Nonlinear transport in p-type SiGe quantum well structure containing Ge quantum dots

We use magneto-transport spectroscopy to study a dramatic instability between a low and high conductivity mode in Si/SiGe-based resonant tunneling diodes with an embedded layer of self-assembled Ge hut cluster quantum dots in the Si barrier. In the low current regime a simple activation-type behavior with an astonishingly low activation energy in the order of 0.1 meV is determined. In the high current regime a region of negative differential conduction can be observed. We discuss the influence of different layer structures and magnetic fields.     

Anomalous quantum-confined Stark effects in stacked InAs/GaAs self-assembled quantum dots

Vertically stacked and coupled InAs/GaAs self-assembled quantum dots (SADs) are predicted to exhibit strong hole localization even with vanishing separation between the dots, and a nonparabolic dependence of the interband transition energy on the electric field, which is not encountered in single SAD structures. Our study based on an eight-band strain-dependent k x p Hamiltonian indicates that this anomalous quantum confined Stark effect is caused by the three-dimensional strain field distribution which influences drastically the hole states in the stacked SAD structures.     

Polarization dependence of intersubband absorption and photoconductivity in p-type SiGe quantum wells

We present a detailed study of the polarization dependence of subband absorption and photoconductivity in Si/SiGe quantum wells. For samples with a hole concentration ofp_s2.8×10¹² cm², bothp- ands-polarized absorptions have been observed and transitions to several excited states are clearly identified by comparison with self-consistent Luttinger-Kohn type calculations. The photoconductivity is surprisingly insensitive to the polarization, which indicates the importance of the subsequent transport process on the photocurrent responsitivity.     

Intraband photoresponse of SiGe quantum dot/quantum well multilayers

In this contribution we study the intravalence band photoexcitation of holes from self-assembled Ge quantum dots (QDs) in Si followed by spatial carrier transfer into SiGe quantum well (QW) channels located close to the Ge dot layers. The structures show maximum response in the important wavelength range 3–5 μm. The influence of the SiGe hole channel on photo- and dark current is studied depending on temperature and the spatial separation of QWs and dot layers. Introduction of the SiGe channel in the active region of the structure increases the photoresponsivity by up to about two orders of magnitude to values of 90 mA/W at T=20 K. The highest response values are obtained for structures with small layer separation (10 nm) that enable efficient transfer of photoexcited holes from QD to QW layers. The results indicate that Si/Ge QD structures with lateral photodetection promise very sensitive large area mid-infrared photodetectors with integrated readout microelectronics in Si technology.     

Theoretical modeling for quantum-confined Stark effect due to internal piezoelectric fields in GaInN strained quantum wells

Recent experimental investigations revealed that the biaxial stress in thin InGaN layers grown on thick GaN layer induces a large piezoelectric field along [0001] orientation that causes red-shift in optical transitions and reduction in oscillator strengths because of spatial separation of the electron and hole wave functions. In this Letter based on theoretical modeling we determined the well width z-dependent effect on red-shifted quantum-confined Stark effect (QCSE) in GaN/In_xGa_1 − xN (x=0.13) strained quantum well structures. Analyses are based on the solution of Schrödinger equation in a finite well including the internal piezoelectric electric field (F) due to the strained polarization as the perturbation potential. Our theoretical results show: (1) the red-shift in optical transition has a quadratic well-width form as it is for infinite wells (Davies, 1998) [1], (2) assuming the model based on a carrier effective mass dependence on the width of quantum wells, m^∗(z), fits the experimental data (Takeuchi et al., 1997) [2] much more accurate compare to the model with constant effective mass, m^∗.     

InGaAs/GaAs photorefractive multiple quantum well device in quantum confined Stark geometry

We have demonstrated photorefractive InGaAs/GaAs multiple-quantum-well devices in the quantum confined Stark geometry. A four-wave-mixing diffraction efficiency up to 0.3% is obtained at a wavelength of 949 nm. Proton implantation strongly reduces the maximum diffraction efficiency although it saturates the diffraction efficiency at smaller grating period comparing to as-grown device. We have also observed higher order diffractions. It is found that the space-charge field changes its pattern temporally from a sinusoidal pattern to a rectangular one with decreasing its modulation depth. Received: 7 December 2000 / Published online: 27 April 2001     

Influence of the quantum-confined Stark effect on the temperature-induced photoluminescence blueshift of In GaN/GaN quantum wells in laser diode structures

Measurements of the excitation power-dependence and temperature-dependence photoluminescence(PL) are performed to investigate the emission mechanisms of In Ga N/Ga N quantum wells(QWs) in laser diode structures. The PL spectral peak is blueshifted with increasing temperature over a certain temperature range. It is found that the blueshift range was larger when the PL excitation power is smaller. This particular behavior indicates that carriers are thermally activated from localized states and partially screen the piezoelectric field present in the QWs. The small blueshift range corresponds to a weak quantum-confined Stark effect(QCSE) and a relatively high internal quantum efficiency(IQE) of the QWs.     

