POWER DEPENDENCE OF THE RECOMBINATION PROCESSES IN THE INXGA1-XAS/GAAS SINGLE-QUANTUM-WELL

We have measured the power dependence of the photoluminesence spectra from a set of strained InxGa1-xAs/GaAs single quantum wells. The result shows that the excitation power has important effect on the carrier recombination processes. When the power increases from 0.5 to 14 mW, the photoluminescence from the barrier becomes more intense than that from the well and the trapping efficiency decreases. At high excitation level, the ratio of the radiative recombination rate to the nonradiative recombination rate of the barrier increases ten times than that at lower excitation level, while it only doubles for the well.

Deviation from the stoichiometric composition of single-crystal 'Er2Co17'

The deviation from the stoichiometric composition of single-crystal 'Er2Co17' has been determined by theoretical analysis. It is found that the composition of this single-crystal 'Er2Co17' is rich in cobalt, and its real composition is suggested to be Er2-deltaCo17+2 delta (delta = 0.14) on the basis of a comparison of calculations based on the single-ion model with a series of experiments. The values of the Er-Co exchange field H-ex and the crystalline-electric-field (CEF) parameters A(n)(m) at the rare-earth (R) site in the 'Er2Co17' compound are also evaluated at the same time. The experiments provide the following data: the temperature dependence of the spontaneous magnetization of the compounds and the normalized magnetic moment of the Er ion, the magnetization curves dong the crystallographic axes at 4.2 K and 200 K, and the temperature dependence of the magnetization along the crystallographic axes in a field of 4 T.

Lapping technique of InP single crystal wafer

The wafer processing of Indium Phosphide (InP) is so important that it is getting more and more attentions. Lapping is a basic step just following the ingot cutting. In this paper, the influences of various processing parameters on the lapped wafer quality and lapping rate have been checked, the double-crystal X-ray diffraction results about lapped wafers also were presented here. According to the experimental results, the optimum lapping conditions have been obtained.

Electrical properties of semi-insulating GaAs grown from the melt under microgravity conditions

A technologically important undoped semi-insulating (SI) GaAs single crystal was successfully grown in the Chinese recoverable satellite as far as we know for the first time by using a similar growth configuration described previously. The experimental results proved that the space SI GaAs crystals have a lower density of defects and defect-impurity complexes as well as a better uniformity.

INVESTIGATION OF C-60 SINGLE-CRYSTAL BY X-RAY-METHODS

C-60 Single crystals grown by a single-temperature-gradient technique were characterized by synchrotron radiation white beam x-ray topography and x-ray double crystal diffraction with Cu K-alpha 1 radiation on conventional x-ray source. The results show that the crystal is rather well crystallized, The x-ray topographies give an evidence of dendritic growth mechanism of C-60 Single crystal, and x-ray double crystal diffraction rocking curve shows that there are mosaic structural defects in the sample. A phase transition st 249+/-1.5% K from a simple cubic to a face centered cubic structure is confirmed by in situ observation of synchrotron radiation white beam x-ray topography with the temperature varing from 230 to 295 K.

Luminescence spectroscopy of ion implanted AlN bulk single crystal

High concentrations of Si and Zn were implanted into (0001) AlN bulk crystal grown by the self-seeded physical vapor transport (PVT) method. Cathode luminescence (CL) and photoluminescence (PL) spectroscopy were used to investigate the defects and properties of the implanted AlN. PL spectra of the implanted AlN are dominated by a broad near-band luminescence peak between 200 and 254 nm. After high temperature annealing, implantation induced lattice damages are recovered and the PL intensity increases significantly, suggesting that the implanted impurity Si and Zn occupy lattice site of Al. CL results imply that a 457 nm peak is Al vacancy related. Resistance of the AlN samples is still very high after annealing, indicating a low electrical activation efficiency of the impurity in AlN single crystal.

Effects of Rapid Thermal Annealing on OpticalProperties of GaInNAs/ GaAs Single Quantum Well Grown by Plasma- Assisted Molecular Beam Epitaxy

国家自然科学基金,国家攀登计划

Effect of SiO2 encapsulation on the nitrogen reorganization in GaNAs/GaAs single quantum well

Effects of SiO2, encapsulation and rapid thermal annealing (RTA) on the optical properties of GaNAs/GaAs single quantum well (SQW) were studied by low temperature photoluminescence (PL). A blueshift of the PL peak energy for both the SiO2-capped region and the bare region was observed. The results were attributed to the nitrogen reorganization in the GaNAs/GaAs SQW. It was also shown that the nitrogen reorganization was obviously enhanced by SiO2 cap-layer. A simple model [1] was used to describe the SiO2-enhanced blueshift of the low temperature PL peak energy.

