967 resultados para Ensino normal Juiz de Fora (MG)
Resumo:
A KrF (248 nm) excimer laser with a 38 ns pulse width was used to study pulsed laser annealing (PLA) on Mg-doped cubic GaN alms. The laser-induced changes were monitored by photoluminescence (PL) measurement. It indicated that deep levels in as-grown cubic GaN : Mg films were neutralized by H and PLA treatment could break Mg-H-N complex. The evolution of emissions around 426 and 468 nm with different PLA conditions reflected the different activation of the involved deep levels. Rapid thermal annealing (RTA) in N-2 atmosphere reverts the luminescence of laser annealed samples to that of the pre-annealing state. The reason is that most H atoms still remained in the epilayers after PLA due to the short duration of the pulses and reoccupied the original locations during RTA. (C) 2000 Elsevier Science B.V. All rights reserved. PACS: 61.72.Vv; 61.72.Cc; 18.55. -m.
Resumo:
We report the device performance of normal-incidence (In, Ga)As/GaAs quantum dot intersubband infrared photodetectors. A primary intersubband transition peak is observed at the wavelength of 13 mu m (E-0 --> E-1) and a secondary peak at 11 mu m (E-0 --> E-2). The measured energy spacing in the conduction band of the quantum dots is in good agreement with low temperature photoluminescence measurement and calculations. A peak detectivity of 1 x 10(10) cm Hz(1/2)/W at 13 mu m was achieved at 40 K for these devices. (C) 1998 American Institute of Physics. [S0003-6951(98)01440-5].
Resumo:
Hole trap levels in a Mg-doped GaN grown by metalorganic vapor phase epitaxy (MOVPE) are studied with deep level transient spectroscopy (DLTS). The Mg concentration of the sample was 4.8 x 10(19) cm(-3), but the hole concentration was as low as 1.3 x 10(17) cm(-3) at room temperature. The DLTS spectrum has a dominant peak D-1 with activation energy of 0.41+/-0.05 eV, accompanied by two additional peaks with activation energies of 0.49+/-0.09 eV (D-2) and 0.59+/-0.05 eV (D-3). It was found that the dominant peak D-1 consists of five peaks, each of which has different activation energy and capture cross section. A relevant model for these levels is presented in relation to the Mg-N-H complexes. (C) 1998 American Institute of Physics. [S0003-6951(98)04340-X].
Resumo:
Mg-GdMg-GdMg-Gd-RE-Zn-ZrMg-Gd Mg-GdGdGdGd8 wt.%Gd12wt.Mg-8GdLRE(La, CeNd)HRE (Y, Dy, Ho Er)NdCeLaYDyHoErMg-8Gd-3RE(Nd+Y)-ZrNdYNdY1 221 Mg-8Gd-2Y-1Nd-0.3ZnMg-8Gd-1Dy-0.3Zn250~275Mg-8Gd-2Y-1Nd-0.3Zn T6 Mg-GdMg5REfccZnMg3RE14H50 nm~100 nmMg15RE3 Mg-12Gd-4Y-2Nd-0.4Zn-0.6Zr300 300 MPa400 100 MPa Mg-GdMg-Gd'
Resumo:
Mg-5Al-0.3Mn-xRE (x = 0~4, wt%RE = Ce, Nd, Sm, Y(CeLa)) Al-RECeAl11Ce3NdSmAl11Nd3 (Al11Sm3)Al2Nd (Al2Sm)YAl2YMg17Al12150Mg-5Al-0.3Mn-1.5Ce, Mg-5Al-0.3Mn-2NdMg-5Al-0.3Mn-2SmAl-REMg17Al12 Mg-5Al-0.3Mn-(1.0, 1.5, 2.0)CeMg-5Al-0.3Mn-2NdMg-5Al-0.3Mn-1.5(CeLa)Mg-5Al-0.3Mn-3Y300-400290-340 MPa50210-260 MPa2260-270 MPa160-190MPa20-22150 AlMgAl-REMg-REMg-AlMg-AlREREAlAl-RE
Resumo:
