共查询到20条相似文献,搜索用时 15 毫秒
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A number of experimental and theoretical studies indicate that DX centers in GaAs, its alloys and other III–V semiconductors have negative U properties. Using far infrared localized vibrational mode (LVM) spectroscopy of Si donors in GaAs under large hydrostatic pressure in a diamond anvil cell we have discovered an LVM of the Si DX center. From the ratio of the LVM absorption lines of SiGa and SiDX and the compensation in our GaAs samples, we show unambiguously that two electrons are trapped when the ionized shallow Si donors transform into negatively charged DX centers, in full agreement with the negative U model.Dedicated to H.-J. Queisser on the occasion of his 60th birthday 相似文献
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DX center has been characterized in four GaAs---AlAs superlattices grown by MBE at 580°C. The structures are uniformly Si-doped or selectively Si-doped in the AlAs layers or in the middle of the GaAs layers or on both sides of the interfaces. Deep level transient spectroscopy measurements (DLTS) put in evidence one dominant electron trap, with an activation energy for thermal emission of about 0.42eV for all the superlattices. This defect shows a thermally activated capture cross section and a large concentration except for the case where the only GaAs layers are doped. For the first time, a study of the capture reveals a capture activation energy of 0.36-0.37 eV, which allows us to locate the DX level nearly 60 meV below the conduction miniband. From these results, we show that the observed DX center is related to silicon in the AlAs layers. For the case when the AlAs barriers are not doped, the DX level is due to the Si diffusion from the middle of the wells towards the barriers, the Si atoms having diffused during the growth. 相似文献
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Abstract We report on activated capture and emission experiments obtained under hydrostatic pressure. The observed structures in the thermostimulated capture curves are interpreted as a competition between capture and emission from the different configurations of the DX center, which are related to the local environment of the Si atom. The analysis of the capture kinetic experiments supports the hypothesis of the negative charge state of the DX center. 相似文献
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The influence of hydrostatic pressure on the energy levels of eight different deep traps in GaAs is determined by means of a transient capacitance technique. Hydrostatic pressure coefficients are shown to be decisive parameters in order to distinguish isoenergetic traps of different origin. For the EL6-, the M3- and the E3-traps (Ec?0.31eV), strongly different pressure coefficients are found. The HK1- and HK2- hole traps exhibit only small pressure coefficients relative to the valence band edge. 相似文献
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P. M. Mooney 《辐射效应与固体损伤》2013,168(1-2):281-298
Abstract The DX center, the lowest energy state of the donor in AIGaAs with x < 0.22, is responsible for the reduced conductivity as well as the persistent photoconductivity observed in this material at low temperature. Extensive studies of the properties of this deep level in Si-doped AIGaAs are reviewed here. Data are presented showing that the characteristics of the DX center remain essentially unchanged when it is resonant with the conduction band (x < 0.22) and that, independent of other compensation mechanisms, the DX center therefore limits the free carrier concentration in Si-doped GaAs to a maximum of about 2 × 1019 cm?3. Recent measurements suggesting that the lattice relaxation involves the motion of the Si atom from the substitutional site toward an interstitial site are also presented. Evidence for the negative U model, that the DX level is the two electron state of the substitutional donor, is discussed. 相似文献
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Abstract Hall coefficient (RH) and electrical resistivity measurements have been performed as a function of temperature (between 77 K and 300 K) and under hydrostatic pressures (up to 15 kbar) on a set of Se-doped GaSb samples with impurity concentrations in the range 8×1017 cm?3 - 1×1018 cm?3. With increasing pressure at 300 K, the electrons are strongly trapped into a resonant impurity level. The pressure induced occupation of this level leads to time-dependent effects at T<120 K. The activated thermal electron emission over a potential barrier E<sb>B = 300×30 meV gives clear evidence for a large lattice relaxation around the impurity centers characteristic for DX-like behavior. 相似文献
