The combinatorial material chip method has been used to study the emission efficiency of InAs/GaAs quantum dots. The photoluminescence spectroscopy is performed to obtain the rule of emission efficiency on the proton implantation dose. A pronounced enhancement of room temperature emission efficiency has been obtained by the optimized quantum dots process condition. The increment of emission efficiency up to 80 itmes has been observed. This effect may be resulted from both the proton passivation and carrier capture enhancement effects. The maximum photoluminescence peak shift is about 23 meV resulted from the intermixing of quantum dots. A linear dependence behavior has been observed for both the non-radiative recombination time and carrier relaxation time on the ion-implantation dose. The maximum enhancement of the photoluminescence is observed in the proton implantation dose of 1.0 x 1014 cm-2 followed by rapid thermal annealing at 700°C. These effects will be useful for the QDs' optoelectronic devices.
The intermixing techniques have been used to modify the behavior of the quantum well infrared photodetector (QWIP). It is demonstrated that the proton implantation assistant intermixing process is very effective to the modification of the quantum well potential. Both the inter-band transition and inter-sub-band transitions are used to study the intermixing effects. After the characterization on the modified detector, the dominant mechanisms in the QWIP are examined.
This paper reports the molecular beam epitaxy growth of the GaAs films on the SrTiO3 (100) substrates. The microstructures of the films are characterized by XRD and SEM. SEM results show the different shapes of islands at different thickness. Micro-Raman studies show that the crystal lattice vibrations of the GaAs films are similar to that of GaAs bulk material. Using the photo modulated reflectance spectroscopy and photoluminescence measurement techniques, optical transitions close to GaAs band gap energy are observed, and large blue shifts are observed.
We have studied the energy band transitions between confined sub-bands in 10 nm surface quantum well based on in-situ Photo-modulated Reflectance (PR) Spectrum in Molecular Beam Epitaxy system. The single surface quantum well (SQW) is confined by the vacuum on one side and by AlxGa1-xAs barrier on the other side. The structure parameters of the SQW are monitored by the Reflective High- Energy Electron Diffraction (RHEED) during growing procedure. In PR spectrum, we have observed clearly the transitions from the hole sub-bands to the electronic sub- bands. The transition of excitation states is first observed in single surface quantum well. The results are well explained by the effective mass approximation with parameters provided by RHEED.
The 1D atom chain with the multi-neighbor interactions is studied as a simplified model for the lattice vibration of ferroelectric with the long-range Coulomb interaction. The real space method to investigate the lattice dynamic of the non-perfect lattice is introduced. The combined 1D chain model to simulate GaAs/SrTiO3 system is proposed and the Raman spectrum is analyzed.
The micro-photoluminescence ((mu) -PL) scanning has been performed on a GaAs/AlGaAs single V-grooved quantum wire (QWR) along the direction perpendicular to the wire. The variation of (mu) -PL spectra in different spatial positions with different quantum structures have been observed. In the region of QWR the PL spectra contain the peaks from QWR, necking quantum well and vertical quantum well while in that of about 1 micrometers leaving away from the QWR the PL spectra show only the peaks from side-wall quantum well and top quantum well. All the acquired spectra have been fitted by Gaussian line shape and the different PL components are decomposed. The intensity variation with the spatial position directly demonstrates the origin of the PL correlated to the different quantum structures. The PL energy for the each quantum structures has been precisely determined.
Due to the mature material growth and device fabrication technology, GaAs/AlxGa1-xAs quantum-well infrared photodetector (QWIP) has been extensively studied and used in remote sensing, particularly in long wavelength range, e.g. the atmospheric window region of 8 approximately 14 micrometers . This paper reports the using of intermixing techniques to modify GaAs/AlGaAs multiple quantum well photodetectors (QWIPs). A red shift in response wavelength of QWIP has been obtained both by rapid thermal annealing (RTA) and proton implantation. The peak response wavelengths has been shifted into the atmospheric window (8.3 micrometers ) from the originally 7.7 micrometers . The response spectra have been measured as the function of the different temperature of the RTA and the ion doses in the range from 4 X 1014 to 5 X 1015 cm-3, respectively. The device performance such as dark current and blackbody response are also measured at different conditions. The effect of RTA and ion implantation on the device performance has been interpreted theoretically by the interdiffusion of Al atoms across the GaAs/AlxGa1-xAs heterointerfaces.