量子阱Si/SiGe/Sip型场效应管阈值电压和沟道空穴面密度模型

Si材料中较低的空穴迁移率限制了Si互补金属氧化物半导体器 件在高频领域的应用. 针对SiGe p型金属氧化物半导体场效应管(PMOSFET)结构, 通过求解纵向一维泊松方程,得到了器件的纵向电势分布, 并在此基础上建立了器件的阈值电压模型,讨论了Ge组分、缓冲层厚度、 Si帽层厚度和衬底掺杂对阈值电压的影响.由于SiGe沟道层较薄, 计算中考虑了该层价带势阱中的量子化效应. 当栅电压绝对值过大时, 由于能带弯曲和能级分裂造成SiGe沟道层中的空穴会越过势垒到达Si/SiO₂界面, 从而引起器件性能的退化. 建立了量子阱SiGe PMOSFET沟道层的空穴面密度模型, 提出了最大工作栅电压的概念, 对由栅电压引起的沟道饱和进行了计算和分析. 研究结果表明,器件的阈值电压和最大工作栅压与SiGe层Ge组分关系密切, Ge组分的适当提高可以使器件工作栅电压范围有效增大.     

Experimental and theoretical study of the quantum-confined Stark effect in a single InGaN/GaN quantum dot under applied vertical electric field

We present a study of the effect of externally applied vertical electric field on the optical properties of single InGaN/GaN quantum dots via microphotoluminescence spectroscopy. This is achieved by incorporating the quantum dot layer in the intrinsic region of a p–i–n diode structure. We observe a large blue energy shift of 60 meV, which is explained by the partial compensation of the internal piezoelectric field. The energy shift dependence on the applied field allows the determination of the vertical component of the permanent dipole and the polarizability. We also present theoretical modelling of our results based on atomistic semi-empirical tight-binding simulations. A good quantitative agreement between the experiment and the theory is found.     

Stark effect in diffused quantum wells

We study the longitudinal Stark effect in diffused AlGaAs/GaAs quantum wells grown along the [1,0,0] direction. The energies of the ground electron and hole states and the first excited hole state are calculated for different diffusion lengths and electric field strengths. The energies of the main optical transitions and their Stark shifts are found. The intensities of the transitions are considered in terms of the bound states spatial distributions. The calculations are carried out within the semi-empirical sp³s ^* tight-binding model including spin and the surface Green function matching method. We compare our results with those obtained by means of other theoretical methods.     

含有δ掺杂层的SiGe pMOS量子阱沟道空穴面密度研究

建立了含有δ掺杂层的SiGe pMOS器件量子阱沟道中空穴面密度的静态与准静态物理模型，并对该模型进行了数值分析.讨论了静态时器件量子阱空穴面密度与δ掺杂层杂质浓度和本征层厚度的关系，阈值电压VT与δ掺杂层杂质浓度NA、量子阱沟道载流子面密度Ps及本征层厚度di等参数间的关系.同时还讨论了准静态时量子阱空穴面密度P′s与栅压VGS的关系. 关键词： δ掺杂层 空穴面密度     

Absorption and Recombination in p-type SiGe quantum well structures

We consider the possibility of obtaining normal incident absorption in the 10-15 μm range, using strained p-type SiGe quantum well structures using a full-scale relativistic pseudo-potential method. We predict the magnitude and the position of the peak absorption response and determine the microscopic (band structure) origin of the peaks. We show that major contributions to the absorption occur away from the centre of the first Brillouin zone, and thus the energy of the peak response cannot be accurately predicted by simple particle-in-a-box models. Also we discuss the possibilities of engineering the band structures of these systems so as to minimize non-radiative (Auger) recombination. Comparisons of the parallel incidence absorption response calculated by our method with recent experimental results are presented.     

Room-temperature direct-bandgap photoluminescence from strain-compensated Ge/SiGe multiple quantum wells on silicon

Strain-compensated Ge/Si_0.15Ge_0.85 multiple quantum wells were grown on an Si_0.1>Ge_0.9 virtual substrate using ultrahigh vacuum chemical vapor deposition technology on an n⁺-Si(001) substrate. Photoluminescence measurements were performed at room temperature, and the quantum confinement effect of the direct-bandgap transitions of a Ge quantum well was observed, which is in good agreement with the calculated results. The luminescence mechanism was discussed by recombination rate analysis and the temperature dependence of the luminescence spectrum.     

Direct-bandgap electroluminescence from tensile-strained Ge/SiGe multiple quantum wells at room temperature

Tensile-strained Ge/SiGe multiple quantum wells(MQWs) were grown on a Ge-on-Si virtual substrate using ultrahigh vacuum chemical vapor deposition on an n+-Si(001) substrate. Direct-bandgap electroluminescence from the MQWs light emitting diode was observed at room temperature. The quantum confinement effect of the direct-bandgap transitions is in good agreement with the theoretical calculated results. The redshift mechanism of emission wavelength related to the thermal effect is discussed.