Photoluminescence from the nitrogen-perturbed above-bandgap states in dilute GaAs1-xNx alloys: A microphotoluminescence study

Using microphotoluminescence (mu-PL), in dilute N GaAs1-xNx alloys, we observe a PL band far above the bandgap E-0 with its peak energy following the so-called E+ transition, but with contribution from perturbed GaAs host states in a broad spectral range (> 100 meV). This finding is in sharp contrast to the general understanding that E+ is associated with a well-defined conduction band level (either L-1c or N-x). Beyond this insight regarding the strong perturbation of the GaAs band structure caused by N incorporation, we demonstrate that a small amount of isoelectronic doping in conjunction with mu-PL allows direct observation of above-bandgap transitions that are not usually accessible by PL.

Influence of growth parameters of frequency-radio plasma nitrogen source on extending emission wavelengths from 1.31 mu m to 1.55 mu m GaInNAs/GaAs quantum wells grown by molecular-beam epitaxy

High (42.5%) indium content GaInNAs/GaAs quantum wells with room temperature emission wavelength from 1.3 mu m to 1.5 mu m range were successfully grown by Radio Frequency Plasma Nitrogen source assisted Molecular Beam Epitaxy. The growth parameters of plasma power and N-2 How rate were optimized systematically to improve the material quality. Photoluminescence and transmission electron microscopy measurements showed that the optical and crystal quality of the 1.54 mu m GaInNAs/GaAs QWs was kept as comparable as that in 1.31 mu m.

Research on nitrogen implantation energy dependence of the properties of SIMON materials

With different implantation energies, nitrogen ions were implanted into SIMOX wafers in our work. And then the wafers were subsequently annealed to form separated by implantation of oxygen and nitrogen (SIMON) wafers. Secondary ion mass spectroscopy (SIMS) was used to observe the distribution of nitrogen and oxygen in the wafers. The result of electron paramagnetic resonance (EPR) was suggested by the dandling bonds densities in the wafers changed with N ions implantation energies. SIMON-based SIS capacitors were made. The results of the C-V test confirmed that the energy of nitrogen implantation affects the properties of the wafers, and the optimum implantation energy was determined. (c) 2005 Elsevier B.V. All rights reserved.

Enhancement of 1.53 mu m photoluminescence from spin-coated Er-Si-O (Er2SiO5) crystalline films by nitrogen plasma treatment

Er-Si-O (Er2SiO5) crystalline films are fabricated by the spin-coating and subsequent annealing process. The fraction of erbium is estimated to be 21.5 at% based on Rutherford backscattering measurement. X-ray diffraction pattern indicates that the Er-Si-O films are similar to Er2SiO5 compound in the crystal structure. The fine structure of room-temperature photoluminescence of Er3+-related transitions suggests that Er has a local environment similar to the Er-O-6 octahedron. Our preliminary results show that the intensity of 1.53 mu m emission is enhanced by a factor of seven after nitrogen plasma treatment by NH3 gas with subsequent post-annealing. The full-width at half-maximum of 1.53 pm emission peak increases from 7.5 to 12.9 nm compared with that of the untreated one. Nitrogen plasma treatment is assumed to tailor Er3+ local environment, increasing the oscillator strength of transitions and thus the excitation/emission cross-section. (c) 2005 Elsevier B.V. All rights reserved.

Magnetism and luminescence evolution due to nitrogen doping in manganese-gallium oxide nanowires

We report a new method for large-scale production of GaMnN nanowires, by annealing manganese-gallium oxide nanowires in flowing ammonia at high temperature. Microstructure analysis indicates that the GaMnN nanowires have wurtzite GaN structure without Mn precipitates or Mn-related second phases. Magnetism evolution due to nitrogen doping in manganese-gallium oxide nanowires was evaluated by magnetic measurements. Magnetic measurement reveals that the magnetization increases with the increase of nitrogen concentration. Ferromagnetic ordering exists in the GaMnN nanowires, whose Curie temperature is above room temperature. Luminescence evolution was investigated by the cathodoluminesence measurement for a single nanowire and photoluminescence measurement in a temperature range between 10 and 300 K. Experimental results indicate that optical properties can be modulated by nitrogen doping in manganese-gallium oxide nanowires. (c) 2005 Elsevier B.V. All rights reserved.

