Hole transport due to shallow acceptors along boron doped SiGe quantum wells

Lateral conductivity and magnetotransport measurements were performed with SiGe single quantum well (QW) structures doped with boron in the QW. The conductivity at low temperatures (T) is shown to be due to hopping over B centers while at higher T, it is due to two-stage excitation: thermal activation of holes from the ground to strain-split B states are followed by hole tunneling into the valence band. The tunneling is due to a potential drop across the QW which is due to hole capture at surface states of the Si cap layer making the surface charged. The external potential applied across the QW essentially changes the lateral conductivity as well as the activation energy. The calculations of band profile, free carrier concentration in the QW and acceptor population, as well as an effect on the transverse electric field were carried out taking into account the charging of surface states.     

High performance infra-red detectors based on Si/SiGe multilayers quantum structure

Recently, single crystalline (Sc) Si/SiGe multi quantum structure has been recognized as a new low-cost thermistor material for IR detection. Higher signal-to-noise (SNR) ratio and temperature coefficient of resistance (TCR) than existing thermistor materials have converted it to a candidate for infrared (IR) detection in night vision applications. In this study, the effects of Ge content, C doping and the Ni silicidation of the contacts on the performance of SiGe/Si thermistor material have been investigated. Finally, an uncooled thermistor material with TCR of −4.5%/K for 100 μm × 100 μm pixel sizes and low noise constant (K_1/f) value of 4.4 × 10⁻¹⁵ is presented. The outstanding performance of the devices is due to Ni silicide contacts, smooth interfaces, and high quality multi quantum wells (MQWs) containing high Ge content.     

Si/SiGe quantum wells: fundamentals to technology

In this paper, we will briefly review the growth of Si/SiGe quantum wells and the effect of strain on the bandstructure. Enhanced electron/hole transport properties in such layers will be demonstrated, and their application in electronic devices such as P and N modulation-doped field-effect transistors (MODFET) will be discussed. At the circuit level, the use of these devices in a complimentary metal-oxide-semiconductor (CMOS) circuit implementation will be considered.     

Band offsets of InXGa1−XN/GaN quantum wells reestimated

Recently In_XGa_1−XN/GaN heterostructures and quantum wells (QWs) have gained immense importance in the application of III-V nitride materials. Reported values of the ratios of conduction band offset to valence band offset for In_XGa_1−XN/GaN QW structures, ΔE_c:ΔE_v, vary widely from 38:62 to 83:17. While trying to explain the unusual shifts in the photoluminescence (PL) spectra, obtained from In_XGa_1−XN/GaN QW structures, it has been found that a band offset ratio, ΔE_c:ΔE_v = 55:45, explains all the experimental data precisely. In this paper detailed theories, procedures, results and discussions to establish the newly estimated band offsets will be presented.     

Coulomb interaction of electron gas in MQWs Si/Si1 − xGex/Si

We present a theoretical analysis of the conduction and valence-band diagrams of SiGe/Si Multiple Quantum Wells (MQWs), having a specific “W” geometry, and designed for emission or photodetection around the 1.55 μm wavelength. Peculiar features have been extrapolated by solving self-consistent Schrödinger and Poisson equations, taking into account the electrostatic attraction induced by carrier injection. As a result, Coulomb interaction strongly modifies the band profiles and increases the electron probability density at the quantum well interfaces; the injected carrier concentration enhances electron–hole wave functions overlap and the in-plane oscillator strength. These MQWs structures, strain-compensated on relaxed Si_0.75Ge_0.25 pseudo-substrates, are potentially interesting for telecom applications.     

SiGe/Si hetero-field-effect-transistor with PN-junction gate

We report the first SiGe/Si HFET with a PN junction as a gate electrode. The epitaxial layer structure of the device is grown by MBE on a relaxed SiGe buffer. A mesa technology is used for device fabrication with implanted contact areas for source and drain and lift off technique for metallization. First DC results show the promising performance of this novel structure with respect to gate leakage current and breakdown voltage.     

High-performance strained Si/SiGe pMOS devices with multiple quantum wells

This paper describes the fabrication and results of the electrical characterization of buried channel Si/SiGe pMOS devices using double and single quantum wells. The devices have been fabricated in an almost standard CMOS technology including shallow trench isolation, rapid thermal annealing, and standard Co/Ti silicidation. The incorporation of 15% and 32% channels provides a strong enhancement (up to 85%) in long-channel mobility. This increased mobility behavior is translated into a 55% higher on-state current for the long-channel devices and a 13% higher on-state current (V/sub gs/-V/sub T/= -1 V and V/sub ds/= -1.5 V) for devices down to L/sub mask/=70 nm while maintaining low leakage and good short-channel and drain induced barrier lowering behavior.     