ABLa(PO_4)_2900 LaPO_4RE~(3+)(RE = Ce,Tb,Dy)ABLa(PO_4)_2Ce~(3+)Tb~(3+)Rc(dd)ABLa(PO_4)_2Ce~(3+)Tb~(3+)Ce~(3+)Ce~(3+)Ce~(3+)Tb~(3+)LaPO_4Ce~(3+) Ce~(3+)Ce~(3+) Tb~(3+)Ce~(3+) Ce~(3+)ABLa(PO_4)_2:Ce,TbTb~(3+)ABLa(PO_4)_2Ce~(3+)Ce~(3+)-Tb~(3+)Ce~(3+)-Dy~(3+)ABLa(PO_4)_2:CeTbCe~(3+)Tb~(3+)B_2O_3Dy~(3+)SiO_2NH_4ClCe~(3+)Tb~(3+)0.20.50.080.2B_2O_3Dy~(3+)SiO_2NH_4Cl
Resumo:
The authors report for the first time, normal incident infrared absorption around the wavelength of 13-15 mu m from a 20 period InGaAs/GaAs quantum dot supperlatice (QDS). The structure of a QDS has been-confirmed by cross-section transmission electron microscopy (TEM) and by a photoluminescence spectrum (PL). This opens the way to high performance 8-14 mu m quantum dot infrared detectors.
Resumo:
(DFT)(PWP)Mg,SiMnGaN,.:,,.MnGaN,Mg(TC),1.0eVMn4+4T1(F)4T2(F),MnGaN1.3eV;SiTC,.
Resumo:
Mg-doped GaN layers prepared by metalorganic chemical vapor deposition were annealed at temperatures between 550 and 950. Room temperature RT Hall and photoluminescence PL spectroscopy measurements were performed on the as-grown and annealed samples. After annealing at 850, a high hole concentration of 8 10~(17) cm~(-3) and a resistivity of 0. 8lcm are obtained. Two dominant defect-related PL emission bands in GaN.. Mg are investigated; the blue band is centered at 2. 8eV BL and the ultraviolet emission band is around 3.27eV UVL. The relative intensity of BL to UVL increases after annealing at 550, but decreases when theannealing temperature is raised from 650 to 850, and finally increases sharply when the annealing temperature is raised to 950C. The hole concentration increases with increased Mg doping, and decreases for higher Mg doping concentrations. These results indicate that the difficulties in achieving high hole concentration of 10~(18)cm~(-3) appear to be related not only to hydrogen passivation, but also to self-compensation.
Resumo:
MOCVD50mm(0001)GaNMg,HallX(DCXRD)(PL).Hall,95051017cm-3,2.5cm;(0002)DCXRD4;PL2.85eV,8,HMg.
Resumo:
A normal-incident SiGe/Si multiple quantum wells (MQWs) photodetector was reported. The structure and fabrication process of the photodetector were introduced. The photocurrent spectra measurement showed that the response spectra was expanded to 1.3 mu m wavelength. The quantum efficiency of the photodetector was 0.1% at 1.3 mu m and 20% at 0.95 mu m.
Resumo:
The annealing of Mg-doped GaN with Pt and Mo layers has been found to effectively improve the hole concentration of such material by more than 2 times as high as those in the same material without metal. Compared with the Ni and Mo catalysts, Pt showed good activation effect for hydrogen desorption and ohmic contact to the Ni/Au electrode. Despite the weak hydrogen desorption, Mo did not diffuse into the GaNepilayer in the annealing process, thus suppressing the carrier compensation phenomenon with respect to Ni and Pt depositions, which resulted in the high activation of Mg acceptors. For the GaN activated with the Ni, Pt, and Mo layers, the blue emission became dominant, followed by a clear peak redshift and the degradation of photoluminescence signal when compared with that of GaN without metal.