Space-grown SI-GaAs and its application

A semi-insulating GaAs single crystal ingot was grown in a recoverable satellite, within a specially designed pyrolytic boron nitride crucible, in a power-travelling furnace under microgravity. The crystal was characterized systematically and was used in fabricating low noise field effect transistors and analogue switch integrated circuits by the direct ion-implantation technique. All key electrical properties of these transistors and integrated circuits have surpassed those made from conventional earth-grown gallium arsenide. This result shows that device-grade space-grown semiconducting single. crystal has surpassed the best. terrestrial counterparts. Studies on the correlation between SI-GaAs wafers and the electronic devices and integrated circuits indicate that the characteristics of a compound semiconductor single crystal depends fundamentally on its stoichiometry.

Optical transitions in GaNAs/GaAs single quantum well

We have investigated GaNAs/GaAs single quantum wells (SQWs) grown by molecular beam epitaxy (MBE) using photoluminescence (PL), time-resolved PL (TRPL) and photovoltaic (PV) techniques. The low temperature PL is dominated by spatially direct transitions involving electrons confined in GaNAs well and holes localized in the same GaNAs layer. This assignment was supported by PL decay time measurements and absorption line-shape analysis derived from the PV measurements. By fitting the experimental data with a simple calculation, the band offset of the GaN0.015As0.985/GaAS heterostructure was estimated, and a type II band lineup in GaN0.015As0.985/GaAs QWs was suggested. Moreover, DeltaE(C), the discontinuity of conductor band, is found to be a nonlinear function of the nitrogen (N) composition (x), and the average variation of DeltaE(C) is about 0.110eV per %N, The measured band bowing coefficient shows a strong function of x, giving an experimental support to the theoretic calculation of Wei et al [Ref.2].

Stoichiometry in GaAs grown in outer space measured nondestructively

A semi-insulating (SI) GaAs single crystal ingot was successfully grown in a recoverable satellite. The two-dimensional distribution of stoichiometry in space-grown SI-GaAs single crystal wafer was studied nondestructively based upon x-ray Band diffraction. The avenge stoichiometry in the space-grown crystal is 0.50007 with mean square deviation of 6 x 10(-6), and shows a better stoichiametric property than the ground-grown SI-GaAs. The average etch pit density (EPD) of dislocations in the crystal revealed by molten KOH is 2.0 x 10(4) cm(-2), and the highest EPD is 3.1 x 10(4) cm(-2). This result indicates that the structural properly of the crystal is quite good.

Yellow luminescence mechanism and persistent photoconductivity in n-GaN single crystal films grown on alpha-Al2O3(0001) substrates by LP-MOCVD

Unintentionally doped and Si-doped single crystal n-GaN films have been grown on alpha-Al2O3 (0001) substrates by LP-MOCVD. Room temperature photoluminescence measurement showed that besides the bandedges, the spectrum of an undoped sample was a broad deep-level emission band peaking from 2.19 to 2.30eV, whereas the spectrum for a Si-doped sample was composed of a dominant peak of 2.19eV and a shoulder of 2.32eV. At different temperatures, photoconductance buildup and its decay were also observed for both samples.. The likely origins of persistent photoconductivity and yellow luminescence, which might be associated with deep defects inclusive of either Ga vacancy(V-Ga)/Ga vacancy complex induced by impurities or N antisite (N-Ga), will be proposed.

Effects and numerical analysis of argon gas flow on the oxygen concentration in Czochralski silicon single crystal growth

Argon gas, as a protective environment and carrier of latent heat, has an important effect on the temperature distribution in crystals and melts. Numeric simulation is a potent tool for solving engineering problems. In this paper, the relationship between argon gas flow and oxygen concentration in silicon crystals was studied systematically. A flowing stream of argon gas is described by numeric simulation for the first time. Therefore, the results of experiments can be explained, and the optimum argon flow with the lowest oxygen concentration can be achieved. (C) 2002 Elsevier Science B.V. All rights reserved.