The photothermal ionization spectroscopy (PTIS) has been employed to study Be shallow acceptor states in GaAs grown by MBE. We have observed the G line, D line and C line transitions which are from the ground state 1s3/2((Gamma) 8+) of Be acceptor to the first three excited odd-parity states 2p3/2(Gamma) 8-), 2p5/2((Gamma) 8-) and 2p5/2((Gamma) 7-), respectively. The transition from the ground state 1s3/2((Gamma) 8-) to the excited state 2p1/2((Gamma) 6-) is identified as well. According to the PTIS, we deduce the binding energy of Be ground state in GaAs is 28.6 mev.
We have studied the longitudinal optical phonon-plasmon coupled (LPP) modes in device quality GaN epitaxy thin films deposited on sapphire substrate using infrared reflection spectroscopy. By theoretical calculation and fitting with the experimental IR reflection spectra for a series of Si doped GaN epilayers we obtain the phonon vibration parameters and the plasmon frequency and damping constant in GaN. The LPP modes have been deduced by the imaginary parts of the reciprocal dielectric function in IR reflection measurement. Both high and low branches of the LO phonon- plasmon coupling mode (LPP+ and LPP-) are well resolved. With the increase of doping level, the frequency of the LPP+ mode shifts to higher while that of the LPP- mode trends toward TO phonon of GaN. The carrier concentration and mobility in GaN have also been deduced. The IR measured concentration of carriers coincides with the Hall measurement. The mobility ratio of Hall to IR is about 1.75 approximately 1.96, implying a dominating mechanism of ionized impurity scattering. Raman measurement has also been performed on the same series of samples. The spectral reveal the similar behavior of the LPP modes to that in IR measurement. Our results show that both IR reflection and Raman scattering are powerful and nondestructive tools to investigate the carrier properties in GaN thin films.
The invention and the investigation of the semiconductor quantum well structures have influenced and changed the condensed matter physics, microelectronics, opto-electronics as well as other related scientific and technological fields tremendously in last three decades. The quantum well, superlattice and their new development or new generation, that is quantum wires and quantum dots and many other microstructures provide us furthermore really new challenge for the infrared application and technology. The cascade infrared laser, the multi-color and tunable infrared detectors, as well as the focus plane array based on the intersubband or interband transitions in usual multi quantum well or type-II superlattice structures are some of the examples. We report here mainly a comprehensive investigation on the application of GaAs/AlGaAs multi- quantum well structures as the long wavelength infrared detectors and their focus plane arrays based on the intersubband transitions of the quantum wells. The fundamental parameters of the devices, the performance of the detectors and the arrays, the modulation and tuning of detection wavelength via atom intermixing between wells and barriers, the coupling of the radiation with the electronic transitions and the demonstration of the imaging will be reviewed and discussed together with the comparison to the traditional infrared detectors.
In this letter, self-aligned dual implantation technique was successfully used to speed up the carrier transportation from sidewall quantum well (SQWL) to quantum wire (QWR) region in V-groove AlGaAs/GaAs QWR structure. Photoluminescence (PL) and time resolved photoluminescence (TRPL) show that the lateral confinement was enhanced after intermixing by intermixing the necking region. Lifetime was obviously enlonged after selective intermixing, which comes from the enhanced lateral carrier confinement. Strong hot exciton relaxation process in QWRs region is observed after selective intermixing.
Because of the isotropic energy band structure of the (Gamma) electrons in GaAs/AlGaAs quantum well infrared photodetector (QWIP), normal incident radiation absorption is not possible so that the optical grating and its optimization become key requirements for the QWIPs. In this work we study the optical grating structure based on Huygen's principle and Kirchhoff's formula. The theory developed in this paper is used to design the optical grating for our GaAs/AlGaAs QWIPs with responding wavelength around 8.0 micrometer. The result for the photoconductive QWIPs of 1 X 128 focal plane array (FPA) working at 80 K is presented. The theoretical model has also been used to design the grating size for the 64 X 64 FPA which results in a good FPA device performance around 8.0 micrometer.