Electroluminescence enhancement of SiGe/Si multiple quantum wells through nanowall structures

The enhancement of light extraction from Si(0.5)Ge(0.5)/Si multiple quantum wells (MQWs) with nanowall structures fabricated by electron cyclotron resonance (ECR) plasma etching is presented. It is shown that the ECR plasma treatment does not damage the crystalline quality. At a driving current of 5.5 × 10(6)?A?m(-2), the light output intensity of the MQWs with nanowall structures shows an enhancement of about 50% compared with that of the original MQWs. In addition to the enhanced light extraction, the improved optoelectronic properties are also attributed to the strain relaxation in nanowall structures.     

SiGe/Si异质结光电器件

SiGe/Si异质结光电器件及其光电集成(OEIC)是硅基光电研究的一个非常引人注目的领域.综述了SiGe/Si异质结材料的基本性质,SiGe/Si异质结光电器件的结构、性能、应用及其光电集成.重点介绍了SiGe/Si光电探测器及其与其他相关器件的集成.     

Transmission electron microscopy and X-ray diffraction studies of quantum wells

A series of In _x Ga_1?x As (x=0·47) quantum wells with InP barrier layers have been grown on InP substrates by metalorganic vapour phase epitaxy (MOVPE) at 625°C. The nominal well widths were defined during growth at (i) 25 Å, 39 Å, 78 Å and 150 Å for one sample and (ii) 78 Å for all 4 wells in another sample. The InP barrier widths have been kept constant at 150 Å. These layers have been characterized by X-ray diffraction (XRD) which from simulation gave the nominally 78 Å well width as 84 Å and the nominally 150 Å barrier width as 150·5 Å. Transmission electron microscopy (TEM) and high resolution TEM (HRTEM) have been carried out on etched and ion-milled samples for direct measurement of well and barrier widths. The well widths found from TEM are 25 Å, 40 Å, 75 Å and 150 Å. TEM micrographs revealed that, while the InP barrier layer is of good quality and the growth is confirmed to be epitaxial, dipoles are detected at the interface and the quantum well has some small disordered regions. These thickness measurements are in good agreement with earlier photoluminescence (PL) and secondary ion mass spectrometry (SIMS) studies.     

Physics and applications of Si/SiGe/Si resonant interband tunneling diodes

Room temperature (RT) current–voltage characteristics of Si/Si_1−xGe_x/Si p⁺-i-n⁺ interband tunneling diodes are presented. The variation of the structural properties results in a more detailed picture of the tunneling process in these diodes, which allows further improvement of the relevant parameter. Special attention is paid to the peak current density (PCD) and the peak-to-valley current ratio (PVCR) of the devices. For an optimized structure with a 3-nm thick Si_0.54Ge_0.46 layer in the intrinsic zone a record PVCR of 6.0 at a PCD of approximately 1.5 kA/cm² was achieved. By reducing the layer thickness to 2.6 nm and simultaneously increasing the Ge content to 54%, the PCD increases to 30 kA/cm² at a high PVCR of 4.8.     

基于高电阻率衬底的Si/SiGe HBT

介绍了一种基于电阻率高达1000Ω·cm的硅衬底的锗硅异质结晶体管的研制.首先根据衬底寄生参数模型分析了衬底对器件高频性能的影响,然后设计了器件的材料与横向结构尺寸,该器件采用掩埋金属自对准技术在3μm工艺线上制备而成,测得其典型直流电流增益为120,BVCEO为9.0V,fT为10.2GHz,fmax为5.3GHz,比同结构尺寸的常规N 衬底Si/SiGe HBT的fT和fmax分别高出3.9GHz和1.5GHz.     

