrier at the HTL/QD interface. However, QLEDs with exceptional brightness and efficiency are achieved, prompting a reevaluation of the traditional hole injection mechanisms. This study examines the hole injection mechanism in QLEDs using a combination of experiments and simulations. The results demonstrate that the applied bias significantly reduces the barrier height between the highest occupied molecular orbital level of the HTL and the valence band (VB) of the QDs, facilitating hole injection. The bending of the lowest unoccupied molecular orbital energy level of the HTL at the HTL/QD interface confines electrons within the QD, effectively minimizing leakage current. Additionally, the triangle-shaped potential barrier arising from the bending of the VB energy level of the QDs creates favorable conditions for hole–tunneling injection. Moreover, both simulations and experiments consistently demonstrate that the predominant pathway for hole injection from the HTL to the QDs in the QLED device involved thermally assisted tunneling. This study is important to understand the hole injection mechanism in QLEDs.     

Super-flat (411)A interfaces and uniformly corrugated (775)B interfaces in GaAs/AlGaAs and InGaAs/InAlAs heterostructures grown by molecular beam epitaxy

Extremely flat interfaces, i.e. effectively atomically flat interfaces over a wafer-size area were realized in GaAs/AlGaAs quantum wells (QWs) grown on (411)A GaAs substrates by molecular beam epitaxy (MBE). These flat interfaces are called as “(411)A super-flat interfaces”. Besides in GaAs/AlGaAs QWs, the (411)A super-flat interfaces were formed in pseudomorphic InGaAs/AlGaAs QWs on GaAs substrates and in pseudomorphic and lattice-matched InGaAs/InAlAs QWs on InP substrates. GaAs/AlGaAs resonant tunneling diodes and InGaAs/InAlAs HEMT structures with the (411)A super-flat interfaces were confirmed to exhibit improved characteristics, indicating high potential of applications of the (411)A super-flat interfaces. High density, high uniformity and good optical quality were achieved in (775)B GaAs/(GaAs)_m(AlAs)_n quantum wires (QWRs) self-organized in a GaAs/(GaAs)_m(AlAs)_n QW grown on (775)B GaAs substrates by MBE. The QWRs were successfully applied to QWR lasers, which oscillated at room temperature for the first time as QWR lasers with a self-organized QWR structure in its active region. These results suggest that MBE growth on high index crystal plane such as (411)A or (775)B is very promising for developing novel semiconductor materials for future electron devices.     

Combined two-band models of resonant tunneling diodes

A satisfactory agreement between calculated voltage-current characteristics of GaAs/AlAs and Si/SiGe heterostructure resonant tunneling diodes and experimental data was obtained by using combined two-band models based on semiclassical and quantum-mechanical approaches. A high sensitivity of the characteristics of GaAs/AlAs-based devices to factors such as the transverse wave vector, changes of the heterostructure??s X-conduction band minimum, the surface charge density on heterointerfaces, and G-X intervalley scattering, is shown.     

Structural and infrared absorption properties of self-organized InGaAs/GaAs quantum dots multilayers

Self-organized InGaAs/GaAs quantum dots (QDs) stacked multilayers have been prepared by solid source molecular beam epitaxy. Cross-sectional transmission electron microscopy shows that the InGaAs QDs are nearly perfectly vertically aligned in the growth direction [100]. The filtering effect on the QDs distribution is found to be the dominant mechanism leading to vertical alignment and a highly uniform size distribution. Moreover, we observe a distinct infrared absorption from the sample in the range of 8.6–10.7 μm. This indicates the potential of QDs multilayer structure for use as infrared photodetector.     

Electroluminescence of InGaAs/GaAs quantum-size heterostructures with (III,Mn)V and Ni ferromagnetic injectors

Electroluminescence characteristics of light-emitting diodes based on InGaAs/GaAs quantum well heterostructures with an injector layer made of ferromagnetic metal (Ni), semimetal compound (MnSb), or magnetic semiconductor (InMnAs) were comparatively studied. The general feature is electroluminescence quenching as the spacer layer thickness between a quantum well and a magnetic injector decreases. It was found that the temperature dependence of the electroluminescence in diodes with Ni and MnSb is caused by thermal ejection of carriers from the quantum well; in diodes with InMnAs, it is caused by the temperature dependence of the carrier concentration in magnetic semiconductor and thermal ejection of carriers from the quantum well in the high-temperature region.     