In this paper we present the observation of the interband transition in the GaAs (100) surface Si-delta-doping potential. Samples with different surface doping concentrations (Ns equals undoped, 3.0 X 1012, 6.3 X 1013, 2.4 X 1014 and 3.6 X 104 cm-2) have been studied at room temperature in the MBE high vacuum chamber using modulated photo-reflection (PR) spectroscopy technique. The MBE chamber guarantees that all the sample surfaces are free of oxidation or uncontrollable contamination. The optical transition of at GaAs bandedge around 1.41 eV is strong and is almost independent of Ns. A relatively weak feature above 1.42 eV has been observed which is clearly enhanced and blue-shifted following the increase of Ns. The experimental results have been analyzed and well explained based on the self-consistent Schrodinger-Poisson equations. The theoretical analysis indicates that it is not proper to attribute the PR spectral peak of 1.42 eV simply to be certain subband-related optical transition. The observed spectral peak of 1.42 eV is more likely to be related to the high-index confined-levels in the half-V-shape conduction band at the sample surface.
Cyclotron resonance (CR) of two-dimensional electron gases (2DEG) in GaAs/AlGaAs heterojunction was studied by the gate voltage ratio spectrum measurement technique. The oscillation behaviors of the intensity of the CR peaks, the electron effective mass, scattering time and mobility obtained by fitting the CR line shape with the magnetic field due to the resonant subband Landau level coupling (RSLC) were observed. Several intersubband energies with high quantum index were measured by this RSLC method at different gate voltage. The results are in good agreement with the self-consistent calculations including the depolarization shift and the exciton effect correction.
Manufacture of AlGaAs/GaAs QDs by visible light lithography and etching is accomplished in this paper, and the size distribution is studied by smaill-spotted PL. The broadening of PL peaks which is caused by the fluctuation of quantum well is studied.
Photoreflectance (PR) spectroscopy system is combined with molecular beam epitaxy (MBE) to accomplish in-situ PR measuring of the Si surface (delta) doping on GaAs (001) with different concentrations at different temperatures. The features observed on the high-energy side of the fundamental gap are attributed to transitions involving electronic subbands in the half V-shaped potential well. We find that the Si (delta) -doping-related spectral structure first shifts to high energy side with the doping concentration increasing, then almost stop shifting with the doping concentration higher than 2.4 X 1014 cm-2 when temperature increases, at certain doping concentration the Si (delta) - doping-related transition shifts toward low energy side. The dependence of the transition on doping concentration is well explained by using a simple theoretical model.
A comprehensive and spectroscopic investigation, including absorption (AB), photoluminescence (PL) and photoreflectance (PR) experiments on the electronic states and their optical transitions in some near-surface and surface quantum well structures of semiconductors are performed and reported here in this paper. The strain relaxation as a function of capping layer, the electronic states on the surface quantum well and the dependence of transition related surface Si (delta) doping on doping concentration.
A long-wavelength 128 by 1 GaAs/AlGaAs multiple quantum wells (MQWs) infrared detector (IRD) array is presented. A good photo-current responsibility Rp equals 2.02 X 106V/W is obtained with the cut-off wavelength being (lambda) c equals 8.6 micrometer and as a result, we obtain a good remanent heat image of a room-temperature subject.
Zeeman splitting of donor levels in silicon proportional to the square of the magnetic field are observed. Theoretical discussion indicated that this phenomenon is induced by mixing of donor states created by an external magnetic field.
The electrochromic property and chemical sensitivity of conducting polymer polyaniline (PAn) film prepared by electrochemical polymerization have been observed experimentally. The physical mechanism of color change of the PAn film has been discussed in light of the theories on the fundamental excitations in quasi-one dimensional conducting systems.
The dependence of intersubband transitions on
temperature and pressure in strained InGa1As/GaAs multiple
quantum wells with different x and well widths has been
investigated by use of the modulated reflection and absorption
spectroscopies. The identifications for dislocation free at the
interface will be discussed.
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