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S. A. Basun A. A. Kaplyanskii A. B. Kutsenko V. Dierolf T. Tröster S. E. Kapphan K. Polgar 《Physics of the Solid State》2001,43(6):1043-1051
Low-temperature luminescence spectra of stoichiometric Cr: LiNbO3 and of congruent Cr, Mg: LiNbO3 were studied. Cr3+ impurity ions preferentially occupy Li+ sites (CrLi) in the LiNbO3 crystal lattice, while Cr3+ ions substituting for Nb5+ ions (CrNb) occur in addition to CrLi centers in codoped Cr, Mg: LiNbO3 crystals. Application of a high hydrostatic pressure leads to a transformation of (dominant in concentration) Cr3+ centers from low-to high-crystal-field centers. Due to a strong pressure-induced blue shift of the 4 T 2 state resulting in crossing with the 2 E state, the replacement of the broad band 4 T 2 → 4 A 2 emission by a narrow R-line emission 2 E → 4 A 2 occurs in the luminescence spectra of the samples. This effect of level crossing was observed for the dominant Cr Li 3+ and Cr Nb 3+ centers at pressures which correlated well with estimations based on the 4 T 2-2 E energy gap (230 and 1160 cm?1) and on the rate of their pressure-induced change (14.35 and 11.4 cm?1/kbar, respectively). 相似文献
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The pressure shift of S excitons in the rutile-type semiconductor tin oxide (SnO2) is measured by two-photon absorption. From these data the pressure coefficients of the band gap (62.0 meV/GPa) and of the exciton binding energy (0.87 meV/GPa) are determined. 相似文献
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We have measured surface photoluminescence properties of Si-doped bulk GaAs using a near-field scanning optical microscope. An apertured fiber probe tip is used as an emitter of excitation laser as well as a collector of luminescence from GaAs. Due to the Fabry-Perot etalon effect, the excitation laser is reflected or transmitted with an oscillation period of λ.He-Ne/2 as the gap between the tip and the GaAs surface varies. The luminescence from GaAs also varies with an oscillation period of λGaAs/2 due to the same etalon effect. Therefore, the intensity of luminescence light collected by the probe tip shows a beating between two oscillations of different periods. When the probe approaches the GaAs surface, the collected luminescence intensity increases due to tunneling of evanescent wave. On the other hand, when we collect the luminescence using a lens, the intensity also increases due to similar coupling of evanescent wave into propagating wave in spite of a shadowing effect of the wide metal coating. 相似文献
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The change of resistivity of the 2.3 MeV-electron-irradiated bulk n- and p-GaAs have been measured at hydrostatic pressure up to 5 kbar at RT. Corrections for the changes in free electron and hole mobilities with pressure have been neglected. The resistivity changes are explained by a dependence on pressure of the ionisation energy of the radiation-induced E- and H-traps. The results indicate that most from these radiation- induced levels moves away from the conduction-band edge (γc-point) at a rate approximately (0.8?1.0)γG, here γG=11.6×10?6 eV bar?1 is the energy gap pressure coefficient for GaAs at RT. The high changes in ionization energies of E2 to E5-traps upon pressure are to be compared with the lower changes in ionization energies found for the deep-lying impurity levels. In accordance with the theoretical investigation it was suggested that most of the investigated radiation-induced levels in GaAs are t2-states of Ga- and As-vacancies. 相似文献
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The pressure dependence of optical transitions in Ga0.64In0.36As/GaAs and Ga0.64In0.36N0.01As0.99/GaAs single quantum well (SQW) structures were studied in photoreflectance (PR) spectroscopy. In order to apply high hydrostatic pressure, up to ∼11 kbar, the liquid-filled clamp-pressure cell with a sapphire window for optical access has been adopted in the PR set-up with the so called ‘bright configuration’. It has been found that the linear hydrostatic pressure coefficient for the ground state transition are equal to 8.6 and 7.3 meV/kbar for the GaInAs/GaAs and GaInNAs/GaAs SQWs, respectively. This result shows that the incorporation of only 1% of N atoms into GaInAs/GaAs leads to ∼15% decrease in the pressure coefficient. In addition, a non-linearity in the pressure dependence of the ground state transition has been resolved for the GaInNAs/GaAs SQW. 相似文献