Recombination property of nitrogen-acceptor-bound states in ZnO

The recombination property of nitrogen (N)-related acceptor-bound states in ZnO has been investigated by photoluminescence (PL), time-resolved PL, and selective PL. Several possible recombination processes were discussed by analyzing the relaxation and recombination properties under large Coulomb interaction. It is strongly suggested that bound exciton emission dominates the recombination process related to the N acceptor. The recombination lifetime is 750 ps and the binding energy is 67 meV for N-acceptor-bound exciton at low temperature. (c) 2006 American Institute of Physics.

Mutual passivation of donors and isovalent nitrogen in GaAs

We study the mutual passivation of shallow donor and isovalent N in GaAs. We find that all the donor impurities, Si-Ga, Ge-Ga, S-As, and Se-As, bind to N in GaAsN, which has a large N-induced band-gap reduction relative to GaAs. For a group-IV impurity such as Si, the formation of the nearest-neighbor Si-Ga-N-As defect complex creates a deep donor level below the conduction band minimum (CBM). The coupling between this defect level with the CBM pushes the CBM upwards, thus restoring the GaAs band gap; the lowering of the defect level relative to the isolated Si-Ga shallow donor level is responsible for the increased electrical resistivity. Therefore, Si and N mutually passivate each other's electrical and optical activities in GaAs. For a group-VI shallow donor such as S, the binding between S-As and N-As does not form a direct bond; therefore, no mutual passivation exists in the GaAs(S+N) system.

Realization of low threshold of InGaAs/InAlAs quantum cascade laser

By optimizing the molecule beam epitaxy growth condition, the quality of quantum cascade (QC) material has greatly been improved. The spectrum of double x-ray diffraction indicates that the interface between the constituent layers is very smooth, the lattice mismatch between the epilayer and the substrate is less than 0.1%, and the periodicity fluctuation of the active region is not more than 4.2%. The QC laser with the emission wavelength of about 5.1 mum is operated at the threshold of 0.73 kA/cm(2) at liquid nitrogen temperature with the repetition rate of 10kHz and at a duty cycle of 1%. Meanwhile, the performance of the laser can be improved with suitable post process techniques such as the metallic ohmic contact technology.

Nitrogen vacancy scattering in GaN grown by metal-organic vapor phase epitaxy

Electron mobility limited by nitrogen vacancy scattering was taken into account to evaluate the quality of n-type GaN grown by metal-organic vapor phase epitaxy. Two assumptions were made for this potential for the nitrogen vacancy (1) it acts in a short range, and (2) does not diverge at the vacancy core. According to the above assumptions, a general expression to describe the scattering potential U(r) = - U-0 exp[- (r/beta)(n)], (n = 1, 2,...,infinity) was constructed, where beta is the potential well width. The mobilities for n = 1, 2, and infinity were calculated based on this equation, corresponding to the simple exponential, Gaussian and square well scattering potentials, respectively. In the limiting case of kbeta << 1 (where k is the wave vector), all of the mobilities calculated for n = 1, 2, and infinity showed a same result but different prefactor. Such difference was discussed in terms of the potential tail and was found that all of the calculated mobilities have T-1/2 temperature and beta(-6) well width dependences. A mobility taking account of a spatially complicate scattering potential was studied and the same temperature dependence was also found. A best fit between the calculated results and experimental data was obtained by taking account of the nitrogen vacancy scattering. (C) 2002 Elsevier Science Ltd. All rights reserved.

Conduction band offset and electron effective mass in GaInNAs/GaAs quantum-well structures with low nitrogen concentration

We have investigated the optical transitions in Ga1-yInyNxAs1-x/GaAs single and multiple quantum wells using photovoltaic measurements at room temperature. From a theoretical fit to the experimental data, the conduction band offset Q(c), electron effective mass m(e)*, and band gap energy E-g were estimated. It was found that the Q(c) is dependent on the indium concentration, but independent on the nitrogen concentration over the range x=(0-1)%. The m(e)* of GaInNAs is much greater than that of InGaAs with the same concentration of indium, and increases as the nitrogen concentration increases up to 1%. Our experimental results for the m(e)* and E-g of GaInNAs are quantitatively explained by the two-band model based on the strong interaction of the conduction band minimum with the localized N states. (C) 2001 American Institute of Physics.