SiGe/Si光电探测器研究进展

本文综述了目前国内外在工作波长１．３～１．５μｍ的ＳｉＧｅ／Ｓｉ超晶格探测器和工作波长为８～１２μｍ的ＳｉＧｅ／Ｓｉ异质结长波长红外探测器方面的研究进展，并分析了存在的问题和材料的各种生长方法。     

SiGe／Si和SGOI材料的Li离子束RBS分析

SiGe合金薄膜中的Ge含量度分布对材料的禁带宽度和制作器件的性能有十分重要的影响。本文用Li离子束卢瑟福背散射分析法对SiGe／Si和SiGe-OI材料样品进行了分析。与TEM，SEM、Raman等分析结果进行比较表明，Li离子束RBS分析可同时测量SiGe层厚度，Ge含量度其深度分布，Si过渡层和SiO2层厚度，并有较好的测量精度。     

Si/SiGe hetero-junction solar cell with optimization design and theoretical analysis

Performances of solar cells, such as short circuit current density, open-circuit voltage, fill factor, and efficiency of solar cells on the multi-crystalline (mc)-SiGe on the Si with different Ge contents, are compared and investigated in this paper. The average Ge concentration was varied from 0% to ~ 20%. Appropriate addition of Ge in crystal Si is a very effective method to enhance the short circuit current density without degrading the open-circuit voltage owing to the modulation of the SiGe band-gap. The band-gap of the SiGe can be extracted by electron-hole plasma (EHP) model. With an optimization of Ge content and clean process condition, the overall efficiency of a Si/SiGe hetero-junction solar cell with Ge content of 8% is found to be ~ 16% and ~ 4% improvement achieved, as compared to the control multi-crystalline (mc)-Si solar cell. The theoretical simulations and analyses can help design the high efficiency Si/SiGe hetero-junction solar cell.     

Electronic structure of interdiffused GaInAs(P)/GaInAsP quantum wells

Band structure calculations are performed by k·p theory on lattice-matched (LM) and strain-compensated (SC) interdiffused GaInAs(P)/GaInAsP quantum wells (QWs) designed for 1.55 μm wavelength response. The evolution of the in-plane band structures as a function of the diffusion length (up to 5 nm) is presented and discussed. The subbands are tightened with consecutive changes in their curvatures and interactions. In the case of LM structures, a densely packed valence subband structure is found with spiky singular behaviors in the curves of density of states. These arise from electron-like subbands and are strongly modified after interdiffusion. The in-plane effective masses of carriers involved in the fundamental excitonic transitions increase by 15% (electrons) and 25% (holes). The subband tightening trend is strongly marked in the case of SC structures with uniform cationic composition, for which narrow QWs are required. On the other hand, this trend is weak in the case of SC structures with uniform anionic composition, in which QWs are rather wide. In this latter case, a good stability in the optical properties of the structures after thermal processing is expected. However, due to the tensile strain in the wells, only heavy holes (HHs) can be confined. Since in-plane motion of confined holes involves HH and light hole (LH) mixing, this restricts the dynamic characteristics expected for these structures.     

Unusual changes observed in the photoluminescence of annealed InxGa1 − xN/GaN quantum wells explained

In_xGa_1 − xN/GaN heterostructures and quantum wells (QWs) are particularly important in the application of III-V nitride materials for light emitting diodes and laser diodes. The photoluminescence (PL) emissions from In_xGa_1 − xN/GaN QW structures have been reported, where, for successive annealing operations, the PL peak suffers a primary red shift, followed by a blue shift. The observed phenomenon remains unexplained because of its complexity. This paper is intended towards a proper explanation of the observed experimental results through suitable quantum mechanical models and computations, whether the band gap of InN is 1.95 eV or 0.7 eV.     

Formation of a two-dimensional electron gas in ZnO/MgZnO single heterostructures and quantum wells

The properties of ZnO/MgZnO heterostructures grown by pulsed-laser deposition on sapphire (112?0) and ZnO (0001?) have been compared. Electron accumulation layers have been observed for ZnO/MgZnO heterostructures grown on sapphire by capacitance-voltage (C-V) spectroscopy. The formation of a two-dimensional electron gas (2DEG) in these structures has been confirmed by temperature dependent Hall effect measurements. From C-V measurements the sheet carrier density in a Zn_0.8 Mg_0.2O/ZnO/Zn_0.8 Mg_0.2O quantum well (QW) structure with a well width of about 5 nm is calculated to be only about 9.0 × 10¹⁰ cm^− 2. For the films deposited on sapphire 2D growth is observed in the Burton-Cabrera-Frank mode, as confirmed by atomic force microscopy. Step flow growth mode was achieved for the homoepitaxial thin films. Quantum confinement effects have been confirmed by photoluminescence (PL) measurements. Homoepitaxial QWs are more homogeneous (smaller inhomogeneous recombination broadening) than heteroepitaxial QWs.