一种新材料结构的RTD器件的设计及实现

设计了一种带有Al0.22Ga0.78As/In0.15Ga0.85As/GaAs发射极空间层和GaAs/In0.15Ga0.85As/GaAs量子阱的共振隧穿二极管(RTD)材料结构,并且成功地制作了相应的RTD器件.在室温下,测试了RTD器件的直流特性,计算了RTD器件的峰谷电流比和可资电流密度.在分析器件特性的基础上,指出调整材料结构和优化工艺参数将进一步提高RTD器件的性能.     

Numerical simulation of the current-voltage characteristics ofheteroepitaxial Schottky-barrier diodes

A numerical model resulting in the current-voltage characteristics of standard and heteroepitaxial Schottky-barrier diodes is presented. Simulations of GaAs diodes, as well as InGaAs diodes grown on GaAs and InP substrates, are presented. The model considers quantum-mechanical tunneling, and is therefore applicable to highly doped devices. A self-consistent drifted-Maxwellian distribution is used to model the electron energy distribution at high current densities. The assumption of a drifted-Maxwellian distribution is shown to lead to higher current at high bias than predicted with the assumption of a Maxwell-Boltzmann or Fermi-Dirac distribution. The presence of a heterojunction at the InGaAs-substrate interface is predicted to lead to an additional series resistance component     

Light-emitting tunneling nanostructures based on quantum dots in a Si and GaAs matrix

InGaAs/GaAs and Ge/Si light-emitting heterostructures with active regions consisting of a system of different-size nanoobjects, i.e., quantum dot layers, quantum wells, and a tunneling barrier are studied. The exchange of carriers preceding their radiative recombination is considered in the context of the tunneling interaction of nanoobjects. For the quantum well-InGaAs quantum dot layer system, an exciton tunneling mechanism is established. In such structures with a barrier thinner than 6 nm, anomalously fast carrier (exciton) transfer from the quantum well is observed. The role of the above-barrier resonance of states, which provides “instantaneous” injection into quantum dots, is considered. In Ge/Si structures, Ge quantum dots with heights comparable to the Ge/Si interface broadening are fabricated. The strong luminescence at a wavelength of 1.55 μm in such structures is explained not only by the high island-array density. The model is based on (i) an increase in the exciton oscillator strength due to the tunnel penetration of electrons into the quantum dot core at low temperatures (T < 60 K) and (ii) a redistribution of electronic states in the Δ₂-Δ₄ subbands as the temperature is increased to room temperature. Light-emitting diodes are fabricated based on both types of studied structures. Configuration versions of the active region are tested. It is shown that selective pumping of the injector and the tunnel transfer of “cold” carriers (excitons) are more efficient than their direct trapping by the nanoemitter.     

High-efficiency light-emitting diodes at ≈1.3 μm usingInAs-InGaAs quantum dots

Light-emitting diodes (LEDs) based on long-wavelength, self-assembled InAs-InGaAs quantum dots (QDs) are demonstrated and characterized. The LEDs consist of a single layer of QDs positioned at λ/2 from a top gold mirror to enhance the extraction efficiency. The external quantum efficiency at room temperature is 1%, which corresponds to an estimated 13% radiative efficiency. High-injection electroluminescence and photovoltage spectra under reverse bias allow us to determine the transition energies of excited states in the QDs and bidimensional states in the adjacent InGaAs quantum well     

Polarization dependences of electroluminescence and absorption of vertically correlated InAs/GaAs QDs

The results of experimental studies concerning the optical polarization anisotropy of electroluminescence and absorption spectra of systems with a varied number of tunnel-coupled vertically correlated In(Ga)As/GaAs quantum dots (QDs), built into a double-section laser with equal-length sections, are presented. One such system is a QD superlattice exhibiting the Wannier-Stark effect. The involvement of heavyhole ground states in optical transitions for light polarized both in the plane perpendicular to the growth axis (X-Y) and along the growth direction Z of the structure was observed. The degree of polarization anisotropy depends on the height of vertically correlated QDs and the QD superlattice: the total thickness of all In(Ga)As QD layers and GaAs spacers between the QDs, which is related to the Z component of the wave function of heavy-hole ground states for vertically correlated QDs and for the QD superlattice.