Nitrogen vacancy scattering in n-GaN grown by metal-organic vapor phase epitaxy

Electron mobility limited by nitrogen vacancy scattering was taken into account to evaluate the quality of n-type GaN grown by metal-organic vapor phase epitaxy. The nitrogen vacancy scattering potential used for our mobility calculation has to satisfy two requirements: such potential is (1) spatially short range, and (2) finite and not divergent at the vacancy core. A square-well potential was adopted to calculate the mobility, because it satisfies not only these two requirements, but also simplifies the calculation. As a result, the estimated mobility shows a T-1/2 temperature dependence, and is very sensitive to the potential well width. After introducing the nitrogen vacancy scattering, we obtained the best fitting between the calculated and experimental results for our high quality sample, and it was found that the measured mobility is dominated by ion impurity and dislocation scatterings at the low temperatures, but dominated by optical phonon and nitrogen vacancy scatterings at the high temperatures. (C) 2000 American Institute of Physics. [S0003-6951(00)04112-7].

Photoluminescence properties of nitrogen-doped ZnSe epilayers

The photoluminescence (PL) properties of nitrogen-doped ZnSe epilayers grown on semi-insulating GaAs(100) substrates by MBE using a rf-plasma source for N doping were investigated. The PL peak which can be related to N acceptor was observed in the PL spectra of ZnSe:N smaples. At 10K, as the excitation power density increases, the energy of donor-acceptor pair(DAP) emission shows a blue-shift and its intensity tends to saturate. As the temperature increases over a range from 10K to 300K, the relative PL intensity of donor bound exciton to that of the acceptor bound exciton increases due to the transfer between two bound excitons.

Quantitative analysis of excitonic photoluminescence in nitrogen-doped ZnSe epilayers

We have investigated the photoluminescence (PL) properties of nitrogen-doped ZnSe epilayers grown by molecular beam epitaxy using a nitrogen radio frequency-plasma source. The PL data shows that the relative intensity of the donor-bound exciton (I-2) emission to the acceptor-bound exciton (I-1) emission strongly depends on both the excitation power and the temperature. This result is explained by a thermalization model of the bound exciton which involved in the capture and emission between the neutral donor bound exciton, the neutral acceptor bound exciton and the free exciton. Quantitative analysis with the proposed mechanism is in good agreement with the experimental data. (C) 1999 American Institute of Physics. [S0021-8979(99)09102-1].

Research on nitrogen implantation energy dependence of the properties of SIMON materials

With different implantation energies, nitrogen ions were implanted into SIMOX wafers in our work. And then the wafers were subsequently annealed to form separated by implantation of oxygen and nitrogen (SIMON) wafers. Secondary ion mass spectroscopy (SIMS) was used to observe the distribution of nitrogen and oxygen in the wafers. The result of electron paramagnetic resonance (EPR) was suggested by the dandling bonds densities in the wafers changed with N ions implantation energies. SIMON-based SIS capacitors were made. The results of the C-V test confirmed that the energy of nitrogen implantation affects the properties of the wafers, and the optimum implantation energy was determined. (c) 2005 Elsevier B.V. All rights reserved.

Liquid nitrogen flowrate alarm system for MBE

Liquid nitrogen is very important for MBE system. Most MBE systems use the liquid nitrogen to absorb the impurity molecules. If MBE cryoshroud is lack of liquid nitrogen, the pressure of the growth chamber will grow. This will affect the film quality. But too much liquid nitrogen is a waste. We have developed a liquid nitrogen flowrate alarm system to monitor the liquid nitrogen status in MBE cryoshroud. In this method, a temperature sensor is placed at the end of the cryoshroud. The temperature varies with changing of the liquid nitrogen status in cryoshroud. If the liquid nitrogen level in the cryoshroud is too low or too high, the LNFA will send out an alarm to warn the user to adjust the liquid nitrogen flowrate. In our experiments, we found this method works well, and the temperature responds sensitively. With the help of this system, people can view the liquid nitrogen status of the entire growth process. Compare with other method. it is very cheap.